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Seismic performance of pretensioned spun high strength concrete piles Taksinrote, Worapol 2001

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Seismic Performance of Pretensioned Spun High Strength Concrete Piles by Worapol Taksinrote Prince of Songkla University, Thailand, 1996 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Civil Engineering We accept this thesis as conforming to the reauire<i-itandard THE UNIVERSITY OF BRITISH COLUMBIA August 2001 © Worapol Taksinrote, 2001 UBC Special Collections - Thesis Authorisation Form Page 1 of 1 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v ailable for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. It i s understood that copying or p u b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver, Canada http://wvvw.library.ubc.ca/spcoll/thesauth.html 9/26/01 ABSTRACT Pretensioned spun high strength concrete piles manufactured by Industrials Concrete Products (ICP) Berhad, Malaysia were studied in this experimental program. The objective was to investigate the seismic performance of the piles under varying axial compression and lateral load reversals. Ten test specimens, ranging in length from 1 m to 4 m, were cut from 250 mm diameter piles. Rather than attempting to simulate the complex loading on a real pile, idealized boundary conditions were used in the test: one end was a fixed support, and the free end of the pile was subjected to a lateral load. Using instrumentation and electronic equipment, a wide variety of data was recorded during the test, and subsequently employed for analysis. Aspects of the test specimens that were investigated include load-displacement characteristics, failure mechanisms, crack patterns, crack widths, strain limits, and curvature capacities. While some diagonal cracking was observed in the very short specimens, the behavior of all specimens was dominated by flexure. The flexural failure mechanisms for the piles involved either concrete crushing in compression or fracture of the prestressing strands in tension. Both failure modes were very brittle. The experiments indicated that the observed compression strain limit is about 0.5 %, and the tension strain limit is between 1.5 % and 2.0 %. It is interesting to note that the tension strain limit determined from the current pile tests are considerably smaller than what was determined from bare bar tests of the prestressing strands. An analytical model called Response-2000 was used to predict the bending moment-curvature relationships and curvature capacities of the specimens. The model was also used to study the shear response of the specimens. The most important result from the current experimental study is the relationship between the curvature capacity of the piles and the applied axial compression. Predictions of the curvature capacity using Response-2000 and the measured strain limits were found to be in good agreement with the test observations. Thus Response-2000 and these strain limits can be used to predict the curvature capacity of other sizes of ICP pretensioned spun high strength concrete piles. 111 TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES vii ACKNOWLEDGEMENT x CHAPTER 1 Introduction 1 1.1 Background 1 1.2 Previous work on PHC Piles 3 1.3 Aim of the Current Experimental Program 8 1.4 Outline of Thesis 8 CHAPTER 2 Experimental Program 9 2.1 Testing Methodology 9 2.2 Testing Apparatus 10 2.3 Test Specimens 12 2.4 Instrumentation 16 2.5 Test Set-up Procedure 21 2.6 Testing Procedure 22 iv CHAPTER 3 Discussion of Experimental Results 26 3.1 Summary of Test Results 26 3.2 Failure Modes 27 3.3 Load-Displacement Relationships 30 3.4 Strains 33 3.5 Crack Patterns and Crack Widths 45 3.6 Analytical Model for Flexural Response. 50 3.7 Comparison between Predicted and Observed Bending Moment -Curvature Relationships 51 3.8 Curvature Capacities 58 3.9 Shear Failure 59 3.10 Comparison of Predicted and Observed Curvature Capacities 62 3.11 Design Tool 64 CHAPTER 4 Summary and Recommendation 69 4.1 Summary 69 4.2 Recommendations 72 REFERENCES 74 APPENDIX A Test Descriptions 75 APPENDIX B Calculation of Initial Strain Estimate 127 v LIST OF TABLES Table 2.1 List of test specimens 14 Table 2.2 Concrete strength of test specimens 14 Table 2.3 Properties of the strand 15 Table 2.4 List of targets and distances between targets for test specimens 18 Table 2.5 Summary of the actual displacements used for each specimen 24 Table 3.1 Summary of test results 28 Table 3.2 Summary of average spacing of test specimens 47 Table 3.3 Material properties used in prediction 52 Table 3.4 Summary of strain and curvature capacities at failure: (a) compression failure, (b) Tension Failure 59 Table 3.5 Summary of shear prediction 62 vi LIST OF FIGURES Fig. 1.1 Reinforcement cage 2 Fig. 1.2 Mould and shaft setting 3 Fig. 1.3 Centrifugal force generator 3 Fig. 1.4 Loading apparatus (Reference 2) 5 Fig. 1.5 Loading system (Reference 3) 6 Fig. 1.6 Example of test specimens (Reference 3) 7 Fig. 2.1 Concept of the test set-up: (a) displacement demands of a typical pile, (b) basic test set-up 9 Fig. 2.2 Test apparatus 11 Fig. 2.3 Dywidag connection 12 Fig. 2.4 The specimen cross section 13 Fig. 2.5 Displacement transducer equipped in the actuator 17 Fig. 2.6 Targets for strain measures 18 Fig. 2.7 Displacement transducers for strain measurements 19 Fig. 2.8 Displacement transducers for rotation measurements 20 Fig. 2.9 Test set-up 22 Fig. 2.10 Loading system by displacement control 23 Fig. 3.1 Appearance of the test in progress 27 Fig. 3.2 Typical tension failure after fracture of strands (Specimen P12D) 29 vii Fig. 3.3 Typical compression failure (Specimen P12C) 29 Fig. 3.4 Typical load-displacement relationship for tension failure 31 Fig. 3.5 Typical load-displacement relationship for compression failure 32 Fig. 3.6 Plot of displacement capacity versus axial compression 32 Fig. 3.7 Load-displacement with tri-linear trend 33 Fig. 3.8 Plots of typical shear-strain relationship (Specimen PI 2D): (a) strains on the the east side, (b) strains on the west side, (c) average strains 35 Fig. 3.9 Plot of bending moment-curvatures (Specimen PI 2D) 36 Fig. 3.10 Plots of typical shear-strain relationship (Specimen P12E): (a) strains on the the east side, (b) strains on the west side, (c) average strains 37 Fig. 3.11 Plot of bending moment-curvatures (Specimen P12E) 40 Fig. 3.12 Plots of strain profile by digital caliper (Specimen PI 2D): (a) strain profile on the east side, (b) strains profile on the west, (c) average strain profile, (d) curvature profile 40 Fig. 3.13 Plots of strain profile by digital caliper (Specimen PI 2D): (a) strain profile on the east side, (b) strains profile on the west, (c) average strain profile, (d) curvature profile 43 Fig. 3.14 Crack patterns: (a) from the specimen with high axial compression (P12C) 47 Fig. 3.14 Crack patterns: (b) from the specimen with low axial compression (PI 2D) 48 Fig. 3.14 Crack patterns: (c) from the short specimen (P4B) 49 Fig. 3.15 Modeled stress-strain relationship: (a) concrete, (b) prestressing strand 51 Fig. 3.16 Bending moment-curvature response of Specimen P12D 53 Fig. 3.17 Bending moment-curvature response of Specimen P12E 54 viii Fig. 3.18 Bending moment-curvature response of Specimen P8B 55 Fig. 3.19 Bending moment-curvature response of Specimen P4B 55 Fig. 3.20 Bending moment-curvature response of Specimen P4E 56 Fig. 3.21 Bending moment-curvature response of Specimen P2B 57 Fig. 3.22 Bending moment-curvature response of Specimen P2E 57 Fig. 3.23 Shear cracking from the short specimen with low axial compression (P2B) 60 Fig. 3.24 Shear cracking from the short specimen with high axial compression (P4E) 61 Fig. 3.25 Shear cracking from the short specimen with high axial compression (P2E) 62 Fig. 3.26 Strain estimate for a 250 mm dia. pile 64 Fig. 3.27 Proposed design chart for 250 mm piles 66 Fig. 3.28 Lateral displacement profile of a pile: (a) displacement profile of the piles, (b) the effective length, le, (c) the curvature profile 66 ix ACKNOWLEDGEMENT I wish to express my gratitude to my research supervisor, Professor Perry Adebar, for his support, encouragement, patience, and valuable discussions and suggestions throughout this research, including the manuscript. This thesis would not have happened without Industrial Concrete Products Berhad, ICP, who provided financial support and supplied the piles for the test specimens. My thankfulness gratefully goes to the company. The assistance and ingenuity from the staff in the structures laboratory and machine shop are gratefully acknowledged. I also would like to thank my assistants, Kevin Chen and Ben Tang, for their help during testing. Suggestions, comfort, and help from Ari, Emilio, Rahul, and Rachel are much appreciated. Finally, I would like to express my gratitude and thank my family in Thailand for their love, support and patience. Worapol Taksinorte August, 2001 Vancouver, British Columbia x CHAPTER 1 Introduction 1.1 Background The seismic performance of pretensioned spun high-strength concrete piles manufactured by Industrial Concrete Products Berhad, Malaysia was investigated in this experimental program. The piles have been successfully used in a variety of applications; however there is concern about use of the piles in high seismic regions such as the Lower Mainland of British Columbia. The procedure used to manufacture pretensioned spun high-strength concrete piles is briefly described as follows. First, a continuous spiral is welded to the longitudinal pretensioning strands using an automatic machine to form a cage of reinforcement as shown in Fig. 1.1. Then the reinforcement cage is placed into a mould (as shown in Fig. 1.2) and coupled to a stressing shaft. High-strength concrete is placed within the mould, and after the longitudinal strands have been tensioned to the specified stress, the concrete is consolidated by the centrifugal force generated by spinning the piles at high speed (see Fig. 1.3). The spinning results in a very dense concrete with a low water-cement ratio on the outside shell of the pile. When combined with longitudinal prestressing, the result is a very durable structural concrete member. Concern about the seismic performance of the piles is due the low level of confinement (large spiral pitch), and the small amount of "confined" concrete that remains after the cover spalls from the hollow cylindrical piles. In addition, the fact that 1 the spirals are welded to the longitudinal prestressing strands raises concerns that the ultimate strain of the prestressing strands may be very limited. As it is, prestressing strands have a much smaller ultimate strain compared to mild reinforcing bars. Fig. 1.1 Reinforcement cage. In the current investigation, one size of pile with an outside diameter of 250 mm was investigated. Rather than attempt to simulate the actual displacement profile of a pile, the methodology used was to apply a simple well defined set of forces onto the pile specimens. One end of the pile was held in a fixed support, while the other end was subjected to a constant axial force and a reverse cyclic lateral load. In addition to measuring the resulting displacements, the maximum curvature adjacent to the fixed support was measured during the tests. The curvature capacity at different axial load levels is a fundamental property of the piles. 2 Fig. 1.2 Mould and shaft setting. Fig. 1.3 Centrifugal force generator. 1.2 Previous work on PHC Piles The series of tests in the experimental program "Seismic Performance of Prestressed Concrete Piers" was published by T. Mori, N. Suzuki, S. Ikeda in Japan in 1999. The objective of the program was to improve performance of reinforced concrete 3 piers under seismic condition by introducing the prestress into a concrete pier. The test program was performed using two methods that twenty-two single column type specimens were made for the testing of reversed cyclic loading and six specimens for pseudo dynamic test. The loading apparatus of the test program is also shown in Fig. 1.4. For reversed cyclic loading tests, the constant axial force was applied in each specimen in the vertical direction whereas the lateral reversed cyclic load was applied by the push-pull type hydraulic jack, see Fig. 1.4. To study the seismic response of the PC columns during an earthquake, pseudo-dynamic tests were performed using the seismic motion from the record of Kobe Maritime Meteorological Observatory (Kobe MMO). The input maximum acceleration was determined from the employed virtual mass and the flexural capacity of specimens based on the following assumptions. The natural frequency of theses specimens was 0.3 sec, and they were designed against the equivalent horizontal seismic coefficient 0.8 in accordance with the design method of the Highway Bridge Specification, 1996. The reversed cyclic loading tests showed that reinforced concrete columns with appropriate prestress have enough ductility and outstandingly decrease the residual displacement. According to the test, the difference observed from the load-displacement relationship is that the RC specimens have typical spindle-shaped or angled diamond-shaped curve while for the PC specimens, the residual displacement is smaller than that of the RC specimens and the curve during unloading tends to approach back to the origin depending on the applied prestressing force. Furthermore, the number of cracks in the PC specimens was smaller than RC specimens and the spacing between the cracks tended to become smaller. 4 Rcactlbosfloor F i g . 1.4 Loading apparatus (Reference 2). The result from the pseudo dynamic tests of PC specimens shows that they have superior seismic performance against the near field earthquake. The response of the RC specimen tended to deviate to one side and the residual displacements also became large due to the fact that the response greatly exceeded the yield range because of the initial large earthquake ground motion. The PC specimen, on the other hand, did not show any deviating response, and yet, left the small residual displacement because of the high restoration capacity. In addition, the response of the PC specimen was not as large as of the RC specimen. An experiment " Degree of Fixation at Pile Head Joint and Failure Strength of Prestressed High Strength Concrete Piles" was performed by Y. Sugimura and T. Hirade in Japan and was presented in 1988. The program was to accumulate information about degree of fixation, i.e., degree of restrain for rotation at pile head and the ultimate strength of pile in the earthquake resistant design of pile foundation. Therefore, the 5 program was set to investigate the experimental results of full-scale bending-shear tests for joint between prestressed high strength concrete pile and footing under various axial load conditions, in order to determine degree of fixation at pile head joint and the ultimate strength of piles. In the test program statically indeterminate loading system was used as shown in Fig. 1.5, which is capable of keeping the similarity of bending moment distribution of pile in the ground due to horizontal force. This experimental program was performed in the two-phase test series. An example of test specimen is shown in Fig. 1.6. Fig. 1.5 Loading system (References). 6 E m b e d d i n g l e n g t h m A n c h o r b : i r S h e a t h Fig. 1.6 Example of test specimens (Reference 3). Three details of joint methods were designed and tested in phase 1 test series. Similar details were also used in phase 2 but with difference embedding length in order to investigate effects of embedding. It was concluded from the series of tests that the important influence factors on degree of fixation at pile head in the allowable capacity design, are the embedding length of pile into footing and the condition with or without axial load. If the pile is embedded to the length corresponding to pile diameter, behavior of pile head becomes similar to rigid joint. And if axial load acts, degree of fixation becomes significantly large. During an earthquake, piles may be subjected to additional alternating axial load due to rocking motion of superstructure. Therefore, degree of fixation of piles located at compression side becomes larger than tension side, and shear force is apt to be concentrated to piles in compression side. This effect of axial load will become very important factor for design method of pile foundation. The final state of each test specimen results in shear failure type. Shear span ratios in these tests are scattering in the range from 1.43 to 3.20. And, therefore, it is advisable to keep sufficient ductility for the case of PHC pile. 7 1.3 Aim of the Current Experimental Program As mentioned previously, pretensioned spun high strength concrete piles have been widely used in non-seismic regions. Industrial Concrete Products, ICP, would like to expand the market of its piles in seismic regions of North America (e.g., the west coast of Canada and the United States). As a result, the seismic characteristics of this specific pile were investigated even though similar work has been done on other piles. The primary aim of the current experimental program was to investigate the fundamental properties of the piles and to develop a simple analytical tool that could be used in the design of the piles. 1.4 Outline of Thesis This thesis consists of four chapters. A complete description of the experimental program is provided in Chapter 2. Chapter 3 presents a summary of the test results and comparisons of the results with analytical predictions, while a complete summary of the detailed experimental results are provided in Appendix A. Conclusions and recommendations for further work are given in Chapter 4. 8 CHAPTER 2: Experimental Program 2 . 1 Testing Methodology Fig. 2.1 (a) shows the demands on a typical pile. When a pile foundation is subjected to vertical load from the superstructure, axial compression in the pile varies over the height as vertical load is transferred to surrounding soil through friction. (a) Demands on a (b) Test set-up. typical pile. Fig. 2 . 1 Concept of the test set-up: (a) demands on a typical pile, and (b) test set-up. 9 In order to resist horizontal movement, lateral load is developed and distributed along the pile and depth as shown in Fig. 2.1. The magnitude of the lateral load acting on the pile depends on type of surrounding soil and the ground water level. Therefore, it is very complicated to conduct a test simulating the real loading on a pile. Furthermore, the result obtained from such a test may be limited to that particular loading. Fig 2.1(b) shows the basic test set-up that was used in this study. The idea was to use a simple well-defined loading: constant axial compression, one end fixed against rotation and the other end free, and lateral load applied at free end. The test setup was not meant to simulate actual loading conditions. Instead, the information from the tests would be used to determine fundamental sectional properties of the piles (e.g., strain capacity, curvature capacity), and then analytical tools can be used to apply this information to actual pile loading conditions. For this experimental study, only one size pile was investigated. The hollow circular pile had an outside diameter of 250 mm and a wall thickness of 55 mm. The pile contained six prestressing strands (cross sectional area of each strand was 50 mm2). The concrete used to construct the pile was high strength concrete and had a compressive strength of approximately 100 MPa (see details in Section 2.3). 2.2 Testing Apparatus Based on the concept described in the previous section, the apparatus was designed in such a way that it would fix a specimen at one end in terms of rotation and displacement but the other end would move freely and would be subjected to lateral load. The 10 apparatus that was designed and constructed to provide a fixed end support is shown in Fig. 2.2. Bolt to strong floor 10- i f f 10 1" V 10* 14' 24 ' 1 M2- 13" b 1/2" 5 1/2' Fig. 2.2 Testing apparatus. The tube was separated into two parts. The top part can be removed and replaced by bolts for pile installation, see Fig. 2.2. The bottom part was welded to four rectangular plates on the surface and to the end plate at the end of the tube in order to fix the tube. Once the top and the bottom parts were assembled together and the specimen was placed in, a gap between the tube and the specimen would occur due to the fact that the diameter of the tube was approximately one inch bigger than that of the specimen. Therefore, non-shrink cement grout was used to fill the gap. 11 The end plate had a 300 mm diameter hole so that a Dywidag bar could be run through the core in the pile and connected to the actuator for axial load applications. The entire assembly was placed onto the strong floor in the structures laboratory. As mentioned above, a high strength Dywidag bar was used to apply axial compression to the specimen. One end of the Dywidag bar was connected to an actuator with a maximum stroke of 300 mm, and the other end was connected to a steel bearing plate placed against the free end of the specimen as illustrated in Fig. 2.3. 2.3 Test Specimens Ten specimens were tested in the current experimental program. The cross section of the specimens is illustrated in Fig. 2.4. The test specimens had an outside diameter of 250 mm and inside diameter of 140 mm. A welded steel cage was formed by wrapping a 5.0 mm diameter continuous spiral wire around six 7.1 mm diameter-prestressing strands. The clear cover to the prestressing strands was 25 mm. 12 |YV3 a Fig. 2.4 77ze specimen cross section. All concrete pile specimens were provided by Industrial Concrete Products Berhad. These piles were manufactured in August 1999 in Malaysia. Four piles were cut to different lengths in order to make the test specimens. Thus, all specimens had the same cross section (concrete dimensions and arrangement of strands) but had different lengths and were subjected to different levels of axial compression as shown in Table 2.1. Information about the material properties, concrete and prestressing strands strength, were provided by the supplier. Concrete strength information is shown in Table 2.2. The concrete strength shown in the table was obtained from tests conducted two days after testing. Al l piles had a record with the manufacturing date, and concrete strength so that they could be identified. However, as concrete strength increases with age, it is expected that by January 2001 (16 months later) the concrete strength of all specimens would have increased from what is shown in the table. 13 Table 2.1 List of test specimens. Specimen Nominal Test Length (ft) Actual Length (ft-in) Axial compression (kN) P12A 12.0 11-11 0 P12B 12.0 11-11 200 P12C 12.0 11-11 600 P12D 12.0 11-11 100 P12E 12.0 11-11 500 P8B 8.0 7-11 200 P4B 4.0 3-11 200 P4E 4.0 3-11 500 P2B 2.0 1-11 200 P2E 2.0 1-11 500 Table 2.2 Concrete strength of test specimens at two days of age. Specimen Concrete strength (MPa) P12A 78.8 P12B 82.2 P12C 82.5 P12D 79.1 P12E 95.0 P8B 82.2 P4B 78.8 P4E 82.5 P2B 82.2 P2E 79.1 Tests of the prestressing strands were conducted at the University of British Columbia by a group of students (Reference 8). Samples of the strands were provided by 14 supplier. Five specimen types were tested: bare strand, welded strand, pre-tested strand which was taken from the specimen that had previously been tested to failure, concrete encased bare strand and concrete encased welded strand. The bare strand specimens were 510 mm long samples of the 7.1 mm strands, while the welded strand specimens consisted of the 510 mm strands but had elements of the spiral wire spot welded at 100 mm intervals. The pre-tested strand specimens were similar to the welded bar except that they were from the tested specimen as previously described. For the last two types, they were made similar to bare strand and welded strand respectively except that they were encased in concrete. However, the results from the last two types were not correct because the failure mechanism did not occur as expected. The results from the tests are summarized in Table 2-3. In addition, the first row of Table 2.3 summarizes the results obtained by ICP. Table 2.3 Properties of the strand. Sample Young's Modulus, E (GPa) Yield Strength Ultimate Strength (MPa) Fracture Strain (mm/m) Strain (mm/m) Stress (MPa) Supplier Tests Bare strand N/A N/A 1485 1518 72.7 UBC Tests Bare strand 195.5 8.5 1385 1438 77.6 UBC Tests Welded Strand 200.4 7.8 1373 1460 40.2 UBC Tests Pre-tested strand 199.1 7.8 1395 1436 58.2 15 2.4 Instrumentation Axial force, lateral force, lateral displacement, and strains at the critical cross section near the fixed end are variables that were measured during the experiments. In addition, strains were measured at various discrete points along the specimen. To measure the axial compression applied to the pile, a pressure transducer was used and placed onto the Dywidag bar connected to the actuator. Axial force was controlled by the hydraulic pressure in the actuator using a load maintainer (see details in Section 2.5). To apply the axial compression to the test specimen, prior to using the actuator for the tests, the actuator was calibrated. The actuator was connected to the Dywidag thread bar to transfer force to the test specimen. At the free end the Dywidag was connected to the steel plate so that the axial force from the actuator could be transferred to the pile (see Fig. 2.3). The transverse displacement of all specimens was measured by a LVDT displacement transducer within the actuator used to apply lateral load. The displacements obtained from the transducer in the actuator represented the displacements on west surface of the clamping device connected to the specimen. The electronic signals from all displacement transducer were converted from analog to digital data, and recorded by a personal computer equipped with a data acquisition program. The data were recorded every half a second during loading. 16 TTW. i. CI Fig. 2.5 Displacement transducer equipped in the actuator. Strains were measured using two methods, targets plus a digital caliper for Specimens P12B, P12D, P12E, P8B, P4B, P4E, and displacement transducers for Specimens P12D, P12E, P8B, P4B, P4E, P2B, P2E as described in the following. For the strains measured using the targets and digital caliper, the targets were glued with epoxy on the surface of each specimen both on the west and east sides as shown in Fig. 2.6. The number of targets and the distances between targets varied as described in Table 2.4. Before the specimen was loaded, five distance readings between each two targets were measured. The average of these number are given in Table 2.4. The displacement readings between the targets were taken during loading while the specimen was held constant in the 3 r d cycle at the peak positive and negative displacements of 17 every displacement level by placing the digital caliper on the two targets horizontally. The displacement readings were manually recorded onto data sheets. 6 Fig. 2.6 Targets for strain measurements. : |< „ _ ^ „„•, .,„ .„„„ ft^,.,,,,,,, ffjtg' -.„: I Table 2.4 Ztsf o/~ targets and distances between targets for test specimens. Specimen No. of targets A (mm) B (mm) C(rnm) D (mm) E (mm) West East West East West East West East West East West East P12B 6 6 88.4 104.9 191.4 192.0 191.6 190.3 190.0 191.5 190.6 192.3 P12D 6 6 214.9 227.6 319.3 318.9 318.3 319.3 317.5 316.9 316.8 317.8 P12E 6 6 216.7 224.6 317.0 318.2 318.3 317.4 318.6 318.8 318.2 318.2 P8B 5 5 219.0 227.5 317.8 314.8 318.6 318.6 318.5 316.8 - -P4B 4 4 216.4 229.3 316.3 318.4 320.5 316.8 - - - -P4E 4 4 215.8 229.2 317.2 317.9 316.1 319.2 - - - -For strains measured using the displacement transducers, two displacement transducers, LVDT4 and LVDT5, were installed at the support and two special targets were glued on surface of each specimen (one on the west side and the others on the east side) in order to measure displacement changes which are parallel to the surface of the 18 specimen from the locations of the displacement transducers to the targets as shown in Fig. 2.7. The distance that the LVDT displacement transducers measured was located away from the pile was accounted for in determining the pile strains. - — — —J»E Ln Fig. 2.7 Displacement transducers for strain measurements at the base. Additional measurements were made to monitor apparatus movements such as rotation and translation of the fixed pile base, and translation of the jack base. These were used to correct the other data. To measure rotational movement, two displacement transducers, LVDT1 and LVDT2, were used to record displacements at the positions in the support in order to detect movement of the support during loading. The displacement transducers were held firmly with magnetic stands placed on the floor. The distance between these two positions was 690 mm (see Fig. 2.8). The displacements obtained from 19 these transducers would be used to correct the displacement acquired from the actuator for the lateral load applications. Fig. 2.8 Displacements transducers to measure rotation of the pile base. One displacement transducer, LVDT3, was used to measure the slippage of the support for the actuator for the lateral load applications. The displacement transducer was installed behind the actuator support by using a magnetic stand as shown in Fig.2-9. The electronic data from all displacement transducers were automatically recorded and converted from analog to digital data, and recorded by a personal computer equipped with a data acquisition program. The displacement data were recorded every half a second during testing. 20 2.5 Test Set-up Procedure To set up each test, the specimen was installed in the apparatus by placing on the bottom part of the tube and setting the specimen in line with the reference line on the strong floor. Prior to placing the specimen on the bottom part of the tube, non-shrink cement paste was used to grout the gap between the specimen and the tube, and the specimen was then placed on the grout and adjusted with the reference line on the strong floor. The non-shrink cement paste was moderately dry and mixed from non-shrink cement and clean water. The setting time of the paste to develop 40% of the 28-days strength (approximately 22.0 MPa) was twenty-four hours. Non-shrink cement paste was also used to fill a gap between the specimen and the top part of the tube. The cement paste was applied on the specimen surface, and then, the top part of the tube was placed on top of the paste. The top and bottom parts were connected together using bolts. During bolting, part of the paste filled in the gap would be squeezed and come out from the tube to ensure that the gap was fully filled in. After placing the specimen in the tube and using the non-shrink cement paste to grout the gap between the support and the pile, the specimen was left in order to let the paste set and develop the required strength for twenty-four hours. Once the paste set, the specimen was connected to the actuator with the clamping device. For the instrumentation part, LVDT1 and LVDT2 were placed at the locations as described in Section 2.3 for rotation measurements. LVDT3 was used to measure the movement of the actuator support. LVDT4, LVDT5 and targets for some specimens as described in Section 2.3 were installed and glued for strain measurements. Al l electronic 21 devices were then connected to a personal computer to record electronic data. The complete test set-up is illustrated in Fig. 2.9. Fig. 2.9 Test set-up. 2.6 Testing Procedure First, the applied axial compression controlled by the hydraulic pressure in the actuator was increased to the specified level using a "load maintainer," which is a mechanical device that works on the principle of a moment balance between a pressure acting on a differential area hydraulic piston and a movable weight on a fulcrum arm (Kelsey Instrument, 1992). 22 The specimen was subjected to lateral load using displacement control, laterally moving the specimen to the specified displacement level within 1 to 2 minutes. At each displacement level, the specimen was subjected to three cycles. A typical load history is shown in Fig. 2.10. The displacement in each displacement level and period of each cycles were programmed in a MTS controller to control the actuator for lateral load applications. Table 2.5 provides a summary of the displacement levels used for each specimen. 2 " " kve] Fig. 2.10 Loading system by displacement control. During the test, all required data, lateral displacements, lateral loads, axial compression, and displacements from LVDT1 to LVDT5, were displayed on a computer screen. 23 Table 2.5 Summary of the actual displacement level used for each specimen. Specimen No. of Displacement Levels Displacement levels (mm) P12A 9 10, 20, 30, 40, 60, 80, 100, 120, and 140 P12B 7 20, 40, 60, 80, 100, 120, and 140 P12C 6 20, 40, 60, 80, 100, and 120 P12D 7 20, 40, 60, 80, 100, 120, and 140 P12E 6 20, 40, 60, 80, 100 and 140 P8B 7 10, 20, 30, 40, 50, 60 and 70 P4B 9 6.5, 8.0, 10.0, 12.5, 15.0, 17.5, 22.5, 35.0 and 40.0 P4E 8 3.0, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 22.5 P2B 8 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 25.0 P2E 6 2.5,5.0, 7.5, 10.0, 12.5, and 15.0 The test was paused in the 3 , d cycle at the peak negative and positive displacements in order to manually measure and record certain data and to observe aspects of the test and specimen. During displacement stages at the peaks in the 3 r d cycle, the cracks in the specimen were marked, measured and photographed as explained below, and target readings for strain measurements using a digital caliper were made. Manual recordings of important data were taken for cross checking. Once the test was completed to a certain displacement level, the specimen was returned to the neutral position in order to record some data manually and save a data file onto a backup disk and then, to program the MTS controller for the next displacement level. The test was stopped when failure occurred. During the test, the cracks in the concrete were marked with lines on the surface of the specimen adjacent to the cracks using a black ink pen, and the crack pattern was photographed at the 3 r d cycle at the peak positive and negative displacements at every displacement level. The crack widths were measured with a crack comparator. The 24 measurements were taken at approximately the location with the maximum crack width (generally in the middle of the side surfaces). A sticker with the width in millimeters was placed on the concrete next to the crack prior to photographing the crack patterns. 25 CHAPTER 3 Discussion of Experimental Results 3.1 Summary of Test Results The experimental results are summarized for each specimen in Appendix A. The information given there for each specimen includes: summary of specimen characteristics, summary of load - deformation relationship, description of what happened during the test, photographs of selected stages, plots of measured strains, a plot of the measured bending moment-curvature relationship, and plots of strain and curvature profiles at discrete points along the length of the specimen. The appearance of a typical test in progress is shown in Fig.3.1. Table 3.1 summarizes the test results of all specimens, indicating the shear force and displacement at first crack, displacement at maximum shear force, maximum displacement, and failure mode. In this chapter, a discussion of the failure modes is given in Section 3.2. Load-Displacement relationships and strains are discussed in Section 3.3 and Section 3.4, while Section 3.5 summarizes observed crack patterns and crack widths. Section 3.6 presents the analytical model and predictions of the test specimen response. Furthermore, comparison between the predicted and observed bending moment-curvature relationships can be found in Section 3.7 and summarized in Section 3.8. The study of shear response is discussed in Section 3.9. Section 3.10 presents a comparison of curvature capacities at various axial compression levels between experimental results and predictions. Finally, a proposed design tool is presented in Section 3.11. 26 3.2 Failure Modes Al l failures were flexural. These were either compression (concrete crushing) or tension (steel fracture) failure. Table 3.1 presents a summary of how each specimen failed of the 27 specimens, four specimens failed in tension (P12A, P12D, P4B and P2B) and six specimens failed in compression (P12B, P12C, P12E, P8B, P4E and P2E). Figure 3.2 shows a typical tension failure. It can be seen from the picture that fracture of the strands, possibly one or two strands, occurred at the location of the flexural crack closest to the base. Figure 3.3 shows a typical compression failure. Unlike tension failures, concrete crushing and spalling near the support were observed in compression failures with significant disintegration of the specimen. Table 3.1 Summary of test results. Specimen Nominal. Test Length (ft) Axial Load (kN) Results Failure Mode At First Crack At First Yield At Max. Capacity Max. Displ. (mm) Shear (kN) Displ. (mm) Shear (kN) Displ. (mm) Shear (kN) Displ. (mm) P12A 12.0 0 7.1 26.1 7.4 29.5 9.0 129.1 139.7 Strand fracture P12B 12.0 200 10.0 25.9 12.0 37.3 17.8 134.4 140.6 Concrete crushing P12C 12.0 600 13.5 52.0 14.3 43.5 18.6 111.4 119.7 Concrete crushing P12D 12.0 100 7.0 18.3 10.7 31.4 14.8 132.7 139.6 Strand fracture P12E 12.0 500 12.9 48.0 13.9 40.6 18.2 125.7 127.5 Concrete crushing P8B 8.0 200 15.7 16.1 15.3 17.2 24.4 68.4 70.8 Concrete crushing P4B 4.0 200 30.8 6.2 36.4 7.3 45.6 20.9 49.2 Strand fracture P4E 4.0 500 38.4 6.4 42.1 8.1 62.2 21.5 22.3 Concrete crushing P2B 2.0 200 92.3 4.1 96.4 4.6 120.1 12.5 25.1 Strand fracture P2E 2.0 500 133.5 7.4 140.2 8.3 157.0 13.9 15.6 Concrete crushing 28 Fig. 3.2 Typical tension failure after fracture of strands (Specimen PI 2D). 3.3 Load-Displacement Relationships A typical load-deformation relationship for a specimen failing in tension is shown in Fig. 3.4. It can be observed in the figure that after yielding, there was significant ability to resist higher forces. From the figure, the maximum forces are about 30% higher than the forces at yielding. The load-deformation relationship for a specimen failing in compression shown in Fig. 3.5 indicates that, due to higher axial compression, the shear force at flexural yielding of the specimen is higher than that of the specimen with low axial compression shown in Fig. 3.4. In addition, the flexural capacity of the specimen with high axial compression is also higher than that of the specimen with low axial compression. The displacement capacity of all specimens is shown in Table 3.1. It is noticed that displacement capacity varied between 119.7 mm to 139.7 for the 12 ft (3632 mm) long specimens, between 22.3 mm and 49.2 mm for the 4 ft (1194 mm) long specimens, and from 15.6 mm to 25.1 mm for the 2 ft (584 mm) long specimens. Displacement capacity for the 8 ft long specimen was 49.2 mm. In comparison for displacement capacity between the specimen with low axial compression in Fig. 3.4 and the specimen with high axial compression in Fig. 3.5, no significant difference of displacement capacity could be seen from the results. In other words, in this particular case, the displacement capacity from the specimen with low axial compression (see Fig. 3.4) was very similar to that from the specimen with high axial compression (see Fig. 3.5). It should be noted, however, that a lightly reinforced specimen with high axial compression failing in compression should have smaller displacement capacity than a specimen with low axial compression given the same property conditions (i.e. the same length, material 30 properties and reinforcement ratio). To emphasize that fact, Fig 3.6 shows a plot of displacement capacity versus axial compression. It is seen clearly from the chart that the displacement capacity drops as axial compression increases. yielding -1§.G ~20TO-Specimen PI 2D P = 100kN L = 12 ft (3.66 m) Displacement (mm) Fig. 3.4 Typical load-displacement relationship for tension failure. It can be seen in Fig. 3.7 that the envelope to the load-displacement response is approximately tri-linear. The first linear segment (line A in Fig. 3.7) is when the specimen was loaded in elastic range. Line B is the line representing when cracking has occurred. Line C is where the stiffness of the specimen is greatly reduced due to yielding of the strands. 31 Specimen Displacement Capacity 0 100 200 300 400 500 Axial Comporession (kN) Fig .3.6 Plot of displacement capacity versus axial compression. 600 700 32 Displacement (mm) Fig. 3.7 Load-displacement with tri-linear trend. 3.4 Strains Due to the fact that the piles used for the specimens were prestressed, the strains measured and discussed in this experimental program are additional or relative strain, not total strains. The calculations for the estimate of the concrete strain, and prestressed strand at time of test can be found in Appendix B. The lower-bound estimate (short term) for the concrete strain is -0.0002, while the upper-bound (long term) is -0.0009. The short term is 0.0058, and the long term is 0.0051 for the estimated strain of the prestressing strand. Strains were measured with two methods as described in Section 2.4, by displacement transducers and a digital caliper. Al l plots of strains for all specimens can be found in Appendix A. The plots in Fig. 3.8 show typical relationships between the strains and the shear force obtained from the specimen with low axial compression, specimen PI 2D, by displacement transducers. 33 Fig. 3.8 (a) is the plot showing the strains measured on the east side of the specimen. It can be seen clearly that the plot has unsymmetrical shape, larger tensile strains than compressive strains due to the fact that the steel area was vastly lower than concrete area. Therefore, in order to balance the resultant force between the compressive force and tensile force, the strains of the strands had to be much higher than those of concrete. The strains measured on the west side are presented in Fig. 3.8 (b). Similarly, the shape of the plot shown in the figure is also unsymmetrical but it is in the opposite direction. Fig. 3.8 (c) illustrates the plot of the average strains across the section. It is interesting to note that this plot is reasonably symmetrical. Observing from the plot, the average strain tended to be zero or turned back to the origin when the specimen was unloaded. Al l of this is because of prestressing force from the strands. Additionally, at this point residual strains reduce to zero. The relationship between the bending moment and curvatures (strain gradient) from the specimen can be seen in Fig. 3.9. These curvatures were determined from the strain difference divided by the distance between two positions, which was located ten inches off the base, used to measure strains, as explained in Section 2.4 and shown in Fig. 2.6. The plot shows that the curvatures increased rapidly after yielding. However, bending moment capacity on the west side was slightly higher than that on the east side. The plots of the shear force versus the strains by displacement transducers for the specimen with high axial compression, specimen P12C, are illustrated in Fig. 3.10. Similar to Fig. 3.8 (a) to Fig. 3.8 (c): Fig. 3.10 (a) shows the strains measured from east side, Fig. 3.10 (b) shows the strains from west side, and the average strains are found in Fig. 3.10(c). 34 •25 20 j •2&J , Strain (a) Stains on the east side. 20 -15... -20 -S% Strain (b) Strains on the west side. 35 •2&-T 20 -15 -20 2&J ,— Ave.Strain (c) Average strains. Fig. 3.8 Plots of typical shear-strain relationship (Specimen PI 2D): (a) strains on east side, (b) strains on west side, and (c) average strains. 80 60 -60 80 Curvature (rad/km) Fig. 3.9 Plot of bending moment-curvatures (Specimen PI 2D). 36 Unlike the specimen with low axial compression, the shapes of the plots on both east and west sides (see Fig. 3.10 (a) and Fig. 3.10 (b)) are relatively symmetrical due to the fact that high axial compression reduced tensile strains and increased compressive strains. For the average strains, it can be observed from the plot in Fig. 3.10 (c) that similar to Fig. 3.8 (c), the apparent strains reduced to zero the explanations when the specimen was unloaded. Fig. 3.11 shows the plot of the bending moment versus curvature from Specimen P12E. It can be noticed from the plot that in comparison with Fig. 3.9, the curvature capacity of the specimen was relatively lower than that of the specimen with low axial compression but the specimen had the higher bending moment capacity. 0.016 Strain (a) Strains on the east side. 37 20 4 as-i Strain (b) Strains on the west side. 25 I i g j 1 Average Strain (c) Average strains. Fig. 3.10 Plots of typical shear-strain relationship (Specimen P12E): (a) strains on east side, (b) strains on west side, and (c) average strains. 38 !0 Curvature (rad/km) Fig. 3.11 Plot of bending moment-curvatures (Specimen P12E). The plots of the strain readings and curvatures obtained from the specimen with low axial compression, specimen P12D, by targets and digital caliper are shown in Fig. 3.12. The procedure of how to measure strain using a digital caliper is described in Section 2.4 and illustrated in Fig. 2.6, and Table 2.4. This instrumentation was used to collect strain data along the pile. The strain profiles on west side and on east side are shown in Fig. 3.12 (a) and Fig. 3.12 (b) respectively. It can be noticed clearly from both figures that the highest concentration of strains occurred in the location closest to the base of the pile, i.e., at the fixed support. In fact, this particular location also had been used to measure continuous strain data by displacement transducers. Consequently, the result obtained from the digital caliper at this location was similar to that from the displacement transducers. Fig. 3.12 (c) shows the average strain profiles. The curvatures at the section closest to the base 39 also agrees well with that obtained by displacement transducers shown in Fig.3.8 (c). The average strains at other positions were almost zero. The curvature profiles are shown in Fig. 3.12 (d). The plot shows the curvatures at various positions along the pile. Again, the maximum curvatures were at the section closest to the base and, then, dropped rapidly at the next position. It can be seen that except at the first position, curvatures were almost zero. 0.025 , . 0.02 -0.01 -0.015 -0.02 -0.025 Target Position (a) Stain profile on East side. 40 0.025 0.02 -0.01 -0.015 -0.02 -0.025 J , Target Position (b) Strain profile on West side. 0.025 . 0.02 0.015 0.01 -0.01 -0.C15 -0.02 -0.025 Target Position (c) Average strain profile. 41 Target Position (d) Curvature profile. Fig. 3.12 Plots of strain profile by digital caliper (Specimen P12D): (a) strains profile on east, (b) strains profile on west, (c) average strain profile, and (d) curvature profile. The plots of the strain readings and curvatures at various positions by targets-digital caliper from the specimen with high axial compression, specimen P12E, are illustrated in Fig.3.13. Fig.3.13 (a), Fig.3.13 (b), Fig.3.13 (c) and Fig.3.13 (d) show the strain profile from west side, east side the average strain profile and the curvature profile respectively. With explanations described for the specimen with low axial compression, the similar trend can be used to conclude the results from the specimen with high axial compression. 42 0.008 0.006 -0.006 -0.008 Target Position (a) Strain profile on the east side. 0.008 -, c 2 0 35 -0.008 I Target Position (b) Strain profile on the west side. 43 0.008 0.006 0.004 0.002 -0.002 -0.004 -0.006 -0.008 . Target Position (c) Average strain profile. Target Position (d) Curvature profile. Fig. 3.13 Plots of strain profile by digital caliper (Specimen P12E): (a) strain profile on east side, (b) strain profile on west side, (c) average strain profile, and (d) curvature profile. 44 Observing from all strain results measured with both displacement transducers and digital caliper of seven specimens, the measured compressive strain limit of the specimen was approximately from 0.45 %, to 0.50 % and the measured tensile strain limit was between 1.8 % and 2.0 %. However, the test results of the bare strand both from ICP and UBC indicated that the strain limit of the strand ranged between 5.0 % and 7.0 % (with and without welding), see Table 2.3. One reason that could account for why the strain limit of the strand measured when in the pile was significantly lower than that of the bare strand is that the bond strength between concrete and the strand was extraordinary high so that no slip could occur. Therefore, once cracking occurred in the specimen, the tensile force in the strand elongated the strand between the cracks only, which had very small length. Given that fact, strain of the strand easily went up to the strain capacity. On the other hand, the observed strain of the strand in the pile during testing was measured from the length over several cracks. In other words, the strain of the strand obtained by either displacement transducers or a digital caliper was the average from the strains of the strand in the cracks over the measured length. 3.5 Crack Patterns and CracksWidths In this section the examples of crack patterns and width measurements obtained from the tests are presented in order to differentiate main crack patterns obtain from various tests of this experimental program. A complete summary of significant crack patterns and widths of all specimens are included in Appendix A. The picture in Fig. 3.14 (a) shows the crack pattern from the specimen with high axial compression, specimen P12C, while the picture in Fig. 3.14 (b) shows the crack 45 pattern from a specimen with low axial compression, specimen P12D. In addition, the crack pattern observed from the short length specimen, specimen P4B, can be seen in Fig. 3.14 (c). In order to photograph the specimen for crack patterns and widths, the procedures as explained in Section 2.4 were followed. The significant points observed from the test are described below. Al l cracks in the specimen with high axial compression were flexural and the pattern was symmetric due to the symmetry of the cross section of the specimen and testing method. The crack pattern obtained from this specimen was due to flexural tensile stresses due to the lateral load applied from the actuator (see Fig. 3.14 (a)). All cracks were perpendicular to the longitudinal axis of the test specimen. Prior to failure, the average spacing was 125 mm, and the maximum spacing between cracks was 200 mm located on east side. Cracks in the specimen with low axial compression were also flexural (see Fig. 3.14 (b)) but on the other hand, spacings between the cracks were generally larger. Prior to failure, the average spacing was 185 mm, and the maximum spacing between cracks was 250 mm. Table 3.4 summarizes the number and average spacings between cracks for all test specimens. 46 Table 3.2 Summary of average spacing of test specimens. Specimen Nominal Test Length (ft) Axial Comp. (kN) No. of Cracks Average Spacing (mm) East West East West P12A 12.0 0 8 8 161 161 P12B 12.0 200 7 10 133 99 P12C 12.0 600 9 9 131 116 P12D 12.0 100 11 10 160 178 P12E 12.0 500 8 11 154 113 P8B 8.0 200 4 4 168 173 P4B 4.0 200 4 2 125 200 P4E 4.0 500 2 3 225 157 P2B 4.0 200 2 2 100 150 P2E 4.0 500 1 1 N/A N/A Fig. 3.14 (a) Crack pattern from the specimen with high axial compression (P12C). 47 Fig. 3.14 (b) Crack pattern from the specimen with low axial compression (P12D). Observations of the differences between the long pile and the short pile are described as follows. Only cracks in pure flexure were observed in the long specimen (see Fig. 3.14 (b)). Al l cracks were perpendicular to the longitudinal axis of the specimen. On the other hand, some cracks that formed in the specimen that had short length as shown in Fig. 3.14 (c) were inclined as a result of the combination of flexural tensile stresses and diagonal tensile stresses due to shear. The diagonal cracks initiated as flexural cracks in the middle of the side surfaces both on west and east sides (i.e., the diagonal cracks were originally flexural in the middle on both surfaces). The inclination of the diagonal cracks was approximately 45 degrees (measured from the longitudinal axis of the specimen). 48 Fig. 3.14 (c) Crack pattern from the short specimen (P4B). Crack widths observed from the specimen with high axial compression (see Fig. 3.14 (a)) were smaller than those from the specimen with low axial compression as shown in Fig. 3.14 (b). At the very first displacement levels, most of the cracks closed completely when unloaded due to the fact that the specimen was prestressed. Prior to failure, the measured crack widths varied from 0.10 mm to 0.30 mm in the specimen with high axial compression whereas the crack widths varied from 0.10 mm to 1.50 mm in the specimen with low axial compression. During loading, cracks widths were continually increasing as the displacement increased. 49 3.6 Analytical Model for Flexural Response Response-2000 was used in this study to make predictions. The program was developed at the University of Toronto by Evan Bentz (1999). Response-2000 is a sectional analysis program that will calculate the strength and ductility of a reinforced concrete cross-section subjected to moment, axial load and shear force. Al l three loads can be considered simultaneously to find the full load-deformation response. Important strain compatibility assumptions used in the program are that the plane sections remain plane, the longitudinal strains are uniform across the width of the section, and the average strain of a prestrssing strand is equal to the average strain of the surrounding concrete plus the initial prestressing strain, Asp. The relationship between the uniaxial compressive concrete stress, f'c, and the corresponding uniaxial strain, sc, used in the program is that suggested by Thorenfeldt et al. (1987) and is given by = . n(ecls'c) JC J C 1 , / I ' \ n-\ + (sclsc) The cylinder compressive strength of the concrete, f'c, assumed in the analysis was 100 MPa. For the concrete of that strength, Collins and Mitchell (1991) suggeste the following parameters which define the shape of the curve: n = 4.83, k = 1.77, and s'c = -0.005 (used in the program). The resulting stress-strain response is shown in Fig. 3.15 (a). The idealized bilinear stress-strain relationship in the program used for the prestressing strands is based on elastic-plastic assumption and shown in Fig, 3.15 (b). 50 120 100 C O u 40 20 -i 0 f'c = 100 MPa / ft = 2.84 MPa 0 Strain, £ c (a) Modeled concrete stress-strain relationship. 1600 ., Strain, Sp (b) Modeled prestressing strand stress-strain relationship. Fig. 3.15 Modeled stress-strain relationship: (a) concrete, and (b) prestressing strand. 3.7 Comparison between Predicted and Observed Bending Moment - Curvature Relationships Three different levels of axial compression were used as input data in the program for the prediction: P = 100 kN, 200 kN, and 500 kN. The predicted bending moment-curvature 51 relationships obtained from the program were compared with those from the experimental results of the specimens with transducers to measure strains, which were PI 2D, P12E, P8B, P4B, P4E, P2B and P2E. In order to obtain the reasonably best fit predicted bending moment curvature relationships compared to the experimental results, different concrete moduli of elasticity were used in analysis for different specimens shown in Table 3.3. Properties of a prestressing strand used in the prediction for all specimens were 1400 MPa for strength and 200000 MPa for modulus of elasticity. Table 3.3 Material properties used in the prediction. Specimen Concrete Compressive strength, f'c (MPa) Modulus of Elasticity E c (MPa) P12D 100 22048 P12E 100 13780 P8B 100 22048 P4B 100 11024 P4E 100 11604 P2B 100 11604 P2E 100 11024 The plots of bending moment-curvature relationships, both the experimental and the predicted results (broken lines), are shown in Fig. 3.16- Fig. 3.22, respectively. From Fig. 3.16, which is for Specimen PI 2D, the plot shows that the predicted bending moment agrees well with the experimental result on east side but is approximately 17 % lower than the observed bending moment capacity on west side. Observed curvature 52 capacity from both the east and west sides are also 23 % higher than predicted results. That is Specimen PI 2D was unsymmetrical in terms of strength. The bending moment-curvature response of specimen P12E is shown in Fig. 3.17. Similar to PI 2D, the observed bending moment capacity on east side is well matched with the one from prediction but on west side, the observed bending moment capacity is about 13% lower than the predicted capacity. The curvature capacity obtained from the prediction is 18 % higher than that from the experimental result. The comparison of the bending moment-curvature response between the predicted and the observed results for the specimen P8B is shown Fig. 3.18. It is noted that the predicted results, both bending moment capacity and curvature capacity, agree well with the observed result. 40 -20 -20 -90 -60 -yf /jk -60 30 60 90 1: ' Predicted Curvature (rad/km) Fig. 3.16 Bending moment-curvature response of Specimen PI 2D. 53 Fig. 3.19 shows the comparison of bending moment-curvature response for specimen P4B. On the east side, the bending moment from the test gradually dropped as the specimen failed in tension on this side. From the plot, the curvature capacity from the prediction is significantly higher than observed on the east side, however, the predicted curvatures match with the observed results on the west side. The bending moment at any given curvature from the prediction fits well the result from the experiment on the west side. Curvature (rad/km) Fig. 3.17 Bending moment-curvature response of Specimen P12E. The response of Specimen P4E, a specimen with 500 kN axial compression, can be seen in Fig. 3.20. It can be concluded in both bending moment and curvatures that the results from the test gave lower capacities than predicted, 12 % lower in bending moment capacity and 16 % lower in curvature capacity. 54 55 The responses of Specimen P2B and P2E are illustrated in Fig. 3.21 and Fig. 3.22, respectively. Only the information on the west side for both P2B and P2E can be used to compare with the result from the prediction due to the problem of the clamping device when the specimen was cycled to east side. Observation from both plots, the bending moment capacity from the prediction is 23 % higher in P2B and 28 % higher in P2E. However, the predicted curvatures agree well with those from the experiment. *aoJ C u r v a t u r e ( r ad/km) F i g . 3.20 Bending moment-curvature response of Specimen P4E. 56 I SO-J Curvature (rad/km) F i g . 3.21 Bending moment-curvature response of Specimen P2B. 80 I 80-J Curvature (rad/km) F i g . 3.22 Bending moment-curvature response of Specimen P2E. 57 With the results and discussions above for the specimens that had the unsymmetrical bending moment-curvature response (P12D, P2B and P2E), possibilities could be as the following. For Specimen P12D (see Fig. 3.16), the alignment of the Dywidag bar used to apply axial compression might have been the main cause. That is, the Dywidag bar aligned off the center of the pile may have resulted in additional bending moments. The predicted maximum shear force for Specimen P2B and P2E is higher than the experimental result due to cracking near the open end of the support of the grouting paste used to fill the gap in the support that allowed the specimen to move easier with lower applied lateral force. 3.8 Curvature Capacity of Piles The summary of observed strain limit, observed curvature capacity and predicted curvature capacity is shown in Table 3.4. The results of the specimens that failed in compression are shown in Table 3.4 (a). It is noticed that the concrete strains at the maximum bending moment are consistent, 5.2 % for maximum in P8B and 4.5 for minimum in P2E. Curvature capacity from P12E is almost the same as that from P4E. P8B had the maximum curvature capacity among the specimens in compression failure. The information from the specimens that failed in tension can be found in Table 3.4 (b). The tensile strains at the bending moment capacity ranged between 18.22 % and 22.2 %. P4B had the maximum tensile strain and P12D gave the minimum result. The curvature capacities range between 87.3 rad/km and 93.3 rad/km for specimens in tension failure. It can be concluded that both tensile strains and curvatures are consistent. 58 Table 3.4 Summary of strain and curvature capacities at failure. (a) Compression failure. Specimen Nor. Test Length (ft) Axial Comp. (kN) Max. Comp. Strain (xlOOO) Curvature (rad/km) Remark P12E 12.0 500 5.11 51.15 Concrete crushing on east side at first cycle P8B 8.0 200 5.20 84.04 Concrete crushing on east side at third cycle P4E 4.0 500 4.80 52.00 Concrete crushing on east side at first cycle P2E 2.0 500 4.52 72.92 Concrete crushing on east side at third cycle (b) Tension failure. Specimen Nor. Test Length (ft) Axial Comp. (kN) Max. Comp. Strain (x1000) Curvature (rad/km) Remark P12D 12.0 100 18.22 87.26 Strand fracture on east side at second cycle P4B 4.0 200 22.18 91.00 Strand fracture on east side at first cycle P2B 2.0 200 18.64 93.30 Strand fracture on east side at first cycle 3.9 Shear Failure Shear action was one of the issues that was to be investigated in this study. The 2 ft and 4 ft long specimens were included in the program in order to obtain information about shear response (e.g., diagonal shear cracking and shear strength). Specimen P4B, P4E, P2B and P2E were tested for this purpose. 59 It turned out that shear deformations were not significant and did not dominate the mechanism of the short specimens. In fact, very little shear action (e.g., some diagonal shear cracking) was observed due to the fact that the piles tested were lightly reinforced {AMc = 0.6%). The appearance of the short specimens while testing is illustrated in Fig. 3.14 (c), Fig. 3.23 to Fig.3.25. Fig. 3.14 (c) and Fig. 3.23 demonstrate some diagonal shear cracking observed in specimen P4B and P2B respectively. Shear cracking developed as previously discussed in Section 3.5. It can be seen from the figures that all shear cracking developed as an extension of flexural cracking. In the short specimens with high axial compression, P4E and P2E, no significant shear cracking was noticed (see Fig. 3.24 and Fig. 3.25). Fig. 3.23 Shear cracking from the short specimen with low axial compression (P2B). 60 Response-2000 was also used to predict the shear response of the specimens. The predicted results compared with the experimental results are shown in Table 3.5. It can be interpreted from the table that shear strength of the specimens obtained from the prediction is vastly higher than maximum shear at flexural failure. The predicted results well support the results from the tests and explain why there was no significant shear action. However, the tests from the short specimens were expected to show some diagonal cracking. Fig. 3.24 Shear cracking from the short specimen with high axial compression (P4E). 61 Fig. 3.25 Shear cracking from the short specimen with high axial compression (P2E). Table 3.5 Summary of shear prediction Axial Compression (kN) Predicted shear strength (kN) Maximum shear at flexural failure (kN) 100 139.4 39.0 200 133.8 44.3 500 147.8 65.3 3.10 Comparison of Predicted and Observed Curvature Capacities Fig. 3.26 shows a chart that compares the predicted curvature capacities with the observed results given various axial compression levels for a 250 mm diameter pile. The chart was built in the sense that it represents curvature capacities obtained from the predicted results in predictions of analytical models using Response-2000 in various axial 62 compression levels and compares those with experimental data observed from the tests. Different strain limits both in compression and tension were employed in the predictions. Two concrete compressive strains were used in the analysis which are: e'c = -0.004 and -0.005. Three different levels of tensile strains are shown in the chart for tension limit: eT= 0.010, 0.015 and 0.020. To establish the chart, the compressive strain limit and the tension strain limit of the pile were assumed. Provided these strain limits and stress-strain relationship of steel and concrete, Response-2000 could be used to model and calculate curvature capacity of the pile subjected to a specific axial compression level, and using different axial compression levels, the curvature capacity profile could be obtained as shown in Fig. 3.26. In this chart, the range of axial compression level used is from 0 kN to 800 kN, which is the allowable load recommended by the supplier for this pile size. It can be seen from the chart in Fig. 3.26 that the predicted curvature capacities obtained from compressive strain limit: s c = -0.005, and tension strain limit: sp = 0.015, are reasonably conservative and match with the experimental results. In compression failure, the experimental results from the specimens with high axial compression (P12E, P4E and P2E) are consistent and about 20% higher than the predicted results (see Fig. 3.26). However, the result from P8B is approximately the same as the predicted result. In tension failure, the experimental results from P12D, P4B and P2B are close to the predicted results. 63 Provided the experimentally determined strain limits and using computer programs such as Response-2000, one can establish design charts for other pile sizes. For piles of much larger size, however, additional experimental work is needed to establish the strain limits. .160. -1000 -800 -600 -400 -200 0 200 Axial compression (kN) Fig. 3.26 Strain estimate for a 250 mm dia. pile. 3.11 Design Tool Fig. 3.27 shows a proposed design chart that can be used to determine the curvature capacity of a pile subjected to specific axial compression in any given earthquake event. 64 Due to brittle nature of the failure of these piles as described in Section 3.2, this chart should be used cautiously. In order to determine the curvature demand, the displacement profile of the pile must be known. Various textbooks on soil mechanics and foundations suggest procedures for computing lateral pile load-deformation based on complex soil conditions and/or non-linear soil stress-strain relationships. In addition, pile deformation and stress can be approximated through application of several simplified procedures based on idealized assumptions. The two basic approaches depending on utilizing the concept of coefficient of lateral subgrade reaction can be found in Reference 4. In this section, an example of calculating curvature demand of a pile is shown. Fig. 3.28 (a) shows the displacement profile of a 15 m long pile subjected to the 300 kN axial compression and confined by medium dense granular silty sand. The effective length, le, with zero slope at one end to zero slope at another end, shown in Fig. 3.28 (b), is 10 m. The drift, A, between the two ends is known to be 50 mm, see Fig. 3.28 (b). The curvature profile within the effective length is shown in Fig. 3.28 (c) and maximum curvature, <pmax, can be calculated as follows: max •4 max (b = 3-=- = 3 rmax . 2 (50mm) e (10000 mm)2 = l-Srad /km 65 (a) Displacement profile of the pile. (b) The effective length, le \0. G I / (c) The curvature profile. Fig. 3.28 Lateral displacement profile of a pile (from (a) to (c)). From the chart it is seen that for axial compression: P = 300 kN, the corresponding curvature capacity, (^capacity, is 28 rad/km. The curvature demand, <fimax, as calculated for this pile in this specific event is 1.5 rad/km. Therefore, the ratio of curvature capacity, ^capacity, to curvature demand, <f)max, is 18.6. In actual design of this pile, the ratio of curvature capacity to curvature demand must be greater than a certain value (i.e., the factor of safety). The factor of safety that 67 should be used in design depends on how confident the design is in the calculation of curvature demand, and the consequences of a brittle failure on the structure supported by the piles. Note that the direction of loading was assumed to be as shown in Fig. 2.4. Additional design charts can be developed for other directions. For applications in design, the worst direction chart should be used as the direction of loading is not known. 68 CHAPTER 4 Summary and Recommendations 4.1 Summary The objective of this research program was to investigate the seismic behavior of Pretensioned Spun High Strength Concrete Pile, which is a product from Industrial Concrete Products Berhad, Malaysia. To make the piles, concrete is consolidated by centrifugal force generated by spinning process. One size of pile (250 mm diameter) was used and cut into difference lengths in order to make ten test specimens. Therefore, all test specimens had the same cross section. The piles were subjected to different levels of axial compression. The behavior of all test specimens was studied and monitored throughout the testing, at first cracking and until failure occurred. Although there was some diagonal cracking in the shorter specimen, the ultimate behavior of all specimens was dominated by flexure. Al l specimens failed by flexural either in compression or tension. Concrete crushing was the cause of compression failure, and fracture of the strands was the cause of tension failure. No significant shear failure was observed due to the fact that the ratio of prestressing strands to concrete cross section area is very small, approximately 0.6 %. As a result, concrete stress in the direction parallel to longitudinal direction of the test specimen reached flexural failure prior to diagonal direction. 69 Strains that were measured and studied in this experiment were relative or apparent strains. The initial strains were also estimated. From all strain results measured from seven specimens, the estimated total compressive strain limit (long term) of the specimen was approximately from 0.54 %, to 0.59 % and the estimated tensile strain limit (long term) was between 2.31 % and 2.51 %. Nonetheless, the test result of the bare strand both from the supplier and UBC indicate that the strain limit of the strand rage between 5.0 % and 7.0 %. Such different strain limits between these two results is due to the fact that the strains obtained from the test specimens were the average strains over several cracks but the strains of the strands in one crack were much higher as explained in Section 3.4. A comparison of crack patterns and crack widths is given for specimen with low axial compression versus high axial compression and long specimen versus short specimen. Comparison between specimen with low axial compression and specimen with high axial compression shows that the cracks both from the specimen with high axial compression and from the specimen with low axial compression were flexural (in the long specimens) and also perpendicular to the longitudinal axis of the pile. The crack pattern was symmetric and was due to flexural tensile stress caused by the lateral applied load. However, crack spacings and crack widths obtained from the specimen with low axial compression were normally larger and wider that those from the specimen with high axial compression. The difference between the long specimen and short specimen is that only flexural cracks occurred in the long specimen but the short specimen had some diagonal cracking due to the combination of flexural tensile stresses and diagonal tensile stresses from 70 shear. The diagonal cracking developed further as flexural cracking in the middle of the side surfaces both on west and east sides. It is clear that the displacement capacity of the pile increases as the length of the pile increases from 2 ft to 12 ft. In addition, as observed from all load-displacement relationships, the envelope of the relationships is tri-linear (see Fig. 3.4), the steepest when in elastic range, the moderate when cracking, and the least steep due to yielding of the strands. Response-2000 was used to make predictions of the bending moment-curvature response of the test specimens. The assumptions used in the program are that plane sections remained plane (compatibility) and that there is no clamping stress across the depth of the beam. Subsequently, only two strain variables (i.e., strain at the centroid scen and curvature (j>) accounted for the complete strain distribution over the cross section. With the modeled concrete and strand stress-strain relationships, corresponding bending moment could be calculated given axial compression. In addition, in order to accurately make the predictions, the effects of tension stiffening, steel relaxation and creep were taken into account in the program. In comparison of bending moment and curvatures between the predictions and the test, the experimental results reasonably match with the predicted results. With all observed strains from the tests and using Response -2000 to determine the curvatures, the curvature -axial compression chart could be accomplished. This chart (see Fig. 3.26) represents estimate curvature capacities given the strain limits, concrete and the strand, in various axial compression levels. Further more, for purpose of simpler use, the proposed 71 design chart was developed with some factors taken into account and can be used as described in Section 3.11. Although only the 250 mm dia. pile was used in the experimental program, a design chart for other pile sizes can be determined using the strain limits measured in this study and a computer model such as Response-2000 to calculate sectional properties. 4.2 Recommendations It may be possible to modify the pile in order to improve the seismic performance. As a consequence, further research would be needed to investigate the behavior of the modified piles. Some possible modifications could be as follows: • Only prestressing strand was used in PHC piles tested in this study for longitudinal reinforcement. Although, prestressing strands have high capacity in terms of strength, they have poor strain capacity. Compared to prestressing steel, normal reinforcing steel or mild steel has much higher strain capacity. With that in mind, normal reinforcing steel could provide additional strain capacity for the pile, once fracture of the strand occurs. As a consequence, a combination of prestressing strands and regular reinforcing steel in various ratios can be used for the modification. • In the observed data from the specimen with high axial compression, one can see that the strength of the specimen greatly decreased after yielding because the specimen substantially lost concrete area due to cover spalling. The modification is to provide additional equivalent concrete area in the critical section (plastic 72 hinge region) to resist axial compressive stress after yielding. In real situations, once the pile moves laterally, the critical section would form at the maximum bending moment sections such as near the connection between a pile cap and the pile (see Fig. 3.28 (a)). It could be an additional steel pipe or steel bars reinforced in the critical section with an appropriate detail connection to the pile cap. Improving the confinement of the pile could also be used. Disintegration of concrete in the specimen with high axial compression was because of very little of confinement of the concrete. In order to improve the confinement, new arrangement of transverse reinforcement and/or concrete clear cover should be considered, increasing area of steel by adding more steel bars, reducing the pitch distance of the spiral steel to improve the buckling load of the steel bars and decreasing the concrete clear cover so that the pile will have more confined concrete area which is important to resist the force after spalling. 73 REFFERENCES 1. Industrial Concrete Products Berhad, "PHC Pile Manual" 2. Mori, T., Suzuki, N. , and Ikeda, S., 1999, "Seismic Performance of Prestressed Concrete Piers," RE A A A Journal, Vol. 8, No. 2, pp. 4-13. 3. Sugimura, Y. and Hirade, T., 1988, "Experimental Study on Degree of Fixation at Pile Head Joint of Prestressed High Strength Concrete Piles," Proceedings of Ninth World Conference on Earthquake Engineering, Tokyo, Japan, Vol. IV, pp 437-442. 4. NAVFAC Design Manual, 1986, "Foundation and Earth Structures," Naval Facilities Command Alexandria, Virginia, pp 234-241. 5. Paulay, T., and Priestley, M.J.N., "Seismic Design of Reinforced Concrete and Masonry Buildings", John-Wiley & Sons, Inc. 6. Collins, M.P., and Mitchell, D., 1991, "Prestressed Concrete Structures," Prentice-Hall Inc., Englewood Cliffs, New Jersey. 7. Bentz, E., 1999, "Response-2000 Manual," University of Toronto, Toronto. 8. Chong, C ; Hong, S.; Ling, A.; Macmillan, C ; Munro, J.; Vanderzwaag, J.; "Effects of Welded Ties on Steel Reinforcing Bars," CIVL 321 Report, Department of Civil Engineering, the University of British Columbia, April 2001, 25 pp. 74 APPENDIX A Test Descriptions Specimen: PI 2 A Characteristics • Test length: Brief Results Axial compression: Crack pattern: Shear force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Crack width at max. shear: Max. Displacement: Failure Type: Test Date: January 10, 2001 11 ft 11 in. (12 ft) OkN Flexural cracks 7.1 kN 26.1 mm 0.15 mm 9.0 kN 1.75 mm 139.7 mm Flexural failure by fracture of rebars Load-Displacement Relationship P12A: Load-Displacement Displacement (mm) 75 Specimen P12A Test Observations: • the specimen was subjected to three cycles at +/-10 mm, and three cycles at +/-20 mm and no cracking was observed • the first crack occurred during the 1st cycle of the +/-30 mm displacement level, when the displacement was equal to +26mm; this crack was a flexural crack located on the west side at the very base of the pile; the width of the crack was measured while the displacement was held constant at +30 mm and found to be 0.15 mm • due to a computer problem, some data was lost during the 3rd cycle to +/-30 mm • during the 1st cycle to +/-40mm, three new flexural cracks were observed on both east and west sides; while holding the displacement constant at +40 mm in the 3rd cycle, the crack widths were measured to be 0.25 mm, 0.25 mm, 0.20 mm and 0.10 mm as shown in Fig. SP1-1; the spacing of the cracks were 125 mm, 250 mm, 375 mm • during the +/- 50 mm displacement level, one new additional flexural crack formed; the widths of the cracks increased to 0.30 mm, 0.30 mm, 0.25 mm, 0.10 mm (new crack), 0.15 mm; the spacing of the cracks reduced to 125 mm, 250 mm, 250 mm, 125 mm • in cycle of the +/- 60 mm displacement level, there were one new additional flexural crack when cycled to +60 mm in the 2nd cycle, and two further flexural cracks in the 3rd; the widths of cracks were observed to be 0.40 mm, 0.35 mm, 0.10 mm (new crack), 0.30 mm, 0.10 mm (new crack), 0.15 mm, and 0.10 mm (new crack); the spacing of the cracks changed to be 125 mm, 125 mm, 125 mm, 250 mm, 125mm, and 375 mm • no new cracks occurred during the +/- 70 mm displacement level • one new flexural crack appeared in the cycle of +/- 80 mm displacement level at 3rd cycle; the crack widths were 0.75 mm, 0.50 mm, 0.20 mm, 0.30 mm, 0.10 mm (new crack), 0.15 mm, 0.20 mm, and 0.10 mm; the spacing were 125 mm, 125 mm, 125 mm, 175 mm, 75 mm, 125 mm, and 375 mm • during the +/-100 mm displacement level at 3rd cycle some concrete spalled off at the very base of the specimen, near the support, but no new cracks were noticed; the widths increased to 1.00 mm, 0.60 mm, 0.40 mm, 0.40 mm, 0.30 mm, 0.30 mm, 0.20 mm, and 0.10 mm • only the change of the crack widths was noticed in the cycle of +/- 120 mm displacement level; the widths were measured to be 1.75 mm, 0.80 mm, 0.40 mm, 0.40 mm, 0.30 mm, 0.30 mm, 0.25 mm, and 0.15 mm, see Fig. SP1-2 • at the last stage failure mechanism was identified at +139.7 mm in Is' cycle and the corresponding shear force was found to be 9.0 kN • the specimen failed by fracture of the strands at the location of the flexural crack closest to the base as shown in Fig. SP1-3 and Fig. SP1-4 76 77 78 Specimen: P12B Test Date: January 30,2001 Characteristics • Test length: • Axial compression: Brief Results • Crack pattern: • Shear force at first crack: • Displacement at first crack • Crack width at the peak: • Max. Shear force: • Crack width at max. shear: • Max. Displacement: • Failure type: Load-Displacement Relationship Load-Displacement: P12B 2M~-r Displacement (mm) 11 ft. 11 in. (12 ft) 200 kN Flexural cracks 10.0 kN 25.9 mm 0.10 mm 17.8 kN 1.25 mm 140.6 mm Flexural by concrete crushing 79 Specimen P12B Test observations: • in the first stage, +/-20 mm displacement level, the specimen was subject to three cycles and no cracks were observed • the first flexural crack, on west side measured when cycled to +25.9 mm in the 1st cycle of the +/-40 mm displacement level; there were two additional flexural cracks on the same side afterwards in the same cycle; the widths of the cracks were measured while the displacement was held constant at +40 mm and found to be 0.10 mm (first crack), 0.10 mm, and 0.05 mm; the spacing of the cracks were found to be 125 mm, 150 mm, and 150 mm; on the east the first flexural crack was found when the specimen was displaced to -30 mm, and two additional cracks were also noticed in the same cycle on this side; these two cracks were flexural ,and the widths of the cracks were 0.10 mm (first crack), 0.15 mm, and 0.05 mm; the spacing between the cracks were 250 mm, and 250 mm; during cycled in the 2nd cycle of this displacement level, one new flexural cracks appeared on west side but the crack width was less than 0.05 mm and was not be able to be measured by using a crack comparator; the spacing was found to be 125 mm as shown in Fig. SP2-1 • one new flexural crack on east side was marked when cycled to -60 mm in 2nd cycle of+/- 60 mm; in the 3rd cycle of +60 mm, two new further flexural cracks were observed; at this stage the widths of the cracks on west side changed to be 0.20 mm (new crack), 0.25 mm, 0.15 mm, 0.10 mm, 0.05 mm, and 0.05 mm (new crack); the spacing between the cracks were 100 mm, 150 mm, 125 mm, 125 mm, and 200 mm, when cycled to -60 mm in 2nd cycle, one new additional crack occurred on east side; the crack was flexural and the width was 0.05 mm; the spacings of the cracks on this side were 250 mm, 250 mm, and 300 mm • during the +/- 80 mm displacement level, concrete spalling at the very base of the pile on west side as well as one new flexural crack were recorded when cycle to +80 mm; one new flexural crack on east side was noticed when cycled to -80 mm in the 1st cycle; there was another flexural crack on east side also marked in the 2nd cycle of -80mm; in this stage the widths of the cracks on west side were 0.20 mm, 0.35 mm, 0.40 mm, 0.35 mm, 0.40mm, 0.25 mm, and 0.15 mm (new crack) , and the spacings were 100 mm, 150 mm, 125 mm, 125 mm, 200 mm, and 188 mm as shown in Fig. SP2-2; for the cracks on east side, the widths increased to 0.50 mm, 0.20 mm (new crack), 0.50 mm, 0.35 mm, 0.25 mm (new crack), 0.15 mm, and spacing of the cracks in the displacement level were 150 mm, 100 mm, 250 mm, 150 mm, and 150 mm • in the +/- 100 mm displacement level when cycled to +100 mm in the 1st cycle, three additional flexural cracks in west side as well as further concrete spalling off near the support on the same side were noted; the widths of the cracks were 0.50 mm, 0.50 mm, 0.45 mm, 0.30 mm, 0.40 mm, 0.35 mm, 0.25 mm, 0.10 mm (new crack), 0.10 mm (new crack), and 0.05 mm (new crack); for the widths of all cracks on east side increased to 0.60 mm, 0.40 mm, 0.50 mm, 0.50 mm, 0.30 mm, and 0.25 mm, and the spacings were the same as the previous displacement level; no further cracks occurred on both for the rest cycles of this displacement level • there was only one flexural marked on east side when cycle to -100 mm in 1st cycle of+/- 120 mm displacement level; the widths of the cracks on west side changed to be 0.80 mm, 0.60 mm, 0.50 mm, 0.35 mm, 0.40 mm, 0.40 mm, 0.30 mm, 0.15 mm, 0.10 mm, and 0.10 mm but there was change in spacings of the cracks; the widths of the cracks on east side were measured to be 0.80 mm, 0.40 mm, 0.60 mm, 0.50 mm, 0.30 mm, 0.25 mm, and 0.15 mm • at the +/-140 displacement level, the failure of the specimen was identified; the failure mechanism was flexural failure by concrete crushing on east side as shown in Fig. SP2-3 when cycled up to +134.4 mm in 2nd cycle; the center of the crushing was 150 mm from the support • the test was stopped at 3rd cycle of+140 mm in this displacement level 8 0 Fig. SP2-1 Specimen: P12C Characteristics • Test length: Brief Results Axial compression: Crack pattern: Shear force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Crack width at max. shear: Max. Displacement: Failure type: Load-Displacement Relationship Test Date: 11 ft. 11 in. (12 ft.) 600 kN Flexural cracks 13.5 kN 52.0 mm 0.25 mm 18.6 kN 0.30 mm 119.7 mm Flexural by concrete crushing January 18, 2001 Load-Displacement: P12C -150 150 180 Displacement (mm) 84 Specimen P12C Test Observations: • the first crack occurred on west side when the specimen was cycled to +52.0 mm in the +/- 60 mm displacement level; there were three new cracks on this side at the same cycle and in the same displacement level; the cracks were flexural and the widths were measured to be 0.25 mm, 0.20 mm (first crack), 0.20 mm, and 0.15 mm; the spacings of these cracks were 125 mm, 200 mm, and 175 mm; the first flexural crack on east side occurred when cycled to -55.0 mm, and in the same side two additional flexural cracks were observed in the 2 n d cycle of -60.0 mm; the widths if the cracks were recorded to be 0.25 mm (first crack), 0.20 mm, and 0.10 mm; the spacings were 150 mm, 175 mm, and 175 mm, see Fig. SP3-1 • during the +/- 80 mm displacement level, two additional flexural cracks on west side were seen while cycled in the 1st cycle observe; another flexural crack occurred during in the 2 n d cycle of +80.0 mm; the widths of the cracks were measured to be 0.20 mm, 0.20 mm, 0.15 mm (new crack), 0.15 mm, 0.10 mm (new crack), and 0.10 mm (new crack); the spacing of the cracks were 125 mm, 88 mm, 112 mm, 175 mm, 125 mm, and 100 mm; on east side there were three new flexural cracks when cycled in the Is' cycle of the this displacement level at 2 n d cycle; the widths of the cracks were 0.20 mm, 0.20 mm, 0.15 mm, 0.10 mm, 0.10 mm (new crack), 0.10 mm (new crack), and 0.10 mm (new crack); the spacings of the cracks were measured to be 150 mm, 175 mm, 175 mm, 150 mm, 125 mm, and 100 mm • two new flexural cracks on west side were observed when the specimen was displaced in the 1st cycle to +100 mm of +/- 100 mm displacement level; the widths of all cracks on west side were measured in this level equal to 0.30 mm, 0.30 mm, 0.25 mm, 0.25 mm, 0.20 mm, 0.20 mm, 0.20 mm, 0.10 mm (new crack), and 0.10 mm (new crack), and the spacing between cracks were 125 mm, 88 mm, 112 mm, 175 mm, 125 mm, 100 mm, 125 mm, and 75 mm as illustrated in Fig. SP3-2; for observations on east side, there were also two further flexural cracks occurred during the 1st to -100 mm; the widths of the cracks increased to 0.30 mm, 0.30 mm, 0.25 mm, 0.25 mm, 0.20 mm, 0.15 mm, 0.10 mm, 0.10 mm (new crack), and 0.10 mm (new crack), the spacings of the cracks were recorded to be 150 mm, 175 mm, 175 mm, 150 mm, 125 mm, 100 mm, 175 mm, and 200 mm • the specimen failed in +/- 120 mm displacement level by flexural failure by concrete crushing when cycled to +120 mm in the 1st cycle; big explosion was noticed when failure occurred; failure mechanism was recorded at +111.4 mm and the corresponding shear force was found to be 18.6 kN as shown in Fig. SP3-3 and Fig. SP3-4 85 Fig. SP3-1 Fig. SP3-2 86 87 Specimen: P12D Test Date: February 7,2001 Characteristics • Test length: • Axial compression: Brief Results • Crack pattern: • Shear force at first crack: • Displacement at first crack • Crack width at the peak: • Max. Shear force: • Crack width at max. shear: • Max. Displacement: • Failure type: Load-Displacement Relationship Load-Displacement: P12D g&rO-T -16,04 O^rO Displacement (mm) 11 ft. 11 in. (12 ft.) 100 kN Flexural cracks 7.0 kN 18.3 mm 0.08 mm 14.8 kN 1.25 mm 139.6 mm Flexural by fracture of rebars 88 Specimen P12D Test Observations; • the first crack was marked during the 1st cycle of +1-20 mm displacement level, when the specimen was cycled to -18.3 mm; this crack was flexural crack located on east side closest to the support; two additional flexural crack were also observed on the same side and in the same cycle; the width, again, were measured while the displacement was held constant at + 20 mm and equal to 0.08 mm, 0.08 mm, and 0.05 mm; the spacing of the cracks were 150 mm, and 225 mm; no crack appeared on west side in this displacement level • during the +/- 40 mm displacement level, the first crack on west side appeared when cycled to +30 mm in the 1st cycle; this crack was also flexural; and two further cracks on the same side were also observed in this cycle; the widths of the cracks on this side were found to be 0.25 mm, 0.15 mm, and 0.10 mm; the spacings were 175 mm, and 250 mm; for observations on east side, three new flexural cracks were noticed during the 1st cycle to -40 mm, two further cracks were also marked on this side, one crack in 2nd cycle and the other in 3rd cycle, but only four cracks were able to be measured width by a crack comparator; the widths of the cracks were 0.20 mm, 0.15 mm, 0.10 mm, and 0.10 mm (new crack); the spacing between the cracks were 150 mm, 225 mm, 175 mm, 225 mm, 100 mm, 175 mm, and 200 mm as seen in Fig. SP4-1 • one new flexural crack appeared on west side at 1st cycle to +60 mm in +/-60 mm displacement level; there is also one new flexural crack in 2nd cycle and two flexural cracks in 3rd cycle to +60 mm on the same side; the widths of the cracks were equal to 0.10 mm (new crack), 0.30 mm, 0.20 mm, 0.15 mm, 0.10 mm (new crack), 0.08 mm (new crack), and 0.08 mm (new crack); the spacing were 100 mm, 175 mm, 250 mm, 325 mm, 375 mm, 150 mm, and 225 mm; when cycled to -60 mm, there were two further cracks occurred on east side; the widths of all cracks on this side increased to 0.35 mm, 0.25 mm, 0.10 mm (new crack), 0.20 mm, 0.15 mm, 0.10 mm, 0.10 mm, 0.10 mm, 0.08 mm (new crack), 0.08 mm (new crack); the spacings were found to be 150 mm, 150 mm, 75 mm, 175 mm, 225 mm, 100 mm, 175 mm, 200 mm, and 250 mm • during the +/- 80 mm displacement level, three additional flexural cracks on west side were observed when the specimen was cycled to +80 mm in the 1st cycle; the widths of cracks were equal to 0.10 mm, 0.45 mm, 0.40 mm, 0.30 mm, 0.15 mm (new crack), 0.10 mm, 0.10 mm (new crack), 0.20 mm, 0.15 mm, 0.08 mm (new crack), see Fig. SP4-2; during cycled to -80 mm in 1st cycle and to +80 mm in 2nd cycle, concrete spalling off near the support was recorded; no new cracks were observed on east side in this displacement level, but widths of the cracks increased to 0.45 mm, 0.40 mm, 0.15 mm, 0.25 mm, 0.25 mm, 0.15 mm, 0.10 mm, 0.10 mm, 0.10 mm, 0.10 mm; the spacings between the cracks remained the same • no new cracks occurred on both west and east sides in the +/-100 mm displacement level; the widths of the cracks on west increased to 0.20 mm, 0.60 mm, 0.60 mm, 0.45 mm, 0.25 mm, 0.15 mm, 0.15 mm, 0.10 mm, 0.10 mm, and 0.10 mm, the spacings were the same as the previous level; the widths on east side changed to be 0.80 mm, 0.45 mm, 0.35 mm, 0.30 mm, 0.30 mm, 0.15 mm, 0.15 mm, 0.10 mm, 0.10 mm, and 0.10 mm, but the spacings of the cracks remained the same • one new flexural crack was observed on east side at 1st cycle to -120 mm in the 120 mm displacement level; the widths of the cracks on west side were 0.30 mm, 1.25 mm, 1.00 mm, 0.60 mm, 0.40 mm, 0.30 mm, 0.15 mm, 0.10 mm, 0.10 mm, 0.10 mm, but there was no change in the spacings; the widths of the cracks on east were 1.50 mm, 0.60 mm, 0.35 mm, 0.30 mm, 0.30 mm, 0.15 mm (new crack), 0.15 mm, 0.15 mm, 0.10 mm, 0.10 mm, and 0.10 mm; the spacings were 150 mm, 150 mm, 75 mm, 175 mm, 100 mm, 125 mm, 100 mm, 175 mm, 200 mm, and 250 mm • in the +/- 140 mm displacement level, a big piece of concrete spalling off was seen on east and west side at the very base of the specimen; the specimen failed by fracture of the strands on east side at the location of the flexural crack closest to the support when cycled in 2nd to -132.7 mm as shown in Fig. SP4-3 and Fig. Sp4-4 89 Fig. SP4-1 Fig. SP4-2 90 Fig. SP4-3 Fig. SP4-4 91 Specimen: P12E Characteristics • Test length: Brief Results Axial compression: Crack pattern: Shear Force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Crack width at max. shear: Max. Displacement: Failure type: Load-Displacement Relationship Test Date: February 12, 2001 11 ft. 11 in. (12 ft.) 500 kN Flexural cracks 12.9 kN 48.0 mm 0.1 mm 18.2 kN 0.30 mm 127.5 mm Flexural by concrete crushing Load-Displacement: P12E ra o (/} -150 180 Displacement (mm) 9 4 Specimen P12E Test Observations: • in the +/-60 mm displacement level, the first crack was able to be observed when cycled to +48.0 mm in the 1st cycle; this crack was a flexural crack situated on west side 125 mm measured form the support, and there were two additional flexural cracks on the same side in this cycle; two cracks appeared on east side in the 1st cycle to -60 mm; the first crack occurred when the specimen was displaced to -50 mm, and the second one was when -51 mm ; the crack were flexural, during the 2nd cycle; two further flexural cracks occurred on west side when cycled to +60.0 mm, and one flexural crack was observed on east side when cycled to -60.0 mm; one additional flexural crack on west side and one on east side were noticed in the 3rd cycle when cycled to +60.0 mm and -60.0 mm respectively in this displacement level; only three cracks on west side were able to be measured the widths by a crack comparator; the widths were found to be 0.10 mm (first crack), 0.10 mm, and 0.10 mm; the spacings of the cracks were 100mm, 125 mm, 125 mm, 150 mm, and 150 mm as shown in Fig. SP5-1; the widths of the cracks on east side were 0.10 mm, 0.10 mm (first crack), and 0.10 mm; the spacing were 175 mm, 175 mm, and 200 mm • three new flexural cracks appeared on west side when cycled to +80.0 mm of the 1st cycle during the +/-80 mm; there was also one new flexural crack on east side at -80.0 mm of the same cycle; in 2nd cycle, one additional crack was marked on west side when cycle to +80.0 mm as well as one on east side to -80.0 mm; on east side in 3rd cycle when cycle to -80.0 mm, one new flexural crack occurred; the widths of the cracks on west side increased to 0.20 mm, 0.25 mm, 0.10 mm, 0.20 mm, 0.10 mm (new crack), 0.10 mm, 0.10 mm, 0.10 mm, and 0.08 mm, the spacing were 100 mm, 125 mm, 125 mm, 50 mm, 100 mm, 150 mm, 175 mm, 75 mm, and 100 mm, the widths of the cracks on east side were 0.25 mm, 0.20 mm, 0.15 mm, 0.10 mm, 0.10 mm (new crack); the rest two cracks on this side were not be able to measured by a comparator; the spacings of the cracks were 175 mm, 175 mm, 200 mm, 200 mm, 175 mm, and 100 mm, See Fig. SP5-2 • during the +/- 100 mm displacement level; two new flexural cracks occurred on west side when the pile was displaced to + 100.0 mm in the Is' cycle; at the same cycle to -100.0 mm, one new flexural crack was also marked on east side; another flexural crack appeared on east side when cycled to -100.0 mm in 2nd cycle; concrete spalling was also observed on east side very close to the support when cycled to +100.0 mm in the 3rd cycle; the widths of the cracks on west side in this level were 0.25 mm, 0.30 m, 0.15 mm, 0.25 mm, 0.20 mm, 0.20 mm, 0.20 mm, 0.10 mm, 0.10 mm, 0.10 mm (new crack) and 0.05 mm (new crack); the corresponding spacings were 100 mm, 125 mm, 125 mm, 50 mm, 100 mm, 150 mm, 175 mm, 75 mm, 100 mm, 100 mm, and 125 mm; the widths of all cracks on east side changed to be 0.25 mm, 0.10 mm (new crack), 0.20 mm, 0.20 mm, 0.20 mm, 0.15 mm, 0.10 mm, and 0.08 mm (new crack) • the specimen was failed when cycled to +125.7 mm in the 1st cycle; the failure mechanism was noticed to be flexural failure by concrete crushing as seen in Fig. SP5-3 and SP5-4; the test was stopped when cycled up to +134 mm in the same cycle 95 Fig. SP5-1 I J J *•• AW- iii 8a 1 9 Fig. SP5-2 9 6 Fig. SP5-3 )'0 0.012 0.008 I 0.004 ) O If) O 10 1^ 4 CM *- fr- ^ ' 1 1 1 i_- ^ uo o m o L \ ^ J . T ^ OJ c - o o 00 1 o (tm) aoJOj jeans CD XT d o d (N>|) ao jo j jeans o p (N*) ooJOd Jeans Specimen: P8B Characteristics • Test length: • Axial compression: Brief Results • Crack pattern: • Shear force at first crack: • Displacement at first crack: • Crack width at the peak: • Max. Shear force: • Crack width at max. shear: • Max. Displacement: • Failure type: Load-Displacement Relationship Test Date: February 20, 2001 7 ft. 11 in. (8 ft.) 200 kN Flexural cracks with trend of shear cracks developed from flexural cracks 15.7 kN 16.1 mm 0.1 mm 24.4 kN 1.25 mm flex., 0.25 mm shear 70.8 mm Flexural by concrete crushing -30 Load-Displacement: P8B 30 Q Displacement (mm) 100 Specimen P8B Test Observations: • three flexural cracks on west side occurred in the +/- 20 mm displacement level when the pile was cycled to +20.0 mm in the Is' cycle; the first crack was observed when the displacement was equal to +16.1 mm, and the second and the third appeared at + 17.8 mm and +20.0 mm; the widths of the cracks on west side were measured while the displacement was held constant at +20.0 mm and found to be 0.10 mm, 0.10 mm (first crack), and 0.10 mm; the corresponding spacings were 165 mm, and 190 mm, see Fig. SP6-1; there were two cracks on east side in the 1st cycle to -20.0 mm in this displacement level; these cracks were flexural; the first crack was marked at the very base of the specimen when cycled to -16.0 mm, and -18.2 mm for the second crack; the widths of the cracks were 0.15 mm (first crack), and 0.10 mm; the spacing of the cracks was 315 mm • in the +/-30 mm displacement level; one additional flexural crack was observed on west side when cycled to +30.0 mm in the 1st cycle; in this displacement level, the widths of the cracks were 0.20 mm, 0.25 mm, 0.15 mm, and 0.10 mm (new crack); the spacings were 165 mm, 190 mm, and 165 mm; when the specimen was cycled to -30.0 mm in the 1st cycle, two cracks were also observed, and these crack were flexural; the widths of the cracks on this side were recorded to be 0.35 mm, 0.25 mm (new crack), 0.20 mm, and 0.10 mm (new crack); the spacings were 190 mm, 125 mm, and 190 mm; there was no significant observation in the rest of this displacement level • for all cycles of the +/-40 mm displacement level, there was no further cracks recorded, but the existing flexural cracks on both west and east sides propagated in the inclined direction toward the support when the specimen was cycled to +40.0 mm and -40.0 mm; the widths of the cracks on west side were 0.25 mm (flexural) and 0.10 mm (inclined), 0.35 mm (flexural) and 0.10 mm (inclined), 0.20 mm, and 0.10 mm; the spacings of the cracks remained the same as previous displacement level • there was also no further cracks another crack on both west and east sides for all cycles in the +/-60 mm displacement level; concrete spalling on both sides at the very end of the specimen near the support when cycled to +60.0 mm and -60.0 mm in the 2nd cycle; the pattern of the cracks on both sides also changed, but due to the fact that pictures in this displacement level were lost so that the widths were not be able to be described in the description • during the +/-70 mm displacement level, when the specimen was displaced to +70.0 mm in the 1st cycle, a big piece of concrete spalled off on east side near the support was noticed, but no further cracks were observed on both west and east side when cycled to +70.0 mm and -70.0 mm; the spacings of the cracks on both sides also remained the same; at the 3rd cycle when cycled to +70.0 mm, failure mechanism of the specimen was identified at 68.4 mm; the specimen failed by concrete crushing on east side at the location of 100 mm measured from the support 101 Fig. SP6-1 102 2 o i f CQ CO D. £ o (w-NM) luaiuoiAi Buipuag > < (NM) JE3l|S Specimen: P 4 B Test Date: February 26,2001 Characteristics • Test length: • Axial compression: Brief Results • Crack pattern: • Shear force at first crack: • Displacement at first crack: • Crack width at the peak: • Max. Shear force: • Crack width at max. shear: • Max. Displacement: • Failure type: Load-Displacement Relationship Load-Displacement: P4B 60-T se-j Displacement (mm) 3 ft. 11 in. (4 ft.) 200 kN Flexural cracks with a few shear cracks developed from Flexural cracks 30.8 kN 6.2 mm 0.15 mm 45.6 kN 1.50 mm flex, 0.80 shear 49.2 mm Flexural failure by fracture of rebars 105 Specimen P4B Test Observations: • the first flexural crack on west side appeared during the l s l cycle of the +/-6.5 mm displacement level; this crack was marked when the specimen was cycled to +6.2 mm; the width of this crack was measured while the pile was held constant at +6.5mm and recorded to be 0.15 mm; the first on east side was noticed also in this displacement level at the Is' cycle to -6.5 mm when the displacement was -5.7 mm; the crack was also flexural located at the very end of the pile near the support, and the width was found to be 0.15 mm; in the rest cycles of this level no further cracking was observed either on west or east side • in the +/-8.0 mm displacement level, the second crack was seen on east side at 1st cycle to -8.0 mm; this was flexural; the widths of the cracks on east side in this displacement level were 0.15 mm, and 0.10 mm (new crack); the spacing between the cracks was 150 mm, see Fig. SP7-1; no new crack occurred on west side, and the width of the crack was the same as the first displacement level • one new flexural crack was observed on west side when cycled to +10.0 mm at the 1st cycle in the +/- 10.0 mm; no further cracking was noticed on east side in this level; the widths of the cracks on west side increased to 0.20 mm, and 0.10 mm (new crack); the spacing of the cracks was 200 mm; the widths of the cracks on east side were 0.25 mm, and 0.15 mm; there was no change in the spacing as shown in Fig. SP7-2 • during the +/-12.5 mm displacement level, one additional crack was marked on east side when cycled to -12.5 mm in the 3rd cycle, but no new cracking was observed on west side; the widths of the cracks on west side were 0.30 mm, and 0.15 mm and on east side were 0.40 mm, 0.25 mm (flexural) and 0.10 mm (shear), but the new crack was not be able to be measured by a comparator; the spacings of the cracks were 150 mm, and 225 mm • no further cracking was observed either on west or on east side for all cycles in the +/-15.0 mm; the widths of the cracks on west side changed to be 0.40 mm, and 0.20 mm (flexural) and 0.10 mm (inclined) as illustrated in Fig. SP7-3; the spacing of the cracks remained the same; the widths of the cracks on east side were 0.60 mm, 0.35 mm (flexural) and 0.15 mm (inclined), and 0.10 mm; the spacings were also the same as those in the +/-12.5mm displacement level • one new flexural crack was recorded on east side in the +/-17.5 mm displacement level when the pile was displaced to -17.5 mm in the 1st cycle, but no further cracking on west side was observed in this level; at the 3rd cycle to +17.5mm and -17.5mm the widths of the cracks both on west and east sides were measured; the widths on west side were 0.50 mm, and 0.25 mm (flexural) and 0.10 mm (inclined); the widths on east side increased to 0.60 mm, and 0.30 mm (flexural) and 0.10 mm (inclined), 0.10 mm (new crack), and 0.10 mm, the spacings of these cracks were 150 mm, 150 mm, and 75 mm • during the +A22.5 mm displacement level, on new cracking was observed either on west or east side, but the change of widths of all cracks was still able to be noticed; the widths of the cracks on west side increased to 0.50 mm, and 0.30 mm (flexural) and 0.10 mm (inclined); the widths of the cracks on east side were 1.00 mm, 0.40 mm (flexural) and 0.20 mm (inclined), 0.15 mm, and 0.10 mm; the spacings on both sides remained the same • the fracture of one strand occurred when the specimen was cycled to -22.5 mm in the 1st cycle during the +/-22.5 mm displacement level; the location of the fracture was on east side at the crack closest to the support; no new cracking was observed on both west and east sides in this displacement level; the failure was identified in this displacement level; the specimen failed by the fracture of the strands • after the failure, the specimen was still subjected to three cycles at +/-25.0 mm, +/-30.0 mm, +/-35.0 mm, and +/-40.0 mm to complete the test; concrete spalling off was observed on east side during the 1st to +30.0 mm; fracture of one strand on west side as well as concrete spalling off on east side occurred when cycled to -30.0 mm in the Is' cycle; in the +/-35.0 mm, fracture of another strand on west side occurred in the 1st cycle to +35.0 mm as shown in Fig. SP7-4 106 Fig. SP7-1 108 Specimen: P 4 E Characteristics • Test length: Test Date: March 1, 2001 Brief Results Axial compression: Crack pattern: Shear force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Crack width at max. shear: Max. Displacement: Failure type: 3 ft. 11 in. (4 ft.) 500 kN Flexural cracks 38.4 kN 6.4 mm 0.1 mm 62.2 kN 0.6 mm 22.3 mm Flexural by concrete crushing Load-Displacement Relationship Load-Displacement: P4E -80--40 Displacement (mm) 111 Specimen P4E Test Observations: • during installing the specimen to the actuator to apply lateral displacements, the specimen was accidentally cracked due to over moving the actuator to connect the pile but no axial compression was applied on the pile and the data and damage were recorded; the crack was flexural crack and located on east side at the very base of the pile, around 25 mm away from the support • the specimen was subjected to three cycles at +/-3.0 mm, and three cycles at +/-5.0 mm and no cracking was observed • the first crack was able to be marked during the 3rd cycle of +1-1.5 mm displacement level, when the specimen was cycled to +6.4 mm; this crack was flexural and was the same crack as the one that occurred due to the damage during the installation; the width of this crack was 0.10 mm; on cracking was observed on west side for the entire cycles of this displacement level • the first flexural crack on west side was noticed during the +/-10.0 mm displacement level, when cycled to +8.8 mm in the 1st cycle as shown in Fig. SP7-1; for the rest cycles of this displacement level, no further cracks occurred either on west or east side; the widths of the cracks were measured while the displacement was held constant at +/-10.0 mm; the width of the crack was 0.15 mm on both west and east sides • one additional flexural crack occurred on west side at the 1st cycle to +12.5 mm in the +/-12.5 mm displacement level; there was also one flexural crack on east side when cycled to -12.5 mm in the 1st cycle; no further cracking was observed for the 2nd and the 3rd cycle to both +12.5 mm and -12.5 mm; in this displacement level the widths of the cracks on west side increased to 0.30 mm, and 0.10 mm (new crack); the spacing of the cracks was 150 mm; the widths of the cracks on east side were 0.30 mm, and 0.15 mm (new crack), the spacing was 225 mm • during the +/-15.0 mm, one new flexural crack was marked on west side when the pile was displaced to +15.0 mm at the 1st cycle; there was also concrete spalling off on east in the 2nd cycle to 15.0 mm, but no further cracking on east side was recorded for the entire cycles of this displacement level; the crack located on west side at the very base of the pile tended to incline during the 2nd cycle to +15.0 mm as well as the crack on east side at the very end of the pile when cycled to -15.0 mm in the 2nd cycle; the widths of the cracks on west side were found to be 0.35 mm, 0.20 mm, and 0.10 (new crack); the spacing between the cracks were 150 mm, and 165 mm; the widths of the cracks on east side were 0.40 mm, and 0.20 mm ,but the spacing remained the same • no further cracking was observed for the entire cycles of the +/-17.5 mm displacement level, but further concrete spalling off on east side was still able to be recorded when the specimen was cycle to +17.5 mm for all three cycles; the widths of the cracks on west side developed to be 0.50 mm, 0.25 mm, and 0.20 mm; the spacings of the cracks had no change; the widths of the cracks on east side were 0.50 mm, and 0.25 mm; the spacing of the was the same as that in the previous level • only further concrete spalling off was recorded in both west and east sides, but no further cracking was noticed for all cycles in this level, the widths of the cracks on west side increased to 0.60 mm, and 0.25 mm as shown in Fig. SP7-2, the widths of the cracks on east side were 0.50 mm, and 0.25 mm; in this level there was no change in spacings of the cracks on both west and east sides • the specimen failed by concrete crushing on east side when cycled to +21.5 mm at the 1st cycle; the center of the crushing was 125 mm measured from the support as shown in Fig. SP7-3 and Fig. SP7-4; the test was stopped in this displacement level 112 Fig. SP8-1 Fig. SP8-2 113 114 Specimen: P2B Characteristics • Test length: Brief Results Axial compression: Crack pattern: Shear force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Max. Displacement: Failure type: Test Date: March 06, 2001 1 ft. 11 in. (2 ft.) 200 kN Flexural cracks with development of shear cracks 92.3 kN 4.1 mm 0.1 mm 120.1 kN 25.1 mm Flexural failure by fracture of rebars Load-Displacement Relationship Load-Displacement: P2B 4-60-J Displacement (mm) 117 Specimen P2B Test Observations: • the first crack occurred on west side when the specimen was cycled at the 1st cycle to +4.4 mm in the +/-5.0 mm displacement level; this crack was flexural situated at the very end of the pile near the support; the width of this crack was 0.10 mm; the first flexural crack on east side was observed when cycled to -4.2 mm in the first cycle; this crack was also located very close the support, and there was a second flexural crack on this side afterward; in this displacement level only the first crack was able to be recorded the width by a comparator; the width of this crack was 0.10 mm; the spacing between the crack was 100 mm as shown in Fig. SP9-1; for the rest cycles in this displacement level, no further cracks were observed on both west and east side • in the +1-1.5 mm displacement level, no further cracking was observed either west or east side; during the 1st cycle to +7.5 mm and -7.5 mm, inclination of the flexural cracks was noticed; the width of the crack on in this level was 0.40 mm; the widths of the cracks on east side were 0.40 mm (flexural) and 0.10 mm (inclined), and 0.15 mm; the spacing was 100 mm • the second flexural crack on west side was marked in the +/- 10.0 mm displacement level when the pile was cycled in the 1st cycle to +10.0 mm; the widths of the cracks on west side were 1.25 mm (flexural) and 0.10 mm (inclined) but the second crack was not be able to be measured by a comparator; the spacing of the cracks was 150 mm; no further cracking was observed on east side except the widths of the cracks; the widths of the cracks on east side were 0.80 mm, and 0.25 mm (flexural) and 0.10 mm (inclined); the spacing remained the same; for the rest cycles in this level, only the change of the pattern of all cracks was noticed as illustrated in Fig. SP9-2 • during the +/- 12.5 mm displacement level, concrete spalling off was noticed on both west and east side, especially near the support; no further cracking was recorded but development of inclination of cracks was able to be seen; the widths of cracks on west side increased to 1.50 mm (flexural) and 0.15 mm (inclined), and 0.20 mm(flexural) and 0.15 mm (inclined); the spacing remained unchanged; the widths of the cracks on east side were 1.50 mm, and 0.30 mm (flexural) and 0.20 mm (inclined); no change of spacing was observed • when the specimen was displaced to +15.0 mm at the 21st cycle in the +/-15.0 mm displacement level, one big piece of concrete on east side fell off, but no further cracking on both side occurred for all cycles of this displacement level; the widths of the cracks on west side were found to be 1.75 mm (flexural) and 0.15 mm (inclined), and 0.25 (flexural) and 0.20 mm (inclined); the widths on east side were 1.50 mm, and 0.40 mm (flexural) and 0.35 mm ( inclined) • the fracture of one strand on east side was noticed when the specimen was cycled at the 1st cycle to -17.5 mm in the +/-17.5 mm displacement level but no new crack was observed either on west pr on east side for all cycles; due to the fracture of the strand, the failure mechanism was identified in this level; the failure was flexural by fracture of the strand on east side, see Fig. SP9-3 • the test was completely stopped at the 1st cycle to +25.0 mm 118 Fig. SP9-1 Fig. SP9-2 119 Fig. SP9 120 in £ • in c ra CQ CL (NM) S O J O J J B O M S ra 111 c '5 (NH.) ao'Od J B 9 M S (ui-NM) luauioifti B u j p u a g (Ni) a o j o j i ee i f s Specimen: P 2 E Characteristics • Test length: Test Date: March 9, 2001 Brief Results Axial compression: Crack pattern: Shear force at first crack: Displacement at first crack: Crack width at the peak: Max. Shear force: Crack width at max. shear: Max. Displacement: Failure type: 1 ft. 11 in. (2 ft.) 500 kN Flexural cracks with significant development of shear cracks 133.5 kN 7.4 mm 0.1 mm 157.0 kN 0.40 mm flex., 0.10 mm shear 15.6 mm Flexural by concrete crushing Load-Displacement Relationship Load-Displacement: P2E « © J Displacement (mm) 122 Specimen P2E Test Observations: • the specimen was subjected to three cycles of +/-2.5 mm, and three cycles of +/-5.0 mm displacement level and no cracking was observed • the first crack was marked during the 2 n d cycle of the +1-1.5 mm displacement level, when the displacement was recorded to be +7.4 mm; this crack was a flexural crack located on west side near the support; the width of the crack was measured to be 0.10 mm as seen in Fig. SP10-1; there was a possible problem due to limitation of the equipment when the specimen was cycles to the negative direction by observing from the recorded data and the clamping device in which it was connected to the actuator to apply lateral displacements; with this problem all results obtained from the negative side was not reliable • during the +/-10.0 mm displacement level, no further cracks occurred, but direction change of the existing crack on west side was noticed; the cracks tended to incline toward the support when cycled to +10.0 mm in the 2 n d cycle; the width of the crack was 0.20 mm (flexural) and 0.10 mm (inclined); the width of the crack on east side was 0.20 mm, but no inclination of the crack was observed • the second crack on east side was marked when cycled to -12.5 mm at the I s' cycle during the +/-12.5 mm displacement level, this crack was a flexural crack; the widths of the cracks on east side were 0.30 mm, and 0.10 mm (new crack); the spacing of the cracks was 125 mm; no further cracks were observed on west side, the widths of the crack on west side increased to 0.40 mm (flexural) and 0.10 mm (inclined), see Fig. SP10-2 • the failure mechanism of the specimen was identified when cycled to +13.9 mm in the 3 , d cycle; the specimen failed by concrete crushing on east side as shown in Fig. SP10-3 123 Fig . SP10-1 125 A P P E N D I X B Strain Estimate Properties: Concrete strength, fc = 100 MPa Elastic modulus of concrete, Ec =40100 MPa Concrete area, Ac = 33694 mm2 Ultimate strength of strand, fpu = 1500 MPa Yield strength of strand, ^  = 1400 MPa Initial Prestress,^, (0.80/ u^) = 1200 MPa Pretensioning strain, Aep = 0.006 MPa Elastic modulus of steel, Ep = 200000 MPa Area of strand, Ap =237 mm Short-term Response Force from pretensioning strands: N = ApEptep N = 120x200000x0.006 N = 2844007V Stress in concrete: N = AJe+Apfp N = AeEeee+ApEpep 127 N = sc(AcEc+ApEp) N £ c ~ (AE+AEJ ec = -0.0002 fc = E c S c fc = -&.2MPa Long-term Response In long-term response, creep, shrinkage of concrete, and relaxation of prestressing strand are taken into account. Assume: Creep coefficient, C t = 2.5 Shrinkage strain, s sn = -0.0003 Relaxation = 5% Modulus of elasticity EP,jf = 0.95^ EP,eff =190000Affa E - E' Eceff = U457MPa Effective prestressing force: ^eff =(Ep,eff£pi)Ap -(Eceff£sh)Ac NeJf = 3860007^ Effective concrete stress: 128 , e #=-0.0009 ,eff ~ Ec,eff£c,eff fc^=\0.5MPa 129 

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