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Some experiments on headed stud connections for precast concrete panels under monotonic and cyclic shear… Bischof, Max 1978

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SOME EXPERIMENTS ON HEADED STUD CONNECTIONS FOR PRECAST CONCRETE PANELS UNDER MONOTONIC AND CYCLIC SHEAR LOADING by MAX BISCHOF Dipl. Ing. ETH, Zurich, 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of C iv i l Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January, 1978 © Max Bischof, 1978 In presenting this thesis in partial fulf i lment of the requirements for an advanced degree at the University of Br i t i sh Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C iv i l Engineering The University of Br i t i sh Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date January 1978 i i ABSTRACT The research on headed stud connections described in this thesis forms a part of a larger program with the objective of pre-dicting the behaviour of precast concrete panel buildings under earthquake loads. The f i r s t objective of this research is to produce experi-mentally a concrete fa i lure of the connection and to compare the actual fa i lure load to the one predicted by the PCI design handbook. The tests show that the PCI shear-tension interaction equation for single headed studs can be used for the prediction of a concrete fa i lure for a connection of the type tested. This method yields conservative results i f a special equilibrium model for the deter-mination of the stud tension force is used, and the bearing capacity of the structural steel angle on the concrete is neglected. The second objective of this research is to determine the bearing capacity of a reversed angle connection. Experiments show that this bearing capacity is equivalent to a force resulting from a stress equal to the concrete strength uniformly distributed over the concrete area enclosed by the structural steel angle 2" x2" . Furthermore, the location of this force can be assumed in the center of gravity of the structural steel angle shape, regardless of whether'or not there is an endplate present. i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES vi LIST OF FIGURES . , v i i ACKNOWLEDGMENTS x i v Chapter 1. INTRODUCTION 1 2. CONCRETE TEST PANELS 5 2.1 Design of the Connection Configuration for the Shear Cone Tests 5 2.2 Design of the Connection Configuration for the Bearing Tests 7 2.3 Fabrication of the Panels 8 2.4 Designation of the Test Panels, Testing Schedule and Fabrication Details "11 3. TEST EQUIPMENT 13 3.1 Load Transfer 13 3.2 Measuring System 13 3.3 Data Acquisition 17 4. CONCRETE SHEAR CAPACITY OF A STUD AS RECOMMENDED BY THE PCI DESIGN HANDBOOK 18 1 V Chapter Page TEST RESULTS 5.1 Concrete Cylinder Compression Tests 5.2 Steel Tension Tests 5.3 Failure Analysis for the Shear Cone Test Panels Zl to Z4 5.3.1 Summary of essential test data 5.3.2 Failure descript 5.3.3 Failure descript 5.3.4 Failure descripti 5.3.5 Failure description for panel Z4 on for panel Zl on for panel Z2 on for panel Z3 5.4 Determination of the Stud Tension Force at the Design Stage 5.5 Failure Analysis for the Bearing Test Panels Z5 to Z8 5.5.1 Failure description 5.5.3 Center of gravity of the bearing force 20 20 22 24 24 24 25 26 27 5.3.6 Numerical analysis of the fa i lure _ for the panels Zl to Z4 2 ? 30 33 33. 5.5.2 Bearing capacity of the reversed angle connection 33 34 6. CONCLUSIONS FOR THE DESIGN 38 BIBLIOGRAPHY 39 APPENDIX A APPENDIX B APPENDIX C Fabrication Details of the Test Panels I l lustrations of the Test Equipment . . Details of the Concrete and Steel Specimen Tests 40 50 56 V Chapter Page APPENDIX D - I l l u s t r a t i on s of the Test of Panel ZI 62 APPENDIX E - I l l u s t r a t i on s of the Test of Panel 12 68 APPENDIX F - I l l u s t r a t i on s of the Test of Panel Z3 7 5 APPENDIX G - I l l u s t r a t i on s of the Test of Panel Z4 83 APPENDIX H - ' i l l u s t r a t i o n s of the Test of Panel 15 93 APPENDIX I - I l l u s t r a t i on s of the Test of Panel Z6 TOO APPENDIX J - I l l u s t r a t i on s of the Test of Panel Z7 106 APPENDIX K - I l l u s t r a t i on s of the Test of Panel Z8 1 1 2 APPENDIX L - Determination of the Shear Cone Surface Area 1 2 0 vi LIST OF TABLES Table P a 9 e 1. Designation of the Test Panels, Testing Schedule , 2. Estimated Ultimate Compressive Strength of the Panels at Their Testing Day 3. Mean Steel Properties 4. Some Test Data for the Panels ZI to Z4 . . . . 5. Coefficients E, for the Effective Ultimate Concrete Bearing Strength . . 6. Compression Test Data for Concrete Cylinders of 6 in . Diameter and 12 in . Length 7. Tensile Test Data for the Steel Specimen . . . V I 1 LIST OF FIGURES Figure Page 1.1 Typical precast 'concrete bu i ld ing . 2 1.2 Welded headed stud connections showing typ ica l appl icat ions in precast bui ldings 3 2.1 Concrete pu l lout capacity for s ing le studs . . . . 6 2.2 St ra in gage locat ions 9 3.1 S t ra in gage measuring scheme 16 5.1 Ultimate concrete compressive strength 21 5.2 Olsen compression and tension test machine . . . . 21 5.3 Mean s t re s s - s t r a i n diagram for the studs and br ight bars 23 5.4 Shear-tension in te ract ion diagram showing tes t resu l t s fo r s ing le studs 29 5.5 Comparison of the stud tension forces from the tests to those computed from various equ i l ib r ium model s 5.6 Equi l ibr ium model fo r the determination of the -stud tension forces 5.7 Equi l ibr ium model of the connection used in the bearing tes t panels 36 5.8 Derived locat ions fo r the bearing force on the reversed s t ructura l steel angle 2" x 2 " 37 A l . Connection deta i l s fo r panels Zl and Z2 41 A2. Connection de ta i l s fo r panels Z3 and Z4 42 A3. Connection de ta i l s fo r panels Z5 and Z6 43 A4. Connection deta i l s for panels Z7 and Z8 44 vi i i ix Figure Page C3. 5/8 in . diam. steel specimen 60 C4. 3/4 in. diam. steel specimen 61 C5. Detail from Fig. C4 61 DI. Load-vertical displacement diagram for panel 63 ZI D2. Panel ZI, after fa i lu re , fa i lure load = 20 kip . . 64 D3. Panel ZI, after fa i lure 64 D4. Panel ZI, after fa i lure 65 D5. Panel ZI, after test 65 D6. Panel ZI, after test 66 D7. Panel ZI, after test 66 D8. Concrete piece with faceplate, angle and studs broken out of panel ZI 67 D9. Concrete piece broken out of panel ZI behind the heads of the studs 67 E l . Load-vertical displacement diagram for panel Z2 • • • • 69 E2. Panel Z2, cycle 17, max load = 18.8 kip 70 E3. Panel Z2, cycle 17 70 E4. Panel Z2, cycle 17 71 E5. Panel Z2, after fa i lure 7 1 E6. Panel Z2, after fa i lure 72 E7. Panel Z2, after test 72 E8. Panel Z2, after test ' 73 E9. Concrete piece with faceplate, angle and studs broken out of panel Z2 73 E10. Concrete piece broken out of panel Z2 behind the heads of the studs 74 X Figure Page F l . Load-vertical displacement diagram for panel Z3 76 F2. Panel Z3, Load = 33 kip 7 7 F3. Panel Z3, Failure load = 38 kip 7 7 F4. Panel Z3, load = 22 kip 78 F5. Panel Z3, after fa i lure 78 F6. Panel Z3, after fa i lure 79 F7. Panel Z3, after test 79 F8. Panel Z3, after test 80 F9. Panel Z3, fa i lure surface 80 F10. Panel Z3, fa i lure surface 81 F l l . Concrete piece, broken out of panel Z3 81 F12. Concrete piece with faceplate, angle and studs broken out of panel Z3 82 Gl. Load-vertical displacement diagram for panel Z4 84 G2. Panel Z4, cycle 14, load = 29.8 kip 85 G3. Panel Z4, cycle 16 downwards, max load = 35 kip. . 85 G4. Panel Z4, cycle 16 downwards, max load = 35 kip. . 86 G5. Panel Z4, cycle 17 downwards 86 G6. Panel Z4, cycle 18 upwards 87 G7. Panel Z4, cycle 18 upwards 87 G8. Panel Z4, cycle 18 downwards 88 G9. Panel Z4, cycle 18 downwards 88 G10. Panel Z4, cycle 18 downwards 89 xi Figure ^ Page G i l . Panel Z4, cycle 19 upwards 89 G12. Panel Z4, after fa i lure 90 G13. Panel Z4, after fa i lure 90 G14. Panel Z4, after test 91 G15. Panel Z4, fa i lure surface 91 G16. Concrete piece with faceplate, angle and studs broken out of panel Z4 92 HI. Load-vertical displacement diagram for panel Z5 94 H2. Panel Z5, cycle 10 upwards, max load = 24.4 kip . . 95 H3. Panel Z5, cycle 10 upwards, max load = 24.4 kip 95 H4. Panel Z5, cycle 11 downwards, load = 10.7 kip . . 96 H5. Panel Z5, cycle 11 downwards, load = 10.7 kip . . 96 H6. Panel Z5, cycle 12 upwards, load = 13.8 kip . . . 97 H7. Panel Z5, after test 97 H8. Panel Z5, fa i lure surface 98 H9. Panel Z5, fa i lure surface 98 H10. Panel Z5, after test 99 11. Load-vertical displacement diagram for panel Z6 " 101 12. Panel Z6, Connection detail 102 13. Panel Z6, max load = 23.1 kip 102 14. Panel Z6, load = 21.5 kip 103 15. Panel Z6, load = 21.5 kip 103 16. Panel Z6, load = 6 kip 104 xi i Figure Page 17. Panel Z6, after fai lure 104 18. Panel Z6, after test 105 19. Panel Z6, fa i lure surface 105 J l . Load-vertical displacement diagram for panel Z7 107 J2. Panel Z7, load = 26.7 kip 108 J3. Panel Z7, load = 26.7 kip 108 J4. Panel Z7, fa i lure load = 27.6 kip 109 J5. Panel Z7, fa i lure load = 27.6 kip 1 0 9 J6. Panel Z7, load = 7.6 kip 11° J7. Panel Z7, load = 7.6 kip HO J8. Panel Z7, after complete fa i lure . . . . I l l J9. Panel Z7, fa i lure surface HI Kl. Load-vertical displacement diagram for panel Z8 113 K2. Panel Z8, connection detail 114 K3. Panel Z8, cycle 10 upwards, max load = 22.9 kip 114 K4. Panel Z8, cycle 11 upwards 115 K5. Panel Z8, cycle 10 upwards, max load = 22.9 kip 115 K6. Panel Z8, cycle 11 upwards 116 K7. Panel Z8, cycle 12 upwards 116 K8. Panel Z8, upper fa i lure surface 117 K9. Panel Z8, cycle 11 downwards, max load = 25.3 kip at scan 315, cycle 10 117 xi i i Figure Page K10. Panel Z8, cycle 11 118 K l l . Panel Z8, cycle 12 118 K12. Panel Z8, lower fa i lure surface 119 K13. Panel Z8, after fa i lure 119 L l . Determination of the shear cone surface area . . . . 121 ACKNOWLEDGMENTS The writer is indebted to Dr. R.A. Spencer for his teaching, advice and guidance. For the assistance provided during the fabrication of the test equipment and test panels, I would l ike to thank the s ta f f in the shop of the C iv i l Engineering Department: Dick Postgate, Wolf Schmitt, Jeff Sharp, and Bernard Merkli. The research was financed by the National Research Council of Canada. 1 1 . INTRODUCTION This thesis deals with a particular type of connection used in precast concrete wall panels for single and multi-story buildings. An example of such a building is shown in Fig. 1.1 and some others may be found in Reference 1. As indicated in the National Building Code of Canada, Supplement No. 1 , the l ikel ihood of occurrence of an earthquake is not zero for quite a large area of this country. Therefore, the earthquake design of those precast concrete buildings is of part icular concern to the structural engineer. Of special interest is the behaviour of the connections of the precast panels, since the shear forces due to cyc l i c loading must be transferred through those connections. At the university of Br i t i sh Columbia, research has been (3) (3 4) done in this f i e l d by Spencerv ' and Neil le^ ' ; . They invest i -gated the commonly used fusion welded headed stud connections in precast concrete panels under monotonic and cyc l ic shear loads. A typical example of such a connection is shown in Fig. 1.2. This research was a continuation of the work already done by Spencer and Nei l le and had two aims: 1. The f i r s t aim was an experimental investigation into the concrete shear cone capacity of a fusion welded stud connection in a concrete panel under 2 Fig. 1 . 1 Typical precast concrete panel building (copied from Reference 1 ) 3 Fig. 1.2 Welded headed stud connections showing typical applications in precast buildings (from Reference 3) monotonic and cyc l ic load. A comparison with the capacity indicated by the PCI design handbook has also been made. The second aim was the experimental determination of the end bearing capacity of a fusion welded stud connection in a concrete panel under monotonic and cyc l i c load. For the connection of interest, the structural steel angle is reversed and may or may not have an endplate (see Fig. A3, A4 and Table 1). 5 2. CONCRETE TEST PANELS 2.1 Design of the Connection Configuration for the Shear  Cone Tests In most of the tests done previously by Spencer and Nei l le , the fa i lure occurred in the Nelson studs and not in the concrete. Neil le noticed that a bending fa i lure in the stud usually occurred at a stud tensile force equivalent to 40% of the y ie ld stress. This information was used to design the studs. From the PCI Design Handbook the concrete pull out capacity was determined for a single stud. In order to be sure of getting a concrete fa i lure the studs had to be chosen such that the, concrete pull out capacity was below 40% of the stud tension capacity. After evaluating Fig. 2.1, i t was decided to make two test panels with Nelson studs of diameter 5/8 inch and 3 inch length. Another two panels were made with 6 inch long studs of 3/4 inch diameter, although Fig. 2.1 did not predict a concrete fa i lure. All the studs were fusion welded to structural steel angles 2x2 X j - 12 inch long. 6 o kip concrete pull out capacity 40% of steel tension capacity 20 . f ' = 6000 psi cu CJ c , f = 4000 psi c o U - /diam. 3/4" -r-> 10 3 O ^diam. 5/8" r — 3 Q. -diam. 1/2" 0 3 4 5 6 inch Stud Length Fig. 2.1 Concrete pullout capacity for single studs 7 2.2 Design of the Connection Configuration for the Bearing Tests These tests were intended to find the bearing capacity of 2x2x^ - -12 inch long structural steel angles with and without end plates. It is shown by N e i l l e ^ that a vertical shear load in such a connection is carried by three components: 1. by direct bearing of the angle (or end plate) on the concrete, 2. by f r i c t ion between the concrete and the structural steel angle, 3. by direct bearing between the stud and the surround-ing concrete. In addition, bending in the studs can carry some shear. For the determination of a single component, i t is convenient to eliminate two of these three components. For our purpose, i t was convenient to eliminate the f r i c t ion and stud bearing by putting styrofor plast ic foam behind the reversed angles and around the "studs." Since the styrofor around the stud would prevent the stud from acting as an anchorage, the stud was replaced by a 1/2 inch diameter and 6 inch long bright bar with similar steel properties. This bar was welded to a structural steel angle 2 x 2 x | - - two feet long, which embedded in the concrete, served as an anchorage. This configuration can be seen in Fig. A3, A4, A10, and A l l . 8 2.3 Fabrication of the Test Panels The firm of W.M. Sommerville in Burnaby fusion welded the Nelson studs to the structural steel angles. The rest was done by the personnel of the c i v i l engineering shop at UBC. In order to determine the forces and moments at both ends of the studs, strain gauges were fastened at those locations, one on top of the stud and one at the bottom (Fig. 2.2). The strain gages were of the type EA-06-250 BG-120 with an e lectr ica l resistance of 120 fit 0.3% and a working range between minus and plus 50,000 micro strains (Supplier: Micro Measurements Romulus, Michigan). The corresponding gage factor was 2.06, i . e . : for a strain of 2.06 x 10" the output wi l l be 1 mV per 1 V exc i -tation. After sandblasting of the surfaces of the studs, the strain gages were glued on to the steel with "M-Bond 610 adhesive" and held in place by scotch tape and a pressure clamp. The strain gauges were then cured in an oven for one hour at a temperature of 150°C. After cooling down, solder was put on the two terminals of the strain gages, to which the two wires were then connected. F ina l ly, the terminals of the strain gages were treated with a corrosion protection paste, and the eight wires belonging to a stud were collected in a p last ic pipe that passed through the bottom of the wooden formwork (see Figs. A6, A7, A8, and A9). 9 Fig. 2.2 Strain gage locations 10 Four panels could be cast in each of the two wooden forms which had been used on previous occasions. A cage of round un-deformed steel bars of 1/4 inch diameter served as a nominal re in -forcement. The geometry of the cage was such that none of the bars should have an influence on the concrete shear cones. On June 23rd, 1977 ready-mixed standard concrete, 4,000 psi high early strength, type 3 cement and 3/4 inch maximum aggregate s ize, was poured into the formwork. The concrete was consolidated with an internal vibrator of a diameter of 1 inch. The curing occurred in the C iv i l Engineering laboratory. The concrete was covered with a p last ic for the f i r s t 7 hours. Then, wet potato sacks were added under the p las t ic . At the fourth day, the side boards of the formwork were removed. F ina l ly , the faceplates (see Fig. B6), which accommodate the 6 bolts to transfer the shear load, could be welded on. The styrofor p last ic foam near the structural steel angles melted because of the heat of welding. In order to determine the compression strength of the concrete 12 cylinders of 6 inch diameter and 12 inch length were made with the standard procedure. They cured at the same place and under the same conditions as the panels. A slump test was not done. The steel tensile test specimens were made by welding three 6 inch long Nelson studs together (Fig. C3). For each stud diameter, three samples were set aside . 11 2.4 Designation of the Test Panels, Testing Schedule and  Fabrication Details The numbering of the test panels as well as the test dates are given in Table 1. The panels ZI to Z4 serve for the shear cone tests, the panels Z5 to Z8 are reserved for the bearing tests. The fabrication details are shown in Fig. Al to A l l . TABLE 1 Designation of the Test Panels, Testing Schedule Panel Designation ZI Z2 Z3 Z4 Z5 16 17 IS Type of Test monotonic cycl ic monotonic cycl ic cycl ic monotonic monotonic cycl ic Stud Diameter Stud Length 5/8" 3" 5/8" 3" 3/4" 6" 3/4" 6" 1/2" 6" 1/2" 6" 1/2" 6" 1/2" 6" Position of the Angle normal normal norma I normal reve rsed reversed re versed, endplate reve rsed, endplate Testing Date •1-Jul-77 13-Jul-77 15-Jul-77 22-Jul-77 10-Aug-77 28-Jul-77 ll-Aug-77 17-Aug-77 Connection Type 3M r.y, a ft • /> . ** » .ft 13 3. TEST EQUIPMENT Prior to testing, the exist ing equipment with a test capa-c i ty of 50 kip was redesigned and par t ia l l y rebui l t to a capacity of 100 kip. 3.1 Load Transfer The concrete panel is held in place by a frame (Fig. Bl to B3). A displacement controlled hydraulic MTS jack of 100 kip capacity applies a vertical load to the steel face plate, which is connected to the loading yoke by 6 high strength f r i c t i on bolts A490 diameter 3/4 inch (Fig. B6). 3.2 Measuring System In each test the following parameters of interest are measured: 1. the applied vertical load with an MTS load ce l l of ±100 kip capacity with an output of 10 volts under fu l l load, 2. the stroke of the hydraulic jack. An output of ±10 volts is equivalent to a stroke of ±2 inches. The jack can be controlled manually or by a function generator. For various periods and 14 amplitudes, the function generator is able to produce a sine or a ramp function, 3. the vertical displacement of the top of the face-plate with respect to the top of the concrete. Two transducers (Fig. B6) are fastened at the top of the concrete. Two measuring probes lead from the centerholes of the transducers to the top of the faceplate, one at each side. This arrange-ment allows the calculation of the average vert ical displacement of the faceplate as well as the corresponding lateral rotation. 4. the horizontal displacement at two points, above and below the faceplate. Again, two transducers (Fig. B5) are used to measure the displacements, from which the rotation about the horizontal axis of the faceplate can be computed. 5. the strains at 4 points of each stud or bar (Fig. 2.2). The insta l lat ion of strain gages on opposite sides of a bar allows the calculation of the axial forces and bending moments. Before each test the transducers are cal ibrated. A metal gauge of a given thickness produces a known displacement and from 15 the voltage change measured the cal ibration can be calculated in inches per volt output. The transducers are Hewlett Packard 7DCDT-500 l inear variable d i f ferent ia l transformers (LVDTs), with a l inear working range between plus and minus 0.5 inch. The principle of the strain gage measuring system is the following: the strain gage undergoes the same deformation as the steel . If the steel elongates, the strain gage does the same. It goes into tension and reduces i t s cross-section area. This, of course, results in an increase of the e lectr ica l resistance. This increase can be measured with a Wheatstone-bridge arrangement as shown in Fig. 3.1. A power supply unit (Fig. B8) produces 6 volts between points A and B. The output voltage measured between points C and D is proportional to the change in the resistance of the strain-gage and proportional to the strain. In order to avoid a measuring error due to long leads, leads of the same lengths L are put between the points E-F, D-G and H-G. Before each test, the strain gage measur-ing system is checked out by putting into the c i r cu i t an additional res istor between the points E and D and measuring the change in voltage. Of the 64 strain gages mounted, only one proved to be defective (Panel Z l , upper stud, upper gage near angle). strain gage in panel, A resistance R Fig. 3.1 Strain gage measuring scheme 17 3.3 Data Acquisition All measurements were made using an integrating digital Voltmeter (IDVM) instal led in a Vidar 5403D-DAS data acquisition (Fig. B4). A scanner allows data from each channel to be acquired either manually or automatically using a timer to scan a l l channels at preset intervals. Data is then recorded in two ways: i t is written on a seven track magnetic tape connected d irect ly to the Vidar, and i t is sent to a PDP-11 (Fig. B9) which processes i t and stores i t on a magnetic disc. The minicomputer calculates the applied load and the corresponding vertical displacements and writes these out on a DEC LA30 console typewriter (Fig. BIO). The MTS load and the vertical displacement of the connection (measured by one LVDT only) are also monitored using a Hewlett Packard 7004B X-Y recorder (Fig. B4). The cal ibration of the X-Y recorder for load was done by means of an input of 6 volts which corresponded to a 60 kip load. The cal ibration for displacement was carried out by inserting a gauge under the LVDT probe. 18 4. CONCRETE SHEAR CAPACITY OF A STUD AS RECOMMENDED  BY THE PCI DESIGN HANDBOOK For combined tension and shear loading on a headed stud, the PCI design handbook gives a l i m i t on the ult imate concrete capacity by the fo l lowing in te ract ion formula: ( p 1 4/3 r V i u x u P' X V ^ u ; u ; 4/3 . .(4.1) where P' u V u applied ult imate tension force applied ult imate shear ult imate pul l out strength of stud, governed by the concrete ultimate concrete shear capacity of the stud. P.' <D4A v ^ T r c (4.2) where bp 0.85 l a t e r a l surface, area of a pa r t i a l shear cone with an angle of 45° with respect to the stud (see Appendix L) f 1 c concrete cy l inder strength 19 V = 0.75 Acn f ' . . . .(4.3) u so s where A shank area of the stud so r ult imate ten s i l e strength of the stud. V should not exceed P' determined for the pa r t i a l shear cone, u u 20 5. TEST RESULTS 5.1 Concrete Cylinder Compression Tests The concrete cylinders were tested in an Olsen compression and tension test machine with a maximum capacity of 400 kip (Fig. 5.2). Groups of three cylinders underwent a standard compression test at a concrete age of 14, 21, 28 and 56 days. The detailed test data are shown in Table 6. Fig. 5.1 shows the average compression strength as a function of time. The ultimate concrete compression strength for the several panels at their testing age can be estimated by interpolation from Fig. 5.1 (see Table 2). TABLE 2 Estimated Ultimate Compressive Strength of the Panels at Their Testing Day Concrete Compressive Age Strength Panel Days psi Zl 15 4500 Z2 20 4700 Z3 22 4800 Z4 29 5400 Z5 48 5600 Z6 35 5500 Z7 49 5600 Z8 55 • 5600 21 psi 6000 5000 4000 3000 concrete age 10 20 30 40 50 60 days s= V s-+J l/l HI > l/l co CD i -Q. E o o Fig. 5.1 Ultimate concrete compressive strength Fig. 5.2 Olsen compression and tension test machine 22 5.2 Steel Tension Test For each stud s ize, three test specimens were taken from samples of the steel used in the connections; The test specimens (Figs. C2 to C5) were machined down 1/8 inch in diameter in order not to get a fa i lure in the threads. The threads were needed for mounting the specimen in the Olsen testing machine (Fig. 5.2). An extensometer measured the average strain over a gage length of 2 inches and force-strain curves were plotted direct ly on an X-Y recorder. The extensometer worked with a transducer manufactured by Hewlett Packard. This transducer only allowed the measurement _3 of strains up to 50x10 . The fa i lure strains were estimated to -3 -3 vary from 140x10 to 293 x 10 , depending on the size of the specimen. The detailed test data are shown in Table 7 and Fig. CI. The mean values for each diameter are summarized in Table 3 and Fig. 5.3. TABLE 3 Mean Steel Properties Stud Diameter Inches 0.2% Offset Yield Strength ksi Ul timate Strength ksi Modulus of E last ic i ty ksi 1/2 73 79.1 30,000 5/8 56 75.5 30,000 3/4 52 64.8 30,000 0 2 10 20 30 40 50 10 Fig. 5.3 Mean stress-strain diagram for the studs and bright bars 24 5.3 Failure Analysis for the Shear Cone Test Panels ZI to Z4 5.3.1 Summary of essential test data The fa i lure loads as well as the corresponding vertical \ displacements are summarized in the following table: TABLE 4 Some Test Data of the Panels ZI to Z4 Panel Type of Test Maximum Shear Load kips Corresponding Vertical Displacement _3 10 inches ZI monotoni c 20.0 (up) 25 Z2 cycl ic 18.8 (up) 20 cyc l ic 18.9 (down) 14 Z3 monotonic 38.0 (up) 98 Z4 cyc l ic 35.0 (up) 112 Z4 cyc l ic 35.0 (down) no 5.3.2 Failure description for panel ZI This panel with the structural steel angle anchored in the concrete by two Nelson studs of 5/8 inch diameter and 3 inch length was tested under a monotonic upward loading. The fa i lure of this 25 connection occurred in the concrete immediately behind the heads of the studs at a load of 20 kip (Figs. DI to D9). A piece of concrete contain-ing the two studs and the structural steel angle rotated about a horizontal axis A-A (Fig. D7) perpendicular to the studs somewhere above the angle. The concrete immediately on top of the steel angle was crushed. The shape of the fa i lure surface as i l lustrated by Fig. D5 to Fig. D7 did not resemble a cone with an angle of 45°. The fa i lure surface was more nearly a plane perpendicular to the axis of the studs (Fig. D8). 5.3.3 Failure description for panel Z2 This panel with the same stud arrangement as in panel Zl was tested under a cyc l ic loading. For the f i r s t cycle, the vertical shear load was applied upwards from 0 to 5 kip, then downwards to 0 again and to -5 kip, and again upwards to 0 . This procedure was repeated three times for a given load leve l , which is defined here as the maximum load in a cycle. The load levels were increased in steps of 5 kip until the fa i lure occurred. The fa i lure of the connection occurred again in the concrete just behind the heads of the studs (Figs. El to E10 — the numbers written at the panels indicate the scan at which a crack was observed for the f i r s t time). The concrete immediately on top of the steel angle was observed to be crushed. The shape of the fa i lure surface as i l lus t rated by Fig. E7 and Fig. E8 was dif ferent from that of panel Zl . In this cyc l ic test, two single shear cones could be recognized with angles somewhat greater than 45°. 26 5.3.4 Failure description for panel Z3 Panel Z3 with the structural steel angle anchored in the concrete by two 6 inch long Nelson studs of 3/4 inch diameter was tested under a monotonic upward loading. The development of the cracks for this test is shown in Fig. F2 to Fig. F6. The f i r s t cracks became v is ib le at a load of 29 kip. Spalling and cracking could be observed on top of the structural steel angle, and diagonal shear cracks appeared in the concrete at the level of the two studs. At a load of 38 kip, the rotation of the structural steel angle about a horizontal axis located above the angle and perpendicular to the studs caused a large vertical tension crack (Fig. F3, scan 63). This crack proceeded almost to the bottom of the panel, since the concrete block below the angle rotated about an axis located at the bottom of the panel. The shape of the fa i lure surface cannot be described by 45° shear cones. As in panel ZI, the fa i lure surface was nearly a plane perpendicular to the axis of the studs. Addit ional ly, there was a fa i lure in a vertical plane through the axis of the studs. A careful observation of the concrete piece in Fig. F12 showed some sp l i t t ing of the concrete on top of the studs perpendicular to the compressive stresses. F ina l ly, a horizontal fa i lure plane was formed at the level of the lower stud. 27 5.3.5 Failure description for panel Z4 This panel with the same stud arrangement as panel Z3 was tested under cyc l ic loading. The load-vertical displacement diagram is shown in Fig. Gl. The cracking history of this test can be followed from Fig. G2 to Fig. G13. Basical ly, a s imilar fa i lure mechanism occurred as in panel Z3. At f i r s t , the concrete fa i led in compression above and below the structural steel angle. Then, the shear cracks at the level of the studs formed. The rotation of the structural steel angle about some horizontal axis perpendicular to the studs at the upper and lower end of the angle caused the vertical tensile crack between the two studs. This crack proceeded then diagonally to the edge of the panel at an angle of approximately 70° (Fig. G i l ) . The fa i lure surface (Figs. G14, Gl5) did not have the shape of two single cones. It was nearly a plane perpendicular to the axis of the studs. Sp l i t t ing of the concrete between the two studs could be observed again as in panel Z3. 5.3.6 Numerical analysis of the fa i lure for the panels Zl to Z4 In a l l panels mentioned above the final fa i lure occurred in the concrete behind the heads of the studs. Since in a l l these tests the structural steel angle rotated about i t s upper or lower end, i t was assumed that the f inal fa i lure of the connection was caused by a fa i lure that was analogous to the "cone" fa i lure used 28 in deriving the PCI interaction equations for a single stud subject to combined shear and tension. Although the shape of the fai lure surfaces had s imi lar i t ies to shear cones only in the case of panel 12, i t was f e l t that this interaction formula (Eq. 4.1) might be useful for predicting the fa i lure, Fig. 5.4 shows the PCI interaction diagram. The correspond-ing shear and tension forces assumed to be acting at fai lure in the panels ZI to Z4 are marked as a point in the diagram.. The tension forces were determined from strain gage measurements near the head of the stud. The shear forces in the two studs were assumed to be equal. In calculating the shear force on a stud, the bearing of the concrete on top of the structural steel angle was considered to be s igni f icant for the panels ZI and Z2, while the tests for the panels 13 and Z4 clearly showed a complete bearing fa i lure before the final collapse. For the shear and pullout capacities, a capacity reduction factor of cf> = 1 was used. In Fig. 5.4, the points representing the test results for fa i lure should l i e close to and above the interaction l ine , i f this method is to be useful for predicting a concrete fa i lure. The results from the panels Z2 to Z4 are reasonably close to the inter-action l i ne , while the fa i lure prediction for panel ZI would be rather more conservative. Fig. 5.4 Shear - Tension interaction diagram showing test results for single studs. 30 5.4 Determination of the Stud Tension Force at the Design Stage. For the use of the PCI shear-tension interaction formula (Eq. 4.1), i t is necessary to know the shear and tension force applied on a stud. Given an external shear load, i t can be assumed, that each of the two studs carries half of the load. The tension forces in the two studs cannot be found easi ly. Since we would l ike to design the connection on the basis of the forces associated with one stud only, a suitable analytical model is needed. Consequently, for various equilibrium models the tension force for the main working stud was computed and subsequently com-pared to the stud force measured for the panels Zl to Z4 (Fig. 5.5). In order to be on the safe side in the design, the tension values computed from the suitable model should be greater than the measured one. This comparison suggests that model (3) would be a reasonable one. For this model, (Fig. 5.6), i t was assumed, that the vert ical reaction occurs in the center of gravity of a triangular compression zone inside the structural steel angle. The concrete compression stress was set to the actual compressive strength f . Furthermore, the tension force in the upper stud was neglected, and the horizontal reaction H was supposed to act at the upper end of the structural steel angle. kips 14 12 3 1 0 u S-o c o •I— CO c QJ -a C O (0) measured values at the head of the stud (3) (0) (1) 131 W (2) (3) 0) m (i) (0T" (3) (0) m (i) Model (1): 1 H m y 8 I plast ic hinge in the stud near angle P2=0.2 P1 Model (2.) P2 8 concrete compression zone: triangular at stress f cu P2=0.2 P1 Model (3) H 10 e i V concrete compression zone; triangular inside the angle at stress f cu P2=0 ZI Z2 up Z2 down Z3 Z4 up Z4 down Test Panels Fig. 5.5 Comparison of the stud tension forces from the tests to those computed from various equilibrium models. 32 Fig. 5.6 Equilibrium model for the determination of the stud tension forces 33 5.5. Failure Analysis for the Bearing Test Panels Z5 to Z8 5.5.1. Failure Description Al l the bearing test panels were equipped with reversed structural steel angles. Furthermore, the angles for the panels Z7 and Z8 hadendplates welded on. The tests were done under a monotonic upward loading for the panels Z6 and Z7, and under a cyc l ic loading for the panels Z5 and Z8. As expected, a l l the panels fa i led outside the ends of the structural steel angles. The sequences of the fai lures are i l lustrated in the appendices H, I, J and K. 5.5.2. Bearing Capacity of the Reversed Angle Connection The vert ical shear load in the test panels was resisted by bearing of the structural steel angle on the concrete and by the shear force taken by the two horizontal bright bars (Fig. A3, A4). This shear force could be calculated easi ly from the known vertical displacement of the face plate. Thus, the bearing force applied on the concrete could be found. A suitable equation for the prediction of the bearing capacity of a reversed structural steel angle 2"x2" would be: P u b = A b ( 5 f c u } . . . .(5.1) where P u b ultimate bearing capacity of the reversed structural steel angle 2 A^ = 4 inch concrete area enclosed by the reversed structural steel angle f actual ultimate concrete strength* cu £ coeff ic ient for the determination of the effective ultimate concrete bearing strength Table 5 shows the test data and the derived values for the coeff ic ients £ . It is interesting to note, that there is not a s igni f icant difference in the coeff ic ient E, for reversed angles with or without end plates. For design purposes, E, could be taken as 1.0. / 5.5.3. Center of Gravity of the Bearing Force For the design of a reversed angle connection, we would l ike to use Eq. 5.1 to determine the bearing capacity. This equation is based on a uniform stress distr ibution over the enclosed area of the structural steel angle. Since the actual stress d is -tr ibution might d i f fe r from the assumed one, we have to determine the location of the center of gravity of the bearing force to en-able the stud tension forces in the main working stud to be estimated. Having measured the tension forces and the moments in the horizontal bright bars, we get the distance d to the center of gravity eas i ly by applying equilibrium to the model shown in Fig. 5.7. Values derived for the tests are presented in Fig. 5.8. Considering the mean and the standard deviation for the d i s t r ibu-tion of the distances d, the bearing force can be assumed to act in the center of gravity of the sturctural steel angle shape, regardless of whether or not there is an endplate welded on. TABLE 5 Coefficients <% for the Effective Ultimate Concrete Bearing Strength Panel Type of Test, Direction of Load Max Shear Load Corresponding Vertical Displacement Shear Taken by Steel Bars Ultimate Load Taken by Bearing Pub P . r _ ub ^ A f A b T cu kip _ 3 10 inches kip kip Z5 cyc l ic up 24.38 41.1 0.42 23.96 1.070 cycl ic down 24.48 36.5 0.37 24.11 1.076 16 monotonic up 23.06 34.5 0.35 22.71 1.032 17 monotonic up 27.59 54.5 0.56 27.03 1.207 18 cycl ic up 22.90 36.3 0.37 22.53 1.006 cyc l ic down 25.33 61.8 0.63 24.70 1.103 CO cn 36 1 4 • Kb H ( J c : : : ; Fig. 5.7. Equilibrium model of the connection used in the bearing test panels. Panel Z5 Up Z5 Down Z6 11 Z8 Up Z8 Down d (inch) 2.38 1.91 1.97 2.16 1.80 1.90 d / a 1.196 0.960 0.990 1.085 0.904 0.955 no endplates endplates mean d = 2.02" standard deviation a = 0.19" 2 CG of the structural steel angle  Fig. 5.8. Derived locations for the bearing force on the reversed structural steel angle 2"x2" 38 6. Conclusions for Design The test results for the panels Zl to Z4, which had normal angles without end plates, showed that the PCI shear-tension interaction equation (Eq. 4.1) for single headed studs can be used for the prediction of a fa i lure of the concrete surrounding the studs. The bearing capacity of the structural steel angle on the concrete should be neglec-ted. For the computation of the tension force in one stud, a l l the vert ical shear is assumed to be carried by a bearing stress of f c u acting on a triangular area defined by the inside of the legs of the angle (as explained in Section 5.4) with the resultant acting through the centroid of this triangular area. The tension in the stud is found by assuming a horizontal compression force acts at one end of the angle, and produces a couple equal to that resulting from the applied shear and the equal and opposite vertical force acting in the concrete. The PCI equation (Eq. 4.1) is then used for one stud which is assumed to carry this tension force and half the total vertical shear. Furthermore, the test results for the panels Z5 to Z8, which had reversed angles with and without endplates, showed that the bearing capacity for this case is equivalent to a force resulting from a stress equal to the actual ultimate concrete strength f c uniformly d i s t r i -buted over a square or rectangular area defined by the outside of the legs of the structural steel angle. The location of this force can be assumed to be in the actual center of gravity of the structural steel angle (not of the square or rectangle), regardless of whether or not there is an endplate present. 39 BIBLIOGRAPHY 1. PCI Design Handbook. Precast and Prestressed Concrete. Prestressed Concrete Institute, Chicago, I l l i no i s , 1971. 2. National Building Code of Canada, Supplement No. 1, Climatic  Information for Building Design in Canada. Associate Committee on the National Building Code, National Research Council of Canada, Ottawa, 1975. 3. Spencer, R.A. and Ne i l le , D.S., "Cycl ic Tests of Welded Headed Stud Connections," Journal of the Prestressed  Concrete Institute, Vol. 21, No. 3, May/June 1976, pp. 70-83. 4. Ne i l le , D.S., "Behaviour of Headed Stud Connections for Precast  Concrete Panels under Monotonic and Cycled Shear Loading," Ph.D. thesis at the department of c i v i l engineering of The University of Br i t i sh Columbia, May 1977. APPENDIX A FABRICATION DETAILS OF THE TEST PANELS Fig. A l . Connection detai ls of panels ZI and Z2 42 +-L2x2x%xT-0" L2x2x% Fig. A.2. Connection details of panels 12 and Z4 I 2 > Section B-B Detail for the anchorage of the angles Fig. A.3. Connection details of panels 15 and 16 L2x2x1/4x2'-0" ..../.*. plast ic foam %x2xl2h * / f i r 1 Section A-A 3 /16K\ r PL%x2x2 r2j \L2x2x% N l K ^ plast ic foam 2x1x6 ^ Y \ T ^ R b r i q h t bar 4>V'x7 |" bl "j, z j, long 4 Section B-B Detail of the anchorage of the angles, Fig. A.4. Connection detai ls of panels Z7 and Z8 45 A 1 24 suspension bar Elevation (studs etc. not shown) A II OIL 1"» 'fir 46 1" cover 24 concrete surface Section A-A Detail suspension bars a l l steel bars diam. 1/4", undeformed, ^ ^ 4 0 ksi Fig. A5. Typical rebar arrangement Fig- A.7. P last ic pipes containing strain gage wires lead through the bottom of the formwork Fig. A.8. Strain gage 4 8 Fig. A . 1 0 . Connection unit for panel Z5 Fig. A . l l Connection unit for panel 17 (with endplate) APPENDIX B ILLUSTRATIONS OF THE TEST EQUIPMENT 0 Fig. B l . Test arrangement Fig. B4. Data acquisition and test control l ing instruments Fig. B5. Transducers for the horizontal displacements Fig. B 7 . Backside of a panel with leads connected to the strain gage termi nal s box containing Wheatstone bridges power supply unit Fig. B 8 . Power supply unit and four boxes containing Wheatstone bridges APPENDIX C DETAILS OF THE CONCRETE AND STEEL SPECIMEN TESTS TABLE 6 Compression Test Data For Concrete Cylinders of 6" diam. and 12" length Testing Concrete Cylinder Area Failure Compressive Mean Standard Date Age Number 2 Load Strength Strength Deviation Days in kip psi psi psi 7-Jul-77 14 1 28.56 128.0 4480 2 28.56 128.5 4500 4490 10 3 28.46 127.5 4480 14-Jul-77 21 4 28.37 137.5 4850 5 28.75 132.5 4610 4690 110 6 28.46 131.5 4620 21-Jul-77 28 7 28.46 155.0 5440 8 28.56 160.2 5610 5450 120 9 28.56 151.5 5310 18-Aug-77 56 10 28.56 160.0 5600 11 28.37 158.0 5570 5620 50 12 28.37 161,5 5690 TABLE 7 Tensile Test Data For The Steel Specimens Specimen No. Nominal Diam. inches Stud Diam. inches Machined Diam. inches Failure Diam. inches Maximum Load kip Maximum Stress ksi Failure Strain 10 " 3 1 1/2 0.498 0.385 0.252 9.4 80.8 156 2 1/2 0.498 0.388 0.250 9.2 77.8 140 3 1/2 0.498 0.384 0.246 9.1 78.6 145 4 5/8 0.620 0.488 0.305 13.8 73.8 198 5 5/8 0.620 0.496 0.316 15.4 79.7 196 6 5/8 0.621 0.491 0.305 13.9 73.4 195 7 3/4 0.746 0.623 0.373 20.4 66.9 226 8 3/4 0.75 0.628 0.381 19.9 64.3 287 9 3/4 0.745 0.624 0.370 19.3 63.1 293 Fig. C2. 1/2" diam. steel specimen Fig. C3. 5/8" diam. steel specimen APPENDIX D ILLUSTRATIONS OF THE TEST OF PANEL Zl Fig. DI. Load - vert ical displacement diagram for panel Zl Fig. D2. Panel ZI, after f a i l u re , fai lure load = 20 kip Fig. D3. Panel ZI, after fa i lu re CTI Fig. D 4 . Panel Z l , after fa i lure Fig. D 5 . Panel Z l , after test Fig. D 6 . Panel Z l , after test Fig. D 7 . Panel Z l , after test Fig. D9. Concrete piece broken out of panel ZI APPENDIX E ILLUSTRATIONS OF THE TEST OF PANEL 12 69 20 Fig. E l . Load - vertical displacement diagram for panel 12 Fig. E2. Panel Z2, cycle 17 max. load = 18.8 kip F ig. E3. Panel Z2, cycle 17 o Fig. E4. Panel 12, cycle 17 Fig. E5. Panel 12, after fa i lure Fig. E6. Panel Z2, after fa i lure Fig. E7. Panel Z2, after test Fig. E8. Panel Z2, after test Fig. E9. Concrete piece with face plate, angle and studs broken out of panel Z2 G O 74 F i g . El0. Concrete piece broken out of panel Z2 behind the heads of the studs APPENDIX F ILLUSTRATIONS OF THE TEST OF PANEL Z3 Fig. F l . Load-vert ical displacement diagram for panel Z3 Fig. F2. Panel Z3, load = 33 kip Fig. F3. Panel Z3, fa i lure load = 38 kip Fig. F4. Panel Z3, load=22 kip Fig. F6. Panel Z3, after failure Fig. F7. Panel Z3, after test ^ 4 Fig. F 8 . Panel 13, a f t e r test Fig. F 9 . Panel Z3, f a i l u r e surface oo o Fig. FT2. Concrete piece with face plate, angle and studs broken out of panel Z3 APPENDIX G ILLUSTRATIONS OF THE TEST OF PANEL Z4 84 Fig. Gl. Load-vertical displacement diagram for panel Z4 Fig. G2. Panel Z4, cycle 14, Load=29.8 kip Fig. G3. Panel Z4, cycle 16 downwards, max. load = 35 kip Fig. G4. Panel Z4, cycle 16 downwards, max. load = 35 kip Fig. G5. Panel Z4, cycle 17 downwards oo Fig. G6. Panel Z4, cycle 18 upwards Fig. G7. Panel Z4, cycle 18 upwards CO Fig. G14. Panel Z4, after test Fig. G15. Panel Z4, fa i lure surface CO 92 Fig. 616. Concrete piece with face plate, angle and studs broken out of panel Z4 93 APPENDIX H ILLUSTRATIONS OF THE TEST OF PANEL Z5 Fig. HI. Load-vertical displacement diagram for panel Z5 to Fig. H2. Panel Z5, cycle 10 upwards, max. load = 24.4 kip Fig. H3. Panel Z5, cycle 10 upwards, max.load » 24.4 kip CO Fig. H4. Panel 15, cycle 11 downwards, load = 10.7 kip Fig. H5. Panel 15, cycle 11 downwards, load = 10.7 kip Fig. H6. Panel Z5, cycle 12 upwards, load = 13.8 kip Fig. H7. Panel Z5, after test <0 Fig. H8. Panel Z5, f a i lure surface Fig. H10. Panel Z5, after test APPENDIX I ILLUSTRATIONS OF THE TEST OF PANEL Z6 101 0.10 inch Fig. II. Load-vertical displacement diagram for panel 16 1 0 3 Fig. 16. Panel Z6, load = 6 kip Fig. 18. Panel Z6, after test APPENDIX J ILLUSTRATIONS OF THE TEST OF PANEL 17 Fig. J2. Panel Z7, load = 26.7 kip Fig. J 4 . Panel Z7, f a i lure load = 27.6 kip Fig. J 5 . Panel Z7, f a i lu re load = 27.6 kip Fig. J 6 . Panel Z7, load • 7.6 kip Fig. J8. Panel 17, after complete fa i lure Fig. J9. Panel 17, f a i lu re surface APPENDIX K ILLUSTRATIONS OF THE TEST OF PANEL Z8 Fig. K2. Panel Z8, Connection detail Fig. K3. Panel Z8, cycle 10 upwards, max. load = 22.9 kip Fig. K4. Panel Z8, cycle 11 upwards Fig. K6. Panel Z8, cycle 11 upwards Fig. K8. Panel Z8, upper fa i lure surface Fig. K9. Panel Z8, cycle 11 downwards, max. load = 25.3 kip at scan 315, cycle 10 Fig. K10. Panel Z8, cycle 11 Fig. KIT - Panel Z8, cycle 12 APPENDIX L DETERMINATION OF THE SHEAR CONE SURFACE AREA Partial shear cone Full shear cone Horizontal cross section through the connection Section A - A Section B - B Surface area A • o partial shear cone : AQ = 1.916 l [l +.dh) - 0.631 d£ fu l l shear cone ; AQ = /2~ A "ir(Jl +'dh) Fig. Ll . Determination of the shear cone surface area 

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