@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix dc: . @prefix skos: . vivo:departmentOrSchool "Forestry, Faculty of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Zhuang, Xiaojun"@en ; dcterms:issued "2009-11-27T01:04:54Z"@en, "2004"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description "Reliability evaluation principles, procedures as applied in the Chinese timber structure design code were reviewed. The general method to establish the design values of Chinese wood strength properties was investigated. In particular, Chinese load information, including the statistical models and parameters, was analyzed. Also, the reliability associated with wood structural design requirements in Canada was studied. The emphasis was placed on the in-grade testing method, which is a more reliable method to get the lumber strength properties compared with small clear wood testing method used in China. Finally, Canadian procedures for establishing the design values of wood strength properties were reviewed. Using Chinese load information and Canadian in-grade testing data, reliability evaluations were conducted for the design values of common Canadian Species in the Chinese timber design code. These design values were previous soft converted from allowable stresses approved by the American Lumber Standards Committee. Reliability results were compared with the target reliability levels tabulated in the Chinese national unified reliability code. This reliability analysis was implemented by using the \"RELAN\" (Reliability ANalysis) program developed by Dr. R.O. Foschi of UBC. Recommendations were made to develop a formal reliability evaluation of the performance of North American dimension lumber under the Chinese load conditions."@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/15856?expand=metadata"@en ; dcterms:extent "6285008 bytes"@en ; dc:format "application/pdf"@en ; skos:note "RELIABILITY STUDY OF NORTH A M E R I C A N DIMENSION L U M B E R IN THE CHINESE TIMBER STRUCTURES DESIGN CODE by X I A O I U N Z H U A N G B.ENG., Shanghai University, 1997 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF THE REQUIREMENT FOR THE DEGREE OF M A S T E R OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES Department of Wood Science We accept this thesis as conforming to the required standard THE UNIYERISITY OF BRITISH C O L U M B I A September 2004 © Xiaojun Zhuang, 2004 JDBCL THE UNIVERSITY OF BRITISH COLUMBIA FACULTY OF GRADUATE STUDIES Library Authorization In present ing this thesis in part ial fulf i l lment of the requi rements for an advanced degree at the University of British Columbia, I agree that the Library shall m a k e it freely avai lable for reference and study. I further agree that permiss ion for extens ive copy ing of this thesis for scholar ly purposes may be granted by the head of my depar tment or by his or her representat ives. It is unders tood that copying or publ icat ion of this thesis for f inancial ga in shall not be a l lowed wi thout my wri t ten permiss ion. X i a o j u n Z h u a n g 0 8 / 1 0 / 2 0 0 4 Name of Author (please print) Date (dd/mm/yyyy) Title of Thesis: R e l i a b i l i t y s t u d y o f N o r t h A m e r i c a n d i m e n s i o n l u m b e r in t h e C h i n e s e t i m b e r s t r u c t u r e s d e s i g n c o d e Degree: M a s t e r o f S c i e n c e Year: 2 0 0 4 Depar tment of W o o d S c i e n c e The University of British Co lumb ia Vancouver , BC C a n a d a g rad .ubc .ca / fo rms/? fo rmlD=THS page 1 of 1 last updated: 20-Jul-04 ABSTRACT Reliability evaluation principles, procedures as applied in the Chinese timber structure design code were reviewed. The general method to establish the design values of Chinese wood strength properties was investigated. In particular, Chinese load information, including the statistical models and parameters, was analyzed. Also, the reliability associated with wood structural design requirements in Canada was studied. The emphasis was placed on the in-grade testing method, which is a more reliable method to get the lumber strength properties compared with small clear wood testing method used in China. Finally, Canadian procedures for establishing the design values of wood strength properties were reviewed. Using Chinese load information and Canadian in-grade testing data, reliability evaluations were conducted for the design values of common Canadian Species in the Chinese timber design code. These design values were previous soft converted from allowable stresses approved by the American Lumber Standards Committee. Reliability results were compared with the target reliability levels tabulated in the Chinese national unified reliability code. This reliability analysis was implemented by using the \" R E L A N \" (Reliability ANalysis) program developed by Dr. R.O. Foschi of UBC. Recommendations were made to develop a formal reliability evaluation of the performance of North American dimension lumber under the Chinese load conditions. ii TABLE OF CONTENTS A B S T R A C T ii T A B L E O F C O N T E N T S iii LIST O F T A B L E S vi LIST O F F I G U R E S vii LIST O F A P P E N D I C E S viii A C K N O W L E D G E M E N T S ix 1. Introduction 1 1.1 Background I 1.2 New Chinese timber design code 2 1.3 Design methods of the code 4 1.4 Reliability evaluation method 4 1.5 Reliability assessment procedure 5 1.6 Objectives 6 2. Limit states design in China 8 2.1 Limit states design equation 8 2.2 Target reliability. 10 2.2.1 Method 10 2.2.2 Load 11 2.2.3 Resistance 11 2.2.4 Results of target reliability analysis 13 2.3 Structural importance factors 14 2.4 Load effect factors 15 2.5 Resistance division coefficient. 16 3. Reliability Analys is of Chinese timber design code 18 3.1 Reliability evaluation 18 3.1.1 Load information 18 3.1.2 Member resistance 19 3.1.2.1 Small clear testing specimen strength 21 3.1.2.2 Quality variability factor KQ 23 3.1.2.3 Geometry variability factor KA 24 3.1.2.4 Analysis model variability KP 25 3.1.3 Results 25 3.2 Wood strength design values 26 3.2.1 Characteristic strength 27 3.2.2 Material property division coefficient 28 4. Chinese load models 31 iii 4.1 Dead load 31 4.2 Occupancy load 32 4.2.1 Sustained occupancy load 32 4.2.2 Extraordinary occupancy load 33 4.2.3 Maximum occupancy load in 50 years 34 4.3 Wind load , 36 4.3.1 The wind velocity and reference velocity pressure 37 4.3.2 The model of reference velocity pressure 37 4.3.3 The national reference velocity pressure 38 4.3.4 The national wind pressure statistical model 40 4.3.5 The national maximum wind pressure in 50 years 41 4.4 Snow Load 42 4.4.1 Annual maximum ground snow load data 42 4.4.2 The statistical model of ground show load 42 4.4.3 The national snow load statistical model 43 4.4.4 The snow load model in the code 44 4.5 Load models used in reliability analysis 45 5. Reliability study of wood in Canada 46 5.1 Material strength database. 46 5.1.1 Small clear wood testing 47 5.1.2 Shortcomings of small clear wood testing 48 5.1.3 In-grade testing 49 5.1.4 CWC lumber properties project 50 5.2 Reliability evaluation 50 5.2.1 Load information 51 5.2.2 Member resistance 52 5.2.3 Results 53 5.3 Specified strengths 55 5.4 Modification factors 56 6. Reliability evaluation of lumber Design Values in Chinese Code 59 . 6.1 Pedormance functions 60 6.1.1 Strength limit states 60 6.1.2 Serviceability limit states 61 6.2 Strength database 67 6.2.1 Species, grades and sizes 62 6.2.2 Resistance distribution model 62 6.3 Load information 6 5 6.3.1 Statistical parameters of load models 66 6.3.2 Load ratio 66 6.4 Bending 6 8 6.4.1 Original data 68 6.4.2 Effect of distribution types and load ratios 69 6.4.3 Target reliability evaluation results 72 6.5 Compression 7 3 6.5.'1 Original data 7 3 6.5.2 Effect of distribution types and load ratios 74 6.5.3 Target reliability evaluation results 77 i v 6.6 Tension 78 6.6.1 Original data. 78 6.6.2 Effect of distribution types and load ratios 79 6.6.3 Target reliability evaluation results 82 6.7 Serviceability 83 6.7.1 Original data 83 6.7.2 Effect of distribution types and load ratio 84 6.7.3 Target reliability evaluation results 87 7. Discussion and conclusion 88 7.1 Target reliability evaluation 89 7.2 Robustness of soft conversion method 90 7.3 Discussion 92 7.4 Conclusion 94 APPENDIX A: 95 REFERENCES 100 v L I S T O F T A B L E S Table 2-1 Load information used in target reliability assessment 11 Table 2-2 Resistance parameters for wood 13 Table 2-3 Existing reliability levels 13 Table 2-4 Target reliability levels 14 Table 2-5 Importance factors 14 Table 3-1 Load information used in wood reliability evaluation 19 Table 3-2 Statistical parameters for testing specimen strength 21 Table 3-3 Testing member strength parameters for Fir in different locations 22 Table 3-4 Statistical parameters for quality factors 23 Table 3-5 Statistical parameters for quality variability factor 24 Table 3-6 Statistical parameters for geometry variability factor 25 Table 3-7 Statistical parameters for model variability factor 25 Table 3-8 p value under dead load plus occupancy (office) load 26 Table 3-9 p value under dead load plus snow load 26 Table 3-10 p value published in the timber design code 26 Table 4-1 Statistical parameters of occupancy loads 35 Table 4-2 Statistical parameters of live loads 36 Table 4-3 Statistical Parameters and distribution types for loads (1984 version) 45 Table 5-1 Parameters for Canadian live load 52 Table 5-2 Snow load data for six Canadian cities 52 Table 6-1 Relationship between Chinese and North American grades 62 Table 6-2 Load statistical information for reliability evaluation 66 Table 6-3 Parameter estimates of Bending at 15% M . C 68 Table 6-4 2-P Weibull (Truncated at 15%) for snow load (bending) 70 Table 6-5 Lognormal (100% Data) for snow load (bending) 70 Table 6-6 Characteristics of the bending strength for S P F No.2 2x8 71 Table 6-7 B values for bending strength with Lognormal (entire data) distribution 72 Table 6-8 Parameter estimates of U C S at 15% M . C 73 Table 6-9 2-P Weibull (Truncated at 15%) for snow load (compression) 75 Table 6-10 Lognormal (100% Data) for snow load (compression) 75 Table 6-11 Characteristics of U C S for DF SS 2x10 76 Table 6-12 B values for compress ion strength with Lognormal (entire data) distribution ...77 Table 6-13 Parameter estimates of U T S at 15% M . C 78 Table 6-14 2-P Weibull (Truncated at 15%) under snow load (tension) 80 Table 6-15 Lognormal (100% Data) under snow load (compression) 80 Table 6-16 Characteristics of the U T S for S P F No.2 2x4 81 Table 6-17 p values for tension strength with Lognormal (entire data) distribution 82 Table 6-18 Parameter estimates of M O E at 15% M . C 83 Table 6-19 Lognormal under snow load (serviceability) 85 Table 6-20 2-P Weibull under snow load (serviceability) 85 Table 6-21 Characteristics of the M O E for HF No.2 2x4 86 Table 6-22 B values for serviceability with Lognormal distribution 87 Table 7-1 Target reliability evaluation 89 LIST OF FIGURES Figure 1-1 Yin Xian W o o d Tower 1 Figure 4-1 Dead load Model 31 Figure 4-2 Sustained live load model 33 Figure 4-3 Extraordinary occupancy load model 34 Figure 6-1 (S - Relation for four distribution types (SPF No.2 2x8,100% data) 63 Figure 6-2 Lognormal fit to 2x4 D F entire test data (Bending) 64 Figure 6-3 Lognormal fit to 2x4 D F lower 100 test data (Bending) 65 Figure 6-4 j3 - relations for four distribution types (bending) 71 Figure 6-5 /3 - relations for four distribution types (compression) 76 Figure 6-6 (3 -

o , the strengths Rni and the parameter k were calibrated by minimization of minimum error theory. This method was used to establish the characteristic values, which was adjusted to a 2x8 size with dry condition (15% moisture content), for bending, tension and compression parallel to grain. 5.3 Specified strengths Specified strength is the strength assigned for use in the prediction of member resistance. The value of the specified strength is published in the Canadian wood design code for engineering calculations [19]. Based on the characteristic strength, the specified strengths in bending can be expressed as fh=C(KD)(dJdsylk(Lc/Ls)m (5.5) where c : Characteristic bending value, MPa KD : 0.8 (duration of load factor) dc : 184mm (characteristic depth) ds : 286mm (specified depth) k : 3000mm (characteristic length) : 4862mm (specified length, at 17:1 span/depth ratio) k : Size factor, 4.3 55 Chapter Five Reliability Study of Wood in Canada In this function, size and duration of load adjustments are made to the characteristic properties to establish the specified strength values. The published strength value is based on the largest common dimension lumber size — 2 x 12 (38 x 286mm). Generally, the biggest size lumber has the lowest strength value. While the original characteristic strength value is based on the size 2x8, the adjustment is made to transfer it into 2x12. One reason for this adjustment is that the resulting factored resistance will still be safe if the designer does not apply the modification for size Kz. Duration of load must be considered in the design process. It is well known that wood, as a structural material, is stronger under the short-term duration load than the long-term load. In order to incorporate the factor for snow and occupancy loads directly into the specified strengths, the duration of load adjustment factor KD is applied to the specified strength. The duration of load factors were developed based on long-term loading tests conducted on full-size lumber. The duration of load factors were derived so as to achieve the same level of reliability under short-term and long-term loading. Similarly, the design procedures for tension strength fh, the compression parallel to grain strength fc and the longitudinal shear strength /„ were also established in reliability based approach. The mean strength of the compression perpendicular to grain / was set equal to characteristic values, while modulus of elasticity was set equal to characteristic mean M O E values for Select Structural, N o . l , No.2 and No.3 grades. 5.4 Modification factors The final factored resistance in the design equation is calculated with additional two groups of adjustment factors. The first group factors are related to material behavior. In the case of bending, bending resistance is expressed as Fh=fb{KDKHKshKT) (5.6) where KD : Duration of load factor KH : System factor 56 Chapter Five Reliability Study of Wood in Canada Ksb : Service condition factor for bending KT : Treatment factor The long term duration of load effect is directly incorporated in the specified strengths. The duration of load for the standard term is taken as 1.00. In the other two cases, KD is taken as 1.15 for short term and 0.65 for permanent duration of loading. The system factor KH is established to account for the high structural capacity of redundant of wood structural systems. A reliability study of the system modification factors was conducted for light frame floors and flat roofs. There are two different degrees of structural interaction (Case 1 and Case 2). Case 1 applies to systems of closely spaced structural components such as light-frame trusses. KH is taken as 1.10 for bending, shear, compression parallel to grain as well as tension parallel to grain. Case 2 includes the conventional wood frame floors, roofs and walls. Different system factors are applied for different materials used in the system. Studies of strength and stiffness changes of dimension lumber due to moisture content show that member capacities and stiffness are higher in dry service conditions than wet service conditions. The specified strengths are derived by assuming the structural member is used in the dry service condition. Therefore, service condition factor Ks is applied to adjust specified strength to the wet service condition in design calculations. Dimension lumber treatments, such as the preservative treatment and fire-retardant treatments, will reduce the strength of the lumber, especially for those small dimensions lumber. For this reason, the treatment factor KT is applied with dry or wet service conditions. The second group of adjustment factors involves the member geometry and configuration, as well as the resistance factor based on the reliability analysis. For the bending resistance moment, it can be expressed as: M^QF^K^K, (5.7) where

the ratio of live load to nominal live load

0.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 Bending Strength, R(MPa) Figure 6-3 Lognormal fit to 2x4 DF lower 100 test data (Bending) Considering the target reliability indices specified in the reliability code were calculated based on the Lognormal distribution, the entire date range fitted to Lognormal distribution is also studied. In sum, two distribution models are chosen in the current study of strength limit states: 2P-Weibull distribution fitted to the 15 percent of the lower tail and the Lognormal distribution fitted to the entire data range. In the serviceability limit states, 2P-Weibull distribution and Lognormal distribution fitted to the entire range data were used. Two different sets of reliability index results in bending, compression and tension, as well as the serviceability case will show us the effect of distribution models. These results could be the reference for the future reliability study. Finally, only one distribution model is used to investigate the reliability levels of design value published in the wood design code. 6.3 Load information Although the new national unified reliability code [7] did not publish detailed information for load models, two important adjustments were explained in the code. First, 65 Chapter Six Reliability Evaluation of Lumber Design Values in Chinese Code the 30-year return period for wind and snow load was updated to 50-year return period, which means, according to this update, the wind and snow load model should be updated. Second, the design occupancy load was increased from 1.5 kN/m 2 to 2.0 kN/m 2 , therefore the occupancy load model also needs to be modified according to this change. 6.3.1 Statistical parameters of load models In this study, the load distribution model and statistical parameters are taken from the Chinese wood reliability evaluation paper [11]. In this paper, the updated distribution models were given to the snow load and occupancy load. Because the wind load was not considered in the reliability study of Chinese wood structures, the distribution model of wind load was not listed. Therefore, the wind load model for the current study is based on the old version 30-year return period model. Detailed load information is shown in Table 6-2. Load Types Mean/Nominal Coefficient of variation Distribution Type Dead 1.060 0.070 Normal Occupancy(office) 0.524 0.288 Extreme Type I Occupancy( residential) 0.644 0.233 Extreme Type I Wind(30-year return) 1.000 0.190 Extreme Type I Snow(30-year return) 1.140 0.220 Extreme Type I Snow(50-year return) 1.040 0.220 Extreme Type I Table 6-2 Load statistical information for reliability evaluation 6.3.2 Load ratio Load ratio is defined as the ratio of nominal dead load to nominal live load in North America. In China, the load ratio is expressed, in reverse, as the ratio of nominal live load to nominal dead load. The typical dead-to-live load ratio for a wood-frame house in Canada was taken as 0.25, which was used in the reliability study for the CSA 086-1. In the Chinese soft conversion method, the dead-to-live ratio was assumed as 0.33. A research of more than 30 roof types in China showed that the live-to-dead ratio of wood roof ranges from 0.14 to 0.6. For the floors in office building, the live-to-dead ratio was about 1.5. In the reliability study, the live-to-dead load ratio 66 Chapter Six Reliability Evaluation of Lumber Design Values in Chinese Code 0.2, 0.3 and 0.5 were taken for the roof. Also, 1.5 was taken for the office building floor case. Given the load ratio definition in North America, the dead-to-live ratio was taken as 5, 3.3, and 2 for roof and 0.67 for the office building floor. The major difference of load ratios between Canada and China are basically caused by two facts. First, different styles of roof structure lead to different definitions of nominal dead loads. Instead of the light trusses in Canada, wood roofs are traditionally constructed using heavy timber in China. In addition, most of wood roofs are finally covered by cement roof tiles, which are much heavier than the weight of roof material typically used in Canada. This partly explains the higher dead load ratio adopted in China. Second, design live loads, such as snow load, are significantly different between two countries. Due to the different weather conditions as well as the snow accumulation level and time, the design snow loads in China are much less than the design snow loads of the major Canadian cities. Considering the variation of the load ratios, several load ratios are used to study the load ratio effect on the reliability levels. First of all, dead-to-live ratio is taken as 0.33, which was also used in the soft conversion procedure adopted in the current Chinese code. In addition, the dead-to-live ratio 0.25 used in the Canadian reliability analysis is also used for reference. A more consistent approach is to define the term \"load ratio\" as the ratio of dead-to-live loads based on the Canadian definition. In the reliability study of the Canadian code, the dead-to-live load ratio is taken as 0.25. Since the average design snow load in Canada is approximately 2.0 kN/m 2 , it indicates that the typical Canadian design dead load is about 0.5 kN/m 2 . On the other side, the design snow load in most of Chinese cities ranges from 0.2-0.5 kN/m 2 . Assuming the same light roof structure is used in both Canada and China, the dead load of both roofs would be 0.5 kN/m 2 . Therefore, dead-to-live load ratio of light roof system in China could be taken as 1 and 2.5. In the case of office floor loads, the dead-to-live load ratio is taken as 0.25, 0.33 and 0.67, which are consistent with the ones adopted in the Canadian reliability study, and also consistent with the assumption in the soft conversion method and the ratio adopted in the Chinese traditional wood structure. 67 Chapter S ix Reliability Evaluation of Lumber Design Values in Chinese Code 6.4 Bending 6.4.1 Or ig ina l data Table 6-3 lists the statistical information for bending strength according to different combinations of all the species, grades and sizes. These parameters are directly taken from the Appendix of Canadian Lumber Properties [18]. It includes: • Parameters of 2-P Weibull distribution (truncated at 15% Percentile) • Parameters of Lognormal distribution (100% data) • Design values fm in Chinese code • Size factor Kz 2-P Weibull(15%) Lognormal Species Grade Size Scale m (MPa) Shape k Mean Standard Deviation fm (MPa) K 2 DF SS 2x10 44.13 4.31 3.77 0.37 15.00 1.10 DF SS 2x8 50.88 4.46 3.97 0.39 15.00 1.20 DF SS 2x4 61.36 5.51 4.15 0.33 15.00 1.50 DF No.2 2x10 27.44 4.68 3.44 0.47 9.10 1.10 DF No.2 2x8 33.23 4.19 3.58 0.48 9.10 1.20 DF No.2 2x4 46.40 3.80 3.86 0.46 9.10 1.50 HF SS 2x10 42.13 4.44 3.68 0.33 14.00 1.10 HF SS 2x8 52.40 4.21 3.88 0.34 14.00 1.20 HF SS 2x4 68.88 4.75 4.15 0.31 14.00 1.50 HF No.2 2x10 32.54 4.30 3.46 0.39 11.00 1.10 HF No.2 2x8 44.26 3.45 3.70 0.43 11.00 1.20 HF No.2 2x4 52.61 4.04 3.96 0.40 11.00 1.50 SPF SS 2x10 38.82 4.77 3.55 0.28 13.00 1.10 SPF SS 2x8 43.44 4.72 3.68 0.29 13.00 1.20 SPF SS 2x4 55.30 5.77 3.97 0.28 13.00 1.50 SPF No.2 2x10 26.41 5.40 3.35 0.36 9.40 1.10 SPF No.2 2x8 34.13 4.41 3.53 0.38 9.40 1.20 SPF No.2 2x4 45.16 4.19 3.76 0.37 9.40 1.50 Table 6-3 Parameter estimates of Bending at 15% M.C. 68 Chapter S ix Reliability Evaluation of Lumber Design Values in Chinese Code 6.4.2 Effect of distribution types and load ratios To further illustrate the difference between bending strength distribution types and load ratios, a reliability index comparison study is conducted. By using the dead load plus snow load (30-year return) combination, reliability indices are calculated by G function 6.7 with two distribution models, 2-P Weibull (15%) and Lognormal (100% Data), each with four load ratios, 0.25, 0.33, 1 and 2.5. Table 6-4 and Table 6-5 show the results of the combination of all species, grades and sizes. Comparing the results in Table 6-4 and Table 6-5, significant difference is found between two distribution types. The Lognormal distribution with entire data results in an approximately 25% higher reliability index (3 than the Weibull distribution. To illustrate this relationship, R- curve, which is similar to Dr. Foschi's study in Canada [15], is developed for SPF No.2 2x8 lumber under the dead load plus snow load (30-year return). Statistical parameters for the four distribution types are listed in Table 6-6. Figure 6-4 shows a graphic illustration of the trend of the results in Table 6-4 and Table 6-5, where the Lognormal distribution produces the relatively higher reliability indices than the others. Considering the requirement of Chinese unified reliability code and Chinese wood reliability study, the resistance needs to be fitted to Lognormal distribution. Finally, Lognormal distribution with entire data range is used in the further study. Table 6-4 and Table 6-5 also compare the reliability results obtained by using different load ratios. It is apparent that the reliability levels do not vary substantially with load ratios. Thus, this effect could be disregarded in the bending case. Since the dead-to-live load ratio 0.33 was used in the soft conversion method to derive the design values, reliability indices of load ratio 0.33 are used in the further study. 69 Chapter Six Reliability Evaluation of Lumber Design Values in Chinese Code Reliability index p Species Grade Size (load ratio) Average (0.25) (0.33) (1) (2.5) P DF SS 2x10 2.449 2.451 2.449 2.429 2.445 DF SS 2x8 2.591 2.593 2.593 2.575 2.588 DF SS 2x4 2.903 2.909 2.925 2.913 2.913 DF No.2 2x10 2.626 2.629 2.632 2.614 2.625 DF No.2 2x8 2.592 2.594 2.591 2.572 2.587 DF No.2 2x4 2.574 2.574 2.568 2.549 2.566 HF SS 2x10 2.534 2.536 2.535 2.516 2.530 HF SS 2x8 2.636 2.637 2.635 2.616 2.631 HF SS 2x4 2.925 2.928 2.933 2.917 2.926 HF No.2 2x10 2.454 2.456 2.453 2.433 2.449 HF No.2 2x8 2.392 2.391 2.381 2.361 2.381 HF No.2 2x4 2.595 2.596 2.591 2.573 2.589 SPF SS 2x10 2.643 2.647 2.651 2.633 2.644 SPF SS 2x8 2.665 2.669 2.672 2.655 2.665 SPF SS 2x4 3.053 3.061 3.082 3.071 3.067 SPF No.2 2x10 2.755 2.761 2.775 2.760 2.763 SPF No.2 2x8 2.673 2.675 2.675 2.657 2.670 SPF No.2 2x4 2.665 2.666 2.663 2.645 2.660 Table 6-4 2-P Weibull (Truncated at 15%) for snow load (bending) Species Grade Size Reliability index (3 (load ratio) Average (0.25) (0.33) (D (2.5) P DF SS 2x10 2.859 2.878 2.959 2.976 2.918 DF SS 2x8 3.001 3.020 3.098 3.114 3.058 DF SS 2x4 3.279 3.309 3.459 3.520 3.392 DF No.2 2x10 2.691 2.700 2.729 2.720 2.710 DF No.2 2x8 2.746 2.754 2.783 2.774 2.764 DF No.2 2x4 2.959 2.971 3.014 3.012 2.989 HF SS 2x10 3.051 3.079 3.207 3.254 3.148 HF SS 2x8 3.266 3.295 3.433 3.486 3.370 HF SS 2x4 3.594 3.633 3.839 3.945 3.753 HF No.2 2x10 2.747 2.763 2.825 2.831 2.792 HF No.2 2x8 2.862 2.876 2.926 2.927 2.898 HF No.2 2x4 3.113 3.132 3.211 3.227 3.171 SPF SS 2x10 3.234 3.274 3.483 3.596 3.397 SPF SS 2x8 3.283 3.321 3.521 3.625 3.438 SPF SS 2x4 3.535 3.579 3.823 3.969 3.727 SPF No.2 2x10 3.031 3.053 3.154 3.183 3.105 SPF No.2 2x8 3.124 3.145 3.238 3.262 3.192 1 SPF No.2 2x4 3.202 3.226 3.332 3.364 3.281 Table 6-5 Lognormal (100% Data) for snow load (bending) 70 Chapter S ix Reliability Evaluation of Lumber Design Values in Chinese Code 2-P Weibull 15% Lognormal 2-P Weibull 100% Normal 5-th Percentile (MPa) Scale m Shape k Mean Standard Deviation Scale m Shape k Mean Standard Deviation 34.13 4.41 3.53 0.38 40.68 3.08 36.37 12.78 17.24 Table 6-6 Characteristics of the bending strength for SPF No.2 2x8 FORM Load ratio 0.25 1 .o -I 1 1 1 1 1 1 1 1 1 1 1 1 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 Performance Factor Figure 6-4 j8 -

curve is developed for the SPF No.2 2x4 lumber under the dead load plus snow load to illustrate the situation. Statistical parameters for the four distribution types are listed in Table 6-16. Figure 6-6 and Table 6-14 and Table 6-15 show the same trend where the results of Lognormal distribution show a slightly higher reliability level than the results of the 2-P Weibull (truncated in 15%). Because of the requirement of the Chinese unified reliability code and reliability study in the Chinese timber design code, the resistance needs to be fitted to the Lognormal distribution. Therefore, the Lognormal distribution with entire data range is used in further study. Table 6-14 and Table 6-15 also show the reliability results obtained using different load ratios. It is apparent that the reliability levels do not vary substantially with load ratios. Thus, this effect could be disregarded in the tension strength. Because the load ratio 0.33 is the assumption of the soft conversion method, the reliability indices of load ratio 0.33 are used for further study. 79 Chapter S ix Reliability Evaluation of Lumber Design Values in Chinese Code Reliability index p Species Grade Size (load ratio) (0.25) (0.33) (D (2.5) DF SS 2x10 2.922 2.933 2.971 2.965 DF SS 2x8 2.866 2.876 2.905 2.896 DF SS 2x4 2.778 2.787 2.812 2.802 DF No.2 2x10 2.642 2.646 2.650 2.633 DF No.2 2x8 2.661 2.665 2.669 2.653 DF No.2 2x4 2.537 2.539 2.539 2.521 HF SS 2x10 2.778 2.786 2.805 2.792 HF SS 2x8 2.922 2.937 2.984 2.982 HF SS 2x4 2.622 2.625 2.629 2.612 HF No.2 2x10 2.621 2.627 2.638 2.622 HF No.2 2x8 2.673 2.676 2.678 2.661 HF No.2 2x4 2.643 2.650 2.665 2.650 SPF SS 2x10 2.765 2.770 2.781 2.767 SPF SS 2x8 2.570 2.575 2.586 2.569 SPF SS 2x4 2.771 2.779 2.802 2.791 SPF No.2 2x10 2.766 2.769 2.771 2.754 SPF No.2 2x8 2.657 2.660 2.664 2.647 SPF No.2 2x4 2.508 2.510 2.509 2.490 Table 6-14 2-P Weibull (Truncated at 15%) under snow load (tension) Reliability index p Species Grade Size (load ratio) (0.25) (0.33) (1) (2.5) DF SS 2x10 2.960 2.981 3.069 3.090 DF SS 2x8 2.874 2.893 2.975 2.993 DF SS 2x4 2.782 2.802 2.884 2.901 DF No.2 2x10 2.609 2.617 2.639 2.628 DF No.2 2x8 2.631 2.640 2.669 2.659 DF No.2 2x4 2.579 2.589 2.621 2.613 HF SS 2x10 2.864 2.881 2.950 2.960 HF SS 2x8 2.803 2.819 2.884 2.892 HF SS 2x4 2.731 2.745 2.796 2.797 HF No.2 2x10 2.576 2.585 2.614 2.605 HF No.2 2x8 2.589 2.599 2.632 2.624 HF No.2 2x4 2.489 2.496 2.519 2.507 SPF SS 2x10 2.913 2.933 3.018 3.037 SPF SS 2x8 2.693 2.708 2.766 2.770 SPF SS 2x4 2.937 2.960 3.061 2.090 SPF No.2 2x10 2.787 2.799 2.841 2.838 SPF No.2 2x8 2.686 2.696 2.727 2.719 SPF No.2 2x4 2.669 2.679 2.712 2.705 Table 6-15 Lognormal (100% Data) under snow load (compression) 80 Chapter S ix Reliability Evaluation of Lumber Design Values in Chinese Code 2-P Weibull 15% Lognormal 2-P Weibull 100% Normal 5-th Percentile (Mpa) Scale m Shape k Mean Standard Deviation Scale m Shape k Mean Standard Deviation 19.61 4.39 3.05 0.45 26.34 2.39 23.27 10.37 9.69 Table 6-16 Characteristics of the UTS for SPF No.2 2x4 x 0) •o c n .3 \"35 OC 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 FORM Load ratio 0.25 2P Weibull 15% Lognormal 2P Weibull Normal 1 1 1 1 1 1 1 1 1 1 1 1 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 P e r f o r m a n c e F a c t o r Figure 6-6 j8 -

> 0) 1\" 3.0 !5 .S \"35 DC 2.5 2.0 3.626 3.484 3.539 3.422 3.140 SS • No.2 — i 1 Bending Compression Tension Load Conditions Figure 7-2 Reliability levels according to grades 90 Chapter Seven Discussion and Conclusion Figure 7-3 shows the reliability levels among the species, in which Spruce-Pine-Fir species has a higher reliability level than the other two species. The biggest fluctuation happened in the bending case. But the level of variation is deemed to be acceptable. Species Reliability Levels Bending Compression Tension Load Conditions Figure 7-3 Reliability levels according to species Figure 7-4 illustrates the variability of the reliability level within sizes is deemed to be not significant. Sizes Reliability Levels 4.0 w 3.5 H 2.0 3.901 3.539 3.630 3 . 6 8 7 , 3.560 12x10 3.354 3-248 3.241 D 2 x 8 • 2x4 Bending Compression Tension Load Conditions Figure 7-4 Reliability levels according to sizes 91 Chapter Seven Discussion and Conclusion This study shows that there is no significant difference in the reliability levels across the grades, species and sizes. This means that the design values published in the Chinese code basically can achieve a fairly balanced the reliability levels across the species, grades and sizes. 7.3 Discussion For a limit states code, the design value should come from a reliability-based calibration procedure, which will lead to a consistent reliability level among species, grades and sizes. Therefore, a formal reliability assessment procedure should be developed to establish the design values of dimension lumber in the Chinese code. To perform this formal reliability assessment, the following issues should be addressed: 1) Testing standard: The current testing standard for wood structure in China is GB/T 50239-2002 \"Standard for methods testing of timber structures\". However, this test method is based on small clear wood testing and is mainly intended for the quality control of wood structural members. The \"2x4\" wood frame structure is a relatively new structural system, and the dimension lumber is also a new structural product in China. For this reason, there is no full size in-grade testing method standard for the dimension lumber yet. One way to solve this problem is to reference international testing standard, such as ISO standard. However, it is important to establish this full size in-grade testing method standard. And test standard should be suitable for the Chinese limit states design; because some test details can significantly affect the final reliability levels. For example, in the full size tension test, the member length has a significant effect to tension strength properties that would be used in the reliability analysis. 2) Material database: The distribution model of the strength properties has significant impact on the reliability levels. It is critical to choose the appropriate distribution model for material strength. The study in Canada showed that the effect of the distribution on calculation reliability was very significant when using the entire data set. Instead, using the 92 Chapter Seven Discussion and Conclusion distribution model with data truncated at 15% lower tail could almost eliminate the influence of the distribution models. Also, the lower 15% value, which is the weak part of the design data, is the most important part data for reliability study. Chinese unified reliability code stipulates that a Normal or Lognormal distribution must be used represent the material strength. Also, the entire data is suggested. However, the study in Chapter 6 shows that the lower tail of Lognormal does not show good agreement with the test data. For this reason, Lognormal distribution with 15% lower tail is recommended for any future study. 3) Load information: Load information is another issue in the reliability evaluation. Although the national snow and wind load models are used in this study, statistical information is not complete. This is due to the lack of statistical information on snow load and wind load for a 30-year to a 50-year return period. This return period change could have significant effect to the reliability levels. For this reason, more accurate load models and statistical parameters need to be obtained for future studies. Moreover, the load ratio needs to be clarified for Chinese structures. Various load ratios under the same load combinations can also produce different reliability levels. The study in the Chapter 6 shows that the dead-to-live load ratio =1 is more suitable for Chinese loads conditions. 4) Adjustment factors: Adjustment factors are important tools to balance the reliability levels. Currently, the adjustment factors considered in timber structure design code only include system factor for bending strength and size factors. These values cannot be taken directly from the North American codes. For the \"2x4\" wood frame structure, most of single members are working in a system. In all of the analysis, however, system effects are ignored. Including the system factor could contribute to a significant increase in the loading carrying capacities of the members in tension, bending or compression. Due to natural defects such as big knots in the full size single testing member, the common failure mode for these single members is brittle mode. However, if the member is in a floor or roof system, the most common system failure could be considered as a ductile failure 93 Chapter Seven Discussion and Conclusion mode. For example, the tension reliability index seems to be lower than the targeted value, but there is reserve conservation if the single tension member is working in a system. In addition, the failure of matching the serviceability target reliability indicates that the appropriate system effect factor needs to be studied in the future study. Therefore, it is important to develop the system effect factors for the Chinese code. Another important adjustment factor, duration of load factor, was assumed as 1 in the soft conversion method used to convert the design properties for North American lumber to the properties in the Chinese code. However, a more rational approach is to establish the duration of load factor through the reliability study based on Chinese load case. Also, the failure of serviceability target reliability indicates that the appropriate system effect factor needs to be studied. 7.4 Conclusion Based on this study, it has been shown that design values established by the soft conversion method can meet the Chinese target reliability in the bending and compression cases, but fail to achieve the target reliability levels in the tension and serviceability cases. It also shows that the soft conversion approach could be used to establish the design values in this initial step of introducing the dimension lumber into Chinese code. A formal reliability calibration procedure is proposed to develop the design values in the future reversions of Chinese timber structure design code. The reliability assessment framework and methodology used in the Canadian limit states timber design code can be applied in the reliability assessment of the Chinese code when the appropriate material properties and load information are specified. To establish a formal reliability evaluation with the study of adjustment factors will not only explore a more appropriate way to establish design values of dimension lumber, but also achieve the reliability-based limit states design of \"2x4\" wood frame structure in the Chinese timber design code, which will technically support the development of wood frame building in China. 94 Appendices APPENDIX A: Commentary on Dimension Lumber Design Values for the GBJ-5 Code 1. B A C K G R O U N D The proposed dimension lumber design values in GBJ-5 are based on the reference strength values found in the latest edition of the Structural Lumber Supplement to the A F & P A / A S C E 16-95 Standard for Load and Resistance Factor Design (LRFD) for Engineered Wood Construction. These L R F D reference strength values for lumber are, in turn, derived from the design values published with the ANSI /AF&PA National Design Specification (NDS) for Wood Construction. The LRFD code follows a limit states format, while the NDS code follows an allowable stress design format. Both are recognized for used with US building codes and contain design values for US, Canadian and, more recently, other foreign wood species. 2. D E V E L O P M E N T O F T H E NDS A L L O W A B L E STRESS DESIGN V A L U E S The NDS design values for the major commercial dimension lumber species are based on tests carried out on full-size in-grade lumber sampled from production. The main motivation for adopting the in-grade lumber testing approach was to more accurately characterize the relative strength of the various grades and species of dimension lumber. This would ultimately lead to better understanding of the strength of lumber used in engineered wood-frame construction, the performance of wood-frame construction, and facilitate the harmonisation of dimension lumber design with not only other wood products, but also non-wood products. For modulus of elasticity, bending, tension parallel-to-grain and compression parallel to grain, data are developed from tests on full-size lumber carried out in accordance with either A S T M D198 or A S T M D4761. Characteristic values are then derived in accordance with A S T M D1990. For the bending, tension and compression strength properties, the characteristic values are derived from the 5 t h percentile statistic, while for modulus of elasticity, the characteristic value is based on the mean statistic. 95 Appendices Although A S T M D1990 permits the development of characteristic values for a single grade or size, the major species or North American dimension lumber were sampled as a \"full matrix\". A full matrix consisted of at least two grades and three sizes, and a target sample size of 360 pieces was sampled for each test cell within the test matrix. For the other properties (longitudinal shear and compression perpendicular-to-grain), data are developed from tests carried out in accordance with A S T M D143 on small clear wood samples. Characteristic values are then derived in accordance with A S T M D2555 and A S T M D245. The characteristic value for longitudinal shear is derived from the 5 t h percentile statistic, and the compression-perpendicular-to-grain property is derived from the mean stress corresponding to a 1-mm deformation. A l l test properties must be adjusted to the reference moisture content of 15%. Characteristic values for bending, tension parallel-to-grain and compression parallel-to-grain need to be further adjusted to the reference sizes before applying the factor to convert the characteristic values to the Allowable Stress Design values. The reference size for Select Structural, No. 1, No. 2 and No. 3 grades is 2x12 (286 mm) at a span corresponding to 17 times the depth (4.9m). The reference size for Construction and Standard grades is 2x4 (89 mm) at a span of 3.7m. A S T M D1990 provides the adjustment equations for moisture content and size; however, any technically supported adjustment equation may be used. Table 1 summarizes the factors to convert the characteristic properties to allowable stress design values. Table 1: Fac tors to C o n v e r t Charac ter i s t ic Propert ies to A l l o w a b l e Stress Design Va lues ( A S T M D1990 & D245) Property and Statistic\"1 Standards Factor Bending strength (5* percentile) ASTM D476112'/ ASTM D1990 2.1 Compression parallel-to-grain (5m percentile) ASTM D476112' / ASTM D1990 1.9 Tension parallel-to-grain (5\"1 percentile) ASTM D4761'21/ ASTM D1990 2.1 Longitudinal shear (5th percentile) ASTM D142 / ASTM D2555 / ASTM D245 4.2131 Compression perpendicular-to-grain (mean) ASTM D142 / ASTM D2555 / ASTM D245 1.67141 Bending modulus of elasticity (mean) ASTM D4761121 / ASTM D1990 1.0 Notes: 96 Appendices [1 ] Characteristic values should be at the standard moisture content of 15% and the reference size before applying the reduction factor. [2 ] ASTM D198 may also be used. [3] This adjustment includes a strength ratio adjustment of 0.5 to account for the presence of fissures. [4] ASTM D143 tests are carried out with the growth rings parallel to the loading direction. This reduction is to account for most unfavourable ring orientation (45° to the loading direction). 3. DEVELOPMENT OF THE LRFD VALUES The L R F D design values are based on a soft conversion process described in A S T M D5457. Section 6.7 of the Standard provides a procedure for generating L R F D reference resistance values based on format conversion from code-recognized allowable stress design. where K — ^ l l ^ . 5 for bending, compression, tension and shear

+a?fDr) • Values of the conversion factor, , used are summarized in Table 3. 98 Appendices Table 3:Strength Conversion Factors to Account for Code Format LRFD and GBJ -5 Design Code Factors Duration of load KD = Dead load factor \\ D = Live load factor XL = Resistance factor = Bending O i n 2 - J U Compression Q m 2 CC CQ - 1 U Tension Q i o CC CQ - J O Shear Q i n CC CQ - I O Comp-Perp Q to 2 CC CQ _i a M O E O i n 2 CC CQ -i a 0.80 1.00 1.20 1.20 1.60 1.40 0.85 1.00 0.80 1.00 1.20 1.20 1.60 1.40 0.90 1.00 0.80 1.00 1.20 1.20 1.60 1.40 0.80 1.00 0.80 1.00 1.20 1.20 1.60 1.40 0.75 1.00 1.00 1.00 1.20 1.20 1.60 1.40 0.90 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Dead.Live ratio y = 0.333 Unit conversion k = 6.895 (KSI to MPa) LRFD to GBJ -5 Reference or Specified Strength Conversion Factors Bending Compression Tension Shear Comp-Prep MOE js GBJ - 5 A IJtFD 4.220 4.468 3.971 3.723 5.585 6.895 5. REFERENCES American Forest & Paper Association; American Society of Civil Engineers. A F & P A / A S C E 16-95. Standard for Load and Resistance Factor Design (LRFD) for Engineered Wood Construction. American Forest & Paper Association; American Wood Council. ANSI /AF&PA NDS-1997. National Design Specification for Wood Construction. A S T M D198. Standard Test Methods of Static Tests of Lumber in Structural Sizes A S T M D245. Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber A S T M D1990. Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens A S T M D2555. Standard Test Methods for Establishing Clear Wood Strength Properties. A S T M D5457. Standard Specification for Computing the Reference Resistance of Wood-Based Materials and Structural Connections for Load and Resistance Factor Design A S T M D4761. Standard Test Methods for Mechanical Properties of Lumber and Wood-Base Stnictural Materials. Supplement: Structural Lumber. Load and Resistance Factor Design Manual for Engineered Wood Construction. 99 References REFERENCES [I] Wu, Xirong, 1995. History of Shu Zhou. Shu Hai Press. Beijing, China, (in Chinese) [2] Ministry of Construction, China. 2003. Code for design of timber structures (GB 50005-2003). China Architecture& Building Press, Beijing, China, (in Chinese) [3] Ministry of Construction, China. 1989. Code for design of timber structure (GBJ 5-88). China Architecture& Building Press, Beijing, China, (in Chinese) [4] Canadian Wood Council. 2002. Introduction to Wood Design. Canadian Wood Council, Ottawa, Ontario, Canada. [5] Anonymous, 2003. Commentary on dimension lumber design values for the GBJ-5 code. Forintek Canada Corp. Vancouver, Canada. [6] Yang, Weijun, Zhao, Chuanzhi, 1998. Reliability-based theory and design for civil engineering. Renmin Transportation Press, Beijin, China, (in Chinese) [7] Ministry of Construction, China. 2001. Unified standard for reliability design of building structures (GB 50068-2001). China Architecture& Building Press, Beijing, China, (in Chinese) [8] Ministry of Construction, China. 1984. Unified standard for reliability design of building structures (GBJ 68-84). China Architecture& Building Press, Beijing, China, (in Chinese) [9] Chinese Southwest Architectural Design Institute. 1993. Wood Structure Design Handbook. China Architecture& Building Press, Beijing, China, (in Chinese) [10] Ministry of Construction, China. 1973. Code for design of timber structure (GBJ 5-73). China Architecture& Building Press, Beijing, China, (in Chinese) [II] Wang, Yongwei. 2002. Reliability Analysis of Wood Structure. Building Science Research of Shichuan. Vol.28, No.2. Cheng Du, China, (in Chinese) [12] Ministry of Construction, China. 2002. Load code for the design of building structures (GB 50009-2002). China Architecture& Building Press, Beijing, China, (in Chinese) 100 References [ 13] Ministry of Construction, China. 2002. Standard for methods testing of timber structures (GB/T 50329-2002). China Architecture& Building Press, Beijing, China, (in Chinese) [14] Ni , Shizhu, Chen, Rongcai. 1980. Distribution types of wood strength as building material. Chinese wood structure technology committee meeting document. Beijing, China, (in Chinese) [15] Foschi, R.O., Folz, B.R., and Yao, F.Z. 1989. Reliability-Based Design of Wood structures. Structural Research Series, Report No.34. Department of Civi l Engineering, University of British Columbia, Vancouver, B.C. [16] Canadian Wood Council. 2001. Wood Design Manual. Canadian Wood Council, Ottawa, Ontario, Canada. [17] Madsen, Borg. 1992. Structural Behavior of Timber. Timber Engineering LTD, North Vancouver, British Columbia, Canada. [18] Barrett, J.D., Lau, W., 1994. Canada Lumber Properties. Canadian Wood Council, Ottawa, Ontario, Canada. [19] Barrett, J.D., Lau, W., Bernaldez. J, 1999. UBC Data viewing program, version 1.1.0 (Software). University of British Columbia, Department of Wood Science, British Columbia, Canada. 101 "@en ; edm:hasType "Thesis/Dissertation"@en ; vivo:dateIssued "2004-11"@en ; edm:isShownAt "10.14288/1.0075016"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Forestry"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Reliability study of North American dimension lumber in the Chinese timber structures design code"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/15856"@en .