Cross-laminated timber(CLT)has different structural characteristics in transverse laminates,and is prone to rolling shear failure under short span shear.Therefore,this thesis mainly focuses on the structural characteristics of transverse laminates of CLTs and their impact on shear performance,as well as the duration of load(DOL)effect of different structural characteristics of CLT under long-term load,It is of great significance to improve the basic theory of CLT materials and product design specifications.In order to promote the application of domestic fast-growing Chinese fir in CLT materials,the thesis used domestic fast-growing Chinese fir to make CLT specimens,based on different structural characteristics of the transverse laminates of CLT,such as aspect ratio,the width of side gap,and the depth of stress release groove.The static and low cycle fatigue mechanical properties of CLT specimens are tested to evaluate the impact of CLT structural characteristics on their shear resistance and DOL effect.1.Investigated the effects of three structural characteristics,namely,the aspect ratio of transverse laminates(3,4,5),the depth of stress release grooves in transverse laminates(0,4,6mm),and the side gaps between transverse laminates(0,4,8mm),on the static out of plane shear performance of CLT by designing L9(33)orthogonal experiments.The results show that when the depth of the stress release grooves and the side gaps are both 0mm,the shear performance of the CLT is optimal;as the depth of grooves and the width of side gaps increase,the shear strength decreases.The maximum shear bearing capacity and average shear strength of the groupⅠof CLT are 7845.97N and 1.93MPa,respectively;the groupⅦof CLT has the lowest average shear ultimate bearing capacity and shear strength,which are 25.03%and 24.35%lower than the groupⅠof CLT,respectively.The width of side gaps and the depth of grooves have a significant impact on shear strength,and there are significant differences between different levels;the aspect ratio has no significant effect on the shear strength of CLT;The optimal combination of structural characteristics for static shear performance:the aspect ratio is 4,the depth of grooves and the width of side gaps are both 0mm.The out of plane shear failure modes of CLT mainly include rolling shear failure in the transverse layers,the failure of adhesive layers,the tensile failure of bottom layer.Various failure modes interact with each other.2.Subjected CLT to trapezoidal cyclic loading and compared the failure cycles of CLTs with different structural characteristics;calibrated the damage accumulation model based on fatigue test data and predict the failure time of CLT;and based on the stress ratio evaluation method,the DOL adjustment coefficients of each group of CLTs were obtained.The results indicate that grooves would reduce the low cycle fatigue performance of CLT,and when there are side gaps in the laminates,the fatigue failure cycles of CLT are higher than that of CLT without side gaps.The main and secondary order of factors affecting the fatigue failure cycle of CLT is as follows:the width of side gaps>the depth of stress gaps>aspect ratio.The preferred structural features are:the aspect ratio is 4,the width of side gaps and the depth of stress gaps is 0mm and 4mm,respectively.By predicting the long-term performance of CLT through the damage accumulation model,the DOL adjustment coefficient of the Group VII of CLT is the smallest(0.37),and the DOL adjustment coefficient of the Group VIII of CLT is the largest(0.70).If the usage conditions are not considered,except for the Group VIII,the DOL adjustment coefficients for all other groups of CLTs under 50 years load duration are lower than the recommended value(0.65)in the CLT handbook.Based on the evaluation of the impact of DOL adjustment coefficients on different structural characteristics of CLT,the DOL adjustment coefficient is the highest for CLT with a lateral gap of 8mm between transverse laminates.In addition,when there are side gaps and grooves in the transverse layer,it is recommended to increase the aspect ratio.3.Established the functional function of CLT specimens under the ultimate bearing capacity limit state based on the design standards for wooden structures(GB 50005-2017),and uses the JC method to analyze the reliability of different structural characteristics of CLT based on the experimental data in Chapter 2 and the statistical parameters of permanent load,floor live load,wind load,and snow load in China.The relationship curves between the reliability and resistance partial coefficients of nine groups of CLT are obtained.The results indicate that for four different load combinations and different structural characteristics of CLT,under the same resistance partial coefficient,the reliability index decrease with the load ratioρincrease.When theρvalues are 1.5,2,and 3,and the resistance partial coefficients are the same,the order of reliability indicators for nine groups of CLT are the same,with the highest being the Group I and the lowest being the Group VII;As the partial coefficient of resistance increases,the difference in reliability indicators between each group of CLTs increases.Under four load combinations,the short-term and long-term reliability analysis of nine groups of CLTs are relatively close.Using domestic reliability analysis methods for wooden structures,the coefficient of variation in load statistical parameters has a more significant impact on the calculation results of CLT reliability indicators. |