Calculations of deflection and reliability analysis of bending wood members in serviceability limit state
Standardised and industrialised wood products like North American sawn lumber,European sawn timber and glulam made of visually graded and machine graded laminations are already incorporated into GB 50005-2017'Standard for design of timber structures',yet only the reliability of bending members made of the original sawn and round timber in the serviceability limit state had ever been analysed.With quite different mechanical properties of the newly incorporated structural timber and different load situations in design of timber structures,calculation and verification of deformation of the bending members thus need to be improved.In this study,long-term bending test of dimension lumber was conducted,the creep behaviour was investigated and the creep model in the form of power law function for structural timber developed.The calculation method of deformation of wood members in bending was suggested,in consideration of the creep model and the randomness of load history.The performance functions with respect to the conceptive damage limit state and the local damage limit state were developed,in which both the deflection and the ultimate deflection were treated as random variables.Reliability analyses were conducted and the deflection limit values for bending members made of various types of structural timber in terms of short-term deformation obtained.It is revealed that the deflection limit value varies with type of structural timber,load combination and the live to dead load ratio ρ.The formulae for the deflection limit value for the bending members made of sawn and round timber were thus presented.For members made of glulam,European sawn timber and so on,the deflection limit value is suggested to take the value for sawn and round timber members timing a factor of 0.85 ifρ0.5 and a factor of 0.9 if ρ＞0.5;for members made of visually stress rated lumber,the deflection limit value is suggested to take the value for sawn and round timber members timing a factor of 0.80.It is verified that the suggested deflection limit value and the improved deformation verification method all meet the reliability requirements more reasonably.
wood member in bendingserviceability limit statereliabilitycreepdeflection limit value
万方数据
维普
