Determining The Strength Design Values Of Wood Based On The Reliability Requirements

The accuracy of design values for wood and the reliability of connections affect the safety and reliability of timber structures. It is, therefore, necessary to specify the strength design values of imported dimension lumber and glued laminated timber and to to evaluate the reliability of connections in a scientific and reasonable way. Based on the existing strength design values of American dimension lumber,the Code for Design of Timber Structures (GB50005-2003) specified the strength design values by using soft conversion method,which means to obtain the same cross-section size of wood member by GB50005-2003 and American National Design Specification under the same design loads. Technical code of glued laminated timber structures which is being developed uses the similar method as dimension lumber to determine the strength design values of glued laminated timber made of visually stress-graded laminations and mechanically modulus-graded laminations. In this study, the feasibility of the soft conversion method is assessed. The results showed that the shortcoming of the current conversion method is that the U.S. standards and the Chinese code have the same reliability requirements for timber structures.In this paper, the imported Canadian dimension lumber is taken for examples, and the JC and MC method are used to evaluate the reliability of imported North American dimension lumber based on the strength design values given in the Code for Design of Timber Structures. The same methods are also used to evaluate the reliability of Glulam made of visually stress-graded laminations and mechanically modulus-graded laminations, based on the strength design values given in the Technical Code Glued Laminated Timber Structures.It is found out that the strength design values given in both codes are so large that do not satisfy the requirment of The Unified Code for Reliability Designof Building Structures GB50068-2001. It is useful to re-establish the strength design values of dimension lumber and Glulam based on the target reliability index specified in China, thus to provide reference for compiling and revising of the related codes.Study of the reliability of connections in timber structures in China is still in an early stage. In this study, the performance function of bolted connections with failure modes ofⅠs,Ⅱm andⅣare presented, and the reliability of the connections is evaluated . This can provide reference for future study.