ROTATIONAL STIFFNESS GUIDELINE FOR ANALYSIS OF METAL PLATE CONNECTED WOOD TRUSSES

摘要

Metal plate connected wood truss (MPCWT) design specifications require accurate structural modelling. However most standards, including the Truss Plate Institute specification and EuroCode 5, do not provide provisions for quantifying rotational stiffness of MPCWT joints beyond general statements referring to test methods. Those test methods generally address stiffness only using axial tests and by establishing a stiffness-based limit on design strength, rather than quantifying stiffness for purposes of structural analysis. Standards are lacking in guidance on how to model joints for accurate analysis of MPCWT, especially with respect to rotational stiffness. Consequently, designers usually model joints as either pinned (zero rotational stiffness) or rigid (infinite rotational stiffness), and many do both, varying by joint type, rather than use of a more accurate partially rigid model. The option of modelling joints as partially rigid is not a viable option for most truss designers who use commercial software, even though volumes of research have been published on the stiffness of joints. Commercial software is usually a requirement due to its ability to address manufacturing and other business processes, and there is substantial resistance to use of the methods recommended by prior research to quantify partial rotational stiffness in commercial truss software. The typical demands on the software are such that excessive iterations of design are not easily handled, so basing stiffness on plate size and repeating structural analyses if plate size changes are not desirable. The research recommendations to date are complex FEA models, limited to specific joint configurations, or too specific to joint characteristics in that stiffness is excessively variable depending upon fastener size and type. The intent of this work was to identify degrees of partial joint rigidity that improve accuracy over the simplified options now typically available (pinned or fully rigid) in commercial MPCWT software, yet do so in a way thought to be viable for implementation in typical MPCWT software. Therefore, available data was used to predict a general lower bound rotational stiffness appropriate for MPCWT commercial software. The rotational stiffness guidelines in this report only depend on member geometry and properties available from current standardized tests.