Stiffness of Bolted Timber Connection

Abstract

he stiffness equation for connections using fasteners in Eurocode 5 is specified as a function of wood density and fastener diameter only. In this research, an analysis of available data sets on various configurations of tested bolted steel-wood-steel (SWS) connections loaded in tension parallel to grain has been undertaken in order to predict the initial stiffness of each connection. From the analysis, it is indicated that the stiffness equation specified in Eurocode 5 for bolted SWS connections does not adequately predict the initial stiffness. There is a need to incorporate other connection parameters such as the geometry of the connection into the equation to improve accuracy. Furthermore, in this research, numerical model has been developed in ABAQUS to study the stiffness of bolted timber connections loaded parallel-to-grain. From this model, numerical predictions of the stiffness values have been made for various densities, bolt diameters, end distances, row and bolt spacings and thicknesses of the timber members. An analysis of the results has shown that the stiffness of SWS timber connections is strongly dependent on the wood density, fastener diameter, bolt spacing, end distance and thickness of timber member where the greater the density, diameter, bolt spacing, end distance and thickness of timber member, the higher the stiffness value of the bolted timber connection. A relationship for the determination of bolted connection stiffness as a function of the SWS connection configuration is presented by using multiple linear regression (MLR). In order to validate the proposed design equation, tests on 50 timber specimens (40 glued laminated timbers and 10 laminated veneer lumbers (LVL)), with steel plates, were undertaken. The number of bolts was kept the same and the connector diameter, timber thickness, and wood density were varied. The results obtained in the experimental tests are compared with those obtained from the design model. A more comprehensive validation has been accomplished by comparing predictions from the proposed equation and the Eurocode 5 equation with experimental tests from other researchers. From the comparison made, the effectiveness of the proposed design equation to predict the bolted connection stiffness was confirmed. Based on the analysis undertaken, the accuracy of the predictions is discussed and the proposed equation provides a better approximation of the initial stiffness for SWS connections than the current Eurocode 5 design provisions.