A practical approach to model the behavior of a metal-plate-connected wood truss system

Graduation date: 1997Metal-plate-connected (MPC) trusses have traditionally been designed based on a\ud tributary load distribution and a simplified truss model. This design method ignores the\ud load-sharing and composite action in MPC roof truss systems, the semi-rigidity of MPC\ud joints, and joint eccentricity.\ud The main objective of this study was to provide a practical approach to model\ud MPC trusses and roof truss systems by using a commercial program and investigate the\ud system performance of MPC roof trusses with plywood sheathing. The model takes into\ud account the complexities of system behavior from load-sharing and composite action, the\ud semi-rigidity of the MPC joints, and joint eccentricity. Model verification was\ud conducted by comparing the predicted deflections, member internal forces, truss\ud strengths, and load-sharing of four nine-truss roof systems with experimental results\ud from the literature. A strength simulation program for trusses and truss systems was also developed.\ud The correlated lumber strength properties were generated using a multivariate normal\ud approach to preserve the correlation between properties. Failure modes examined in this\ud project included wood member failure and joint failure. Joint failure criteria were based\ud on the experimental strengths of heel joints, bottom-chord-tension-splice joints and web\ud at the bottom chord joints from the literature.\ud This study provided a practical approach to model MPC trusses and truss systems.\ud Predictions for truss deflections, strengths, member internal forces, and load-sharing\ud agree with the experimental results. Through strength simulations, it was found that the\ud predominant failure mode for simulated 3:12 and 6:12 slope, 28-foot-span trusses is heel\ud joint failure, and if a weakest-link theory is used, no strength increase was observed for\ud trusses inside of truss systems, but significant load-sharing was found for localized\ud single truss loading