A practical method to analyze the system effects of a metal-plate-connected wood truss assembly

Graduation date: 2000This study presents a practical method to model an actual Metal-Plate-\ud Connected (MPC) roof truss assembly using a commercial program, SAP2000, to\ud investigate its system performance. Truss assembly modeling was examined\ud because the conventional single truss design method ignores system effects, such as\ud variability of modulus of elasticity (MOE), interaction of sub-assemblies, realistic\ud boundary conditions, etc.\ud Two types of semi-rigid MPC joint models, linear spring (LS) joint model\ud and a truss plate manufacturer's (TPM's) joint model, were used for the truss and\ud truss assembly models. To verify the truss models using the LS joint model, the\ud predicted deflections of individual trusses and the load sharing of nine-truss roof\ud assembly models were compared with experimental results from the literature.\ud Fourteen individual trusses (the components of the actual roof truss assembly)\ud using TPM's joint models were also verified by comparing the Combined Stress\ud Index (CSI) values with the CSI values provided by the TPM. Both design and one\ud set of random material properties were used in the analysis of the actual roof truss\ud assembly model. The predictions for truss models using the LS joint model for truss\ud deflections and load sharing effect agree with the experimental results. The CSI\ud values for individual trusses with the TPM's joint model matched the CSI values\ud provided by the TPM.\ud The load distribution in an actual roof truss assembly is strongly influenced\ud by the interaction of sub-assemblies and by the boundary conditions. In the truss\ud assembly, the prediction of location and value of maximum CSI are different from\ud those for the single truss. The truss with the maximum CSI value of 0.91 among\ud fourteen individual truss types decreased to 0.52 and 0.51 when this truss is in the\ud assembly with design and random material properties, respectively. Moreover, the\ud truss with a maximum CSI of 1.03 in the assembly (with design properties) had a\ud CSI value of only 0.95 as an individual truss. Although the CSI of one truss type\ud increased over 1.0 in the assembly, the CSI of most other trusses decreased (by as\ud much as 43%). So, the behavior of a single truss is different when the truss is in the\ud assembly. The benefits of using an assembly model compared to the conventional\ud truss design method are in providing increased safety through improved analysis\ud and in a potential reduction in construction cost