Analysis of Metal Plate Connected Wood Truss Assemblies under Out-of-Plane Loads

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Virginia Tech

In 2012, falls from elevation in construction industry represented 36% of the total fatalities. The Occupational Safety and Health Administration requires workers to use fall protection systems where workers are 6 feet or more above a lower level. Anchors for fall protection systems attached to roof trusses may cause out-of-plane loading on these structures. Metal plate connected wood trusses (MPCWT) are not designed to carry out-of-plane loads and MPCWT performance under these loads are not evaluated in the design process.

The goal of this research is to model and analyze MPCWT assemblies under out-of-plane loads. The rotational stiffness of truss-wall connections, and truss bracing elements are included in the structural component model. Previous experimental data of fall arrest anchor loading were used for model validation. A parametric study considering loading location, joint stiffness and dimension of trusses was conducted.

The structural analog of the MPCWT assemblies were found to have first truss deflections within 4% difference, thereby the models were validated. From parametric study results, the load location was not changed the ultimate deflection in the truss assembly by maximum value of 9%. Out-of-plane joint stiffness was the parameter that caused a large difference in the deflection results, when the joists were assumed as either rigid or simple connections. The rotational stiffness of lateral and diagonal bracing should be included as model inputs for the accurate representation of experimental behavior. Truss lengths increased the deflection at the top chord of the first truss in the assembly as truss width increased.

Metal Plate Connected Wood Trusses, Personal Fall Arrest System, Residential Construction, Visual Analysis Software, Joint Stiffness, Modeling Validation