Stability Bracing Behavior for Truss Systems

The stability bracing behavior of trusses was investigated using experimental testing and computational modeling. The laboratory experiments were conducted on twin trusses fabricated with W4x13 sections for the chord and web members. Spans of 48 and 72 feet were used in the tests that included both lateral load tests and buckling tests. Most of the tests were done on the regular (Howe) truss, except the lateral stiffness tests which were also done on the inverted (Pratt) truss. Computational models were developed using the three-dimensional finite element program, ANSYS, which were validated using the laboratory test data. A variety of models were used to simulate both as-built and idealized truss models.The experiments demonstrated that the buckling capacity of the truss with torsional bracing largely depended on the brace stiffness and the number of intermediate braces. Similar behavior was observed in the truss with lateral bracing. The tests results demonstrated that cross sectional distortion dramatically reduces the effectiveness of the torsional braces. The experiments provided valuable data for validating the finite element models that were used to conduct parametric studies on torsional bracing of truss systems. The results from the parametric studies were used to develop stiffness requirements for torsional bracing of trusses.