Linear Static and Nonlinear Dynamic Analyses on Collapse Behaviors of Staggered-Truss Systems

The thesis investigates the linear and nonlinear collapse mechanism in Staggered Truss Systems using two computational programs (SAP2000 and ABAQUS finite element software). The thesis particularly focuses on the understanding and modelling of the collapse mechanisms of Staggered Truss Systems when a critical column was removed from the structure. AISC-LRFD steel structures design code and AISC 14 guidelines for staggered truss systems were used to design a full 3-D 10-story model by SAP 2000. The structure was built with Staggered Truss System (STS) in transvers direction and Moment Resistance Frame (MRF) in longitudinal direction. Linear Static and Nonlinear Dynamic Time-History analyses were then performed in accordance with UFC 2013 and GSA 2013 codes to determine the collapse potential in the existing model following removal of a load bearing element from different locations. When the results of Linear Static and Nonlinear Dynamic time-history analyses were studied in detail, it was observed that the nonlinear dynamic analysis not only yields more accurate results in revealing the collapse potential at different portions of the structure, but also is more economical in allocating this method for designing structures against progressive collapse. Based on the software results, some indices of linear and nonlinear behavior of the systems such as yield load, vertical deformations, ductility, concrete deck effect, damping percentages, plastic rotations were analyzed. However due to limitations of SAP2000 software, the results were not comprehensive enough to provide insight understanding to the failure mechanisms. Therefore, a more advanced finite element model using ABAQUS software was then developed. The finite element model was a full 3-D truss located between 5th and 6th floors of the existing model designed by SAP2000 with the same dimensions and the same sections using the Solid Part option in ABAQUS. The material properties, geometric and material nonlinearity and the loads were identical to the model developed using Sap 2000. The results indicates that the failure zones of the Staggered Truss Systems using both finite element software were comparable, however, the finite element model using ABAQUS also provided insights to the failure mechanisms such as plastic hinges on gusset plates and the exact location of plastic higes on truss chord were also obtained. Keywords: Progressive Collapse, Linear Static, Nonlinear Dynamic, Time History, Plastic Hinges, Plastic Rotation, Vertical Deflection