Rotation and Strength Demands for Simple Connections to Develop Catenary Action for Progressive Collapse Resistance

Following the collapse of the Murrah Building in Oklahoma City in 1999, the General Services Administration (GSA) initiated publication of a comprehensive set of guidelines for minimizing the susceptibility of structures to progressive collapse.  For nonexempt structures, GSA guidelines mandate structures possess the robustness to withstand the threat-independent condition of “instantaneous” removal of any single column for a single story. 

This project is developing a parametric study to assess behavior of typical floor framing systems considering various layouts, member sizes, and connection types under loading consistent with column loss scenarios.  Strength, stability, and ductility are examined for floor systems utilizing various connection types including i) bolted top and seat angle connections, ii) bolted web angle connections, and iii) welded shear tab connections under typical gravity loading. 

A component model for bolted connections has been adopted from previous work and modified to allow additional softening at the large rotations necessary to develop catenary action.  In addition, preliminary finite element modeling of single plate shear tab connections has been performed to develop an additional component model.  Simplified component models are then assembled into a fiber model representing an entire connection, capable of capturing the interaction between tensile and flexural behaviors. 

In order to assess the overall behavior of floor framing systems under column loss scenarios, a floor framing system analysis framework developed in Matlab is implemented.  The fiber models representing various connection types are integrated into the analysis framework which considers nonlinear geometry and material properties.  Capable of tracking the behavior of connections and framing members independently, the analysis framework can determine displacement and rotation demands on each of the connections for use in future physical testing of connection subassemblages.  Further, the effects of various connection parameters on system behavior will be explored and preliminary recommendations for enhancing the multihazard robustness of steel structures will be developed.

This work will lead to the development of an experimental program to evaluate the performance of gravity framing connections under demands consistent with the analysis results. Hybrid testing will be performed, linking the demands from numerical simulations with the resistances from physical connection tests. Both currently used and improved connection designs will be tested. The work will culminate with a large-scale test to collapse of a steel gravity framing system. Results of the experimental and analytical programs will be used to make recommendations for improving the multi-hazard life-safety robustness of the common steel gravity framing system.