9410473 Hajjar This is a Research Initiation Award to study the force displacement response and ultimate strength behavior of composite subassemblies of unbraced frames. Structural engineers are increasingly realizing the economic benefits of using concrete filled steel tube (CFT) beam-columns in low and medium-rise construction, and they expect the demand for CFTs to grow significantly in the next decade. Detailed but efficient numerical simulation, coupled with experimental research, is the only practical means of understanding CFT behavior. Yet only insufficient research has been conducted on CFTs to date. The subassemblies to be studied in this project consist of steel I girders framing into rectangular CFT beam-columns subjected to either monotonic or cyclic loading. The project's objectives are: 1) to develop a practical, three-dimensional, nonlinear, fiber-based finite element formulation to represent CFT beam columns; 2) to develop compatible nonlinear models to represent the girder-to-column connection and panel zone region; 3) to implement these formulations in an existing composite frame analysis system, and to calibrate the formulations against experimental data; and 4) to conduct comprehensive parametric studies of individual CFT beam- columns and composite subassemblies. The parametric studies will be conducted to provide the data required to improve the accuracy and scope of current non-seismic and seismic design specification provisions. This fiber analysis will also facilitate investigation of new composite CFT systems, and permit experimentalists to both predict and interpret their test results. ***
