Structural Engineering Report No. ST-03-1 DAMAGE ASSESSMENT OF CONCRETE-FILLED STEEL TUBE MEMBERS AND FRAMES FOR PERFORMANCE-BASED DESIGN

Damage evolution of rectangular concrete-filled steel tube (RCFT) members, connections, and frames as documented in experimental tests was investigated in this research. Based on the experimental data, appropriate limits states for RCFTs were defined at different levels of loading. For each limit state, the performance of the specimens was judged with the use of damage indices. The report also documents how to use these damage measures to assess capacity within the context of a reliability-based performance-based design methodology. A database study was first conducted to document worldwide experimental RCFT research. RCFT members, including columns, beam-columns, panel-zones, pinned and momentresisting connections, and frames, were covered in the database for both monotonic and cyclic loading conditions. Detailed information about the material and geometric properties of the specimens were recorded in the database. In addition, the peak force and deformation capacities of the specimens were stored. For each RCFT member type, the specific damage levels observed during the tests were also identified. The occurrence time of the damage levels during the tests were entered into the database in terms of appropriate force and deformation quantities. Two types of damage indices were defined and used to assess damage, including a deformation-based damage index and an energy-based damage index. These damage indices were applied to the RCFT members, connections, and frames stored in the database. The damage index values attained at the specific damage levels were correlated to the geometric and material properties of the RCFT members and equations were derived to estimate damage index values. These damage index values thus provided quantified data to determine the governing damage levels for the RCFT members at different levels of loading. A parametric study was then conducted for the equations derived to explore the relative magnitude of the damage indices for the different limit states. Based on the results from the parametric study, each damage level identified for the RCFT members was mapped onto appropriate performance objectives, including immediate occupancy, life safety, near collapse, and collapse prevention, to identify how this information may be used in the context of a performance-based design methodology.