Nonlinear seismic response analysis of high-rise flat plate buildings

Modern seismic codes allow engineers to design high-rise flat plate buildings, together with an appropriate lateral load resisting system, in regions of high seismicity. Despite increased popularity and usage of the flat plate system in highly seismic zones, slab-column connection design checks are conducted only using a capacity design approach during the design process. Furthermore, nonlinear behavior of slab-column connections is ignored in performance-based design or assessment processes, due to limitations of commercial analysis programs. Therefore, this study was conducted to investigate nonlinear behavior characteristics of flat-plate systems, including slab flexural yielding in column strips, slab flexural yielding in the moment transfer ( ) region, and possible punching shear failure in the flat plate. In this study, nonlinear response history analyses are conducted on different 3D building model configurations. Slabs are represented using equivalent beam elements (effective beams) in three model configurations. Two additional nonlinear model configurations, one with rigid diaphragm constraints and without any slab elements, and the other with elastic slab elements, are generated as alternative solutions to effective beam modeling of slabs, for checking interstory drift ratios. Three effective beam models are created to compare different modeling and design approaches in various design codes including TEC 2018, ACI 318 and ASCE 41. The so-called overstrength factor is considered as key parameter in two of these models, where overstrength in calculation of slab punching stresses is included in the design process of one model, whereas it is neglected in the other. The last model is created according to design provisions of the new TEC 2018. The nonlinear analysis results show that all five models satisfy necessary strength, stiffness and ductility requirements, though they necessitate different slab reinforcement amounts at the slab-column connections. However, significantly larger column cross-sectional dimensions are required for the model designed according to TEC 2018.