Seismic energy response of a 42-story reinforced concrete tall building

Energy based design approach is an alternative way to design earthquake resistant buildings by implementing strength and displacement characteristics of the building together, along with the effect of ground motion duration. Although there have been reasonable number of studies, there are still many unknowns on this concept; therefore, energy balance concept can not be used for design and evaluation of earthquake resistant buildings in current practices and design codes yet. In this study, a 42-story reinforced concrete dual system building was used to investigate energy components, particularly the dissipated inelastic energy as well as its damage potential and distribution among structural members along building height. Beside these relation between event distance, earthquake significant duration, and hysteretic energy to input energy ratio is investigated. The building was designed by a renowned U.S. engineering company, Englekirk Partners, Inc., for a Pacific Earthquake Engineering Research Center (PEER) project as a reinforced concrete dual system building, i.e., moment-resisting frame building with central core walls. Analyses were conducted in Perform 3D-V6 for three hazard levels, namely, serviceability level earthquakes (SLE), design basis earthquakes (DBE), and maximum considered earthquakes (MCE). Each hazard level included 15 pairs of ground motion data. Perform 3D is capable of checking the energy balance at each time step during the analysis by calculating the energy imparted to the building due to external (earthquake) loads and energy dissipated by the internal (e.g. damping, hysteretic) components. Total energy absorbed by the building equals to the sum of the internal energy components and assumed to be the input energy. Conclusions that were drawn from the analysis of a 42-story reinforced concrete dual system building showed that amount of hysteretic energy increase as the input energy increase, hysteretic energy demand is maximum at beams (columns, shear walls and coupling beams follow it respectively) and lower stories. Hidden shifts on storywise distribution of hysteretic energy occur in case of stiffness differences between the building floors. Direct relation between the the ratio of hysteretic energy to the input energy, significant duration, and event distance were not observed. This thesis summarizes a preliminary investigation of nonlinear energy response of tall reinforced concrete buildings based on energy balance concept. Energy-based seismic design gives important clues to the designer regarding the location of potential damage along the building members and the stories. The amount and distribution of the dissipated energy can be useful to understand the overall behavior of a building, as it provides a measure for the cyclic behavior in terms of both maximum (ultimate) deformation and cumulative deformation due to several cycles. Use of dissipated inelastic energy (versus maximum deformation only) would give more accurate results in terms of damage, therefore, may be considered to estimate demand-to-capacity ratios in seismic performance assessment of buildings.