Development of fragility functions for code conforming low-rise reinforced concrete buildings

Abstract

In this study, fragility functions are developed and compared for low-rise (2 and 3-story), reinforced concrete (RC), moment-resisting frame (MRF) buildings, which are designed per the Turkish Seismic Codes (TSC) released in 1998 and 2018, at eight different locations in Istanbul, Turkey. In the preliminary design of each building, the minimum conditions defined in the corresponding seismic code are followed. Moreover, the capacity design principles are taken into consideration as defined in the seismic codes. To increase the representa tiveness of the dimensions (i.e., footprint, structural member dimensions, story height) of the buildings, the past studies about the characteristics of the low-rise buildings in Turkey, and the structural drawings belonging to the existing buildings designed per the corresponding seismic codes are examined and used. Considering eight different locations, two different story numbers, and two seismic codes, a total of 32 buildings are designed and analyzed. The nonlinear analyses of the buildings are conducted by using the OpenSees Software (Open System for Earthquake Engineering Simulation Pacific Engineering Research (PEER) Center Version 3.0.3). The structural elements (beams and columns) are modeled with frame elements. The distributed plasticity (fiber) is considered for the columns whereas lumped plasticity (plastic hinge) is considered for beams. To generate the fragility functions for the buildings, multiple stripe analysis (MSA) together with the maximum likelihood estimation (MLE) method is utilized. Spectral displacement (Sd) and spectral acceleration (Sa) are selected as the intensity measure (IM) parameters whereas the maximum inter-story drift ratio (MIDR) and top displacement (Dtop) are used as engineering demand parameters (EDP). The fragility functions are developed for four damage states which are slight damage, moderate damage, extensive damage, and complete damage. While deciding the limit values of the EDPs for each damage state, we perform pushover analysis to decide the limit values of top displacements from the idealized pushover curves. With regards to the limit values of MIDR, they are taken from Hazus MR4 Technical Manuel, which is defined for low-rise, high-code MRF structures. For MSA, eleven intensity measure levels (stripes) are defined, and for each stripe, 22 pairs of ground motion records are selected and used. To select the ground motion records for each stripe, a code-based target response spectrum is developed for each IM level. By making use of the devel oped response spectra for each IM, 22 pairs of ground motion records are selected from PEER Ground Motion Database for each IM level (stripe). The fragility functions based on the different types of IMs (Sa and Sd) and the different types of EDPs (MIDR and Dtop) are developed and compared for the 2 and 3-story low-rise RC buildings designed per TSC1998 and TSC2018.