Development of Simulation-Based Fragility Relationships for the Seismic Risk Assessment of Buildings
A number of driving engines are required for earthquake loss estimation and mitigation, including an inventory of exposed systems, seismic hazards of the study area and fragility relationships. The number of existing buildings in the UAE that may be at risk because of insufficient seismic design provisions cannot be underestimated. A crucial role in the recovery period following an earthquake is also played by emergency facilities. Therefore, a systematic seismic vulnerability assessment of a diverse range of reverence structures representing pre-seismic code buildings and emergency facilities, in a highly populated and seismically active area in the UAE, has been conducted in this study. Detailed structural design and fiber-based modeling were carried out for nine references structures. Forty earthquake records were selected to represent potential earthquake scenarios in the study area. Three limit states, namely Immediate Occupancy, Life safety and Collapse Prevention, were selected based on inelastic analysis results as well as the values recommended in previous studies and code provisions. Over 8000 inelastic pushover and incremental dynamic analyses are performed to assess the lateral capacity and to derive a wide range of fragility relationship for the reference structures. Vulnerability functions were also developed for the buildings that proved to have unsatisfactory performance, and hence proposed to be retrofitted using different mitigation techniques. It was concluded that pre-code structures were significantly more vulnerable than emergency facilities. This is particularly true for low-rise buildings due to their inefficient lateral force resisting systems. Far-field records have much higher impact compared with near-source ground motions. The results reflect the pressing need for the seismic retrofit of pre-code structures to reduce the probability of collapse, and for certain emergency facilities to ensure their continued service. Four retrofit approaches are therefore assessed, namely reinforced concrete jacketing, fiber reinforced polymers wrapping, adding buckling restrained braces and installing externally unbounded steel plates. The highest positive impact of retrofit are observed on the pre-code buildings, especially frame structures, since they were only designed to resist gravity and wind loads. The reductions achieved in the vulnerability of the retrofitted structures confirmed the effectiveness of the techniques selected for upgrading the seismic performance of buildings and mitigation earthquake losses in the study area.