Seismic fragility analysis on low-ductile reinforced concrete frame with inadequate lap splice length

Abstract

In Malaysia, many existing buildings, particularly old buildings, are not designed for credible seismic actions. Most of the residential buildings in Malaysia which below 20 stories typically features an open space ground floor and the upper floors are featured with infill brick wall, deriving a higher lateral stiffness than the ground floor. Consequently, the safety of such buildings could be jeopardised by such uncertainties. Therefore, suitable risk management strategies such as fragility analysis should be adopted. Hence, there is a need to derive the seismic fragility curve for buildings with inadequate lap splice length in Malaysia. In this research, the seismic fragility curves for 3-, 6- and 9-story reinforced concrete frame with inadequate lap splice length were derived. All structural models were initially designed in accordance with the specification of BS 8110. The geometry orientation, material properties and reinforced detailing were also in accordance to the common practice in the construction industry of Malaysia. All structural models were subjected to 15 far-field seismic ground motion records. ETABS v2016 was used to carry out the nonlinear time-history analysis and incremental dynamic analysis to determine the inter-story drift demand and inter-story drift capacity of all the structural models. All structural models were excited by time-history data with increasing PGA from 0.05g to 0.50g with an increment of 0.05g. Three levels of seismic performance criteria were evaluated, namely immediate occupancy (IO), life safety (LS) and collapse prevention (CP) to assess the structural performance. Seismic fragility curves were plotted for all structural models. The results reveal that the nature of damage state of all structural models depends largely on the seismic wave frequency that resonate the natural frequency of the structural models. In general, the higher the building height, the lower the probability of damage exceedance induced onto the structural models. The results also show that the absence of adequate lap splice length at the both end of columns at first story could significantly increase the probability of damage exceedance for all seismic performance criteria in all structural models.