Influence of advanced structural modeling technique, mainshock-aftershock sequences, and ground-motion types on seismic fragility of low-rise RC structures

Abstract

Large earthquakes are rare natural hazards, having catastrophic impact on society due to loss of lives, damage to constructed facilities, and business interruption. Because of damage accumulation due to the main strong shaking, aftershocks potentially endanger the safety of residents and subsequently increase financial loss due to downtime and repair costs. Therefore, accurate prediction of the seismic performance of structures in the post-earthquake stage is critical for disaster risk mitigation. This paper employs an advanced structural modeling technique, which can simulate various features of cyclic degradation in material and structural components using nonlinear fiber beamcolumn elements. The model accounts for inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement and can simulate multiple failure modes of reinforced concrete structures under dynamic loading. Furthermore, a comprehensive ground motion selection accounting for multiple types of ground motions, such as shallow crustal, deep inslab, and subduction earthquakes, is implemented. Finally, a new set of fragility curves has been developed for each ground motion type, which accounts for the aftershock effects and influence of ground motion types on cyclic degradation and failure modes of low-rise reinforced concrete structures. It was found that slight and moderate damage is not significantly affected by major aftershocks for different ground motions types. However, considering aftershocks increases the probability of exceedance of damage for extensive and complete damage up to 5% and 10% for inslab and crustal event, respectively. The proposed methodology significantly improves the accuracy of seismic risk and vulnerability assessment by reducing the uncertainties associated with structural modeling and variability of earthquake ground motions.

The Behavior of Rectangular and Circular Reinforced Concrete Columns Under Biaxial Multiple Excitation

“…As mentioned before aftershocks have the potential of increasing the damage to RC structures. It was shown in previous studies [Salami, Kashani and Goda (2019)] that lowcycle fatigue damage index of RC elements increase under multiple excitation. The impact of aftershocks on rectangular and circular RC columns using the buckling model are presented in Fig.…”

“…The numbers of fibers and the section discretization method are based on the recommendations provided by Berry and Eberhard [Berry and Eberhard] (2006). For more information regarding the methodology, formulation, calibration and validation of the model please refer to Kashani et al [Kashani, Salami, Goda et al (2017); Salami, Kashani and Goda (2019)]. Validated against experimental results, this computational modeling technique is capable to account for cyclic degradation of reinforcing bars due to inelastic buckling and low-cycle fatigue failure.…”

“…The accumulation of damage and degradation in the structure due to the mainshock and the following aftershocks potentially endanger the safety of residents. The potential of having additional damage due to mainshock-aftershocks (MSAS) have been investigated for RC structures [Faisal, Majid and Hatzigeorgiou (2013) Kashani and Goda (2019)]. These studies confirmed that there is a lack of conservatism in the safety of conventionally designed structures subjected to multiple earthquakes and more research is warranted in this field.…”

“…These studies confirmed that there is a lack of conservatism in the safety of conventionally designed structures subjected to multiple earthquakes and more research is warranted in this field. In the study conducted by salami et al [Salami, Kashani and Goda (2019)], on the seismic performance of low rise RC buildings under multiple excitations, it was found that aftershocks have a potential to increase the damage of RC columns due to low-cycle fatigue and it is more severe for long duration ground motion caused by subduction earthquakes. Moreover, in an experimental/analytical study conducted by Hachem et al [Hachem, Mahin and Moehle (2003)] on the seismic performance of RC columns subjected to ground motions they found that columns with short periods might be susceptible to low-cycle fatigue failure.…”

“…The model accounts for inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement and can simulate multiple failure modes of reinforced concrete structures under dynamic loading. A comprehensive detail of the model is available at Kashani et al [Kashani, Salami, Goda et al (2017); Dizaj, Madandoust and Kashani (2018); Salami, Kasani and Goda (2019)]. In addition to the advanced structural modeling, a comprehensive ground motion selection accounting for shallow crustal is implemented, as the hypothetical column is assumed to be located in Los Angeles, US.…”