عنوان مقاله [English]
Different structural solutions are employed to enhance the capacity of weak structures under the earthquake excitations to satisfy the target of the rehabilitation regulations. These retrofitting methods include adding new seismic-resistant components or increasing the strength and ductility of existing components. Given the probability of the earthquake occurrence, it is necessary to evaluate the effect of different retrofitting scenarios on the probabilistic performance of the structure. In this paper, a framework using fragility curves is presented to select the most efficient retrofit scenario in terms of the cost-benefit analysis. For this purpose, two methods of adding reinforced concrete (RC) shear walls and use of polymeric reinforced carbon fiber (CFRP) sheets are employed to retrofit weak RC frames of 5, 8 and 12-stories. Different retrofitting scenarios for RC frames were compared using the proposed framework.
Following the presented framework, the damage indices of structures of each scenario are extracted from the incremental nonlinear dynamic analysis. Then, the fragility curve, the damage probability matrix, and the expected annual damage costs are obtained. In the last step, different scenarios were compared using cost-benefit analysis. The benefits and costs included in the cost-benefit analysis were the reductions of the annual damage cost and cost of each structural retrofitting scenario, respectively. The higher the benefit-cost ratio, the more economical the scenario is. IDARC  software was employed for dynamic nonlinear structural analysis. For modeling the hysteresis deteriorations in dynamic analyses, stiffness, resistance, and pinching deterioration parameters were employed. These parameters are obtained based on the relationships proposed in  to accommodate the hysteresis of the numerical modeling with the experimental one. The weak RC frames were retrofitted with the basis rehabilitation target by the Iranian rehabilitation Guidelines , signifying that the performance level of the structure is life safety (LS) under the design seismic risk (0.25 g). Also, for better evaluation of the retrofitting methods, retrofitting was conducted at two higher levels.
The results of the nonlinear dynamical analysis showed that shear walls can reduce the inter-story drift ratios significantly more than CFRP sheets do. The results of the cost-benefit analysis revealed that retrofitting with the CFRP sheets is a more preferable method than retrofitting with the shear walls in terms of the economic approach, especially for the shorter height structure (5-story frames). It is because the cost of executing shear walls and shear wall foundations is very expensive. By increasing the structural height (from 5 to 8 and 15 stories), CFRP sheets outperformed shear walls, while for the 15-story frame, adding the CFRP sheets was a better solution than adding the shear walls. For high- and middle-height structures (8- and 15-story frames), the differences in the cost-benefit ratio of the two methods were ignorable. The CFRP sheets further reduced the exceedance probability of damages at low earthquake hazard levels, while shear walls further reduced the probability of damage occurrence and damage exceedance (especially high-performance levels such as collapse prevention). This is especially the case for higher-rise structures where the collapse probabilities are higher than for the shorter structures, leading to a close cost-benefit ratio of the two retrofitting methods.
1. Valles, R.E., et al. (2009) IDARC2D Version 7.0: a Computer Program for the Inelastic Damage Analysis of Buildings. NCEER, State Univ. of New York at Buffalo, technical report MCEER-09-0006.
2. Bakhshi, A. and Asadi, P. (2013) Probabilistic evaluation of seismic design parameters of RC frames based on fragility curves. Scientia Iranica, 20(2), 231-241.
3. Strategic Oversight Deputy, Technical System Affairs (2013) Guideline for Seismic Rehabilitation of Existing Buildings, Publication No. 360, (1st revision) (in Persian).