Integrating socioeconomics in the development of criteria for optimal aseismic design of r/c buildings

An approach for developing cost-effective criteria for optimal aseismic design of a class of R/C buildings is proposed. Design criteria is formulated on the basis of minimum expected life-cycle cost which involves a trade-off between the initial and the expected damage costs of a structure over the life of the structure. The approach requires that a structure with typical geometry and framing system be designed for several seismic base coefficients for different safety levels following an existing aseismic code; e. g. the UBC. Probabilistic damage assessments are performed for all the designs in order to estimate the reliability (or risk) of the various designs subjected to given earthquake ground motion intensities. The present worth of the expected cost of damage from future earthquakes within the life of the structure is estimated on the basis of the risk and realistic cost functions which include: repair cost, cost of the damaged contents, cost associated with loss of life, cost of injuries and economic loss. Actual data and available information are used to quantify these costs. Expected life-cycle cost functions are then developed for given intensities and the target reliability is defined as the reliability corresponding to the minimum expected life-cycle cost for that given intensity; whereas for all possible intensities the expected life-cycle cost is integrated over all intensities for a given earthquake. Finally, the conditional reliabilities are integrated over the lifetime probabilities of occurrence of the intensities according to the hazard curve for the site. The optimal base shear coefficient is obtained as that associated with the optimal target reliability. The formulation is extended to the upgrading of existing structures. The approach is applied to the design and upgrading of buildings in Mexico City for earthquake protection. Sensitivity of the results for design and upgrading is examined, particularly with regard to variations in the costs of fatality and injury. From the results obtained it is concluded that: (1) the socio-economic aspects are significant for optimal aseismic design, (2) the base shear coefficient recommended for soft soil zone by the current code of Mexico City is close to the estimated optimal base shear coefficient for minimum life-cycle cost and (3) the number of people killed per unit floor area of collapsed building is an important parameter to quantify the cost of life loss and is modeled as a function of the floor area of collapsed building.