Reliability-Based Design Spectra Modification Factor for Reinforcement of Tilted Structures

Abstract eng:
A reliability-based methodology to estimate the additional strength required for the reinforcement of existing tilted structures, is proposed. Several nonlinear time history analyses of structural systems with different levels of asymmetric yielding are carried out. The seismic analyses consider the effect of two orthogonal components of the seismic ground motions as well as the influence of soil-structure interaction. Results indicate that the annual rate of exceedance of the ductility demand for asymmetric yielding structures may be much higher than those corresponding to symmetric structures, such increment depends on several factors: tilting angle, ductility demand of the structure, and ratio between the vibration period of the system and that of the soil. Based on the results, a simplified mathematical expression to estimate strength amplification factors of tilted structures to achieve a similar reliability to that of symmetric structures, is proposed. The expression depends on the tilt angle, the ductility of the structure, and the ratio of the fundamental vibration period of the structure to the dominant period of the soil. Finally, the proposed expression is compared with that recommended by the Mexico City Building Code, and its advantages and disadvantages are discussed.

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