Exploring the distribution of seismic loads in tunnel-form concrete buildings using the probable area method

Abstract

Equivalent static analysis is a simplified method that is widely used by designers and structural engineers in seismic design codes. However, the accuracy of this approach is affected by various parameters and uncertainty sources. Moreover, its reliability for different seismic demand and performance levels is not well-established, which raises doubts about its application for performance-based analysis. In this study, a new method called the probable area approach is proposed to address the shortcomings of the equivalent static method. The suggested method is based on multi-level response modification factors and probabilistic distribution of corresponding intensities, providing a more reliable estimate of the lateral loads at different levels of the structure compared to the current deterministic lateral forces. To evaluate the effectiveness of the probable area method, the lateral load distribution for three multi-story tunnel-form concrete buildings with 5, 7, and 10 stories under the design basis hazard level (10% probability of occurrence in a 50-year service life of the building, and a return period of 475 years) is computed using both the equivalent static and probable area methods. The attained results show that the equivalent static method is not suitable for estimating the base shear and lateral load distribution of seismic forces and results with an average error of 80% and 60%, respectively, compared to near-exact responses derived from time-history analysis. On the other hand, the proposed method significantly reduces the errors in estimating the base shear and lateral story forces, with maximum error values of 18% and 9%, respectively. These findings highlight the potential of the probable area method to improve the accuracy and reliability of the simplified equivalent static analysis methods.