Effect of Ductility Level on the Seismic Response of Moment-Resisting Frames on Soft Soil

Abstract

The selection of a lateral force resisting system in a soft soil area (Site Class SE) is a complex engineering challenge due to the high seismic deformation amplification. This study aims to evaluate and compare the seismic performance of a four-story office building in Pekalongan using three alternative moment resisting frame systems: SRPMK Reinforced Concrete, SRPMM Structural Steel, and SRPMB Structural Steel. The evaluation was conducted based on the SNI 1726:2019 standard through the Response Spectrum Analysis method using ETABS software. The review parameters focused on the weight efficiency of the structure, the design base shear force, and the fulfillment of the story drift allowance limit. The comparison results show that the use of steel material reduces the total weight of the structure by up to 35% compared to reinforced concrete. However, the difference in ductility factor (R) reverses this advantage. SRPMB Steel (R=3) carries twice the design base shear force of SRPMK Concrete (R=8), which forces the use of massive steel sections and is very uneconomical. In terms of serviceability, SRPMM steel performed the most flexibly and failed to meet the safe drift requirement. In contrast, SRPMK concrete showed superior stiffness in controlling lateral deformation. It was concluded that a pure moment frame system made of steel is not rational for application in soft soils, so the use of additional bracing elements is recommended to control lateral drift effectively.