IMPROVEMENT OF STRUCTURAL ANALYSIS BY MODIFICATION OF SITE RESPONSE ANALYSIS AND EARTHQUAKE FORCE DIRECTION

Abstract

The seismic resistance design of buildings in Indonesia is usually performed based on the
most recent Indonesian Seismic Code (ISC). Improvement of the ISC will sometimes produce different
(increasing or decreasing) earthquake forces for building design. This paper describes the study of building
evaluation by conducting a modified Site Response Analysis (SRA) and a modified incoming earthquake
force direction. The modified SRA was performed as a result of in-complete soil boring investigation
through the bedrock elevation, using 30 m (soil boring investigation) and 50 m (microtremor investigation)
soil profile models. The earthquake force towards the building is computed using a pair (East-West/EW and
North-South/NS) of ground motion (acceleration time histories) models. Due to the unpredictability of
incoming earthquake forces, these models are improved by adjusting the ground motion direction to the
building by rotating a pair of ground motions from 0o to 180o at 10o intervals. The time histories were
developed according to the Deterministic (DSHA) and Probabilistic (PSHA) Seismic Hazard Analysis. The
analysis was performed by evaluating the moment capacity ratio of the building’s existing column
reinforcement in resisting the earthquake force. The surface time histories and spectrum accelerations
computed using the 50 m model is slightly higher (10%) than the same output calculated using the 30 m
model. In terms of the moment capacity ratio, the existing column reinforcement of the building is strong
enough to resist seismic earthquake scenarios, and the minimum value is observed when the ground motion is
rotated by 40o
.