Impact of changing seismic response reduction Factor (R) from life safety to immediate occupancy on building construction costs

Seismic design codes typically adopt the Life Safety (LS) performance level using a high response modification factor (R), allowing structures to undergo inelastic deformations during strong earthquakes. However, higher performance objectives such as Immediate Occupancy (IO) require lower R values, resulting in higher design forces and increased construction costs. This study investigates the impact of reducing the response modification factor from R = 8 (LS) to lower values (R = 3, 2, and 1) on building construction costs. A reinforced concrete building was modeled and analyzed using finite element methods under identical loading conditions, with only the R factor varied. Results show that reducing R from 8 to 1 increases total construction cost by approximately 52%, primarily due to significant increases in concrete volume and structural member sizes. The findings highlight a clear trade-off between seismic performance and economic cost, providing valuable insight for performance-based seismic design decisions.Using a lower response reduction factor (R = 3) slightly increases initial costs (under 16%) but is justified by lower future maintenance and repair costs due to improved earthquake resistance.