Comparative Study of a Commercial RCC Building as per IS 1893:2016, NBC 105:2020, and NBC 105:2025

Abstract

Reinforced concrete structures are analyzed using seismic design codes under seismic loading to ensure the safety and optimal performance of the structures. The primary objective of this study is to investigate and compare the effects of Indian and Nepalese seismic design codes on the seismic behavior of RCC structures. In this study, a G+4 commercial Reinforced Cement Concrete building situated in Soil Type D is modeled and analyzed using the response spectrum method of analysis. ETABS (Version 22) is used to analyze the seismic characteristics of reinforced concrete buildings under NBC 2020, NBC 2025 (ULS & SLS), and IS 1893:2016, as per codal guidelines, and their results are interpreted. In this study, drift, displacement, and base shear are used as comparison parameters, and their corresponding findings are compared.

In NBC 2025 (ULS), the drift and displacement are observed to decrease by approximately 7% compared to the 2020 version, while SLS experiences a notable reduction of nearly 30%. Among all the cases, the values obtained from IS 1893:2016 are the lowest, reflecting the reduction in drift and displacement by more than 50%. The base shear was found to be similar for NBC 2020 and NBC 2025 ULS (reduced by around 4% from NBC 2025 SLS); however, the results from IS 1893:2016 were quite lower (dropped by nearly 30%). These observations indicate that NBC 105:2025 shows greater control over deformation compared to NBC 105:2020, while IS 1893:2016 results in significantly lower seismic demand. However, despite showing lower seismic demand, IS 1893:2016 results in higher longitudinal reinforcement in both beams and columns than NBC codes. This is primarily due to factors such as unmodified stiffness factor, higher load combination factors, and higher importance factor, showing that lower seismic demand does not necessarily indicate lower material consumption.