Influence of soft storey height on seismic response of low-rise RC buildings using linear time history analysis

Soft storey irregularity remains one of the most critical causes of seismic vulnerability in reinforced concrete (RC) buildings, particularly in low-rise urban constructions where functional requirements often dictate increased ground storey heights. Variations in soft storey height significantly influence stiffness distribution, mass participation, and dynamic characteristics of buildings subjected to earthquake loading. This research investigates the influence of soft storey height on the seismic response of low-rise RC buildings using linear time history analysis. Numerical models of a typical low-rise RC frame were developed with varying soft storey heights while maintaining identical structural configurations for the upper storeys. Linear time history analyses were performed using recorded ground motion data to capture realistic seismic excitation effects. Key response parameters such as peak inter-storey drift ratio, base shear, roof displacement, and storey acceleration were evaluated and compared across models. Statistical tools, including regression analysis and one-way ANOVA, were employed to quantify the significance of observed variations in structural response due to changes in soft storey height. The results demonstrate a pronounced increase in lateral deformation demands and concentration of drift at the soft storey level with increasing storey height, while a corresponding reduction in base shear capacity was observed. The findings highlight the sensitivity of seismic performance to vertical irregularities introduced by soft storey height variation. The research confirms that even modest increases in soft storey height can substantially alter seismic response patterns, potentially leading to premature damage concentration during earthquake events. The outcomes emphasize the importance of rational soft storey design and provide quantitative insights that can support performance-based seismic assessment and design strategies for low-rise RC buildings.