Effect of 3D models on seismic vulnerability assessment of deficient RC frame structures

Earthquakes pose critical danger for seismically deficient structures. This phenomenon becomes more pronounced in underdeveloped countries where such structures are common. 2D analysis of such structures can yield reasonable results but requires very careful definition of joint constraints. However, possible shortcoming of 2D analysis is that it does not cater to the relative displacement effects of the transverse members to longitudinal, which is reasonably accommodated in 3D models. This research aims to differentiate the seismic vulnerability assessment of 2D and 3D structural models. Typical deficient three-, five- and eight-storey reinforced concrete buildings constructed in Pakistan were selected as case study and modelled as 2D and 3D structures. Static cyclic analysis was performed and seismic vulnerability assessment was carried out using the capacity spectrum method. The results are then compared with the standard Global Earthquake Safety Initiative curve for deficient structures. It is observed that 3D models are brittle, crack earlier and are more vulnerable seismically compared to their 2D counterparts. It is also concluded that 2D models are more conservative compared to 3D models in terms of seismic response.