Structural Behaviour of Multi-Storey Buildings with Circular and Rectangular Columns under Earthquake Loads: A Review

In seismically active areas, reinforced concrete (RC) moment-resisting frames are still the most commonly used structural system for multi-story buildings and the seismic behaviour of RC moment-resisting frames is highly dependent on the size, shape and detailing of the columns. Until now, the use of circular columns was limited to member-level and connection-level analyses and no studies have investigated their full benefits and performance at the entire building scale under earthquake loading, although the columns are known to provide more uniform core confinement and an isotropic flexural stiffness distribution at earlier stages of investigation.This review aims to consolidate current knowledge, highlight the methods and technologies used and reveal the key research gaps underpinning the nonlinear static (pushover) assessment of RC buildings, while summarising 30 years of research with a specific focus on those that compare the seismic performance of circular and rectangular column sections in some way, directly or indirectly.Despite the documented limitations of pushover analysis, with regard to invariant load patterns and single-mode idealisation, reviewed literature shows that pushover analysis has been the most popular nonlinear static method for performance-based seismic evaluation, evolving from the Capacity Spectrum Method of ATC-40, through the Displacement Coefficient Method of FEMA-356, to the equivalent linearization procedure of FEMA-440. Extensive member-level and, in more recent publications, building-level studies have all shown that, in general, circular RC columns have lower base-shear attraction, slightly lower storey drift points and more favourable equivalent-linearization points than rectangular columns of the same cross-sectional area as a result of more uniform confinement and the absence of stress-concentrations at sharp corners. New findings like machine-learning surrogate models for prediction of capacity curves as well as developments in textile- and polyurea-based retrofit systems are now starting to expand and in some instances contradict the findings of classical pushover studies.High priority research needs identified in this review are full three-dimensional, building-scale parametric studies that consider column shape as a variable only; incorporation of explicit shear and joint failure criteria into the nonlinear static procedures; validation of conclusions from pushover analyses against nonlinear time-history and shake-table analysis; and development of standardised design guidance for circular RC columns in multi-storey moment-resisting frames, where current code provisions are relatively under-developed compared to their treatment of rectangular columns.