Seismic response of steel columns in MRFs under multi-axial earthquake components

The present paper assesses the structural response of steel columns under different seismic loading conditions, e. g. horizontal earthquake ground motions and combined horizontal and vertical components. A low-rise Moment Resisting Frame (MRF) was designed in compliance with modern seismic codes of practice. Linear and nonlinear time-history analyses were carried out to investigate the local and global response quantities in terms of stiffness, strength, ductility, energy absorption and dissipation. A suite of seven records of the 2011 Christchurch (New Zealand) earthquake were employed for the response-history analyses. It is found that the response of the sample MRF is detrimentally affected by the combined horizontal and vertical components of earthquake ground motions. Central columns at the ground floor of the multi-storey MRF exhibit reduced ductility and energy dissipation. Columns with reduced levels of axial loads show low flexural resistance due to the yielding caused by the vertical variation of axial loads. Experimental and further analytical work is deemed necessary to establish design rules to account for the effects of horizontal and vertical components of earthquake ground motions on steel and composite steel and concrete framed systems.