Seismic Response of RC Members Subjected to the 2009 L'Aquila (Italy) Near-Field Earthquake Ground Motions

摘要

The present work assesses the seismic response of reinforced concrete (RC) members subjected to horizontal (HGMs) and vertical (VGMs) ground motions recorded during the 2009 L???Aquila (Italy) earthquake. Normalized axial loads in beam-columns as well as the peak ground acceleration ratios between horizontal and vertical ground accelerations are emphasised as they are considered parameters of paramount importance for the assessment of structural components and systems subjected to combined horizontal and vertical ground motions (HVGMs).Results of extensive parametric nonlinear dynamic analyses carried out on simplified structural models are discussed in detail. The sample models comprise cantilever RC columns and a two-storey, two-bay plane frame designed for gravity loads. The response quantities for the performed analyses are expressed in terms of axial loads, axial deformations, bending moment-axial load interaction and shear demand/capacity ratios. It is found that the variation of axial loads is significant in columns under HVGMs, especially in compression. For values of normalized axial loads (v) corresponding to actual RC columns in framed building structures, e.g., normalized axial load v>0.10, the average increase of the compression load ranges between 174% (v=0.20) and 59% (v=0.50). For high values of normalized axial loads the computed axial load-bending moment pairs lie beyond the threshold interaction curves and, in turn, the RC members fail. The shear demand-to-supply ratio is also detrimentally affected by the high fluctuations of axial loads in the columns. Net tensile forces were computed for columns with low-to-moderate axial gravity preload. In multi-storey framed buildings, the response of central columns is significantly affected by the HVGMs. Reliable seismic performance assessment of framed systems requires that combined HGMs and VGMs should be accounted for in the analyses.