Effects of Vertical Earthquake Ground Motions on RC Structures

摘要

The present work assesses the seismic response of reinforced concrete (RC) members subjected to horizontal (HGMs) and vertical (VGMs) ground motions of the 2009 L'Aquila (Italy) earthquake. Results of comprehensive parametric nonlinear dynamic analyses carried out on sample beam-columns and a two-storey two-bays framed model are discussed in a detailed fashion. It is found that the variation of axial loads is significant in columns under combined HGMs and VGMs, cspecially 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 increase of the compression load ranges on average 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 horizontal and vertical earthquake ground motions. Reliable seismic performance assessment of framed systems requires that combined HGMs and VGMs should be accounted for in the analyses.