Inelastic Seismic Shear in Multi-Storey Cantilever Columns

Abstract eng:
Seismic shear force magnification in the columns of multi-storey precast structures entering far into inelastic domain is addressed in the paper. Such structures consist of an assemblage of cantilever columns connected with ties. Considering analogy with cantilever walls, it has been expected that during inelastic response the actual shear forces in multistorey cantilever columns could be considerably higher than the forces foreseen by traditional equivalent elastic analytical procedures (equivalent lateral force or modal spectrum). A parametric study of a set of realistic three-storey structures/columns was performed. These structures were designed according to Eurocodes and shear forces were determined by the equivalent elastic (modal spectrum) analysis. Average values of the shear forces obtained by the inelastic response analysis were compared to those of the traditional (modal spectrum) procedure. They were also compared to magnified shear forces predicted using the shear magnification factor ε suggested in Eurocode 8 for RC ductile walls. In parallel, modelling issues related to the inelastic response analysis of multi-storey cantilever columns were also discussed. Very large seismic shear force magnifications (up to 3 times and more) were observed. Therefore it is essential to account for this phenomenon in the seismic (capacity) design of cantilever columns in multi-storey precast buildings. It was demonstrated that for this purpose the expression given in Eurocode 8 to account for seismic shear force magnification in ductile cantilever walls could be used with some minor modifications.

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