Shear Concentration Effects in RC Walls above Transfer Structures

Abstract

Transfer structures are often adopted in tall building structures to provide open spaces at lower storeys for facilitating various functional uses. However, the complicated interactions of transfer structures and supported shear walls prohibit succinct physical models or design guidelines to rationalise the design process. Significant shear stress concentration on supported shear walls above deformed transfer structure is revealed to critically dominate the design of the buildings under combined effects of gravity and seismic loads. Without adequate prior knowledge and modelling techniques, engineers could under-design the building by overlooking the effect or adopting an unfavourable structural layout at the preliminary design stage leading to difficulty in subsequent detailed member design. This paper aims at studying the structural behaviours of in-plane loaded coupled shear walls supported above a transfer beam. A comprehensive physical model explaining the causes for such shear concentration is presented, in which the shear concentration on the walls above the transfer level is attributed to the forces induced by slabs and beams to restrain the differential movements of adjacent shear walls above the deformed transfer structure. The controlling parameters, comprising the symmetric and asymmetric shear wall arrangements, positions of supporting columns and transfer beams, and span-to-depth ratio of the transfer beam are identified through parametric studies using elastic finite element models. Remedial measures are highlighted for moderating the detrimental effect of shear concentration on supported walls above the transfer level.