Investigation of shear lag effect in tall tube-type buildings

Abstract

The dominant structural systems used for high-rise buildings are tube-type systems. Tall tube-type structures act as a cantilever box girder and become prone to the shear lag phenomenon. This phenomenon causes nonlinear stress along the side of the tubular structures, while the beam theory assumes the stress to be linear. This mechanism reduces the efficiency of tube-type structural systems to resist lateral loads. This study explains a detailed discussion of the shear lag effect and the cause of its existence in two cases, positive and negative, through simple numerical analyses. To this end, the impact of lateral deformation on the shear lag effect was investigated in three tube-type structural systems: framed tube, diagrid, and hexagrid with different heights of 50-, 80-, and 110- story buildings subjected to wind load. The lateral deformation of the model structures was compared with the planer deformation (shear and bending deformation) of the cantilever box girder as the benched mark. Analysis results illustrated that the tube type structural system configuration affected the shear and bending deformation portions and the shear lag effect. Based on the results, the direction of the shear flow was changed according to the slope direction of the tangent line of the deflection curve (first deviation) and caused two cases, positive and negative ones. From the numerical results of candidate models, when the tangent line's angle became zero, the shear lag became minimum. When the curvature of the deflection curve (second deviation) was changed (upward into inward), the shear lag became maximum.