Displacement Induced Torsion in Structures

Abstract

Satisfying the equations of motion in the deformed configuration leads to actions that inherently contain secondary effects. Similar to the product of vertical loads and lateral displacements which leads to the PΔ effect in structures, lateral displacements may cause significant secondary torsion due to the presence of lateral loads. A simple finite-element formulation is presented in the paper to capture this effect. This formulation is verified by means of the Corotational approach and the updated Lagrangian formulation for acceptable drift limits in structural engineering practice. A simple single-story structure and a 7-story RC and steel structures with no predefined mass eccentricity are subjected to an ensemble of bi-axial ground motions recorded on different soil conditions to demonstrate secondary effects. The paper shows that when the period of the structure is not identical in the two horizontal directions secondary torsion is important and may result in significant torsional amplification.