Stiffening solution of façade frames for reducing the eccentricity in plan-irregular buildings

Abstract

Adjusting to architectonic and urbanistic constraints in dense cities frequently require plan irregularities in structures. One recurrent case is the combination of a frame in the façade, to allow parking access, with structural walls in other perimeter axes, for drift control. In long plan buildings, this creates large eccentricities between the mass and stiffness centres. In this paper, we propose one solution that increases the stiffness of the façade frame, without affecting its functionality. The concept consists on creating vertical elements in the inner spans of the intermittent stories, producing a Vierendeel-effect in the frame. The feasibility to improve the seismic performance is investigated through non-linear models. The stiffened frame reduces the distance between the centres of stiffness and mass. The possible variation of the failure mode is discussed, and recommendations for the capacity design of the façade frame are given. It is found that the additional vertical element does not contribute in the gravity load system, so it should not be considered as an intermittent column irregularity. The concept is applied to a 10-storey plan-irregular building, with hypothetical location in Lima (Perú), and its seismic performance is assessed. Compared to the solution with the standard frame, the maximum floor displacement was reduced up to 30%. The dominant period of vibration was reduced up to 15%. The recommended capacity-design condition allowed ductile behaviour without local collapse for demands larger than the MCE.