Global stability analysis and structural performance of buildings braced by infilled frames

Abstract

A closed-form solution is given for the in-plane buckling analysis of infilled frames. The dominant stiffness characteristics are established as the shear stiffness (associated with the beams and the masonry infill) and the bending stiffness (whose value can be most effectively estimated by the global second moments of area of the columns). Guidelines are given to maximise the critical load of infilled frames. A simple procedure is presented for the three-dimensional global stability analysis of buildings braced by infilled frames. The value of the global critical load depends on the basic (sway and torsional) critical loads and their interaction. Particular attention is paid to torsional behaviour. The most effective ways to improve torsional behaviour are shown, leading to optimum structural performance. The global critical load ratio is introduced as a performance indicator. It is demonstrated that there is a direct link among stability, dynamic behaviour and global deformations. When a bracing system is properly designed for stability, then the building, under horizontal loads, normally develops rotations and translations of acceptable magnitude and its fundamental frequency tends to be sufficiently great. Three worked examples show the easy use of the methods and the application of the global critical load ratio to monitoring structural performance.