Vulnerability of existing R.C. buildings under gravity loads: A simplified approach for non sway structures

The evaluation of the structural safety of existing buildings is a worrying problem in many countries that have been recently shocked by unexpected, “spontaneous” structural failures. Although several studies have tried to investigate the inherent structural deficiencies associated to such collapses, a uniform approach for the evaluation of a building’s static vulnerability under gravity loads, accounting both for potential failures in vertical and horizontal elements, does not exist yet. This paper takes up this challenge, investigating the dependence of the different failure mechanisms of the main structural elements, in a Gravity Load Designed (GLD) Reinforced Concrete (R.C.) non-sway frame, on a number of design and material factors. In particular, applying basic principles of plasticity theory to the slabs, the beams and the columns of the structural system for different failure mechanisms, the collapse multipliers for the main structural elements are established. The proposed simplified formulations highlight the dependence of each failure condition on proper design parameters and mechanical properties; moreover they allow the explicit evaluation of the effect of some design errors or execution defects.