The cost of satisfying design requirements on progressive collapse resistance – Investigation based on structural optimisation

Abstract

This work is concerned with the explicit treatment of progressive collapse resistance within the structural design process. Progressive collapse resistance is associated with the damage tolerance of a structural system and controls the ability of the system to sustain local damage by absorbing the potential of triggering system collapse and suffering disproportionally large consequences. This work focuses on the design of elastoplastic steel frames. The measure of progressive collapse resistance employed is expressed as a ratio comparing the limit loads obtained with elastoplastic analyses of the intact structure and of an artificially damaged structure ('damage' is caused by the notional removal of a column from the intact structure). This measure is used to incorporate a constraint on progressive collapse resistance into a structural design optimisation formulation, which -in its classical form -takes only standard design code constraints into account and aims at minimising the structural cost. The developed optimisation approach is capable of producing cost-effective structural designs with acceptable system damage tolerance. By enforcing the satisfaction of the additional design requirement on progressive collapse resistance, structural cost is inevitably increased due to the need for extra material. This increase is quantitatively explored with the presented structural design optimisation approach.

Optimized Retrofit of Seismically Designed Structures to Withstand Progressive Collapse

“…Its aim is to minimize the total cost of the retrofit materials. The advantage of this procedure is that it does not dictate a particular strategy, such as a localized 'bridge'-type strengthening over the artificially damaged area, which might not be the most cost-effective strategy [8]. Additionally, it allows the utilization of multiple methods in one retrofit design.…”

“…One of the measures proposed to reduce the potential for progressive collapse is the alternate load path method [2,[5][6][7][8]. According to this method, the assessed structural design should be able to redistribute successfully the acting loads when local failure takes place, without extensive propagation of structural damage, which indicates the initiation of a chain reaction that might lead to collapse.…”

“…The alternate load path method is implemented by artificially removing certain structural members from the structural system [2,5,7,8]. The gravitational loads are then applied incrementally on the damaged building by means of a non-linear structural analysis.…”

“…However, intensive investigation of such phenomena, as well as of methods to reduce their effects, started only after the collapse of the World Trade Center towers in September 11, 2001. Design strategies to control the damage propagation or reduce the probability of occurrence of the initial failure have been proposed [1][2][3][4][5][6][7][8]. Up to now, due to the non-compulsory nature of the design strategies, a very limited number of existing buildings has been designed against progressive collapse.…”

“…The Evolution Strategies optimization algorithm is employed in order to minimize the total retrofit cost, subject to constraints on (a) the safety of structural members, (b) the structural system resistance against earthquake and (c) the building's capacity to sustain failure of load-bearing elements without disproportionate propagation of the structural damage. Structural optimization approaches to achieve progressive collapse resistance in a cost-effective manner in the design phase of a building have been presented in [7,8].…”