A Measure of Lifetime Structural Robustness

The concepts of structural robustness, disproportioned failure and progressive collapse are usually associated to damage suddenly provoked by accidental actions and abnormal loads. However, damage could also arise gradually in time from aging of structures. Depending on the damage propagation mechanism, such kind of damage may also involve disproportionate effects. For this reason, it is of great interest to develop suitable measures of lifetime structural robustness. In this paper, the time-variant robustness of deteriorating concrete structures is investigated with respect to the ultimate limit state of collapse. The effects of the damage process are evaluated by using a proper methodology for lifetime assessment of concrete structures exposed to diffusive attacks from environmental aggressive agents. The evolution of the collapse load is evaluated by means of a time-variant limit analysis. The percentage residual carrying load capacity of the structure is related to the total amount of structural damage and, in this form, assumed as suitable lifetime measure of structural robustness. This measure is finally used to formulate a robustness criterion to verify if a structural system is robust or weak. The proposed approach is illustrated through the application to the lifetime robustness assessment of an existing reinforced concrete arch bridge.