ESTIMACIÓN DEL IMPACTO DEL TIEMPO DE CORROSIÓN EN LA EVOLUCIÓN DEL RIESGO DE ESTRUCTURAS DE CONCRETO REFORZADO

Abstract

Over the last three decades an increase in cracks and spalling of concrete in elements of reinforced concrete structures has been observed. These damages are related to the corrosion of reinforcing steel under the action of environmental effects, which have normally caused worldwide premature deterioration of structures. This implies that, apart from strength, durability should be considered to prevent this deterioration, such that the probability of satisfactory performance of the structure during its lifetime is acceptable. Consequently, it becomes relevant to assess the risk posed by this type of structures subject to corrosion over time and, accordingly, adopt preventive measures to ensure their durability. To address this situation, this piece of research deals with the relationship between the steel corrosion time and the evolution of risk for a reinforced concrete structure, by developing a model to estimate the reliability index variation during both the initiation time and the corrosion propagation process, by means of the modification of an existing deterioration model. With the proposed model, the reliability index of the reinforced concrete structure subject to corrosion damage (considering the case of a vehicular bridge) was obtained. To do so, it was required to carry out the quantitative estimation of the cracking of concrete cover and its evolution over time, analyzing several of its structural elements damaged by corrosion. Following on from this, the reduction on diameter of the steel bars of each of the elements was determined, along with the corresponding loss of its cross-sectional area and the load decrease, thus increasing the likelihood of failure and reducing the reliability index. With the example developed and the results obtained, it was observed that the corrosion damaged elements showed reductions not only in stiffness but also in its nominal yield moment, during the propagation of corrosion. This led to reductions on the structure reliability index (achieving values lower than 2 for seismic action), and in its lifetime of 15%, for the most critical failure (presented simultaneously in two structural elements). Thus, the working hypothesis has been proven, showing that a reinforced concrete structure subject to corrosion over its lifetime, has changes in its structural rigidity and reduces their ability to withstand loads, reducing its reliability index to values lower than 2 for seismic actions, and shortening by 20% or more of its lifetime (although for the studied case the reduction was only 15%). Finally, a comparison was made of the results obtained with the developed model, and the reliability index estimated by using a durability existing model for the studied structure. The results were similar in terms of the corrosion initiation time, the corrosion propagation time, and the time for which the structure exceeds its ultimate limit state, for the most critical failure.