Fragility functions for reinforced concrete columns incorporating recycled aggregates

Using recycled aggregates in the production of structural members is a relatively new application that has the potential to become a mainstream practice with effective green policies. Therefore, performance-based seismic assessment of structures constructed using recycled aggregates gains importance. Fragility curves, cumulative distribution functions that represent the probability of being in or exceeding a threshold for a selected engineering demand parameter, can be used in risk evaluation of these structures. In this study, fragility functions are generated by compiling the data of reinforced concrete columns incorporating recycled concrete aggregate available in the literature. The data is first evaluated through physical damage states, and three different damage states, namely Damage State 1, Damage State 2 and Damage State 3, are defined. Each damage state is then mapped to a certain repair category (cosmetic repair, structural repair or structural enhancement) so that damage can be defined in terms of economic loss, which would provide a road map in the disaster management decision making process. Drift ratio is selected as the engineering demand parameter since generally displacement demand is taken into account in the evaluation of seismic performance of structures. Based on the results of the statistical analysis, the median drift ratio values of 0.30%, 1.21%, and 3.25%, and logarithmic standard deviations of 0.95, 0.42, and 0.45 are determined for Damage State 1, Damage State 2, and Damage State 3, respectively, for columns incorporating recycled concrete aggregates. Furthermore, the effect of parameters on the relationship between drift demand and damage is investigated. In addition, seismic performances of the columns are discussed in terms of their ductility capacity. It is also shown that the ductility limit defined according to Paulay and Priestley (1992), and UBC (1997) for the reinforced concrete columns made of natural aggregate concrete is valid also for the columns made of recycled aggregate concrete. Besides, fragility functions are also generated for columns made of natural aggregate concrete in order to compare damage progression in columns made of recycled aggregate concrete with the aim of identifying the variability in drift demand. From the comparison of the fragility curves of these columns, it is found that at the same drift ratio, damage exceedance probabilities of both column types are similar for Damage State 1 and Damage State 2. However, for Damage State 3, at the same drift ratio, the damage exceedance probability of columns incorporating recycled concrete aggregates is higher than that of the columns made of natural aggregate concrete owing to relatively lower lateral load capacity of these columns.

Automated summary

The study generates fragility functions for reinforced concrete columns incorporating recycled concrete aggregates, and defines three different damage states to map physical damage to repair categories for disaster management decision making. Additionally, ductility capacities of the columns’ seismic performances are discussed, showing that the ductility limit defined for columns made of natural aggregate concrete is also valid for columns made of recycled aggregate concrete. Moreover, fragility functions are also generated for columns made of natural aggregate concrete to compare damage progression and drift demand variability with columns made of recycled aggregate concrete.