Fragility curves for different classes of existing RC buildings under ground differential settlements

Existing reinforced concrete (RC) buildings can be affected by different actions that can induce permanent or transient effects on them. While applications concerning the seismic vulnerability of existing RC buildings have been largely proposed in literature, the evaluation of the structural vulnerability because of hazards different from earthquake has been less dealt with. The focus of this work is to estimate the probability that the simulated RC buildings stock could reach a given Limit State for a certain intensity of imposed monotonically increasing ground differential settlements. A set of simulated FEM models, considering the geometrical and mechanical uncertainties in the representation of the existing RC frame buildings designed only for gravitational loads, has been created. The structural frames differ from each other for geometrical features and mechanical materials properties, obtained through a simulation process. The non-linear behavior of columns and beams is considered by applying a modeling approach specifically elaborated for RC members with plain bars. A FEM model for each simulated structural frame has been developed using the Open Application Programming Interface by using the programming and numeric computing platform MATLAB to run the modelling software SAP2000. Time by time, by scaling up the amplitude of the imposed base displacements, a non-linear static incremental procedure has been implemented. At each step of the analysis, a code-based seismic safety assessment has been carried out with reference to a specific ultimate Limit State considered in the Italian and European codes. The goal of the analysis has been to find the values of the significative structural response parameters (identified in this work as the maximum differential settlement and the deflection ratio) at the onset of the selected Limit State by using the critical demand to capacity ratio. Considering that these values are lognormally distributed, the structural fragility is then derived, showing how the vulnerability of the considered RC buildings stock is affected by the impact of the geometrical features and by the application direction of the differential settlements.

Automated summary

This study aims to assess the structural vulnerability of existing reinforced concrete buildings under hazards other than earthquakes. A set of simulated FEM models considering uncertainties in geometry and materials properties have been created, and a non-linear static incremental analysis has been conducted to evaluate the structural response parameters under specific ultimate limit states. The results show that the vulnerability of the RC buildings stock is affected by the geometrical features and the direction of differential settlements.