Introduction of Fragility Surfaces for a More Accurate Modeling of the Seismic Vulnerability of Reinforced Concrete Structures

Pierre Gehl (1) , Darius Seyedi (1) , John Douglas (1) , Mahmoud Khiar (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Earthquake shaking represents complex loading to a structure. It cannot be accurately characterized by a single parameter such as peak ground acceleration. The goal of this work is to compare the role of various strong-motion parameters on the induced damage in the structure using numerical calculations. The most influential parameters are then used to build multi-variable fragility functions, in order to reduce some of the uncertainty inherent in the response to seismic loading. To this end, a robust structural model of an eight-story reinforced concrete building on which dynamic calculations can be performed at an acceptable cost is used. In the model, all elements have a linear behaviour, except the ends of each column and each beam to which a nonlinear behaviour based on damage mechanics and plasticity type (plastic-hinges model) is assigned. Several hundred nonlinear dynamic analyses are carried out on the structure and the damage levels are identified using the inter-story drift ratio, which can be linked to standard damage scales. The spectral displacements, SDs, at the first two modal periods T1 and T2 are used to represent the seismic loading as the most useful parameters reflecting the structure´s response. Each pair of points [SD(T1), SD(T2)] is associated with a probability of exceeding a given damage level. This probability P is evaluated by considering the damage levels attained by other points located in its neighbourhood. A scalar parameter R = f[SD(T1), SD(T2)] is then built up and we can construct an analytic equation for the fragility curve P = g(R) = g(f[SD(T1), SD(T2)]). This results in an equation for a fragility surface that offers a more complete and accurate view of the structure´s vulnerability. A comparison between different profiles obtained by the generated fragility surfaces and conventional fragility curves shows the significant role of the second parameter in accurately estimating the probability of damage. Such fragility surfaces can be implemented within earthquake risk evaluation tools and they should provide more precise damage estimations. It is expected that this procedure can lead to more accurate land-planning and retrofitting policies for risk mitigation.

Mots clés: reinforced concrete building; fragility curve; fragility surface; non-linear time-history analysis; vulnerability assessment; strong-motion parameters

Domaines: Mécanique des structures [physics.class-ph]; Mécanique des structures [physics.class-ph]

Pierre Gehl, Darius Seyedi, John Douglas, Mahmoud Khiar. Introduction of Fragility Surfaces for a More Accurate Modeling of the Seismic Vulnerability of Reinforced Concrete Structures. COMPDYN 2009 - ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Jun 2009, Rhodes, Greece. Paper n°228. ⟨hal-00560523⟩