Cédric Desprez

Seismic vulnerability assessment of a RC structure before and after FRP retrofitting

In earthquake engineering, reliable vulnerability assessment tools suitable to existing reinforced concrete structures are necessary in order to mitigate the seismic risk. Furthermore, amongst the wide range of technical solutions available for structural upgrading, external reinforcement by fiber reinforced polymer (FRP) is often an interesting option. Nevertheless, the use of FRP is limited, one of the reasons being the lack of predictive numerical tools allowing for vulnerability assessment. Based on a case study, this article presents a simplified modeling strategy to assess the seismic vulnerability of an existing reinforced concrete building before and after FRP retrofitting. The structure is simulated using multifiber beam elements and constitutive laws based on damage mechanics and plasticity, while the dynamic characteristics of the numerical model are validated using in-situ ambient vibration records. Nonlinear transient dynamic analysis studies are performed using a synthetic earthquake signal compatible with the Eurocode 8 spectra. Local indicators are adopted to quantify the damage level in the structure before and after FRP retrofitting, in correspondence with the European Macroseismic Scale 98. One of the main conclusions of this study is that the use of local indicators can lead to contradictory assessment results with the evaluations based on global indicators as adopted in HAZUS or Risk-UE.

A multifiber beam model coupling torsional warping and damage for reinforced concrete structures

This paper is dedicated to the numerical modelling of structures using multifibre beam elements. A formulation is developed to account for torsional warping in the deformations of an arbitrary-shaped composite cross section. The resulting warping profiles are validated by comparison with the axial displacements obtained by three-dimensional modelling of beams in torsion. The warping kinematics is then implemented in a Timoshenko multifibre beam element. The material is modelled by a 3D damage law, and warping is updated throughout the computations to account for damage evolution. Non-linear parameters of the constitutive model are identified using a genetic algorithm. A comparison of torque–twist curves predicted with enhanced and classical beam elements to experimental curves highlights the importance of including warping in the model. The analysis of damage patterns further ascertains the effect of warping.

Toward a large-scale seismic assessment method for heritage building: vulnerability of masonry baroque churches

The seismic assessment of historical masonry structures is a crucial field in architectural heritage. However, due to the large panel of these structures and the lack of numerical tools, vulnerability assessment of heritage buildings in seismic areas is still a complex issue in civil engineering. Through a case study dealing with baroque religious heritage in French Savoy, this paper presents the development of a simplified numerical strategy suitable for a large-scale study. Thanks to field surveys, a large data base has been built for 200 buildings. A limited number of homogeneous structural types have been defined. A parameterised meshing tool, suitable for finite element modelling has been developed, making it possible to take into account the specificities of each structural type. Then a dynamic analysis strategy is used to study the response of the model considering specific modelling variations. Finally, damage criterion choice is discussed comparing numerical results and in situ post-seismic feedback.

Seismic risk: Structural response of constructions

ABSTRACT This paper presents numerical techniques for computing the response of reinforced concretes structures. From the one degree of freedom case and after the formulation of the equations of dynamic equilibrium, the general case is considered. Two main aspects are treated, the one related to the modal analysis which, in the linear regime, leads to the mode shapes and the natural frequencies, and the one related to the seismic vulnerability analysis which, in the non linear regime, is able to describe the damage location and the critical zones of a given structure. Applications show that the strategy opens on tools useful to design the reinforcement of existing building.

Tools For A Large-scale Seismic Assessment Method Of Masonry Cultural Heritage

The preservation of architectural heritage against natural hazards, especially seismic risks, is extremely challenging. Countries presenting a medium seismic risk like France still want to protect this particularly sensitive but also numerous heritage. Our research work therefore seeks to meet those two requirements. Firstly the large-scale of the study deals with a large number of buildings to be diagnosed across the studied region. Furthermore we need to propose a relevant analysis of the seismic behaviour of masonry historic structures, by inexpensive ways. We rely on studying the rich heritage of vernacular Baroque churches and chapels in the highest valleys of French Savoye. We first present the choices we made and the tools we developed to meet the identified requirements. Then we develop how we used ambient noise measurements in order to calibrate and validate initial models of unfamiliar complex structures. Finally we explain how we defined a damage threshold criterion by comparing different approaches,