Cédric Giry

Cracking analysis of reinforced concrete structures

The study of a reinforced concrete beam tested under four-point bending is proposed in this article. An analysis of the behaviour of this beam from the global response down to local information such as cracking is performed. In order to describe the progressive degradation of the beam, a damage model is used, associated to a stress-based non-local regularisation method. A post-treatment of the finite element analysis is then performed to characterise the cracking pattern (crack spacing and crack opening). In this article, two different methods of post-treatment are compared: the topological search and continuous/discontinuous crack opening and the global/local analysis. Results show the capability of both methods to give a good estimation of cracking. Finally, the main advantages and drawbacks of both methods are underlined.

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.

How are the equivalent damping ratios modified by nonlinear engineering demand parameters

When attempting to predict the seismic response of reinforced concrete (RC) structures , a trade-off has to be found out between a realistic representation of the dissipations through material behavior law and a numerically more efficient modeling with a controlled computational demand such as a Rayleigh-type damping model. Anyway, constitutive laws only describe internal dissipation and actually need a complementary dissipation term often chosen as a proportional damping matrix to take into account external dissipation sources such as interactions with the environment. Decoupling these two contributions in global dissipation measurement from experimental tests is still challenging. To address this problem, a numerical study based on an experimentally identified structural model is here presented. To this end, an experimental campaign has been carried out on RC beams set up on the AZALEE shaking table of the TAMARIS experimental facility operated by the French Alternative Energies and Atomic Energy Commission (CEA). In this paper, the experimental campaign is first presented. Secondly, a suited constitutive model is formulated and identified from the experimental results. Third, numerical dynamic experiments are carried out in order to assess the influence of several parameters on the energy dissipation and on the equivalent viscous damping ratio through two different methods. The validity of these results is assessed on a numerical case where a nonlin-ear model and an equivalent linear model are compared with each other. Experimental results of dynamic tests are also used as reference in order to estimate the additional viscous damping necessary to take into account the whole energy dissipation.

MODELING AND SIMULATION FOR AN OPTIMIZED DESIGN OF A DYNAMIC BENDING TEST

Performance prediction of fibre-reinforced concrete structures under impact is of major importance in a wide range of industrial applications. Therefore, the study of the dynamic behaviour of the material is necessary to quantify the dynamic mechanical properties of the material in terms of both mechanical response and fracture behaviour : dynamic fracture energy and tensile strength. This study aims to design a modified Hopkinson bar bending test with a series of numerical simulations prior to the actual test in order to select a feasible experiment configuration. Results of a dynamic bending experiment on a steel fibre-reinforced concrete specimen loaded up to failure are presented.

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,