Stéphane Grange

A Simple and Efficient Intensity Measure to Account for Nonlinear Structural Behavior

A fundamental issue that arises in the framework of probabilistic seismic risk analysis is the choice of ground motion intensity measures (IMs). A new structure-specific IM, namely, relative average spectral acceleration (ASAR), is being proposed herein, and a comparison with current IMs is performed based on (1) a large data set of recorded earthquake signals; (2) numerical analyses conducted with state-of-the-art finite element (FE) models, representing actual load-bearing walls and frame structures, and validated against experimental test; and (3) systematic statistical analyses of the results. According to a comparative study of the case of nonlinear structural behavior, the ASAR proves to be the most efficient IM with respect to demand parameters, such as maximum interstory drift, frequency drop and maximum ductility demand. Beyond the sufficiency and simplicity of its formulation, which allow for the use of existing ground motion prediction models, the ASAR offers a promising IM for performance-based seismic design and/or assessment.

Simplified modelling strategies for reinforced concrete structures

ABSTRACT Three simplified modelling strategies are proposed to simulate the non linear behaviour of reinforced concrete (RC) structures submitted to severe loadings. The Equivalent Reinforced Concrete model (ERC) is suitable for very squat RC walls and it is based on the Framework method coupled with damage mechanics and plasticity constitutive laws. The multifiber Timoshenko beam can be used for slender or squat structures submitted to severe shear or torsion. Finally, the SSI macro-element coupled with the multifiber beam is able to reproduce soil structure interaction phenomena on the foundation and the structure.

A comparison of displacement-based Timoshenko multi-fiber beams finite element formulations and elasto-plastic applications

Various formulations of displacement-based Timoshenko multi-fiber beams are compared in this article. After a short literature review, the presentation of the shape functions leading to the stiffness matrices and the consistent nodal forces relative to each formulation are presented and their performances are studied using elastic or elastic perfectly plastic constitutive laws and simple to complex static loadings. The advantages and disadvantages of each formulation are highlighted and general conclusions are drawn on the use of displacement-based Timoshenko multi-fiber beams in engineering. An innovative solution is finally proposed to improve the performance for the case of axial-bending interactions.

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.

Simplified strategies based on damage mechanics for concrete under dynamic loading

Based on previous work, the µ damage model has been designed to figure out the various damage effects in concrete correlated with monotonic and cyclic loading, including unilateral effects. Assumptions are formulated to simplify constitutive relationships while still allowing for a correct description of the main nonlinear effects. In this context, the paper presents an enhanced simplified finite-element description including a damage description, based on the use of multifibre beam elements and including strain rate effects. Applications show that such a strategy leads to an efficient tool to simulate dynamic loading at low, medium and high velocities. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’.

Traditional Timber-Framed Infill Structure Experimentation with Four Scales Analysis (To Connection from a House Scale)

The aim of this paper is to contribute toward a better understanding of the seismic behavior of timber-framed infill structure. For this purpose, the results of a multi-scale experimental program are presented. The paper presents also the feasibility to use a DIC analyse on a full-scale of a house tested on a shake table.

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.

Behavior of a RC Frame Under Differential Seismic Excitation

ABSTRACT Two very dense seismographic arrays were deployed in a seismically active area in Greece to incorporate the difference in amplitude and phase between two stations located within the dimension of a structure. The spatial variability in seismic ground motion is generally attributed to the wave passage effect, the incoherence effect, and the local site effect. It can cause severe damage on lifeline structures. This article studies the behavior of a reinforced concrete 2D frame structure subjected to differential seismic excitation at the supports. Both linear and nonlinear finite multifiber element models of the seismic behavior of this structure are used. The nonlinear behavior of the structure, under these different cases, displays different damage patterns and maximum displacements. This study allows evaluating the uncertainty that can be propagated through the finite element model, aiming at reducing variability for structural design purposes.Two very dense seismographic arrays were deployed in a seismically active area in Greece to incorporate the difference in amplitude and phase between two stations located within the dimension of a structure. The spatial variability in seismic ground motion is generally attributed to the wave passage effect, the incoherence effect, and the local site effect. It can cause severe damage on lifeline structures. This article studies the behavior of a reinforced concrete 2D frame structure subjected to differential seismic excitation at the supports. Both linear and nonlinear finite multifiber element models of the seismic behavior of this structure are used. The nonlinear behavior of the structure, under these different cases, displays different damage patterns and maximum displacements. This study allows evaluating the uncertainty that can be propagated through the finite element model, aiming at reducing variability for structural design purposes.

ENHANCEMENT OF MULTIFIBER BEAM ELEMENTS IN THE CASE OF REINFORCED CONCRETE STRUCTURES FOR TAKING INTO ACCOUNT THE LATERAL CONFINEMENT OF CONCRETE DUE TO STIRRUP

To assess the seismic vulnerability of existing reinforced concrete structures, a large number of degrees of freedom is involved. Consequently, efficient numerical tools are required. In the case of slender elements, enhanced beam elements have been developed to try to introduce shear effects, but in these models, the transverse steel is sometimes taken into consideration with approximated manner or often not at all. However, as shown by some experimental tests, the amount of transverse reinforcement triggers significantly the behavior of beam elements, especially under cyclic loading. Thus, the main goal of this work is to investigate solutions for an enhanced multifiber beam element accounting for vertical stretching of the cross section, occurring due to the presence of transverse reinforcement. The efficiency of the proposed modeling strategies is tested with results obtained from tension and flexure tests conducted on an elastic linear material.

SEISMIC FINITE ELEMENT ANALYSIS OF AN EXISTING OLD CONCRETE STRUCTURE BY USING MULTIFIBER BEAMS: INTRODUCTION OF AN ADAPTIVE PUSHOVER METHOD

The study of the seismic vulnerability of existing structures is an important issue. Many researches have been developed in order to investigate the structural behavior of these structures, and extract the basic informations needed to establish retrofitting guidelines in order to reduce the seismic risk to acceptable levels. The most accurate analysis procedure for the structures subjected to strong ground motions is the time-history analysis. This method is time-consuming though for application in all practical purposes. The necessity for faster methods that would ensure a reliable structural assessment or design of structures subjected to seismic loading led to the pushover analysis. Pushover analysis is a non-linear static analysis based on the assumption that structures oscillate predominantly in the first mode or in the lower modes of vibration during a seismic event. The present work deals with seismic vulnerability assessment of an old existing reinforced concrete structure – Perret tower – located in Grenoble, France. After a brief description of the structure in exam, a preliminary computation of the mass of the building and the definition of every existing section are performed. A simplified 3D numerical model is carried out using a finite element code based on multifiber beams approach. Firstly, a non-linear temporal dynamic analysis is performed, then a conventional and adaptive pushover analysis is carried out. The results obtained of the studied cases are then compared: it is observed that the conventional pushover analysis should be adjusted in order to take into account the change of dynamic characteristics due to the formation of plastic mechanisms. Finally, the tower critical levels in term of damage are highlighted. 3491 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3491-3505