In the field of reflective cracking initiation and propagation in pavement structures, an Accelerated Pavement Testing (APT) has been developed. The numerical method is also supported. Numerical results obtained by calculations made with the finite element CESAR-LCPC software are then compared with the experimental data. The reflective cracking APT experience is the first step in the development of a new laboratory equipment to evaluate the design of bituminous layers to repair pavements. The experiment was performed on a 30 m track where eight discontinuities were established by cutting-off the sub-bases in order to ensure a crack development in the bituminous layer. The conditions that promote crack propagation were reproduced by the application of heavy periodic loads using the Fabac ALT-APT test rig. The width of the bituminous layer was decreased to facilitate the observation of the crack propagation, while avoiding creep of the material.
The structure has a large number of sensors that measure longitudinal and transverse deformations at the bottom and at the surface of the bituminous layer. The deflections and the displacements are measured at several levels of the structure, as well as the temperature and the lateral edge cracking which is monitored by cracking sensors on both sides of the track.
Preliminary results on two joints were used to determine the mechanisms of rupture of the structure. Four more tests with improved sensors have completed the information. Experimental and numerical results are compared in order to validate the analysis of the fatigue process (debonding, damage and cracking) in full scale pavement. Previous article in issue. Next article in issue.
CESAR is a finite element software for structural analysis designed and verified by the IFSTTAR institute (formerly known as LCPC - Central Bridges and Roadworks Laboratory). Under continuous development since 1983 in order to meet civil engineering standards, CESAR is dedicated to underground works, civil works, soils mechanics, hydrogeology and environmental challenges.Since 2003, itech joined the software’s development team and brings its expertise in designing powerful and accessible user interfaces. Thus, the close collaboration between IFSTTAR and itech brings CESAR as a highly featured and professional software both in 2D and 3D.
Safety factor and Strength Reduction methodsThe results of a Finite Elements analysis (stresses, displacements fields) reflect the mechanical equilibrium of the model. However limit state or safety-factor analysis is often required for the design of geostructures. CESAR integrates:. the strength reduction method, also named “c-phi reduction”. It provides a safety factor against collapse,.
a limit analysis procedure by piloting the loading sets. It provides a safety factor against bearing capacity. DynamicsCESAR computes, by means of direct integration, the response of a structure submitted to a dynamic load; it enables proceeding with a step-by-step resolution of the dynamic equilibrium equation.Another methods consists of computing, by means of modal superposition (eigenvalues seeking is included), the response of a structure submitted to a dynamic load.
Two types of problems have been considered herein:. estimation of the maximum response by means of spectral computation (an SRSS- or CQC-type superposition),. computation of the full response. CESAR is equipped with a large set of CAD tools so that user feels comfortable as it is similar to his CAD software environment. Circles, lines, splines, NURBS, blocks.
Imports: DXF, LANDXML, STEP. Intersections: volume/volume, volume/surface, surface/surface, edge/edge. Operations: translation, rotation, symmetry, extrusion.Also, because several structures are suited for parametric design, we integrate assistance for the model generation, from geometry (tunnels as example) to results analysis. Our tools are based on XML files and PYTHON scripts.The workflow of CESAR has been designed so that user will easily have an overview of the model status: geometry, mesh, material properties, boundary conditions and loading sets.The “Tree view” window is the heart of the model. User will see here at once all the analysis carried on the model in the “Calculation tree”. He can also access and check the properties of the model in the “Data tree”. Finite Elements library.
Isoparametric displacement-type elements. Tetrahedron. Hexahedron, pentahedron. Beam elements. Shell elements. Contact elements. Truss elements.
Spring elements. Nodal special elements (heat transfer, damping.). Isoparametric diffusion-type elements. Exchange elements.
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Two-dimensional isoparametric elements with three degrees of freedom per node (two displacements, hydraulic load) for consolidation problems. Isoparametric elements with five degrees of freedom per node (three displace¬ments, pore pressure, temperature) for thermomechanical problems in porous media.