Abstract
Abstract. The present paper is concerned with the elastic design optimisation of continuous composite beams. This optimisation is based on the analysis of the beam in the inelastic range including the concrete creep and shrinkage, the tension stiffening and temperature difference effects as well as the possible local buckling instability. The finite ele-ment program PONTMIXTE (adapted to study continuous beams at real scale with short time computation) is first presented with its different sections: Pre-design (in accordance with Eurocode specifications), Non linear finite element calculation and Post-processing. In order to validate the proposed model, the numerical calculations are compared against experimental results from tests on a two-span beam in reduced scale (7.5 m length for each span) without taking into account the local buckling phenomenon avoided in the experimental test by using web-stiffeners. Next, special attention is paid to study the influence of the local buckling instability on the internal moment redistribution coefficient between hogging and sagging zones. The application concerns different 3-span beams of bridge at real scale with medium span lengths (40–60–40 m). The post-buckling behaviour represented by moment-rotation curves (M-θ) is deduced from a 3D finite element model of the cross-section developed using Castem finite element code. The M-θ curves describing the local buckling phenomenon are approximated using hyperbolic functions and implemented in PONTMIXTE using a specific rotational spring finite element. The influence of this instability on the moment redistri-bution coefficients calls the Standart predictions into question.
Highlights
Steel-concrete composite structures are common practice today in bridges and industrial buildings
This study attempted to show that it is possible to simulate at a real scale the inelastic behaviour of a steel-concrete composite bridge beam with the proposed finite element (FE) formulation
A hyperbolic model was proposed involving three parameters: the buckling point (Mv, θv) and the horizontal asymptotic line M = M0. This model was implemented in the code PONTMIXTE and several numerical simulations were carried out to show the significant influence of the local buckling instability on the moment redistribution coefficient from hogging to sagging zones in the case of a 3-span beam bridge at real scale
Summary
Steel-concrete composite structures are common practice today in bridges and industrial buildings. Depending on the hogging cross-section class, the prEN 2003 – Eurocode 4: Design of Composite Steel and Concrete Structures – Rules for Bridges – Part 2, Stage 34 Draft Revised, give the max moment redistribution coefficient allowed in the case of cracked or uncracked elastic global analyses, so the knowledge about the influence of some phenomena in the inelastic range on the proposed values can reduce significantly the costs. Porter et al (1975) assumed that the failure will occur when a certain region of the web yields as a result of the combined effect of the inclined tensile membrane stress field and the web buckling stress It appears that the combined rigidity of compressed flange and the web, for a steel panel under negative bending moment, remains the first parameter influencing the load carrying capacity of the cross-section. Guezouli et al Local Buckling Influence on the Moment Redistribution Coefficient
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