Connexions par adhérence pour les ponts mixtes acier-béton

Abstract

When building new bridge structures, or widening or replacing existing bridges, the duration of on site work has a significant influence not only on the costs, but also on the potentially harmful effects (noise, pollution, traffic jam, deviation) of the construction work. Thus, it is of interest to design structures in such a way as to minimize the construction time. Steel-concrete composite bridges are ideal for this purpose: the steel beams may be welded and the concrete slab precast in the shop, leaving only the erection and assembly work to be performed on site. Currently, however, the steel-concrete connections used in composite bridges are not well adapted for the use with precast slabs, as they tend to slow down the assembly work and decrease the durability of the slab. Consequently, there is a need to develop new types of connections. Connections by adherence, whose resistance is due to friction between the various interfaces, constitute a very promising solution to this problem. The current state of knowledge is incomplete, however, and should be improved in order to make the use of connections by adherence possible in practice. The goals of the research presented herein are to evaluate the practical value of connections by adherence, to develop analysis method and tools making it possible to predict their behaviour and to propose a design method for composite beams employing connections by adherence. To achieve these goals, the requirements that must be met by connections in steel-concrete composite bridges are first defined. Then, the behaviour of connections by adherence is studied in the following steps: - model the behaviour of confined interfaces loaded in shear with the help of experimental and analytical studies, - study the mechanical behaviour of connections by adherence, and especially their deformation behaviour, with the help of push-out tests, - create and validate an analysis tool that makes it possible to predict the behaviour of connections by adherence, - use this model in a parametric study to obtain results to be used in the development of a simplified design method capable of predicting the ultimate shear resistance, - develop and validate a design method for steel-concrete composite beams with connections by adherence. Finally, a comparison between the requirements defined at the beginning of the study and the calculated or measured characteristics of connections by adherence is performed. This makes it possible to evaluate the practical value of these connections and to define the needs for further research. Several important conclusions are drawn from this work. First, it is shown that connections by adherence meet the specified requirements of robustness, economy and reliability. Their high longitudinal shear resistance and stiffness ensure excellent static behaviour, both under service and ultimate loads. Secondly, it is demonstrated that the behaviour of these connections may be explained and modelled with the help of laws governing the behaviour of confined interfaces loaded in shear. The confinement is due partially to the strong interaction existing between the different interfaces and partially to the effect of the concrete slab around the connector. Finally, it is shown that, although a plastic calculation of the shear forces along the bridge axis can not be performed with these connections, it is possible to perform a plastic design of the cross section provided that the consequences of this calculation on the elastic longitudinal shear force distribution are taken into account. The work carried out in this thesis has made it possible to propose design tools for composite beams with a connection by adherence. Those tools, scientifically founded, should help to increase the use of such connections in practice.