Performance of Embedded Bolt Shear Connectors

A laboratory research program carried out at the University of Waterloo featured the testing of three large-scale steel-concrete composite beam specimens with embedded bolt shear connectors. A detailed assessment of the connector performance was made, facilitating a comparison with similar beams with welded stud connectors previously tested in the same laboratory. It is proposed that the embedded bolt detail may be viewed as a viable alternative to welded studs, given the observed favourable fatigue performance and ease of deconstruction. High cycle fatigue testing and economic analysis of material and installation costs are recommended. The benefits of this connection are particularly suited for precast composite construction. The performance of shear connectors in composite bridges is an increasingly important issue as new bridges are designed with accelerated construction and extended service lives in mind. Welded shear studs are currently the standard connector despite fatigue performance limitations. Fatigue concerns result in most bridges in North American requiring more than double the number of studs needed for ultimate strength purposes. This leads to high material costs and construction challenges, particularly for precast construction. High strength bolt shear connectors may be a viable alternative to shear studs, providing greater fatigue resistance and having higher material strengths than conventional welded studs.

Connexions par adhérence pour les ponts mixtes acier-béton

Michel Thomann

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.

EPFL2005

Etude du comportement réel des ponts mixtes et modélisation pour le dimensionnement

Construction methods for steel-concrete structures have developed significantly over the last quarter of a century, and the number of steel-concrete bridges on road and rail networks is continually increasing. However, design methods for bridges have not evolved to the same extent as those for buildings and are not completely adapted to the limit state concept. Furthermore, the behaviour in service of steel-concrete bridges is raising questions about requirements for deck slabs (durability, cracking) and about design models applicable in this domain. The main aim of this research was to study the behaviour of steel-concrete composite bridges and to propose a model for the verification of structural safety. Objectives of the research were : measurement and numerical simulation of the influence of actions on the behaviour of steel-concrete composite bridges during construction and in service in order to analyse the effectiveness of methods for improving this behaviour, analysis of steel concrete composite bridge behaviour at the ultimate limit state and proposals for simplifying design. The research progressed in the following order : Serviceability detailed study of the behaviour of young concrete, analysis of different types of prestressing and prestressing losses over time, synthesis of the various causes of tensile stresses in deck slabs and proposa1 of design criteria as a function of structural properties and deck behaviour requirements. Structural safety critical evaluation of current design methods and possibilities for the plastification of sections, definition of limits for plastic design as a function of the type of bridge, and analysis of the influence of time-dependent effects in the concrete on the behaviour at the ultimate limit state. For the serviceability limit state, a study of the actions that create tensile stresses in deck slabs led to the determination of the principal parameters influencing the formation of transverse cracks. The restraint coefficient β, defined as the ratio of steel beam and concrete cross-sectional areas, was shown to be the key parameter for evaluating the probability of cracking with time. Methods for limiting the tensile stresses in the slab were analysed and compared as a function of the type of bridge. For the verification of structural safety, a study of the actual behaviour of steel-concrete composite sections led to the justification of using plastic design calculations in order to determine the resistance of midspan sections. Limits for the application of this approach were defined, and simplified methods for considering imposed deformations such as shrinkage and temperature effects were proposed.

EPFL1997

Connexions par adhérence pour les ponts mixtes acier-béton

Michel Thomann

EPFL2005

Etude du comportement réel des ponts mixtes et modélisation pour le dimensionnement

EPFL1997