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

EPFL, 1997
Thèse EPFL

Résumé

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.

Official source

https://infoscience.epfl.ch/record/32215?ln=fr

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Concepts associés

Chargement

Publications associées

Chargement

EPFL, 1997
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/32215?ln=fr

À propos de ce résultat

Concepts associés (14)

thumb|upright=1.0|Un mètre cube de béton (représentant la production mondiale annuelle de béton par habitant). Le béton de ciment, couramment appelé béton, est un mélange de ciment, de granulats, d'e

vignette|upright|Les grues sont essentielles pour des travaux importants tels que les gratte-ciel. La construction est le fait d'assembler différents éléments d'un édifice en utilisant des matériaux

Limit State Design (LSD), also known as Load And Resistance Factor Design (LRFD), refers to a design method used in structural engineering. A limit state is a condition of a structure beyond which it

Afficher plus

Concepts associés

Chargement

Publications associées (63)

Publications associées

Chargement

Development of a consistent approach for design and assessment of structural concrete members using stress fields and strut-and-tie models

Filip Niketic

Designing new concrete members and assessing the strength of existing elements subjected to in-plane stress state conditions is often conducted by means of Stress Fields (SF) and Strut-and-Tie Models (STM). These methods are usually accounting for identical load-carrying mechanisms for design and assessment, even if the goals for these two tasks are not the same. When designing new elements, the aim is to obtain solutions that are in equilibrium with external actions, with simple reinforcement layouts while ensuring satisfactory behaviour at serviceability limit state. When assessing the ultimate strength of existing elements, the goal is to avoid an unnecessary strengthening and limit the amount of retrofitting. The required complexity of assessment models depends on the strength requirements, and need to be gradually refined if the results from current models prove to be insufficient. This refinement process ultimately leads to increasingly more exact solutions that eventually correspond to the largest possible strength according to the limit analysis. This thesis presents various strategies which can be employed to develop SF and STM suitable for the design and assessment of structural concrete members. The idea of a gradual model refinement (both for design and assessment) is introduced through practical examples, while potential challenges related to each solution are indicated and discussed. Moreover, the accuracy and the generality of exact solutions obtained using Elastic-Plastic Stress Fields (EPSF) are investigated. To do this, ultimate loads estimated with EPSF are compared to test results found in the literature. To facilitate further studies by other researchers, they are available online. The analysis of structural members with insufficient anchorage and indirectly supported concrete elements with EPSF are presented and discussed. Furthermore, this thesis focuses on a sensitivity analysis of the EPSF, to investigate the stability of the results as a function the size, shape and orientation of the finite elements. The influence of the number of iteration steps on the accuracy of EPSF models is evaluated, and clear recommendations are provided. Stress fields based on exact solutions of the theory of plasticity simulate the physical behaviour of structural concrete members more accurately than current code provisions. On this basis, a procedure for tailoring partial safety factors for steel and concrete is presented and discussed. Reduced PSF could potentially be used when assessing the strength of existing reinforced and prestressed concrete elements, which would (could?) lead to significant cost reductions in the field of structural maintenance. To better understand the mechanical origins of concrete compression softening (important for an accurate application of stress fields), a mechanical model for estimating the effective concrete compressive strength is developed and discussed. Concrete cover spalling, concrete crushing and crack sliding are taken into account. Special attention is given to the dowel action of the reinforcement and its effects on the surrounding concrete matrix. The model is validated using experimental results found in literature. Finally, the pertinence of existing semi-empirical approaches for determining the effective concrete compressive strength is evaluated and discussed.

EPFL2017

Chargement

The reduction of green-house gas emissions is one of the global challenges that our society is facing and the production of cement plays a major role because concrete is the most used material worldwide. For every 1000 kg of cement produced, 900 kg of CO2, are released in the atmosphere. In addition, for structural concrete, the generous concrete cover, prescribed by current codes of practice, yields to robust but also to relatively heavy and massive members. Textile Reinforced Concrete (TRC) is a novel building material made of high-strength fabrics embedded in a fine grained mortar matrix. The implementation of non-corrosive reinforcement materials allows to reduce drastically the concrete cover requirements. That empowers to cast extremely thin-walled structural elements and to reduce the structural dead-load up to 90 % (with respect to conventional Reinforced Concrete). In addition to substantial material savings associated to the structure and its foundations, low-clinker-content cements can be used, since no passivation of the reinforcement is required. That, reduces further the environmental footprint and allows to build more sustainable load-bearing structures. Despite its advantages, TRC is hardly implemented in current engineering practice. On one hand there is a lack of design regulations, but on the other, there is also a shortage of construction experiences. With the aim to promote the widespread of TRC, this work addresses both hurdles at three different levels of analysis: First, the tensile response of TRC is investigated by means of an extensive experimental programme. It includes, tests on bare fabrics, the plain mortar and composite tension ties. On the basis of the experimental observations and the coaxial ring analogy, a mechanical model has been derived, allowing to predict the deformation capacity and resistance in a unified manner. That is fundamental to understand the effects of fabric-coating, impregnation, tie- and load introduction length on the load-bearing behavior at a micro-level. More complex loading conditions have been investigated at a meso-scale. Full-scale load tests of thin-walled flanged members have been instrumented with external photogrammetric measurements. These have allowed to validate and adapt the Elastic-Cracked-Stress-Field approach for TRC linear members. The method allows to model beam- and discontinuity regions in a comprehensive manner as well as predicting the response under serviceability conditions and at failure in a unified way, while accounting for both, bending and shear. Finally, the application potential of TRC is addressed at a macro-level. Starting from previous ferrocement works, different formworking materials, casting methods and connections of thin walled members have been explored. The obtained results have been condensed to design, build and erect a full-scale, demountable, prototype pavilion within a three-weeks workshop. Eventually, a proper architectural language has been derived for light-weight structures made of thin-walled TRC members. The structural design can be performed in a comprehensive manner with the Elastic-Cracked-Stress-Field approach, while the resistance of the composite can be estimated with the coaxial ring model. That contributes to the development of code-like prescriptions for TRC and its future implementation in common construction practice for sustainable structures.

EPFL2020

Chargement

Comportement et modélisation des éléments de structure en béton fibré à ultra-hautes performances avec armatures passives

Dario Redaelli

The present research improves the experimental and theoretical knowledge on the behaviour of structural elements made of ultra high performance fibre reinforced concrete (UHPFRC) with ordinary reinforcement. UHPFRC is a recently developed material with much higher mechanical properties and durability than ordinary concrete. However, it has been used so far in a limited number of structural applications. A better knowledge on the behaviour of UHPFRC in structural members is needed to be able to take advantage of its outstanding properties in structural design. One of the ways in which the structural efficiency of UHPFRC can be studied is to investigate the improvement in structural performance that is gained by using UHPFRC instead of ordinary concrete in common structural members. As an alternative, new structural shapes and structural concepts can be explored, more adapted to the specific material properties. The work presented in this thesis focuses on the first approach by considering the behaviour and modelling of UHPFRC structural members loaded in tension and in bending with axial load, and reinforced with ordinary steel reinforcement. The experimental and theoretical study carried out on tensile members contributes to the understanding of the fundamental mechanisms that control cracking of a tensile member reinforced with both fibres and bars, in service and at ultimate. A numerical model has been developed to solve the differential problem of bond in the presence of strong mechanical non linearity. This model has been used to simulate the main aspects controlling bond in a UHPFRC member. The results obtained with the model help in clarifying the differences between cracking in ordinary concrete and in UHPFRC ties. The model allows identifying the parameters that influence the strength and ductility of the tie and was used to validate simplified assumptions to model the behaviour of UHPFRC ties in service. The behaviour of columns has been studied with a theoretical and experimental approach. The results of two test series on UHPFRC and HPFRC columns are reported in the thesis. An analytical model has been developed to study the behaviour of a confined concrete member in compression. A numerical model has been implemented to simulate the non linear behaviour of ordinary concrete and UHPFRC columns. The models have been used to simulate test results reported in this thesis or taken from the literature. The numerical model has been used to evaluate the effect of variations of the mechanical behaviour of concrete on the structural behaviour of a column, with or without reinforcement. The results of those parametrical studies help understanding the influence of mechanical properties on structural response. This thesis contributes to a better understanding of the behaviour of UHPFRC members with ordinary reinforcement. The comparative approach used in the research makes it possible to show the differences between the structural behaviour of ordinary, high strength and fibre reinforced concrete. Indications are also given on the possible ways in which an effective use of UHPFRC in structural members can be achieved.

EPFL2009

Chargement

Development of a consistent approach for design and assessment of structural concrete members using stress fields and strut-and-tie models

Filip Niketic

EPFL2017

Comportement et modélisation des éléments de structure en béton fibré à ultra-hautes performances avec armatures passives

Dario Redaelli

EPFL2009

EPFL2020