Key words
(English)
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shear stud, read bridges, assessment, structural safety, multiaxial fatigue, design codes, damage equivalent factor
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Key words
(French)
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goujon, pont-routes, évaluation, sécurité structural, multiaxial fatigue, normes et dimensionnement, facteur de correction
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Short description
(English)
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Shear studs are common connectors in steel-concrete composite bridges and, similar to other steel details, the fatigue limit state should be verified for this detail. However, little information about crack propagation or fatigue failure in this type of detail is available in the literature. The first part of this project is thus to gather relevant information on reported cases of damages in shear stud connections. Then, typical steel-concrete girder bridge cases will be selected for a detailed study. Time history analyses, due to passage of trucks over the bridge, will be carried out to obtain the normal and shear stresses in the stud detail subjected to fatigue. These analyses will allow defining the relevant stress patterns in the detail (proportional or non-proportional, multiaxial) and the stresses ranges levels. The simulation results will be compared to design codes verifications. Comparisons between the different verification methods, together with reported damage cases, will allow drawing conclusions on the relevance of shear stud fatigue failure during bridge service life and on shortcomings in fatigue design of shear studs.
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Short description
(French)
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Les goujons sont les connecteurs usuels utilisés dans les ponts-mixtes acier-béton et, de même que pour les autres détails en acier, ils doivent être vérifiés vis-à-vis de l'état limite fatigue. Cependant, peu d'informations sur la propagation de fissures de fatigue dans ce type de détail ou de rupture par fatigue est disponible dans la litérature. La première partie de ce projet est donc de recueillir des informations pertinentes sur des cas de dommages dans les goujons. Ensuite, des cas types de poutres de ponts mixtes acier-béton seront sélectionnés pour une étude approfondie. Ces cas seront analysés pour obtenir les histoires de chargement, provenant du passage des camions, et pour en déduire les contraintes normale et de cisaillement dans le détail du goujon soumis à la fatigue. Ces analyses permettront de définir les schémas types d’évolution des contraintes dans le détail (proportionnel ou non-proportionnel, multiaxial) et le niveau des différences des contraintes. Les résultats des simulations seront comparés aux résultats des vérifications avec les normes. Les comparaisons entre les différentes méthodes de vérification, ainsi que les cas de dommage signalés, permettront de tirer des conclusions sur la pertinence la possibilité de rupture par fatigue des goujons durant la vie des ouvrages et sur les lacunes dans la méthode de calcul en fatigue des goujons.
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Project description
(English)
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Introduction
In a design based on the SIA codes or the Eurocodes, engineers perform the fatigue verification of bridges using a simplified fatigue load model and the fatigue equivalent factors concept, which is represented by the ? factors. Fatigue equivalent factors are obtained for certain cases of bridge static systems considering S-N curves slopes. Since neither the calculations have been done using shear studs influence lines, nor the S-N curves of the shear stud with a slope of 8 (in shear) were applied, the fatigue equivalent factors in SIA 263 are not calibrated for shear studs. Furthermore, the current definition of the fatigue influence length is not applicable for shear studs. In both these two areas, improvements should be made in order to better represent reality. Fatigue equivalent factors are being studied in another research project, AGB-2007/004: Fatigue life assessment of road bridges with actual traffic loads. In addition to the project AGB-2007/004 objectives, this project will reuse the software DSUM-L and the outcome the fatigue influence length definition.
Damage cases
An important task in this project is to search for information regarding relevant published cases, as well as unpublished ones, in particular outside scientific journals, of damages in shear stud connections. This will be done by contacting, in different countries, authorities, construction companies, etc. Of the cases found, the ones linked with fatigue will be identified. This information will be used to help deciding which typical steel-concrete girder bridge cases to select for further analyses.
Simulations
The selection of typical steel-concrete girder cases will be made based on experience, fleet of existing road bridges and damage cases. Time history analyses of these typical cases, due to passage of trucks over the bridge, will be calculated to obtain the normal and shear stresses in the stud detail subjected to fatigue. Fatigue behavior of stud connection is complex because it is under shear range, due to the variation of the horizontal shear force between the slab and the girder, as well as normal stress range in the top flange of the girder on which the studs are welded. Moreover, the repeated applied loads due to the truck passage can result in either in-phase or out-of-phase forces variations (shear and normal) on the stud detail. For this, the traffic simulation program (WinQSIM [1]) and the software DSUM-L developed during the research project AGB-2007/004 will be used to simulate traffic over each bridge and determine fatigue damage sum (and fatigue failure probability) at end of service life. The problem is complicated since the concrete condition (uncracked or cracked) also changes the internal distribution of the forces. Different bridge girder cases, with different stud positions, will be modeled to find combined normal and shear stress histograms due to truck passages.
Code verifications
The stress differences resulting from the SIA 261 code fatigue load model will be computed. Using the S-N curves for the shear stud detail under normal and under shear stress ranges, the code checks from SIA 263 (separate checks for normal and shear) and from Eurocode 4-2 (both separate as well as interaction check) will be made.
Comparisons and conclusions Comparisons will be made between the design checks outcomes from the simulations (damage sums) and the design codes verifications. Together with reported damage cases, this will allow drawing conclusions on the relevance of shear stud fatigue failure during bridge service life and on shortcomings in fatigue design of shear studs.
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Expected findings/ usefulness, beneficiaries
(English)
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This project will allow gathering information about fatigue issues in shear studs. This project also provides an analysis of shear studs under road way traffic. Such knowledge will increase the understanding of fatigue behavior of shear studs and relevance of the problem in practice. It will also determine discrepancies in design of shear studs using different codes in comparison with detailed fatigue analysis. This project will serve as input to the relevant group within the general framework of the revision of structural Eurocodes in the period 2010-2014. At national level, it will also serve for future amendments of the design codes SIA 261, SIA 263 and SIA 264, as well as the series on assessment of existing structures, SIA 269.
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Methods
(English)
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The first method is to make a solid update of knowledge through literature (scientific journals as well as non-scientific publications such as ASCE civil eng. magazine, etc) to find damage cases. The state of knowledge will be supplemented by conducting an international inquiry (at authorities, companies, renowned experts). Also, the theoretical background of the codes implemented methods will be reviewed. The analysis of the typical cases will be done using a finite element program, which will be able both to model the interaction effect in shear studs, and to do the time history analysis. The categories of results will be selected based on the interaction phase of normal-shear stresses, level of stress, studs location and bridge type. The Monte-Carlo traffic simulation program (WinQSIM) will be applied to simulate the real traffic. The latest weight-in-motion (WIM) measurement of Switzerland will be used as a statistical traffic database in the software. In the damage software DSUM-L, the necessary modules will be developed in Microsoft C# to calculate fatigue damage sum especially for shear studs. The existing damage cases and analysis results will then be compared with SIA and Eurocodes design checks. Research will eventually supplemented by the theoretical development and decision support. This will also be validated by different applications.
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Special tools and infrastructure
(French)
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Néant, l’EPFL et le laboratoire dispos des moyens informatiques et logiciels nécessaires à ce travail
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Overview of research activities
(English)
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The combination of the two types of loading on the stud-plate-slab detail as to approach the real behavior is difficult and few tests have been performed. Other studies focused on shear resistance of studs under fatigue load. Jeong et al. [2] studied on static and fatigue behavior of the shear studs according partial interaction of steel and concrete. Oehlers [3] developed procedure that allows for calculation of strength reduction in shear studs in composite bridges due to applied fatigue loads. Lee et al. [4] investigated on static and fatigue resistance of large shear studs and compared their results with conventional design equation. Base on their results fatigue endurance of large shear studs slightly lower than design codes. Hanswille et al. [5, 6] gave analytical expressions to predict the fatigue life and strength reduction of shear studs depending on static strength and the peak load and the range of cyclic loading. Their tests results under constant amplitude have shown that the magnitude of peak load of the cyclic loading has a significant effect on the crack from occurring at the stud foot. Based on their results, evaluation of the tests with multiple block loading sequences on the basis of the linear damage accumulation according to Palmgren–Miner yields unsafe results. They also proposed improved Palmgren-Miner for damage accumulation of shear studs which considers effect due to crack propagation and local concrete damage. The fatigue resistance of shear studs in SIA 263 [7] code corresponds to following detail categories: 1) N 6 which considers effect of shear connectors on base material and 2) N 9 which is shear resistance of studs under shear stress. However, the verification does not consider the effect of multiaxial stress condition. Eurocode 4 [8] gives an equation for the interaction effect on shear connectors in addition to uniaxial controls in SIA. The equation limits linear summation of equivalent normal stress to normal strength and equivalent shear stress to shear strength to 1.3. This proposition is different of those in the IIW [9] and Eurocode for multiaxial fatigue [10].
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Overview of research activities
(French)
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Project aims
(English)
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The main objective of this project is to clarify the relevance and practical importance of the question of fatigue of the shear connection in steel-concrete composite road bridges. It is seen as the first but necessary step in studying this problematic. More precisely, this project will give:
– A compilation of information on reported shear studs damages and fatigue failures in steel-concrete connections
– The determination of internal forces and stresses histories acting on shear studs under realistic traffic loads
– Conclusions on the probability of shear stud fatigue failure during bridge service life and on shortcomings in code fatigue design of shear studs. If this mode of failure is found relevant, a second step is foreseen, with a new project to fill the knowledge gaps on fatigue strength of shear studs in steel-concrete composite beams under realistic multiaxial loading.
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Project aims
(French)
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L'objectif principal de ce projet est de préciser la pertinence et l'importance pratique de la question de la fatigue de la connexion par goujons dans les ponts-routes mixtes acier-béton. Elle est considérée la première, mais indispensable étape, dans l'étude de cette problématique. Plus précisément, ce projet permettra:
– La compilation des informations sur les dommages dans les goujons et les ruptures par fatigue dans les connexions en acier-béton
– La détermination des historiques d’efforts intérieurs et des contraintes agissant sur les goujons sous des charges de trafic réalistes
– Des conclusions sur la probabilité de rupture par fatigue des goujons durant la durée de vie des ponts-routes et sur les lacunes dans la méthode de calcul des normes pour la fatigue des goujons. Si ce mode de rupture se révèle pertinent, une deuxième étape prévue, avec un nouveau projet pour combler les lacunes dans les connaissances sur la résistance à la fatigue des goujons dans les poutres mixtes acier- béton sous un chargement multiaxial réaliste.
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Research agenda
(English)
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The research plan includes following tasks to be carried out within the year of the project.
1. State of the art (months 1 to 6)
Inquiries at authorities, construction companies, etc., a literature review and consultations with international experts will be performed to find information regarding damages in shear studs. The information gathered will be analyzed to find for each case the damage causes. The literature review will also be done to supply information needed in the other tasks.
2. Definition of bridge cases to be studied (months 4 to 5)
Typical bridge cases will be chosen to model and define internal stresses histograms in shear studs due to passage of vehicles. Obtaining the histograms for the cases at different positions of the studs, the results will be summarized in some categories. The extreme cases with higher degree of fatigue solicitation will be identified to focus the rest of study on.
3. Simulations (months 6 to 10)
3.1 Traffic simulations
For each defined typical bridges cases, the traffic will be simulated over the bridge using simulation program (WinQSIM [1]).
3.2 Damage computations
The damage sums at the end of the bridges service lives will be calculated using detailed realistic structural models of bridge girder with studs by adding necessary modules in the DSUM-L software developed during the research project AGB-2007/004.
4. Verifications using codes (months 7 to 10)
Design methods from SIA 263 and Eurocode 4 part 2 will be applied to perform fatigue verifications (under uniaxial stress ranges and interaction formulas).
5. Comparisons (month 11)
The results from tasks 3.2 (damage sums) and 4 (stress ranges) will be compared with fatigue obtained from real traffic simulations. Comparisons will be made in terms of fatigue lives and compliance degree.
6. Conclusions (months 11 and 12) The results will be reported according to the findings of all tasks. In case this mode of failure is found relevant, proposition for a continuation to fill the knowledge gaps on fatigue strength of shear studs in steel-concrete composite beams under realistic multiaxial loading will be made
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Transfer and application
(English)
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This research is practice oriented and should improve the fatigue design of structures. It will add some flexible modules in the software developed in the research project of AGB-2007/004 which make in capable of determining fatigue damage sum of shear studs. It will improve understanding of actual level of security, which results in designing more economical bridges and reduce inspection requirements
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Berichtsnummer
(German)
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661
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Berichtsnummer
(English)
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661
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Literature
(English)
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1. Meystre, T. and M.A. Hirt, Évaluation de ponts routiers existants avec un modèle de charges de trafic actualisé - VSS 594. 2006, Laboratoire de la construction métallique ICOM, EPFL: Lausanne.
2. Jeong, J., et al., Field and laboratory performance of a rectangular shaped glass fiber reinforced polymer deck. Composite Structures, 2007. 81(4): p. 622-628.
3. Oehlers, D.J., Design and assessment of shear connectors in composite bridge beams. Journal of Structural Engineering-Asce, 1995. 121(2): p. 214-224.
4. Lee, P.-G., C.-S. Shim, and S.-P. Chang, Static and fatigue behavior of large stud shear connectors for steel-concrete composite bridges. Journal of Constructional Steel Research, 2005. 61(9): p. 1270-1285.
5. Hanswille, G., M. Porsch, and C. Ustundag, Resistance of headed studs subjected to fatigue loading - Part I: Experimental study. Journal of Constructional Steel Research, 2007. 63(4): p. 475-484.
6. Jeong, Y.J., S.H. Kim, and J.H. Ahn, Partial-interactive behaviour of steel-concrete members under static and fatigue loadings. Magazine of Concrete Research, 2005. 57(5): p. 289-300.
7. SIA 263, Construction en acier. 2003, Société suisse des ingénieurs et des architectes: Zurich, Switzerland.
8. EN 1994-1-1 , Design of composite steel and concrete structures, in General rules and rules for buildings. 2004, European Committee for Standardization.
9. EN 1994-2 , Design of composite steel and concrete structures, in Bridges. 2005, European Committee for Standardization.
10. IIW document XIII-1965-03 / XV-1127-03, Recommendations for fatigue design of welded joints and components. 2005.
11. EN 1993-1-1, Design of steel structures in General Rules and Rules for Buildings. 2005, European Committee for Standardization.
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