Experimental investigation of a keying joint cast in UHPFRC between precast UHPFRC bridge elements

Numa Joy Bertola, Eugen Brühwiler, Enrique García, Ngoc Thanh Trinh
2022
Article

Résumé

Ultra High-Performance Fiber-Reinforced Cementitious Composite (UHPFRC) is increasingly popular for new structural designs thanks to its high resistance both in tension and compression. When UHPFRC is complemented with steel reinforcing bars or prestressing tendons, the structure remains waterproof and crack-free under service conditions, significantly improving the durability compared to conventional reinforced-concrete designs. The Aiguillon Bridge is one of the first railway bridges entirely made of UHPFRC. Built in 2021 in Switzerland, this bridge has a single span of 6.6 m and a width of 5.4 m. The bridge is designed for a narrow track and 2 walkways. Two prefabricated elements in UHPFRC have been assembled on-site by a longitudinal cast-in-place UHPFRC keying joint. This paper presents the full-scale laboratory experiment to validate the keying joint suitability for railway bridges. This experimental investigation involves a static test on a transverse beam composed of two precast elements and the keying joint. Results show that the structure presents a post-peak ductile behavior as well as an elastic behavior under service loads. Digital-Image-Correlation measurements provide details on the cracking patterns of the interface between the keying joint and the precast elements. As the maximum resistance obtained during the experiment is in agreement with the analytical-model predictions, the concept of the keying joint is validated.

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https://infoscience.epfl.ch/record/292866?ln=fr

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Numa Joy Bertola, Eugen Brühwiler, Enrique García, Ngoc Thanh Trinh
2022
Article

Résumé

Official source

https://infoscience.epfl.ch/record/292866?ln=fr

À propos de ce résultat

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Assessment of Shear Strength for Existing Bridges with Low Amounts of Shear Reinforcement

Miguel Fernández Ruiz, Aurelio Muttoni, Michael Markus Rupf

Design of concrete girder bridges has significantly evolved during the last decades. This has been particularly relevant with respect to shear design, motivated by changes in actions and design models. As a consequence, assessing the shear strength of existing bridges leads in many cases to unsatisfactory safety levels. Furthermore, many existing bridges do not comply with current code regulations with respect to minimum amounts of shear reinforcement. This situation can lead to expensive retrofitting and strengthening of a significant number of existing bridges. The assessment of the shear strength of these bridges has thus become a significant task for structural engineers. Design codes are not always appropriate for assessing the strength of existing bridges. They propose safe models providing sufficient accuracy for design of a wide number of structures. However, these models do not account for some particularities of prestresses bridges and neglect a number of shear-transfer actions that can be relevant for their strength. This is typically the case of shear carried by the inclination of the compression chord, the increase of the stress in the tendons or the effective strength of concrete in the web of cracked prestressed girders. Accounting for more realistic approaches for these parameters may significantly increase the estimated strength of a structure with respect to code provisions, avoiding in many cases unnecessary retrofitting or strengthening. In this paper, the results of a tests campaign carried out at Ecole Polytechnique Fédérale de Lausanne on 10 prestressed concrete girders (10 meters long, 0.78 m high) are outlined. The specimens were provided with very low amounts of shear reinforcement and some of them present defective stirrup anchorage to simulate realistic conditions of existing structures. The experimental results are discussed with reference to the stress field method where the role of the different shear-transfer actions is investigated and compared to current code provisions.

fib Symposium Tel-Aviv 20132013

Chargement

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

Chargement

The aim of this thesis is to provide rational engineering methods for the fatigue safety examination of existing railway bridges. Increasing railway traffic loading and enhanced structural analysis allow for higher exploitation of the capacity of bridge elements. This implies that increasing action effects due to higher service loads may become fatigue relevant in the future. The application of the results allows for more precise fatigue examinations. As beneficial consequence, most railway bridges may be operated safely in the future without costly strengthening measures. Calculated stress ranges in the reinforcement that governs the fatigue resistance of structural elements are too high when using conventional resistance models. The load carrying contribution of non-structural elements and a not entirely developed crack pattern lead to fatigue relevant reduction of the stress range in the rebars. A theoretical study shows that reductions of 5 – 15 % may be obtained by considering the composite effect of the continuous rail grid. Measurements of the dynamic traffic effects were conducted on a single-track bridge. The effects of passenger and freight trains at different velocities on the structural response were measured. The results are interpreted based on the observed vertical shape of the railway track. The observed dynamic behaviour could be correctly represented by simulations using simple dynamic models. The effect of other velocities and in-creased carriage loading degrees are investigated in a parametric study. The findings of previous investigations for road bridges and the investigations of this research work for railway bridges show that the Dynamic Amplification Factor (DAF) decreases for increasing loadings. Thus, smaller DAFs are applied for fatigue relevant causing heavy vehicles. Fatigue stress ranges may be reduced by supplementary 3 – 6 %. A method based on Linear Elastic Fracture Mechanics theory is presented for fatigue life determination. Fatigue life typically is very sensitive to different calculation parameters, rendering the calculation of a reliable fatigue life difficult. The refined analysis of fatigue tests reported in literature allows better understanding of the fatigue behaviour of bridge elements. Thus, a fatigue safety concept is established that compensates the inconvenience of the high sensitivity of fatigue life calculations. This fatigue safety concept is based on the observed load carrying behaviour of inspected bridge elements. The specific fatigue behaviour with visible signs allows for the examination of fatigue safety in a pragmatic way. Specific inspection of bridge elements becomes pertinent as soon as general examinations exhibit an insufficient fatigue resistance. Fatigue behaviour of Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) is characterised by increasing deformations during cyclic tensile loading. Under a maximum tensile stress level of 4 MPa the deformation of the UHPFRC layer becomes stable during cyclic loading. For slightly higher stresses, the deformation increases and the UHPFRC layer fails due to steel fibre pull out. Application of the UHPFRC layer in the flexural tension zone considerably reduces the fatigue stresses in the steel reinforcement. As the UHPFRC layer deforms, the stress range in the reinforcement is effectively and permanently reduced and may remain below the nominal fatigue limit. For design of members with a layer of UHPFRC for waterproofing and fatigue strengthening, the maximum allowed strain for stable behaviour under tensile fatigue loading should be verified.

EPFL2008

Chargement

Assessment of Shear Strength for Existing Bridges with Low Amounts of Shear Reinforcement

Miguel Fernández Ruiz, Aurelio Muttoni, Michael Markus Rupf

fib Symposium Tel-Aviv 20132013

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

EPFL1997

EPFL2008