Résistance au déversement des poutres métalliques de pont

Steel and steel-concrete composite bridges made of plate girders represent an economical structural form and are largely used for short and medium spans. Two parallel plate girders connected by cross-beams define a twin-girder bridge. This type of bridge transfers the loads from the deck to the supports essentially through bending and shear of I-girders. Associated with the two resistance modes are the following instability modes: lateral torsional buckling (LTB) and local buckling. Design experience of steel bridges made of plate girders shows that LTB determines the dimension of the upper flange of an I-girder at mid-span during construction phase, and the dimension of the bottom flange next to the intermediate supports during construction by launching or in service. In practice, LTB verification is carried out using reduction curves (i.e. buckling curves) which decrease the resistance of a beam with respect to the sensitivity to LTB; thus, the more sensitive the beam, more severe the reduction. A comparison of different standards shows reduction curves available for steel bridge girders have non-negligible differences which can reach 30 % of the resistance. A more refined study of the buckling curves shows that it is semi-empirical in nature, where the empirical part is mainly based on numerical and experimental research for building sections. These findings justify the goal of this thesis which is to propose a verification method for LTB that better takes into account the special features of bridge girders. To reach this goal, study of parameters that influence LTB, like re-sidual stresses, geometric imperfections, cross-beams, loading and beam geometry, is required. In this research, the experimental studies carried out on the residual stresses propose a new model which takes into account flame-cutting and welding of thick plates used in the fabrication of steel bridge girders. Experimental measurements of geometric imperfections performed on real bridge girders show the difference between fabrication tolerances and imperfections measured. These results are then used as input data for numerical simulations of LTB by two approaches: beam and bridge. The beam approach, which considers a simple span I-girder with fork support and a constant bending moment, reveals that the influence on the resistance to LTB can reach 10 % for the residual stresses and 12 % for the geometric imperfections. The bridge approach, which considers a twin-girder bridge with cross-beams and a constant load on the upper flange, shows that the influence reaches 17 % for cross beam spacing and 27 % for the type of cross-beams (frame, truss, diaphragm). Based on the experimental and numerical results, a design method for LTB is proposed. It recommends the use of reduction curve c for SIA263:2013 or reduction curve c of Eurocode EN1993-2:2006.

Composite action of FRP bridge decks adhesively bonded to steel main girders

Herbert Gürtler

Up until today reinforced concrete has been used in most cases for the manufacturing of bridge decks. Depending on the quality of the work carried out, defects can already occur after only a few years. These defects mostly appear in the form of corrosion of the steel reinforcement due to concrete's sensitivity to de-icing salts and water. To reduce maintenance costs, which are mainly caused by corrosion of the steel reinforcement, attempts were made to eliminate the steel reinforcement in the bridge deck. This was achieved for example by replacing the whole concrete bridge deck with an FRP1 bridge deck. FRP bridge decks, besides the advantage of the absence of steel reinforcement, exhibit the advantage of a low dead load (approx. 20% of a comparable concrete deck) combined with high strength. These properties resulted in the fact that today more than 200 bridges with FRP decks are in service worldwide. Most of them need steel or concrete main girders to bridge the required span. Despite the many bridges already in service, assessment of their load-bearing capacity or deflections still remains difficult. Some of the reasons for this this are as follows: Geometry and material properties vary considerably between different FRP bridge-deck types. The problem of the connection between main girders and bridge decks has only been partially solved. No design method exists which allows determination of the stresses and deflections of composite girders, and takes the degree of composite action of the bridge deck into account. This thesis contributes to solve these problems. Experiments with two different bridge decks were carried out in order to determine the necessary system properties (in-plane compression and shear resistance and in-plane compression and shear stiffness) for the calculation of the load-bearing behavior of steel/FRP composite girders. The method developed to determine the system properties can also be applied to other FRP bridge decks (e.g. sandwich decks). In a second step, four composite girders (two with each bridge deck) were manufactured by bonding the bridge decks onto conventional steel girders. Local failure of the bridge deck, as occurs in girders with stud or bolt connections, is therefore prevented and a clear load transfer in the joint is assured. One of the two girders, with each bridge deck system, was tested statically and the other statically and under fatigue loads. The results of the girder experiments showed that adhesive bonding is a reliable connection technique, since failure always occurred first in the bridge deck and then in the adhesive layer. The stiffness and failure load of the composite girders could be increased considerably in comparison with the pure steel girder. The determined system properties concerning in-plane shear and compression stiffness were confirmed with the girder experiments. The results of the experiments with the composite girders were compared with results of an analytical design method for concrete/wood girders adapted for steel/FRP composite girders. It was shown that the load-bearing behavior of composite girders consisting of steel main girders and adhesively- bonded FRP bridge decks can be determined with good accuracy in the linear-elastic region. Furthermore a design method was developed which allows the loadbearing capacity of the steel/FRP composite girders investigated in this thesis to be determined with very good accuracy. Subsequently a parameter study was carried out in order to verify the assumption of full composite action in the adhesively- bonded joint. This is one of the requirements for application of the developed design methods. The study showed that the assumption is applicable for different adhesives and even for thicknesses up to 50 mm. ---------------------------------------- 1 Fiber Reinforced Polymer

EPFL2005

Comportement dynamique des dalles de roulement des ponts en béton sollicités par le trafic routier

The management of a network of existing road bridges involves interventions in order to maintain safety and the priority of these interventions is often determined by safety criteria. During the evaluation of safety, the dynamic effect of traffic actions is considered using equivalent static loads determined by multiplying the effect calculated using traffic load models by a dynamic amplification factor. During the evaluation of a deck slab, the application of inappropriate dynamic amplification factors could have significant financial implications, all the more since the local dynamic effects of overloaded trucks are determinant for this type of structural element. Dynamic amplification factors defined in codes have usually been derived from the measurement of global traffic action effects in the main structural elements of bridges. Unfortunately, local dynamic effects in deck slabs have not been studied in detail until now. A better understanding of the dynamic behaviour of deck slabs will lead to the definition of more accurate dynamic amplification factors and avoid the use of values that are too conservative. The behaviour of deck slabs of six typical Swiss highway bridges has been simulated in order to study their dynamic response during the passage of trucks. The structural arrangement of the deck slab was different for each of the six bridges. A parametric study was based on the simulation of various scenarios involving the passage of trucks for various combinations of speed, path and road surface roughness. Deck slab response was obtained by numerical simulation based on models of the bridge, truck and road surface. This system was resolved using a prediction - correction algorithm that considers the dynamic interaction between a bridge and trucks. Dynamic amplification factors were subsequently calculated from strains and deflections obtained from independent static and dynamic simulations. The simulation of numerous scenarios enabled the evaluation of the influence of different parameters on the dynamic response of a deck slab: The road surface roughness was found to be one of the most important parameters, with an increase in roughness leading to an increase in dynamic amplification factors. An overloaded truck produces a lower dynamic amplification factor in a deck slab than an empty truck. The truck speed influences the dynamic interaction, but a clear relationship between speed and dynamic amplification factor could not be identified. The maximum dynamic amplification factor does not vary significantly from one point to another over a deck slab in a girder bridge. The structural arrangement of a deck slab in a girder bridge has little influence on dynamic amplification factors. Overall, the different deck slabs on the girder bridges studied were all equally sensitive to the dynamic effects of road traffic. In many cases considered for the framed slab bridge, the maximum dynamic amplification factor was found to occur over the supports. For such bridges, the sensitivity of the deck slab to the dynamic effects of road traffic is not uniform. Finally, two approaches to evaluating deck slabs of existing road bridges are proposed. The first approach is only applicable in certain situations and involves a simplified evaluation using an updated traffic load model and a dynamic amplification factor. In situations where a simplified evaluation is not applicable, the second approach is to evaluate a deck slab using numerical or experimental analyses.

EPFL1999

Modeling of through-thickness stress state in adhesive joints connecting pultruded FRP bridge decks and steel girders

Thomas Keller, Martin Schollmayer

The through-thickness performance of adhesive joints connecting pultruded FRP bridge decks and steel girders subjected to loading in the transverse bridge direction was investigated. Deck-to-girder adhesive joints can be assumed as being loaded by uplift forces only (and not by additional bending moments) if the adhesive layer has a minimal thickness of approximately 10 mm. If possible, however, steel web stiffeners should not be connected to the upper flange in order to allow free flange rotation. The tensile stress distribution in the adhesive joint is non-uniform with high stress concentrations below the FRP webs of the cellular deck and above the steel girder web. Alternately inclined deck webs cause significantly higher stresses below the vertical webs. An analytical model allowing the calculation of a representative approximation of the complex uplift stress state in the joint is proposed and validated by numerical and experimental results. Based on this model, a design method for adhesive joints connecting FRP decks and steel main girders can be established. © 2009 Elsevier Ltd. All rights reserved

2009

Composite action of FRP bridge decks adhesively bonded to steel main girders

Herbert Gürtler

EPFL2005

Comportement dynamique des dalles de roulement des ponts en béton sollicités par le trafic routier

EPFL1999