Amelie Outtier

Determining geometric out-of-plane imperfections in steel tied-arch bridges using strain measurements

The structural behavior of steel tied-arch bridges is determined by the presence of a large compressive force. As a consequence, slender steel arches are highly sensitive to in-plane as well as out-of-plane buckling. At present, no specific buckling curves for out-of-plane buckling exist for nonlinear or curved elements in the international codes and calculation methods. This research is mainly concerned with quantifying the geometric imperfections of real arch bridges based on the results of on-site strain measurements. The arches of six bridges have been equipped with strain gauges along their entire length. For the actual determination of the imperfections, a detailed finite-element model has been developed. It is assumed that the actual geometric imperfections are a linear combination of a number of theoretical imperfections. These imperfections are characterized by a theoretical lateral displacement in a single cross section of the arch. The influence of these theoretical imperfections can be calculated using the described finite-element models. The actual imperfections are determined based on the comparison of measured strain values with the strain values based on a linear combination of theoretical imperfections. This method is verified using the results of topographical measurements of one of the studied bridges. Both sets of results are in agreement when it comes to size and shape of the imperfections. The shape of the resulting geometric imperfection is a half-sine wave for most of the studied bridges. However, the most important result is that for all considered bridges, the size of the imperfections is substantially smaller than the one predicted by design codes.

Application limits for continuously welded rails on temporary bridge decks

The possibility of omitting rail expansion devices from the track configuration, when continuously welded rail is continued over temporary bridge decks, is investigated in detail. More specifically, the related rail track to temporary bridge interaction phenomena are analysed using finite element modelling. A first parametric analysis assesses the additional rail stresses due to moving trainloads and temperature variations, based on stipulations provided in the unit identification code 774-3R. In addition the model is expanded to a more complex structure that is able to simulate the buckling behaviour of the rail track using non-linear methods. Using this model, a second parametric study is performed in which only thermal loading is considered. This allows for determining the parameters, which are predominant in determining the critical buckling temperature of the rails, and for assessing the magnitude of the safety margin necessary, when it comes to thermal buckling of the rails and the temporary bridges. It can be concluded that, depending on the magnitude of two main factors, the lateral ballast resistance and the amplitude of the initial track misalignment, a considerable reduction of the track stability might arise. Therefore, a minimal characteristic lateral ballast resistance of 4 kN is recommended along with a maximal allowable misalignment amplitude of 7 mm has to be prescribed when thermal track buckling has to be considered in the design.

Weld Penetration in Orthotropic Steel Bridges

This paper reports the results of experimental research concerning the connection between the deck plate and the web of the longitudinal stiffeners in an orthotropic plated bridge deck on a microscopic scale. An important number of test specimens of a weld are studied with the help of a video microscope, to detect the efficiency of the root of the weld. The second part of the paper is concerned with parametric analysis of the lack of weld penetration by using accurate finite element modeling. The results demonstrate that the weld quality often required cannot always be assured, which surely has important consequence on the stresses in the weld and the fatigue resistance.

Efficiency assessment of CFRP laminate reinforcement of a partly deficient post-tensioned fly-over

Immediately after construction, five spans of a newly built concrete fly-over showed insufficient concrete resistance. Carbon fibre reinforced polymer (CFRP) laminates with little compression stiffness were glued to the lower surface of the superstructure to strengthen the concrete slab decks. After installing, assessment of this reinforcement was made by a first loading test, during which concrete strain measurements with wireless gauges were carried out. In addition, the fundamental frequencies have been determined by accelerometers and impact excitation of the viaduct. Comparing the results from these tests on acceptable and deficient decks confirms the insufficient concrete quality of the suspect spans. The time-dependent evolution of creep changes this situation and the CFRP laminates actively influence the characteristics of the five strengthened decks. Hence, strains were monitored constantly during a period of 5 months. Finally, loading tests with trains as well as acceleration measurements were carried out to confirm the effect of the reinforcement.

Penetration of the Stiffener Web to Deck Plate Weld in Orthotropic Plated Bridge Decks

This paper reports the results of experimental research concerning the connection between the deck plate and the web of the longitudinal stiffeners in an orthotropic plated bridge deck on a microscopic scale. An important number of test specimens of a weld are studied with the help of a video microscope, to detect the efficiency of the root of the weld. The second part of the paper is concerned with parametric analysis of the lack of weld penetration by using accurate finite element modelling. The results demonstrate that the weld quality often required can not always be assured, which surely has important consequence on the stresses in the weld and the fatigue resistance.

Autonomous Systems for Strain and Vibration Measurements

This paper will describe how it is often necessary to resort to monitoring of certain structural parameters when studying the long-term behavior of structures. This paper discusses two such applications. A first prototype was used to monitor strains in a concrete fly-over with carbon fiber reinforced polymer (CFRP) reinforcements. The second prototype was used recently to monitor the vibrations in a continuous fashion during four weeks of speed tests on a new section of the European High Speed Train network. This paper gives an overview of these experiences and lessons learned concerning power supply and possible electromagnetic interference in harsh construction site conditions. In addition, the paper describes the intention to build a new completely autonomous third prototype for thermal strain monitoring. Furthermore, the most important results of both test cases are discussed, including the effectiveness off the CFRP-reinforcement and the natural frequencies of a massive concrete fly-over.

Separation of structural and practical functionalities for wearing courses on steel box girders

Steel box girders are frequently used for road bridges. They are an economical solution and are easily built using modern construction techniques. During the day, a box section is subjected to the influence of the diurnal solar radiation cycle. This paper describes a new research project which focuses on the quantification of the thermal behaviour of these steel boxes. The objective of the research is to reach a new and fundamental insight in the problem and the behaviour of closed steel box girders, subjected to a variable thermal load, and the repercussions of such a loading combined with the live load on the stability of the box section, be it as the main arch of the bridge or as a part of the deck structure. This paper reports on the initial results of the finite element modelling of such thermal loading and its consequences for future wearing courses, which would benefit from a separation of the structural and practical functionalities.