Ken Schotte

Fatigue strength application of fracture mechanics to orthotropic steel decks

Modern fatigue design in civil constructions is mainly limited to the use of S-N curves and the hypothesis of Palmgren-Miner, as described in design standards and Eurocode. While using the latter, the fatigue evaluation may be conservative, since the outdated S-N curves are compared to current construction technology and weld properties. This shortcoming has a direct influence on the current design of orthotropic steel decks. To increase the understanding of the fatigue behaviour, an improved analysing tool using linear elastic fracture mechanics and extended finite element model is proposed. As a result, thickness effects are evaluated for both the longitudinal stiffener and the deck plate. These calculations indicated that increasing the thickness of the deck plate and the longitudinal stiffener increases the fatigue life of the structure. However, the thickness should be limited to maintain the advantage of a light-weighted construction.

Laser Scanning for Precise Ovalization Measurements: Standard Deviations and Smoothing Levels

AbstractMonitoring of measurements needs to be supported by a thorough knowledge of the achievable accuracy of the measurement equipment and the processing methodology. This study on ovalization monitoring with laser scanning in tunnels under construction focused on fast-performing laser scanners and their achievable accuracy. This research also investigated the optimum smoothing level of the laser scanning data to achieve the best estimates of ovalization. The experimentally based standard deviations indicate that the used phase-based laser scanner delivers highly accurate results with standard deviations between 0.34 and 0.58 mm, depending on the applied smoothing level. In this research, this laser scanner was used, together with a [x – 0.008 rad; x + 0.008 rad] smoothing interval on the calculated radius values to meet the accuracy requirement requested by the client (0.5 mm), even when using multiple setups. Another used type of laser scanner (pulse-based) also delivers standard deviations around thi...

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.

Verification of the performance of the precast concrete lining in the Diabolo Tunnel and Liefkenshoek rail tunnel

During construction of the Diabolo tunnel and the Liefkenshoek railway tunnel in Belgium, strains were monitored in several cross-sections of the precast concrete segmental lining. The obtained measurement data allow evaluating the in situ behaviour of the concrete lining under numerous loading conditions during and after tunnel drive works. The gradual development of strains in the initial stage after ring erection is discussed in relation to the grout loading, hydraulic jack forces and transferred soil and water pressures. Measurement sections below the River Scheldt show that the water level variation, linked to the tides of the North Sea, is clearly depicted in the strain results as a half-daily fluctuation. Results show that despite the rough site conditions, strain monitoring proves a useful verification of tunnel lining performance and an important addition to tunnel design practice.

Impact of Different Conditions on Resin Coated Mortar

In order to increase the structural performance, various techniques are being evaluated, tested and adopted. Structures exposed to adverse environmental conditions, are facing issues i.e. lifespan reduction and pre-mature failure. World-wide polyester resin is considered to be applied for re-novation, repair, especially for structural elements which are facing environmental degradation. This manuscript evaluates the quantitative performance of resin as a coating agent on mortar, under different controlled conditions. The experiment involved casting of specimens, coating 1–3 layers polyester resin on samples, exposure to environmental conditions and water. Compressive strength provide evidence that resin coats increased compressive strength of cubes by 69%. Whilst significant water absorption reduction was also noted which is proportional to number of coats. Univariate general linear model were evaluated by with respect to various parameters on the two conditions i.e. ambient environment and exposure to water. This study concludes that polyester resin may be used in primary structural element members, which are exposed to different environmental scenarios.

Measuring Residual Stresses in Orthotropic Steel Decks Using the Incremental Hole-Drilling Technique

Manufacturing processes such as welding cause residual stresses which exist in most steel civil structures, causing plastic deformations without any external loads. This type of stress is often overlooked during design. Nevertheless, residual stresses can have serious influence on the material strength and the fatigue life of the construction. This is also true for orthotropic steel decks which have many complex welding details. Since little is known about the distribution of residual stresses due to welding, a semi-destructive experimental test setup is developed for a stiffener-to-deck plate connection of an orthotropic steel deck. In particular, hole-drilling is used. The test procedure has been optimized to reduce measurement errors. The most important influencing factors on measurement accuracy are the surface preparation and the precision of the determination of the zero-depth. Once these measurement errors are optimized using proper grinding and visual inspection tools, a clear residual stress pattern becomes visible. The results confirmed the theoretical assumption of high tensile yield stresses near the weld location. However, at small distance from the weld, the residual stresses tend to decrease to almost zero.

INFLUENCE OF TEMPERATURE EFFECTS IN STEEL BOX GIRDERS

A number of recent monitoring project of steel box girders in Belgium have indicated that daily temperature variations can be an important load condition. The resulting behavior is not always included in the design loads according to the codes. As part of a large-scale project in order to improve the accessibility of the Belgian capital by train, the existing railway line between Brussels and Ghent is expanded from 2 to 4 tracks over a length of 25 km. This line crosses the valley of the river Pede by a 523 m long historic viaduct, built in the 1930s. In those days the viaduct was chosen over large backfills in the valley due to poor soil conditions. With respect to the protected work of art, two additional lateral fly-overs consisting of steel box girders with variable hollow section are integrated in the existing viaduct. This paper shows the results of the detailed monitoring program verifying the design and behavior of the newly built superstructure. Extensive strain measurements were performed during a two-day load test, together with acceleration measurements in order to evaluate the dynamic response of the structure. In addition long term strain monitoring was carried out in order to study the effects of temperature gradients on the closed steel box girders of the fly-overs. The measured temperatures are introduced into a finite element model. Stresses resulting from this model are compared with measured stresses and stresses based on calculation using the same model but based on Eurocode load combinations. While the size of temperature variations is more or less as was expected the resulting behavior is more complex and less homogeneous than is generally assumed.

Ovalisation measurements of newly built concrete tunnels by means of terrestrial laser scanning

This paper discusses the practical implementation of terrestrial laser scanning for ovalisation measurements of newly built concrete railway tunnels. Also an accuracy assessment is performed and then an overview of the measured deviations is given. This research is based on the ovalisation monitoring of concrete railway tunnels for the first projects of this kind in Belgium. These tunnels are measured with laser scanning during the first three months after construction. For all measurements, the concrete surface of the tunnel rings is scanned with a lateral resolution of 5 mm or higher with a phase-based Leica HDS6100 laser scanner. Based on the recorded point clouds of the tunnel rings, the deviations from ovalisation and the changes in ovalisation during the first three months after construction are determined. During this research, a workflow has been developed to determine the deviations from ovalisation and the changes during the first three months after placement. The differences that are observed between the control measurements at the different points in time show a stabilization of the construction after one or two weeks after construction.