In-plane compression and shear performance of FRP bridge decks acting as top chord of bridge girders

This paper reports on the composite action developed between pultruded FRP bridge deck systems and the supporting main girders for road bridges. Presented are requirements that an FRP deck must satisfy in order to function as part of the upper chord of the main bridge girders. It is shown that the deck must exhibit adequate in- plane compression and shear capacity and stiffness in the longitudinal direction of the bridge. Laboratory experiments using an existing FRP deck system with trapezoidal cell geometry are presented and their results analyzed to establish in-plane system properties for bridge design and dimensioning. These system properties include the effects of the material properties, the cross-sectional geometry and the adhesives used to bond the individual pultruded shapes to form the deck. The influences of the cell geometry (trapezoidal or triangular), the fiber architecture and the adhesive used for the deck joints (epoxy or polyurethane) on the system properties are discussed. © 2004 Elsevier Ltd.

Hybrid FRP-lightweight concrete sandwich system for engineering structures

Erika Schaumann

Hybrid slab systems combining fiber-reinforced polymer (FRP) composites with concrete are promising load-bearing structures, and an increasing number of applications has demonstrated their high potential in terms of structural performance and durability. Hybrid slabs are currently manufactured mainly on site however, which limits their economic advantages. The aims of this research are to develop a novel concept for a lightweight hybrid FRP-concrete sandwich slab system, which can be prefabricated and easily installed on site, and provide a corresponding engineering-adapted design method. The proposed system uses three layers of different materials: an FRP sheet with T-upstands for the bottom skin, which also serves as formwork, lightweight concrete (LC) for the core material and ultra-high performance fiber-reinforced concrete (UHPFRC) for the top skin. No additional shear reinforcements are used, resulting in a simple and cost-effective slab manufacturing process. Analytical and experimental investigations on the proposed system indicate that one of the governing failure mechanisms is shear failure of the LC core. A fracture mechanics-based model to predict the shear resistance of the hybrid sandwich slab is presented. To verify the modeling, experiments were performed on twelve hybrid beams comprising two different types of LC materials for the core: sand lightweight aggregate concrete (SLWAC) and all lightweight aggregate concrete (ALWAC). The proposed model demonstrates good agreement with experimental results and highlights the importance of considering not only the LC static strength, but also fracture mechanics properties such as characteristic length. Furthermore, a continuous direct load transmission model is developed to model the behavior of the sandwich slab with loads next to the support. The model consists of a diagonal bottle-shaped strut with an infinite number of transverse ties and is based on the principles of strut-and-tie models for direct load transmission. The statically indeterminate system allows the stress redistribution resulting from post-peak material softening after concrete cracking to be taken into account. This leads to an accurate modeling of the varying experimental responses of eight hybrid short-span beams. Again, the considerable influence of LC brittleness on load-bearing behavior is demonstrated, something which is not taken into consideration in classic strut-and-tie models. In a final step, design examples demonstrate the feasibility of the hybrid FRP-concrete sandwich slab and illustrate an appropriate selection of material properties in accordance with the proposed design method.

EPFL2008

Capacité portante de ponts en arc en maçonnerie de pierre naturelle

Alix Grandjean

Historical masonry arch bridges are an integral part of our cultural heritage and deserve the attention and the efforts required to safeguard their patrimonial value. There is currently a diverse range of methods available to engineers for evaluating the load-bearing capacity of masonry arches. The major drawbacks are that these methods are either too conservative or computationally intensive. The study presented here proposes a model based on the theory of plasticity. The result is a transparent model that is both rapid and easy to use. Moreover, its application does not involve heavy computation tools. The model is validated by comparison with available experimental results and with the results of a widely-recognised analysis software. In order to take into account the material and structural behaviour of an arch in an optimal way, the present thesis provides a new integral model divided into three evaluation levels. At the micro-level, the response of masonry under pure compression is used to characterise the material of an arch. At this level, numerical models are used to describe the behaviour of natural-stone masonry. These models distinguish between the constitutive units and mortar as well as the unit – mortar interface. The shape and arrangement of the units have the most influential role in defining the failure mode in comparison to the properties of each constitutive material. At the meso-level, the material behaviour from the preceding level is used to define the limit for the local plastification of an arch section under combined compression and flexure. This phenomenon is described as the formation of a hinge. The resistance of an arch section can be expressed using the bending moment – normal force interaction diagram based on the stress-strain curve of the masonry material. Each point along the interaction diagram refers to a state of stress causing the local plastification of an arch section due to the formation of a hinge. The macro-level focuses on the structural analysis of a masonry arch – a structure with four degrees of indeterminacy. The arch failure corresponds to the successive formation of four hinges defined by the yielding condition determined at the meso-level. The analytical model developed in this study considers an arch at the state of being a statically determinate structure – after three of the four hinges are developed. Using the principle of equilibrium, the model calculates the load-bearing capacity of the arch at the ultimate limit state. A large number of existing natural-stone masonry arches include deficiencies accumulated throughout years of service without any regular maintenance. Three common types of deficiencies on these bridges are considered. The model is extended to take into account their effects on the load-bearing capacity of arches. Finally, the model developed in this study is incorporated into a global methodology for the examination of masonry arch bridges. This methodology implies two complementary approaches, which have to be applied parallel to one another. The first uses the developed model and gives a quantitative evaluation of structural security. The second includes a qualitative appreciation of the risk, based on the condition survey of the structure. This methodology allows an objective examination of the structure and recommendations for intervention measures.

EPFL2010

Model-Free Methodologies for Data-Interpretation during Continuous Monitoring of Structures

Irwanda Laory

Most civil engineering infrastructures, especially bridges worldwide, are approaching the end of their designed lifespan. They are continuously deteriorating due largely to material aging, excessive loads and changing environments. Therefore, it is crucial to evaluate the performance of existing structures to prevent catastrophic events. Structural Health Monitoring (SHM) has the potential to provide a proper assessment of structural performance and to further reduce cost through early damage detection and thus replacement avoidance. SHM integrates technologies to monitor structural behaviour and with current advances in sensor technology and measurement systems, the number of bridges that are continuously monitored is increasing. The bottleneck in SHM is data interpretation and this task is even more challenging in the presence of environmental variations. The main stream of data interpretation in SHM involves physics-based modelling and validation. However, building a model can be expensive, time consuming and difficult due to the structural complexity and uncertain environments. This research focuses on model-free methodologies for continuous monitoring of civil structures under environmental variations. The work involves important aspects of SHM such as damage detection, measurement system configuration and environmental variations. For damage detection, a novel model-free methodology that combines Moving Principal Component Analysis (MPCA) and regression analyses is proposed. Such approach aims to exploit the advantages of both MPCA and regression-analysis methods. The methodology has been tested on numerical and experimental studies including a full-scale bridge application. Results of a comparative study with other model-free methodologies demonstrate the superior performance of the proposed methodology in terms of damage detectability and time to detection. This research work also compares the performance of model-free methodologies for predicting natural frequencies of a continuously monitored bridge under environmental variations. Relative importance of environmental factors and traffic loading is also evaluated. Results of the case study reveal that traffic loading and temperature variations are the most influential parameters. A structural identification strategy that takes advantage of thermal variations is developed. The strategy utilizes thermal variations as load cases to evaluate structural performance. Results exhibit the promising potential of the strategy for enhancing structural identification tasks. As for measurement system configuration, a systematic approach that involves multi-objective optimization and Multi Criteria Decision Making (MCDM) methodologies is proposed. The approach is able to accommodate model-free methodologies for damage detection and provide support for selecting the best compromise configuration. It is also applicable for situations where several model-free methods are used for data interpretation.

EPFL2013