The structural behavior of tiled laminate GFRP composites, a class of robust materials for civil applications

This paper focuses on the structural behavior of tiled laminate composites. Such laminates, in which the plies are not parallel to the outer surfaces are found in GFRP bridge deck panels. The technology is developed for the construction of robust GFRP panels useful in highly loaded structures such as bridges or lock gates. In civil structures, the drawback in traditional FRP sandwich structures has always been debonding of skin and core. Such a debonding problem may occur after unintentional impact, followed by fatigue loading. Through the concept of using overlapping Z-shaped and two-flanged web laminates, alternating with polyurethane foam cores, debonding is no longer possible in vacuum infused GFRP bridge deck panels. In such panels, the fibers in the upper and lower skins as well as in the vertical webs run in all directions, rendering a resin-dominated crack propagation impossible. As a result of the integration of core and skin reinforcement, a skin material is created in which the reinforcement is not parallel to the outer surfaces, but tiled. Based on experimental results and numerical simulations the relevance of tiled laminates for civil applications is demonstrated

Design framework and multi-level mechanical characterization for tiled composites in bridge decks

Het onderzoek verkent gelaagde composieten (GC), dit zijn materialen geïnspireerd door natuurlijke structuren met een schuin gelaagde opbouw. In tegenstelling tot natuurlijke analogieën, zijn door mensen gemaakte GC's samengesteld uit star met elkaar verbonden lagen. Het onderzoek heeft als hoofddoel het begrijpen van de mechanische eigenschappen en schadetolerantie op verschillende niveaus, van structuur tot laminaat. Het onderzoek heeft belangrijke implicaties voor brugconstructie, met name voor voetbruggen. Het ontwikkelt een analytische ontwerpprocedure voor GC-kern versterkte sandwichpaneel voetbruggen, gericht op efficiënt materiaalgebruik en structurele integriteit. Bovendien onderzoekt het de impact van mens-structuurinteractie op trillingen in voetbruggen, wat het comfort en de veiligheid van dit type bruggen moet verbeteren. Het onderzoek benadrukt ook de robuustheid van GC-structuren, wat de duurzaamheid verhoogt en onderhoudskosten verlaagt. Daarnaast analyseert het de mechanische eigenschappen van gelaagde laminaten, wat nuttig is voor materiaaloptimalisatie in toepassingen die stijfheid en sterkte vereisen. Het onderzoek breidt zich uit naar hybride staal-GC composieten, met doel langere en efficiëntere brugoverspanningen mogelijk te maken. Ondanks enkele beperkingen biedt dit onderzoek solide basisinzichten voor ingenieurs en ontwerpers en draagt het bij aan technische innovatie en oplossingen voor uitdagingen in de bouwkunde. Het verbetert materiaalgebruik, voetgangerscomfort, duurzaamheid en technische mogelijkheden in de praktijk

FRP bridges in the Flanders region : experiences from the C-bridge project

At the start of the C-Bridge project in 2018, the number of fibre-reinforced composite bridges in the Flanders region of Belgium was limited to a handful. These limited achievements were largely due to the poor knowledge of clients (public and private), project managers, design engineers, and contractors, which made the option of composites either unknown or still viewed with a certain degree of suspicion. In addition, there were no standards at the Belgian or European level for the design of such constructions. The C-Bridge project (roadmap into design, guidelines, and execution of composite bridges in Flanders) aimed to stimulate the design, the realization and the construction of composite bridges in Flanders by providing the necessary knowledge to the construction sector in the most suitable form. This knowledge consists of the current state of the art of composites in bridge construction, selection criteria for composite bridges, recommendations for specification texts, and in situ testing of composite bridges and structural and vibration analysis. This C-Bridge project should allow the awarding authorities and contractors to be able to make informed choices regarding fibre-reinforced polymer (fibre composite) bridges but also offer the possibility of making the necessary transformation to this new and promising material to various Flemish companies. The results of the project enable Flemish clients to draw up specifications for FRP bridges in the correct manner. Moreover, they can correctly interpret the calculation notes made available and make a correct assessment. The Flemish engineering firms, on the other hand, will be able to make their own designs of FRP bridges and bridge components. They can also build up a value chain within Flanders with Flemish contractors and producers. From the producers and suppliers' point of view, the results of the project will lead to a clearer profile of their products on the public and private market. Finally, the general contractors and constructors will be armed to withstand the challenges that FRP bridges entail to subcontractors in terms of execution, follow-up, delivery, and maintenance. The findings are helpful for the acceptance of fibre-reinforced composite bridges as an alternative to timber, steel, or concrete bridges and should generate a market expansion for FRP in the traditionally conservative bridge-building sector first in Flanders and later internationally

Measured dynamic properties of web-core sandwich panel FRP composite footbridges and their relation to pedestrian comfort analysis

This paper reports experimental data for the dynamic properties (i.e.first fundamentalflexural frequency,damping ratio, comfort class) of ten web‐core sandwich panel FRP composite footbridges in Belgium, whichcontributes to the assessment of relevant input parameters for design and assessment of this promising bridgetype, quickly gaining popularity in recent years. The data is gathered based on smartphone accelerometers,enabling easy, quick, affordable, and abundant measurements, while at the same time yielding reliable exper-imental values. Given the relatively short spans, the heel and excitation test methods are used, rather than theambient vibration method. The tests indicate damping ratios of one to three percent, which are strongly depen-dent on the number of people on the bridge during the measurement. Additionally, comfort analysis tests withup to 58 people (0.5P/m2) were conducted onfive out of the ten bridges. The results indicate that the currentdesign guidelines for pedestrian comfort analysis are overconservative and do not reflect the effect ofpedestrian‐induced damping, which is especially apparent for this bridge type given its very low modal massand relatively low damping ratio

Influence of SLS design requirements on the material consumption and self-weight of web-core sandwich panel FRP composite footbridges

This paper reports a parametric study on the influence of the serviceability limit state design requirements onthe material consumption and self‐weight of web‐core sandwich panel FRP composite footbridges. It describesthe initial design process of a typical FRP web‐core sandwich panel footbridge, focussing on the relevance ofthe various design checks on the overall material consumption at a given slenderness. It is clear that over awide range of input parameters, only the SLS requirements are relevant for the design of this bridge type.Consequently, thefinal material consumption and achievable slenderness strongly depend on the code require-ments. These requirements are non‐uniform over various international codes, but are shown to have a hugeinfluence on the material consumption. Thefinal results heavily depend on the input value of the damping fac-tor. In addition, human induced damping is not included in current design procedures, which may lead to asignificant underestimation of the effective damping and consequently to over‐design. The results contributeto understanding the mechanical behaviour of this promising bridge type, point to the relevance of the choiceof SLS requirements in codes and to the lack of fully understanding the vibrational behaviour currently adoptedin calculation models

Mechanical Characterization of GFRP Tiled Laminates for Structural Engineering Applications: Stiffness, Strength and Failure Mechanisms

This study investigates the mechanical properties of tiled laminates, frequently used in FRP bridges, and a completely new class of composites for which currently no experimental literature is available. In this paper, first a microscopic examination of laminates extracted from bridge deck flanges is performed, revealing complex multi-ply structures and tiled laminates in the transverse direction of the bridge deck. The subsequent fabrication of tiled laminates in the transverse (i.e., weak) and longitudinal (i.e., strong) span direction explores stiffness and strength characteristics depending on the stacking angle. It is observed that the stiffness in both directions is only slightly reduced with increasing stacking angles, reaching a maximum decrease of 10%, while the failure strength is significantly reduced, particularly with longitudinal tiling, dropping by approximately 70% for a 2° stacking angle. Transverse tiling demonstrates a more moderate 45% strength reduction due to the presence of some 90° plies. Given the small reduction in the stiffness and the fact that in many applications the design is mainly governed by serviceability (i.e., stiffness) requirements than strength, this strength reduction may be acceptable, considering other advantages of the concept. Additionally, this research sheds light on failure mechanisms, emphasizing the role of ply assembly in stress distribution and highlighting the importance of gradual ply ends in reducing strain concentrations. These findings provide valuable insights for optimizing tiled laminates in structural applications, ensuring their effective and reliable use

FRP bridges in the Flanders region: Experiences from the C-bridge project

Currently, the number of fibre reinforced composite bridges in the Flanders region of Belgium is limited to a handful. These limited achievements are largely due to poor knowledge of clients (public and private), project managers, design engineers and contractors, which makes this option either unknown or still viewed with a certain degree of suspicion. In addition, there are no standards at Belgian or European level for the design of such constructions. The C-bridge project (roadmap into design, guidelines and execution of composite bridges in Flanders) aims to stimulate the design, the realization and the construction of composite bridges in Flanders by providing the necessary knowledge to the construction sector in the most suitable form. This knowledge will allow the awarding authorities and contractors to be able to make informed choices regarding fibre reinforced polymer bridges, but also offer the possibility to various Flemish companies to make the necessary transformation to this new and promising material. The paper presents results from the C-bridge project including a state of the art report, an analysis of the selection, cost determination and project specifications in Flanders, an overview of structural analysis and calculation methods, and a case study related to a recently built fibre reinforced composite bridge in Flanders. The results are helpful for the acceptance of fibre reinforced composite bridges as an alternative to timber, steel or concrete bridges, in Flanders and internationally

Modal Parameter Identification and Comfort Assessment of GFRP Lightweight Footbridges in Relation to Human–Structure Interaction

With the emergence of slimmer footbridges and the introduction of lighter materials, the challenge of vibrational comfort assessment becomes more and more relevant. Previous studies have shown that each pedestrian will act both as an inducer and a damper, referred to as human–structure interaction. However, this interaction is currently not implemented in design guidelines, which leads to a poor comfort estimation for small lightweight footbridges. Derived from smartphone-based vibration measurements, this paper provides an overview of the modal parameters at various pedestrian densities and a comfort assessment of a selection of simply supported GFRP and steel lightweight footbridges in Flanders. The results indicate that the initial structural damping ratios for GFRP bridges exceed the values set in design guidelines and that they increase with an increasing pedestrian density. Further, it is shown that the measured accelerations do not relate proportionally to the pedestrian density. From both results the relevance of human–structure interaction is confirmed. Finally, while the first natural frequency is analytically predicted accurately, the vertical accelerations are substantially overestimated. Here, a better estimation can be made based on the experimentally measured damping ratios. The results contribute to a better understanding of human–structure interaction and the vibration assessment of lightweight footbridges. Practical applications include optimizing footbridge design, focussing on better performance and improving safety and user experience

Influence of the stacking angle on the strength and stiffness properties of tiled laminates for civil applications: a DIC based approach

Tiled Composites (TC) are a bio-inspired oblique layered material, composed of stacking individual plies in a tiled fashion and joining them together with a polymer to form a rigid structural material. This concept has great potential in different sectors (i.e. bridge building, offshore construction, ship building, lock gates, fire resistance panels, …) as it allows the manufacturing of composite plates from tiled strips of fabric which opens up the door for robotised production of panels of any shape and size. Because this is a relatively new concept, less is known about the mechanical properties of the material such as the strength, the local and global stiffness and the fracture mechanics properties. Further, the classic laminate theory does not fully describe a TL as opposed to plane-parallel laminates and international literature is virtually non-existent. Although numerical finite element (FE) models are available, experimental data is needed to validate, calibrate and corroborate these models. In previous research, the longitudinal stiffness was described by strain gauges and extensometers, leading to scatter/variation in the results due to the specific location of the measurement equipment on the laminate, which cannot be justified by the FE models. This paper studies the full strain field in a TL under uniaxial tension by digital image correlation (DIC) and compares the results to the numerical FE models. Furthermore the influence of the stacking angle and laminate lay-up will be assessed. As a guidance for the uniaxial tensile tests, ASTM D3039 was used even though the specimens are not symmetric or balanced as prescribed by this standard. The results show that the strains along a path in the FE models on the top and bottom of the TL show large variations and that the peak values at the free edges in the FE models need to be averaged out over a relatively large distance. Further, the stacking angle and laminate lay-up have a significant influence on the stress distribution along the specimen and the failure mechanism. Finally, the tests allow for good local and global stiffness characterisation of a TL and will make it possible to establish a set of verified material parameters for the considered TL composites, which will serve as an input to the verification of the FE models