Punching shear in hollow FRP bridge deck components with cementitious overlays

Abstract

Fibre-reinforced polymer (FRP) sections offer a durable and lightweight alternative to traditional steel and reinforced concrete in structural applications. Since the early 1980s, the number of bridges adopting FRP for all or a portion of their deck components has increased steadily. Although there is a good knowledge base on how FRP elements behave independently, uncertainty remains as to their composite behaviour when combined with a concrete topping. This understanding is essential for the wider adoption of FRP bridge deck components and the development of consistent design practices. FRP composites are less ductile than steel and more likely to fail suddenly upon reaching their ultimate strength. In the particular case of highway bridges, FRP deck components may be subject to significant concentrated loads, this in turn poses a fundamental design challenge. As comparatively thin-walled elements, hollow FRP components can be vulnerable to localised failures that may arise from concentrated loads such as wheel loading. The strategic use of concrete toppings, acting compositely with the FRP component, can enhance the section’s resistance to such local failures as well as enhancing the overall flexural capacity and stiffness. Currently, no punching shear data on pultruded hollow section composite FRP-concrete deck components are readily available in the existing research literature and no specific guidance on this exists in the prevalent design codes. In view of this, the present study focusses on the behaviour of these types of bridge deck components subject to punching shear. The methodology adopted in this work involved both physical experiments and numerical modelling using finite element analysis. In the experimental work, six pultruded glass fibre-reinforced polymer (GFRP) deck components (338mm x 600mm x 80mm) were examined: two plain panels and four with polymer concrete toppings of either 15mm or 30mm. In comparison to the plain GFRP panel, a 67% and 280% increase in ultimate load capacity was observed with addition of the 15mm and 30mmm polymer concrete topping respectively. In parallel, corresponding increases in initial stiffness of 60% and 199% up to the peak load were observed, demonstrating a good degree of composite action. Using a finite element modelling approach validated against these experiments and other related experiments from the literature, an extensive parametric study was then undertaken to investigate the influence of key geometric and material parameters. The results revealed that moderate increases in the polymer concrete topping can lead to a change in failure mode from localised punching shear to a more combined mode involving global flexure. Similarly, for the various different topping thicknesses examined, it was observed that the increase in ultimate punching shear force follows a non-linear trend with increasing topping thickness. The results from the parametric study were then used to propose a design equation to predict punching shear capacity of a given GFRP-polymer concrete deck arrangement. The predictive equation consistently provided a reasonable lower-bound estimation of the experimental and numerical modelling results, pointing towards its potential as a design tool.