Behavior of an adhesive joint under weak-axis bending in a pultruded GFRP bridge deck

Abstract

It has been more than twenty years since the application of GFRP bridge decks in construction fields. Recently, a few studies by governments and individual researchers have investigated in-use GFRP bridge decks. Areas of trouble include the problems of cracking, spalling and the de-bonding of the pavement or the wearing surface on GFRP bridge decks, all of which affect the long-term durability and serviceability of these new construction materials. Related to these problems, reflective cracks on asphalt pavement are directly related to pultruded GFRP bridge decks.In this paper, the behavior of an adhesive joint under weak-axis bending was investigated to identify the causes of pavement cracks in in-use pultruded GFRP bridge decks. In detail, this paper initially describes a designed section of a pultruded GFRP deck tube while accounting for the effects of the section geometry through bending tests and for the connections to the girders. The study also describes connection methods of creating adhesively bonded joints between GFRP tubes and panels and presents possible sources of pavement cracks on the GFRP decks. The flexural stiffness and the load-carrying capacities in strong and weak axes are measured during bending tests on pultruded GFRP decks. Next, tensile local failures of an epoxy adhesive due to the concentration of deformations at adhesive joints are identified via a weak-axis bending test. Finally, the tensile failure of an epoxy adhesive due to the local concentration of deformation at an adhesive joint under weak-axis bending is verified through a finite element analysis.The bending tests and FE analyses of a pultruded GFRP bridge deck under weak-axis bending show that local deformations are prone to concentrate at the adhesive joints which form a flexible and weak region due to the relatively low elastic modulus and strength of the epoxy adhesive. Strong-axis bending has a dominant influence on the global behavior of a deck subjected to bi-directional bending. On the other hand, weak-axis bending, which affects the behavior of adhesive joints, also has a strong influence on pavement cracks. Reflective cracks on the pavement of pultruded GFRP bridge decks can occur due to the local concentration of deformations at adhesive joints on the surfaces of GFRP decks under weak-axis bending, even before the tensile failure of the epoxy at the edges of the adhesive joints due to the higher elastic modulus and the lower tensile strength of the asphalt pavement compared to these properties of the epoxy. To prevent reflective cracks on the pavement of pultruded GFRP bridge decks, design improvements or reinforcing measures for deck connection structures which distribute and minimize the concentrated local deformation on adhesive joints are required.