Precast composite bridge decks fabricated with GFRP (glass-fiber-reinforced plastic) are a promising alternative to conventional decks made of materials such as concrete, steel, and wood for new bridges as well as for rehabilitation of existing bridges owing to their many advantages such as light weight, high strength and durability, low maintenance costs, and ease of installation. This material has been used for field applications since the 1990s in the U.S., Europe, and China.
Recently, a common guideline and the associated inspection procedure for the maintenance of in-use GFRP decks have developed by bridge owners and independent researchers. These investigations revealed severe problems such as cracking, spalling, and de-bonding of pavements or wearing surfaces of GFRP decks. Thus, there are concerns surrounding the long-term durability and serviceability of such decks. Particularly, in the case of pultruded GFRP decks, such damages are visible as reflective cracking along the bonding lines of adhesive joints between deck tubes and deck panels upon assembly of the overall deck system. Therefore, it is necessary to identify the structural causes underlying reflective cracking of pavements or wearing surfaces of a pultruded GFRP deck and investigate design improvements for structural joints and for appropriate pavement systems as countermeasures to the reflective cracking of pavements or wearing surfaces.
This study is focused on the weak-axis bending behavior of a pultruded GFRP bridge deck because this deck shows different behaviors under strong- and weak-axis bending, especially in terms of flexural stiffness and moment capacity, owing to material and shape orthotropy. I investigate overall behavior of the deck under weak-axis bending; local behaviors of the adhesive joints, which can lead to reflective cracking of asphalt pavements; and local failures of adhesive joints in a pultruded GFRP deck by closely examining deformations and stresses through tests and finite element analyses. Finally, a design study of structural joints in a pultruded GFRP deck is carried out.
In detail, I introduce the concept of reflective cracking on asphalt pavements in in-use pultruded GFRP decks, as well as the definitions of the GFRP deck’s strong and weak axes for identifying the structural causes of reflective cracking in asphalt pavements on a GFRP deck. Furthermore, I describe the effects of section geometry on weak-axis bending based on the results of a preliminary study and describe the design history of a pultruded GFRP deck called “Delta Deck TG200.”
Through three-point loading tests and FE analyses of beam-type deck specimens, the independent behavior of pultruded GFRP decks under strong- and weak-axis bending was investigated. It was found that highly localized deformation occurs at the edge of the adhesive joints in deck surfaces under weak-axis bending, and this deformation could be the cause of pavement cracking. In addition, structural safety in terms of the maximum moment and normal section forces along the deck’s strong- and weak axes, and resistance to various failure modes of the given adhesive joints under bidirectional bending at the SLS (service limit state) and the ULS (ultimate limit state) were determined. This was achieved by carrying out finite element analyses of EOP (equivalent orthotropic plate), SHL (shell element), and SLD (solid element) models. Moreover, a design study of structural joints in a pultruded GFRP deck for minimizing localized deformation at adhesive joint edges was conducted considering joint geometry and adhesive strengths.
Through this study, it was concluded that flexural stiffness and moment capacity of pultruded GFRP decks under weak-axis bending are considerably lower than the corresponding values under the strong-axis bending. This is ascribed to the local bending and shearing of individual members such as the top plate, bottom plate, and webs due to transverse shear deformation of the deck section. It was confirmed that the asphalt pavement could crack owing to highly localized deformations, as well as owing to the tensile failure (cracking) of epoxy adhesives at adhesive joint edges in deck model surfaces under design limit states.
Furthermore, this study proposed that the flexural stiffness and the moment capacity under weak-axis bending should be increased by improving section design for ensuring moment safety and increasing the deck’s load carrying capacity. In addition, it is proposed that resistance to the failure modes of the given adhesive joint should be enhanced by improving joint design and increasing adhesive strength. Furthermore, for improving joint design to minimize the localized deformation of adhesive joint, a pultruded GFRP deck with hybrid snap-fit joints considering the effects of scarf joint configuration, adhesive layer thickness, and lap joint length was proposed.