Structural characteristics and failure prediction of hybrid FRP-concrete bridge deck and superstructure systems
Alnahhal, Wael I
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It is a major challenge to build bridge systems that have long-term durability and low maintenance requirements. A solution to this challenge may be to use new materials or to implement new structural systems. Fiber reinforced polymer (FRP) composites have continued to play an important role in solving some of persistent problems in infrastructure applications because of its high specific strength, light weight, and durability. Structural engineers always have valued the combination of materials into a hybrid structural system that takes advantage of the properties inherent in each of its constituents. In this study, the concept of the hybrid FRP-concrete structural systems is applied to both bridge superstructure and deck systems. The hybrid FRP-concrete bridge superstructure and deck systems are intended to have durable, structurally sound, and cost effective hybrid system that will take full advantage of the inherent properties of both FRP materials and concrete. The hybrid-FRP deck system can be installed in new construction, or can be attached to existing deck substructure after removing deteriorated concrete deck. In this study, two hybrid FRP-concrete bridge systems were investigated. The first system consists of trapezoidal cell units forming either a bridge superstructure or a bridge deck unit. The second one is formed by arch cells. The two systems rely on using cellular components to form the core of the deck system, and an outer shell to warp around those cells to form the integral unit of the bridge. Both systems were investigated analytically by using finite element (FE) analysis. From the rigorous FE studies, it was concluded that first system is more efficient than the second. Therefore, the first hybrid FRP-concrete system had been used to investigate the feasibility of the FRP-concrete structural systems in the remainder of the study. The proposed system consists of trapezoidal FRP cell units surrounded by an FRP outer shell forming a bridge system. A thin layer of concrete was placed in the compression zone. Concrete was confined by GFRP laminates which provide protection from environmental exposure. Moreover, the concrete layers reduce the local deformation of the top surface of the bridge under concentrated loads. Webs of the box section were designed at an incline to reduce shear force between sections. For the experimental phase of the study, a prototype bridge superstructure was designed as a simply-supported single span one-lane bridge with a span length of 18.3 m. Geometrical parameters of the proposed bridge system were determined by detailed finite element analyses. FEA was used to verify the structural behavior of this hybrid bridge superstructure prior to embarking on manufacturing and testing. Performance of this hybrid bridge superstructure was examined both experimentally and computationally. A test specimen, fabricated as a one-fourth scale model of the prototype bridge, was subjected to a series of loading tests: nondestructive tests (flexure, off-axis flexure, and negative flexure), and destructive tests (flexure and shear). Also, as a trial case for FRP-concrete bridge deck supported on steel girders, a prototype bridge system was designed as a simply supported steel bridge with a hybrid FRP-concrete deck. Details for connecting the hybrid decks with steel girders were investigated both experimentally and computationally. A test specimen, fabricated as a 3/4 scale model of the prototype bridge, was evaluated by series of service flexural loading tests under different loading conditions. Moreover, the composite action between the hybrid deck and steel girders was analyzed and tested. The effective flange width in the hybrid FRP-concrete deck acting compositely with the steel girders was evaluated at service conditions. Three different constitutive models for GFRP composites were integrated in the finite element analysis to examine the inelastic behavior and to predict failure of both the hybrid bridge deck and superstructure. Results from the both experimental and computational analysis for both the hybrid bridge superstructure and deck systems confirmed that the hybrid FRP-concrete bridge systems have an excellent performance from structural engineering point of view. The experimental results showed robust performance where cracking in the exterior GFRP laminates, interface failure, and slippage between GFRP and concrete under AASHTO design loads for the hybrid bridge superstructure were not exhibited. Also, both test specimens satisfied the AASHTO live load deflection limit. In addition, the shear connections at girder-deck interface of the deck specimen on steel girders demonstrated an excellent performance under service load. Furthermore, it was observed that the hybrid deck and the steel girders are interacting as a partially composite system under service-load conditions. The effective flange width for hybrid decks are less than AASHTO prescribed effective width for reinforced concrete decks. It was shown that a detailed finite element analysis could predict behavior of the test specimens under different loading conditions up to the failure point.