Comportement des poutres précontraintes renforcées extérieurement à l'aide de PRFC

Abstract

This research investigates the strengthening of prestressed concrete bridge girders using advanced composite materials. The strengthening of concrete bridge girders using conventional methods such as steel plates (bonded or mechanically anchored) or external prestressing are rather widespread techniques. The use of fibre reinforced polymers (FRP) is a very attractive alternative. This research project includes two main parts: the experimental work and the theoretical study. The experimental program consists of testing a total of eight half-scale standard CPCI 900 mm deep concrete prestressed bridge girders. The tested beams were divided into two series. Series I was devoted to investigate the flexural behaviour while series II was devoted to investigate the shear behaviour of the prestressed concrete beams strengthened with carbon FRP laminates. Series I includes four beams; two were strengthened using different configurations of longitudinal carbon FRP laminates and two control beams. Series II includes four beams; three were strengthened using different configurations of transverse carbon FRP laminates and one control beam. The theoretical study includes the establishment of the design equations of the strengthened concrete beams using composite materials according to the available design codes for prestressed concrete members in both flexure and shear. Also, two available software were used to analyze the experimental results. The main objective of this study is to evaluate the potential of using externally bonded CFRP laminates as a strengthening technique for prestressed concrete girders type AASHTO (American Association of State Highway and Transportation Officials) subjected to flexure and shear. In addition, this research aims to check the feasibility of using this technique to improve the behaviour of such bridge girders and to validate the predictions of the design equations and software. The principal conclusions obtained from this study are as follows: (1) Theoretical predictions using the design equations and the software are in good agreement with the experimental results of the strengthened beams. The theory slightly over-estimates the strength of the beams; (2) The strengthening using CFRP laminates results in an increase in the flexural strength and stiffness of the tested beams compared to those of the unstrengthened control ones; (3) The loss of two prestressing cables simulated in the experimental program, can be compensated by the addition of CFRP longitudinal laminates; (4) The use of CFRP U-shaped anchorages at the ends of the beams decreased the end slip of the CFRP longitudinal laminates; (5) The addition of the CFRP U-shaped transverse strips improved the shear capacity and increased the rigidity of the beams; (6) The two horizontal CFRP strips bonded to the top side faces of the beam, as anchorages for the U-shaped strips, also contributed to the improvement of the behaviour of the beams in flexure, by preventing the debonding of the U-shaped strips.