Study Of The Structural Behaviour Of Concrete Bridge Deck Slabs Strengthened With NSM FRP Reinforcement

Due to the rapid increase in traffic volume and loading in recent years, the current requirement of transportation cannot be subsequently satisfied in some bridge structures designed by the previous standard. In addition, it has become increasingly evident that the corrosion of steel reinforcement due to the de-icing salts and long-term exposure to harsh environment has been one of major factors in the deterioration of concrete deck slabs. Strengthening method using Fiber Reinforcement Polymer(FRP) is an effective solution to enhance the structural behaviour of the existing deteriorated bridge deck slabs. However, the construction method of traditional externally bonded strengthening method is complicated. Furthermore, external factors have a strong effect on the properties of strengthening materials, which could cause the second structural deterioration. Bonding failure is the common failure mode in the externally bonded strengthened concrete structure. Compared to the externally bonded FRP strengthening scheme, the Near Surface Mounted(NSM) FRP reinforcement strengthening method has some advantages:(i) high construction efficiency;(ii) strong bonding effect;(iii) small susceptible to interface. It has been recognized that bridge deck slabs in typical slab-and-beam-type bridges have inherent strength due to in-plane forces set up as a results of the restraints provided by the boundary conditions, including supporting beams, diaphragms and slab continuity. This is known as compressive membrane action(CMA), which has a strong influence of the structural behaviour of concrete deck slabs. Therefore, concrete bridge deck slabs strengthened by NSM FRP reinforcement was used as the analytical model in this study. The effect of CMA and NSM strengthening method on the behaviour of concrete deck slab is investigated through experimental tests, finite element analysis and theoretical study. The major research works in this thesis can be summarised as below:(1) Study of bonding behaviour between NSM FRP reinforcement vs. concrete and the behaviour of NSM FRP strengthened flexural concrete structures: Firstly, the bonding test of NSM FRP reinforcement and concrete is carried out to investigate the failure mode and the effect of the variation of NSM strengthening materials. Secondly, the behaviour of concrete beams strengthened with CFRP, GFRP and BFRP respectively will be investigated by the structural tests. The analytical results will be used as the basis for the further study of the behaviour of NSM strengthened concrete deck slabs.(2) The experimental study of the behaviour of NSM FRP strengthened concrete bridge deck slabs: A series of one-third scaled experimental tests of near surface mounted FRP strengthened concrete bridge deck slabs supported by steel I-beam and concrete beam under static patch loads is carried out. In the first phase of tests, the reinforcement ratio and support beam size are varied. The study of the second phase is focused on the influence of the type of strengthened FRP on the performance of the deck specimens. In both two groups of experiment tests, the test models strengthened by transverse NSM method and longitudinal externally bonded plates are conducted and tested. Thereafter, to analyse the behviour of bridge deck under static patch load, the variation of some structural parameters were compared and studied, which include vertical deflection of deck specimens, support beam lateral deflection, crack pattern, failure mode, the strain values in steel reinforcement and NSM FRP reinforcement. In addition, the analytical results is used to evaluate the influence of CMA and NSM strengthening method. Finally, the discussion and conclusion of the behaviour of NSM FRP strengthened concrete deck slabs are presented.(3) Finite element simulation of the behaviour of NSM FRP strengthened concrete deck slabs: A finite element software named as ABAQUS is selected. The accuracy of the proposed numerical model is validated by the comparison of the results from the test and finite element analysis. Based on a good correlation of the FEA and the test results, this numerical model could be adopted as a tool for the study in the similar structural type. Additionally, the effect of CMA and the values of effective width of compressive membrane thrust are presented and investigated by the proposed finite element model.(4) Theoretical model of NSM FRP strengthened concrete deck slabs: After the comparison of the loading-carrying capacity from the test and the prediction results by the existing theoretical models for FRP strengthened concrete structures. It was found that those model yielded high conservative prediction results due to the neglected effect of CMA. By using the flexural capacity provided by ACI 4402-08, a theoretical model with consideration of CMA was modified to predict the ultimate strengths of NSM strengthened concrete deck slabs. It was found that this theoretical model provide accurate and reliable predictions. Subsequently, a parametric study using this theoretical model was conducted. It can be summarised that the strengthening percentage and strengthening material type for NSM FRP strengthened concrete deck slabs should be determined by taking account of the effect of CMA and steel reinforcement percentage.