بررسی رفتارهای سازه ای مهار شده جانبی GFRP دال های بتن مسلح

The corrosion of reinforcement in concrete bridge deck has been the cause of major deterioration and of high costs in repair and maintenance. Glass fibre reinforced polymer (GFRP) reinforcement is a more durable alternative to steel reinforcement and has higher strength to weight ratio. Due to the low value of elasticity and brittle behaviour of GFRP, the service behaviour of GFRP reinforced concrete structure is critical. However, laterally restrained slabs, such as those in bridge deck slabs, exhibit arching action or compressive membrane action (CMA) which has a beneficial influence on the service behaviour such as the deflection. This paper presents the results of experimental tests and numerical analysis of laterally restrained GFRP reinforced concrete slabs with varying some structural variables. The analysis results are discussed and conclusions on the compressive membrane action in GFRP reinforced concrete slabs are presented.

It has been increasingly evident that the corrosion of steel reinforcement due to the de-icing salts has one of the major factors in the deterioration of reinforced concrete bridge decks [1] and [2]. One solution to these corrosion problems is the use of alternative non-corrosive materials to replace steel reinforcement, such as fibre reinforced polymers (FRPs) [3]. Because glass FRP bar is more economical than the available types (carbon and aramid) of FRP reinforcing bars [4], it is more attractive for infrastructure applications and to the construction industry. However, the majority of recent research using GFRP reinforcement has concentrated on simply supported slabs. Due to the low elastic modulus and brittle behaviours of GFRP, the deflection in the GFRP reinforced sections is greater compared to steel reinforced concrete slabs. Therefore, the deflection criterion tends to control the design of intermediate and long spanning sections reinforced with GFRP bars [5], [6], [7] and [8]. Conversely, it is the ultimate strength governing the structural design of steel reinforced concrete sections. Interestingly, in laterally restrained slabs, such as bridge deck slabs, it is generally laterally restraint stiffness and concrete compressive strength which govern the structural behaviours and independent to the percentage and type of reinforcement [9]. It has been recognised for some time [10], [11] and [12] that laterally restrained slabs exhibit strengths far in excess of those predicted by most design codes. The load capacities are enhanced significantly due to the arching action or compressive membrane action (CMA), which are far larger than those predicted by flexural methods [13]. Furthermore, research by Kirkpatrick et al. [14] and [15] has shown that CMA also has a beneficial effect on the serviceability of laterally restrained slabs. As a result, it is possible to produce an economic and durable concrete slabs by utilising the benefits of GFRP reinforcement in combination of CMA. The aim of this paper is to study the structural behaviours of GFRP reinforced concrete slabs with lateral restraint stiffness. A series of experimental tests was carried out to investigate the influences from some structural variables on the response of concrete slabs, which included concrete compressive strengths, boundary conditions, reinforcement percentage and type of reinforcing materials. The experimental results were ultimate loads, deflections and reinforcement strains. To this end, a commercial software named ABAQUS [16], which accommodates non-linear 3D FEM models, can be employed. The proposed numerical model showed good convergence ability and an excellent agreement of structural behaviours with the validations of experimental tests by authors. Subsequently, the observed structural behaviours of laterally restrained slabs and effect of CMA in this non-metallic structure were presented.

The aim of this study was to extend the existing research on compressive membrane action in laterally restrained slabs with GFRP bars as reinforcement. From the experimental and numerical results, the following conclusions have been drawn: 1. The experimental observations were consistent with the development of compressive membrane action in the laterally restrained GFRP reinforced concrete slabs. 2. Due to the existing of compressive membrane action inside the laterally restraint slabs, the GFRP reinforcement percentages could not influence the serviceability and ultimate strengths significantly. The ultimate strengths of laterally restrained GFRP reinforced slabs were more dependent on the concrete compressive strength and horizontal restraint stiffness than reinforcement percentage. 3. Due the existing of compressive membrane action, the crack widths of laterally restrained GFRP reinforced concrete slabs at service load level were not influenced by the reinforcement percentages and reinforcing materials. 4. The deflections in the slabs without lateral restraints were significantly great which were larger than the service allowable deflection. The provision of lateral restraint reduced the mid-span deflection and the restrained GFRP reinforced slabs with low reinforcement percentages showed better service behaviour compared to the equivalent laterally restrained steel reinforced slabs. 5. Without consideration of CMA, current design standard cannot predict ultimate strengths and deflections of the laterally restrained concrete slabs accurately. 6. The ultimate capacity obtained from NLFEA showed excellent agreement with the experimental results. The selected material models were able to simulate the behaviours of GFRP reinforced concrete in in-plane restrained slabs and the proposed failure criterion of balance of forces provided an accurate prediction of ultimate strengths. Based on accurate validation of proposed numerical procedure with experimental results, NLFEA provided the capability of investigating some structural parameters, such as stress and strain distribution through the thickness of deck slabs, which are not easily obtained through other method of analysis. 7. GFRP reinforcement in laterally restrained slabs can produce both economical and durable concrete design.