بررسی رفتار سازه ای دال های عرشه بتنی تقویت شده GFRP از طریق NLFEA

This paper presents a numerical study of the structural behaviour of concrete bridge deck slabs under static patch loads and dynamic traffic loads and an investigation of compressive membrane action (CMA) inside slabs. Those deck slabs were reinforced with Glass Fibre Reinforced Polymer (GFRP) bars. Non-linear finite element analysis (NLFEA) models were established using ABAQUS 6.10 software packages. Experimental data from one-span bridge structures by author and other researchers are used to validate and calibrate the proposed FEM models. A series of parametric study is conducted to investigate compressive membrane action (CMA) in concrete bridge deck slabs. In the simulation of behaviour of GFPR reinforced concrete bridge deck slabs under traffic loads, a field test using calibrated truckloads of Cooshire-Eaton Bridge in Canada was used to validate the accuracy of proposed numerical models in dynamic analysis. Some structural parameters were varied in the dynamic analysis to investigate the influences from the introduction of CMA in structural design. The NLFEA results were discussed and conclusions on behaviour of FRP reinforced concrete bridge deck slabs were presented. The numerical results showed that the benefits of CMA could provide the acceptable service performance of GFRP reinforced concrete bridge deck slabs with low reinforcement percentages.

Due to the non-corrosive properties, fibre reinforced polymer (FRP) bars have been used as the replacement of steel reinforcement in concrete bridge deck slabs, which is an alternative solution to improve the service life of bridges [1]. Currently, Glass Fibre Reinforced Polymer (GFRP) is one popular material used in the existing bridges [2]. Because of the low elastic modulus of GFRP materials, GFRP reinforced sections exhibit higher deformability when compared to equivalent reinforced steel sections. Therefore, the deflection criterion tends to control the design of intermediate and long spanning sections reinforced with GFRP bars [3], [4], [5] and [6]. Because the current design methods for the bridge decks reinforced with FRP composite bars was originally made with steel bars using flexural design method [4] and [5], a direct substitution of GFRP to replace steel is not recommended [3] and [5]. However, bridge deck slabs in typical beam-and-slab-type bridges have inherent strength due to in-plane forces set up as a result of the restraint provided by the slab panel boundary conditions, including beams, diaphragms, and slab continuity. This is known as compressive membrane action (CMA) or arching action. This compressive membrane effects is due to the significant difference between tensile and compressive strengths of concrete. On the application of load, a crack occurs due to the relatively weak tensile strength. Under this condition, the neutral axis moves toward the compression face. If the ends of the slab are restrained by a stiff boundary, an arching thrust develops which ultimately enhances the flexural capacity of the slab. Therefore, in bridge deck slabs, it is generally lateral restraint stiffness and concrete compressive strength which govern the ultimate strength and independent to the percentage and type of reinforcement [7], [8] and [9]. It has been recognized for some time [10], [11] and [12] that concrete bridge deck slabs exhibit strengths far in excess of those predicted by most design codes. Furthermore, research by Kirkpatrick [13] and [14] has shown that CMA also has a beneficial effect on the serviceability performance of bridge deck slabs. As a result, it is possible to produce an economic and durable concrete deck slabs by utilizing the benefits of GFRP reinforcement in combination of CMA [9]. In the past research, most of research works on the structural behaviour of GFRP reinforced concrete deck slabs has focused on experimental tests [3], [7], [15] and [16]. However, due to the high cost and significant time requirement in conducting experimental testing, particularly in developing dynamic traffic loading tests, it is hard to establish comprehensive investigations of this non-metallic bridge deck slabs. Furthermore, some structural variables were difficult to be obtained by experimental tests, such as stress–strain relationship through the depth of slabs and stress distribution at the slab surfaces. Therefore, refined and completed studies are required to investigate the structural behaviour of deck slabs reinforced with GFRP bars. The availability of high-speed computers and commercial finite element packages facilitate the development of these tools through 3D FEA [7]. The aim of this paper is to study how GFRP reinforced concrete deck slabs work under static patch loads and dynamic truck loads with consideration of CMA. In this study, a commercial software named ABAQUS [17] was employed. The proposed numerical model showed good convergence ability and an excellent agreement of structural behaviour with the validations of experimental tests in the laboratory and field tests [1], [3], [15] and [18. Subsequently, the observed structural behaviour of deck slabs were presented. Thereafter, some parametric studies are conducted to investigate the effects of CMA on this structural type.

This paper reveals a comprehensive study of NLFEA of structural behaviour of GFRP reinforced concrete bridge deck slabs under static patch loads and dynamic traffic loads. NLFEA results indicate that compressive membrane action has sufficient effect on ultimate behaviour and serviceability of GFRP reinforced concrete bridge deck slabs. However, current design standards of FRP reinforced concrete structures, such as ACI 440-R06 [5], underestimate behaviour of bridge deck slabs under ultimate and serviced load level. Based on this study, the following conclusions can be drawn: 1. The proposed NLFEA method is capable of predicting the behaviour of GFRP reinforced concrete bridge deck slabs under static patch loads and dynamic traffic loads, such as the loading-carrying capacities, failure modes, displacements and stress developments. 2. Based on accurate validation of proposed numerical procedure with experimental results, NLFEA provided a capability of investigating some structural parameters, such as stress distribution through the depth of slabs and stress distribution at the deck surfaces in the whole process of moving truck loads. These values are difficult to be obtained through experimental tests. 3. In the investigation of failure mechanisms, it was found that punching failure was the common failure mode and the punching effect became stronger with the increasing compressive membrane action. 4. During the entire moving truck loading procedure in NLFEA, the maximum stress of concrete slabs was less than 5% of ultimate strengths of concrete material and the maximum tensile stress of GFRP bars was less than 1% of ultimate stress. The largest deflection of deck slabs was smaller than the limit value (span/800). 5. The increase in reinforcement percentage can reduce compressive membrane action in GFRP reinforced concrete bridge deck slabs. However, effects of compressive membrane action and loading-carrying capacities can be enhanced by increase in horizontal restrained stiffness and concrete compressive strength. 6. With an introduction of compressive membrane action, the GFRP reinforcement percentages were reduced by around 50% compared to existing bridge deck slabs. However, this reinforcement configuration has insufficient effect on structural behaviour of GFRP reinforced concrete deck slabs under ultimate and service state. 7. Based on the cheap cost and lower time requirement compared with the experimental tests, the proposed NLFEA models can be used by engineers and researchers for the structural analysis, assessment of the loading capacity and parametric studies of FRP reinforced concrete bridge decks.