Sherif El-Gamal

Behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer bars under concentrated loads

While the expansive corrosion of steel reinforcement is a major concern in reinforced concrete bridge deck slabs, the noncorrosive fiber-reinforced polymer (FRP) composite bars provide an excellent alternative reinforcement. In this paper, the behavior of edge-restrained concrete bridge deck slabs reinforced with glass FRP and carbon FRP bars was investigated. Six full-scale deck slabs 3000 mm long x 2500 mm wide x 200 mm deep were constructed and tested to failure in the laboratory. Three deck slabs were reinforced with glass FRP (GFRP) bars, two deck slabs were reinforced with carbon FRP (CFRP) bars, and the remaining slab was reinforced with steel bars as control. The test parameters were the reinforcement type and ratio in the bottom transverse direction. The deck slabs were supported on two steel girders spaced at 2000 mm center-to-center and were subjected to a monotonic single concentrated load over a contact area of 600 x 250 mm to simulate the footprint of sustained truck wheel load (87.5 kN CL-625 truck) acting on the center of each slab. The experimental results were presented in terms of cracking, deflection, strains in concrete and reinforcement, ultimate capacity, and mode of failure. It was observed that the mode of failure for all deck slabs was punching shear with carrying capacities of more than three times the design factored load specified by the Canadian Highway Bridge Design Code. It was also concluded that the maximum measured crack widths and deflections at service load level were below the allowable code limits. In addition, a new empirical model to predict the punching shear capacity of restrained FRP-reinforced bridge deck slabs was introduced and verified against the available models and experimental results of others researchers. The proposed model showed goad agreement with the available test results.

Tensile properties degradation of glass fiber-reinforced polymer bars embedded in concrete under severe laboratory and field environmental conditions

This paper presents the test results of an experimental study to investigate the durability of newly developed glass fiber-reinforced polymer bars. The main objective of this study is to investigate any degradation in the tensile properties of the glass fiber-reinforced polymer bars using accelerated aging methods. Glass fiber-reinforced polymer bars were embedded in concrete prisms and exposed to several environmental conditions for 6, 12, and 18 months. The environments included exposure to tap water and seawater at two temperatures (room temperature and 50°C), seawater dry/wet cycles and alkaline solution at 50°C. In addition, two typical field conditions of the Kingdom of Saudi Arabia (Gulf area and Riyadh area) were included. The performance of the glass fiber-reinforced polymer bars was evaluated by conducting tensile tests on the bars extracted out from the concrete prisms after exposure to different conditions. In addition, scanning electron microscope was used to investigate the degradation mechanism of the bars. After 18 months of exposure, test results showed that both the tap water at 50°C and the alkaline solution at 50°C had the maximum harmful effect on the tensile strength of glass fiber-reinforced polymer bars. The two field conditions showed almost no degradation in the tensile properties of the tested bars.

A New Punching Shear Equation for Two-Way Concrete Slabs Reinforced with FRP Bars

Synopsis: Recently, there has been a rapid increase in using the non-corrodible fiberreinforced polymers (FRP) reinforcing bars as alternative reinforcements for concrete structures especially those in harsh environments. The elastic stiffness, ultimate strength, and bond characteristics of FRP reinforcing bars are quite different from those of steel, which affect the shear capacity. The recently published FRP design codes and guidelines include equations for shear design of one-way flexural members. However, very little work was done to investigate the punching shear behavior of two-way slabs reinforced with FRP bars. The current design provisions for shear in two-way slabs are based on testing carried out on steel reinforced slabs. This study presents a new model to predict shear capacity of two-way concrete slabs that were developed based on extensive experimental work. The accuracy of this prediction model was evaluated against the existing test data. Compared to the available design models, the proposed shear model seems to have very good agreement with test results with better predictions for both FRP and steel-reinforced concrete two-way slabs.

Performance of near surface mounted glass fiber reinforced polymer bars in concrete

Near surface mounted fiber reinforced polymer reinforcement has become very popular method in strengthening of reinforced concrete structures. The major problem that accompanied the near surface mounted technique is the bond between fiber-reinforced polymers and concrete that corresponds to the stress transfer from concrete into fiber-reinforced polymers. This article presents the test results of pullout tests of near surface mounted glass fiber reinforced polymer bars to investigate the effect of different parameters on the bond performance of this strengthening technique. The test parameters include: adhesive type, groove size, bonded length, environmental condition, and concrete strength. A total of 40 near surface mounted–fiber-reinforced polymer bars, installed in C-shaped concrete blocks, were constructed and tested to failure. Five types of cement and epoxy-based adhesives were used. Two groove sizes and three bonded lengths were also investigated. Normal and high strength concrete were also used. In addition, the effect of two harsh environmental conditions on the performance of the strengthening system was also investigated. The results are presented in terms of pullout loads, free end slip, and mode of failure.

Bond strength of glass fiber-reinforced polymer bars in concrete after exposure to elevated temperatures

This paper presents the test results of an experimental study to investigate the effect of elevated temperatures on the bond properties of glass fiber-reinforced polymer bars in concrete. For this purpose, a total of 39 pullout specimens with glass fiber-reinforced polymer bars were cast for bond strength tests. In addition to the laboratory temperature, specimens were exposed to heating regimes of 100, 200, 300 and 350℃ for a period of 1, 2 or 3 h. The test results are presented in terms of bond strength, bond–slip relationship, and mode of failure. All specimens failed by shearing of the concrete corbels surrounding the bars and almost no damage was seen in the glass fiber-reinforced polymer bars. The results showed that the bond strength decreased as the temperature or exposure period increased. Reductions of about 20% of the original bond strength were recorded after exposure to 100 and 200℃ for 3 h. Significant reductions of about 50% in the bond strength were recorded after exposure to 350℃ for periods of 2 and 3 h. A modification to the ACI (American Concrete Institute) and CEB-FIP (Comité Euro-International du Béton-Fédération Internationale de la Précontrainte) equations was developed to consider the effect of elevated temperatures and it showed good agreement with test results.

Testing of Large-Scale Two-Way Concrete Slabs Reinforced with GFRP Bars

Few studies were conducted to investigate the structural behavior of GFRP-reinforced concrete two-way slabs. This paper presents preliminary results of an extended research project aims to developing the FRP technology reinforcing bar for parking garage structures and to introducing design guidelines for such structures. The results of five full-scale isolated interior parking flat slabs which are part of a 20-specimen experimental program are presented and discussed. Four slabs were reinforced with GFRP bars and one reference slab was reinforced with steel. The test parameters are: (i) reinforcement type and ratio; (ii) slab thickness; (iii) column size; and (iv) compressive reinforcement. The test results showed that there was no significant difference between the specimens in term of general behavior and mode of failure.

Laboratory and field performance of FOS sensors in static and dynamic strain monitoring in concrete bridge decks

There is a growing need for designing and constructing innovative concrete bridges using FRP reinforcing bars as internal reinforcement to avoid the corrosion problems and high costs of maintenance and repair. For efficient use and to increase the lifetime of these bridges, it is important to develop efficient monitoring systems for such innovative structures. Fabry-Perot and Bragg fibre optic sensors (FOS) that can measure the strains and temperature are promising candidates for life-long health monitoring of these structures. This article reports laboratory and field performance of Fabry-Perot and Bragg FOS sensors as well as electrical strain gauges in static and dynamic strain monitoring in concrete bridge decks. The laboratory tests include tensile testing of glass FRP bars and testing of full-scale concrete bridge deck slabs reinforced with glass and carbon FRP bars under static and cyclic concentrated loads. The field tests include static and dynamic testing of two bridges reinforced with steel and glass FRP bars. The obtained strain results showed satisfactory agreement between the different gauges.

Tensile Properties of GFRP Bars after Exposure to Harsh Laboratory and Field Environmental Conditions

This paper presents the test results of an experimental study that investigates the durability of a new generation of Glass Fiber Reinforced Polymer (GFRP) bars. A total of 60 GFRP bars were embedded in concrete prisms and exposed to ten environmental conditions for 6 and 12 months. The environments included exposure to ordinary tap water, sea water, and alkaline solution at two temperatures (room and 50°C). The environments also included two typical field conditions of the Kingdom of Saudi Arabia (Gulf area and Riyadh area). The performance of the GFRP bars was evaluated by conducting tensile tests on the bars extracted out of the concrete specimens after exposure to the environmental conditions. After 12 months of exposure, the test results showed that the tap water at 50°C had the maximum effect on the tensile strength of the GFRP bars. The two field conditions did not show any harmful effect on the tensile properties of the bars after 12 months of exposure.

Deflection Behaviour of Concrete Beams Reinforced with Different Types of GFRP Bars

GFRP bars are non noncorrosive reinforcing materials having relatively lower tensile modulus compared to steel. The design of flexural concrete members reinforced with GFRP bars are usually governed by serviceability limits, deflection, and crack width. This paper describes an experimental study conducted to investigate the deflection behavior of concrete beams reinforced with GFRP bars. The bars came from three different manufacturers. A total of 8 beams measuring 4250 mm long ×200 mm wide×400 mm deep were built and tested up to failure under four-point bending. The study’s main parameters were reinforcement type (GFRP and steel) and amount (three reinforcement ratios). The midspan deflection of all the beams tested were recorded and compared. The test results were used to assess the equations in different FRP codes and guidelines.

Cracking and Deflection Behavior of One-Way Parking Garage Slabs Reinforced with CFRP Bars

In this paper a laboratory investigation on the flexural behavior of carbon fiber reinforced polymer (CFRP)-reinforced concrete slab specimens extracted from Laurier-Tache Parking Garage (National Capital Region - Canada) after being in service field conditions for about eight years (1997-2005) is described. A total of four specimens, measuring 3 m long × 1 m wide × 0.19 m deep each, are extracted from the parking garage and then tested in flexure under four-point bending set-up. In addition, five FRP bar samples are extracted from the slabs and tested in tension to evaluate the strength or stiffness degradation of the CFRP bars, if any. The test results are presented in terms of deflection, crack widths, strains in concrete and reinforcement, ultimate capacity, and mode of failure. Based on the test results, the current provisions, provided by different FRP codes and design guidelines, are evaluated. The results showed that the CFRP bars as well as the CFRP-reinforced concrete slabs have not been adversely affected after being in service for eight years.