Amr Ali Abdelrahman

Test Model for the First Canadian Smart Highway Bridge

Carbon fiber reinforced plastic tendons (CFRP) were used for the first time in Canada to pretension six girders of a concrete highway bridge. The bridge was constructed using 13 T-bulb section pretensioned precast concrete girders in each span. Continuity of the two spans was achieved by using post-tensioned steel tendons extending along the entire length of the bridge. This paper reports on an experimental study to examine the behavior of four pretensioned concrete T-beams of the same span-depth ratio as the bridge girders. The beams were tested to examine the various limit state behaviors, ultimate capacities, and failure modes. Two beams were tested in static, and two were tested under cyclic loading. After completion of 2 million cycles, the beams were loaded to failure to evaluate the effect of fatigue loading on the behavior of the beams. Predicted values based on the compatibility and equilibrium approach, and measured values, are compared and discussed. The authors propose a ductility model for beams prestressed by FRP tendons. Design recommendations and construction details of concrete beams prestressed by CFRP tendons are presented.

Serviceability of Concrete Beams Prestressed by Carbon-Fiber-Reinforced-Plastic Bars

The use of carbon-fiber-reinforced-plastic (CFRP) as prestressing reinforcement for concrete structures, has increased rapidly in the last ten years. The non-corroding characteristics of CFRP reinforcement could significantly increase the service life of concrete structures. In addition, CFRP prestressing reinforcement has the advantages of high strength-to-weight ratio, good fatigue properties, and low relaxation. However, the linear elastic behavior of the material up to failure requires special design consideration to ensure sufficient deformability of the members. In this paper, partial prestressing using low-jacking stresses, is proposed for the design of concrete members prestressed by CFRP reinforcement to reduce the cost and improve their deformability. The paper summarizes a study undertaken to examine the flexural behavior of concrete beams partially prestressed by CFRP reinforcement. The experimental program consists of testing eight concrete beams prestressed by CFRP bars and two beams prestressed by conventional steel strands. The parameters considered in this experimental program are the prestressing ratio, degree ofprestressing, and distribution of the CFRP bars in the tension zone. The various limit states behavior of concrete beams prestressed by CFRP bars in terms of cracking and deflection prior and after cracking are examined. The different modes offailure and the deformability of such beams are discussed.

Design Recommendations for Bridge Deck Slabs Reinforced by Fiber Reinforced Polymers

The linear characteristics of fiber reinforced polymers (FRP) up to failure and their relatively low elastic modulus and strain at ultimate has raised concerns with structural engineers regarding their use as reinforcement for flexural members. Based on a nonlinear finite element analysis and testing of a full-scale model at the University of Manitoba, Canada, design guidelines on the use of glass and carbon fiber reinforced polymers (GFRP and CFRP) as reinforcement for bridge deck slabs are proposed. The accuracy of the nonlinear finite element model is demonstrated by comparing the predicted behavior to test results of two models. The influence of the degree of edge restraint, percentage of reinforcement of CFRP and GFRP, type of reinforcement and presence of top reinforcement on the structural behavior and mode of failure of continuous concrete bridge decks is discussed. Based on serviceability and ultimate capacity requirements, reinforcement ratios of CFRP and GFRP for typical bridge deck slabs are recommended.

Behavior of bonded and unbonded prestressed normal and high strength concrete beams

Abstract The major disadvantage of using ordinary reinforced concrete (RC) elements is the corrosion of steel, which occurs due to effect of cracks in tension zones. The main advantage of the fully prestressed concrete system is the absence of cracks in the concrete at the nominal service load and therefore better durability will be achieved. Combining the PC system with the use of high strength concrete is a milestone, which will potentially result in a new design approach. The disadvantage of the use of this combination is referred to the reduced ductility of concrete members. This paper presents an experimental program conducted to study the behavior of bonded and unbounded prestressed normal strength (NSC) and high strength concrete (HSC) beams. The program consists of a total of nine beams; two specimens were reinforced with non-prestressed reinforcement, four specimens were reinforced with bonded tendons, and the remaining three specimens were reinforced with unbonded tendons. The overall dimensions of the beams are 160 × 340 × 4400-mm. The beams were tested under cyclic loading up to failure to examine its flexural behavior. The main variables in this experimental program are nominal concrete compressive strength (43, 72 and 97 MPa), bonded and unbonded tendons and prestressing index (0%, 70% and 100%). Theoretical analysis using rational approach was also carried out to predict the flexural behavior of the specimens. Evaluation of the analytical work is introduced and compared to the results of the experimental work.

Simplified Model for the Torsional Strength of Concrete Beams with GFRP Stirrups

AbstractAn international committee on shear and torsion reported that giving physical significance for the torsion design is an upcoming challenge. The purpose of this paper is to propose a reasonably accurate and relatively simple model capable of predicting the torsional strength of concrete beams reinforced with glass fiber–reinforced polymer (GFRP) stirrups. In this paper, a database for concrete beams reinforced with GFRP stirrups, tested under torsion, is compiled. The implementation of the torsion design provisions of the conventional steel-reinforced-concrete design codes is discussed. A few selected strength models were used to predict the ultimate torsional strength of the tested beams. The predicted strength was compared with that measured during testing. The comparison showed that more improvement is required in calculating the inclination of the diagonal concrete strut and the effective strain in the GFRP stirrups. Two strength models were modified and proposed. The proposed models showed bet...

Use of ACM in Rehabilitation Projects in Egypt

Use of ACM in the form of FRP laminates in rehabilitation of concrete structures is the prime application of ACM in Egypt. FRP laminates are applied for strengthening reinforced concrete slabs or beams in flexure and shear as well as for confinement of reinforced concrete columns. This paper briefly introduces selected projects to demonstrate the current practice of FRP in Egypt. In the first application, carbon FRP (CFRP) laminates in the form of strips and sheets were applied to strengthen a public building suffering from differential settlement of the foundation. In a different application, CFRP laminates were used to upgrade a residential building to be used for commercial purpose. The paper summarizes the design aspects, construction details and recommendations for future application of ACM.

Experimental and analytical investigation of the lateral load response of confined masonry walls

Abstract This paper investigates the behavior of confined masonry walls subjected to lateral loads. Six full-scale wall assembles, consisting of a clay masonry panel, two confining columns and a tie beam, were tested under a combination of vertical load and monotonic pushover up to failure. Wall panels had various configurations, namely, solid and perforated walls with window and door openings, variable longitudinal and transverse reinforcement ratios for the confining elements and different brick types, namely, cored clay and solid concrete masonry units. Key experimental results showed that the walls in general experienced a shear failure at the end of the lightly reinforced confining elements after the failure of the diagonal struts formed in the brick wall due to transversal diagonal tension. Stepped bed joint cracks formed in the masonry panel either diagonally or around the perforations. A numerical model was built using the finite element method and was validated in light of the experimental results. The model showed acceptable correlation and was used to conduct a thorough parametric study on various design configurations. The conducted parametric study involved the assessment of the load/displacement response for walls with different aspect ratios, axial load ratios, number of confining elements as well as the size and orientation of perforations. It was found that the strength of the bricks and the number of confining elements play a significant role in increasing the walls’ ultimate resistance and displacement ductility.

Interfacial shear behavior of composite flanged concrete beams

Abstract Composite concrete decks are commonly used in the construction of highway bridges due to their rapid constructability. The interfacial shear transfer between the top slab and the supporting beams is of great significance to the overall deck load carrying capacity and performance. Interfacial shear capacity is directly influenced by the distribution and the percentage of shear connectors. Research and design guidelines suggest the use of two different approaches to quantify the required interfacial shear strength, namely based on the maximum compressive forces in the flange at mid span or the maximum shear flow at the supports. This paper investigates the performance of flanged reinforced concrete composite beams with different shear connector’s distribution and reinforcing ratios. The study incorporated both experimental and analytical programs for beams. Key experimental findings suggest that concentrating the connectors at the vicinity of the supports enhances the ductility of the beam. The paper proposes a simple and straight forward approach to estimate the interfacial shear capacity that was proven to give good correlation with the experimental results and selected code provisions. The paper presents a method to predict the horizontal shear force between precast beams and cast in-situ slabs.

Behavior of post-tensioned fiber concrete beams

Abstract This paper presents an experimental and analytical study on the behavior of post-tensioned concrete beams with variable discontinuous fibers’ content. Eleven half scale T-shaped post-tensioned simple beams were cast and tested in four points bending under the effect of a repeated load using a displacement control system up to failure. The test parameters were the fibers’ type (steel and polypropylene) and content, as well as the prestressing ratio (partially or fully). Key test results showed considerable enhancement in the crack distribution, crack width and spacing, concrete tensile strength and flexural stiffness in all beams with steel fibrous concrete. The latter aspects were directly proportional to the steel fibers’ contents. On the other hand, beams containing polypropylene fibers demonstrated a slight decrease in the flexural strength and a slight increase in flexural stiffness. In addition, the tensile steel strains decreased in all fibrous concrete beams, with lowest values in steel fibrous concrete specimens when compared to those of the polypropylene fibers. Furthermore, fibrous concrete beams also demonstrated enhanced ductility and energy absorption, which reached the highest values for steel fibrous concrete specimens. Generally, it can be concluded that steel fibers proved to have higher structural efficiency than polypropylene fibers, when used in the tested specimens.

BEHAVIOUR OF RC COLUMNS RETROFITTED BY FIBRE REINFORCED POLYMERS UNDER CYCLIC LOADS

Retrofitting of reinforced concrete (RC) elements with FRP wraps is one of the techniques used successfully for the last few years. RC rectangular columns are used extensively in both residential and commercial buildings. Consequently, a comprehensive study of the different parameters affecting the seismic behavior of RC columns strengthened with FRP is vitally needed. The objectives of this research are to study the behavior of rectangular RC columns wrapped with FRP sheets under cyclic lateral and axial loading. The main parameters investigated in the research are: different anchorage systems, volumetric ratio of FRP and spacing between FRP layers. Five columns with dimensions 150x 450x2300 mm were tested under both cyclic lateral and axial loading. Different recommendations are provided for the use of FRP in strengthening rectangular columns.