Papers by Keyword: Fiber Reinforced Polymer (FRP)

Abstract: This paper reports on an experimental study on the flexural behavior of fiber reinforced polymer (FRP)-concrete-steel double skin cantilever beams (referred to as DSTBs) that were tested under reversed cyclic loading. The beams were manufactured using a high-strength concrete (HSC) mix and they were 150 mm in diameter and 1.2 m in length. The main parameters of the experimental study included the size of the inner steel tube and the use of mechanical connectors in the form of steel rings welded on the inner steel tube. Test results indicate that DSTBs are capable of developing a highly ductile behavior under reversed cyclic lateral displacement excursions. It is found that the addition of mechanical connectors on the steel tube has no significant influence on the lateral displacement capacity of the test specimens, but they can eliminate the slippage between the concrete and inner steel tube. Examination of the test results has led to a number of significant conclusions on the influence of the beam parameters on the performance of DSTBs, which are discussed in the paper.

Abstract: This paper presents an experimental investigation on the influence of prestress on axial compressive behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs). A total of 12 aramid FRP- (AFRP) confined high-strength concrete (HSC) specimens with circular cross-sections were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and their unconfined concrete strengths were approximately 100 to 110 MPa. The influence of FRP prestress was examined by applying 3 different levels of lateral prestress ranging from 4.29 to 7.27 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of non-prestressed specimens. On the other hand, the influence of prestress on axial strain was found to be minimal, with prestressed specimens displaying a slight decrease in ultimate strain, compared to their non-prestressed counterparts. The results also indicate that prestressing the AFRP shell prevents the sudden drop in strength, typically observed in FRP-confined HSC specimens, that initiates at the transition point which connects the first and second branches of the stress-strain curves.

Abstract: This paper presents the results of an experimental study on the influence of concrete age on the compressive behavior of fiber reinforced polymer (FRP)-confined normal-strength (NSC) and high-strength concrete (HSC). The first part of the paper presents the results of 18 FRP-confined and 18 unconfined concrete specimens tested at 7 and 28 days. To extend the investigation with specimens with concrete ages up to 900 days, existing test results of FRP-confined concrete was assembled from the literature. Based on observations from both short-and long-term influences of concrete age on compressive behavior of FRP-confined concrete, a number of important findings were drawn and are presented in the second part of the paper. It was observed that, at a same level of FRP confinement and unconfined concrete strength, the stress-strain behavior of FRP-confined concrete changes with concrete age. This difference is particularly pronounced at the transition zone of the stress-strain curves. It is found that, in the short-term, the ultimate condition of FRP-confined concrete is not significantly affected by the age of concrete. However, in the long-term, slight decreases in the compressive strength and the ultimate axial strain are observed with an increase in concrete age.

Abstract: The use of structural timber has never caught on in Malaysia despite the fact that the country is a major exporter of many commercially important hardwoods such as dark red meranti, kapur and keruing, among others. Chief concern among structural designers is the fact that due to its brittle tensile behaviour, timber tends to fail abruptly under the application of flexural loads. The presence of localized defects such as knots also tend to aggravate the problem as these localities are obviously not only weaker compared with the overall strength of the timber member considered, but also tend to be stress concentration regions. For engineered wood products (EWPs) such as glued laminated timber, the introduction of finger joints further compounds the predicament of the structural engineer as these joints are now crack initiation locations because these joints tend to open up when experiencing tensile forces due to flexural loads. However, it is possible to address these concerns by carrying out flexural strengthening of timber members using materials as varied as steel, fibre reinforced polymers (FRPs), biological fibres, and perhaps timber itself, albeit of a higher strength. This paper seeks to review the current strategies undertaken by international researchers to fortify and bolster the flexural strength of timber in order to make it an attractive construction material to architects, engineers and builders alike.

Abstract: Elements of aircraft that are in direct interaction with the environment are exposed to the destructive effects of weather phenomena and the factors influencing them, as well as local environmental phenomena. One such factor is ultraviolet radiation emitted by the sun. This article presents the results of the influence of solar radiation (UV) on the strength properties of laminates with different types of reinforcement. The composites are susceptible to impact damage; therefore, to investigate the effect of UV radiation on such damaged composite, part of the samples were subjected to impact loads. The composites were made of the epoxy resin Epidian 52 with hardener Z1, and reinforced with glass fabric and carbon fabric. In order to carry out the research, we designed two devices – one for the production of low-energy impact and a second device to expose composite on UV radiation. As a result of studies, it was found that the UV radiation has a negative impact on the aesthetic qualities of the composite as well as the flexural strength of the materials. The decrease in strength of the samples subjected to shock loads and the influence of UV radiation is at a level slightly above 50%.

Abstract: Structural rehabilitation involving upgrading of existing structures and buildings conservation has becoming increasingly important. In this paper an experimental campaign on natural stone masonry columns axially confined by fiber reinforced polymers (FRP) is presented and discussed. Two different FRP wrapping system have been used: CFRP (carbon-fiber-reinforced polymer) embedded in epoxy resin, and FRMC (fiber-reinforced-cementitious matrix) embedded in two layers of a special mortar acting as bonding agent. A comparison between the two systems has been carried out. Results show that the ultimate load, stiffness and ductility significantly increase compared with unreinforced columns. Pre-damaged columns strengthened with CFRP and FRCM recover their load bearing capacity and improve their ductility. In addition, experimental results have been compared to theoretical strength previsions provided by literature analytical models, and findings have been analyzed and discussed.

Abstract: FRP strengthening technique provides a promising alternative for masonry structures. This paper presents research results of quasi-static tests investigating the in-plane mechanical behavior of RC-brick masonry walls with opening strengthened with basalt fiber reinforced polymer (BFRP). Two half scale RC-brick walls were constructed, one without any strengthening scheme served as the reference specimen, another one was directly strengthened with BFRP in mixed strengthening configuration. All specimens were tested under low frequency cyclic loading. BFRP can effectively improve the lateral strength of the wall by a factor of 0.16, and the improvement in the lateral deformation capacity was much significant. The seismic performance of the composite wall strengthened with BFRP can exceed the unreinforced reference, which verifies the effectiveness of BFRP strengthening technique to strengthening RC-brick composite masonry structures in seismically endangered regions.

Abstract: To evaluate the interface strength of externally bonded fiber-reinforced polymer (FRP) composites to concrete structures, the method of the Linear Elastic Fracture Mechanic (LEFM) model is simply used. The parameters defining the material properties, describing bond action of the FRP-concrete interface is used , which was got recently by Obaidat from three-dimensional (3D) finite-element simulation results. Both the fracture energy and shear strength of the interface are determined by a function of concrete compressive strength and the adhesive shear stiffness, the maximum transferable load is predicted by LEFM interface bond-slip model. Comparison between the predicted and the experiment results shows good agreement and a certain degree of safe estimation.

Abstract: A progressive collapse of a RC frame structure may be initiated by an event that damages one member of the structure. FRP is widely used in the field of structural reinforcement for its high strength ratio, convenient construction and corrosion resistance. In this paper, the collapse scene of a RC frame specimen with the failure mid-column in three programs has been simulated by LS-DYNA. We can infer the ultimate bearing capacity of the structure is raised about 10% (retrofitted by CFRP), 15% (retrofitted by GFRP) by comparing the results of finite element analysis.

Abstract: This paper reports on part of an ongoing experimental program at the University of Adelaide on FRP-concrete-steel double-skin tubular columns (DSTCs). The main emphasis of the study reported in this paper was to investigate the influence of loading pattern on the axial compressive behavior of DSTCs. To this end, 12 hollow and concrete-filled DSTCs were manufactured and tested under monotonic or cyclic axial compression. All of the specimens were manufactured using high-strength concrete (HSC). The results of the experimental study indicate that that concrete in cyclically loaded hollow DSTCs exhibits slightly larger strength and strain enhancement ratios than concrete in companion monotonically loaded DSTCs. The results also indicate that concrete in filled DSTCs exhibit slightly larger strength enhancement ratios than and similar strain enhancement ratios to concrete in monotonically loaded DSTCs.