Investigation on flexural performance of cracked concrete beam strengthened using CFRP with intermediate anchors at cracked locations

The flexural performance of heavily cracked reinforced concrete (RC) beams strengthened with different carbon fibrereinforcedpolymer(CFRP) arrangements was investigated. In total twelve CFRP-strengthened and non-strengthened RC beams with a span of 1900 mm were tested. : Initially, a transient load was applied to the non- strengthened beams until 3 mm wide cracks appeared. Load versus deflection was monitored. The wide cracks were filled using a high-pressure epoxy injection prior to strengthening. CFRP sheets were epoxy bonded to the tension face of the beams and CFRP U-strap anchors were introduced at discrete locations to mitigate both end and intermediate span debonding. All specimens were tested using a four point 1 bending configuration. On average, an 80% to 118% increase in flexural capacity was noted for | the pre-cracked and repaired strengthened beams and the average strength gain noted for noncracked beams strengthened with CFRP was 37%. Cracked beams strengthened with CFRP with polymer U-shaped anchors showed optimum performance. De-bonding was the dominant failure mode in most tested specimens

Design of fibre reinforced polymer (FRP) strengthened beam for flexure

Nowadays, upgrading civil engineering structures is a very important issue, particularly for concrete bridges and buildings. For concrete bridges, increase in traffic load and deterioration caused by environmental factors are the two main reasons for a decrease in safety. FRP strengthening technique is widely gaining appeal in civil engineering infrastructures due to its superior properties and ease of construction and strengthening. However, the application of this technique is very limited in Sri Lanka. This is mainly due to lack of knowledge about FRP applications, selection of materials and also design procedures. The paper presents the background and detailed design procedures for FRP strengthened beam subjected to flexure

A Review on alternative bonding techniques to delay end debonding of CFRP/concrete composites

Externally bonded Fiber Reinforced Abstract: Polymers (FRP) has been widely used for flexural strengthening of reinforced concrete structures. End debonding is a critical issue which causes a significant reduction of ultimate capacity of the strengthening system. End debonding occurs due to cracks induced by high interfacial shear and normal stresses caused by the abrupt termination of the plate. The failure can be in two modes; plate end shear failure and anchorage failure at last crack. The common attribute of both these failure modes is that delamination occurs along the track with minimum fracture energy. By introducing a proper anchorage, stresses can be effectively transferred to the concrete element and energy required to the failure can be increased. There are many research works that have been carried out to investigate possible techniques to delay end debonding failure. However there is no any record of effort taken to scale those techniques in to a single study. This research paper presents a review on usage of FRP wraps to delay end debonding. It summarizes different wrapping methods used to delay end debonding which have proposed in the literature and compares them in terms of efficiency

Investigation on effectiveness of NSM CFRP Vs EBR CFRP for strengthening concrete members

This paper is based on literature review on Carbon Fibre Reinforced Polymers (CFRP) materials used as near surface mounted (NSM) reinforcement in order to strengthen Reinforced Concrete (RC) structures. Rehabilitation of structures is a complicated task that has been made simple by the utilization of CFRPs. Out of the two methods of externally bonded reinforcement (EBR) and near surface mounted (NSM) reinforcement it has been proven that NSM methods provides better results. This paper presents alternative methods that can be used to improve the bond performance of NSM CFRP on RC structures. It also highlights research gaps that need to be addressed in order to sharpen the knowledge and improve the common practices of CFRPs

Investigation on effective use of CFRP laminates for flexural performance

Use of Fiber Reinforced polymer (FRP) materials for strengthening concrete structures is widely gaining appeal worldwide due to its superior properties such as light weight, high strength and stiffness, resistance to corrosion and flexibility. Among those materials, Carbon Fiber Reinforced Polymer (CFRP) has extensive properties over other fiber types; negligible affect by water and high resistance to ultra violet radiations etc. Therefore it is veiy beneficial to use CFRP for retrofitting infrastructures. They can be used to strengthen structures basically for shear, flexure, torsion and confinement of concrete columns. When considering flexural strengthening, there are two main failure modes; classical failure and premature failure. The latter is the most common failure mode. Most of CFRP strengthening systems undergo de-bonding failure before reaching their full capacity. Therefore the frill capacity of CFRP sheet is under-usage. This study was conducted to investigate the effects of CFRP laminate width on performance and premature failure of the system. Seven CFRP strengthened reinforced concrete beams were tested by three point bending test method. This paper presents the test program, results and recommendations

A Review on fracture-mechanics based models on debonding nature of CFRP/Concrete composites

Debonding failure of externally strengthened CFRP/concrete composites is the most critical failure mode which needs to prevent to achieve a beneficial strengthening solution. Many theoretical and numerical models have been developed to predict the failure load of CFRP/concrete composites. Existing theoretical models are grounded on strength-based and fracture-mechanics based approaches. The use of strength-based models is obsolete due to their inability to estimate the failure behaviour throughout the debonding process. By means of fracture-mechanics based models, both the initiation and propagation of cracks can be explored in terms of interface fracture energy. In the present study, existing fracture-mechanics based models are evaluated using a database and the reliability of the models are analyzed using statistical parameters and suggests best models which can accurately quantify the debonding failure load of CFRP/concrete composites. In addition, a new reduction factor aGF is introduced for interfacial fracture energy for the debonding failure mode which takes place along the CFRP/concrete interface

Investigation on enhancing flexural p erformance of CFRP strengthened concrete beams

Strengthening of reinforced concrete structures is inevitable to preserve structural integrity and protracted service life due to the effects of numerous elements contained within the natural or artificial environment surrounding it. Carbon Fibre Reinforced Polymer (CFRP) composites have been progressively more utilized for decades as a strengthening material due to its outstanding characteristics such as high strength to weight ratio, reduced weight, excellent resistance to corrosion and environmental degradation and ease of handling during construction which have distinguished it well apart from the other strengthening techniques. However, the ultimate load capacity of CFRP strengthened concrete composites is comparatively lower than CFRP material due to premature debonding which reported as the most frequently observed failure mode in CFRP/concrete composites. In the current study, alternative bonding techniques were investigated to achieve enhanced bond performance by delaying premature debonding failure. A total of 18 CFRP strengthened concrete beams with different bonding techniques were tested using three point bending test. The test results show convincing evidence on strength enhancements. Moreover, a numerical model was also developed to inspect the performance of existing CFRP anchors. Finally, a parametric study was carried out and a new type of anchor; “Tri-leg anchor” is introduced. This paper summarizes the overview of the test programme, finite element modeling, results and analysis

Behaviour of Concrete Produced with Cement and Rice Husk Ash

Disposal of rice husk and its ash has been identified as a major problem in areas where rice production is abundance. Cement is an expensive material which plays a major role in the construction industry. This study shows the utilization of Rice Husk Ash (RHA) in concrete by conducting the laboratory experiments. Replacement of cement with RHA enhances both compressive and tensile properties of concrete. For this study, RHA was obtained from Bio-Energy power plant located in Ampara, Sri Lanka. As received RHA was sieved in order to prepare two types of samples with different particle sizes. Enhanced performances of Ordinary Portland Cement (OPC) can be achieved with 10% replacement of OPC by RHA regardless of particle sizes. Moreover, the adverse environmental impacts associated with RHA can also be reduced by utilizing the RHA in cementitious systems

Bond performance of CFRP/steel composites: state of the art review

Over the past decade, CFRP (Carbon Fibre Reinforced Polymer) has been established as an excellent strengthening material to use in the metallic structures. Performance of CFRP strengthened steel members is directly dependent on the quality and the integrity of the adhesive bond. However, the insufficient knowledge on the bond behaviour of the CFRP/steel bonded joints is the major drawback in the lacking of real world applications of this system. Bonding procedure, including the surface preparation, different loading conditions and environmental conditions experienced can critically affect the bond behaviour and its performance. Studies have shown that dynamic loadings (fatigue/impact) can contribute to the strength and stiffness reduction of the bond while aggravating the results in severe exposed conditions. Also, these structures are frequently exposed to environmental conditions such as temperature variations, humidity conditions, UV radiation and marine environment. The consequence is severe when these exposure conditions are combined. This paper presents a state of the art review on bond performance of CFRP strengthened steel members for different load effects

A Review on alternative bonding techniques to delay end debonding of CFRP/Concrete composites

Externally bonded Fiber Reinforced Abstract: Polymers (FRP) has been widely used for flexural strengthening of reinforced concrete structures. End debonding is a critical issue which causes a significant reduction of ultimate capacity of the strengthening system. End debonding occurs due to cracks induced by high interfacial shear and normal stresses caused by the abrupt termination of the plate. The failure can be in two modes; plate end shear failure and anchorage failure at last crack. The common attribute of both these failure modes is that delamination occurs along the track with minimum fracture energy. By introducing a proper anchorage, stresses can be effectively transferred to the concrete element and energy required to the failure can be increased. There are many research works that have been carried out to investigate possible techniques to delay end debonding failure. However there is no any record of effort taken to scale those techniques in to a single study. This research paper presents a review on usage of FRP wraps to delay end debonding. It summarizes different wrapping methods used to delay end debonding which have proposed in the literature and compares them in terms of efficiency