Use Of Carbon Fiber Reinforced Polymer Research Articles

Efficient Strengthening Technique to Increase the Flexural Resistance of Existing RC Slabs

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-surface mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the...

Improving seismic performance of deficient reinforced concrete columns using carbon fiber-reinforced polymers

Reinforced concrete columns lacking transverse reinforcing steel do not possess necessary ductility to dissipate seismic energy during a major earthquake. The study reported herein investigates the use of carbon fiber-reinforced polymer (CFRP) wrapping as a method of retrofitting nonductile square reinforced concrete columns with low strength concrete and plain bars. Five specimens representative of transverse steel deficient flexure dominated columns in existing buildings were tested under lateral cyclic displacement excursions and constant axial load. The main parameters under investigation were the number of layers of CFRP wrap and presence and absence of the axial load on the column during strengthening. It was found that upon CFRP retrofit, deficient columns were able to withstand larger deformation demands without strength degradation. The test results were also compared with the results obtained from the analytical study that was conducted using a simple plastic hinge model considering the effects of FRP confinement and slip of plain bars. A good agreement between analytical and experimental results was observed.

Behavior of Prestressed Concrete Strengthened with Various CFRP Systems Subjected to Fatigue Loading

Many prestressed concrete bridges are in need of upgrades to increase their posted capacities. The use of carbon fiber-reinforced polymer (CFRP) materials is gaining credibility as a strengthening option for reinforced concrete, yet few studies have been undertaken to determine their effectiveness for strengthening prestressed concrete. The effect of the CFRP strengthening on the induced fatigue stress ratio in the prestressing strand during service loading conditions is not well defined. This paper explores the fatigue behavior of prestressed concrete bridge girders strengthened with CFRP through examining the behavior of seven decommissioned 9.14m(30ft) girders strengthened with various CFRP systems including near-surface-mounted bars and strips, and externally bonded strips and sheets. Various levels of strengthening, prestressing configurations, and fatigue loading range are examined. The experimental results are used to provide recommendations on the effectiveness of each strengthening configuration. Test results show that CFRP strengthening can reduce crack widths, crack spacing, and the induced stress ratio in the prestressing strands under service loading conditions. It is recommended to keep the prestressing strand stress ratio under the increased service loading below the value of 5% for straight prestressing strands, and 3% for harped prestressing strands. A design example is presented to illustrate the proposed design guidelines in determining the level of CFRP strengthening. The design considers the behavior of the strengthened girder at various service and ultimate limit states.

Static and Dynamic Testing of a Concrete T-Beam Bridge Before and After Carbon Fiber-Reinforced Polymer Retrofit

This paper summarizes the design and execution of field studies to improve the performance of a deteriorated bridge through the use of carbon fiber-reinforced polymer (CFRP) material. The objective of the CFRP retrofit was to extend the life of Bridge 2028 in Cayey, Puerto Rico, by increasing its load rating. Field testing before and after the retrofit was performed to evaluate objectively improvement in load capacity and stiffness. The field testing program included both static load tests and dynamic tests. The first set of field tests was conducted in November 2002 to capture baseline bridge performance characteristics before the retrofit. The CFRP retrofit was installed in October 2003, and a second set of nearly identical field tests was performed in August 2004. The test results indicated that the retrofit increased the bending stiffness of the bridge by 15% and decreased the tensile strains in the bottom rebars of the concrete T-beams by about 13%. Furthermore, the maximum rebar strains under a heav...

Experimental Study of Strengthening for Increased Shear Bearing Capacity

The need for structural rehabilitation of concrete structures all over the world is well known, and a great amount of research is going on in this field. The use of carbon fiber-reinforced polymer (CFRP) plate bonding has been shown to be a competitive method with regard to both structural performance and economic factors. This method consists of bonding a thin carbon-fiber laminate or sheet to the surface of the structure to act as an outer reinforcement layer. However, most research in this area has been undertaken to study flexural behavior. This paper deals with shear strengthening of reinforced concrete members by use of CFRP. Tests on rectangular beams 3.5 to 4.5 m long have been undertaken to study different parameters, such as fatigue, anchorage, and others. The strain field in shear spans of beams simultaneously subjected to shear and bending is also studied. The tests presented also contribute to the existing literature on tests of concrete members strengthened for increased shear capacity.

Fatigue Tests of Reinforced Concrete Beams Strengthened Using Carbon Fiber-Reinforced Polymer Composites

The use of carbon fiber-reinforced polymer (CFRP) composites has been identified as a viable technique for use in strengthening deteriorating or structurally deficient reinforced concrete bridges. This article presents the results of a study that consisted of repeated-load fatigue testing 10 reinforced concrete beams strengthened using two different types of externally-bonded CFRP composites. The results indicate that the bond between the composite laminates and surface of the concrete can degrade at load amplitudes corresponding to extreme load conditions for a bridge. The stress range applied to the reinforcing steel and maximum stress applied to the composite laminates were the controlling parameters that limited the fatigue life of the specimens under study. The authors conclude that an upper limit on stresses generated along the composite-concrete interface may have to be set during design to avoid premature debonding after a limited number of load cycles.

Upgrading of slab–column connections using fiber reinforced polymers

The results of an experimental program on upgrading of reinforced concrete slab–column connections subjected to monotonic shear and unbalanced moment transfer are presented in this study. Externally installed carbon fiber reinforced polymer (CFRP) stirrups acting as shear reinforcement around the slab–column connection area were used with two patterns of CFRP arrangements. It was found that the proposed method resulted in punching shear capacity increases up to 60% relative to the specimen without any strengthening. In some cases punching shear failure was eliminated with the use of CFRPs as shear reinforcement. Capacities of test specimens were evaluated using punching shear strength provisions of ACI 318-02 and yield line analyses for the test specimens. On the basis of the results of this study, use of CFRPs as externally installed stirrups was found to be successful in strengthening slab–column connections.

Strengthening concrete beams for shear with CFRP sheets

The method of strengthening concrete structures with FRP composites has existed for over a decade; the most common way to strengthen structures is in bending, but also wrapping of columns is quite common. There are also needs for strengthening concrete structures in shear, for example concrete beams, slabs, columns, etc. A typical structure can be a parking garage. However, strengthening concrete structures for shear is not as common as for bending and confinement. This paper presents examples to strengthen concrete beams for shear. First traditional strengthening methods are presented briefly, then the use of CFRP (Carbon Fibre reinforced Polymers) composites for shear strengthening is presented. Tests on beams strengthened in shear with CFRP sheets are presented and a short presentation on how to design for shear strengthening with CFRP is given. Furthermore, a field application of a parking slab strengthened for shear with CFRP unidirectional fabric is presented. The laboratory tests show the importance of considering the principal directions of the shear crack in relation to the unidirectional fibre. The field application shows that it is easy to strengthen existing structures for shear with CFRP fabrics.

Carbon Fiber-Reinforced Polymer Wraps for Corrosion Control and Rehabilitation of Reinforced Concrete Columns

This paper discusses the use of carbon fiber-reinforced polymer (CFRP) wraps as a rehabilitation technique for corroded reinforced concrete columns. The effect of applying the wraps at early ages of the columns and its effect on corrosion propagation is addressed. Interaction between corrosion phenomena and the CFRP wrapping is studied through simple combinations of both factors. The lab work included testing of 52 reinforced concrete cylinders. The testing procedures are described. It was concluded that applying CFRP wraps significantly decreases corrosion activity when applied over the entire specimen. The application of the wraps before corrosion propagation will prevent corrosion from taking place, while the application of the wraps after corrosion occurrence will drop the rate of corrosion sharply. This effect is likely due to the epoxy saturant used to apply the CFRP sheets and not from the fibers themselves.

Reinforced concrete beams externally retrofitted with advanced composites

This study investigates the effect of externally bonded carbon fiber reinforced polymer (CFRP) laminates on the ductility of reinforced concrete beams used in the repair of damaged bridge structures. Reinforced concrete structures deteriorate over time due to environmental aging, fatigue, excessive loading, chemical attack, and other factors. Strengthening and rehabilitating these concrete structures by externally bonding carbon laminates is one of many economical engineering solutions. Eight rectangular beams with varying internal steel reinforcement were retrofitted with CFRP strips on the tension faces and tested under four-point bending. The beams were instrumented to monitor strains, deflection, and curvature over the entire spectrum of loading, and determine the structural response of the beams. An existing analytical model using the discrete yield and ultimate values of the load-deflection and moment-curvature curves was modified to an energy-based model, and used to predict the ductility of the beams. Numerical results indicated an increase in strength, a decrease in ductility, and validated the analytical model. Ultimately, this study will aid in the development of design guidelines governing the use of CFRP.