Carbon Fiber Reinforced Polymer Wrapping Research Articles

Performance of Axially Loaded Short Rectangular Columns Strengthened with Carbon Fiber-Reinforced Polymer Wrapping

This paper presents results of a comprehensive experimental investigation on the behavior of axially loaded short rectangular columns that have been strengthened with carbon fiber-reinforced polymer (CFRP) wrap. Six series, a total of 90 specimens, of uniaxial compression tests were conducted on rectangular and square short columns. The behavior of the specimens in the axial and transverse directions is investigated. The parameters considered in this study are (1) the concrete strength; (2) the aspect ratio of the cross section; and (3) the number of CFRP layers. The findings of this research can be summarized as follows: The CFRP wrapping enhances the compressive strength and the ductility of both square and rectangular columns, but to a lesser degree than that of circular columns. The ultimate strength and the ductility of the CFRP confined concrete increase with increasing number of confining layers. The increase in strength and ductility is more significant for lower strength concrete, representing poor or degraded concrete, than for normal-to-high strength concrete; that is, the maximum gain in strength that can be achieved for 3 ksi concrete wrapped columns is approximately 90%, as compared to only 30% for 6 ksi concrete wrapped columns. The CFRP confining jacket must be sufficiently stiff to develop appropriate confining forces at relatively low axial strain levels. The gain in compressive strength obtained by the CFRP confined concrete depends mainly on the relative stiffness of the CFRP jacket to the axial stiffness of the column.

Strengthening of concrete columns with carbon fibre reinforced polymer wrap

Reinforced and prestressed concrete columns with one or two layers of carbon fibre reinforced polymer (CFRP) wrap were tested to failure in axial compression. When the results were compared with the maximum load predictions of two proposed design methods, the predictions consistently underestimated actual loads. The design methods are thus conservative. A simple analysis for circular columns reveals that the confining effect of the wrap is not engaged until the concrete actually starts failing and dilating. A finite element model of a chamfered square column confirms this analysis, as do strain readings from the tests. It is shown that strength gains are not linearly related to wrap thickness. The failure mechanism suggests that design should not be based on the ultimate strength or strain of the wrap and that strength gains can be expected to reduce with increasing brittleness of the concrete and with increasing eccentricity.Key words: concrete columns, FRP wrap, reinforced, strengthening.

Performance of Reinforced Concrete T-Girders Strengthened in Shear with Carbon Fiber-Reinforced Polymer Fabric

Results are presented from an experimental investigation into the performance of 20-ft-long reinforced concrete (RC) T-girders strengthened in shear using epoxy-bonded bidirectional carbon fiber reinforced polymer (CFRP) fabric. The aim was to evaluate and gain insight into the effectiveness of shear strengthening of large-scale girders with externally bonded CFRP under a low shear span condition. Four series of tests, corresponding to stirrup spacings of 5.5, 8, 16, and 24 in, were considered. Each series of girders included control specimens with no CFRP wrap and specimens retrofitted in shear with 1, 2, and 3 layers of CFRP wrap. Results indicate that for unwrapped specimens, values for nominal shear predicted by ACI underestimated, by 40-80%, the shear resistance of beams developing arch action, such as those considered herein. For wrapped specimens, the maximum shear force as well as the midspan deflection generally increased with the number of CFRP layers. The optimum number of layers to achieve the maximum gain in shear resistance was found to depend on the internal shear steel reinforcement provided. The effective CFRP strain used to calculate the contribution of the CFRP to the shear capacity was correlated to the total shear reinforcement ratio consisting of steel stirrups and CFRP wrap. Retrofitting RC girders in shear with CFRP wrap also increased the ductility. Experimental evidence shows an optimum combination of CFRP layers and steel stirrups exists for a maximum increase in ductility.

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.

Flexural Strengthening with Carbon Fiber-Reinforced Polymer Composites of Preloaded Full-Scale Girders

This paper presents results of an experimental investigation on the effectiveness of flexural strengthening with epoxy-bonded, carbon fiber reinforced polymer (CFRP) laminates. The laminates were applied to 20-ft-long reinforced concrete (RC) T-girders preloaded to different levels of stress. The study's aim was to evaluate the performance of precracked girders under service load, where the service load is defined as a percentage of the yield strength for the section. The girders were loaded at a predefined stress level, locked into place, and retrofitted with CFRP fabric. Eight T-girders were tested. A control girder with no wrap and a reference girder with 2 layers of CFRP wrap were tested up to failure in one run for comparison purposes. In the other girders, the level of preload and the wrapping method used were varied. The girders were preloaded up to 65, 85, and 117% of control yield moment and locked and strengthened with 2 layers of CFRP wraps before resuming the loading to failure. Results show the feasibility of rehabilitating and strengthening damaged RC structures with CFRP wrap while under service load.