International Concrete Abstracts Portal

The research described encompasses laboratory as well as in-situ testing of reinforced concrete beam-column joints and multicolumn bridge piers rehabilitated with FRP composite jackets. Fourteen RC beam-column joint tests were performed and a design equation was developed which determines the thickness of the FRP composite jacket and the orientation of the fibers for maximum effectiveness in enhancing shear capacity and ductility. Several in-situ tests were conducted at the South Temple Bridge in Salt Lake City, which included a three-column bridge pier without an FRP composite seismic retrofit, a pier retrofitted with FRP composite jackets, and a pier retrofitted with FRP composite jackets and a reinforced concrete grade beam. The design of the seismic retrofit was based on rational criteria, which included the design of the foundation and column retrofit, and the design equation for retrofitting reinforced concrete beam-column joints, developed in the laboratory tests. The performance target for the seismic retrofit was a displacement ductility twice that of the pier without the FRP composite retrofit. The FRP composite jacket was able to strengthen the cap beam-column joints of the pier effectively and the displacement ductility was increased to the designed level.

This paper presents the results of an experimental investigation on the axial behavior of medium and large scale Reinforced Concrete (RC) columns of circular and non-circular cross-sections strengthened with unidirectional Carbon Fiber Reinforced Polymer (CFRP) wraps. A test matrix was developed to investigate the effect of different variables, such as the geometry of the specimen cross-section (circular, square, and rectangular), the side aspect ratio, and the area aspect ratio. A total of 22 specimens were divided into six series of three specimens each and two series of two specimens each. The largest and smallest columns featured cross-sectional areas of 0.8 m2 (9 ft2) and 0.1 m2 (1 ft2), respectively. All the specimens were subjected to pure axial compressive loading. The experimental results are compared with available data on RC specimens with one minimum dimension of the cross-section of 300 mm (12 in.). This evaluation allowed confirming that among circular and non-circular specimens of the same cross-sectional area and FRP volumetric ratio, the level of confinement effectiveness decreases as the side aspect ratio increases. Additionally, size effect within specimens of circular cross-section does not appear to be significant; however, for the case of non-circular specimens, scatter and limitation of data-points does not allow at the present time to draw a definite conclusion. A new analytical method that allowed estimating the confining pressure in non-circular cross-sections from the transverse strains at the corners is proposed. The obtained confining pressures and experimental results from this study allowed calibrating a strength model, which was validated with the available experimental data in the literature. Finally, the predictions of this strength model were compared to the ones by the model of Lam and Teng yielding close agreement.

This paper presents the performance of a full-scale reinforced concrete cor¬ner beam-column-slab specimen that was first severely damaged under bidirectional quasi-static loading, then rehabilitated and retested. The specimen was built using the pre-1970s construction practices including the use of low-strength materials ( =3000 psi [21 MPa], Grade 40 reinforcing bars) and deficiencies in reinforcement detailing. The rehabilitation process consisted of: (1) epoxy injection, (2) addition of a bar within the clear cover of the column at the inside corner, and (3) external application of a multilayer composite system made of unidirectional carbon-epoxy layers placed at different orienta¬tions. The carbon fiber-reinforced polymeric system was heat-cured at a temperature of 80°±10°C (176°±18°F) for 6 hours. The performance was evaluated both before and after rehabilitation based on the progression of damage and the hysteretic behavior including the changes in the strength, stiffness, and energy dissipation characteristics. The results indicated that even a severely damaged corner joint can be effectively rehabilitated using CFRP to achieve a ductile beam failure mechanism. The joint was upgraded to withstand story drift ratios of up to 3.7% applied simultaneously in both directions.

Development of the full inelastic lateral capacity of a reinforced concrete pile shaft is likely to require the formation of a plastic hinge below grade level. It has been shown through analytical and experimental investigation that the soil around the pile has a significant confining effect on the pile shaft, allowing the development of larger plastic strains in the compression zone than would be predicted based on the amount of transverse reinforcement provided. It was postulated that this confining effect could be built into precast prestressed piles by the addition of a GFRP jacket in the potential plastic hinge region during the construction process. Two large-scale prestressed pile specimens were thus fitted and tested in flexure to simulate a typical subgrade moment pattern. The piles exhibited higher flexural strength and significantly lower ductility capacity than a control specimen which did not have a GFRP jacket. Failure was through complete tendon rupture at a wide flexural crack which opened at the point of maximum moment. High clamping pressures from the jacket upon the tendons were caused by dilation of the compression zone. This pressure ‘anchored’ the tendons under the jacket, preventing bond slip over a wide region and forcing large inelastic strains into the short tendon length exposed at the major flexural crack. The ACI 318 equation for development length was found to give a reasonable quantitative prediction of the enhanced bond strength, expressed as reduced flexural transfer (i.e., development) length of the tendons by considering active confining pressure.

The paper discusses the potential use of fiber reinforced polymer composites for repair and retrofit of existing reinforced concrete (RC) column-tie beam assemblies. Results of an experimental program performed on large-scale specimens repaired and strengthened with two types of wet lay-up composite systems are presented. Each column-tie beam assembly specimen was subjected to a constant axial load simulating gravity loads, and incremental cyclic lateral loads simulating potential seismic forces. Displacements, strains and loads were continuously monitored and recorded during all tests. Evaluations of the observed strength and ductility enhancements of the strengthened specimens are made and limitations of such retrofit methods are highlighted for design purposes. Experimental results indicated that the two composite systems used in this study succeeded in enhancing the strength, stiffness and the ductility of the column-tie beam assembly. As compared to the unstrengthened specimens, the strengths of the retrofitted specimens were 152% and 154% for carbon/epoxy and E-glass/epoxy composite systems, respectively.