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.

Externally bonded carbon fiber reinforced polymer (CFRP) is a feasible and economical alternative to traditional methods for strengthening and stiffening deficient reinforced and prestressed concrete bridge girders. The behavior of bond between FRP and concrete is the key factor controlling the behavior of these structures. Several experiments showed that debonding failure occurs frequently before FRP rupture and therefore the FRP strength can not be fully utilized. For design accuracy, the FRP strength must be reduced. This paper analyzes the effect of the bond properties on the response and failure modes of FRP-strengthened RC beams. A nonlinear RC beam element model with bond-slip between the concrete and the FRP laminates is used to analyze a test specimen subjected to monotonic and cyclic loads typical of seismic excitations, and to investigate the corresponding failure mode, and whether it is due to FRP rupture, debonding, or concrete crushing. The model is considered one of the earliest studies to numerically evaluate the behavior of FRP-strengthened girders under seismic loads. The model was also used to study the reduction factor of FRP tensile strength of simply supported strengthened RC girders due to debonding failure. This reduction factor seems to be directly affected by the bond strength between FRP and concrete interface. The study concludes with a numerical evaluation of the current ACI-440 guidelines for bond reduction factors.

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.

The effectiveness of discrete and continuous CFRP wrapping arrangements for reinforced concrete (RC) short column subjected to monotonic and cyclic compressive loading is assessed in this work. The experimental program is composed of four series of RC columns with discrete wrapping arrangements and one series of full wrapped RC columns. Each series is composed of a monotonic and a cyclic test. Strain gauges were installed along the height of each column to measure the strain field in the CFRP during the test. The variation of the stiffness of the unloading and reloading branches of each loading cycle was determined. A constitutive model to simulate FRP-confined RC concrete elements subjected to cyclic compressive loading was developed and implemented into a computer program based on the finite element method. This model was appraised with the data obtained from the carried out experimental program.

A simple hysteretic model is proposed to define the cyclic response of reinforced concrete (RC) beam to column joints retrofitted with (carbon fiber reinforced polymer (CFRP) composites. This model includes the option to consider strength degradation resulting from damage within the joint region. The model consists of two nonlinear springs connected in series and positioned at the ends of linear elastic beam elements. The hysteretic models representing these springs were empirically derived from beam to column joint specimens retrofitted with CFRP composites and are capable of describing the hysteretic characteristics of reinforced concrete members in the column as well as in the joint hinge region. The model was subsequently used to evaluate the response of two test units that were retrofitted with CFRP composites at different damage levels. Key experimental results along with the proposed models and simulation results are presented and discussed in this paper. The analytical results were able to reproduce reasonably well the experimental data.