Search

Unanchored U-wrapped externally bonded carbon-fiber-reinforced polymer (CFRP) fabrics are widely used to increase the design shear strength of existing reinforced concrete slab-on-beam structures, but current design models do not accurately predict the degree of enhancement. Experimental investigations further indicate that some T-beams retrofit with externally bonded CFRP fabric fail at lower shear loads than nominally identical nonretrofit reference counterparts, suggesting a negative experimental CFRP contribution. This work finds a new application for the upper-bound theorem of plasticity in analyzing the problem of U-wrapped externally bonded CFRP-retrofit beam behavior. The study provides insight into the poor historical prediction of the CFRP contribution, and demonstrates the limitations of a widely used experimental approach to determining this contribution. The analysis suggests a new way of thinking about the behavior of slab-on-beam structures retrofit with unanchored U-wrapped externally bonded CFRP. The upper-bound plastic analysis provides better predictions of retrofit shear capacity than some widely used design models, indicating that this approach can lead to better design of retrofit interventions in future. This work proposes a new design limit on enhancement that can reduce the likelihood of unsafe design in practice.

The strategic road network (SRN) in England carries 33% of traffic in England and Highways England's bridge management systems plays a crucial role in the maintenance of infrastructure assets along the SRN. Reinforced concrete half-joint structures are susceptible to deterioration and hard to inspect, hence they require special attention. Inspection data relating to half-joint structures on the SRN was gathered. Within this portfolio, 252 structures with half-joint-related defects were interrogated to classify the most common defects and identify any potential shortcomings in current inspection practice. Clear correlations were shown to exist between defect classes, emphasising the need for quality control and proper workmanship. A revised inspection methodology for half-joint structures that provides more comprehensive information about crack details, and a greater alignment between defect information and indicators of structural measures, is proposed. Concurrently, knowledge of the zonal crack location, crack orientation and crack severity helps inform decision making about the structural condition. There is scope for use of the methodology in conjunction with automated processing procedures to identify half-joint structures with particular defect characteristics and profiles. In this way, asset managers will be better able to allocate resources to structures with an increased risk of failure.

The authors wish to gratefully acknowledge the financial support of the United Kingdom Engineering and Physical Sciences Research Council (EPSRC) through Grant EP/I018972/1.

An experimental investigation was undertaken into the effectiveness of unanchored and anchored externally bonded (EB) U-wrapped carbon fibre reinforced polymer (CFRP) shear strengthening for reinforced concrete T-beams at a range of realistic sizes. The T-beam sizes, geometry and reinforcement were chosen to reflect existing slab-on-beam structures with low levels of transverse steel shear reinforcement. Geometrically similar reinforced concrete T-beams were tested across three sizes ranging from 360 to 720 mm in depth and with different amounts of EB CFRP shear reinforcement. The beams were subjected to three-point bending with a span to depth ratio of 3.5. All the beams failed in diagonal shear. The experimental results indicate significant variability in the capacity of unstrengthened control beams, and a number of these control beams showed greater shear capacity than their EB CFRP strengthened counterparts. Greater thicknesses of CFRP reinforcement did not lead to increased shear capacity compared with lesser thicknesses of unanchored or anchored EB CFRP, but anchored EB CFRP did lead to moderate increases in shear capacity compared to both control and unanchored EB CFRP strengthened beams.

This study reports the findings of an experimental investigation into the behavior of an inclined shear plane in reinforced concrete, such as a diagonal crack in the web of a beam, strengthened with externally bonded carbon fiber–reinforced polymer (CFRP) fabric. A modified push-off test of novel geometry was developed for this study. This test generates a diagonal failure plane subject to combined shear and tension. Both unwrapped and wrapped tests were conducted, allowing the load sharing and load-displacement behavior of the reinforced concrete, and the reinforced concrete with externally bonded CFRP fabric, to be investigated. Fully wrapped and U-wrapped CFRP fabric configurations were tested. Results indicate that for the arrangement tested, concrete, steel, and CFRP contributions to resistance are not independent, and that effective anchorage lengths given in the United Kingdom and United States guidance for U-wrapped CFRP may not be adequate in some cases.