Use of Carbon Fiber Reinforced Polymer Composites to Increase the Flexural Capacity of Reinforced Concrete Beams

A large portion of the off-system bridges and some on-system bridges in Texas were constructed in the 1950s using vehicle loads that are less than the current design standards. As a result, the legal load that is permitted to cross these bridges is often limited and many are scheduled for replacement. The use of carbon fiber reinforced polymer (CFRP) composites to increase the flexural capacity of reinforced concrete bridges was investigated in this research project. The overall goal was to develop design procedures for strengthening existing bridges using CFRP to avoid replacement of bridges that have been functioning satisfactorily for many years.

The first two phases of the research project are described in this report. A total of twenty-two, rectangular reinforced concrete beams were tested during the first phase of the project. The beams were strengthened using four CFRP systems and were subjected to monotonically increasing load. The primary test parameter was the layout of the CFRP system. Two layouts were identified that prevented premature debonding of the CRFP composites from the surface of the concrete.

Eight rectangular beams were strengthened using two of the previously tested CFRP systems and were subjected to fatigue loads in the second phase of the project. The composite/concrete interface did not degrade under the fatigue loads. Strengthened beams sustained one million cycles at service levels with only a negligible influence on the measured behavior.

An analytical model was developed to calculate the behavior of the strengthened beams. The model provided reasonable estimates of the measured mid-span deflections. However, the model was not capable of reproducing the measured strains in the materials due to local debonding of the CFRP from the surface of the concrete.