Increasing the Flexural Capacity of Typical Reinforced Concrete Bridges in Texas Using Carbon Fiber Reinforced Polymers

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 third phase of the research project is described in this report. Four full-scale specimens representative of bridge construction during the 1950s in Texas were constructed, strengthened, and tested in the laboratory to assess the effectiveness of the CFRP composites for increasing the flexural capacity. Results from the laboratory tests indicate that the composite materials may be used successfully to strengthen existing bridges. The strength of all specimens was controlled by debonding of the CFRP composites from the surface of the concrete.

An analytical model was verified using the measured response of the laboratory specimens. The model was able to reproduce the overall response of the specimens, but did not reproduce the local modes of failure. Therefore, the model may be used to design strengthening systems for reinforced concrete bridges, but the maximum strain in the CFRP composites must be limited to reflect the observed modes of failure. Design guidelines for CFRP systems are presented.