A. Objectives
The primary objectives of this study are to
1. Assess the impact of environmental conditions on the strength and behavior of reinforced concrete (RC) bridge girders strengthened with carbon fiber-reinforced polymers (CFRP) for shear and quantify possible long-term durability issues.
2. Investigate the behavior of reinforced concrete bridge girders strengthened with CFRP and exposed to combined accelerated environmental aging and fatigue to evaluate durability of CFRP repairs for shear.
Results will be used to direct possible changes to design specifications and provide guidance for field inspections.
B. Scope
Many concrete bridges remain in the national inventory that are lightly reinforced for shear, contain poor flexural steel details, and are exhibiting diagonal cracking and distress. For these bridges, strengthening techniques are often employed to increase the rating of the bridge and extend service life. One of the most promising materials for strengthening RC bridges is bonded CFRP. The CFRP is used to provide supplemental external shear reinforcement on the face of the girders. It is common for the CFRP repair to be considered only a temporary solution based on uncertainty about the longer-term durability of CFRP repairs under repeated loading and in-situ environmental conditions. Recent research at OSU on fatigue response of full-size RCDG girders repaired with CFRP indicated that the CFRP did not exhibit strength degradation under high-cycle fatigue. However, environmental deterioration of the bonded CFRP remains uncertain and some researchers have suggested that the combined effects of repeated loading and environmental effects may be worse than response under isolated conditions.
The uncertain long-term performance of CFRP strengthening schemes under environmental and combined environmental effects with repeated loading requires that these issues be addressed to ensure desired design outcomes over the expected life of the FRP repairs, and indeed that the design life can be reasonably estimated.
C. Methodology
Full-size RC girders strengthened with surface bonded CFRP for shear will be tested in the Structural Engineering Research Laboratory at Oregon State University. The specimens will be 4 ft deep, and 24 ft long and contain typical flexural reinforcing ratios, but deficient stirrups. After construction, loads will be applied to induce diagonal cracking. Cracks will be epoxy injected and the girders strengthened with externally bonded CFRP strips. The repaired specimens will be pre-loaded to service levels (cracking will be re-imposed for some of the specimens) and then subjected to environmental exposure conditions. Two conditions will be investigated: 1) freeze-thaw with saturated and unsaturated thaw cycles and 2) water saturation at ambient temperature. For a second group of specimens, environmental effects will also be combined with high-cycle fatigue. After environmental exposure, the specimens will be tested to destruction. Results will be compared with previous test specimens not subjected to environmental exposure and findings will be used to recommend design, analysis, and inspection methods.
