Emergency repair of damaged bridge columns using fiber reinforced polymer (FRP) materials

• PI: M. Saiid Saiidi, University of Nevada, Reno
• Research assistant: Ashkan Vosooghi, University of Nevada, Reno
• Sponsor: California Department of Transportation
• Project monitor: Saad El-Azazy
• Project dates: July - September 2009

Project summary

Past effort in the seismic design of concrete bridges has been on detailing of bridges to prevent collapse. During earthquakes, reinforced concrete bridge columns are designed to undergo cracking, spalling, and yielding of steel and provide significant rotational capacity at plastic hinges so that the integrity of the overall structure is maintained.

With proper design and construction, this objective can be met. However, the serviceability of the bridge after the earthquake is in question.

The level of damage to different columns of a bridge varies depending on the intensity of the ground shaking, type of earthquake, and the force/deformation demand on individual members.

Based on the inspection of the damaged columns, engineers have to determine whether the bridge is sufficiently safe to be kept open to traffic. They should also recommend repair methods for the columns.

Any delay in opening of the bridge to traffic can have severe consequences on the passage of emergency vehicles, detour lengths, and traffic congestion in the area. Rapid and effective repair methods are needed to enable quick opening of the bridge to minimize impact on the community.

This project subjected three one-third scale single columns to Sylmar earthquake with gradually increasing PGA using one of the shake tables at the University of Nevada, Reno and the mass-rig setup. After each test, the column was repaired rapidly, using CFRP wrapping, and retested to evaluate the emergency repair performance.

New design high shear column

In this test, the two ends of the column are fixed to apply a double-curvature deformation inducing a high shear demand. The main objective of the test is to achieve the highest repairable damage with no bar rupture (DS-5). At this level of the damage, many spirals and longitudinal bars are visible, some of the longitudinal bars are beginning to buckle, and the edge of concrete core is damaged. No bars are ruptured.

The column underwent approximately 6.4% drift during the shake table test.

The entire repair process consisted of the following steps:

• Straightening the columns
• Concrete chipping (In this step, only the loose concrete was removed)
• Pressurized epoxy injection of the cracks
• Fast set concrete pouring/patching
• CFRP wrapping
• Curing

Old design high shear column

In this study, the column is substandard. It has lap splice at the base and deficient lateral reinforcement. The two ends of the column are fixed to apply a double-curvature deformation inducing a high shear demand. The failure mode of the column is shear. The main objective of the test is to achieve the highest repairable damage with no shear failure.

After the first test, major shear cracks appeared at the column base.

The entire repair process consisted of the following steps:

• Pressurized epoxy injection of the cracks
• CFRP wrapping
• Curing

Old design low shear column

In this study, the column is substandard. It has lap splice at the base and deficient lateral reinforcement. The column is cantilever with low shear. The failure mode of the column is degradation of the lap-splice bond.

After the first test, major ring cracks merged to shear cracks appeared at the column base at the end of the lap splice. At the compression side of the column base, extensive spalling was observed.

The entire repair process consisted of the following steps:

• Remove the loose concrete and repair the spalled area using a fast set / non shrink mortar
• Pressurized epoxy injection of the cracks
• CFRP wrapping
• Curing