During the summer of 2007, Structural Preservation Systems (SPS) completed a unique pre-stressed beam repair project for a new parking structure for a government office building in the Washington, DC area.  The project required the repair of two post tensioned beams damaged after being overloaded during construction.  The beams were repaired using external post tensioning encased in a concrete section enlargement.

The initial repair option was to remove and replace the damaged beams.  To do this, the post tension slab above the damaged beams would require detensioning and extensive shoring, which would need to be extended through several levels below.  This would be a costly repair option that would result in significant delays.

SPS developed an alternate, in place repair solution that involved enlarging the damaged beams using self consolidating concrete (SCC) and post tensioning with mild steel reinforcement to add strength.  As it was impossible to estimate the damaged capacity of the beams, it was assumed that the original reinforcement had yielded and would no longer contribute to the load carrying capacity of the beam.  Therefore, the SPS retrofit would include the same amount of post tensioning in the original beam and the enlarged section would have to be bonded such that the new and old sections acted compositely in order to restore the load capacity desired.

The enlarged sections on the sides and bottom of the beams were placed by properly preparing and roughening the surface (1/4" amplitude with open pores) and by using a form and pump concrete placement method.  In this technique, the concrete is pumped under pressure to force it into the pores of the existing concrete surface such that the new concrete section becomes composite with the existing beam.  After initial cure, the post tensioning cables were stressed to the specified forces and the repair was complete.

This project highlighted SPS's ability to:

• Solve the beam repair issue for the General Contractor and Owner
• Work with the Engineer on the technical design aspects of the proposed repair
• Address the aesthetic concerns of the Architect and the Owner
• Complete the repairs faster and at half the cost of the total replacement option

As a result, the General Contractor, Owner, Engineer and Architect were overwhelmingly  pleased with the finished product and thoroughly impressed with SPS's technical proficiency, attention to detail and focus on safety.