Load Testing of Precast Box Beams for Naval Facility Trestle Structure


A trestle structure at a U.S. Naval Facility extends approximately 9,000 ft seaward and provides access to three pier structures.  The trestle was reportedly constructed in the early 1990’s and incorporates 172 spans and 623 individual precast concrete box beams. During the first 20 years of service, several of the box beams reportedly exhibited signs of significant distress in the form of concrete cracking and corrosion of embedded reinforcing steel.  During subsequent repair efforts, it was noted that the thickness of bottom and side concrete surfaces on some box beams was variable and nonconforming due to misplacement or movement of polystyrene inserts use to form and fill the beam void spaces during fabrication. This finding prompted the Navy to undertake a box beam repair program that included strengthening of 173 individual box beams using Carbon Fiber Reinforced Polymer (CFRP).

As part of the Trestle 1A repair project, the Navy requested that two separate load tests be performed to evaluate the structural behavior of two representative box beams. Two load tests were performed on each of two selected box beams. The first load test (Pre-Strengthening Load Test) was performed with the box beams in the in situ, as-found condition. The second load test (Post-Strengthening Load Test) was performed after the beams had been strengthened with CFRP. CTLGroup was retained to execute the required load tests on behalf of the repair contractor. The load test program included instrumentation of the two selected box beams and using a locomotive provided by the Navy to apply load. Measured strain data recorded during the load tests was used to verify the effectiveness of the applied CFRP repairs.


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