One Tribe Place, Post-Tensioned Structural Slab and Building Envelope Repair, Williamsburg, VA
The College of William & Mary purchased an existing hotel to convert into a student housing complex. The facility was constructed in the 1970s with two later additions. The garage serving the original structure is two stories below grade with one elevated post-tensioning (PT) concrete structural slab. During renovations of the building, several failed PT tendons were noted. WDP was retained to conduct a forensic structural evaluation of the PT concrete structural slab to assess the extent of, and potential causes of, PT tendon failures in the garage. No PT shop drawings were available for the garage, so an as-built PT tendon lay-out plan was developed by WDP using surface penetrating radar (SPR) to locate tendon groups along with exploratory openings to assess the conditions of the PT tendons. Based on the results, WDP performed structural analyses to assess the prestress loss due to de-tensioned tendons and provided repair and strengthening recommendations for the garage. WDP further examined the conditions of PT slabs on four remaining floor and roof slabs and determined that other remaining floor and roof slabs did not have significant structural deficiencies. The College had developed a repair program in 2018 and restricted use of the building until repairs were completed. WDP developed the repair documents of project drawings and specifications, which included remaining PT tendon condition assessment, failed PT tendon repair, concrete repair, subgrade waterproofing repair, courtyard waterproofing replacement, pool deck waterproofing, exterior wall thru-wall flashing repair, and traffic coating installations.
The identification of post-tensioning problems in the garage was brought to the College’s attention during the first phase of a major renovation to the facility which was required to accommodate incoming students. WDP was tasked with investigating and analyzing the condition of the post-tensioned structure on a fast schedule so that the College could determine if the garage was usable without major structural repairs and if repairs were required to define the scope for potential inclusion with the renovation. WDP worked closely with the Construction Manager responsible for the renovation and completed the field investigative phase over a two-week period. The analysis and development of the repair design was completed within approximately 45 days of completion of the field investigation which permitted the College to obtain cost data through the Construction Manager and make decisions related to the timing of repair to the garage structure.
WDP prepared design documents to address repair of the post-tensioning system which included anchorage replacements, tendon replacements and provisions for strengthening the slab using carbon fiber reinforcing. WDP also provided a safe load rating for the slab which permitted the College to use the area pending the issue of funds to complete the repairs.
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