Water Tank Structural Upgrade Project - City of Brisbane, CA
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The City of Brisbane is a small community located in the northern part of San Mateo County on the lower section of the San Bruno Mountains. It is surrounded by the Cities of South San Francisco and Colma and is next to the San Francisco Bay. The City has a population of approximately 3,600 residents and offers water storage and distribution throughout the City.
The 1.0 million gallon (MG) Crocker Tank was completed in 1966 and has a vertical cylindrical post-tensioned concrete structure. Over the past several years, the exterior concrete wall surfaces of the tank started showing visual signs of corrosion of the high strength post-tensioning wires and some delamination of the protective concrete cover over the corroded areas. The City was concerned that over time these defects could jeopardize the structural integrity of the tank.
The 0.5 MG Margaret Tank and the 1.0 MG Guadalupe Tank were completed in the 1990’s and are welded steel tanks without anchors to the existing ring foundation. The City was concerned that during a large seismic event these tanks would shift from their foundation without anchorage.
The City of Brisbane retained Pakpour Consulting Group to structurally analyze the Crocker, Margaret and Guadalupe Tanks. Over the course of 18 months Pakpour Consulting Group along with our structural subconsultant Beyaz and Patel completed a comprehensive structural evaluation of all three tanks. The evaluation included measuring and mapping prestressing strands on Crocker Tank using electrical current.
The structural evaluations indicated the Margaret and Guadalupe tanks did not need any structural modifications saving the City a considerable amount of money on retrofits. Crocker tank required only minor surface rehabilitation following testing and analysis. Pakpour Consulting Group prepared the plans, specifications and cost estimate for the rehabilitation of the Crocker tank.
