Carraizo Dam is owned and operated by the Puerto Rico Aqueduct and Sewer Authority (PRASA). The dam was constructed for the primary purpose of supplying water to the San Juan metropolitan area. The dam, which was completed in 1954, is a concrete gravity structure and includes eight spillway bays with radial arm or "tainter" gates. During Hurricane Hugo in September 1989, the reservoir overtopped the spillway tainter gates by approximately 4 meters. The gates remained closed during this event due to the loss of power to operate the gates and an inoperable emergency generator. The dam and gates survived this loading without failure, which is testimony to the soundness of the original design and construction. In June of 1998, several gate members were damaged when the associated hoists attempted to lower the gates beyond the fully closed position, causing excessive load on the end of the chains fastened to the top of the gates. Rehabilitation work on Gate No. 3 began in August of 1998. The original scope of work was to replace approximately half of the gate. A detailed inspection of the gate was performed in October of 1998. The extent of corrosion during the inspection was found to be more extensive than originally anticipated. Soon after, a decision was made to stop the rehabilitation work and replace all eight gates, due to the severe deterioration. The design of the new gates has been completed and replacement of all gates is scheduled to be complete in 2003. This paper will discuss the unique design and construction issues associated with replacement of the 50-year old tainter gates, specifically, evaluation and rehabilitation of the trunnion brackets and anchor bolts.
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