Brighton Dam: Working Together to Repair Unanticipated Damage and Deterioration to Tainter Gates

Brighton Dam is an Ambursen-style concrete slab and buttress dam. The dam is on the Patuxent River approximately 13 river miles upstream of Laurel, Maryland. The 86-foot high, 995-foot-long dam was constructed in 1943, with storage of 19,000-acre feet. The dam features a central gated spillway in a 600-foot-long concrete dam and earthen embankment sections at each abutment (total length of 395 feet). The spillway is equipped with 13 steel tainter gates. Brighton Dam is classified by the Maryland Department of Environment Dam Safety Program as a High Hazard structure.
A comprehensive rehabilitation of the dam was undertaken starting in May 2017 to address deficiencies that affected the safe operation of the spillway. The project included rehabilitation of the 13 Tainter gates by replacing seal plates, adding bracing on strut arms for seismic and operational loading, recoating, and replacing ancillary parts. After initial blast cleaning to remove the existing coating, significant section loss was observed on some of the gate members. AECOM structural engineers immediately mobilized to perform a close-up inspection of each gate to evaluate the extent of deterioration.
AECOM observed a total of 26 unanticipated deficiencies with the Tainter gates, ranging from significant corrosion and deflection of steel members to potential operation issues (racking and friction). AECOM also observed unanticipated as-built conditions, such as additional steel plates, that conflicted with the rehabilitation design. After completing the inspection, AECOM worked concurrently on a repair design and three-dimensional model of the gate to analyze the observed deficiencies. The analysis indicated that the deflected members were overstressed due to a combination of the increased friction and gate racking during operation. The analysis also showed that the strength and serviceability of the gates would be acceptable with AECOM’s repair design.
AECOM worked closely with the contractor through the process to develop a repair design that would limit schedule delays and work stoppage and would be cost effective. To limit the amount of demolition and field welding, AECOM’s repair design that involved cutting and completely removing the bottom portion of each gate. This limited the amount of demolition and field welding, allowing most of the repair to be shop fabricated. Even with the number of unanticipated conditions observed on the gate, the gate repairs were completed without a stoppage in work and with minimal impact to the project schedule.