Prestressed Anchorage for Large Tainter Gate

Unusually large 50-ft-wide by 65-ft-high tainter gates in the Wanapum Project led to the search for an economical way of anchoring 7,560 kips of thrust into the pier. A heavily reinforced concrete block supporting the gate trunnions and anchored with fourteen prestressed cables, each of 635 kip capacity, provided the answer. Because of the complicated three dimensional state of stress inside the anchor block and the monolithic construction with the pier, extensive structural model tests were necessary. Aluminum models (stress coat and strain gages) and a three dimensional photo-elastic model were used. Analyses were used for backup and provided tools for design of similar anchor blocks in the future without model tests. Each cable of 635 kip capacity consisted of 90 1/4-in.-diameter high-strength steel wires with button head ends of the BBRV type. All cables for a single pier were prefabricated into a single assembly. A construction joint between the anchor block and the pier permitted uninterrupted concrete placement. Swift progress of all phases of work confirmed the practicability of the scheme. A significant cost advantage resulted, compared with a structural steel, unbonded anchorage.