(c) Gate Design.--The gate was designed for a head of 50 feet at the bottom seal. The design was based on the following unit stresses in pounds per square inch:

Assumed coefficient of side seal friction brass on stainless steel

Assumed coefficient of trunnion pin friction, bronze on steel

(d) Radial Gate Hoist Design.-- Two 125,000-pound-capacity radial-gate hoists are installed on the operating deck of the spillway for raising and lowering the 20- by 50foot radial gates. Each hoist consists of a center drive unit located at the centerline of the gate and two drum units, one located above each end of the gate just above the gate connections.

The center drive unit consists of a 7-1/2-horsepower, 155-r.p.m. gear motor with a motor-mounted, electrical-release, disk type brake and a commercial 47 to 1 spiral bevel, helical gear reduction unit with a double extended drive shaft. Each end unit is connected to the center unit by a floating shaft and two flexible couplings suitable for floating shaft application.

The end units consist of two stages of grease-lubricated spur reduction gearing and a 29-inch pitch-diameter drum with right- and left-hand helical grooving. Two parts of 1-1/2-inch-diameter, 6 by 19 wire rope with independent wire rope core extend from the drum and are attached to an equalizer bar located on the upstream side of the gate leaf, near the bottom of the gate.

Antifriction bearings are used throughout the design of the hoists. The hoists were designed with a safety factor of 5 based on the ultimate strength of the material and assuming 60 percent of the total rated torque could be applied on one end unit. Also, each part was designed so that the stress will not exceed 80 percent of the yield point of the material, based on the breakdown torque of the motor and assuming 50 percent of the torque applied at each end unit. The hoist ropes were designed with a safety factor of 6 based on the breaking strength of the rope.

A screw type, double-acting, snap-action limit switch mounted on one of the drum units on each hoist limits the travel in both the hoisting and lowering directions.

63. Trashracks for Outlet and Power Intake Structures. - (a) Description.-- The trashracks are installed in formed concrete grooves located in the submerged outlet and power intake structures. There are 56 rack sections approximately 12 feet 2 inches wide and 9 feet 3 inches high installed on each of the two structures at a 1 to 1 slope. There are 6 rack sections approximately 12 feet 2 inches by 9 feet 3 inches and 10 rack sections

of different sizes installed on horizontal supports at elevation 5533. 29 at each of the two structures. A total of 72 rack sections are installed on each of the two structures. Installation of the trashracks is shown on figure 79.

(b) Construction.-- The trashrack sections consist of 2- by 5/8-inch trash bars supported by 10- by 1-1/4-inch load-carrying plates which in turn transmit the load to the side channel members. Each of the 12-foot 2-inch by 9-foot 3-inch rack sections is fitted with dowels which engage in the adjacent rack, thus maintaining a uniform alinement of the trashbars. In order to secure the racks in the structure and to protect the painted surfaces of the side members, 6- by 3/4-inch bars are welded to the channels at the points of sliding contact with the concrete grooves. The 5-inch clear opening between the power penstock trash bars conforms with recommendations of the turbine manufacture, and the 5-inch clear opening between the river outlet trash bars is considered sufficient protection for the 96-inch hollow-jet valves. The trashracks were designed for a differential head of 20 feet at a stress of 33, 000 pounds per square inch.

64. 19.67- by 28. 03-Foot Fixed-Wheel Gates. - (a) Requirements.--One 19.67by 28.03-foot fixed-wheel gate is installed at the outlet tunnel intake and one at the power tunnel intake on the face of the dam. The gates are required for emergency closure of the outlet and power tunnels in case of damage to the tunnels, outlet works, control equipment, or turbines. The applicable gate is also closed when unwatering the outlet or power tunnel for inspection and maintenance purposes.

(b) General Description.--The general arrangement and details of the gate installations are shown on figure 80 and on drawings 456-D-267 through 281* and 339 through 350. * The fixed-wheel gates were furnished under invitations No. DS-3835 and DS-3963.

The outlet and power tunnel intakes at the face of the dam have theoretical openings of 19.67 by 28.03 feet, which is the nominal size of the gate for each opening. The gates operate in slots in the concrete intake structure on a slope of 52° 30' from the horizontal. The slots extend from the tunnel invert to the top of the dam. The gates are normally held in the open position directly above the tunnel intakes by hydraulic hoists. The bottoms of the hoists are located above the maximum reservoir level of about elevation 5621. On the downstream side of each gate, at the top of the tunnel, the tunnel is vented to atmospheric pressure by an air vent pipe extending to the top of the dam.

The gate is a flat structural steel member of riveted construction. It was fabricated and shipped in five separate units to facilitate handling, shipment, and field assembling. A skinplate is fastened to the downstream side of the main gate framework. The framework consists of 11 horizontal beams, framing into double vertical girder beams at each end of the gate. Seven wheels are located between each pair of vertical girders and serve to transfer the hydraulic load from the gate to the corrosion-resisting steel tracks. The tracks are fastened to steel bases embedded in the concrete at the downstream face of the gate slot. The normal gate travel from open to closed position is 29 feet. Lateral movement of the unloaded gate is controlled by guide rollers, on each end of the gate, which contact metal guides embedded in the concrete at each end of the gate slot.

Solid rubber, double-stem seals with brass-clad bulbs are provided around the four edges of the skinplate on the gate. When the gate is closed, the side seals contact stainless-steel seal seat plates which are an integral part of the embedded track bases. The top and bottom seals contact seats on embedded horizontal seal seat bases. A single hoist stem connection is located on the gate directly above the center of gravity of the gate.

The estimated weight of one gate is 280, 000 pounds, and of one gate frame and guides is 103, 000 pounds.

(c) Gate Design.--The gate was designed for a head of 179 feet assumed to be uniformly distributed over the entire gate leaf. The hoist connection on the gate was designed for the pullout force of the hoist. Investigation of friction forces from the loaded wheels, pins, seals, etc., showed that these forces were too large to positively assure gate closure by its own weight under a 179-foot differential head. The hoist was therefor designed to exert an additional downward force if necessary to close the gate.

*Not included.