The design criteria for the columns, ribs, arch portion of the trashrack structure, and roof were similar to the criteria indicated for the outlet works trashrack. The base of the trashrack, which extends upstream from the massive pilasters, was designed as a simple cantilever, supporting its own dead weight, the weight of the columns, ribs and a 20-foot portion of the arch above the top rib, and the metal trashracks. Moments and shears from the simple cantilever base are distributed partially to the pilasters on each side by longitudinal bars and shear steel, and partially by transverse reinforcement extending downstream beyond the face of the dam. The reaction of the load into the pilaster area will be resisted by hanger bars which extend for three bays in height above the base. The shoring of the forms for the base was not removed until the concrete in the dam, for the height of the first two bays, was at least 14 days old. The pilasters above the second bay were considered self-supporting.

The following design criteria were established for the design of the gate hoist structure above the roof of the trashrack:

Frame below elevation 6045

Condition 1.--Assume stoplogs in place and water surface at elevation 6040; temperature change of plus 5° F.

Condition 2.--Assume water surface below hoist structure. Temperature change of about 25° F.

Vertical temperature reinforcement in frame was arbitrarily established as

follows:

In walls attaching to dam--1-1/8-inch-diameter bars at 12-inch centers
each face

In outer wall--1-inch-diameter bars at 12-inch centers each face

Floor at elevation 6045

Live load--125 pounds per square inch

Walls above elevation 6045

Temperature change of about 25° F.

71. Steel Penstocks. Three penstocks (fig. 90) conduct water from the reservoir through the dam and to three turbines in the powerplant. The penstocks begin as 10-footinside-diameter pipes at the downstream ends of the formed concrete rectangular-tocircular transition in the upstream face of the dam at centerline elevation 5850.0. Extending downward toward the toe of the dam, they level off through reducing bends (fig. 91) to an inside diameter of 9 feet at centerline elevation 5601.0 and emerge from the dam. They immediately enter the penstock gallery of the powerplant. Sleeve-type coupled makeup sections 7 feet long connect the penstocks to the turbine spiral cases. The makeup sections are designed and supported so that they may be disconnected and displaced laterally to permit access to the penstocks for major inside inspection and maintenance. The average length of each penstock is about 334 feet. Minimum and maximum penstock plate thicknesses are 1/2 and 1-1/16 inches.

A 16-inch-outside-diameter penstock filling pipe cross connects the three penstocks near their upstream ends. If one of the penstocks is full, the other two may be filled by operating individual 16-inch-diameter control valves.

(a) Design. -- The penstocks were designed for a maximum head of 526 feet including water hammer, measured at the centerline of the generating units. The maximum designed static head is 444 feet at this point. Water hammer was calculated for the most severe combination of reservoir water surface elevation with a normal discharge and turbine wicket gate closure time of 5 seconds from full-open position.

Each turbine discharge is 1,420 second-feet at 365-foot rated head. The corresponding average velocities in the penstocks are 18.1 and 22.3 feet per second for the 10- and

9-foot diameters, respectively. Penstock diameters were designed by estimating minimum annual costs.

Sleeve-type coupled field joints in the penstock gallery of the powerplant were designed to allow small angular displacement in alinement of the penstocks.

Penstock sections and stiffener rings were fabricated of steel plates conforming to ASTM Designation A 285, grade C, firebox quality. Middle rings and sealing glands of sleeve-type couplings were fabricated of steels conforming to ASTM Designations A 242 and A 7, respectively.

All permanent joints were welded. All girth and longitudinal welds in penstock shells were X-rayed in accordance with the ASME Boiler and Pressure Vessel Code -- Unfired Pressure Vessel Section.

Code basic design working unit stresses for ASTM A 285 and A 242 steels used were 13, 750 and 17, 500 pounds per square inch, respectively. Joint efficiency was 90 percent for both steels.

Completed sections of penstocks, including sleeve-type couplings, were hydrostatically tested at pressure computed from the formula:

T = minimum thickness in inches of plate course in section tested, and

D = internal diameter of pipe, in inches.

A 30-inch-inside-diameter manhole is located upstream of the first bend of each penstock. The formed inlet transitions may be reached from these manholes. Two piezometer orifice stations 65 feet apart are located on each penstock. Individual 3/4-inch pipes lead from each piezometer connection into the powerplant.

The penstock sections were installed under the prime contract, excepting makeup sections, which were installed under the completion contract, specifications No. DC-5700.

Interior surfaces of penstock were coated with coal-tar primer and coal-tar enamel. Penstock exterior embedded surfaces were not coated. Exterior surfaces of penstocks, makeup pieces, and sleeve-type couplings exposed to view in the powerplant were coated with phenolic-resin aluminum paint.

72. 8.27- by 15.82-Foot Fixed-Wheel Gates. Three fixed-wheel gates are located in the sloping penstock gate structures on the upstream face of the dam and serve to shut off flow to the penstocks. The gates will always be opened under balanced pressure, noflow conditions, and will normally be closed under the same conditions. However, the gates are designed for safe closure under emergency conditions with full flow of water through the penstocks. The gates were manufactured under invitation No. DS-5508 and the frames under invitation No. DS-5501.

(a) Description, -- The general arrangement and details of each 8.27- by 15.82-foot fixed-wheel gate installation are shown on figures 92, 93, and 94; and figure 95 shows one of the completed gates photographed in the manufacturer's shop.

Each gate is made in two units and is fabricated of structural steel sections and plate, using bolted connections. Six wheels on each side of the gates carry the waterload to the sloping tracks which are supported on embedded frames in the upstream face of the dam. Rubber seals are mounted like a picture frame on the downstream skinplate, and bear against the embedded metal seats which surround the penstock intakes. Rollers at the sides of the gates provide lateral guidance when the gates are in operating position and bear on embedded guides in the gate slots. Above the operating position, during installation or removal, guide shoes on the gates center the gates in the concrete gate slots.