54. LOCATING PENSTOCKS. (a) General.-Eight 15-foot-diameter steel penstocks for delivering water to the turbines in the powerplant are embedded in the dam (figs. 129 and 130). The centerline of each penstock intake is at elevation 3470 which is about 45 feet above estimated silt elevation after 150 years of reservoir operation. The minimum water surface for power operation is elevation 3490. A 13.96- by 22.45-foot fixed-wheel hydraulically operated closure gate which can operate under unbalanced head was provided at the upstream face of the dam for each penstock. An unlined transiton section from rectangular to round was provided at the entrances of the penstocks for a smooth increase in flow velocity and to reduce the width required for each closure gate (fig. 131). A reinforced concrete trashrack structure (fig. 132), with structural steel trashracks, protects the entrances. Guides and seats for stoplogs were installed upstream from the closure gate to provide a means for inspecting the gate frames and guides if required. Special joints to take movement in three directions were designed for the penstocks, where they leave the dam, to provide for movements of the dam under variable load. These joints were set in special vaults at the toe of the dam (fig. 133). The penstocks are supported between the dam and the powerplant on reinforced concrete piers which, in turn, are carried to bedrock (figs. 134 and 135). The backfill in the area between the dam and powerplant was placed above the top of the penstocks, and a drainage system was provided as shown on figure 83.

(b) Layout. The layout of the penstocks in the dam was dependent upon the following criteria:

(1) The penstocks had to be radial at the upstream face of the dam, and so located that the trashrack structures did not cross contraction joints.

(2) The minimum distance from the centerlines of the the penstocks to the radial contraction joints in the dam had to be at least one and one-half pipe diameters.

(3) There were to be no bends in the penstocks between the dam and the powerplant.

(4) The minimum permissible bend radius was to be four pipe diameters.

(5) The spacing of the generators in the power plant was to be 65 feet on centers.

In addition to the above criteria, there were limits to the permissible spacing of the contraction joints in the dam. To preclude difficulties in cooling of the blocks and grouting of the contraction joints, the minimum and maximum block widths, measured along the axis of the dam, were 40 and 70 feet, respectively. The layout criteria were satisfied by selecting a system of blocks using maximum and minimum permissible widths, bending two of the penstocks inside the powerplant structure, and anchoring horizontal bends to the mass concrete in the dam where the bends were near the downstream face of the dam.

55. STRUCTURAL DESIGN. (a) General.-The design was based on concrete having a compressive strength of 3,000 pounds per square inch at 28 days for structural concrete and 2,500 pounds per square inch at 28 days for mass concrete. The allowable working stresses are shown on figure 71 except that the allowable stress in the reinforcement around the pipe in the dam was increased to 25,000 pounds per square inch.

(b) Trashrack Structures.-The concrete trashrack structures were designed for a differential waterload of 20 feet, temperature effects, and dead load. The gate guide supports were designed for unwatering the gate guide area with normal water surface.

(c) Gate Hoist Structure. --The gate hoist structure was designed for the following conditions: (1) A 25° F. temperature change.

(2) A 20-foot differential waterhead around structure and 5° F. temperature change.

(3) Stoplogs in place-water on sides-thrust from stoplog seats.

(4) A pullout hoist load of 668,000 pounds which included the force to overcome any jamming of gate during lifting operation.

The gate hoist structure has a removable cover (see fig. 136). For details of the gate hoist structure see figure 137.

(d) Gate Hoist and Stem Storage Platform. -The gate hoist and stem storage structure is shown on figure 138. It was designed to store the gate hoist and the