« PreviousContinue »
distribution was investigated and was found to be nearly uniform with a maximum base pressure intensity of 3, 500 pounds per square foot, which is well within the safe bearing capacity of the foundation material.
The vertical shaft and the 90° bend were reinforced as needed to withstand the stresses produced by the assumed loadings. Allowable stresses for 3,000-pound concrete were used in the design.
(c) Trashracks.— The five trashrack sections for the canal outlet works intake structure are each approximately 8 feet 3 inches wide by 7 feet 7 inches high. Each section consists of 2- by 5/8-inch trash bars supported by 8- by 1-1/4-inch horizontal plates . The ends of the horizontal plates are attached to vertical side members . The open space of 4-7/8 inches between trash bars is considered adequate protection for the high-pressure gate. The trashracks were designed for a differential head of 40 feet and a stress of 33,000 pounds per square inch.
27. Pressure Conduit. - The 5. 5-foot-diameter pressure conduit mentioned in section 25 extends from the intake structure to approximately station 4+68.00. The conduit is about 208 feet long and is divided into five 28-foot sections and one 36. 5-foot section, connected by 4. 5-foot closure sections. Each of the six sections is provided with a cutoff collar. A reach of the conduit is shown in figure 20.
Figure 20. --Pressure conduit of canal outlet works. Workmen are compacting backfill adjacent to conduit. 328-701-3295, November 23, 1951.
(a) Loadings.— In the design of the pressure conduit, vertical loads were considered equal to the weight of the embankment above the centerline and distributed uniformly. Lateral loads were assumed to have a trapezoidal distribution and be equal to one-third of the vertical load at any elevation. The following loading conditions were investigated:
(1) Embankment saturated to phreatic line for normal reservoir water surface elevation; conduit empty.
(2) Embankment saturated to phreatic line for normal reservoir water surface elevation; conduit filled with water and reservoir water surface at elevation 2785.0.
Figure 21. --Canal outlet works—Gate chambers and stilling well details
Figure 21. --Canal outlet works—Gate chambers and stilling well details. (Sheet 2 of 2.) From drawing 328-D-9S1
(3) Embankment dry (optimum moisture content); conduit filled with water and reservoir water surface at elevation 2785.0.
(4) No lateral loads on outside of conduit; a full hydrostatic pressure for reservoir water surface at elevation 2785.0 applied on inside.
The loading conditions that resulted in the most critical stresses were used in the design of concrete and reinforcement. The moments, thrusts, and shears were computed with Beggs Deformeter coefficients and checked graphically. A shell thickness of 21 inches was determined by the requirement for shear, so that no stirrups would be necessary for circumferential reinforcement.
28. Emergency Gate Chamber. -The emergency gate chamber is adome-shaped structure with its centerline at station 4+80.00. (See sec. 25 and fig. 21.) In the design of the emergency gate chamber, vertical and lateral loads were considered. The vertical load was assumed to be uniformly distributed on a horizontal projection of the gate chamber dome and equal to the weight of the embankment material above the top of the dome. The lateral loads were assumed to have a trapezoidal distribution and be equal to one-third ofthe vertical load intensity at any elevation considered.
The encasement for the high-pressure gate frames was designed for stresses produced by a hydrostatic head corresponding to a reservoir water surface at elevation 2785.0. This hydrostatic head was also used for determining stresses for reinforcement design. The dome was assumed fixed to the mass concrete encasing the high-pressure gate frames, and the stresses used for determining the concrete thickness and reinforcement bar sizes were computed for an assumed loading condition by conventional methods for statically indeterminate structures.
Figure 22. --Control house and stilling well for canal
29. Horseshoe Conduit. - The 8-foot 2-inch horseshoe conduit mentioned in section 25 extends from station 4+90 to station 7+27.58, or from the emergency gate chamber to the control house. This conduit accommodates a walkway, a56-inch-diameter steel pipe, and a ventilating duct.
(a) Loadings.— In the design of the conduit no internal loads were considered and the embankment was assumed to be saturated to the phreatic line for normal reservoir water surface elevation 2752.0. In addition, the following loading conditions were considered:
(1) Vertical loads distributed uniformly at top and bottom of conduit; trapezoidal distribution for lateral loads on both sides of conduit.
(2) Vertical loads distributed uniformly at top of conduit and at the bottom of a triangular distribution ranging from twice the load intensity assumed for the top at each edge to zero at the vertical centerline of conduit; a trapezoidal distribution for lateral loads on both sides of conduit.
(3) Vertical loads distributed uniformly at top and bottom of conduit; no lateral loads on conduit.
(b) Design Considerotions.— The vertical loads at top and bottom of the conduit were considered equal to the weight of the embankment above the elevation of the centerline of the conduit. Stresses produced by the various loading conditions were used in the design of the concrete reinforcement. Moments, thrusts, and shears were computed and checked by the method indicated in section 27 .
30. Outlet Pipe. - The 56-inch-diameter outlet pipe, located inside the horseshoe conduit, extends from the emergency gate chamber to the control house, a distance of approximately 244 feet. The upstream and downstream ends of the pipe are bolted to metal transitions near the gates. Plate-steel supports, spaced about 36 feet apart and welded to the steel pipe, provide support for the pipe above the invert of the conduit. The supports rest on base plates attached to concrete piers which have been constructed in the bottom of the conduit. Provision was made in the design of the supports to permit axial movement of the pipe caused by temperature changes. An expansion joint, located about halfway between the upstream and downstream ends of the pipe, compensates for changes in the length of pipe resulting from temperature change. Manholes located near the upstream and downstream ends of the pipe provide access to the interior.
The pipe was designed in accordance with the 1943 edition of API-ASME code for the "Design, Construction, Inspection and Repair of Unfired Pressure Vessels for Petroleum Liquids and Gases." At maximum reservoir water surface elevation 2785, the maximum head at the axis of the pipe is 113 feet. The minimum shell thickness required to provide sufficient rigidity for handling and transportation was the determining factor in the selection of the pipe shell thickness, as this thickness was greater than that necessary to resist design load stresses . A thickness of one-fourthinchwas selected for the pipe shell and one-half inch for the inner sleeve of the expansion joint The pipe was fabricated from low-carbon steel plates in lengths ranging from about 15 to 36 feet. Each section of shop-fabricated pipe, including the expansion joints, was given a hydrostatic pressure test at 100 pounds per square inch. The interior surface of the pipe was coated with coal-tar enamel, and the exterior surface was painted with coal-tar paint. This work was done in the field under specifications No. 3047.
31. Control House and Stilling Well. - The control house and stilling well were constructed monolithically. The combined structure is located at the downstream end of the 8-foot 2-inch diameter horseshoe conduit. The control house is rectangular shaped in plan and contains a chamber for a 4- by 4-foot high-pressure gate . Provision is made for access to the 56-inch outlet pipe from this structure. The stilling well is an octagonal, vertical shaft with the bottom at elevation 2666. 75, an inside distance of 16 feet between parallel sides, and a discharge lip elevation of 2700.00 For distribution of flow, dentates are provided in the inside of the stilling well on the side opposite the gate opening. A view of the control house and stilling well is shown in figure 22. A trapezoidal outlet channel with a 16-foot bottom width, 1-1/2 to 1 side slopes, and protected by riprap for the first 65 feet downstream from the stilling well is provided for the canal discharge.
(a) Design Considerotions.— In the design, the walls of the gate chamber were considered as fixed at the stilling well shaft. The walls were designed for moments produced by floor and roof loadings. The stilling well floor was assumed to be loaded with