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<br />4.3 STRUCTURAL DESIGN <br /> <br />General <br /> <br />Structural design of the spillway structure includes design of reinforced concrete floor <br />slab, west wall of the inlet structure, and the chute extension. Reinforced concrete <br />structures are designed in accordance with ACI 318-89 and applicable federal guidelines <br />and criteria included in the USBR design of small dams. <br /> <br />Ogee Crest and East Wall <br /> <br />The crest and east wall are relatively free from cracks and displacement except for the <br />spall at the base of the wall. Failure along the base is attributed to placement of the <br />waterstop to close to the concrete surface, insufficient reinforcement in the wall and poor <br />cleanup of the construction joint. This defect is addressed by saw cutting the concrete <br />along the toe, removing the damaged concrete and buttressing the wall with the new floor <br />slab. To insure stability of the wall when the damaged floor slab is removed, a 3-foot <br />wide strip of floor slab will remain in place. This strip will be anchored to the foundation <br />by anchors, which will remain in place. The new floor slab will be anchored to the 3-foot <br />wide strip with grouted reinforcing bars. Anchoring the strip will further enhance the <br />stability of the ogee crest and wall. <br /> <br />Floor Slab <br /> <br />The underdrain system of the floor slab is assumed to be effective, so the floor slabs only <br />function is to protect the foundation from eroding during spillway operation. The slab is <br />reinforced with two layers of steel to guard against excessive cracking and movement <br />from the affects of the foundation anchors. The anchors are designed for an arbitrary <br />loading of 10 feet of uplift, which is a common practice. The anchor bar loading is <br />considered to be an unusual loading. Anchor bars will be tested to determine pullout <br />resistance. <br /> <br />West Wall <br /> <br />The west wall is designed assuming the drainage system is effective. Loading includes <br />unsaturated soils and surcharge. Both faces of the wall are reinforces to prevent <br />excessive cracking. <br /> <br />Chute Extension <br /> <br />The walls and floor slab are designed for unsaturated fill and a surcharge load. Both <br />faces of concrete \\"ill be reinforced for load stresses and to prevent excessive cracking. <br />The upstream end of the chute extension is attached to the existing concrete by grouted <br />reinforcement and the existing reinforcement protruding from the chute. A downstream <br />cutoff wall protects the structure from downstream movement and erosion. Riprap is <br />included in the outlet channel for erosion protection. <br /> <br />5 <br />