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<br />94 <br /> <br />The second approach makes use of the design curves presented at the end of this chapter. <br />To make use of the design curve, the user need only determine the actual equivalent fluid <br />weight (Yeq) based on the assumed surcharge condition (Section 6.2). For slab design all that <br />is required is the depth of water above the basement floor. <br /> <br />11.6 Wall and Slab Design <br /> <br />11.6.1. Walls <br /> <br />Lateral forces from soil and water are calculated as described in Chapter VI, and then <br />applied to the walls as follows. The walls may be treated as a beam with a triangular load <br />assuming ground and water surface elevations coincide as shown in Figure 11.7. The max- <br />imum bending moment that can occur in the "beam" is Mu. The calculations that follow are <br />for a beam. However, the wall has four edges contributing support, not just two. Because of <br />this ability to act somewhat as a plate, the moment that must be resisted, Mu, may be <br />reduced by ten percent. In ultimate strength design, a load factor of 1.4 is used to provide a <br />margin of safety. Both the load factor and moment reduction may be included in the Mu <br />equation by applying them to the equivalent fluid weight as follows <br /> <br />1.4 <br />Yu = 1.1 yw <br /> <br />The "working load" equivalent fluid weight then becomes <br /> <br />yw - 0.786 Yu <br /> <br />Equivalent fluid weight was introduced in Chapter VI. It is the fluid unit weight to be used <br />in calculations that will account for both soil and water loadings. <br /> <br />Yw= <br /> <br />By substitution and rearrangement of the Mu equation: <br /> <br />4.716 Mu <br />a3 (B + 20 va ) <br />3 3 <br /> <br />The value that is computed, yw, is the equivalent fluid unit weight that can be resisted by <br />all the given conditions, incorporating the load factor discussed above. <br /> <br />The equation for yw then takes on a slightly different form for each type of wall. <br />Developed equations for each type of wall are presented below (Reference No.24). <br /> <br />Type: Reinforced Concrete (Ultimate Strength Design) <br /> <br />yw = 4.244 bd2f' eq(1 - 0.59q) <br />a' (B'z.g Vii) 12 <br />3 3 <br /> <br />q ~ Asfy <br /> <br />bdf'e <br /> <br />Where <br /> <br />b = Width of "beam". Calculations are per one foot width of wall. <br /> <br />d = Effective depth; distance from compression face to centroid of tension steel. <br /> <br />As = Cross-sectional area of steel per b width, expressed as square inches. <br /> <br />Fy = Yield strength of steel in psi. <br /> <br />Fe = Compressive strength of concrete in psi. <br />