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Concrete Beams Design Problem 1 - Determine the dimensions of a concrete beam:
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Size the initial dimensions of rectangular beam with only tension reinforcement to carry a moment load, Mn = 110,020 lb-ft. Use 3500 psi concrete and 40,000 psi steel.
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1. From the concrete beams submenu open the required beam dimensions calculation, ReqBeamDim.aspx. Input the "Title" of the calculation, the "Designer/Checker" information and the variables.
Check the box to use steel reinforcement ratio, p = 0.18f'c/fy and use 1.8 for the value of d/b. Click on the "Calculate" button and read the results. Steel reinforcement ratio, p = 0.0158, bd^2 = 2343.784 in^3, d = 16.158 in, b = 8.977 in, area of steel, As = 2.285 in^2. h = d + 2.5 in = 18.658 in. Rounding to the nearest inch use h = 19 in and b = 9 in.
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2. Summary
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The required dimensions of the concrete beam are b = 9 inches and h = 19 inches. The area of steel may be reduced if desired by plugging the final bd^2 into the equation and solving for the new steel ratio, p. However it is conservative to use the initial area of steel, As = 2.285 in^2.
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