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Bulkhead Design for AMD Page 10 October 27-29, 1998 <br />The compressive load toward the upstream (water side) face of <br />the bulkhead must be balanced by the tensile reinforcement from the <br />rebar cage a few inches from the downstream (air side) face. Deep <br />beam design assumes that a uniform compressive stress equal to 0.85 <br />times the specified concrete compressive strength acts over an area <br />1 ft wide by 0.85 times the centroidal distance in depth (a) below <br />the loaded surface. The constant, 0.85, is reduced 0.05 for each <br />1,000 psi the concrete strength exceeds 4,000 psi. The method, as <br />further described by Wang and Salmon (1985, p 43-99), assumes the <br />tensile reinforcing steel yields before the concrete crushes under <br />bending induced compressive stress. Tensile reinforcement design <br />for the typical reinforced concrete deep beam bulkhead follows: <br />Compressive force C = ~(f~)ba = 0.85(f~)ba (14) <br />Tensile force T = Asfy (15) <br />b = beam width (in.) <br />a = compression zone depth (in <br />As = steel area (sq in./ft) <br />fy = steel yield stress (psi) <br />f~ = concrete strength (psi) <br />The method presented by Wang and Salmon (1985) assumes that the <br />compressively stressed concrete area is no deeper into the beam <br />than necessary to carry the bending moment develgped compressive <br />force at the ACI specified compressive stress of 0.85 times the <br />specified compressive strength. The calculations equating C to T <br />using equatiohs (19) and (15), using 3000 psi concrete and 60000 <br />psi yield strength rebar follow: <br />C = T 0.85(f~)ba = Asfy 0.85(3000)12a = 60000A5 <br />Asfy coooaAS = 1.96078As (16) <br />a = = o.estsoooiiz <br />o.as(e~)iz <br />Summation of moments about center of the compressively <br />stressed area, substituting the compression zone depth from <br />equation (16) <br />Mu - AsfyCd-2~ = AsfyC(L-mom)-z~ (17) <br />d = depth, top of beam to center of reinforcing <br />steel (in) = L-m~ <br />M„ = factored design beam bending moment (in•lb) <br />m~ = minimum cover, form face to rebar surface <br />(inches) <br />- 10 - <br />