A Stage Structural Design of Concrete Cantilever Retaining Wall
As stated in the introduction to this appendix, the second stage of the wall design entails the structural design of the concrete wall, to include the dimensioning of the concrete base slab (the toe and heel elements) and stem, and the detailing of the reinforcing steel. All reinforced-concrete hydraulic structures must satisfy both strength and serviceability requirements. In the strength design method, this is accomplished by multiplying the service loads by appropriate load factors and by a hydraulic factor. The hydraulic factor is used to improve crack control in hydraulic structures by increasing reinforcement requirements, thereby reducing steel stresses at service loads. The service loads are those determined in the first design stage presented previously.
Each of the three structural elements is designed as a cantilever, one-way slab for flexure and shear loadings, in general accordance with EM 1110-2-2104 (HQUSACE 1992), with the exception of the grade steel of the reinforcing bars. The following example uses Grade 40 steel, which is in line with the design examples in EM 1110-2-2502 (HQUSACE 1989). However, EM 1110-2-2104 (Section 2-2) recommends that Grade 60 reinforcing steel be used. Four-inch cover is used in the example, per EM 1110-2-2104 (Section 2-6). Where design criteria is absent in EM 1110-2-2104 and EM 1110-2-2502, ACI 318 (American Concrete Institute 2002) was used. Figure A-4 shows the structural wedge and the externally imposed stresses determined in the first design stage. Also shown in Figure A-4 are the critical locations for evaluating shear and bending moment for the stem, heel, and toe elements.
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Figure A-4. Critical locations for shear and bending moment, per ACI 318 and EM 1110-2-2502
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