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Receiving a compression reinforcement error message in Slab Design

The effective depth is the depth from the compression face in a concrete section to the center of the area of reinforcement we are considering, allowing for the effective cover. The steel is layered in the X and Y-directions, the program uses the same effective depth d for the top and bottom steel in any given direction. The program uses the Wood and Armer equations to transform the bending and torsional stresses to effective bending moments in the X and Y-directions. This procedure yields design bending stresses in the top and bottom faces of the slab that are suitable for calculating the required reinforcement in the top and bottom faces.

Figure 1: Error message

This error usually occurs when the section is relatively shallow, and the neutral axis lies above the top layer of reinforcement (i.e., the reinforcement cannot work in compression). Meaning the section requires compression reinforcement, and the program is unable to calculate the amount of compression reinforcement. The solution is to either move the reinforcement higher up, but it implies a reduction in the concrete cover, and this is not desirable. Alternatively, the section depth can be increased which is probably the only sensible thing to do. If the rebar is located on the neutral axis of the section, it won’t be effective in resisting the bending. The top steel will never be in the compression block and the program will complain about it.

Note: This error can occur in anyone of the concrete design modules that design sections for flexure.