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If checked, the program will calculate the shear capacity of the concrete using the iterative beta method in LRFD Appendix B5. This value is then compared to the shear capacity already calculated using the internal decision table (see Section 5.7/5.6) and the larger of the two values is used for the current member.
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If checked, the program will calculate the shear capacity of the top slab of a 3-sided culvert with more than 2 foot of fill using LRFD 5.14.5.3/5.12.7.3, which is usually only used in 4-sided culverts. However, some states allow this provision to be used for 3-sided culverts as well.
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In LRFD, when the shear capacity of the concrete is calculated using the iterative approach in Appendix B5, a preliminary estimate of the reinforcing steel is based on moment demand. Then the area of steel is used to calculate the shear capacity and checked against the shear demand. If the preliminary estimate of the area of reinforcing steel is unsatisfactory the program enters a loop inside the shear calculations to increase the area of steel until this requirement it met. This area of steel should be limited to around 2.0 in2in2/foot for practical purposes, and can be adjusted up or down here. If this limit of the reinforcing steel cannot be satisfied then the program increases the member thickness, recalculating the structural steel demand, and re-starts the shear demand loop.
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