Concrete Shear Strength
The shear stress (fv) is computed as follows:
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Where the member thickness is equal to or greater than 16 inches or the member is in tension, the program uses the iterative approach in Appendix B5 for the calculation of beta used in Eq. 5.8.3.3-3/5.7.3.3-3, due to the lack of transverse reinforcing assumed in the design algorithm. A value is assumed for theta, which is used in Eq. B5.2-1. From this we can use Table B5.2-1 to look up a new value for theta. This process is repeated until successive values for theta are approximately the same. Once the calculations for theta have converged, theta is used in Table B5.2-1 to obtain a value for beta.
The proper selection of the governing provision in LRFD can summarized by the following flow chart:
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4-sided structure
Fill depth >= 2 feet
Use 5.14.5.3 for slabs
Use 5.8.3/5.7.3 for walls
If wall thickness >= 16” or member is in tension, use 5.8.3.4.2/5.7.3.4.2 (beta calculated using App. B5)
If wall thickness < 16”, use 5.8.3.4.1/5.7.3.4.1 (beta is a constant 2.0)
Fill depth < 2 feet
Use 5.8.3/5.7.3 for all members
If member thickness >= 16” or member is in tension, use 5.8.3.4.2/5.7.3.4.2 (beta calculated using App. B5)
If member thickness < 16”, use 5.8.3.4.1/5.7.3.4.1 (beta is a constant 2.0)
3-sided structure
Any fill depth
Use 5.8.3/5.7.3 for all members
If member thickness >= 16” or member is in tension, use 5.8.3.4.2/5.7.3.4.2 (beta calculated using App. B5)
If member thickness < 16”, use 5.8.3.4.1/5.7.3.4.1 (beta is a constant 2.0)
Note that the iterative beta method (beta calculated using Appendix B) is actually usable in all situations, regardless of the member thickness or location.
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