In AASHTO LRFD, there are three methods available, as specified in LRFD Art. 5.8.3: simplified and general, and Vci, Vcw approach. The simplified method uses β and θ, as specified in LRFD Art. 5.8.3.4., namely θ = 45 and β = 2.0. The Vci, Vcw method is the simplified method for prestressed and non prestresses sections as per LRFD Art. 5.8.3.4.3. The general method computes β and θ, as specified in LRFD 5.8.3.4.2.
For shear and torsion calculations, the effective shear depth, dv, is used, as specified in LRFD Art. 5.8.3.4. The value dv is considered to be the maximum value obtained from the following three equations:
where
| de | = | distance from extreme compression fiber to center of tensile reinforcement |
| h | = | height of beam |
| a | = | depth of concrete rectangular fiber computed as follows |
where
| As | = | area of tension reinforcement |
| fy | = | yield strength of reinforcement |
| f'c | = | compression strength of concrete |
| b | = | width of member |
Note: The effective steel area at each section is used to compute
a.
The maximum spacing is based on Art. 5.8.2.7. Th program reports the additional required effective steel (Alx). This already accounts for excess effective steel present at that section, which is more than the required flexural.
Beam properties for torsion (Aoh and ph) consider the stirrup size, specified or chosen for Auto Design. For the calculation of Aoh, the program uses the rebar clear cover for sides to be equal to the value specified on A/D parameters dialog for cap side cover. Computed Avs/s is the required steel for shear only, 2Ats/s is the required steel for two legs of torsion, and Av/s is the total computed steel due to shear and torsion at that section. When torsion is present at a section, the program also calculates longitudinal steel.
