Section 4.3.8 Design shear resistance of beams
Included code sections - 4.3.8.1 to 4.3.8.8, 4.3.8.10
Excluded code sections - 4.3.8.9
Vco is calculated per equation 54. The flange/web intersection is not checked.
Vcr is calculated per equation 55
The value of Vc is used as shown in the following table.
Moment | Vc Implementation |
---|---|
M < Mo |
Vc = Vco Vc = (stress)bvh |
M ≥ Mo and tension is on the "tension" face * |
Vc = min (Vco, Vcr) Vc = (stress)bvh |
M ≥ Mo and no tension on the "tension" face * |
Vc = min (Vco, Vcr) Vc = (stress)bvh d = dt (assumed) As = 0 (none in "tension zone") Aps = 0 (none in "tension zone") |
"d" is defined as the depth to the centroid of the tension force in the tension zone (including rebar and post-tensioning). This is slightly different (and likely more rational) than the distance from the extreme compression fibre to the centroid of the tendons as defined in the code.
" dt " is defined as the maximum depth to any longitudinal mild reinforcement, or the depth to the centroid of the tendons, whichever is greater.
The vertical tendon force component is ignored.
For sections with multiple concrete mixes, the minimum fcu is used in calculations.
Longitudinal reinforcement designed by Minimum, Service and Strength designers is considered in the determination of As used in the calculation of vc.
bv is adjusted by considering any tendons in the shear core. The full width of unbonded tendons is deducted, and two-thirds of the width of bonded tendons is deducted from bv.
For cross sections with multiple tendons, the fpu and fpe values used in the calculations are averaged.
vc is calculated per Note 2 of Table 3.8, including the fcu modifier term, with (Aps + As) used in place of As. See section 3.4.5 for detail of the implementation of this table.
When unbonded tendons are used, the value of vc is reduced by a factor of 0.9 [TR 43, 6.11.1].
Shear reinforcement is calculated per 4.3.8.6 to 4.3.8.8.
Link spacing is calculated per 4.3.8.10, with lateral spacing requirements ignored. The "web thickness" used in the calculations is the same as the shear core width - this may be incorrect if the core width is made up of multiple webs. In such cases, multiple design sections or design strips can be used; each containing only one web.
Links are only provided in the regions required by calculation, not the whole length of the beam.