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

V_co is calculated per equation 54. The flange/web intersection is not checked.

V_cr is calculated per equation 55

The value of V_c is used as shown in the following table.

Table 1. V_c rule mapping
Moment	V_c Implementation
M < M_o	V_c = V_co V_c = (stress)b_vh
M ≥ M_o and tension is on the "tension" face *	V_c = min (V_co, V_cr) V_c = (stress)b_vh
M ≥ M_o and no tension on the "tension" face *	V_c = min (V_co, V_cr) V_c = (stress)b_vh d = d_t (assumed) A_s = 0 (none in "tension zone") A_ps = 0 (none in "tension zone")

Note: * The calculation of M_o uses only 80% of the stress due to prestress. This can produce the rare case where the section is in reality uncracked and has a tension face different to that calculated with M_o. For the unusual case of M ≥ M_o and the section is actually uncracked (when considering the full prestress force) the conservative assumptions of column four are made.

"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.

" d_t " 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 f_cu is used in calculations.

Longitudinal reinforcement designed by Minimum, Service and Strength designers is considered in the determination of A_s used in the calculation of v_c.

b_v 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 b_v.

For cross sections with multiple tendons, the f_pu and f_pe values used in the calculations are averaged.

v_c is calculated per Note 2 of Table 3.8, including the f_cu modifier term, with (A_ps + A_s) used in place of A_s. See section 3.4.5 for detail of the implementation of this table.

When unbonded tendons are used, the value of v_c 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.