In the post RC Design Functions 9.03; compression strut angle adjustment I recommended that when finding the longitudinal force due to shear according to AS 5100.5 (Amendment 1), the effect of increased vertical shear reinforcement should be limited in accordance with the Canadian code requirements; i.e.  Phi.Vus < V*. The spreadsheets RC Design Functions and py_UMom have now been updated with an option to apply this limit. The updated spreadsheets can be downloaded from:

RC Design Functions9.zip

py_UMom.zip

I have also updated the graphs showing bending moment capacity variation with increased shear steel. The input data used is shown below:

Cross section and longitudinal reinforcement:

Shear reinforcement:

Results are plotted for the following cases:

• AS3600-1: Longitudinal force due to shear to AS 3600 with Theta values set to minimum.
• AS3600-2: As above with Theta adjusted so that shear capacity = applied shear, up to a maximum of 50 degrees.
• AS5100-1: Longitudinal force due to shear to AS 5100.5, with Theta set to minimum value and no limit on Vus.
• AS 5100-2: As above but phi.Vus set with a maximum value of V*.
• AS 5100-3: As ASS5100-1, but with Theta adjusted.
• AS5100-4: As AS5100-2 with Theta adjusted.

Results were initially calculated with the reduction factor for bending set to 0.8 for both codes, and for shear set to 0.75. This was done so that the difference in the results was entirely due to the different procedures for calculating the longitudinal force due to shear:

With 10 mm reinforcement the section shear capacity is very close to the applied shear force, and the two AS 3600 methods give the same results. The AS 5100 results for 10 mm reinforcement are lower because the code requires the area of steel required for the longitudinal force due to shear to be calculated using a reduction factor of 0.7, rather than 0.8 (Equation 8.2.7(3)).

Applying the limit to Vus the AS 5100 moment capacity reaches a maximum about 20 kNm higher than AS 3600 with 14 mm diameter shear reinforcement when the minimum Theta value is used. With adjustment of Theta the maximum capacities from AS 3600 and AS 5100 are very close.

Results with the reduction values set to the values specified in the codes:

Applying the AS 5100 reduction factor for bending (0.8) the maximum AS 5100 results with minimum theta are very close to the equivalent results from AS 3600. With adjustment of Theta the AS 5100 maximum results are about 20kNm lower than the equivalent AS 3600 results.