AS 3600 AMDT 2 Equation 8.2.7(2) additional longitudinal tension forces caused by shear 2

[kww2008]

I have recently had a look at this amendment. This is now different from the same equation in AS 5100.5 as phiV_us has been replaced by (V* - phiV_uc), and "gamma_p P_v" by "0.5 gamma_p P_v". This equation is also different from those of AASHTO and the Canadian code. Does anyone know the reasons for these changes?

A potential problem arises if adopt this equation in AS5100.5, and use it for load rating to AS 5100.7.
When using (V* - phiV_uc) instead of phiV_us, there is an implicit assumption that the ligaments (stirrups) provided is such that phiV_us + phiV_uc > V*, which is okay for designing bridges. Section-shear deficient bridges have [phiV_us + phiV_uc] < V*, i.e., [V*-phiV_uc] > phiV_us. If we use the AS 3600 equation to load rate force in the longitudinal steel, this introduces inaccuracy as the amount of force deducted (V* - phiV_uc) is larger than phiV_us. The canadian code has a limit "V_s not to be taken great than V_u" for their equation which uses V_s.

 

[rapt]

But you come up with a value of top force = -bottom force!

You will find their diagram is not complete also because it does not include Applied loads. We look at that diagram and then developed our own and did the complete equilibrium check for all forces at the cut. That resulted in the same equation as Collins and Mitchells based on Vuc + Vus.