Shear induced Tension in concrete design

[pmastro]

Hi there,

I've been looking around for information about this topic, but can't seem to find much. The problem I'm currently having is that I'm verifying the capacity of an existing concrete structure to see if it can be used for storage (7.2 kPa, 150 psf), and many provisions regarding shear induced tension were not in place when the building was built. As such, nothing in 11.3.9 in the A23.3-04 standard is satisfied at the supports, mostly because the bottom steel isn't properly developed.

In clause 11.3.9.5 it says that in the formula (Vf - 0.5Vs - Vp) * cot (theta), Vs cannot be higher than Vf. However, I've been told that the Vs that should be used in the formula is the portion that the steel will resist - or rather the portion that the concrete cannot resist - and should be calculated as Vs = Vf - Vc.

Can I really use Vs = Vf? Any input on this topic would be greatly appreciated.

Thank you for your time.

 

[JAE]

Can you clarify the concrete code / year under which your question is based?

 

[pmastro]

Sure, sorry about that. It's the Canadian National Building Code, 2005. The building being checked was built in 1969.

 

[amecENG]

Vs is the shear resistance of the stirrups. There is some additional information in th Explanatory Notes

 

[BAretired]

I do not have the latest A23.3-2004 so I don't know if it differs from A23.3-94 respecting development of longitudinal reinforcement. Using the older version, Vs is determined on the basis of stirrups provided, i.e. Vs = Φ[sub]s[/sub]A[sub]v[/sub]F[sub]y[/sub]d/s.

You cannot us V[sub]s[/sub] = V[sub]f[/sub] unless you have enough shear reinforcement, which would be unusual in most beams.

At the supports of simple spans and at the exterior supports of continuous spans, the flexural tension reinforcement must be capable of resisting a tensile force of V[sub]f[/sub] - 0.5V[sub]s[/sub] at the inside edge of the bearing area where V[sub]s[/sub] is the value based on the stirrups at that location.

BA

 

[rapt]

pmastro,

The definition of Vs is stated very clearly in the code.