RAM Concept Shear failure due to ignored transverse reo

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You will need the update release 5.2.1 released date 4/2/2015.

What Concept 5.2 was doing:

1. Assume minimum stirrups are not provided
2. Calc Vuc based upon the min stirrup assumption
3. Calc Vu,min which is also based upon the min stirrup assumption
4. Determine the maximum spacing based upon the values in 2 and 3 (function of Vuc)
5. Check the maximum spacing based upon the value in 4…if the maximum spacing (or min density) is not satisfied, this was consistent with our original assumption so call it done. If it is satisfied, assume min stirrups are provided and restart calcs at stage 2.

However, you can see that because the Vuc in 2 was based on β without stirrups, the determination of maximum spacing in 4 could have been too stringent and if we could have calculated a maximum stirrup spacing that is too small, thus potentially invaliding an otherwise valid design in the final check.

The solution in v5.2.1:

1. Determine if density satisfies minimum density (without checking spacing requirements)
2. Calc Vuc based upon result of 1
3. Calc Vu,min based upon result of 1
4. Determine the maximum spacing based upon previous results
5. If max spacing is sufficient all our previously calculated values are good and we can proceed, using any available transverse reinforcement to calculate Vus. If max spacing was not sufficient, Vuc and Vu,min are still based upon the result knowledge that density was adequate, but in the final check Vus = 0.

Thanks Seth - great post.

Is 5.2.1 the latest version? I'll have to get onto IT to update mine.

Out of curiosity where do I find the release notes for this latest version?

Yes, 5.2.1 is the current release. Release notes for Ram Concept would usually be in this area, but I don't see anything added for 5.2.1.
communities.bentley.com/.../4021.ram-concept-release-notes
I can tell you that it included several minor fixes, but all the rest seem quite rare.

Hi Seth,

I'd like to just confirm something with you. I've pasted the calc log in question below. AS3600-2009 Clause 8.2.

In this case, the V* is greater than 0.5*Phi*Vuc, which usually means you will need atleast minimum shear steel. However the beam in question is relatively shallow and wide with the depth being less than half the width.

I assume the reason why the program has not designed minimum shear steel is due to Clause 8.2.5 (i), which says for shallow beams with relatively low shear you technically don't require any stirrups.

Just double checking this is the case. Perhaps you could add a quick clause reference for the reason why min shear steel is waived.
"Ligs are not required considering 8.2.5 (i)."

Ps. It's a good idea (conservative) for the program to ignore any shear steel that doesn't satisfy max spacing or min density.

Thanks Seth


Starting 8.2 Shear Check
Considering Effect of Torsion on Shear:
No torsion to consider
No torsion reinforcement required
Using 0.8D for do
General Shear Design Parameters
bv = 2849 mm
do = 344 mm
bvd = 980200 mm²
Ac = 1489000 mm²
Ast = 0 mm²
Apt = 2328 mm²
Ac = 1489000 mm²
fc = 40 N/mm²
fsyf = 500 N/mm²
V* = 494.4 kN (absolute value)
M* = -507.6 kN-m
Mo = -339.4 kN-m
Pv assumed to be zero.
Calculating Web-Shear Cracking Vuc (8.2.7.2(b))
Precompression Stress = 1.734 N/mm² (at centroid)
Failure Tensile Stress = 2.277 N/mm²
Shear Stress Limit = 3.022 N/mm² (at centroid)
I = 2.225e10 mm⁴
Q = 78090000 mm³
Vt = 2453 kN [(limit stress) * bv * (I/Q)]
Vuc (web cracking) = 2453 kN (Vt + Pv)
Calculating Flexure-Shear Cracking Vuc (8.2.7.2(a))
Beta1 = 1.382
Beta2 = 1
Beta3 = 1
Shear Stress Term = 0.4563 N/mm² ([..]¹´³)
Vuc (flexure-shear) = 948.5 kN
Vuc = 948.5 kN
Vu,max = 7842 kN
Ligs are not required.
Less than minimum ligatures required, using large shear lig spacing (0.75D or 500 mm)
Maximum lig spacing = 322.5 mm (considers torsion lig spacing also)
Calculating Compression Strut Angle
Using 0.6062 instead of 0.6 for compatibility of 8.2.8, 8.2.9 and 8.2.10
Asv,min = 697.4 mm² (at max spacing)
Vu,min = 1593 kN
Vu,max = 7842 kN
V*/phi = 706.3 kN
Theta-v = 30 degrees
Adjusted Vu,max = 7842 kN (after considering 8.3.3)
Minimum density or maximum spacing requirements not satisfied - ignoring all transverse reinforcement
Total Vus = 0 kN
Vu = 948.5 kN
phi Vu = 663.9 kN