Is this sentence wrong? (Shear Reinforcement)

A bit further in eurocode2 you will find listed exceptions for elements where it is possible to put no shear reinforcement whatsoever (eg. planks/slabs, concrete joists etc.)

Maybe ... depending on the type of structural member... If the structural member comply with one of the clause 6.2.2(2) thru 6.2.2(7), you are not required to provide any shear reinf.

Chapter 6.6.2 is for the verification VEd ≤ VRd,c assuming without shear reinforcement.

"I might be missing something here, but should there not always be some shear reinforcement?"
No. Instead of looking at the code, I suggest that you study reinforced concrete behavior; more specifically what mechanisms contribute to shear strength in a reinforced concrete member.

"Is there a difference between minimum reinforcement and minimum shear reinforcement?"
Yes. Furthermore, there is no such thing as "minimum reiforcement"; the type of reinforcement must be specified before it can be referred to as "minimum reinforcement".

PS. Why are you reading reports about design that you are clearly not familiar with? I urge you to take this up with your supervisor.

bojoka said:

"Calculations show there is no need for shear reinforcement". Did they perhaps mean "Calculations show there is no need for shear reinforcement beyond minimum shear reinforcement"?

Click to expand...

Yes, the quoted code reference is headed "Members not requiring design shear reinforcement".

Where design shear reinforcement is not required the minimum shear reinforcement specified by the code is still required. In some cases that is zero, but where the code requires minimum shear reinforcement, you have to provide it.

centondollar - I'm not sure what your point was, but it sounds like you are saying if your understanding of the mechanisms that contribute to shear strength in a reinforced concrete member indicate that shear reinforcement isn't necessary, you don't need to provide any, even if the code has minimum shear reinforcement requirements for that case. If that is what you meant, I disagree.

Doug Jenkins
Interactive Design Services

It would help if you showed the whole clause including the formula for

vmin = .035 k ^ 2/3 fck ^ .5

where k = 1 + (200 / d) ^ .5

presumably it is the minimum interface shear stress assumed for concrete (a minimum value for eqn 6.2), independent of the amount of longitudinal reinforcement supplied.

It is not the shear force supplied with minimum shear reinforcement!

The is the clause for sections that have less than minimum shear reinforcement.

Eurocode requires minimum shear reinforcement in all beams except minor importance such as lintels.

Just a follow up question; what is the difference between shear reinforcement and punching shear reinforcement? Are they one and the same just that maybe the direction of the two differs?

IDS:

Obviously, if the code requires minimum stirrups (e.g., for tying column longitudinal rebar), it should be provided. I was referring to the general principles of RC shear design.

My point was clear: one should not look to the code to find explanations for basic principles of structural design or structural mechanics.

rapt:

As far as I know, the minimum shear reinforcement for beams according to EC2 is required to improve confinement of concrete (improving compression capacity), increase the dowel effect of flexural rebar, restrict shear cracks along web edges, and restrict flexural cracks (placing flexural rebar inside stirrups reduces the splitting stress near the flexural rebar); it is not related to providing resistance to shear force per se.

centondollar said:

My point was clear

Click to expand...

I'm sure it was clear to you.


Doug Jenkins
Interactive Design Services

Actually, I am sure the minimum shear reinforcement is required in Eurocode because shear is a non-ductile failure mode and the code wants to make sure the member will fail in a ductile manner.

Shear reinforcement adds ductility, but it is not mandated for slabs in EC2 - and yet, slabs are also usually designed to fail in a ductile manner. Therefore, the minimum stirrup requirement (for beams) is probably not primarily related to ductility, but to the other factors mentioned in my previous post.

Another interesting detail related to shear design in Eurocode 2 is that if shear reinforcement is added, it is designed to resist the entire shear force; the resistance provided by aggregate interlock, flexural rebar dowel effect and shear capacity of uncracked parts of the cross-section is not superimposed with stirrup capacity in Eurocode 2.

PS. Most chapters of Eurocode 2 do not explicitly address ductility of RC members; Eurocode 2 doesn't prohibit over-reinforced sections, for example.

Slabs are able to redistribute loads and the so ductility requirements are reduced in most codes.

many codes required minimum shear reinforcement for beams when

V* > .5 Vuc

and for slabs when

V* > Vuc

That was recognizing the ability of those slabs to redistribute the shear stresses compared to beams that do not have that ability.

Eurocode and the old BS8110 went one step further and recommended minimum shear steel in beams no matter what, while slabs still used the V* > Vuc limit.

The Canadian Bridge code went a different way and has a variable limit instead of the 2 limits of .5 and 1.0, dependent on the section depth. The latest Australian code has gone that way as well.

I do not want to reply any of the specific post but apparently there are misunderstandings of the EC- 2 for shear design.

I will suggest to look the following books ;

- worked examples 6.4 ,6.5, 6.6 ( EC2 Worked Examples by European Concrete Platform )

- Eurocode 2: Design of concrete structures EN1992-1-1 symposium notes ( by J.C. Walraven )

EDIT: The link for Design of concrete structures EN1992-1-1 symposium notes ( by J.C. Walraven )