Shear Strength of Mass Concrete 1

[sybie99]

Good Evening Guys

I have a simple question: What is the shear strength of mass concrete? I know some people use 0.34n/mm2, which relates to the formula in BS8110. Of course it would relate to the compressive strength, but how is it calculated? I have searched the forum as I would have thought this to be quite a simple question, but could not find any relevant posts.

If anyone could shed some light please

Thanks

 

[msquared48]

Square root of f'c for unreinforced concrete.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[IDS]

Square root of f'c for unreinforced concrete.

That's about 6 MPa!

There must be a factor missing.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[hokie66]

Don't know if it of assistance to you, but in the Australian Standard AS3600, the design strength in shear of a one way member is defined as 0.7 (strength reduction factor) x .15 bD x (fc')^1/3. So for 25 MPa concrete, about .31 MPa. For 40 Mpa, about .36 MPa. In the same range as your .34 MPa.

For two way action, there are other requirements.

 

[cntw1953]

In the US, shear strength for normal concrete structure is phi*2*(fc')^.5*b*d (phi=0.85). However, if I rember correctly, USCOE allows higher shear strength for hydraulic mass concrete structures (up to 10*(fc')^0.5, mainly for deep beams), you may want to check it out. USCOE Engineer Manual - "Strength Design for Reinforced-Concrete Hydraulic structures", EM 1110-2-2104, June 1992.

 

[IJR]

I am no good and others have already done better. Let me share the following

Shear strength comes from tensile strength of concrete, some friction, some dowel action and whether your concrete mass is in tension or compression.

Dowel action and type of stress are tough to follow, but friction can be reliable.In regular beams for example friction is usually ignored, in deep beams it is not.

Have you got the book by McGregor? Got good science in it.

respects
ijr

 

[Splitrings]

Approximate actual shear capacity for a rectangular section is 2*((f'c)^0.5)bd

Allowable (ACI 22.5.4) 4/3*((f'c)^0.5)bd

 

[frv]

Check ACI 318, section 22.5.4.

One way: Vn=(4/3)*sqrt(f'c)*bw*h

 

[BAretired]

Vc in CSA A23.3-94 may be taken as 0.2*[λ]*[φ]_c[√]f'_c
[λ] = 1.0 for normal concrete (0.75 for low-density concrete)
[φ]_c = 0.6 (resistance factor for concrete)

For 25 Mpa concrete, Vc = 0.6 by the Canadian code, nearly twice the value in the Australian code.

BA

 

[sybie99]

Thanks guys, always great to get immediate answers, appreciate it!

 

[Lion06]

Here's a good paper. It's geared to cold joints, but it does get into shear strength of large blocks cast monolithically (as a control group against the blocks with cold joints).