Shear resistance of a corner of a concrete structure

[user277418]

Hello

I am designing a joint of two precast walls. The joint should be capable to resist a bending moment of about 13kNm. The joint is not a very good solution, but this is a desire of a client.

I have worry about a shear capacity of a corner due to a compression component of a couple of forces due to the bending moment. As this corner is critically important for a bending resistance, I want to determine it's shear capacity. Hence a maximum compressive stress to the corner. I have assumed that the case is shear of plain concrete.

The problem is σc,max=2.55MPa << fcd=17MPa (fcd is a design compression strength of reinforced concrete). Hence MRd=7.5kNm

The questions are:
- are there any other methods to determine the shear capacity of the corner? Maybe by other codes than Eurocode.
- if the shear capacity is so low, why the corners don't spall in standard joints (for example hollow core slabs supported by a precast wall)?
- maybe I should not worry about the corner? Why?

Best regards

 

[PROFR]

This is a typical plain concrete bearing resistance problem. It is covered in section 10.14 of the ACI 318-11 Code.

Cheers..!!

 

[user277418]

section 10.14 of the ACI 318-11

This? I don't see, how it could help. Here described central load application with spreading on full cross-section, but it is not my case. And could you say what value of the reduction factor? I am not familiar with ACI code.

 

[mmarlow]

I agree with PROFR. Essentially its just like running checks for a concrete beam. at steel yielding , the steel takes all of the tension and the concert takes the compression. you can approximate a Whitney stress block on the compression face, and check ACI 10.14.1 (or the formula for concrete bearing per your local code.).

Id run an out of plane bending check, with axial and flexural loads. Calc. Pure flexure, Pure compression, and balance point. Then plot an interaction diagram. Depending on the height of your wall and your end conditions you may see increased moments due to P-Delta.. I would conservatively make sure that your pure flexure strength (no axial) is not exceeded by the primary moment and p-delta secondary moment. Axial loads on the wall may not be there all the time, and they help this can help the flexural strength of the wall (see an interaction diagram). However, when checking your bearing, include amplified moments and axial loads to get max comprehensive forces.

This is my take at least, and I hope it helps.

-MMARLOW EIT

 

[user277418]

... and check ACI 10.14.1 ...

I would agree with all that said before and after, but this check related to the situation like on the picture below

But my case is little different. Imagine a concrete cube and you stend on a tip of it's edge. Will the tip crack?

 

[mmarlow]

Im not understanding your problem I suppose. I would think that the rebar would stop (resist) this "Cube" from standing up on its tip? I hope someone can address your question.

Best,
Morgan

-MMARLOW EIT