Minimum reinforcement of flexural members 2

[sushilDhungana]

As per ACI 350-06 minimum reinforcement in the flexural member is given in section 10.5. I understand 10.5.1 and 10.5.2 but I don't understand 10.5.3 can anyone elaborate me this section I'm designing hydraulic machine RCC wall. This section jpg file is attached in this post.

 

[hokie66]

What don't you understand about it? The first two requirements are minimum steel, irrespective of the design moment. The third requirement allows you to reduce the minimum reinforcement as long as you provide capacity substantially in excess of the design moment. To apply these provisions, first you need to know the design moment, and the reinforcement required to provide capacity to suit.

Is your wall a flexural member? There may be other provisions which apply to your wall.

 

[sushilDhungana]

Dear hokie66
Yes, my wall is a flexural member having biaxial moments and axial forces. I donot understand the third requirement please elaborated me with some example.

Thank you
Sushil

 

[hokie66]

First you have to demonstrate that you know how to calculate the requirement for flexural reinforcement. Forget the minimum reinforcement provisions until you know how to design a beam for its design moment.

 

[serrojo]

Sorry, you nave to read the posting guidelines. We are here to share experiences and opinions, not to elaborate professional solutions.
Try other way:
1 - Design your wall, the way you can.
2 - share a plan or picture with your solution, (don't worry if you find it absurd, here we are very respectful specialists).
3 - Ask if anyone have an opinion on your solution and share your hypothesis assumed.
4 - Appreciate the other's Time!

Hope you get you solution!
regards.


MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[dik]

serrojo... why? I never have, but, it hasn't stopped me.

Dik

 

[dik]

Does minimum ACI reinforcing apply to walls, footings and slabs? or is the provision and the 33% increase for flexural beam items. Walls, footings and slabs minimum steel > temperature steel. Not sure, just wondering. Don't have my ACI copy at home here.

Dik

 

[Shu Jiang PEng SE]

The minimum reinforcement requirement can be waived when the reinforcement is at least 33% more than required in term of member bending strength. For example, the required bending moment is 100kip-ft and the design bending strength is 133kip-ft with specific As (assuming ductile controls the member bending strength), then As dose not need to meet the minimum reinforcement requirement required by section 10.5.1 and 10.5.2.

 

[dik]

Thanks Shu Jiang... often used that 33% increase. It's been a provision for several decades.

Dik

 

[hokie66]

Shu Jiang is correct, but I think that is looking at the provisions backwards.

My approach would be like this for a common beam:

1) Your reinforcement requirement by analysis is 400 mm^2, so 2-16mm bars.
2) Minimum reinforcement by the 10.5.1 and/or 10.5.2 provision is 900 mm^2, or 2-24mm bars.
3) Providing 2-20mm bars, 620 mm^2, satisfies 10.5.3, so that is your design.

Dik, walls, footings, and slabs have different provisions.