## 4000 psi VS 5000 psi Concrete

## 4000 psi VS 5000 psi Concrete

(OP)

Hi everyone,

I am involved in reviewing shop drawings for a sewage treatment plant project. The treatment reinforced concrete tanks were designed based on 5000 psi concrete, the design plans are showing 16" thick walls and # 7 @ 9" vertical rebars.

A new structural engineer has been assigned to the project. I received the concrete mix design shop drawing for a 4000 psi

and report from the new structural engineer stating that the concrete section capacity is only 1% less if 4000 psi to be used instead of using 5000 psi. He attached a simple calculation of the moment using As x fs value times (d-a/2) for 4000 then calculate the moment using the same equation to get the value of "a" based on 5000 psi to get new value of

(d-a/2)then the moment value for 5000 psi indicating that the difference is only 1% in the section moment capacity and can be neglected so 4000 psi concrete is ok to be used for the same section and rebars which have been designed based on 5000 psi concrete.

I do not agree to use 4000 psi because I do not think that his conclusion is right.

I have requested to re-design the tank all over based on 4000 psi. Please advice if you agree or disagree on the conclusion of using 4000 psi VS 5000 psi would decrease the section capacity by 1% and it can be used for the same section and reinforcement.

Thank You

I am involved in reviewing shop drawings for a sewage treatment plant project. The treatment reinforced concrete tanks were designed based on 5000 psi concrete, the design plans are showing 16" thick walls and # 7 @ 9" vertical rebars.

A new structural engineer has been assigned to the project. I received the concrete mix design shop drawing for a 4000 psi

and report from the new structural engineer stating that the concrete section capacity is only 1% less if 4000 psi to be used instead of using 5000 psi. He attached a simple calculation of the moment using As x fs value times (d-a/2) for 4000 then calculate the moment using the same equation to get the value of "a" based on 5000 psi to get new value of

(d-a/2)then the moment value for 5000 psi indicating that the difference is only 1% in the section moment capacity and can be neglected so 4000 psi concrete is ok to be used for the same section and rebars which have been designed based on 5000 psi concrete.

I do not agree to use 4000 psi because I do not think that his conclusion is right.

I have requested to re-design the tank all over based on 4000 psi. Please advice if you agree or disagree on the conclusion of using 4000 psi VS 5000 psi would decrease the section capacity by 1% and it can be used for the same section and reinforcement.

Thank You

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

## RE: 4000 psi VS 5000 psi Concrete

Dik

## RE: 4000 psi VS 5000 psi Concrete

I don't know if the ultimate flexural strength controlled for the tank but changing from 5000 to 4000 psi has dropped the shear capacity, dropped the cracking capacity and increased deflections and development lengths. But maybe none of this is a concern for your tank.

B

## RE: 4000 psi VS 5000 psi Concrete

Shear loss can be an issue... one we have under construction now has about 40' of soil over it... and shear is critical.

As noted, the biggest loss is in the durability of the concrete...

Dik

## RE: 4000 psi VS 5000 psi Concrete

ULS bending moment: +2.5%

ULS shear force (no shear reinforcement): +7.7%

SLS bending moment (reimforcement stress limit): +0.5%

SLS bending moment (0.25 mm crack width): no change

Flexural stiffness: +1.7%

Doug Jenkins

Interactive Design Services

http://newtonexcelbach.wordpress.com/