concrete design

[alphatarget1]

So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

 

Is there a question here, or are you just ranting poorly?

 

[skyking]

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

concrete has virually no tensile strength. It is all based on compressive loads. If you pre- or post-tension reinforce it, the bending properties of the reinforced member will determine the absolute load. There are varying grades of concrete, but once a member goes from compression into tension, it will fail. By pre- or post tensioning it and providing camber, you can load the crap out of the tensioning steel or cables within the concrete.

 

[MustangSVT]

Originally posted by: skyking

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

concrete has virually no tensile strength. It is all based on compressive loads. If you pre- or post-tension reinforce it, the bending properties of the reinforced member will determine the absolute load. There are varying grades of concrete, but once a member goes from compression into tension, it will fail. By pre- or post tensioning it and providing camber, you can load the crap out of the tensioning steel or cables within the concrete.

concrete knowledge +1

 

[Quasmo]

Originally posted by: MustangSVT

Originally posted by: skyking

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

concrete has virually no tensile strength. It is all based on compressive loads. If you pre- or post-tension reinforce it, the bending properties of the reinforced member will determine the absolute load. There are varying grades of concrete, but once a member goes from compression into tension, it will fail. By pre- or post tensioning it and providing camber, you can load the crap out of the tensioning steel or cables within the concrete.

concrete knowledge +1

confusion +3 😕 😕 😕

 

[skyking]

A few years back I was on the crew installing some concrete I-beams for a bridge. They were 6' tall, with a wider upper flange, and weighed 1000 pounds per running foot. The beams were 120' long, and very fragile in any other direction but the designed load. It was an interesting experience, because there was no way a single crane could do the job. The beams were handed from crane to crane with passing plates, and went across to the middle of the river on a girder launcher, a kind of box girder assembly with a little car on top.

 

[everman]

Originally posted by: MustangSVT

Originally posted by: skyking

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

concrete has virually no tensile strength. It is all based on compressive loads. If you pre- or post-tension reinforce it, the bending properties of the reinforced member will determine the absolute load. There are varying grades of concrete, but once a member goes from compression into tension, it will fail. By pre- or post tensioning it and providing camber, you can load the crap out of the tensioning steel or cables within the concrete.

concrete knowledge +1

I :heart: concrete.

 

[skyking]

Originally posted by: Quasmo

Originally posted by: MustangSVT

Originally posted by: skyking

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

concrete has virually no tensile strength. It is all based on compressive loads. If you pre- or post-tension reinforce it, the bending properties of the reinforced member will determine the absolute load. There are varying grades of concrete, but once a member goes from compression into tension, it will fail. By pre- or post tensioning it and providing camber, you can load the crap out of the tensioning steel or cables within the concrete.

concrete knowledge +1

confusion +3 😕 😕 😕

You can't pull on concrete much, but you can push on it like mad. put some cables into extreme tension in the bottom of a beam, and it will bend or bow upward in the middle. now you can place a load onto that beam and pull even harder on those cables. it is all copacetic till that beam gets flat, and you try and stretch on the bottom web with more load. BOOM!

 

[Dubb]

Good example:

http://www.lmc.ep.usp.br/people/hlinde/Pef-2200/masp6.jpg

the whole building is suspended from 2 massive reinforced concrete beams (post-tensioned) considering the size of the building, that's damn impressive.

edit: more pic:

http://www.cuoretriveneto.it/newsimg/2527.jpg

 

[opticalmace]

^ that is freaking sweet.

 

[rahvin]

Originally posted by: alphatarget1
So the professor talked about underreinforced concrete and overreinforced concrete on friday. Underreinforced concrete = more warning and overreinforced concrete = sudden failure. All is good until I started doing the homework, in which ALL of the problems are limited by the compressive strength threshold of the concrete... wtf?

I really don't understand your confusion. The concrete is the design material, the steel is only there to compesate for the lack of tensile strength. So of course the properties of the concrete are what will control the design.

 

[newParadigm]

Originally posted by: opticalmace
^ that is freaking sweet.

I agree