Regarding A36 Yield Strength 2

[kaffy]

Good Evening fellow engineers,

I am working on a project with a36 beam. I know that tensile yield stress for a36 is 36000 PSI and based on steel designer handbook shear yield stress is 0.57 of that of tensile yield which makes it *36000 = 20520 PSI. Based on Matweb data, the compressive yield strength of a36 is 22000 PSI.

Now here is my question.
During Bending, top layers are in compression, bottom layers are in tension and there is a shear force as well. So my question is while calculating the section modulus what allowable stress I should use. Is it 22000 PSI, 36000 PSI or 20520 PSI?
In ASME code B44, It just says stress should not go beyond 88/ of yield stress(doesn't say which). I could just use 20520 PSI but I do not want to be overdesign it. Can anybody please enlighten me?

Also, my understanding is that if I am designing a column, I will use 22000 PSI as my allowable stress, on Something with tension, I will use 36000 PSI. On shear only, it will be 20520 PSI. Am I doing it right?

Thank You

 

[WARose]

During Bending, top layers are in compression, bottom layers are in tension and there is a shear force as well. So my question is while calculating the section modulus what allowable stress I should use. Is it 22000 PSI, 36000 PSI or 20520 PSI?

It certainly won't be 36 ksi....but you need to get a AISC steel manual to get a allowable. Quite simply because the allowable load could be based on some mode of buckling that could cut the allowable load down to something very low.

 

[BAretired]

Also, my understanding is that if I am designing a column, I will use 22000 PSI as my allowable stress, on Something with tension, I will use 36000 PSI. On shear only, it will be 20520 PSI. Am I doing it right?

No, you are not doing it right.

The minimum yield strength of A36 steel is 36,000 psi in both tension and compression. You are in Canada, so you should be following the steel design code which means you should be using LSD (Limit States Design). There is no such thing as "allowable stress" in LSD. That is the old WSD (Working Stress Design) term and is no longer recognized in Canada.

If the project is in Canada, you should be using the CISC manual, not the AISC manual.

BA

 

[dik]

I'm curious to know... Is A36 still commonly used in the US? or is it just for BAR and plate stock?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

I'm curious to know... Is A36 still commonly used in the US? or is it just for BAR and plate stock?

I still see it used for stuff like channels, angle, and so on.

Not anymore for W shapes.

 

[canwesteng]

A36 is still common for channels and angles, although apparently 50 ksi is now more common for channels.

 

[JStephen]

I find "B44" code gives me "Essentials - A17.1/CSA B44 Safety Code for Elevators and Escalator".
Presumably, that code doesn't address the particulars, thus the question.
Generally, the steel codes will specify allowable stress or strength- but also specify how that is to be calculated.
In a great many cases, strength or stress will be limited by buckling considerations rather than yielding.
Where yielding is the limiting factor, design strength may be based on plastic bending, rather than just reaching yield at the outermost surface.

 

[JLNJ]

Mechanical guys tend to think in terms of safety factors and percent of yield strength. That’s a bit too simplistic for most structural engineering work.

For compression elements, there are complex buckling modes which cause sudden and catastrophic failure way before material yield strength. (Think of a wood 2x4 12’ long. It will buckle in compression long before getting near the crushing strength of wood.)

- Shear isn’t normally combined with flexure.
- Demand (loading) is defined by the type and certainty of the loads.
- bending strength can be governed by the compression side buckling rather than simple compression yielding.

 

[dik]

Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kaffy]

@BA Thank you very much for your response. Sorry, I am confused as Matweb says compressive yield is 22000 PSI only. Do you have any reference showing the same yield stress in both tension and compression.
I have been working with temporary steel structures (short duration) so far and was using ASD with high factor of safeties. I will look into CISC and try to incorporate that into my future designs.

 

[kaffy]

@Jstephen thank you very much. I will look into CISC

 

[kaffy]

@JLNJ. Thank you. The way I was doing the design checks so far was find moment, use the minimum allowable stress from all scenarios and calculating minimum section modulus I need. Afterwards, running a linear static FEA on the part just to cross check but it seems, I was missing one important scenario (buckling happening due to compressive stress generated from bending).

 

[BridgeSmith]

For steel, the yield stress is the yield stress - in tension or compression. Maximum allowable stress varies depend on the code used, and maximum buckling stress depends on the dimensions and bracing conditions. Not sure what you're getting from Matweb, but either it's not the yield stress, or it's wrong. I looked it up, and in the comment column for Compressive Yield Strength it says "Allowable compressive strength".
Rod Smith, P.E., The artist formerly known as HotRod10

 

[BAretired]

I took a quick look at Matweb, but could not find the properties of A36 steel, so I used Google and found the properties listed below. Yield strength is slightly over 36000 psi. As you can see, there is no distinction between tensile yield and compressive yield.

A36 steel was used in Canada many years ago, but is not commonly used today. The usual steel specification today is G40.21 steel which has a higher yield strength than A36.

Working stress design was used exclusively in Canada when I started practicing in 1956, but in recent years (can't remember exactly when it changed), the Canadian standard switched to Limit States Design, so you really must get a copy of the CISC manual if you want to be able to say your design complies with the current code.

BA

 

[dik]

First year steel design used limit states in '65. We were the first class. Same with concrete design... also first class. Other than checking others' designs, I've not used working stress for either concrete or steel with the exception of some highrise buildings in Minneapolis back in 1969 where working stress was used for the column design... slabs were post-tensioned, and done by others.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[kaffy]

Sorry to cause confusion, here is the Link I was referring to. Thank You

http://www.matweb.com/search/datasheet.aspx?matguid=d1844977c5c8440cb9a3a967f8909c3a&ckck=1

My bad. I didn't check the comments section

 

[kaffy]

Thank you very much all for valuable inputs and clearing the confusion. It is very helpful for a young engineer like me.
Have a good day

 

[dik]

If you're not careful, you'll end up like some of us... 'old engineers'...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik