Combining stresses to compare with yield stress

[SuG89]

Hello,

I am checking a steel beam element. How can I combine the maximum stresses due to bending and shear so that I can compare a single value with the yield strength of the material?

Is it wrong to combine them as the maximum bending stress is at the cross-section extremes and the maximum shear at the center of cross-section?

Thanks in advance

 

[IFRs]

That's quite a question for a structural engineer !

 

[HofOblivion]

Typically, I separate the bending stress and shear stress as they are applied in a different direction. Bending is just a glorified tension-compression within a cross section (in&out of cross-sectional plane), but the shear is in a planar direction.

I do use combined stress by using square root of sum of squares for guard rail weld capacity check.

 

[DaveAtkins]

For a steel beam, bending stress and shear stress are typically checked independently of one another.

If you are checking some sort of localized stress situation, I think you should use the von Mises formula to combine stresses.

DaveAtkins

 

[patswfc]

Generally you would not combine these.

The design code that you use should have a check for shear and then a separate check for bending (including lateral torsional buckling, if applicable to the form of construction).

When you have high shear, this can effect the beams moment capacity and your code should probably have 2 different equations when checking out bending capacity, one for low shear and one for high shear (the later will give a lower bending capacity). The use of the correct equation depends on the magnitude of the shear load. This is the only interaction that i would think that you would need to account for.

 

[Lomarandil]

Yes, for a typical beam element, it is wrong to combine maximum bending stress and maximum shear. Primarily because the resulting check there is meaningless.

Furthermore, for steel beams, the yield strength of the material may not fully define the capacity of the member.

If you can provide some additional detail for your application (beam section, span, supporting and bracing elements, etc), we can attempt to point you in the right direction. Otherwise, you need to consult an experienced structural engineer.

----
The name is a long story -- just call me Lo.

 

[klaus.]

the combination formulas are given in the codes
Not sure which country you are from but this is actually a very basic question for an structural engineer


best regards
Klaus

 

[SuG89]

Hello everyone, thanks for your answers and apologies for my late response. I am using Eurocode 3 which states "2 different equations when checking out bending capacity, one for low shear and one for high shear".

I am a simulation engineer by education but want to make a career in structural design. Could you please recommend a book or some other source of education so that I can develop some basic skills in structural engineering?

Best regards,
Su

 

[Ron]

Unfortunately, being completely self-taught in structural engineering is not practical. There is no single book, nor even a single university course that will give you all that you need.

A typical time that you use "combined" stresses is for a check called a "unity" check. This is where stresses from two different sources, compared to their respective maximums in a ratio are added together or combined to see if those two ratios are less than a unit value of 1. In some codes and some applications, this is a mandated check.

 

[Jerehmy]

Sug89,

I'd read a structural analysis book cover to cover, a mechanics of materials book cover to cover, and a steel design book cover to cover. Do you have a structural PE that can mentor you? A solid mentor is priceless.

 

[SuG89]

Thanks Jerehmy and Ron for your comments!
I'll start with a structural analysis book for now - Structural and stress analysis by T.H.G. Megson.
I don't have a mentor. There are some colleagues who may help but this depends on their availability.

 

[BMart006]

One of the best resources I've found is Blodgett's Design of Welded Structures. Though the book solely focuses on steel structures, the explanations and fundamentals presented are great. The book really starts from a beginner's level education on material types (again, with regards to steel) and progresses through the analysis of beam-columns, weld groups, cyclic loading cases, various connection designs, etc.

 

[SuG89]

I'll look up for a copy of this book. Thank you!
Does anyone know if there is a book which is similar to "Schneider - Bautabellen für Ingenieure" in English language?

 

[klaus.]

well you can find the same formula in the English Version of the steel Eurocode




best regards
Klaus

 

[SuG89]

Yes that's correct. But usually the formulas in this book are accompanied with some text which may help to get a better understanding of things.