Any Structural Engineers Out There?

[Sphere]

I doubt I will get much of a response, but there is a question that is nagging me.

In any intro to mechanics course you learn about the interaction of shear and normal forces; the whole Mohrs circle thing. I know in automobile and aerospace industry this is taken into account using finite element analysis.

In structural engineering, however, this isn't accounted for. Especially in the building codes which have you do a check for bending/compression/tension strength, and then do a separate check for shear strength. This is theoretically unsafe as these forces are acting simultaneously and therefor have a combined effect.

The reason for leaving this out might be that area's of large shear and large moment usually occur in different locations in a member and thus combined forces would not normally control the design. But could there be a situation where it would control the design? If so would it be worth the complex calculations?

I guess what nags me this: Is the shear-normal force interaction left out of design calculations for theoretical, or practical reasons?

[Old_Rome]

I could see how this would be important in an earthquake zone if the soil was loose or the building was built on fill dirt.

[chriscase]

I doubt I will get much of a response, but there is a question that is nagging me.

In any intro to mechanics course you learn about the interaction of shear and normal forces; the whole Mohrs circle thing. I know in automobile and aerospace industry this is taken into account using finite element analysis.

In structural engineering, however, this isn't accounted for. Especially in the building codes which have you do a check for bending/compression/tension strength, and then do a separate check for shear strength. This is theoretically unsafe as these forces are acting simultaneously and therefor have a combined effect.

The reason for leaving this out might be that area's of large shear and large moment usually occur in different locations in a member and thus combined forces would not normally control the design. But could there be a situation where it would control the design? If so would it be worth the complex calculations?

I guess what nags me this: Is the shear-normal force interaction left out of design calculations for theoretical, or practical reasons?

I am guessing that simplifications, when made (correctly), are made on the authority of established studies that justify them.

I don't have enough of an engineering background to say for certain, but this looks like it might be such a study, made in regards to beams used to support bridges.

[Yaga Shu Ra]

I'm going against forum etiquette with reviving an old thread, but...

One of my teachers used to be involved in the automotive industry (formula 1 racing if I'm not mistaken) before he made the switch to structural engineering.
I'll try to mind posing him your question when the oppertunity arises. Perhaps he can shed some light on this?

[Sphere]

After a little further investigation, I stand somewhat corrected. I have indeed found a part of the Concrete Code that takes this into consideration. In the rare case of a concrete beam without any shear reinforcement, you are required to use a normal/shear stress-interaction formula based on a 1963 study.

However, I haven't found another instance of this yet in other codes, and indeed the Concrete Code drops this idea once you add shear reinforcement.

[Nik]

A general question, do you mean a mechanical failure analysis where the end result of the calcuation are failure modes and/or stress at failure or just general stress calcuations when designing a structure (concrete or steel)?

FEM-Codes have become a staple of engineering, but only since the needed computer power became affordable. Beforehand, a lot of investment went into theoretical models that where simple enough to catch the important features of a given problem, and the experimental data (for the matieral and failure behavior) and regulating laws where built around those models.
Most often, a full 3D Stress-Strain solution with failure check offers no real advantadge over a tried and true approximate model secured with a bootload of data, or the solution takes far to long to be economical. Accidents happen when someone advances into a new area and continues to use the old models, not realizing that the whole underlying data became worthless.

[Sphere]

I am talking about designing beams, columns, slabs etc. You do a check for bending capacity then you do a separate check for shear capacity. But mechanical theory says these two forces interact, which means your bending forces add to your shear forces and vice versa.

I found one part of the concrete code that acknowledges this (it combines shear forces and bending forces into one equation).

I am assuming most FEM programs do this. Although I am not sure they do when it comes to structural design programs, because they generally have the building codes built into them. So it the building codes don't have it, the program shouldnt either.