Stress Concentration

[ABV97]

Hi All,
I have the following problem - I have an I-beam. This I beam is replaced with e new I beam, same material, but the middle of the beam is beefed up, which is a stress concentration. Any hints, how should I get away with the new design, addressing the fact that I have a higher stress concentration? Main load of the beam is tension/compression.
Thank you all in advance,

 

[CTW]

Can you describe what you mean by "beefed up"?

 

[JStephen]

If it's mainly tension/compression, why would you need to beef up the middle?

 

[rb1957]

i think he means mid-span ...

the beefed-up section is designed for the higher loads at the mid-span, right?
you also need to check the un-beefed-up section, where the loads are highest

i guess you can look into the stress concentration effect ... i'd've thought your in-service loads would be so low that you were near the endurance limit of your steel. you wouldn't combine stress concentration with static design loads, right?

Quando Omni Flunkus Moritati

 

[ABV97]

...the beefed up midspan of the beam was because a hole must to be drilled, so I am planning by comparison of Moment of Inertia prove that the beam is OK, but I am not sure how should I get away with the stress concentration!

 

[rb1957]

are you looking at statics or fatigue ? if statics, neglect Kt.

are you looking at the Kt due to hole or at the beefing up transition ? at either location it should be easy enough to calc the stress from bending, and to pick a Kt from somewhere.

Quando Omni Flunkus Moritati

 

[chicopee]

Where are you drilling the hole?

 

[ABV97]

the hole is vertically oriented, in the middle of the cross section. Statically should be OK, my concern is from fatigue point of view in both around the beefedup area and around the hole!

 

[rb1957]

so you have a hole in the tension flange ... what's the problem analyzing that ? Kt = 3 ??

Quando Omni Flunkus Moritati

 

[ABV97]

yes, I do agree, kt=3. So I guess my approach would be to find the max stress and from published fatigue life data in cycles(MMPDS)show that it will be OK for certain amount of cycles?
Thank you all for your thoughts!

 

[rb1957]

sounds like a plan ... make sure you're using stresses from typical loadcases (not static design cases)

Quando Omni Flunkus Moritati

 

[ABV97]

I will, I am working on it, thank you rb1957, appreciate your thoughts!

 

[rb1957]

btw, Kt = 3 is reasonable for an open hole (like for a system penetration), if you're filling the hole with a fastener Kt should much less (unless it's a load transfer fastener, when it'll be much higher!)

Quando Omni Flunkus Moritati

 

[ABV97]

No, the hole is a drain hole, so it is considered opened hole.

 

[rb1957]

'bout as open as they get!

Quando Omni Flunkus Moritati