Strength of a Shortened S-Shape Monorail

Question

Strength of a Shortened S-Shape Monorail

GrimesFrank (Mechanical)

(OP)

12 Feb 07 11:19

Odd situation/request but here it goes nonetheless;

Currently have a S12x31.8 monorail (aprrox. 60' long / 5 cantilever supports) supporting a 5 ton chain hoist.

Without getting into detail, I want to shorten the depth of the rail.  I fully expect to analyze the condition but I'm trying to work out feasability right now.

I talked to our steel supplier and he said we could not get/buy a custom S-shape to what I wanted.  He said they could make what I want out of plate.  I don't necessarily want this as I want the S-shape maintained.

If analyzed for loading still within capability for my application;
1)  Could I cut a section out of the web and re-weld longitudinally and maintain the majority of my strength?

2)  Is this more work than adjusting to make use of custom plate beam (~W shape)?

Frank "Grimey" Grimes
You can only trust statistics 90% of the time.

civilperson (Structural) · Answer 1 · 2007-02-12 12:31:09

Yes, but the strength is proportional to "d" squared. A 10" section cut and welded into a 8.25" section will have 32% less bending capacity and 44% less capacity due to deflection criteria (proportional to "d" cubed).

miecz (Structural) · Answer 2 · 2007-02-12 13:10:21

Grimesfrank-

I believe it will cost less to cut the S shape down and re-weld it. For one, there is less welding involved, and rolled steel is less expensive than plate steel

civilperson-

I think the "d" squared and cubed relationships work for rectangular shapes, but not for S shapes. The strength reduction will be less.

JStephen (Mechanical) · Answer 3 · 2007-02-12 13:14:15

Beware of weld distortion. If it's an assembly-line process (as in making T-shapes out of beams), this can be accounted for in the process. But on a one-off fabrication, you can get some weld distortion that is not easily corrected.

GrimesFrank (Mechanical) · Answer 4 · 2007-02-13 12:54:24

Thanks all.

I was hoping to get the cut/weld done offsite, but you're right the thing will warp by the time they get to the other side to weld. Whats ideal on paper..........

Time to get back to the drawing board.

Frank "Grimey" Grimes
You can only trust statistics 90% of the time.

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Strength of a Shortened S-Shape Monorail