Knee Braces

[ToadJones]

I've got a scenario right now; one that I have had to analyze many times, with a crane runway with knee braces.
First of all, from my experience with runways knee braces = BAD as they cause the runway connections to fatigue and break.

My question is, did the original designers count on these knee braces for bending capacity of the runway or simply for stability?
My suspicion in review design loads on old drawings is that the knee-bracing was strictly intended for stability.

 

[ToadJones]

Pad-
Seems like a lot of your career was spent industrial settings.
As usual, I appreciate the input.

 

[JAE]

Pad - one of my mentors started his career in 1927. Two others in 1947 and one in 1949. I don't feel insulted by anything here and neither should you.

The statement by ToadJones was that the indicated moments didn't correlate with the presence of the knees. Thus, the engineer (not you - the actual design engineer on this particular project) didn't account for them in the analysis. These are just factual observations of what TJ described.

 

[paddingtongreen]

JAE, It wasn't Toad that I was annoyed with, Toad and I agree on more than we disagree. I think SlideRuleEra and someone else said, more than once, that the designer might have used the braces to limit deflection even though Toad said that they were not in the bending moment design.

My point is; that to say they limit deflection, while at the same time not affecting the bending moment would be unprofessional, unless it were done out of ignorance.

Now, I'm done with this subject.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JAE]

Pad - thanks for the reply - I just took those comments to be more for LATERAL deflections rather than vertical deflections. A lot of "us" older engineers learned from "even older" engineers the concept of designing a straight-up gravity frame and then adding knee braces, bottom chord joist extensions, etc. to limit wind deflections and add, in a seat-of-the-pants way, the lateral drift of a structure.

That is what I think a lot of crane beam rail designers used to do. (I don't do that at all but I've seen it done)

 

[SlideRuleEra]

Paddingtongreen - You say that I, SlideRuleEra, have both insulted and annoyed you. For the record, here, in total, is what I said on this thread:

In my opinion, neither. Probably for a third reason: reduce beam deflection to the recommended L/600 to L/1000 range.

and

Why not make an easy calc to see if the knee braces were used for defection control, or not?
You know that the beams were designed as simple spans. What would the defection be for this simple span? If simple span deflection is greater than (approximately) L/600, then the knee braces (intentionally) contribute to deflection control.
If assumed simple span deflection is less than L/600, then the knee braces have little or nothing to do with deflection control.

I don't see anything said, or implied, about your comments or professional opinions on this thread.

To the contrary, if the calculations that I suggested in my second post are performed the results will likely make my first comment look foolish. That's ok with me. As far as I'm concerned, Engineering-Tips is all about good engineering practice and accurate results - NOT "insults" or "annoyance".

There's more that I could say... but that's enough.

SlideRuleEra

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net