The origin of the 2% bracing force? 4

[GalileoG]

Does anyone know the origin of this rule of thumb? Where does it come from? It seems everyone knows the 2% rule but no one knows where it comes from! Is it in any way related to the 2% that the code allows for out of plumbness? <scratch head>

Clansman

"If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.

 

[youngstructural]

Hey Bridgebuster: Any chance you could post a scan of the NYSDOT "unofficial" standard sheet for rivet replacement? I have done a fair amount of bridge work, including supervising some rivet replacement, however I'm always on the hunt for more resources...

If it's no longer available, perhaps it is also appropriate for SlideRuleEra's website?!

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[bridgebuster]

Here it is

 

[youngstructural]

Looks like a good sheet of criteria... It would be interesting to know where it came from, however I'm guessing it may be lost to history. Very much like the 2.5% brace force for that matter.

A star for the sheet bridgebuster!

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[JoshPlumSE]

Chapter 12 of the SSRC's (structural stability research council) book Guide to Stability Design Criteria for Metal Structures is all about bracing.

It's probably the best source for this type of question. I took a quick look at it, but do not particularly care to read the whole chapter right now. But, here are some quotes:

"For stiff brace systems the brace force approaces Fbr=Po*Delta_o/L. The brace force is a linear function of the initial out-of-plumbness".

They give a lot of technical references for the chapter that probably give you a better response than I am capable of.

Josh

 

[jheidt2543]

This got me looking around and I found the following note on page 336 of "Stresses in Framed Structures" by Hool & Kinne, 2nd Edition 1942, 1st Edition 1923:

"The lateral bracing of the compression chords or flanges of trusses and deck girders and between the posts of viaduct towers shall be proportioned for a transverse shear in any panel equal to 2-1/2 percent of the total axial stress in both members in that panel, in addition to the shear from the specified lateral forces."

There was no citation or reason given in support of the 2-1/2 percent number.