Connecting Two Steel Beams....Help Needed 2

[Abuh001]

Hi

I have recently been interested in the effects of "connecting" two beams together via a diaphragm (smaller beams or parallel flange channels). How would this effect lateral torsional buckling and deflection?. However,I am having a hard time finding any resources especially ones that refer to euro-codes. Does anyone have any ideas on where I can find such information.


Page 42 from the document "Stability of Steel Beams and Columns" by the SCI refers to what I am talking about, good free download that I highly recommend.

This document was helpful

https://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9445(2008)134:9(1487)

Thanks

 

[jayrod12]

I think you're going to need to be slightly clearer in your question.

If the compression flanges of the beams are connected directly to the diaphragm then I would consider them braced for LTB.

Regarding deflection, it would depend a significant amount on the type of diaphragm and the connection between the beam and diaphragm.

 

[JoshPlumSE]

I think he meant to post this as a "helpful hint" post instead of a question.

 

[Abuh001]

Sorry, my question was more about asking for useful resources dealing with LTB and deflection design of double braced beams.

 

[ukbridge]

You've basically created a ladder deck, which will have a significant effect on LTB. The beams will now buckle laterally together with an effective length of either:

1) Lcr = kL, over some portion of the whole span magnitude similar to L/3 (dont use this number to actually design it please...)
2) Lcr = Lb, i.e. buckling half wavelength with a spacing equal to the bracing centres.

What your Lcr is depends on the spacing of the bracing, the beams, the stiffness of the bracing etc etc.

You want to work out Mcr for the braced deck to work out your Mb,Rd in the Eurocodes. There are 2 ways of doing this basically:

1) Run an eigenvalue buckling analysis using 3D shell elements to directly work out Mcr.

2) Use the old BS5400 guidance given in section 7 or 8 of PD 6695-2 (the published document for EN 1993-2) to work out an equivalant Lamda_LT. It depends on the actual bracing arrangement whether its torsionally or laterally restrained, a sketch is handy.....

This link should be a lot of help

https://www.steelconstruction.info/Bracing_systems

PS You also need to look into:

1) Designing the connections for these bracing forces
2) Meet the stiffness requirements of the bracing, which are in the same published document

gl

 

[Bobby46]

This is some of the research that the AISC steel code references for beam bracing. I'm not sure how it relates to Euro-Codes. It has methods to determine if diaphragms are stiff enough to prevent LTB. I think it includes methods for calculating stiffness to use in deflection calculations.

https://www.aisc.org/globalassets/aisc/research-library/bracing-for-stability.pdf

http://www.ecs.umass.edu/cee542/handouts/Fundamentals_of_Beam_Bracing.pdf