Single & Double Angles for Steel Bracing

[J1D]

Both single and double angles are used for bracings in steel structures. Back-to-back double angles are more popular since the saving of connection bolt (due to double shear) and no worry about the entire buckling around weakest axis z (in an angle to x or y). Can anybody advise your rule of thumb and experience in using single angle bracing?
Thanks in advance.

 

[dawn836]

well i use this rule of thumb
you try single angle until angle size 80x80x8
if it exceed more than this you should better use 2 angles back to back for economy

Note:- 80x80x8 are dimensions for european sections and
are 80mms height of both legs and 8mms thickness of
both. (i do not know it equavliant in american
sections)

another solution is to use two angles forming star shape

 

[dbuzz]

My rule of thumb for the selection of a trial section is to have (a) the slenderness ratio (L/r) less than 180 and (b) sag due to self weight less than L/150.

 

[pmkPE]

Are these anles in exterior environment or interior? Exterior angles, back to back or even star shape have problems with corrosion between the legs - tough to clean and repaint. A single angle or a WT section is better.

 

[flamby]

My thumb rule is to use double angles where some compression or bending is likely (star shape is my favorite too). In tension only members, it does not matter much whether it be single or double.

 

[dbuzz]

I agree with pmkPE re preference for single angles ot tees (or even hollow structural sections) for agressive environments.

 

[jike]

Aren't star shapes and tees very poor torsionally? OK for tension only members, but I would avoid using them in compression.

 

[J1D]

Thanks for the input.

I have never used star shape, it is just for painting convenience, I guess. But it traps dirt as well, and needs more connection bolts. In addition, the interconnection is not as easy/good as back-to-back angles. The local buckling of single piece between interconnectors may be larger concern.

Whether use angle, WT, HSS, or WF can be another big topic. It is determined in many cases by client's or fabricator's preferences without structural reason.

Regards,

 

[am]

I believe two angles in starred configuration [preferably equal angles] are excellent in compression, you get quite a large radius of gyration and that will reduce slenderness ratio followed by larger capacity. I have used this section successfully in a few situations and did not receive any negative feed back so far.

Regards

AM

 

[pappyirl]

I always try to ensure that the bracing system is such that none of the bracing members are in compression. An example of this would be the traditional end bay bracing detail. This way you can use the more efficient tensile capacity of the steel. A single angle in this respect is ideal due to ease of connection.