Design of connector spacers for Double Angle 1

[harmsgundam]

Hi all,

We have a project regarding retrofitting of communication towers wherein I'll add an aditional angle bar to an existing diagonal member which is an angle bar as well of the same size. So the resulting section is a double angle. Now regarding the spacers to be place along the length of this double angle, of course after computing the required spacing base on AISC, I am planning to connect the spacers to the double angle section by means of bolts. The question is how will I know the right size of spacer and bolt/s to apply (i.e. the dimension and thickness of the spacer and the diameter of bolt to use)?

Thanks in advance to those who can enlighten me on this matter.

 

[BAretired]

Spacers are optional; they are not structurally required. Spacing of bolts S should be such that S/r[sub]min[/sub] of a single angle is less than or equal to L/r[sub]min[/sub] of the double angle.

BA

 

[LuisUgarte]

You might find helpful the attached paper. I think there is a good design criteria on the first page.

Regards

 

[Hokie93]

Another source for this is the Steel Interchange article from the June 2010 issue of Modern Steel Construction.

The article is available at:

http://msc.aisc.org/globalassets/modern-steel/archives/2010/06/2010v06_interchange.pdf.

The brackets in the equation do not appear correctly in the on-line version of the article. The equation should read:

F[sub]s[/sub] = (α[sup]2[/sup]/α[sup]2[/sup]+1)*P[sub]y[/sub]*(1-P[sub]cr[/sub]/P[sub]y[/sub])

 

[harmsgundam]

@BAretired Thanks for the response. For the single angle section, the r[sub]min[/sub] you're saying is equivalent to r[sub]z[/sub] or the minimum of r[sub]x[/sub] and r[sub]y[/sub]?

 

[BAretired]

Use r[sub]z[/sub] but use a maximum spacing of L/3, i.e. connectors at third points.

When calculating the capacity of the double angle member by CSA S16, replace the actual length with an equivalent length Le which accounts for the slenderness of the component angles between connectors.

Le = r[sub]x or y[/sub]√[(KL/r[sub]x or y[/sub])[sup]2[/sup] + (KS/r[sub]z[/sub])[sup]2[/sup]]

where L is the length of the double angle and S is the spacing of connectors; Le is the equivalent length for design purposes.

BA

 

[harmsgundam]

@LuisUgarte , thanks for the response and the attached paper. Based on it, do you think that the resulting spacing and size of bolts/ weld to use is on the conservative side using the mentioned approach?

@Hokie93, thanks for the response as well. That's a direct equation for computing the shear force, the only problem is to determine the critical buckling load. Any reference on this one how to get the P[sub]cr[/sub] (critical buckling load)?

@BAretired, thanks for the useful information.

 

[humanengr]

If your design is per AISC, then "S/rmin of a single angle is less than or equal to L/rmin of the double angle" is not correct. It should be less than or equal to: [3/4 *(L/rmin)]
(Ref. AISC E6.2)