Double Angle Compression Members
Double Angle Compression Members
(OP)
In AISC 9th Edition the discussion for double angle compression members on page 3-53 seems to indicate that the tables are based on adding a minimum of two connections between members.
In a condition where truss diagonals and verticals are constructed with double angle members with no connections between angles it appears these tables do not apply even for buckling about the X-X axis. Am I reading this correctly? Thanks.
In a condition where truss diagonals and verticals are constructed with double angle members with no connections between angles it appears these tables do not apply even for buckling about the X-X axis. Am I reading this correctly? Thanks.






RE: Double Angle Compression Members
RE: Double Angle Compression Members
If so, they must be connected. Otherwise, as mentioned above, all you have are two single angles.
Why are you using AISC 9th edition? Is the 13th or 14th in effect for your project?
RE: Double Angle Compression Members
RE: Double Angle Compression Members
BA
RE: Double Angle Compression Members
When design the double angle compression capacity, modified slenderness ratio is used as per AISC 360-05 E6-1 to account for interconnection bolt at spacing = 4’ = 1.2m
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
RE: Double Angle Compression Members
>>even if the length of the member is say 5'
I normally don't use table and use spreadsheet to make my own table and chart so that everything is under my control. Anyhow you can verify the table with your own calc.
For BOLTED double angle member under compression or tension there is an eccentricity between bolt group center line and built up section neutral axis line. That creates a eccentric moment and bring down the member's resistance a lot up to 60% less. Someone may think that applies to hor. brace only similar to WT section, but actually for vertical double angle brace, it has larger eccentricity than hor. brace in many double angle sections. Please check it. None of the table consider the connection eccentricity case and only give you the resistance of pure compression case, which is not the actual condition as eccentricity exists in the BOLTED double angle brace connection.
Back to the batten plate issue, normally the steel fabricator default to use 4’ as the batten/connecting bolt spacing in the shop drawing. For design engineer we put max 4’ batten/connecting bolt spacing in the steel general notes. That’s the conventional way throughout US and Canada.
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
RE: Double Angle Compression Members
RE: Double Angle Compression Members
I believe unless fatigue is a consideration, the eccentricity you mention can be ignored (AISC J1.7).
DaveAtkins
RE: Double Angle Compression Members
1. In AISC LRFD 1999 Section J1.8 the eccentricity is allowed to be neglected.
2. In AISC LRFD 2005 AND 2010 the LRFD1999 Section J1.8 “… negligible effect on the static strength of such members” has been taken out
3. In AISC LRFD 2005 AND 2010, the wording doesn’t NOT mean the eccentricity can be neglected in terms of static member strength
Attached AISC EJ went through the actual load test and draw the following conclusions
1. In AISC LRFD 1999 Section J1.8 the eccentricity is allowed to be neglected. That’s not true compared to real load test
2. For WT and Double Angle section with eccentricity > 1.5” = 38mm, axial compression/tension + compression interaction design is required.
Please also check AISC EJ 2002 Q3 Influence of Bolt-Line Eccentricity on WT Tension Member Capacity
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
Eccentricity in WT & Double Angle Connection
1. In AISC LRFD 1999 Section J1.8 the eccentricity is allowed to be neglected.
2. In AISC LRFD 2005 AND 2010 the LRFD1999 Section J1.8 “… negligible effect on the static strength of such members” has been taken out
3. In AISC LRFD 2005 AND 2010, the wording doesn’t NOT mean the eccentricity can be neglected in terms of static member strength
Attached AISC EJ went through the actual load test and draw the following conclusions
1. In AISC LRFD 1999 Section J1.8 the eccentricity is allowed to be neglected. That’s not true compared to real load test
2. For WT and Double Angle section with eccentricity > 1.5” = 38mm, axial compression/tension + compression interaction design is required.
Please also check AISC EJ 2002 Q3 Influence of Bolt-Line Eccentricity on WT Tension Member Capacity
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
RE: Double Angle Compression Members
Thanks
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
DaveAtkins
RE: Double Angle Compression Members
You are right.
How about WT section, any thought ?
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com
RE: Double Angle Compression Members
But don't take my word for it. The Commentary for this section does state explicitly that this eccentricity has long been ignored and has a negligible effect on the static strength of such members.
RE: Double Angle Compression Members
A view in the plane of the member per Fig. C-J1.3 shows welds balanced about the neutral axis of the angle.
If you cut a section through the plane of the member, there is still an eccentricity between the longitudinal axis
of the member and the welds. The question; should this latter eccentricity be considered in the member design?
RE: Double Angle Compression Members
BA
RE: Double Angle Compression Members
RE: Double Angle Compression Members
BA
RE: Double Angle Compression Members
How about WT section, any thought ? Find anything AISC saying on WT ?
anchor bolt design per ACI 318-11 crane beam design
http://www.civilbay.com