Torsional effect on welded tubular connection

[nour75]

Hi All,
I have to design a welded tubular connection that connects 2 tubular members (like a T shape) in an off-shore platform jacket. One of the tubulars is a column (2225x80mm) and the other is a brace(1100X25mm). The brace exerts torsion on the column beside in-plane and out-of-plane bending moments. Is there a simple way or a closed formula that can be used to design this connection considering the torsional stresses. Actually, I want to stay a way from any "time consuming" FEM modelling.
As far as I know, according to AP-RP2A-WSD, tubular joint capacity considers axial and bending actions only (no torsional actions are involved). Is there any suggestion regarding how to consider this torsional moment in the tubular joint connection? (from AISC, API or any other codes or text books)
Thanks in advance

 

[Ron]

Assuming I understand your issue correctly, the torsion in the brace would transfer as a moment to the column. You would consider the induced moment on the column and consider the shear in the weld for the brace-to-column connection.

 

[canwesteng]

What does the connection look like? If it's all around weld, google "torsional stresses in thin walled closed sections" or something to that effect, and you can determine the stress from torsion in the weld.

 

[KootK]

I've never seen an "official" method presented anywhere. What I've done is try to resolve all of the torsion utilizing weld capacity available in only the welds that are mostly parallel to the longitudinal axis of the supporting member. My rationale is that those welds don't induce distortion in the supporting member when loaded and therefore I don't have to sweat interaction with the other connection forces.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

I do basically the same thing as Koot, easy calc and is generally conservative.

 

[SAIL3]

assuming that the members are not circular ....connecting the brace to the col is the easy part...as Koot suggested the forces from the torsion will eventually be resisted by the component that has the greatest stiffeness and in this case, with no additional reinforcement to the col, would be a couple with forces paralel to the axis of the col...the questions in my mind are what happens to the other two components of the torsion and their affect on the col? or , in other words,how does one get this Torsion(applied moment) from the face of the col into the remaining portion of the col?...these are very large members...
without going into a long step-by-step analysis and not knowing the loads, the following would be my first crack at it...
add a ring to the col at the top and bottom of the brace....then add an internal pipe space truss inside the col to carry the loads from the face of the col to the remaining portion of the col......
another less desireable option would be to add a pl diaphragm to the col internally at the top and bottom of the brace....
reinforcing the col locally may change the stiffeness of the brace/col interface and one may want to check the torsion connection assuming egual sttiffeness all-round...from Blodgett..shear=Tc/J, J={(b+d)^3}/6,
c={(b^2+d^2)^1/2}/2