STEEL CONNECTION DESIGN QUESTION!!

[SmithJ]

Hello,

I am designing column splices in a large airplane hangar. I seem to recall that splice connections (and other steel connections) are designed for the higher of:

i) 50% of the allowable moment based on the section modulus at the connection plus appliacble shear and axial

or

ii) The actual applied moment at the connection plus applicable shear and axial

However, I can not remember the basis or code requiremnet that drives this rule. Is any one out there aware of this rule or is it just some obsolete rule of thumb that I picked up along the way?

Thank you all in advance.

JS.

 

[Focht3]

Actually, I thought that splices had to be at least as strong as the adjacent sections i.e. the splice was to be designed so that a failure would not occur at the splice but could occur nearby. However, that "rule of thumb" may come from a welded, not bolted, splice environment (although I don't think so.)

I look forward to hearing other comments -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[CSEllc]

The "rule of thumb" still applies.

You can refer to the "Structural Steel Designers Handbook" section 5 isd on connections. Section 5.26 is on tension splices and section 5.27 is on compression splices.
Another reference is "Structural Steel Design" by McCormac. Section 20-2 of the 3rd edition discusses splices. AISC does not really discuss column splices in the manuals. I believe the first edition (red) "Detailing for Engineering" does cover splice design.

The logic behind the 50% rule is simple. Since most column splices occur at about the mid-height of a column, the moment in the column at that point should be approximately or approaching zero. The column ends should be milled so that the axial loads are transferred thru bearing, but I would still design the connection for the full axial load and shear.

 

[southard]

Fortunately I haven't had to do this yet. I agree with the above post. Try to locate the splice at or near zero moment locations. For part of some research I did while getting my master I looked into trying to splice some beams using circular hollow tube steel members. Prying had a major impact on the tension force in the bolts when being pulled apart. One design example is in AISC hollow structural section connections manual page 6-31. Also I know of research an still developing equations for moment base plates to foundation connections for signs. Needless to say the best configuation is where you have a thick plate and the bolts located as close to the beam or tube as possible. This reduced the effects of prying action on the bolts. Of course using full penetration welds with stiffeners if possible is always ideal since the full moment capacity of the section is developed. Also for column splice details see ASD connections manual or the LRFD 3rd edition steel manual.

later,

John