Spandrel Beams
Spandrel Beams
(OP)
I have a very typical situation but cannot find any good practical information on design. I have a spandrel beam at a stair tower that must support a brick facade which is eccentric to the beam. With the opening from the stairwell there is no place to install bracing to counter the torsion. So I have no other option than to design the beam for torsion. However the loads are pretty high and the eccentricity is over 12" which makes a wide flange not very efficient. So I want to either use a tube or weld plates on the side of the beam to make a tube which is more efficient. But I cannot find any (practical) design methods for designing the tube. AISC Design Guide 9 makes discussion on tubes but typically Cw is zero which makes "a" zero and makes the tables useless. Is there any practical solution for such a typical problem?






RE: Spandrel Beams
look further into section 4.4 for closed sections. if you still need help, let me know.
ted
RE: Spandrel Beams
RE: Spandrel Beams
RE: Spandrel Beams
these sections are written for the general case of torsion and torsional stress. notice Tu is used to find the shear stress at a point, just like we find the bending stress for a given value of Mu along the length of a beam.
RE: Spandrel Beams
also, refer to your mechanics of materials textbooks.
RE: Spandrel Beams
For addtnl data on torsion design suggest "Design of Welded Structures" by Blodgett.
RE: Spandrel Beams
If you make the spandrel beams to be closed sections, the calculation is very simple. In addition to other stresses as a beam, you just add the torsional shear stress as per Eq. (4.4) of the design guide. A critical place is at the ends, you need to make the closed section all the way into the columns.
Other than spandrel beams with eccentric load, I don’t know if you can have separate beams for the facades, for example, channels under the wall and laterally ties to the spandrel beams.
Another thought: can you make the spandrel beam to be offset as well to suit the facade?
RE: Spandrel Beams
I read the Blodgett book over the weekend and it has the exact case I have. Its approach is a little different then the AISC design guide but it works and is very practical.
Thanks all of the good info.