Perimeter beam design

[m1ke99]

I am reviewing the structural steel design for a school. The building is 2 storeys with steel beam/column framing and open web steel joists. The walls consist of vertical steel studs between columns. The studs are connected at the bottom to the concrete floor slab and connected to the top at the underside of steel I beam.

For wind analysis, the studs will distribute a portion of the wall load to the connection at the I beam. Since the joists are connected to the top flange, what is the best approach to check for the additional load in the beam between supports?

Also, the columns only see a small tributary portion of wind load. Correct?

 

[hokie66]

Just follow the stiffness. In your arrangment, depending on the size of the beams, you may need to brace the bottom flange. If as described, be sure to allow the beams to deflect, which will require a compensating head at the top of your studs. Just curious, what is the cladding of the building? If a veneer of some sort, how is the veneer supported laterally through the beam depth? A section would help in understanding your situation.

 

[BAretired]

The steel beam should be free to deflect under gravity load. This requires a gap between stud and beam.

Lateral wind forces from studs to the beam flange are usually resisted by the flange spanning between supports. Diagonal braces from flange to joist or bottom chord extensions of the joists are sometimes used to reduce the span so that the combined stresses in the flange are acceptable.

BA

 

[rowingengineer]

Agree with BA, make sure you have a good gap for the studs in the deflection head unless the concrete beams are designed not to deflect. the little amount of load transfer kills the studs.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[SteelPE]

I would stay away from bottom chord extensions bracing the bottom flange of the beam. The wind loads will act in both directions requiring you to weld the extensions to the beam to develop tension and compression forces. Once you do this the joist will need to be designed to resist moments.

 

[Hokie93]

In this situation, depending on the span and depth of the spandrel beam and the magnitude of the load, I typically provide a diagonal brace (often an L3x3) to the bottom flange at either mid-span or at third points. If braces are not provided, the wide-flange beam should be evaluated for torsion from the eccentrically-applied lateral load, in addition to strong- and weak-axis bending (and axial load if the spandrel beam is a collector member).

 

[slickdeals]

This article is a good reference.

http://www.modernsteel.com/Uploads/Issues/August_2012/082012_steelwise web.pdf

 

[slickdeals]

There's also a webinar on AISC's site

http://www.aisc.org/content.aspx?id=31616

 

[LOKSTR]

You can also refer to examples in the AISC design guide-22 for facade attachment.

 

[a2mfk]

This is a very common wall detail. Ditto The Hokies' comments.

You will have the benefit of likely having a good portion of the dead load in place by the time the metal studs are installed.