W Beam Lintel and Unbraced Length

[LPPE]

I have a W beam lintel, supporting CMU. First course of CMU on top flange is a bond beam with 2 bars, and shear studs on top flange of W beam at 16" oc. Masonry wall runs 10 feet up clear before intersecting roof elements.

Question is - Does the CMU (bond beam or other) brace the top flange of the W beam? Simply put, can the beam be designed as continuously braced or unbraced it's entire length (neglect composite action of shear studs embedded in first course bond beam)? This has been a topic of discussion for as long as I've been practicing, with different thoughts by different engineers.

 

[Lion06]

If your bond beam only has support for gravity (i.e. if it would be counting on the wall to support it out-of-plane for the brace force from the lintel), then I would say it doesn't brace it.

 

[bjb]

In order to consider the beam braced, the masonry wall and the connection to the wall need adequate strength and stiffness prevent torsion of the beam or lateral movement of the compression flange. Appendix 6 of the 2005 AISC spec has guidelines for designing stability bracing for beams.

I am of the opinion that the beam should be designed as unbraced. You will need a stiff beam anyway to control cracking in the masonry, so I don't think checking the strength as an unbraced beam will have a significant penalty in terms of beam weight. You also don't have to rely on the workmanship of the masons.