BWally
Structural
- Sep 29, 2006
- 21
I have a pair of parallel beams that I'd like to brace with a flat steel plate (of at least 3/16" thickness) spanning between them. This plate would be continuously welded to the top flanges of the beams, and also to any cross-beams that might exist. This plate would also have angles welded beneath it to stiffen it for carrying live psf gravity loading. (For the purposes of this analysis, I'd like to ignore the contribution to beam bracing offered by the cross-beams and the angle stiffeners since there may be a situation in the future where these don't exist.)
So, I would like the plate to act as a beam brace and also be able to directly carry transverse loads itself.
I have researched the topic of "diaphragm-braced beams" by ordering and reading several papers published in the late 1960s to mid 1970s in the ASCE Journal of the Structural Division. The paper "Columns and Beams Braced by Diaphragms" by Errera, Pincus, and Fisher gives formulas for calculating the critical lateral-torsional buckling moment "Mcr" when diaphragm bracing is present. However, their equations are dependent on a quantity called "Q", the shear rigidity of the diaphragm, which is the product of diaphragm cross-sectional area "Ad" and effective shear modulus "Geff". The authors state that "Shear rigidity ["Q"] of diaphragms was determined experimentally because no general theory of diaphragm behavior was available. Such theory is necessary for the general application of the results of the investigation to practical design situations".
None of the other papers I reviewed presented a general theory of diaphragm behavior applicable to my welded flat steel plate.
Have any theories or data been published since then that I could use for my situation? The most helpful information would be values of "Q" to use in the equations presented by Errera, Pincus, and Fisher in "Columns and Beams Braced by Diaphragms". Also, is there any information on how the bracing capability of the diaphragm is diminished when it is loaded transversely?
So, I would like the plate to act as a beam brace and also be able to directly carry transverse loads itself.
I have researched the topic of "diaphragm-braced beams" by ordering and reading several papers published in the late 1960s to mid 1970s in the ASCE Journal of the Structural Division. The paper "Columns and Beams Braced by Diaphragms" by Errera, Pincus, and Fisher gives formulas for calculating the critical lateral-torsional buckling moment "Mcr" when diaphragm bracing is present. However, their equations are dependent on a quantity called "Q", the shear rigidity of the diaphragm, which is the product of diaphragm cross-sectional area "Ad" and effective shear modulus "Geff". The authors state that "Shear rigidity ["Q"] of diaphragms was determined experimentally because no general theory of diaphragm behavior was available. Such theory is necessary for the general application of the results of the investigation to practical design situations".
None of the other papers I reviewed presented a general theory of diaphragm behavior applicable to my welded flat steel plate.
Have any theories or data been published since then that I could use for my situation? The most helpful information would be values of "Q" to use in the equations presented by Errera, Pincus, and Fisher in "Columns and Beams Braced by Diaphragms". Also, is there any information on how the bracing capability of the diaphragm is diminished when it is loaded transversely?