Use Of Knee Bracings In Steel Framed Seismic Zone 4? 2

[IJR]

Dear Pals

Most of us here use codes with judgement. What is your reaction to a design which includes a special moment frame in Seismic Zone 4(The most intense to UBC97 or IBC2000) reinforced with knee braces? By knee braces I mean a diagonal elements placed around 45 degrees to the column connecting both column and beam below floor level. Without this brace the beam-column connection would be a pure moment connection/shear.

I am personally against this use of knee brace. Dont they present an action similar to the prohibited K braces?. Are they pre-qualified. By pre-qualification I mean any structural system or connection configuration that has been well tested/researched and known to perform well for a specified use.

Your input will be highly appreciated.

respects
ijr

 

[SlideRuleEra]

I have not purchased the paper, but knee braces appear to have been researched for this application and, according to the abstract, can be made to work. Here is a link

http://www.extenza-eps.com/TELF/doi/abs/10.1680/stbu.152.2.147.38971

http://www.SlideRuleEra.net

 

[samdamon]

I personally prefer to not use knee braces for main lateral force bracing. They can be made to work, but it has to be done carefully. With certain geometries you will get tremendous, unrealistic axial loads in the braces.