Steel Moment Frame 1

[Dannnnnny]

I previously designed IMF for 3-story house.
The lateral resisting system of the two top floors were wood shearwall and the lowest floor was IMF.

So, based on "standard quality assurance plan for steel moment frames" provided by the city,
it is given that the steel column must extend at least 3" more than top level of the steel beam then the cap plate sits on top of the column.
So, the recent RFI i received was if is it fine to ignore that 3" extension for easier construction.
As a solution, I was considering to use 1" cap plate instead of the current 3/8" (I believe, that is because the cap plate will now work like the top continuity plate)
Do you think this should resolve?
Also, I don't really understand what's the purpose of that min. 3" requirement.
Is there any theory of it?

 

[sandman21]

The LADBS QA plan and details was setup before AWS D1.8 and AISC 341 had fully flushed out plans and details. Per the guidelines of LA the QA is a template not required. STRUCTURAL DESIGN GUIDELINES FOR STEEL MOMENT-RESISTING FRAMESThe height and details should be based on your design and detailing not standard detailing.

 

[arkansas_civil_struct]

Steel structures are mostly braced and cannot be considered as moment resisting ones as steel is a very light material.

 

[SteelPE]

Steel structures are mostly braced and cannot be considered as moment resisting ones as steel is a very light material.

I have no idea what arkansas is even talking about. I have designed hundreds of steel moment frames. Steel moment frames are used all of the time. Are they as rigid as a brace frame? No, but they may not need to be.

 

[arkansas_civil_struct]

SteelPE moment frames = concrete frames.

 

[arkansas_civil_struct]

most steel structures are pinned.

 

[r13]

arkansas,

I don't know from where you got that impression that only concrete can make a moment frame. Not true, as most of today's hi-raise building wouldn't be there if no such thing as "steel moment frame", which was used alone, or in combination with other systems to provide required strength and ductility. Suggest you to have quick review on "steel moment connections". Link & Link