huangyhg

lateral deflection of moment frames
lateral deflection of moment frame is difficult to handle. calculation showed that moment frame is 100% expensive than ordinary braced frames. is there any other option expect to moment frame when we have no option to provide bracings.

depending on your loads, try a fmc frame. it is very inexpensive as you size top and bottom angles to take lateral load only and have a typical shear connection. this requires no welding. this is the lateral system we use on almost all of our steel buildings.
sometimes you have to be quite creative in locating bracing or using different types of bracing to avoid using moment frames. in commecial buildings, i usually look for stairwalls, elevator walls or bathroom walls in which to hide bracing. you might have to configure the bracing to provide a passthru for doors or aisleways.
canstruct,
what type of building is this?
it's a 2 storied shopping mall. architect needs a moment frame. structural eit if you don't mind, can u attach some pdf to show this concept, it's look interesting and economical too. actually for my case, i know there is no replacement to braced frame, if you want frame to deflect same for seismic loading, just to have moment connection might not equivalent to bracings. but i think it is economical to provide more moment frames if they are economical.
i will do that on monday. they are in my binder at the office.
don't be so sure that fmc connections won't work - depending what area of the country you are in. we use them on a lot of buildings (we have used them up to 13 stories), but we are in the northeast where wind usually controls.
canstruct,
yes portal frames are more expensive. but there is only one type of building that is the cheapest to build (a braced box), but as long as architects are involved you will never be designing that building.
cost comparisons only have meaning if you are comparing between alternatives, comparing to a system that is no good for your situation is meaningless.
as jike suggested, use bracing where you can to minimise the requirements for portal frames.
csd

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