huangyhg

problem with light gauge steel framing
i did not receive satisfactory replies for my previous question. so i decided to post it as another forum.it is very important for me. here is my problem:
in 鈥淧rescriptive method for residential cold-formed steel framing鈥?there is a restriction for alignment of the structural framing. the distance between the centerline of the wall stud and that of the floor joist is restricted to be no more than 0.75 inches. we are using a rollformer machine and a computer program specifically designed for the machine. it is nearly impossible to satisy this condition with the computer program we are currently using. is there an exception for the above restriction?
my c shaped floor joists are connected to the flanges of a u section used as a track on the walls. and same u section runs along the top and bottom of the wall panels also. can i design the u section at the end of the floor joists so that it distributes the loads from both upper story and from joists? in my further calculations can i assume the vertical loads from the upper story鈥檚 studs and from the floor joists are uniformly distributed along the bottom story鈥檚 wall. should i take any special precautions against distribution of the seismic loads (we are building in an area of high seismic hazard.)? i am looking forward to hear about your opinions.
thanks for your help....
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i would be careful about exceeding the 3/4" limit with the standard cross section system normally used at floor/wall intersections. it sounds like you initially are using this standard section where the steel joists sit on top of a u section (legs turned down and lapping over the wall studs). an end track (u section turned sideways with legs of u lapping the top and bottom flange of the studs) which is lined up with the outside surface of the wall studs. another upper wall resting on top of the joists and lined up with the wall below.....am i accurate in the above description?
one thing we have done in the past...and works well in seismic regions, is to use a steel tube section atop the wall, just under the joists. this tube can certainly distribute your off-center joist loads which takes care of the 3/4" restriction. in addition, the tube serves as an excellent collector for dragging in seismic loads to shearwalls or other bracing.
one concern,though, is that as a collector, it is located well below your actual floor diaphragm (by the depth of the joists). thus, you need to design the end track of the joists to transfer the diaphragm shear into the collector.

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