multi storey frame

[oneintheeye]

HI, designing a multi storey frame. Not done many before. I've designed my members for the vertical loading but now need to consider the horizontal effects. The wind loading is next to nothing due to height/clad elements etc. For nominal horizontal load, 0.5% of total imposed loading. Is this then applied as a line load across the storey being considered? and whats the best way of checking out stability?

 

[JAE]

Yikes...I would ask an engineer within your firm who has done this before....not asking us on a web forum.

 

[oneintheeye]

yes but I prefer to have a stab at these things and do a bit of research from alll sources before i do. Get more from it that way.

 

[JAE]

What code are you designing under? IBC?

 

[oneintheeye]

no british standard but I believe the figure for notational loading is same (by that I mean percentage wise) even if its not analysys is analysis even if your figure (im guessing yiour us is slightly different.

 

[csd72]

herewegothen,

I doesnt really matter exactly how you apply it as long as the load at each frame is proportionate to the vertical load on that same frame. A point load at each frame will be sufficient. The only reason for this load is to allow for out of plumb of columns, and their tendency to sway under this.

 

[valleyboy]

What type of lateral system are you adopting for your frame design?

If the frame is designed as a simple braced frame, then notional horizontal forces only need by considered on the braced bays, as these resist the NHF in isoloation. There is an excellent SCI publication which deals with the design of such frames.

If you are using moment resisting connections and the in-plane stiffness of the beams and columns, then the procedure is slightly different:-

1 Analyse the frame subject to NHF only. These loads will be o.5% of the ultimate load acting on the frame at that level.
2 Note the deflections due the the NHF, and for each storey evaluate the elastic critical load factor. (The most critical storey is usually ground to first floor). If the ECLF is less than 4.6, then second order analysis of the frame is required to properly account for second order effects. If 4.6 < ECLF < 10, then the forces and moments in the frame should either be modified by the amplification factor 'K amp', or the sway mode effective lengths in BS 5950 should be used for member design. If ECLF > 10, then second order effects may be neglected and the frame designed using the moments, shears, and axial loads from the first order elastic analysis results.

Hope this assists.