calculate column effective length and braced length 4

[Kennylie]

Hello fellow engineers,
I have to design a ballroom using steel section

i have a little trouble calculating column effective length to calculate the axial capacity since it braced in it's weak axis using pin connected beam

and i'm not sure if the brace is stiff enough to precent LTB

for more details see attached picture below


thankyou for your anawers

 

[BAretired]

The weak axis of the column is braced at 4m centers only if the brace is prevented from translating horizontally. This is usually accomplished by cross bracing between the foundation and the brace in at least one bay and preferably two.

The strong axis of the column is braced at 8m centers provided the end walls are deemed to be shear walls and the roof is deemed to be a diaphragm, otherwise the effective length of the column is greater than 8m and would need to be analyzed to determine its effective length.

BA

 

[racookpe1978]

That single column (the one with the pin connections noted) would be "braced" as above only if the pinned connections (tie rod tension connection points ?) are parts of a cross brace that prevents the connections from moving sideways.)

So you would need true crosses made of tension rods (attached to ?? points on the other columns) or braces stiff enough to prevent movement by themselves under compression.

 

[rowingengineer]

Say we get good horizontal restraint, would the sender be 4m is K=1 or could he consider a lower K of say 0.85?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[BAretired]

Say we get good horizontal restraint, would the sender be 4m is K=1 or could he consider a lower K of say 0.85?

If connections are pinned, k = 1.0 as column can buckle in opposite directions above and below the brace.

BA

 

[LeonhardEuler]

Bracing of 4m is only for the direction that the tie beams brace into the column. I would assume the roof could be used as a diaphragm and your other axis is 8ft with a pinned- pinned end condition, which means k=1.

 

[rowingengineer]

BA,
What about the base and eave connection? if we were to treat it as fixed we would get K=0.7, the base you could detail as fixed and not really get a large load, the rafter to column would be harder. However if we could prove partial would you consider less than 1 for a lightly loaded column?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[LeonhardEuler]

The more I look at this I would say Leff is 4m for each axis. There are beams framing into each side with the concrete slab acting as a rigid diaphragm.

OP what system are using to resist lateral loads? Is there a moment frame in this design, or a shear wall? Make sure to consider second order leaning column effects.

 

[BAretired]

BA,
What about the base and eave connection? if we were to treat it as fixed we would get K=0.7, the base you could detail as fixed and not really get a large load, the rafter to column would be harder. However if we could prove partial would you consider less than 1 for a lightly loaded column?

I thought we were talking about minor axis effective length.

For the major axis, you could detail the base as fixed, but the diagram indicates that it is pinned. Before assigning a K value to major axis buckling, we have to determine how lateral loads are carried as mentioned by LeohhardEuler above. We also have to decide whether or not the slab, together with the spandrel beams constitutes a brace for the major axis. I suspect it does but personally, I would feel more comfortable with a more direct connection between slab and column.

BA