Duration effects for live loads?

[LUGuy]

Since this this board is overdue for a post...

I'm figuring a wood floor for a restaurant. The live load is 100psf per code. Presumably, a large portion of that value is due to actual loading by people amassed together. Its on a 2nd floor with no elevator, so there is no possibility for the rare occasion of having a car show inside.

Is there a provision for considering the duration factor to be somewhere between the seven day and 10 minute values, since the given loading can't possibly last more than 7 days?

 

[SlideRuleEra]

Most building codes, such as IBC 2000, have an acceptable load reduction allowance based on the size (square footage) of the floor. Increasing the magnitude of the load duration factor in addition to this could get risky. If you look at all the required load combinations (Dead Load, Live Load, Impact, Seismic, Wind, etc.) in the proper manner it is probably theoretically possible, BUT I would not recommend doing so.

 

[CSEllc]

It has bewen my experience that building codes do not allow live load reduction when the required live load is 100 psf or more regardless of area.

The load duration factor, which are allowed in the "wood" code, for live loads is 1.0......so you should just use the 100 psf.

 

[LUGuy]

I am not trying to apply the live load reduction in this case, although it might be legitimate. My question is more generic and theoretical in that I am wondering why there is no duration factor for the shortest of all common loading intervals. Or is it simply up to the Engineer's discretion to apply an appropriate duration factor for such short duration loadings?

 

[AlohaBob]

A strict reading of the IBC says the reduction restriction applies to live loads exceeding 100psf. So it seems you have discretion here too.

 

[esj]

The term duration of load refers to the accumulated length of time that a load is applied during the life of the structure, not just for a single application of the load, therfore, even if the load will not ever be applied for more than 7 days in a row, you still cannot apply the duration factor.