ad load factor in asd

huangyhg

0.6 dead load factor in asd
i have been designing anchors for natural stone facades using asd. and i have conditions where my anchors are subjected to wind load and dead load, but they generate a moment on opposite directions, then i used asce combination:  0.6d+w.
i assume 0.6 factor is to consider that may be a case where not all the dead load is present, but i am thinking that this might be based for many critical structural designs. and i don’t think this is the case for me, since all my natural stone is cut to a 1/16in precision, plus the density of it does not vary more than 2%.
i know is the code, and like a law, it should be followed, but as the laws, the codes factors may not be the right ones for some of the cases.
do i have an argument trying to use 0.9 factor, instead of 0.6 for the dead load?
thanks in advance
i think the only issue with that is that you would essentially be designing for the actual design wind event and would have no reserve capacity for a larger wind event.
on another note, the codes aren't "laws" per se. they are meant as a guide. experience can teach you when, where and why exceptions can be made.
lets assume you are designing something. all your assumptions during the design process tend to be a bit conservative. if when you check the capacity of your   
if you are not going to use 0.6, why bother with 0.9?
i think in this case the code should be followed. besides, if it ever fell off, you could be blamed because you didn't follow the code, whether or not that in itself was the cause of the problem.
when designing a building it is common for engineers to use a coservative estimate of the dead load when designing for gravity loads.  if those dead loads were used to check building overturning the result would be unconservative.
in the past this was addressed sometimes by designing for a resisting moment equal to 1.5 times the overturning moment.  this accounted for the over estimation of dead load and provided for an additional factor of safety. using 60 percent of the dead load would produce similair results.
i don't know if this is the justification given for the 0.6 load combination in asce 7 or not.  however there is an asce forum on this web site that you could also post your question if you have not already done that.

the 0.6 is to give a factor aof safety of 1.5 against uplift.
the 0.9 factor should never be used with asd, it a a lrfd factor.
thank you all for your responses.
although i am using natural stone i have pretty much control over it (dimensions and weights), then i don’t see why i should be using so much conservative design with 0.6 factor.
let’s take for example, in an event where there is very low wind load, or none at all, which would happen most of the time, there will be no overturning, and the dead load will be the only one that will be supported by my anchors, then i will use only the next combination:
100%d
then why should i be conservative in the event of a wind load, and not with the dead load acting alone?
if i were talking about lrfd then my dead load acting alone would have a factor also, but not for this case asd.
should that means that the 0.6 factor is most because i have no control over the wind load, more than that i have no control over dead load? if so, then why when both loads are applied and creating a moment in the same direction, why the combination for this case it is only:
d+w (notice than there is no factor for the wind load)
what that tells me is that the 0.6 factor is due to the unknowing of the dead load accurately, and returning to my point, what if i have total control on my dead load design? can i substitute the 0.6 for 0.9?
you have a factor of safety built in to bearing pressure, you dont have one for dead weight.
see my first post in
urielcdc - you don't give any information on where you are practicing.  codes in georgia are given the full force of law since they are referenced by an ordinance that adopts them either fully or as amended by the ordinance.  the best person to answer this question is the reviewer for the authority having jurisdiction.  right or wrong, you'll have to meet their requirements.
quote:
i assume 0.6 factor is to consider that may be a case where not all the dead load is present
well...sort of. but the 0.6 factor is primarily a safety factor to account for potential extreme variations both in dead load and on the actual wind load applied.  despite the fact that the factor is placed on the dead load, it is there to provide essentially a 1.5 factor against overturning, extreme unbalanced winds, etc.  
you are right to think you have complete control over the dead loads - but i also feel i have very good understandings of structural floor dead loads.  
its all about the level of safety, not the uncertainty over the variation of dead loads.
use your own engineering judgement, as long as state laws don't prohibit it, but don't expect everyone else to agree.
i can see some logic in your approach but definitely would not use 0.9. perhaps i would think about using closer to 0.75 but i would probably just use 0.6.