IBC 2003: 0.6D vs. 150% factor of safety for stability

[seattlemike]

For wind, I used to design with a 150% factor of safety for the overturning of shear walls per code. And sometimes, to simplify calculations, I applied the 150% overturning stability factor to the 0.9D combination for earthquake as well.

Now that we are using 0.6D under the basic load combinations (IBC 2003), it seems that 150% factor is already included. Is that correct? (yes, I did read 1609.1.3 for the alternate load combinations)

Thanks!

 

[jheidt2543]

As long as sme76 and seattlemike raised the point about hair-pins I'll add something to think about.

When you rely on hair-pins to carry the horizontal load from a metal building frame you have to have a floor slab! Most of the time, at least in our area, the floor slab is poured AFTER the building is erected and the roof and wall panels are on (to prevent damage to the slab during construction). That means the hair-pins are not active until the slab is poured and up to strength. So, there is a gamble that the wind doesn't blow and there is no snow on the roof - the two largest components of horizontal loading.

Just one more little headache to think about!

 

[cap4000]

ScareBleu

I sense your frustration with IBC. I just found another mistake in IBC 2000 Table 2305.3.7.2 pg 558. They indicate a 0% full height sheathing and a 0.33 factor which has been taken out of the 2003 edition. After calling IBC directly you are suppose to check their website for thier ERRATA. Go Figure. IBC should change to "MMM"- Money Making Machine. Just check their publications. Commentary to the Commentary to the Workbook to the Code and no errata. Unreal $$$. BOCA come back please.

 

[14159]

"Now that we are using 0.6D under the basic load combinations (IBC 2003), it seems that 150% factor is already included. Is that correct? (yes, I did read 1609.1.3 for the alternate load combinations)"

My opinion is that the 1.5 safety factor is included in the 0.6. I looked ad nauseam in the IBC for a statement that overturning, uplift, and sliding had to have a 1.5 FS, but couldn't find it, unlike previous model codes.

I don't buy the argument that the 0.6 is to account for common overestimation of loads. I think that's what the original 0.9 was for.

From the practical side, there are many instances (metal building foundations for example) where the design will be absolutely and comletely asinine if 1.5 FS is applied simultaneously with the 0.6 factor.

DBD