Loads for use in combined shear and uplift

[DM2222]

The tables in the SDPWS for combined shear and uplift (Table 4.4.1 in the 2008 AWC SDPWS) are calculated assuming that the only nails that resist uplift are the ones that are in addition to the ones that are required for resisting shear. Typically in a usual house with a hip or gable roof, the shear demand in the wall will be the greatest, (and hence govern the shear nailing) when the uplift is the lowest and vice versa. My question is how do most of you handle calculating the uplift load to be applied simultaneously with the full shear load? It seems overly conservative to use the maximum uplift and the maximum shear in these tables as these two loads will occur under two different load cases/wind directions. This may be more of a ASCE7 loadings question. The way I see it, the wind cannot blow on a house directly perpendicular to the front. (load case with maximum shear in the side walls) and also blow directly perpendicular to the side (load case with maximum uplift on the side walls assuming a hip roof). How do you all handle this? I know I can just assume the worst and specify two rows of nails to get the loads needed, but I've framed a few houses, and am not naïve enough to think each wall will be properly nailed with rows staggered 3/4" apart with such tight spacings. Looks good on paper, but is not a very achievable design in my opinion.

Thanks in advance everyone.

 

[KootK]

It seems overly conservative to use the maximum uplift and the maximum shear in these tables as these two loads will occur under two different load cases/wind directions.

Depending on your roof configuration, it very well may be that your worst uplift and highest shear demand occur simultaneously in one direction. I would either:

1) Take the conservative approach that you'd suggested but would like to avoid or;

2) Figure out the specific code uplift that accompanies the peak shear wall demand in either direction and apply them at the same time.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.