From: Bill Polhemus <bpolhem(--nospam--at)swbell.net>
Date: Thu, 18 Jan 2001 07:31:38 -0600
> frp2000 wrote:
> ACI-318, Chpt 9 has no mention whatsoever of the ultimate strength factor for
> snow loads. It has 1.4 D + 1.7 L
> ASCE 7-98, Chpt 2 has 1.2 D + 1.6 L + 0.5 S
> and 1.2 D + 1.6 S + 0.5 L
> For Pennsylvania, what load combinations should I use...???
Nowadays, when I use ACI, I use the ASCE load factors, and then the strength
reduction factors found in Appendix C of ACI 318-99 (believe it was in 95 also).
According to ACI 318, you're only "supposed" to use these when you have a
"combination" structure (e.g. steel AND concrete). But the truth is that
disclaimer is put there as a bit of petulance because ACI has resisted
conforming to the "state of the art" stochastically-derived load factors for
YEARS (because their feelings were hurt that they WERE on the cutting edge back
in the early sixties with "strength design", but they got stuck in that rut and
other material codes have since passed them by).
But the Appendix C factors CAN be used by themselves on an all-concrete
structure (why the **** not?) and the ASCE 7 load combinations are MUCH more
IMNSHO, the "load code" oughta be ASCE, and the material-based codes should only
be responsible for the corresponding resistance factors. That keeps everything
neat and consistent.