I would say yes, a roof deck is a deck per ASCE. I treat it the same as I would a balcony or anything like that where people could conceivable be decently close together on a nice day/evening. I wouldn't really get the argument for just treating it as a 40 psf live load. I do think that treating it as 100 psf though is overkill (for a residence).
I've said this before, but I always judge it on "will this deck be packed to watch fireworks" criteria. I've been on some wildly loaded decks and balconies before so that's why I almost always go to 60 psf even in residential.
The argument is this is what the code says:
The proof is pudding, though. There are lots of things that are hard to believe but can be borne out by rigorous study. Deck failure is one of the most consequential structural failures in residential construction. If a deck fails and it's seen that the designer used anything more than CD=1.0 in design, they're likely to be crucified for it whether it was the real cause or not. So unless you have a detailed analysis of loading on decks that backs that up (and such studies are out there...just don't know if they looked at decks specifically), I would not suggest going higher than 1.0.
I see what you're saying, I just think that stacks with the deck provision as well. We're all calling it a roof deck here. I get there's a level of semantics here, but I would say the occupancy served is a deck in a residential and thus gets the 1.5*40 psf.
That's reasonable. I'll be honest I do tend to be reasonably conservative for the wood design keeping in mind that many of the details will not be constructed as indented. I'll use the method for maybe justifying a bending value, but connection design all gets done with the normal Cd values. I was using this as a bit of a code exercise to challenge some of my own engineering opinions/ideas and Cd is one where I have some gripes I suppose.
I disagree. Using ASD makes it way more efficient from an engineering perspective as most members I size are controlled by deflection. I would probably retire if I was forced to use strength design for wood.
Wood already takes a statistical approach. Most published reference design values are the 5% exclusion. Only time average strength is used is for fire design. LRFD is fantastic, but there's nothing wrong with ASD for light/heavy timber (mass timber is a different story).
You can use LRFD per the NDS code if you really want to. I've never heard of anybody doing this, but the option does exist. FWIW, I've run through the exercise before of comparing LRFD to ASD and as a broad takeaway, I concluded there was no real difference. I suppose you could game it to use one or the other as it benefitted you, although this would be rather questionable behavior I think. If you have a copy of "Design of Wood Structures" by Breyer they do run through design examples using both methodologies.
This is a perfect comment here. The only thing I'll add is that decks usually have a lot less redundancy and "additional strength" compared to a house. No sheetrock or subfloor or family photos that help provide some alternate load paths.
Lots of examples of deck failures that make 100 psf not seem ridiculous. What if that 180 lb person and all his friends start jumping up and down? Now you factor in lack of maintenance that could reduce capacity. I'm probably not going to try to cut hairs on a deck design to save a few bucks.
Not semantics. There are clearly two distinct line items in table 4.3-1 addressing each condition.
At some point, you should assume others will do their job. I work with a lot of contractors and most take pride in their craftsmanship. If they don't understand or cannot achieve a detail I've provided, they usually call me. If they don't, that's on them. Yes, I detail A LOT. I've seen a lot of plans and engineering provided by others and often, they lack adequate detailing. Usually, the rationale is that there isn't enough fee to provide the site specific detailing required for the project. Most of the details are generic and don't correctly represent the actual condition. In these situations, no amount of "over engineering" will compensate for inadequate detailing.
No amount of "over engineering" will compensate for lack of maintenance. At some point, you need to assume others will do their job.
I'm not saying to over engineer just to compensate for lack of maintenance, but I know if a deck fails (and there are many examples) there are frequently serious injuries or deaths. I don't want to be scrutinized because I attempted to justify a lighter design load or high duration factor even if lack of maintenance turned out to be the root cause. The risk of misuse of a deck is very real.
Thanks for that.
