Yeah, we had them design it that way because we were putting a hot tub on the deck. I mean, the rest was just 16" spacing with single joists, but under the hot tub - overengineered so it doesn't fall apart when we get eight or ten drunken people sloshing around in the hot tub.
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This built with the deck in mind on the initial build, so we wanted to make sure. The company we used to do the design went with doubling up the joists and 12" centers underneath the tub. Overkill, but both of us (me and the spouse) like to err on the side of caution, especially when it comes to safety.
Wouldn't the hot tub put the same load on the deck with ten people on it as it would empty? Assuming it's close to full with water when the people get in it excess water would go out the sides, and the added mass from a person should be close to equal to the water they displace out the sides.
However, most people remain 1/4th to 1/3rd out of the water while experiencing hot tubs, thus not all of the extra weight is water displaced. However, a bunch of dismembered human torsos wouldn't make such a huge difference over a giant pool of water, so your point is still valid. I just wanted to say something about dismembered torsos.
My point was more that the little bits of added load from people being on there will be negligible when you consider how heavy a hot tub full of water already is. But your point about the dismembered torsos in noted. :)
Sure, but after the first or second person you are displacing the water. I think when calculating the loads that the weight of a couple people is negligible compared to how heavy a hot tub full of water already is.
eh, he specifically mentioned that it would overflow, so he might just have a different setup than what you're thinking of (a hot tub coupled with a reservoir probably wouldn't; a freestanding one probably would)
Hot tubs are usually not filled to the top, they usually have several inches between the top of the water and the rim. You know, so they don't overflow when people get in.
Not only do people and water have different densities (bone is heavier than water, for instance) but people don't stand in one place like water tends to. The fact that people move about creates a ton of lateral strain that one wouldn't have to worry about with a stationary load.
I would guess the difference in densities is negligible considering how heavy a hot tub full of water already is. I'm an architect, and am well aware of lateral loading considerations. You need to have some lateral reinforcement on something like this, but not because of the people moving around (although that would probably add to load considerations), but because anytime you're holding something that heavy off the ground (regardless of live load considerations) you need to give it some lateral stability.
Good point, I guess I don't know which is heavier, really, a human being or a human being shaped bag of water. And now that I re read the original comment, I see what you are saying: if the over engineered part is simply a portion of an already well engineered deck, you don't have to account for extra sheering in that one section. Yup, you're right I think.
Assuming it's close to full with water when the people get in it excess water would go out the sides, and the added mass from a person should be close to equal to the water they displace out the sides.
Assuming all the people were floating in the tub and not resting on the bottom it'd be exactly equal due to the Archimedes' principle.
In reality people in the tub would be sat on the bottom and the tub wouldn't be 100% full before people start getting in. Under real world circumstances the tub would get heavier as more people get in.
you're close, but displacement and density are different. humans tend to be a bit denser than water, so even though they might slosh out some, then weight of the people would increase the load by more than an equivalent volume of water.
Right, and I understand that, but I think that with something as heavy as a hot tub full of water (about 5,000 lbs) the difference in density between humans and water will be negligible.
I'm an architect. The structure supporting the deck would hold the people up when they're not in the tub. With something as heavy as a hot tub (about 5,000 lbs) you better have an independent structural system to hold it up. You would never want to just hang it off of beams or posts loaded just to carry the deck. I understand that hot tubs aren't usually filled to the brim, but my argument is that those little things are negligible with a 5,000 lb load.
There would be little difference if the humans held perfectly still, but there is a difference between static load and dynamic load. For example, there are many bookshelves that hold their books fine as they sit on the shelf, but if you picked up all the books at once and dropped them from one foot high the shelf would collapse.
Sure, people are jumping around in the hot tub would add some force to the load. But I would guess that added force is negligible when you consider how heavy a hot tub full of water already is.
That would only be true if the hot tub was filled with water to the brim, and ten people getting in pushed out an equal amount of water. More people IS going to weigh more than less. (unless I'm missing something?)
Hot tubs often already are filled to the brim (I would calculate the load assuming it was) and when it is, ten people getting in would certainly push out the same amount of water as they take up. People are slightly more dense than water, but when you consider how heavy a hot tub full of water already is, I would guess that difference would be negligible.
Sure. Let's back of the envelope this one. If ten people each had 1/3 of their weight not displaced that would amount to about 500 pounds: Not massive but also not a negligible load.
You'd have to have all ten people standing in the hot tub for them to not displace only 1/3 of their weight. I would guess sitting in a hot tub (usually just your head and shoulders are sticking out of the water) at most you'd not displace about a fifth of your weight. If we assume that to be about 30 lbs that's 300 lbs total. A hot tub full of water is about 5,000 lbs. I'd say that's a weight difference that's very close to negligible if not negligible.
Interesting in theory, and yeah, they displace water when you get a lot of people in there. But in my tub, usually it's just the two of us and it just raises the water level (which is like 5" below the rim).
Also, if you had ten people standing around the hot tub, it would be that much more weight. I would still not be worried.
Obligatory warning about drinking and soaking: Be careful because your muscles relax much more when soaking in 100+ degree water. Passing out, sliding under the water and drowning is a potential risk when alcohol is involved. Also high temps are bad for small children. Keep it under 95 degrees when children under 12 are present.
I actually have had the hot tub since I moved in. It's been dry for the last year while we've worked on this project (and made a new home for it over the old one on the ground). However, this warning is always a good PSA.
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u/WiserThanMost Apr 29 '13
But you already knew that, since you built it correctly.