Hi Janderso,
What you want to do is common and you should have no serious problems if you do it right. I went through a lot of these calculations as I was remodeling my 90 year old house (very heavy plaster walls and a slate roof provided large loads).
People hang things from their ceiling all the time. So you might ask what it the difference from hanging a weight and from putting weight on a floor. How much weight will a floor support before yielding? It obviously depends on the room size as it depends on the span(length) of the joists as well as the joist height, width and spacing. Of course the weight on a floor is distributed over 2 dimensions.... rather than your approach of hanging things on a single joist. So there are a lot of assumptions, but people/engineers have done these calculations many times before. Here is an easy to use link to calculate the loads vs span on floors which will give you some feel for things. The result is load per square foot, but there are similar tools for single beams. As you can see the load bearing ability depends both on the cross-section of the joist as well as on the length and the joist density (16" centers?) and of course the joist material. Not all woods are equal in strength. https://awc.org/codes-standards/calculators-software/spancalc The one thing about this is this engineering assumes there are multiple joist so that if one is flawed the others pick up the slack. Boards are not perfect, they have knots and cracks so there is some danger in relying on a single joist. You have to recalculate a bit or look for the calculation for beams.
First, how will you hang this lift. From over the top of the joist? Will you prevent the joist from twisting and so having the load on the thin direction of the board, ie. is it attached to the neighboring joist as a floor joist would be by the floor sub-flooring boards? So you would definitly be better off if you could hang the weigh from a support that is sitting on more than one joist.
You basically have a beam that you want to hang weight on. I-beams have the top and bottom of the "I" shape to keep them from bending in either direction as well as to provide more strength. So sistering (screwing them) multiple beams together helps. If you are willing to sister, you might want to purchase engineered lumber rather than a board. Engineered lumber is really just extra long plywood that has been ripped to make 2x8 or other sizes of almost any length. You can also get "I" shaped beams from engineered lumber suppliers but they do not sister well.
So these folks sell engineered lumber beams that are used to support the joist of the next floor up. Very close to what you want to do, except you are sort of putting most of the load at a single point. Anyway, they have tables for these calculation for you. https://lpcorp.com/resources/produc...solidstart-lvl-technical-guide-english-canada
Lastly, a comment on sistering joist. Becareful not to break the original board! If you have old wood for the joist, you can bust it when you put in the bolts/screws. Commonly old joists that have been under load or not will be cupped. If you try to sister and screw the new board to the old so tight that it straigthens the old board cup it will commonly crack the board. The strength of a beam comes mostly from placing the bottom of the board in compression while the top of the board is in tension (this is the second reason for the top and bottom of an "I" beam the top and bottom are where all of the forces are exerted. The center line of the beam has little force and so can be quite narrow, but do hold the beam together. So near center line is a much better place to put the bolts/screws rather than creating a lot of holes in you beam at the top and bottom. The rule of thumb would be to keep the bolts/screws way from the edges of the beam by 1/3 of the height of the beam .
Oh, yes, one other issue. When you look at floor loads you will see there are two types of loads. Static and dynamic. The static load can be much larger than the dynamic load. Simply think.... how many people can stand(static) in a room versus how many can be dancing (dynamic) in the room. When people all jump up and down in phase (dancing to a beat) the impulse forces (load) are considerably larger than when static.
PS. One of the advantages to using steel I beams is that they bend (yield) under load and the weight comes down less dramatically. Wood breaks after it deflects!
Good luck and happy learning,
Dave
What you want to do is common and you should have no serious problems if you do it right. I went through a lot of these calculations as I was remodeling my 90 year old house (very heavy plaster walls and a slate roof provided large loads).
People hang things from their ceiling all the time. So you might ask what it the difference from hanging a weight and from putting weight on a floor. How much weight will a floor support before yielding? It obviously depends on the room size as it depends on the span(length) of the joists as well as the joist height, width and spacing. Of course the weight on a floor is distributed over 2 dimensions.... rather than your approach of hanging things on a single joist. So there are a lot of assumptions, but people/engineers have done these calculations many times before. Here is an easy to use link to calculate the loads vs span on floors which will give you some feel for things. The result is load per square foot, but there are similar tools for single beams. As you can see the load bearing ability depends both on the cross-section of the joist as well as on the length and the joist density (16" centers?) and of course the joist material. Not all woods are equal in strength. https://awc.org/codes-standards/calculators-software/spancalc The one thing about this is this engineering assumes there are multiple joist so that if one is flawed the others pick up the slack. Boards are not perfect, they have knots and cracks so there is some danger in relying on a single joist. You have to recalculate a bit or look for the calculation for beams.
First, how will you hang this lift. From over the top of the joist? Will you prevent the joist from twisting and so having the load on the thin direction of the board, ie. is it attached to the neighboring joist as a floor joist would be by the floor sub-flooring boards? So you would definitly be better off if you could hang the weigh from a support that is sitting on more than one joist.
You basically have a beam that you want to hang weight on. I-beams have the top and bottom of the "I" shape to keep them from bending in either direction as well as to provide more strength. So sistering (screwing them) multiple beams together helps. If you are willing to sister, you might want to purchase engineered lumber rather than a board. Engineered lumber is really just extra long plywood that has been ripped to make 2x8 or other sizes of almost any length. You can also get "I" shaped beams from engineered lumber suppliers but they do not sister well.
So these folks sell engineered lumber beams that are used to support the joist of the next floor up. Very close to what you want to do, except you are sort of putting most of the load at a single point. Anyway, they have tables for these calculation for you. https://lpcorp.com/resources/produc...solidstart-lvl-technical-guide-english-canada
Lastly, a comment on sistering joist. Becareful not to break the original board! If you have old wood for the joist, you can bust it when you put in the bolts/screws. Commonly old joists that have been under load or not will be cupped. If you try to sister and screw the new board to the old so tight that it straigthens the old board cup it will commonly crack the board. The strength of a beam comes mostly from placing the bottom of the board in compression while the top of the board is in tension (this is the second reason for the top and bottom of an "I" beam the top and bottom are where all of the forces are exerted. The center line of the beam has little force and so can be quite narrow, but do hold the beam together. So near center line is a much better place to put the bolts/screws rather than creating a lot of holes in you beam at the top and bottom. The rule of thumb would be to keep the bolts/screws way from the edges of the beam by 1/3 of the height of the beam .
Oh, yes, one other issue. When you look at floor loads you will see there are two types of loads. Static and dynamic. The static load can be much larger than the dynamic load. Simply think.... how many people can stand(static) in a room versus how many can be dancing (dynamic) in the room. When people all jump up and down in phase (dancing to a beat) the impulse forces (load) are considerably larger than when static.
PS. One of the advantages to using steel I beams is that they bend (yield) under load and the weight comes down less dramatically. Wood breaks after it deflects!
Good luck and happy learning,
Dave