Ceiling/roof sag problem Q's

[GTS225]

FNG with a couple Q's. Reasonable intelligent, but no materials engineer, so.....

My 24'x24' garage has a roof and ceiling joist sagging problem. At the moment, I've got it supported by a 20' I-beam and jack posts, but that isn't really desirable to have a pair of jack posts in the middle of the floor.
What I'm envisioning is to run a longer I-beam from front to rear, fastening the beam to the garage door header, and supporting the back end with another beam, fastened to the wall vertically. I have access to 4" beam, but don't know the strength. Dimensionally, it's 4.25" tall, 4" wide, 1/4" thick in both the flanges and web. I do not know the material, but it does appear to be hot-rolled, probably a general utility-type steel.

My question(s) are; Approximately how much weight would such a beam support with supports only on each end? (I hope enough to run a trolley on the beam) I also worry about the door header, (doubled 2x10's) sagging under the load. (I can augment the header strength with 1/4" plate if needed.)


Thanks.....Roger

 

[maddog]

FNG with a couple Q's. Reasonable intelligent, but no materials engineer, so.....

My 24'x24' garage has a roof and ceiling joist sagging problem. At the moment, I've got it supported by a 20' I-beam and jack posts, but that isn't really desirable to have a pair of jack posts in the middle of the floor.
What I'm envisioning is to run a longer I-beam from front to rear, fastening the beam to the garage door header, and supporting the back end with another beam, fastened to the wall vertically. I have access to 4" beam, but don't know the strength. Dimensionally, it's 4.25" tall, 4" wide, 1/4" thick in both the flanges and web. I do not know the material, but it does appear to be hot-rolled, probably a general utility-type steel.

My question(s) are; Approximately how much weight would such a beam support with supports only on each end? (I hope enough to run a trolley on the beam) I also worry about the door header, (doubled 2x10's) sagging under the load. (I can augment the header strength with 1/4" plate if needed.)


Thanks.....Roger

I have a few thoughts. Cant help with the weight, I would need to see it and the I beam etc. Here is a thought -

What ever you end up doing, jack things up first (even the center of the garage door header ) before attaching things. Do all your bracing, hanging whatever, then take the jack out. It just gives you a little head start on the sag if its going to. Done right it will sag right down to where it should be.

Do you know what a truss is. (i will assume you do ) They are really strong, and you can make them yourself. Some 2 x 4's , 2 x 2's lots of glue (coat all surfaces that make contact ) and plywood sides (ply would run verticly) lay it out on you driveway ( or build in place) and screw the **** out of it and wait for the glue to dry. They are really strong for the weight.

could you put this truss next to the garage door header and hang the Ibeam from that?

A truss could also be used to straighten the sagging cieling ( it would most likely be in the attic )and then the I beam could be hung from the truss or the cieling.

If the attic is empty You could jack things up to straight and make a truss out of the cieling joist and rafters that are existing . Again some sticks, ply and glue. Screws or nails (old wood is very hard, use screws or a nail gun) to hold things till the glue dries.

I dont know if this makes sense to you. Take pics and send them. I can sketch the best (in my opinion) solution

Let me know

 

[wilbilt]

Load support specs for steel beams are generally stated in terms of "allowable deflection". The beam will sag a lot before it snaps, so the acceptable load is determined by how much it can be allowed to sag.

Your 4.25 x 4.00 x .250 beam sounds like a "wide flange beam". These are classified by the height (depth) of the beam x the weight of the beam in lbs. per foot of length.

This site may be helpful:

http://www.efunda.com/math/areas/RolledSteelBeamsW.cfm

There are load calculating formulas contained in publications such as Machinery's Handbook, and they may be available online as well.

As for the roof problem, what is the type of construction? Is it trusses, or ridge & rafter, or?

It sounds like you have a structural issue to deal with before hanging a trolley on that beam. The door header was designed to carry the weight of the wall above the door, not the entire roof.

 

[maddog]

Load support specs for steel beams are generally stated in terms of "allowable deflection". The beam will sag a lot before it snaps, so the acceptable load is determined by how much it can be allowed to sag.

Your 4.25 x 4.00 x .250 beam sounds like a "wide flange beam". These are classified by the height (depth) of the beam x the weight of the beam in lbs. per foot of length.

This site may be helpful:

http://www.efunda.com/math/areas/RolledSteelBeamsW.cfm

There are load calculating formulas contained in publications such as Machinery's Handbook, and they may be available online as well.

As for the roof problem, what is the type of construction? Is it trusses, or ridge & rafter, or?

It sounds like you have a structural issue to deal with before hanging a trolley on that beam. The door header was designed to carry the weight of the wall above the door, not the entire roof.

Well said. I bet you can use a slide rule. Those things amaze me.

 

[wilbilt]

Well said. I bet you can use a slide rule. Those things amaze me.

LOL...No way in H**l can I use a slide rule. I can use a formula and punch the numbers in on a calculator....

If he's got a ridge and rafter, I like the idea of jacking up straight and using the existing collar ties to hold it together. Maybe add one to each rafter to double them if the existing ones have failed.

Will

 

[maddog]

LOL...No way in H**l can I use a slide rule. I can use a formula and punch the numbers in on a calculator....

If he's got a ridge and rafter, I like the idea of jacking up straight and using the existing collar ties to hold it together. Maybe add one to each rafter to double them if the existing ones have failed.

Will

Exactly. Lets you and I jump on a airplane and just go do it for him. I'm sure he'll feed us.

HERE WE COME, PUT THE COFFEE ON.

 

[wilbilt]

Yeah....coffee>>>!!!

 

[mike944]

Well, I'll see if i can answer your question, as i'm an engineer. It's been quite a while since i've had to do these calculations, and for legal purposes, i'll have to say "consult a licensed structural engineer before doing anything" as i'm not a structural engineer, i'm an aerospace design engineer. I never work with structural steel.

That being said, at first glance, that beam seems way too small. So, i dug up some old textbooks, and did some math. Sure enough, after some math, a 4.25" tall steel I-beam isn't really going to help much at a 24' span. It's way too small.

The weight of the beam alone, before you even put a load on it will cause about 3/8" deflection in the middle. If i use 25 lb per linear foot for your roof structure loading (probably WAY too low) you have about 1.25" deflection in the middle. Probably won't help your sagging problem much. Adding 500lbs for a trolley lift (including the weight of the trolley and hoist itself) you're looking at about 2.5 inches deflection. This will be extremely "springy". I haven't calculated how much load it takes to actually fail this beam, but this loading is probably close, if not over the max load for failure.

All these calculations do not take your supports into account. Your double 2x10's definitely won't cut it. Remember, now they'd have to support not only the weight of the beam, but half the roof as well. If you sandwich the 1/4" plate in between them, it could possibly handle it. But as i said above, this beam isn't big enough, so you're looking at significantly more weight with a properly sized beam. Not to mention the 2x4's that support the door header are probably going to be over loaded too now.

Really, i only see 3 ways for you to solve the sagging roof problem.
1. add a much larger I-beam, complete with I-beam door header, and possibly new door header supports.
2. the collums you have now. Of course, without footings, they'll eventually crack the slab.
3. Maybe you could jack up the ceiling (like you are now) and go into the attic, and add "trussing" to whatever structure you have up there, and then remove the collums.. Unfortunately, you'll loose the use of any attic space you had, but from the sounds of your sagging ceiling problem, you're probably not using it anyway.

 

[GTS225]

SIGH..........I was afraid that I'd hear the above. Looks like I'm going to have to think along other lines to correct this problem.

What I'd really like to do is tear down the whole thing and build a three-stall with a high center for a lift.

Thanks, guys.....Roger

 

[mike944]

I think trussing the attic is a half-way decent solution, and probably not all that difficult.

Post a photo of the current attic structure. I think you might have bigger structural problems than just a sagging ceiling. Do your garage walls "taper"? I.E. is the size of your garage a different width at where the walls meet the foundation, and where the walls meet the ceiling?

Depending on the size of the current ceiling joists, and how well they're attached at the ends, it might be as simple as adding a single vertical 2x4 from the ridge beam to the ceiling joists, for each set.

 

[73GRAND]

FYI, 10 years ago I built my two story garage. I had an engineer here at work size the beam. He was a Structural Engineer. He died last year. The depth of the garage is 26foot and the width is 32foot. The beam runs front to back. We sized it at as a W8x18. This is twice the size of yours. Also Iplaced a 4"dia. column in the middle which is anchored to a 3'x3'x3' footer four feet below the concrete floor. This footer sits directly on the undisturbed clay below.

 

[mike944]

That's a good sizing reference for a beam. Your beam may be twice the height, but it's approximately 6x as much weight carrying capacity. a small change in the height of the beam makes a huge difference in the strength.

Using the same calculations, your beam has only about 1/4" deflection with the same 25 lb/ft roof load, and you have a longer span. Your column seems like overkill. With the collumn, it turns into 2 seperate 13' beams, which the deflection is essentially non-existent.

 

[73GRAND]

Yep, No sag no worry. Overkill Yes. I thought at one time about building an apartment up there too.

 

[GTS225]

Guys.....brought this old thread back up to post a "progress" report.

Hadn't had a lot of opportunity to dig further into this until very recently. Refferring to the info offered by responders, got out into the garage to look things over a bit closer, and realized that there aren't any trusses, (in the normal sense) in the roof structure. The rafters and ceiling joists are all that exist. There are a few flimsy plywood "ties" running from the center of the span up to the ridge board, and a 2X4 running front to back tieing all the ceiling joists together, but that's as strong as it gets.

Thanks loads for the info that you all offered, as it pointed me toward what I needed to figure out. It seems to me that at this point, all I need to do is get into the attic and add the classical "W" style truss webbing, and I can do away with the center support beam entirely. The "W" webbing should spread the "load" throughout the roof structure and be "self-supporting", without the I-beam support from underneath.

Thanks, again folks.....much obliged.

Roger