Reinforcing Engineered wooden I-beam trusses...


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Old 01-24-06, 02:48 PM
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Reinforcing Engineered wooden I-beam trusses...

I have a split level house with the wooden I-beam trusses. The trusses are 9.5" high spaced 19" on center spanning a 15'. To me it seems like there is a lot of bounce in the floor. I am guessing the floor is to code but it probably meets minimum requirements. I am looking to finish off my basement and I'm worried that the bounce in the floor will split the seems easily when I sheetrock the ceiling. Anyone have suggestions for reinforcing the I-beams or will the sheetrock have enough flexability. I've seen on various websites about I-beams that you can put web bracing in and full depth bracing in but it looks like that is more for under concentrated load points. I don't want to damage the integrity of the beams with improper bracing but I also don't want to have to redo the ceilings each year as seams split. Any suggestions would be greatly appreciated. Thanks!
 
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Old 01-24-06, 03:12 PM
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Best bet would be to use an drop ceiling. It won't crack at seams and you can access your plumbing and electrical without destroying the ceiling.
 
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Old 01-24-06, 05:44 PM
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I've thought of the drop ceiling and have had them in previous homes but would prefer the look of a sheetrocked ceiling - assuming it doesn't split.
 
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Old 01-25-06, 02:17 AM
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GSR: Those I trusses are designed to have a little give in them. However, they really do not give as much as you think that they do. Most of it is sound and not a physical movement. Those are sheetrocked all the time. The trick is to use 5/8" sheetrock, and screw it on and not nail it.. It should be fine. Thanks for the question. Good Luck. PS We just finished a basement ceiling today with a 26 foot span. Not a problem, nor will there be.
 
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Old 01-25-06, 04:38 AM
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Without knowing the manufacturer of your truss-joists, it is not possible to determine if your TJIs are adequate or undersized for the spans or spacing.

Depending on the type of TJI used and the width of the flange, they may be undersized.

But even with appropriately sized TJIs, 'bounce' is a chronic and ongoing problem and TJI manufacturers are well aware of the issue. Engineers will often overcome the problem by simply upsizing TJIs above the minimums suggested by the manufacturers for spans and spacings and this can usually work.

The 'bounce' is not related to excess defelection but rather is a natural undulation of the floor caused by walking on it. It is like the waves in a pond.

Using webstiffeners and cross bracing will only slightly help the problem and in severe cases the only practical corrective method will be to construct a center girder at mid point of the span to eliminate and sag or bounce.

Otherwise you can add additional TJI's mid-point between existing trusses effectively decreasing the on-center spacing. This is not practical if wiring, plumbing or ductwork runs through successive joists.

If the TJIs are undersized, hanging drywall from the underside will overtax the already too high dead loading and make matters worse.

Your best choice in such a case really would be a suspending ceiling.

But without knowing the manufacturer of the truss joists and the type of truss-joist used...it is impossible to say whether or not your floors are adequately sized or undersized given the spans and spacing.

According to some manufacturer's span tables, your floor is severely undersized....
 
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Old 01-25-06, 05:40 AM
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I-beam detail...

Thanks for all the input so far. So far I've been giving the builder the benefit of the doubt I was at a local home improvement store last nigth and looked at two different charts 1 said we were fine and the other said the span should only be 14' or he should have put them 16" OC. My wife is dead set against the drop ceiling idea.

Stamped on each beam is the following information.

LP-Mill 437 LPI-32 PFSNER#QA-251 NER612 CCMC 12412-r ICBO PFC-4787 LA CITY RR 25099 8/10/03 21:58

The beams themselves are 9 1/2" high, have 3/8" web and cut lumber for the top and bottom that is 1 3/8" tall x 2 1/2" wide

More info about the area above the floor it is 15' wide and about 35' long with a vaulted ceiling the rooms above it are a dining room, kitchen and living room that are all open to each other.

I don't necessarily feel the bounce when I walk but I hear it sometimes from a picture that moves. I notice it more if we sit at the dining room table and someone shakes their foot - the whole table starts bouncing then.

Thanks again for all the input.
 
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Old 01-25-06, 02:31 PM
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Lousiana Pacifc LPI-32

What you have are Louisian Pacific LPI-32 truss joists.

According to their span tables they have been installed within acceptable loads presuming a 40psf live load and 10-15psf dead load.

You can see the LP span table here on page 3:

http://www.lpcorp.com/literature/lp_...tech_guide.pdf

But it should be noted that acceptable engineering practice sees this size TJI as being able to bear the loads for the spans and on-center spacing, but barely.

Standard proceedure today is to increase manufacturer's recommended designs by using larger TJIs, decreasing spans, decreasing on-center spacing, or all of the above to reduce the 'bounce' you are experiencing.

Apart from reducing the spans by constructing a girder, not much you can do now but learn to live with the bounce especially if you plan to increase the dead loads by adding 5/8" drywall (a must)...
 
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Old 01-25-06, 06:21 PM
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Thanks

Thanks for all the info. It looks like from the tables adding web stiffeners wouldn't change much.

Two more questions -
Would using 2 thinner layers of sheetrock with staggered edges make a difference or would that just increase the likelyhood of sags and splits?

When framing around mechanical work do I need to attach the framing to both the top and bottom of the beam (as opposed to just the bottom) to keep the bottom from potentially seperating from the webbing or isn't that a concern?
 
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Old 01-26-06, 05:39 AM
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Codes require 5/8" drywall for spans over 16". You can't use double layers of thinner drywall.

"When framing around mechanical work do I need to attach the framing to both the top and bottom of the beam (as opposed to just the bottom) to keep the bottom from potentially seperating from the webbing or isn't that a concern?"

I have no idea what the above quote means...
 
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Old 01-26-06, 06:44 AM
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Framing clarification (i hope)

The duct work for the HVAC hangs below the trusses so I need to box around them to sheet rock the duct work in and the box will be hanging from the truss.

My original plan was to frame around it kind of like a normal wall only it would be ~1' tall and hang from the ceiling rather than have the floor to support it.

When I was searching the web for info on the I beams I saw something that mentioned not attaching to just the lower board of the beam otherwise the weight or force could pull the beam away from the center webbing. It mentioned attaching to both the top and bottom board on the beam.

Not sure if that clears it up, if not I'll try to take/draw a picture.

Thanks for all the help!
 
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Old 01-26-06, 07:17 AM
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Simply applying 5/8" drywall to the bottoms of your I-joists will stiffen and stabilize this floor system. Mid-span solid blocking would help, too. The 'sponginess' you feel is caused by lateral deflection of the bottom chords of the I-joists. The drywall ceiling below will function as a shear diaphragm. Screwing the drywall ceiling should be OK but designed gypsum-board shear walls often specify fastening such as "cooler nails" or other nails.
Good luck!
 
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Old 01-27-06, 06:34 AM
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gsr said:

"When I was searching the web for info on the I beams I saw something that mentioned not attaching to just the lower board of the beam otherwise the weight or force could pull the beam away from the center webbing. It mentioned attaching to both the top and bottom board on the beam."

Ahhh....the lights go on!
Sorry I didn't get that from the way you first explained it...Probably me.

Fastening to the top and bottom cord of the truss seems to make the most sense and be the most prudent method.

I don't know the authoritative answer to that and would defer to what the manufacturer of the I-joists requires.
 
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Old 01-27-06, 06:53 AM
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Thanks all...

Thanks everyone for the advice and information.

I'll attach the framing to the top and bottom of the truss and use 5/8" sheetrock.
 
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Old 01-28-06, 08:33 PM
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Reinforcing Engineered wooden I-beam trusses...

Don't expect something like sheet rock to be a long term solution to any structural problem. It will always weigh the same and the stiffening effects will decrease with time and with every pass of a load over them.

You have an engineered wood floor system that is adequate to meet the MINIMUM standards for support and deflection. The only long term improvement would be a structural modification (i.e. stiffen or decrease the span).

You are never wrong meeting the code, but you may not be right.

Dick
 
 

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