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Question DetailsAsked on 5/26/2016

Main support i-beam is dipping 1/4" to 1/2" in center. can't see other side due to finished basement. Is this ok?

It's the main support beam for the house. There's 1/4" to 1/2" sag from the side towards the center. The floors above this area slope towards the center of the house. Is this normal? The lolly support post in the garage was replaced about a year ago and placed on the original footer. I can't see to measure the other side due to the basement being finished.

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3 Answers

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To measure the other side, assuming the drywall is tight to its framing, you could just measure along the bottom of the ceiling drywall (if not a highly textured finish) to detect sag. Of course, if measuring from the floor to determine sag, you would first have to determine if the floor is level - generally not in a garage. Better to level or laser shoot the beam directly to determine amount of sag.


Not knowing the beam size/length or design loads, hard to tell if this is "normal". A 1/4-1/2" sag would commonly be well within the normal range for a long-span wood beam which has had a decade or more to develop progressive load creep (which can reach 2-3 inches or so over the years for a 20-something foot beam) - actually 1/4" or so would be normal shortly after construction assuming it was perfectly straight to begin with. 1/2" would be probably at or beyond the normal deflection under load for a STEEL I beam. Certainly, if this is "new" or increasing settlement rather than the result of a decade or more or creep, then one would worry about whether the beam is undersized or the post foundation is settling, in which case getting a Structural Engineer in there to look at it would probably be a good idea. If staying the same and the lolly post seems to be carrying its load OK, most likely not an issue unless you care about the floors being out of level, in which case jacking it back up level can be done as an aesthetic measure.


However - since it has a center lolly support post, which would be unusual in itself for a steel beam unless exceeding about 20-25 feet, so I am assuming you are talking a TJI (wood I-beam with laminated or solid wood top and bottom flanges with OSB (shudder) or plywood web. For a main supporting center beam in a 24-36 foot "deep" house (depth being the smaller dimension) presumably the beam is running down the length of the house, so supporting floor joists which run across the "depth" direction of the house so say 12-18' long floor joists on each side of it, the beam would normally span up to about 14-28 feet across the garage, with another (or several) beams extending the rest of the length of the house under the upstairs floors. TJI and similar built-up wood beams are known to have creep issues and commonly (especially in humid climates) sag more than solid beams - but as long as they remain intact (glue joints not coming apart) generally it is an aesthetic rather than a structural issue.


Since it has a lolly post in the (presumably) center of the garage, obviously it is either not designed to span the whole width (which would usually require a say 6-10" wide by 16-24" high glulam beam) or it had a post put in some time ago due to the sagging - so I would presume the post is necessary.


My guess - when the post was replaced, the contractor may have not put in tight-fitting stulls (temporary support posts wedged in under the existing beam, typically 4x4 or 6x6's but sometimes a temporary stubwall section) wedged tight under it to lift it a bit, so when the old lolly post was taken out the beam was allowed to sag a bit, or had some slack in the post support that allowed that. Another possibility (you don't say WHY the original post was replaced - was it settlement or rust or car impact damage ?) is that the foundation pad for it is settling.


At any rate - assuming the pad shows no sign of settling, the normal solution would be to temporarily prop up the beam with stulls, remove any fasteners at the top of the post, wedge or jack the stulls to raise the beam back up to slightly above level, put in hardwood or rustproof/painted metal (better) shim piece between the beam and the post as a tight fit, then replace the mounting hardware for the post, making sure the fasteners are properly gripping the beam and not just the shim. Generally, this would be a Simpson or similar metal fitting that wraps around the side of the beam and connects to the post, not just nailing or bolting into the bottom of the beam as that weakens it.


Another approach, sometimes simpler especially if the beam in concealed in the ceiling, if putting supporting wood (typically 4x6) under the ceiling on each side of the lolly post to spread the load along the beam a ways, jack those up with screw jacks to pick up the load, unbolt the bottom of the post (if bolted to the foundation pad), jack the beam up level, put a galvanized or rustproof painted metal shim plate under (large enough that the post bears fully on it), rebolt the post, lower the jacks so the post carries the load, and tighten down the mounting bolts. With some installation easier to leave the screw jacks in place for several days and fill the gap under the jacked-up column with high-strength grout designed for foundation / base plate use. This is actually the more professionall way to do it because the grout ensures full bearing of the post base, and also lifts it a bit off the floor so reduces or eliminates rusting. Post should also be cleaned of corrosion and repainted during the repair if rusting, but not so bad it is reducing its load capacity.

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BTW - when talking to contractor about HOW he will fix it, be sure to talk about jacking up the beam - with a solid or laminated wood beam or steel beam, one would normally take the stulls (wood posts) and put a piece of plywood above them as a slip plate, and just hammer the precut stulls into place to lift the beam. Do NOT do this with a wood I-beam - the bottom pieces cannot handle that kind of treatment - should be jacked up to allow slipping the stulls into place. This can be done with wood posts on a cylinder jack and slipping the stulls in, or by using full-height foundation screw jacks (like are used in some basements as permanent lolly posts) both for the jacking and the temporary support while the lolly post is worked on.

Answered 2 years ago by LCD

0
Votes

Hi LCD,


I did have a structural engineer come out and take a look. It's a steel i-beam (don't have measurements) spanning 19' width of the house. He said the i-beam is more than capable of handling that load without the two lolly post (one in the center of the garage and the other in the basement under the basement stairs).


The i-beam has been raised on the left side (not sagging) due to the masonry block wall bowing in just in due to hydrostatic pressure. That's the same side where the downspouts come down into an underground French drain. The gutters were cleaned, but I need to check the acutal drain itself and will probably have to have a new one installed.


That part of the house, you can feel a slope in the floor right above on the first floor.


We have a pretty steep grade hill that allows water to drain into the back yard towards the house. Not controlling the drainage is our issue. Bowing basement and garage walls is the tell tale sign.


Thank you for your answer. While I'm not happy with the work that has to be done, the engineer said the house won't fall down tomorrow. It took 50 years for it to get where it is now. Just have to fix it and not let it get worse over another 50. :)

Answered 2 years ago by Guest_9551729

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Votes

Good news the structural engineer said it is load capable - surprised he did not advise you on how you could fix the floor sag, through.


Note that while the beam may be able to safely carry the load, it will deflect (sag) under load - so if you take the intermediate lolly columns out the sag will increase, and if they are about mid-span and you remove them the sag will increase by a multiple of about 16 in magnitude as you effectively double the beam span, because the deflection at midpoint is proportional to the effective span to the fourth power - double the span and deflection goes up by a factor of 2 to the fourth power = 16 ! - so probably not something you want to do unless you are prepared to significantly shim up the joists all across the house. Plus likely to result in undesireable visual effect in sagging ceilings, and could also set of an alarm in potential buyear's home inspector reports.


I would leave the columns and shimming the lolly columns up as I described would be the usual fix. IF there is any doubt about the ability of the lolly column foundations to carry the load, then replacing them with properly designed and sized footings should be done instead - reusing the existing columns should be possible if in good shape.


If your floor joists just sit on top of the beam or in the web without fasteners (rare and not to current code) you could individually hardwood shim each joist to the right elevation.


Note also where the maximum sag is - if it is over the beam, then the above will work. However, the individual floor joists will also deflect under the load above them and also over time due to creep if wood - so if the low point of the sag is more at the midpoint of the joists (between outer wall and the beam) than right over the beam, raising the beam or the joists at the beam would help little or none.

Answered 2 years ago by LCD




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