Main beam being compressed at post locations?

I'm throwing this one out there before I get into trying to fix the situation in case anyone has encountered this and might offer some advice.
This is a two story colonial style house built in 1990. From some general observation and measurement, the center of the house has settled about 1/2 to 3/4". It can easily be seen at the doorways. I've found that the cause seems to be the main beam that runs the length of the house (three sistered 2x12s) is compressing at the posts in the full basement.
I figured one way to verify the distance of settling would be to use a water level to compare the floor joist height at the sill to the height at the beam. I'd repeat this at each joist across the span to get an overall profile.
One of my major dilemmas is moreso how to correct the problem. Some initial thoughts were to use jack posts on either side of the permanent posts to relieve the weight in order to install pieces of angle iron under the beam at each post perhaps extending 8" in either direction to distribute the force rather than simply shimming.
Does anyone know if this is a common problem? Is there a way to figure out if the builder installed enough posts for the span? I'm assuming the current problem is good reason to assume NOT.
Bobby
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What was the original warranty on the structure? No matter your not the original buyer. I would be calling the building inspection people and asking a lot of stupid questions.
Taking this on alone is fool hardy. You might get someone to step up and take ownership.
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Ive used screw jacks and 1/4 inch plate steel , get the steel from a scrap dealer. A problem could be the footing for the jack as a floor will lilely crack if you just add another one beside it. Do you have a screw jack or solid post. Best might be removing the post and insert a screw jack support in its place. While suppporting it on either side tempoarily so it doesnt fall.
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m Ransley wrote:

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The existing posts are solid, not screw jacks. I wouldn't think screw jacks would be up to code in permanent situations. The biggest problem I see with putting screw jacks in place of the old posts is that the beam can continue to compress. Perhaps it has as much as it ever will, but I'd definitely want to get some steel plate under it to distribute the weight.
I was thinking of building some supports on either side by stacking concrete block 2 at a time and using a hydraulic jack. I'd do this on either side of the existing posts. I am concerned with cracking the slab though. I don't know how large the footings are. If I can get the pressure off the existing posts, I can at least shim it to make up for the sag. At best I'd like to get 1/4" angle iron under it. The other side of the angle would go up the sides of the beam on either side for added weight distribution. Then I might install some 3/8 bolts through the angle and beam for added security.
Someone suggested I get the original builder involved even though I'm the 3rd owner. Exactly how do I find out who the builder was?
Bobby
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(snip) Sounds like not enough beam and/or posts for a house that big. IMHO, it shoulda been a steel I-beam, or at least an engineered lam or something. You are right, you need a professional engineer to look at it. Need to see if the posts are too far apart, if they had adeqaute footers under them, etc. 3/4" sounds like an awful lot of compression- is the beam splintering?
Probably lotsa ways to fix, the engineer will know. Some of the basements I have seen while house-shopping have had all sorts of kludgy secondary beams/posts added, or steel gussets added to wood beam. Jacking the house and adding a steel cradle to catch the weight over a wider area sounds like a decent idea, but the housing inspector (for when you sell), and probably your insurance company, will be happier if there is an engineer's stamp on the working diagrams. Adding more posts isn't that hard, if it won't make basement unusable, but does involve a lot of dust and dirt from jackhammer to punch through slab, and mixing or carrying concrete to add footers to catch the new posts.
I would definitely call the builder in to look, if he is willing. (or have the inspector call him) You won't get a freebie, since place is 15 years old, and probably in no danger of actual collapse. But he may be embarrassed enough to offer to do the work at a cut rate, assuming you trust him after he fubar'd it in the first place.
aem sends....
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2' angle iron will bend. I tried it. Screw jacks are code if they are strong enough, they have ratings and are custom ordered. You have to jack it maybe 1/16" a few days, a hydraulic may loose pressure.
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Check out your neighbors houses if they were built at the same time.
Mark
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That's a decent idea, but this is a newer home in a neighborhood of homes ranging from 1-230 years old and I can think of only one other home built at nearly the same time (totally different design however).
RE: screw jacks.. I actually have two screw jacks. I'm wondering if placing them on either side of the permanent post will have enough strength to lift the beam enough for shimming. What would be a good base to use to distribute the force across the slab?. I was thinking of stacking a couple 2x12 blocks.
I'm actually thinking about leaving it be and just reset all the door jambs. I'm planning on laying some tile and hardwood flooring and if I'm going to fix the sagging even a little, now's the time to do it.
Bobby
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