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I had smart jacks installed in my basement. The wooden

Customer Question
I had smart jacks...

I had smart jacks installed in my basement. The wooden girders they used to lift the joists are pressure treated 4 by 4’s. The grain of the girders runs parallel to the floor. This is a bad design, correct? The girders are starting to bow and I think this is because the grain is going the wrong way

Tutor's Assistant: OK. Is there anything else the Structural Engineer should be aware of?

The jacks are approximately 8 feet apart

Submitted: 3 months ago.Category: Structural Engineering
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Answered in 14 minutes by:
3/28/2018
Structural Engineer: walkereng, Consultant replied 3 months ago
walkereng
walkereng, Consultant
Category: Structural Engineering
Satisfied Customers: 2,994
Experience: Over 30 years of Structural Engineering experience.
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Do you have any pictures you can share with me?

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Customer reply replied 3 months ago
I’m not home right now - I’m trying to find someone who can take some pictures
Structural Engineer: walkereng, Consultant replied 3 months ago

That would be great. You know what they say, a picture is worth a 1,000 words.

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Customer reply replied 3 months ago
Have you ever worked with smart jacks or basement/crawl space stabilization by jacking up floor joists?
Structural Engineer: walkereng, Consultant replied 3 months ago

Yes

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Customer reply replied 3 months ago
Ok, I’ll send the pictures as soon as I get them
Structural Engineer: walkereng, Consultant replied 3 months ago

OK, thanks

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Structural Engineer: walkereng, Consultant replied 3 months ago

Can you explain in a bit more detail why you had to jack up your floor joists?

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Customer reply replied 3 months ago
Was trying to level the floor. House was built in 1900 and one side sink about 6 inches over time. The structural engineer I hired during inspection suggested stabilizing and potentially lifting to level out the floor. I hired a “basement expert” company who came in and installed the jacks. I think they are installed incorrectly because of the orientation of the girders.
Customer reply replied 3 months ago
One side sunk over time
Customer reply replied 3 months ago
What’s your assessment?
Structural Engineer: walkereng, Consultant replied 3 months ago

So it sounds like they jacked up the floor, but did not solve the settlement problem. The 1st thing that needs to be done in a situation like this is to determine why there is settlement. Then you need to fix the settlement before you jack the floor back to level, or it will just keep settling.

The continued settlement is most likely not related to the the grain or type of timber used to jack the floor back up. I would have used larger members than 4x4's, if the spacing of the jacks are 8' o.c.

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Customer reply replied 3 months ago
Settlement is not the issue. The Structural Engineer that I mentioned above said the settlement probably happened a very long time ago. What I want to know from you is whether or not the 4 by 4 wood beams/girders are incorrectly placed since the wood grain runs parallel to the floor, not perpendicular. The beams are bending/bowing in some areas plus they are pressure treated wood which is softer than non pressure treated wood. It seems like a no brained to me, but I wanted to get the opinion of an “expert”. If you have an 8 ft 2 x 4 and lay it flat across an opening (grain parallel to the ground) and try to walk across it, it will bend and maybe break but if you turn it on it’s side with the grain perpendicular to the ground, you could walk across it no problem. I’m very surprised you don’t understand the concept or am I just explaining it wrong
Structural Engineer: walkereng, Consultant replied 3 months ago

I fully understand your question. I understand your analogy of the 2x4, but the reason that a 2x4 bends more on it's side rather that when it stands on it's edge is relative to the Moment of Inertia of the shape, which is directly proportional to the cube root of the depth of the member. So roughly on it's side (1.5" cubed is 3.375) as compared to on it's edge (3.5" cubed is 42.875). That is over 12 times the strength roughly on it's edge, everything else being the same.

I would say your issue is that the 4x4's that are being jacked up against the bottom of your floor joists, have too much jacking force on them for an 8' clear span between jacks. You really need to replace the 4x4's with 4x6's or 4x8's.

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Customer reply replied 3 months ago
Moment of Inertia doesn’t tell the whole story. If I did the same test with a 2 x 2 board I’d get a similar result. Read the following - this is the information I was looking for and proves my point. I google wood strength and grain and found a website called Woodstrengthcompanion.com: Compression strength tells you how much of a load a wood species can withstand parallel to the grain. How much weight will the legs of a table support before they buckle?
Bending strength (also known as the modulus of rupture) shows the load the wood can withstand perpendicular to the grain. How much weight can you hang on a peg?
The website shows the results of bending vs compression tests with many varieties of wood. In all cases the bending strength (grain parallel) is nearly double to that of compression strength (grain parallel)
Structural Engineer: walkereng, Consultant replied 3 months ago

You are a bit misguided with your internet research. The beams in question are not having issues due to compression, like a column or post or legs on a table would have. Your beams are having issues with Bending Strength, which is related to tension forces. If your beams are not blocked correctly, they can have lateral buckling issues. I was just trying to show you a relative magnitude between the two beam orientations in your example.

It seems like you are comfortable with the data you are obtaining over the internet, so there is probably no need to continue this Chat. You have not been charged. Good Luck with your issue.

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