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StructuralEng
StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6681
Experience:  Structural Engineer
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I have sagging 2x 10 floor joist across a 10' section that I

Customer Question

I have sagging 2x 10 floor joist across a 10' section that I would like to shore up with a jackpost and an I beam. They are sagging because when the house was built 55 years ago, the plumbers cut 1/2 way through the center beam in 2 places to install bathtub drains. what size steel I-beam (S beam?) would I need
Submitted: 9 months ago.
Category: Structural Engineering
Expert:  StructuralEng replied 9 months ago.

Can I get back to you in the morning?

Customer: replied 9 months ago.
I have no answers yet that satisfy my needs
Expert:  StructuralEng replied 9 months ago.

What exactly is the span of the beam and what will be the joist length on each side of the beam? Will it support any ceramic tile?

I assume this will be supporting this single floor only and nothing else?

Customer: replied 9 months ago.
When you say span of the beam are you referring to the joist length or the length of the I-beam? I expect the I beam to take load over 8'2",perhaps 10' at the most. The joist length is 14".from wall to existing basement I beam. The cut joist is cut at 3'10 and 6'8 inches from the wall. Due to the basement layout, I plan to put a jackpost 4'4" from the wall.
Customer: replied 9 months ago.
you are correct, it supports a single floor and of course the roof above
Customer: replied 9 months ago.
there is ceramic tile in both of the bathrooms above, floors and walls with heavy bathtubs
Expert:  StructuralEng replied 9 months ago.

Is there a wall above where this beam will go? If not then it won't support the roof

Customer: replied 9 months ago.
Good point. Yes, there is a wall, but it is not a load bearing wall...To the I-beam, it is just the weight of the wall
Expert:  StructuralEng replied 9 months ago.

Thank you. I'm running numbers now.

Expert:  StructuralEng replied 9 months ago.

You can plan for a W5x19 beam ASTM A992 Gr. 50. It's 5" deep x 5" wide and weighs 19 pounds per foot

Customer: replied 9 months ago.
Thinking about it there is a load bearing wall that is above the proposed I-beam. the wall is 8 foot long, and is 5 1/2 foot from the exterior wall. Only 3 foot of it would be above the are projected to have the beam, the other 5 foot would be beyond the edge of the beam
Expert:  StructuralEng replied 9 months ago.

So right now there is a load bearing wall near the mission of joists? With no wall or beam below the joists at that location? That doesn't sound right. I will size the beam for that if you want me to, but that doesn't sound right. It would be exceptionally uncommon to have a bearing wall load joists and not have a beam or wall below

Customer: replied 9 months ago.
I will make and attaché a pdf to show you what it looks like, perhaps words are failing me
Customer: replied 9 months ago.
maybe this will help. I scribbled out the sagging area that I put down the first time
Customer: replied 9 months ago.
I am stepping away from the computer for about an 60-90 minutes. Not sure if I can see this on my cell phone
Expert:  StructuralEng replied 9 months ago.

I will assume it's supporting the roof, too. What is the city and state so I can look at snow loading?

Customer: replied 9 months ago.
Fairfax VA
Customer: replied 9 months ago.
OK. I am back online now
Expert:  StructuralEng replied 9 months ago.

W6x20

Customer: replied 9 months ago.
This I bean will be supported by only 1 jack stand and the stand will not quite be centered. Does that make a difference?
Expert:  StructuralEng replied 9 months ago.

Yes. That's completely unstable.

Customer: replied 9 months ago.
I intend to screw the I beam to the joists at the end of the span. Am I just taking the wrong general approach?
Customer: replied 9 months ago.
I have a local engineer who came up with a solution using joist hangers and blocking as close to the end of the cut joist as possible and the 1 joist next to it. This would shore up the cut joist, but that does nothing to restore the sag that it has caused
Expert:  StructuralEng replied 9 months ago.

Yes. That's relying on the joists to keep it stable. That's not prudent if the load resultant is directly over the post. It will not be, which makes it much worse. Two posts are critical

Expert:  StructuralEng replied 9 months ago.

Exactly. You need two posts for the beam

Customer: replied 9 months ago.
OK, I can do that I think, but I cannot put the posts at the extreme ends of the beam. Perhaps within 2 1/2 foot of the end, but then the beam would have to be 21' long
Expert:  StructuralEng replied 9 months ago.

21'? I thought the beam only needed to be 10' long maximum. If it's going to be 21' that will make a big difference.

Customer: replied 9 months ago.
Only a 10' cross section of the joists are affected. I cannot put a jackpost at that end though as it is in the middle of the basement floor...Of my woodworking shop where I move large 4x8 sheets and lumber sometimes 12 foot long. I would have to locate the jackpost at the other end wall (not shown in the diagram I sent you) just to get it out of the way. Perhaps I abandon the I-beam idea and as a way of shoring up and eliminating the existing say and just add the additional joist and hangers per my local engineer. Granted it will not fix the sag, but it may be just to hard and expensive to go the I-beam route. Thoughts?
Expert:  StructuralEng replied 9 months ago.

How much of the joist depth is cut away? Do you have utilities running through the joists?

Customer: replied 9 months ago.
The joist has at a 2 " deep by 6 inch long cut an a 3 inch deep by 6 inch long cut in the 2 places I showed you on the drawing I attached earlier the deeper cut is closer to the middle. Those cuts are made so the drain lines can come out of the tubs Also,, right next to that cut is a 2 inch hole where the drain lines go through the joists after they come down and go through their P trap. Would a picture help?
Expert:  StructuralEng replied 9 months ago.

A picture would be great. Bid the sag only in the couple joists that were notched?

Customer: replied 9 months ago.
No, the sag starts 4 joists away and progressively gets worse to the damaged joist - about 1/4 inch more per joist. I do not think the joists are going to fail - they've been like this since the house was built 50 years ago. I would like to stop it from getting worse and eliminate the sag if I can. The attached picture shows the cut joist
Expert:  StructuralEng replied 9 months ago.

What is the smallest unobstructed dimension from the bottom of the subfloor to the highest obstruction on the side with the highest obstruction at the lowest elevation?

Customer: replied 9 months ago.
I'm not trying to be dense, I too am an engineer (electrical), but I do not understand your question. what do you mean by "highest obstruction on the side with the highest obstruction at the lowest elevation?" what are you referring to as an obstruction?
Expert:  StructuralEng replied 9 months ago.

Anything that would prohibit sistering the joists

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