structural questions for residential construction.

[Ronald F.]

Hello everyone, I will begin by saying I am new here, I'm not sure if I am doing this correctly or if this is the right place to post a question. However, I am a new engineering student, so I believed this to be the most appropriate section.
Okay, so I am rebuilding an old house (the thing that led me to engineering school in the first place) and I am doing some work on the foundation. It is a 24'x28' concrete slab with 8"x8"x16"CMU walls. It has 3 completely solid walls that are mostly underground with one side fully exposed. I decided to take down that side and turn it into a 3-car garage. i have a drawing of its current state below (image 1), however, I was so focused on other things (beam spans, columns, footings, etc.) i completely did not consider the aspect of wall bracing. I'm building everything according to the I.R.C. or the A.W.C. WFCM/WCD-1, which have an excellent section on how much wall bracing is needed per wall line using whatever method of wood framing you choose, but when it comes to masonry I am very unfamiliar.
So my question is, what needs to be done for this to be structurally sound? I'm not sure if it will make a difference but there will be a diaphragm floor on top of the garage with a typical 2"x4" structure on top of that. My initial plan was to use 4-2"x12" beams for the built-up-header, with some type of Simpson strong tie holding it to the "lug walls" (I think there called) and two columns in between. (image 2/3). But after considering bracing, I'm not sure if that will be enough. So I started thinking reinforced concrete with a custom rebar bracket that holds the header, (image 4/5). But after drawing that idea, it seems not right. Perhaps it would be simpler to just frame the opening with steel? (I-beam-header, etc.) or maybe I need to put some kind of masonry wall back?
Thank you in advance for any help.

 

[Ron247]

You are in the right place for a student. This site requires students to use this "Student Engineer General Discussion" and no other. It's in the policy.

Also, for the most part, no one will give you final design info, even me. But we are here to help students some degree and many of us do not mind. If you are in an area that requires an engineer on residential projects, tread lightly if you are not licensed yet. If you are in college, you may wind up in trouble. Where I live, you do not have to be an engineer to modify a residence unless the building inspector gets uncomfortable with what you are doing and requests one. I have no idea about where you are. You need to find out.

Next, what you have depicted in your drawing is referred to as a "Daylight Basement" by some. It has one or more sides that are not underground. If your drawing is correct, you need a strut that can also serve as a beam for floor loads, not wall bracing. You have opposing soil loads.

If you have already removed the wall, you are already starting off in a hole, as both a contractor and as a future engineer.

 

[Ronald F.]

@Ron247 , thank you much for the reply and also confirming that I am posting in the right place.

I understand that you cannot give final design info I’m assuming due to the ethics involved in engineering. I have been working with the borough though and the people that do the inspections. So right now I’m just trying to come up with some kind of plan that I can give to them or give to a professional engineer if need be.

Can you possibly point me in the direction of any literature that may be of some help to my situation, or possibly some design examples of what a similar strut might look like?

Again, I thank you for your reply, your help, and your time.

 

[Ron247]

I do not know how far along you are in school, but this is not a design that there is a specific piece of literature that will provide guidance. It is a fairly lengthy education into loads, load paths, action-reaction, redistribution of loads when you tinker with removing components from an existing and loaded structure. I assume from your first picture, the wall was already removed since you state the picture was what you currently have.

I was a carpenter/contractor before going to engineering school. The dos and don'ts I learned in remodeling usually were learned because someone did something that would be ill-advised in the engineering world. In essence, beam design should not be that difficult if you have already had courses in the material of choice (wood, steel, concrete, etc.). The real problem is coming up with all design loads, keeping the structure stable during modifications, etc.

Here is just a sample of what I see right now in your drawing that an engineer would have thought out BEFORE removing the wall:

1. What forces are in the wall now. The soil push from the ends is pushing partly on the wood floor diaphragm and partly on the wall to remove. When the wall was removed, the load in the wall had to redistribute somewhere. I assume you braced the floor joists above, but did not consider the potential for the basement walls leaning in after removal?
2. How well did you investigate the attachment of the floor system to the ALL of the basement walls? Wall removal will most likely add load to this connection. Half the basements I have ever looked at did not have a mechanical connection, they relied on friction. The building code requires a connection generally, but OLD houses were probably built with a less sophisticated code.
3. The wood beam that runs parallel to the removed wall, has the joists setting on top if it, not framing into the side. Will removing the wall, cause more compressive load to go this beam. If so, (and it will by the way), will the beam get less stable since nothing appears to brace the bottom. The base of the columns in your picture don't look really capable of resisting much more than vertical load and a little horizontal. They will not contribute to minimizing buckling of the beam above. Here is a good basic rule to remember all through engineering. Anytime a member or some portion of it is in compression, you have a stability issue to consider. Also, whatever load shifted from the removed wall to the floor system in some fashion, most likely will not move back after the repair. Wherever it moved to, it will most likely stay.
4. Did you check for a functioning French Drain for the wall. If not, hope a heavy rain doesn't show up till you get it fixed. Heavy rain and a poor drain can add more wall pressure.
5. Did you document current conditions before wall removal.? Typically, never done, but should be. Distance from corner to corner, plumbness of both corners, any existing basement cracks etc. Measurements, digital pics. This is how you have a chance to see if removal caused a problems other than your recollection.

It is good you are working with the local AHJ (Authority Having Jurisdiction) but unless you are very familiar with this really preliminary list of concerns, don't try to think out what to tell an engineer, just let them do their thing. They will want to lay their eyes on the building, make their own assessments. They may tell you my list is too conservative, I have no idea, I am looking at a drawing and relying on my background.

 

[Ronald F.]

@Ron247 , I am still very new to engineering school, about 13% completed. I have taken some writing classes so far, calc I, calc II, physics 150, Engn 101, but no engineering science or anything that would help with this specific scenario.

To answer your question, yes the wall has already been removed, but I wasn't too worried about loads shifting or redistributing elsewhere because what i took down was barely a wall to begin with. I didn't have to do anything to the left side because it was already a garage opening with an old rotted header sitting on top, in the middle was a window with a cracked header on top, next to that was a door and a cinderblock header that was only held in place by sitting on top of the door, and on the right side was the largest section of actual wall but that had a huge crack on the side that stopped pretty much where that gusset looking section remains in my original drawing. I will attach a new drawing to you can see exactly what i took down (image 1).

I'm not too concerned with designing a beam for shear loads, The WFCM has a section for prescriptive design as well as engineered design, my main concern is when i thought about any kind of racking due to wind loads or any lateral type loads (image 2). I'm guessing with the back wall being solid and acting as a brace, the building would never be able to do that, along with the side walls being mostly underground, not allowing them to move as depicted either. but I'm still uncertain and thinking that i might need additional support. If the "lug walls" on each side were 4 ft. I wouldn't be worried at all and know that the side walls would have plenty of support, but then i couldn't fit 3 openings.

So idk, like you mentioned, there is not going to be a single piece of literature that will give me an exact answer. I'm thinking my only option is to hire an engineer for the job. Either way, thank you for sharing your insights and knowledge with me, I have also been in carpentry for most my life and just now taking a chance at doing something more with it.

 

[Ron247]

The soil on the left and right were assisting in preventing racking because while they opposed each other, the wall was the "spacer" that maintained their distance. Now, the spacer is gone and you are relying on the wooden floor system to function as a diaphragm and be the spacer Previously, it was a simple span diaphragm due to the wall being present, now it has to function 3-sided, and more like a cantilever.

How was the floor system attached to the wall? Even though the wall condition was poor, it was providing the needed load path. Also, think about how much solid wall was there before, and it was performing poorly. Imagine it being less now.

Also, 4 lineal feet of wall is not that stiff. Also, wall design, rebar embed, and other features are a necessity in shear wall design. Even though you have soil on each end, if anyone ever removes the soil on one side, there goes the offsetting loads. That is why you need to design as if there is no soil on one side.

I would definitely contact an engineer for at least a consultation at a minimum. Seismic can also be a concern if you are in a high seismic area. The building you have is more of a diaphragm and shearwall concept, than beam and post. Now you are trying to replace a poorly performing shearwall with a Beam and post system. They tend to need an area to brace.

 

[Ron247]

I am still very new to engineering school, about 13% completed. I have taken some writing classes so far, calc I, calc II, physics 150, Engn 101, but no engineering science or anything that would help with this specific scenario.

Nothing to do with your wall project; does the school you are going to have the entire 4-year curriculum or is it a community type college that provides freshman and sophomore level classes only. I see you are taking math and physics. What does Eng 101 cover? You won't get anything that deals with existing structures even in a BS degree. What you are doing is generally learned after graduation. You will get classes on steel, concrete and wood as a Junior or Senior, but nothing dealing with tinkering with an existing structure.

Calculus is not that needed in structures unless you get into some weird loadings and structures. I have never needed it. The physics that is not related to electricity and magnetism is helpful.