Wood Joists on top of central Steel Support Beam

Miacol · Sunday at 7:03 PM

I will replace an insufficient wood support beam with a steel W or H beam.
The joists sit on top of the beam. Because it is an old house there is a lot of electric and plumbing over the beam so I cannot raise the beam.
Currently the joists are nailed (actually ledger screwed) to the wood beam.
Note it is a central beam with the joists going from the beam to the outer walls on both sides.
Question 1: When I replace the wood beam with a steel beam, do I also have to attach the joists to the new steel beam, or can the joists "float" on top??
Question 2: To attach, can I drill a small hole in the flange under each joist and use a structural screw? (I guess not allowed!)
Question 3: Or should I weld an angle bracket to the top of the steel beam (How easy is this to do? It is not easy to access above the beam).
Question 4: To keep the welding effort to a minimum, can I weld the angle bracket on only one side of the joists, then add wood blocking between joists over the beam?
Question 5: Does the angle bracket need holes so I can drive a nail into each joist?
Question 6: Can any angle bracket be used or do I need a special kind that can be welded?
Gee that is a lot of questions! So I numbered them to make it easier to understand.

RontheRedneck · Sunday at 8:15 PM

I would assume that the top flange of the beam has to be braced. (Unless you analyze it as un-braced) So you can't just set joists on top f it.

The most common detail I see around here is a 2X plate bolted to the top flange, and the floor joists nailed to it.

SE2607 · Sunday at 8:38 PM

RontheRedneck said:
I would assume that the top flange of the beam has to be braced. (Unless you analyze it as un-braced) So you can't just set joists on top f it.

The most common detail I see around here is a 2X plate bolted to the top flange, and the floor joists nailed to it.

I recommend a 4x nailer on top of the steel beam. If a 2x is used, the bolts attaching the nailer to the steel beam would project above the nailer and would interfere with the joists. With a 4x nailer, the nailer could be counter bored to receive the nut and washer so that the welded stud does not project above the nailer.

Eng16080 · Sunday at 9:13 PM

I'd consider it bad practice to not connect the joists to the beam. If you were going to do this, though, then you should design the steel beam as laterally unbraced for its full length. This will likely result in a much larger beam section, and any savings in not providing connections will probably be offset by the extra cost of steel.
I've used this detail a few times. It's unconventional and requires a high level of coordination if the holes will be shop drilled, but I see no reason why it can't work.
I would avoid field welding due to the fire risk. (I was involved in a renovation project once where a fire started due to field welding. The building was essentially destroyed.)
Again, I recommend not welding.
I wouldn't use a steel angle connection, although if you were to do this, I would have the angle provided with shop drilled holes and then have field drilled holes in the beam top flange, with bolts to connect them. Or you can shop drill the beam holes if you're really confident that you have the locations correct.
As mentioned above by others, a wood top flange nailer which would be bolted to the beam top flange is preferred in this situation. From there, you can make a wood to wood connection. I would probably have the joist locations field measured and then the beam fabricated with holes set in locations to miss the joists (and any other obstructions). That way you can avoid countersinking the bolts. If the total beam depth is critical, I would typically just use a 2x (1.5" thick wood nailer). I also wouldn't be overly concerned with countersinking into a 1.5" thick plate if you have to, as long as you're not removing more than half the thickness (0.75"). If the nailer will add too much depth to the assembled beam, then use the method from Question 2.

SE2607 · Monday at 3:13 AM

Eng16080 said:
I'd consider it bad practice to not connect the joists to the beam. If you were going to do this, though, then you should design the steel beam as laterally unbraced for its full length. This will likely result in a much larger beam section, and any savings in not providing connections will probably be offset by the extra cost of steel.

If the nailer was attached to the steel beam with a nailer and welded studs, and the framing had a positive connection to the nailer (A35s, TNs, etc), then I would consider the top flange of the steel beam laterally braced.

Eng16080 said:
I've used this detail a few times. It's unconventional and requires a high level of coordination if the holes will be shop drilled, but I see no reason why it can't work.

That's why I suggested a 4x nailer. The hole can be counterbored so that the threads, nut and washer are at or below the top surface of the nailer.

Miacol · Monday at 3:26 AM

Thanks all. I do have a height requirement. I need the basement height from finished floor to finished ceiling under the beam to be 6'-6" for livable space requirement.
So a top nailer will probably not be ok. (The wood beam I am replacing is 8" depth nominal, sagging and is well under the 6'-6" ceiling height. I am hoping to replace it with steel H beam w/ 6" depth to just satisfy the ceiling height requirement. So a nailer on top won't do.
So the nailer is bolted onto the beam through the flange? Then the flange can be drilled through?
That was my Question 2.
I suppose I could drill on site, straight up through the 3" flange into the joists. I could alternate with left side of flange, then right side of flange, so the holes are 2x16" apart. Any idea what hole size or screw I should use? And I will need to research how these holes affect the beam calculation.
Is there any objection to this approach?

XR250 · Monday at 11:17 AM

SE2607 said:
I recommend a 4x nailer on top of the steel beam. If a 2x is used, the bolts attaching the nailer to the steel beam would project above the nailer and would interfere with the joists. With a 4x nailer, the nailer could be counter bored to receive the nut and washer so that the welded stud does not project above the nailer.

2X nailers are used all the time without issues and saves 2" of beam height. They can counterbore carriage bolts. I have seen 3/8" carriage bolts used and just cranked down and they get pulled flush without counterboring.

Eng16080 · Monday at 12:56 PM

SE2607 said:
If the nailer was attached to the steel beam with a nailer and welded studs, and the framing had a positive connection to the nailer (A35s, TNs, etc), then I would consider the top flange of the steel beam laterally braced.

I agree. (I wasn't meaning that the joists had to be connected directly to the steel beam.) I would probably use shop holes and bolts rather than welded studs. I called for welded studs on a recent project for this exact purpose and was told it's much more costly than drilling the holes and providing bolts. I imagine this might be shop dependent though.

SE2607 said:
That's why I suggested a 4x nailer. The hole can be counterbored so that the threads, nut and washer are at or below the top surface of the nailer.

FWIW, I often do the same with a 2x nailer and 1/2" bolts. I don't think it's an issue if it's the bolt head that's recessed (versus the nut end), at least for normal loading. If the bolt was in tension, then I'd probably use a thicker plate like you do.

gte447f · Monday at 7:57 PM

So the nailer is bolted onto the beam through the flange? Then the flange can be drilled through?
That was my Question 2.
I suppose I could drill on site, straight up through the 3" flange into the joists.

Of course the flanges can be drilled, but not easily in the field, and not by a low-end contractor. Typically this fabrication should be done in the shop by the steel supplier, so it has to be a real steel fabricator, not one of these on-line steel beam warehouses. The cost of such fabrication is usually not anticipated and accounted for by low-end contractors. Also, if the locations of the holes are critical and must be coordinated to align perfectly with the locations of the existing, in-situ joists, that complicates things and is an opportunity for error. Also, think about your entering and tightening clearances (even though we are talking about screws instead of bolts) for installing a screw through the top flange from the bottom. There is not much space between the flanges of a W6 for screw, cordless drill, etc. These are just some of the reasons that a wood nailer on the top flange is preferred. If you do drill the flange of the beam, then yes, you should analyze the beam for any reduction of bending capacity.

The architectural constraints of this beam installation sound a little unreasonable or unwise to me. Using a 6 inch beam to just barely meet a 6'-6" head clearance for habitable space? I would suggest trimming the joists and setting the beam up into the floor space so that you can use a reasonable beam depth and achieve a reasonable head clearance. Reroute MEP as needed, although I'm sure that will be vetoed due to the time, effort, and cost associated with the MEP.

I assume you have already ruled out an engineered wood beam as a viable alternative?

XR250 · Monday at 8:33 PM

gte447f said:
If you do drill the flange of the beam, then yes, you should analyze the beam for any reduction of bending capacity.

I have honestly never done this as every I-beam I have ever designed was serviceability controlled and not even close to yielding - especially now with 50ksi the norm.

gte447f · Monday at 8:50 PM

XR250 said:
I have honestly never done this as every I-beam I have ever designed was serviceability controlled and not even close to yielding - especially now with 50ksi the norm.

Same here usually, and if you have a level of comfort based on your experience and engineering judgment, then fine, but based on the OP's questions, my impression is that they should do the analysis to make sure.

SE2607 · Monday at 10:03 PM

XR250 said:
2X nailers are used all the time without issues and saves 2" of beam height. They can counterbore carriage bolts. I have seen 3/8" carriage bolts used and just cranked down and they get pulled flush without counterboring.

Often, in my cases, the steel beam is either a drag strut for lateral loads or part of a moment frame. Therefore, I need the "meat" to transfer the shear from the sheathing, through the blocking in the joists, through the nailer, through the welded studs into the steel beam. By the time you c'bore a 2x to allow for the washer, head and a few threads, you would be lucky to have an inch of material to facilitate that transfer. If you are talking about a carriage bolt heads, then you have to drill the flange. Welded studs, in my area, are cheaper because the welding is automated.

Miacol · Tuesday at 3:28 AM

Thanks all again.
Yes, above the beam is all the MEP, plus HVAC tubing, all needing re-routing, plus a rough framed bathroom that will need to come down.
So it is costly to raise the beam flush with the ceiling.
I am hoping steel will save me from doing this.

I've got 2 new ideas though:
New Idea 1: Pack the H beam with 2 2"x5" LVL's, on each side of the web. Bolt both sides together through the steel web.
Since the 6"x6" has flanges about 2.75 inches on each side (because of the web thickness), the LVLs will stick out about 3/4 inch (1.75"+1.75"=3.5").
Under each joist I attach an angle bracket to the LVLs and joist.
So I get a higher beam, stronger than LVL, and attached to the joists.

New Idea 2: Sister two 6" deep C-Channels to the original LVL beam, bolted together through the LVL beams with 1/2" bolts. Since the LVL is already attached to the joists, that problem is solved. The double C-channels are likely stronger than the original LVL beam.
I'll have to rip off the bottom inch or so from the LVL before I attach the C-channels and so I'll need to support the beam with a temporary post.
So I get a stronger, higher beam attached to the joists! Plus I don't need to rip out an old beam!

Any thoughts?

Thanks again!

bones206 · Tuesday at 11:56 AM

You can also consider PAFs for nailer attachment. contractors seem to love it.

gte447f · Tuesday at 2:58 PM

@Miacol What is the size and span length of the existing LVL beam?

Also, how are the existing joists connected to the existing LVL beam? You said "ledger screwed", but I don't know what you mean by this. Are they toe-nailed, but with screws?

I think both of your new ideas have some merit if you cannot set a new beam up into the floor space.

For New Idea 1, you will need a lot of holes in both the steel beam web and the seat angles. I assume you will get all those holes shop fabricated ($$).

For New Idea 2, to address in-situ sagging, you will need to jack up the existing LVL beam before reinforcing with steel channels, but it sounds like you are planning to do that already. Even so, when reinforcing wood with bolted-on steel, I am a little skeptical that you get the full effect of the reinforcing until some deflection has occurred, so actual deflection may be greater than theoretical deflection calculated for the reinforced beam section.

Miacol · Wednesday at 3:31 AM

The beam is 10', triple 2'x8" LVL (nominal), with lots of MEP fixtures attached.

I see there are some long structural screws (red color, the kind used for sistering LVLs, or maybe for attaching a deck to ledger board) toe-nailed through the top of the beam 45 degrees into the joist above, on one side. I should add some to the other side too.

For New Idea 1, I will get the holes in the web done by the fabricator, based on a pattern to be determined. For the screws I wanted to use 3 5/8" LedgerLok Flat heads.
For the angles I thought I could use an HL33, but the bolt size says 1/2" which is too big. Maybe the steel shop can make some angles.
A hard part for this solution is ripping out the old beam.

For New Idea 2, I am confused about the physics. Say the LVL beam sags by an inch. I should lift it to be horizontal before sistering on the steel C-channels?? Is that correct??
Once the C-channels are bolted on, I assume the wood LVLs won't contribute at all to the strength of the new composite beam. I count them simply as dead weight, or "added load" on the beam. So I assume the sag will be way less than with the original wood LVL beam alone.
I am thinking the "double C-channels" will be close to, say 95%, as strong as an H beam of same size. But my head is spinning! so I might not be thinking clearly.

I think New Idea 2 is easier than New Idea 1, so I am leaning toward it. I can have the manufacturer drill holes on one beam, but then I need to drill through and find where the drill contacts the C-channel on the other side, then drill the hole there, and bolt them. The logistics give me a headache.

gte447f · Wednesday at 12:42 PM

@Miacol What is your role in this project? Are you a structural engineer? If not, you should hire one. Are you performing this work yourself? Is this a DIY project? What is your goal with this project? Have you actually analyzed the existing beam to determine if it needs to be reinforced or replaced. Have you actually measured the deflection and determined that it is excessive?

For New Idea 1, if you want to use prefab Simpson clip angles, then use whatever type and size Simpson screws will work with the chosen clip angles. Otherwise, get the steel shop to fabricate custom angles and use whatever fasteners you like. Either way, my preference would be for the vertical leg of the angle that will be fastened to the wood ledger board (that is attached to your steel beam) to have at least 2 holes for stability to prevent any side to side rotation.

For New Idea 2, any load on the beam before the reinforcing is installed will remain on the wood section and will not be resisted at all by the steel sections. Any new load placed on the beam after reinforcing will be shared by the wood section and the steel section in proportion to the respective bending stiffness of each section. Any existing deflection of the wood beam will also remain unless you jack up the beam before and during installation of the steel reinforcing. Jacking up the wood beam prior to installing the steel reinforcing also has the effect of "removing" the existing loads on the wood beam, so that after the steel reinforcing is installed and the jack(s) are removed, all of the load will be shared by the wood and steel in proportion to their stiffnesses as described above.

What I meant in my previous post when I mentioned that the actual deflection of the reinforced beam might be greater than the theoretical calculated deflection of the reinforced beam is based on my belief that there is some slop in the reinforced system that will have to be taken up and equalized before the loads are truly shared the way that we idealize them. For example, slop between the through bolts and the bolt holes will allow some deflection before loads are fully transferred between wood and steel. If all of the loads are introduced through bearing on the top surfaces of the wood and steel simultaneously this won't be an issue, but if the loads are introduced through bearing on the wood and must be transferred to the steel by the through bolts, then it is an issue. Regardless, this effect should be marginal, but it still might result in actual deflections marginally greater than theoretical calculated deflection. Even so, if done correctly the deflection of the reinforced beam will be less than the deflection of the unreinforced beam.

I don't necessarily think that New Idea 2 is easier than New Idea 1. In fact, I think New Idea 2 is likely to be less reliable at achieving the desired outcome if you do not fully understand the mechanics of how to properly reinforce the existing beam. New Idea 1 is very basic, in that the procedure for removing an existing beam (or wall) is performed routinely in repair and/or remodeling projects. For New Idea 1, you should note that to remove the existing beam you will need to temporarily shore the existing floor joists, and of course, if you want to remove the existing deflection, you will also have to jack up the existing floor joists.

One more note about New Idea 2: there is no reason to have to drill either of the steel channels in the field. They should both be drilled or punched with the correct matching pattern in the shop, then you simply drill the holes in the wood beam to match the pattern, using one of the channels as a template or whatever, and then mate up the channels on opposite sides of the beam. You should avoid drilling any structural steel in the field. Without the proper tools, it can be difficult to nearly impossible.

XR250 · Wednesday at 12:58 PM

gte447f said:
One more note about New Idea 2: there is no reason to have to drill either of the steel channels in the field. They should both be drilled or punched with the correct matching pattern in the shop, then you simply drill the holes in the wood beam to match the pattern, using one of the channels as a template or whatever, and then mate up the channels on opposite sides of the beam. You should avoid drilling any structural steel in the field. Without the proper tools, it can be difficult to nearly impossible.

If you are trying to save money, they can be field drilled. Just need a nice drill, some good bits and oil. A Drill doctor is nice to use every 5 or so holes to sharpen up the bit. Start with 1/4"Ø and go to 3/8" and then 1/2" Time consuming but actually quite cathartic (for me anyway). I have done a dozen or beams this way. I have a portable drill press that clamps on to the beams and makes it a lot easier. You could also rent a mag drill. Not sure how much you would save at that point.

gte447f · Wednesday at 1:28 PM

XR250 said:
If you are trying to save money, they can be field drilled. Just need a nice drill, some good bits and oil. A Drill doctor is nice to use every 5 or so holes to sharpen up the bit. Start with 1/4"Ø and go to 3/8" and then 1/2" Time consuming but actually quite cathartic (for me anyway). I have done a dozen or beams this way. I have a portable drill press that clamps on to the beams and makes it a lot easier. You could also rent a mag drill. Not sure how much you would save at that point.

Great to know. Thanks for sharing your experience. Have you mainly had success field drilling steel before installation, meaning when you can freely maneuver the pieces for best access? What about in-situ pieces? I would imagine that access to and orientation of in-situ pieces could effect whether or not you can maintain proper alignment and adequate pressure for drilling. Has that been your experience?

I still advise clients against it, because not everyone is as industrious and conscientious as you.

P.S. Are you a contractor as well as an engineer, or were you in a past life?

XR250 · Wednesday at 2:06 PM

gte447f said:
Great to know. Thanks for sharing your experience. Have you mainly had success field drilling steel before installation, meaning when you can freely maneuver the pieces for best access? What about in-situ pieces? I would imagine that access to and orientation of in-situ pieces could effect whether or not you can maintain proper alignment and adequate pressure for drilling. Has that been your experience?

I still advise clients against it, because not everyone is as industrious and conscientious as you.

P.S. Are you a contractor as well as an engineer, or were you in a past life?

Never done it in-situ although my steel guy has done that for me. He uses what is called a reamer bit in his 1/2" hand drill. Drilled 4 holes in about 1/2" thick material in about 15 minutes.
Not a contractor but have built 3 houses for myself that contained a fair bit of steel. It does take a fair amount of pressure.
Around here drilling the holes costs as much as the beam itself so i saved a fair chunk of change doing it myself if I don't count the opportunity cost of my time LOL.

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