Reinforce wooden beam

[verktygsgurun]

Once, I had to make 120mm holes in the joists of an old house to install plumbing. The joists were approximately 170mm, and I did as you are planning. Plates on each side of the beam were screwed and glued. It became super stable! It has since been covered with self-leveling compound and tiles, and nothing has cracked yet. (3 years ago now)

 

[Marre666]

Once I had to make a 120mm hole in the joist in an old house to be able to run plumbing. The joist was about 170mm and I did just as you are planning. Metal plates on each side of the beam that were screwed and glued. It became super stable! It has since been leveled with self-leveling compound and tiled, and nothing has cracked yet at least. (3 years ago now)

What thickness did you use?

 

[GK100]

If you can access both sides, perform the operation with sheet metal there as you initially planned and choose something less cumbersome than 10 mm, for example, 4-5 mm on each side. Screw as protte suggested reasonably on the top and bottom edges of the strips, and if you set cc 200 mm, stagger 100 mm between the sides so the screws essentially sit in a triangular shape similar to the nodes in a truss. Pre-tension upwards a bit before you glue and screw, and it will be really good. Attempting to create an I-beam afterward by placing sheet metal under the wooden beam is likely worse and more difficult to get right.

 

[verktygsgurun]

Don't remember exactly but 4-5mm.

 

[Marre666]

Thank you all for the help, I will probably go with 5 mm steel plate screwed on both sides! 👌 I'll come back with pictures and how the result turned out/feels.

 

[prototypen]

Quote from the investigation

The glue is assumed to provide a perfect connection between the wood laminates and between wood and steel.
 Only a small number of wooden beams are tested in each configuration, which means that statistical certainty cannot be established.
 No long-term effects on the glued laminated timber beams are investigated.

The investigation was done only with steel at the top, bottom, or both, with both being thinner than single-sided.
Then it was with perfect glue and long-term effect, an event from real life.
The sports hall at Hagaskolan in Umeå had a roof construction with steel and wood, and it contributed to the roof collapsing under the weight of snow.

Steel and wood move differently, so the glue will be subjected to high forces just from that, and then the glue has to support the construction as well.

Place the plate on the side, a U beam is stronger for the same weight but use a thicker plate.

Protte

 

[GK100]

Two thinner ones are better than one thick one, and we can see the glue as an extra luxury, not something entirely necessary.

 

[Marre666]

Hmmm, this isn't easy ;0

The prototype:

Do you think I should use U-channel on one or both sides and 10 mm thickness? Does the height matter or is 100 mm sufficient?

Regarding screws, is 6 mm sufficient and should I countersink them?

 

[prototypen]

200 mm is four times stiffer than 100 mm.
I would go for flat sheet metal, looks the least unsightly and will reduce the flex in the floor.

Protte

 

[smurfen72]

But can I just as well use sheet metal then, or does the U make it much stronger than a regular flat sheet metal... sorry for all the questions, but I need to be completely sure before I proceed, and I've caught a bit of "Tröghetius Dummus" today 😀

The U prevents it from buckling as easily, and as previously explained, it becomes 2 flat irons separated by a standing plate, which provides the strength. If you want to further reinforce the U-beam, you can weld web plates into it, but that shouldn't be necessary if it's attached to the wood.

 

[Kaboff]

hand up on steel plate on both sides bolted together anyone against

 

[Björn Melander]

Most suggestions, including your own initial proposal, will likely work just fine. It's probably more about what is most convenient for you and the construction height. If you plan to use steel plates, you can bend L-profiles on each side that are screwed together without glue. Regarding the K-Plyfa I mentioned in my previous post, you'll get significant reinforcement against deflection in the span intended here if the plywood is centered. I've reinforced flooring that way with good results. However, if it's about extremely large point/line loads, you might need to have an engineer calculate it.

 

[roli]

Why complicate things when a plate at the bottom is sufficient? When reinforcing a beam, steel or wood, you want the center of gravity of the reinforcing area as far from the neutral axis of the beam as possible. Installing a plate on the side of the beam does not provide as much reinforcement as placing it on the bottom of the beam, far from the beam center.

The goal is to increase the beam's bending resistance (W-value), and when you examine the formula for calculating bending resistance, it quickly becomes clear where reinforcements should be placed. Simply placing a reinforcing plate on the bottom (taking the tensile stress of the beam) requires there to be something that can take compressive stresses on the top side if you want to maximize the benefit of the reinforcement. It could be a floor material on top of the wooden beam. We don't really know how it looks in this case.

All the variants that have been presented provide reinforcements to the wooden beam, but if you want to use as little reinforcing material as possible and achieve maximum reinforcement, the reinforcing plate should be placed at the bottom of the beam and fastened with the most screws at each end. In the middle, almost no screws are needed.

 

[Stefan1972]

Why complicate things when a plate at the bottom is enough? When reinforcing a beam, steel or wood, you want the center of gravity of the reinforcing area as far from the neutral axis of the beam as possible. Mounting a plate on the side of the beam does not provide nearly as much reinforcement as placing it on the underside, far from the beam center.
It is the beam's bending resistance (W-value) that you want to increase, and by studying the formula for calculating bending resistance, it quickly becomes clear where to place reinforcements. Simply placing a reinforcing plate on the underside (which takes the beam's tensile stresses) requires that there is something to take the compressive stresses on the top if you want to get the maximum benefit from the reinforcement. It could be a flooring material on top of the wood beam. Now we don't really know what it looks like in this case.

All the variants presented provide reinforcement to the wood beam, but if you want to use as little reinforcing material as possible and achieve maximum reinforcement, the reinforcing plate should lie at the bottom of the beam and be screwed down with the most screws at each end. In the middle, almost no screws are required at all.

What you say is true in theory but not in practice. You will never get it fastened so tightly that you can utilize these forces. Furthermore, there will be some inherent deflection since the rest of the house is made of wood and will flex.

 

[Marre666]

Tested holding a 10 mm flat steel today, if you hold it flat it bends and "wobbles" a bit, but if you set it on its edge it doesn't move a mm!

I don't understand how a lying flat steel against the underside of the wooden beam would make much difference, the weight, etc., will bend it?!