On the other hand, you can home-build a completely glued boat. It's not like you're in a factory, working with clean new lumber and tight temp & moisture control. I'm not sure I trust site-glued connections, for structural work. If you are planning to put ceramic tile on the floor I suggest you reconsider because of the compromised stiffness of the structure. Someone should stand by with a fire extinguisher and the wood should be shielded and wetted before welding in the area. You would have to be very careful about starting a fire when working around that old wood. Someone would have to design the truss and attachments. If you want to do it with steel, then someone skilled with a welder could fabricate an open truss around those pipes to carry the loads. It is certainly possible to replace the support with a shallow steel beam but it would be expensive unless you can get steel for scrap prices or less. However, it would wreck that tounge-and-groove floor that appears to be installed in the area. I can't tell enough about the details but that might be the easiest way to do it. If you were to remove the floor above you could reinforce the area by putting a 4x8 ft piece of 3/4" exterior grade plywood on top and bottom of the joists, running the direction of the joists, glued and screwed, to make it into a box girder. Those 2x4s that look like headers will not do anything but provide local support to the floor if they are cut off where they intersect that joist, and they will probably have to be removed to allow you to properly reinforce that joist. That joist with the notch looks like it is cut almost all the way through at the top. As described above, you don't want to put in as many nails as would be required without glue. The purpose of the nails is to clamp the parts together until the glue cures. The best repair to achieve both the strength and the stiffness of the original joist is to GLUE a reinforcement both above and below the cutout so the repaired joist has properties of an I-beam. There are special timber fasteners that are designed to carry greater loads but they are not practical for this application. Therefore, to develop the tension capability of a reinforcement to replace that material at the bottom of the beam where the notch is cut out would require 6300/150 = 42 nails ON EACH SIDE OF THE NOTCH.īolts are not any better because the limit of strength is the bearing strength of the wood. A 2x4 reinforcement with an area of 1.5 x 3.5 = 5.25 square inches, and an allowable tensile stress of about 1200 psi, has a tension capability of 6300 pounds.Ī 10d nail has a design load capability of maybe 150 pounds. You would still have a soft floor because you would need 9 of them to replace the stiffness.Ī reinforcement is not effective unless it is attached in a manner that transfers the load to the reinforcement. To replace the strength of the joist with 2x4s you would need 4 of them, and they would have to be secured to the joist adequately to carry the load across the cutout area. Therefore, a 2x8 at 7.5" deep is 4.6 times as strong and 9.8 times as stiff as a 2x4 that is 3.5" deep. The strength of a rectangular beam or joist varies as the square of the depth, and the stiffness to resist deflection varies as the cube of the depth. Here is some rationale for what works to reinforce a joist. If there is less than 3" of solid wood at an edge, add a reinforcement on one side. If the joist is cut through to the edge, put the reinforcement on both sides. The reinforcement should extend from the edge of the joist to the pipe. The easiest way to repair a situation that has been described would be to get some good quality kiln-dried 2x4s and 2圆s, a good supply of carpenters glue, and a framing nailer with lots of nails.Ĭut and fit pieces of the reinforcing material long enough to extend about 3 ft past the damaged area on both ends, and glue and nail them on the sides of the damaged joists. You would need to put that large number of fasteners in a steel strap to attach it securely to the wood. If you look at the splice plates on both sides of the lower chord of a wooden truss you get some idea of the number of fasteners required to connect to a wood structural member. Also, the strap doesn't replace the shear strength of the beam so it would be necessary to insert a substitute for the "web" of the beam and fasten that web to the steel. The problem is that it is very difficult to fasten the steel to the wood with enough fasteners to transfer the loads to the steel. Replacing some part with a piece fastened on, such as a steel strap on the bottom, is really making it into a composite joist. "Sistering" a damaged joist with steel requires engineering, unless you are replacing the full strength and stiffness with the "sistering" piece.
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