Bar joist Retrofit and Modification

[Luke Goedecke]

I am looking to make an approximately 6'0" x 8'0" hole in an existing 4"concrete floor structure. This is to allow HVAC equipment to be installed in the attic
It is going from the 2nd Floor to an attic. This is merely an access hole. It is my intent to infill the concrete opening later with a Shaftwall system whereby in the future there will be an access point to load equipment into the attic.The A/E has proposed ripping out all the concrete and barjoists and then replacing it from wall to wall and installing W12 beams which I believe is major overkill. Can anyone provide any connection detail to remove and retrofit the barjoists as I want to do?

 

[SteelPE]

Have you approached the A/E with the idea you are asking here? Maybe there is a reason why the A/E would like to just take the joists demolished and replaced? I think if you were to have a conversation with the A/E laying out your reason for why you think it should be done differently other than "it seems like overkill".

It does seem to be a bit much, but then again, your joists are probably small, and making modifications to small members is not an easy task. There just isn't much surface to weld to. I have taken part in many joist modifications in the past. I have seen about 40% of them messed up due to lack of knowledge and attention to detail.

 

[dhengr]

Luke Goedecke:
You need a 6’x8’ opening, so the Arch. decides to cut a 12’x22’ opening out of the slab, new beams and all? That’s real economy. That was his first and only thought, and he could pick it out of a beam table without having to think. Look at something which may be easier than snaking old SJ’s out and new W12’s into the bldg. Saw cut the conc. slab down the center of two SJ’s, 8’ apart, nicking the top 2/3rds of the stl. deck. Break the conc. out and remove the stl. deck, taking care not to damage the existing SJ’s. Move two SJ’s left and two right, to be tight against and tied to the existing unmoved jsts. Then, header across btwn. the pairs of triple jsts. to provide about a 7 or 8’ opening. The bearings on the headers bear on the top of all three SJ’s at each end, and at a SJ panel point which may need some reinforcing. Infill the 8’ wide slab space with some thin precast slabs, of some sort, which span about 7’, 8’ & 7’ = 22’. This usually gets you about the same max. shear on the SJ’s and a slightly smaller max. moment and deflection at the center, if you’ve taken good care of the SJ’s in moving them. Obviously, you need some special attention at the bearings of the triple SJ’s at the ext. walls.