What is tgi joist?

TGI is the common name for a TJI, because it rolls of the tongue easier.

It is a Truss Joist I-beam. They come in a variety of depths, typically 9-1/2" to 16" and they come in different levels, 100, 200, 300, etc...

They consist of a top and bottom cord - which can be 2x3, 2x4, or an equivalent sized engineered wood material depending on the level. And between the top and bottom cord is OSB around 3/8" thick, again depending on the level.

They are similar for construction purposes to dimensional lumber (2x10 or equivalent) in that you order up a stack of a certain length and cut them to length as needed. They don't need X bracing but can require extra "squash" blocking under bearing walls.

They have small knock-out holes for wiring and can have holes cut through them, based upon certain criteria. For example, a 14" deep TJI can have up to an 8-1/2" hole, in certain locations. Can't do that with a 2x10.

Depending on how your floor system is designed, it can be just as rigid as any other floor system. If you go 24" o/c with 3/4" sheeting, most floor systems will give you some bounce. So add a couple of joists and go 19.2" or 16" o/c.

The drawback with TJI over dimensional or open web, is the burn-through time. A 2x10 or a 2x4 constructed open web will last longer in a fire than a TJI. Rumors that I've heard say that a fireman will never own a house with TJI's. Supposedly they could burn through and collapse within 5min. But that could always be overcome with a product like No-Burn which reduces the flame spread rating of lumber to make it practically non-combustible.