Strengthening an existing glulam beam
Strengthening an existing glulam beam
(OP)
I have a 19" glulam beam that will see an increase in demand due to a heavy mechanical equipment. We can deepen it to a 24" beam, but the exterior of the beam is architecturally sensitive. That is, we cannot sister steel or wood to the side for strengthening. I am calculating about 6 kips/ft of shear flow using v=VQ/I. A preliminary design would be 1" lag screws at every 4" which is way excessive.
My question is, are there any products or design guides that can allow me to increase the shear flow capacity at the interface between the 5" add-on member and the existing glulam? Either adhesive, or some kind of toothed plate that has approved capacity? Or even a split ring connector to act as a shear lug? Thanks in advance.
My question is, are there any products or design guides that can allow me to increase the shear flow capacity at the interface between the 5" add-on member and the existing glulam? Either adhesive, or some kind of toothed plate that has approved capacity? Or even a split ring connector to act as a shear lug? Thanks in advance.






RE: Strengthening an existing glulam beam
Bolt brackets to the bottoms of the GLB at each end and run a rod along the bottom - pretension it.
RE: Strengthening an existing glulam beam
h
There's design guides in there, too. They were written in the year one, but they still work. NDS also has a section on them.
I did a design a couple of years ago and used split rings to improve the connection capacity. I specified them, drew them into details, did everything but hold the contractor's hand. He of course, "forgot" them. Fortunately, the capacity still was enough without them.
RE: Strengthening an existing glulam beam
Seriously though, what about just adding beams to either side of the existing, not adjoining, but a distance away, in order to share the load?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Strengthening an existing glulam beam
http://www.diydoctor.org.uk/projects/weakbeam.htm
Only problem with this option is that it will increase the shear flow on the existing glue joints possibly to above their capacity.
RE: Strengthening an existing glulam beam
Simpson has an unpublished report of their SET epoxy being used to anchor an allthread rod into a wood beam. Not really the application you've got but it does indicated the glue will bond to wood. Of course you could use white wood glue (the drying time would be unacceptable) but at least nobody would be bitching about using concrete epoxy on wood.
RE: Strengthening an existing glulam beam
Gougeon has a new product called the West Six10. I have personally used this and it would be my choice if I were doing this again. They developed a mixing tube that mixes the epoxy correctly using a standard caulking gun. Mixing the epoxy was a bit of a nuisance when we purchased this in 5gal pales.
Another adhesive I have done some simple tests with is the PL Premium. It is rated as a structural adhesive, but I was never able to find sufficient technical data. In my little tests I did find it performed as well as the epoxy, and it is far less expensive as well as easier to procure.
Brad
RE: Strengthening an existing glulam beam
RE: Strengthening an existing glulam beam
BA
RE: Strengthening an existing glulam beam
Timber rivets are an interesting and under utilized means of making connections in some wooden structures. Your's was a clever use of them. Did you have any trouble rationalizing the concentrated end reactions of the plate tension near the ends of the glue lams where the horiz. shear is also at its max.? You would have pretty high shear transfer through the bottom laminations into the rest of the member depth. Or, did you distribute the rivets along the entire length of the cover plate?
RE: Strengthening an existing glulam beam
In my case, the beam had adequate strength, both in shear and flexure as designed but its deflection was excessive. The cover plate was primarily intended to increase the moment of inertia. The rivets were installed throughout the length of plate, but the spacing varied according to the expected shear flow. A concentration of rivets was added near each end for good measure.
BA