glulam reinforcement 1

[kauri]

Hi, I'm trying to strengthen an existing glulam beam. I plan on nailing/bolting a steel plate to the underside of the beam. I've done calculations for the bending stresses in the glulam and steel sections; from my understanding the bolts should have to resist the difference in stress between the glulam and steel. In this case stress in the glulam is 4000kPa, and in the steel 100,000kPa. This is impossible for the bolts to resist. Where am I going wrong in my understanding?

For reference, span is 7.1m, glulam section 90x450 GL8. Calculations attached.

Also, I've looked into bolting the plate to the side, but I don't want to ruin the structural integrity of the glulam. Also there doesn't seem to be steel plates the full depth of the section available. Does anyone know of a way to do this?

 

[JoshPlumSE]

You want to calculate the FORCE transmitted through the bolts/nails. You could calculate shear flow and such.... Or, just calculate the total force in the steel plate and make sure the bolts can handle that. Bolts themselves as well as bearing against each of the base materials.

 

[kauri]

For shear flow that would be τ=VQ/It? If that is the case then I might go with nails - how do I consider the required withdrawal strength?

 

[BAretired]

How about using glulam rivets in pre-drilled holes through the plate? You are concerned with shear strength, not withdrawal strength.

BA

 

[struct_eeyore]

just be careful - I dont know how you are bolting this thing together, but just be sure to check the shear flow between all the plies in the glulam in your final design.

 

[BAretired]

The beam is 90 x 450 and a 10 x 90 plate is to be fastened to the bottom of the beam.

I did a similar strengthening many years ago using glulam rivets. The beam was jacked up at midspan to relieve dead load stresses before driving the rivets. It worked very well.

BA

 

[kauri]

Thanks BAretired! The calculations using the Australia NZ rivet design guide was hefty but I'm really happy with the solution! Thanks for mentioning that you jacked it up too- I hadn't thought of that. I'm still a rookie haha

 

[BAretired]

You're welcome kauri. I hope it works as well for you as it did for me.

BA