I have poor knowledge of strength calculations and would like help with a project I am planning. I am going to build a bridge with a span of 7-8 meters. The idea is to build 2 load-bearing beams from pressure-treated timber 45 x 195 Class C24. Attached is a sketch of what I am planning. The idea is to bolt together 3 pieces of 4800 mm beams with M10 bolts which I place at cc 400. The requirement is to be able to load with about 1 ton. Will this work?
I am really not an engineer, but I calculate that a single 45x195 beam of C24 quality, which is 8 meters long, bends 34 cm at a midpoint load of 1 ton (simply supported).
The moment of inertia scales linearly with the width of the beam, so a corresponding beam that is 3x45 mm wide bends one-third as much, i.e., just over 11 cm.
With such a triple-wide (3*45)x195 on each side of the bridge, the deflection should be half if the load is symmetrically distributed, i.e., approximately 5.5 cm.
Doesn't feel completely rigid. What happens when you make a (3*45)x195 by bolting together several 45x195 as you have drawn, I have no idea. Reasonably, the strength should be worse compared to a single solid beam?
Calculated with an 8-meter long 45x220 instead, the deflection becomes only just under 2.4 cm instead of 34 cm, i.e., just under 4 mm with two beams (3*45)x220. The height of the beam is your friend, not the width! Deflection scales with (1/beam width) but (1/beam height^3)!
Hi
Don't do that, you're essentially building a hinge.
Glued laminated timber beam, is that an option?
Iron beam? My bridge at home is probably 8 meters, it has an iron beam and is sturdy to walk on.
Tell me more about what you're thinking, what you want to achieve, and what it may cost?
