Building an Arched Wooden Bridge
Step 1. Making the template for the arch
To make the arch template, 3 stakes will need to be hammered firmly into the
ground and braced opposing the bending forces (see picture).
Space the stakes as per the dimensions shown in the accompanying picture.
The arch beams are made by bending and gluing and screwing four lengths of 90mm x 19mm (3/4" x 3 1/2") treated pine together.
When the glue is dry (the next day) this newly made laminated arch beam can be ripped (cut) down the middle (lengthwise) to create two arch beams for the base of the bridge, one each side. (See Step 4 "cutting the arch boards")
The arch handrail is made the same way, using the same template.
Step 2. Making the laminated arch beam
Bend a piece of 90 mm x 19 mm (3/4" x 3 1/2") knot free board, 2400 mm (8ft) long, between the arch template pegs. Bend a second board against the first, putting a generous amount of glue between the two boards.
Repeat this action until four boards are in place forming the arch.
Clamp the boards together and also screw along the arch approx every 300 mm (12") with 50 mm (2") stainless steel screws on both sides.
Ensure no screws are placed along the center line of the arch beam as this line is to be cut.