The engineering staff at RollingBarge.com was challenged to design a portable bridge for a gentleman with property in Alaska. Since we build Aluminum Gangways for our floating docks we basically used the same design with some enforcements to handle the load requirements The bridge had the following requirements:
- Free Span 32 feet at 8 feet wide
- Carry 2000lbs of ATV, Rider, and Trailer
- The longest piece in the kit could be no more than 12 feet long to allow the bridge to be easily transported.
- Allow assembly with only battery operated tools like a screw gun.
- Completely bolt together (no welding).
- The bridge will be installed near the coast and needed to hold up to salt air.
Before shipping we decided to completely assemble the bridge so that we could test it and get some photos. The fully assembled frame weighed about 585lbs. Before installing the deck, we moved it to a scenic location outside where we could get some nice pictures. We put a dolly under the back of the frame and set the front of the frame on a trailer towed by an ATV. Once the frame was in place we set each end up on concrete blocks so that we were truly free spanning. The next step was to set the plywood in place. Before screwing down the plywood, we leveled the bridge side to side and we measured the bridge corner to corner to make sure everything was even. With the deck in place, it was time to give it a try! Our ATV and rider was probably only 650lbs and the trailer was probably less. We were looking to get a better test so… …we grabbed a nearby Toyota Previa and drove on up. The deck is 5/8” thick fir plywood and the joists are on 24” centers. This is not designed to carry the lbs per square inch that would be generated by the little mini-van tires. So we covered the deck in 2×6 boards to help distribute the load.
While this is more load than this particular bridge is warranted for, the engineering shows that it should support this weight at rest and still have a safety factor of 3.0 (this means that forces three times greater will be required to break something).
Properly assembled and installed, this bridge should provide a lifetime of trouble free service as an ATV bridge in the wilds of Alaska or wherever it is placed.