The basic type of bridge is the beam or girder bridge. The process of building a beam bridge, while requiring a crane and other specialty construction equipment, is fairly straightforward. It is the least expensive and most used type of bridge for underpasses and other narrow spans. Here is how to build a beam bridge.
Placement and Design
Determine the placement of your beam bridge. Take into account traffic patterns, conditions of the soil and span length. For an overpass it may make sense to cross at an angle other than 90 degrees because the surrounding roadway may call for such a thing.
Specify the materials to be used to build the beam bridge. Pre-stressed concrete, which is concrete with metal in it called "rebar" that has been pulled taught while the concrete is curing, is most commonly used for smaller beam bridges. As the name implies, a steel girder is also sometimes used.
Make calculations and design drawings for the construction company to complete the bridge. These are required for approval from your governing authorities. A structural engineer who has overseen the project's design should stamp the drawings with an engineer's seal.
Cost Estimation and Bidding
Do your takeoffs from the construction drawings. For this you should have a good construction estimator who is familiar with the necessary items needed for a beam bridge or girder bridge project.
Create an itemized bid to build the beam bridge. This will include every item and the estimated labor cost for the placement of each item. For instance, you may need to include crane rental for placement of the girder.
Submit your bid. In most governing authorities, these bids are submitted closed, then opened at the same time at a special meeting.
Break ground. The first thing that will be needed is to prepare the surrounding ground to support the beam of the beam bridge. Build up or excavate as necessary to get to the elevation and distance required.
Compact the filled earth and prepare the cut earth for the concrete abutment pour. This will include compaction machines and even dynamite to level off any places where you've hit bedrock.
Pour the abutments. The design will call for a concrete pour with rebar already in place, if the pillars are concrete.
Lift the steel girder or girders in place. This is most likely pre-fabricated to the engineer's specifications. Here is where you will need to rent a large crane if you don't already have one. Once the beams have been lifted, secure them to the abutments.
Apply the decking. This is most likely a concrete slab reinforced with rebar, but it can also be aluminum or composite material.
Paint the lines and enjoy your new bridge. If something other than concrete decking was used, the construction drawings will call for additional paving material to be applied first.
Building a bridge is a long, complicated and dangerous process. This should only be attempted by a building company experienced in the bridge building process.