Permanent structures for bridge begin to rise
Permanent, above-ground structures are beginning to take shape on the Grand Avenue bridge project. This week the contractor will pour 226 cubic yards of concrete to complete the north traffic bridge abutment. This amounts to approximately 23 trucks worth of concrete. So you may be wondering, what is an abutment and how are we building it?
An abutment is a structure that is located at the end of each bridge: It’s where the bridge ends and the road begins. Piers handle the vertical load of the bridge and the abutments handle the horizontal load. The abutments for the new traffic bridge terminate at the west end of the Hot Springs parking lot and on the south past the Seventh street alleys to create an open view of both alleys from under the bridge.
The new abutment on the north end of the traffic bridge is much larger than the current traffic bridge abutment. They are 15.5 by 82.5 feet, approximately double the width of the current Grand Avenue bridge abutments. In addition, two wing walls will be built on each side of the abutment for structural support and as a design feature of the bridge.
How do we build it?
Construct caissons: The traffic bridge abutments sit on two caissons, or foundations. Each caisson is 60 feet long can carry a load of 2 million pounds. The caissons for the abutments are the longest caissons on the project.
Bearing seats: The abutment is built with three bearing seats or blocks. The bearing seats are places where the steel sections of the bridge will rest.
Place rebar: The abutments contain nearly 28,000 pounds of reinforced steel known as rebar that add strength to the concrete. After it is placed, the rebar looks like a cage.
Construct plywood forms: Plywood forms are used to give the concrete the desired shape.
Pour concrete: Concrete is poured into the plywood form and around the rebar.
Strip gorms: The plywood forms are removed exposing the cured concrete.
Place exterior finish: The final covering is then placed over the concrete, in this case a red stone veneer. Nearly every exposed face of the abutments will be finished with stone.