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From The US Department of Transportation.
Removing Existing Segmental Concrete Bridges
By Myint Lwin (For posting 9/2003)
As bridge engineers we are more used to designing and building new segmental concrete bridges than demolishing them. Occasionally, existing bridges have to make room for improvement or expansion.
Three precast segmental concrete bridges have to be removed in the expansion program of the Florida's Fort Lauderdale-Hollywood International Airport1. The bridges, measuring 1,183 ft. (8 spans), 808 ft. (7 spans), and 477 ft. (4 spans), are only 15 years old and in good condition. These bridges were constructed by the balanced-cantilever method. However, due to the rapid growth in traffic, these two-lane bridges are already functionally obsolete.
How do we demolish segmental concrete bridges built by the balanced-cantilever method? By reversing the way the segments were installed. After studying the original as-built plans and analyzing the design forces, the design-build contractor and the design subcontractor2 decided to take down the bridges in the reverse way they were put up.
One of the three bridges was removed by making a saw-cut at the midspan, and then removing one segment at a time, alternating from one side of the cantilever to the other side. The segments were lowered to the ground and crushed by a pulverizer. Photo 1 shows the saw cutting and Photo 2 shows the lowering of a segment. This was a slow and tedious process.
Photo 1 Saw Cutting a Segment
Photo 2 Lowering Segment for Crushing
In the process of the removal, the contractor found that the grout in the post-tensioned tendons was sound and strong. There was no sudden release of the prestressing force. With this knowledge, the contractor was able to crush the segments in place by a pulverizer. The crushing started with the wings, then the webs as shown in Photo 3. The top and bottom slabs were then removed, as shown in Photo 4.
Photo 3 Removing the Web
Photo 4 Removing the Bottom Slab
Demolition of a segmental concrete bridge must be planned carefully. It should be started with an inspection and evaluation of the existing conditions of the bridge and then analyze the present state of the stresses. The stresses at various stages of the proposed demolition sequence should be checked to assure safety of the people and stability of the remaining portion of the structure.
For more information on the demolition of the three segmental concrete bridges described in this article, contact Dr. Luis Vargas of Beiswenger Hoch and Associates2 of Miami.
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Photo 1 Saw Cutting a Segment
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Photo 2 Lowering Segment for Crushing
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Photo 3 Removing the Web
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Photo 4 Removing the Bottom Slab
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From The Sunrise Sentinal Target Store Addition @ Sawgrass Mills in Florida
Hero of the Week:
Hero of the week goes to Brant Lesogor and his crew for being effective, safe, and quiet as possble and thanks also to everyone working on this project - it was a good job.
Williams Company - Southeast
Bill Elferdink, Project Manager
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From: Bob Canney - General Superintendent
RE: This is in reference to the project by Archer Western at the Jensen
Beach Causeway Bridge replacement project.
I can not say enough about the incredible performance of your crew, their professionalism and tenacity to get the job done in half the scheduled time.
For those of you on the other side of production, you have been removing the bascule piers at the Jensen Beach Causeway Bridge with a 7 man wire saw team. The team was split into two groups and both have been working 24 hour shifts since March 16th. The work was non-stop over open water, with the only down time being a severe lightning storm. Archer Western's projection for the bascule removal was one month. Brant's crew accomplished this monumental feat in only 13 working days!!!
I would like to take this time to thank these men who truly exhibited Brant's "whatever it takes" philosophy.
* The 7 men for their exceptional effort and stellar performance in the field.
* And Especially Brant Lesogor who worked day and night to supervise the operations
of both crews and bring this project in way ahead of schedule.
Please take the time to thank these gentlemen when you see them; for securing all of our futures by propelling Brant's crew even further ahead as the leaders in our industry, and for a tremendous effort that truly was "above and beyond" the call of duty.
Thankfully yours,
Bob Canney-GS
Archer Western
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