Solving Construction Issues from Design to Field
Lee Roy Selmon Crosstown Expressway
Selected over international companies for performance, price and schedule, CGLLC landed the contract to design, supervise construction and instrument the segment setting system for this 7 mile elevated, high tech Tampa roadway.
There were approximately 3500 precast concrete segments to be lifted onto the steel erection girders and pulled into place. Vertical concrete pylons every 160 feet provided support. Two erection assemblies (called headings) were built for PCL. Chain drive systems, designed by CGLLC, were installed along with massive gear boxes and electronic motor controls.
The motor controls were designed and built at CGLLC’s facility in Baltimore, shipped to Tampa and installed. Heading Two had hard-wired remote controls. 100 foot control cables were built in-house.
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Applying technology developed for electric motors in industrial plants, CGLLC was able to quickly design and implement a safe, accurate, and virtually bullet-proof electric drive system for setting these segments in a very short time frame. All controls were interlocked to prevent misuse. Industrial switches and relays were used for maximum reliability.
Due to working conditions- in the median of an active highway, using a crane to set segments along the length of the erection girders was not possible, thus the segments had to launched from one end and pulled into place. This roadway project resembled construction of a span-by-span precast segmental bridge.
Operation was simple- green button for forward, red button for stop. The ‘creep’ controls allowed for setting the 80 ton precast segments at a crawl pace of 3/8” per section, allowing for precise segment location. Forward speed was designed with smooth acceleration in mind- from 0 feet per second to a maximum of 15 feet per minute over a thirty second period. Stop function also had deceleration function to avoid 80 tons of concrete from jerking to a halt. Two 15 horsepower electric motors (one for each girder) were used, but 7.5 horsepower motors would have proved sufficient.
Erection was initially planned for each 160 foot span to be completed every three days, working double shifts. The entire system proved so efficient, this was reduced to a two day period.