COLORADO — Mammoet was recently contracted to assist in two phases of work to set 12 steel rail bridge girders and the team came up with an innovative solution using a unique cantilever setup on top of self-propelled modular transporters (SPMTs) for a quicker and safer installation.
The girders were located directly under Interstate 70 in Colorado, which made it difficult for cranes to perform the work.
The initial plan was for Mammoet’s team to use a skid system to launch each girder, which measured about 70 feet long, over an existing dirt pit. Once in position, each one would then be transferred to another skid system which would shift the girders sideways, above each bearing pad, indicates a release, adding climbing jacks would then lower each girder into their final setting position.
While onsite for this execution, the field supervisor and team came up with the idea to use a cantilever setup on top of SPMTs instead, which Mammoet engineers later approved.
In terms of the process, two 98-foot spans of Mammoet transport frame beams were lashed to the back of an SPMT trailer and then 60,000 pounds of counterweight was stacked over the lashing arrangement, acting against the uplift created by the cantilever when holding the load, as the girders themselves weighed about 40,000 pounds each.
The 30-metre span of the transport frame beams provided the 40 feet of reach necessary to position each girder over its bearing pads. The method was tested at Mammoet’s yard prior to execution.
Once on site, a crane was used to set each girder from the roadway onto the SPMT trailer configuration. The cantilever trailer then drove into position so that the girder’s centre of gravity was underneath the air hoist (hook).
Another three-ton chain hoist was used to secure a small fraction of the girder weight near the front end of the trailer to prevent unwanted movement during driving and lowering. The girder was then lifted and driven further forward about 121 feet until it was over its set position, then lowered down approximately six feet, the release explains. Once in position, it was secured and unhooked from the cantilever.
Per girder, the entire operation took about an hour from start to finish, compared to the previous skidding plan which would have taken up to three days.
“The decreased handling time made this method of operation safer and allowed the site to be released ahead of schedule, reducing disruption,” the release states. “This continued collaboration through the phases with the customer, field personnel and engineering allowed Mammoet to reduce total time onsite for its scope, and ultimately kept the customer’s budget and schedule in order.”