When LPR Construction crews set out to assemble and install a Big R Tied Arch Pedestrian Bridge over busy I-225 near Denver, CO, they never imagined that their challenges would be so dramatic.
A car crash and a lightening storm
One morning during assembly, a speeding vehicle crashed through a gap in the jersey barriers, running into the assembly site and striking an arch section. A week of thorough inspections confirmed there was no damage to the arch.
Later, as the arch sections were about to be lifted into place during a night closure, a huge storm cloud threatened and the cranes had to be quickly boomed down for safety. Heavy rain and lightening pushed the start of the installation back a few hours.
Installation still completed within weekend night closure windows
Prior to the installation weekend, the bridge sections were pre-assembled on a snug, wedge-shaped site next to an off-ramp about a mile south of the installation site. A 75-ton rough-terrain crane was used to assemble the bridge and arch truss halves.
Bridge section installed on the first night closure
Once the assembly was complete, the bridge was ready to be transported to the installation site in two phases. A 500-ton all-terrain crane was used to load the 192′ bridge portion onto a transport truck and two trailers joined by transport girders. With the scheduled eight-hour closure started, the travel rig began to slowly slowly roll down the off-ramp and along the highway at a top speed of 1 mph. The crane was boomed down and moved to the set location at the same time.
The bridge was lifted and rotated into position fitting perfectly onto the anchor rods and supports. The anchor rods were tightened, the rigging was disconnected and the crane returned to the assembly site. The crews proceeded to connect the lower tie rod ends to the arch bearing supports and tension the tie rods.
This entire move phase, including set-up, tear down, travel and clean up, was complete in about 2.5 hours – in plenty of time to re-open for morning traffic.
Arch sections installed on the second night closure
The next evening, two cranes were used to lift the two arch sections onto the same travel rig and install them at the site. After the lightening storm delay, they lifted and lowered the arch halves into position and the arch pins were installed at the outer end bearing supports.
Then the middle ends of the arches were gently lowered so the mid-span arch beam bolted splice connections could be made. With the connection made and the anchor bolts loosened, one of the cranes pulled the deflection angle out of the bridge so the dangling hangers could be connected to the corresponding stub-outs. The anchor rods were tightened and the bridge camber was surveyed before the crane was released.
Despite the storm delay, all was completed well ahead of the morning opening.
The new bridge connects an RTD commuter rail platform to a medical centre as part of a new line through Aurora to the Denver International Airport.