Bigge manages precision lifts

Once completed, the new Gerald Desmond Bridge Replacement Project in Long Beach, CA will be the second-tallest cable-stayed bridge in the U.S. It will have the highest vertical clearance of any cable-stayed bridge in the nation.

Positioning the pier decks called for patience and precision. Bigge Crane and Rigging used Enerpac’s strand jack technology to lift the decks into position over a 10-hour period.

Built in the late 1960s, the Gerald Desmond Bridge is in urgent need of replacement. It stretches over the entrance to the Inner Channel of the Port of Long Beach, the second-busiest container port in the U.S. When the bridge was built, cargo ships were one-sixth the size they are today. While the Port’s outer harbor docks are handling huge cargo vessels, the bridge prevents large cargo ships from reaching the inner harbor.

The new bridge features a cable-stayed design based on two 515-foot concrete towers that transition from an octagonal base to a diamond shape at the top. Forty steel wire cables will connect each tower to the bridge deck in a fan-like pattern. The longest cable will be 573 feet.

Bigge’s task was to lift the 1.35-million-pound pier tables for each of the two towers to form the east and west ends of the 2,000-foot main span. In preparation for the positioning on the pier tables, four-column falsework was installed on each of the two towers. Bigge used Enerpac strand jacks to lift the pier tables.

“The strand jack is perfect for this kind of job,” said John Levintini, Bigge’s project operations manager. “It would have been impractical to use a crane given the size and weight of the pier table. The strand jack is the best choice in terms of both lifting capacity and cost.”

Post tensioning principle

The strand jack lifting technique originates from the concrete post tensioning principle. A strand jack can be considered a linear winch. In the strand jack, a bundle of steel cables, or strands, are guided through a hydraulic cylinder. Above and below the cylinder are anchor systems with wedges that grip the strand bundle. By stroking the cylinder in and out while the grips are engaged in the anchors, a lifting or lowering movement is achieved. Enerpac has refined the strand jack technique making it easier to deploy and manage with automated locking/unlocking operation, as well as enabling precision and synchronous lifting and lowering by a single operator. Telescopic strand guide pipes, and “palm trees” prevent bird caging and allow easier cable management. Heavy lifts of thousands of tons are possible using strand jacks.

“Strand jacks pack tremendous lifting capacity into a small footprint,” said Mike Beres, sales director, Americas, Enerpac Heavy Lifting Technology. “Moreover, the system software can control up to 60 jack/pump combinations so the potential for large-scale synchronous lifting is quite scalable.”

Enerpac HSL 5000 strand jacks, each with 48 strands, were used to lift the steel framework pier table positioned around the base of the tower onto the four-column falsework. Synchronized controls allowed all four jacks to lift simultaneously, ensuring the structure remained balanced. Each incremental lift was 18 inches, with the entire lift of the pier table taking 10 hours. Bigge synchronized the lift though a strand jack computer.

“The lift was straightforward. However, maneuvering the pier table into its final resting position on the falsework was a delicate operation – the final alignment was coordinated with the strand jack and visual feedback by engineers on the piers,” Levintini said.

Installation of the pier tables took place during April and May. First, one pier table was installed, then the four strand jacks deployed to the falsework on the other tower for the second pier table lift.

With the east and west towers’ pier tables in position, the first cable strands have now been installed. Following the removal of the falsework, cranes will be lifted onto both pier tables to begin the balanced-cantilever construction of the main span. Bridge segments will be added symmetrically on both sides of each pier table, extending toward each one’s respective end bent (where the main span meets the approaches) and the center of the bridge over the water.