Borger barges timber trusses Bor ger Cranes manage a complex lift in bridge demolition

Borger Cranes recently completed a complex lift for NSW Roads and Maritime Services (RMS) involving the removal of timber truss spans from the Old Sportsman Bridge in Lawrence. BORGER BARGES TRUSSES IN BRIDGE DISMANTLE

THE PROCESS TO COMPLETE THE LIFT WAS not the most straightforward process. The complications included barging a 600t capacity crawler crane to site, the closure of the Pacific Highway, restrictions with tide times and daylight hours, and managing the barge’s ballast to ensure stability throughout the lift.

The Borger Cranes team worked closely with New South Wales Roads and Maritime Services, as well as barge provider Ausbarge Marine Services, to ensure the safe removal of the timber trusses from the redundant bridge.

Ausbarge Marine Services provided the tug and barge services to the project. Given the choice of crane that Borgers had recommended to NSW Roads

Total weight of the lift was 76t including the rigging equipment.

and Maritime Services was a Demag CC2800, and the size of the bridge trusses themselves, the project required a barge with significant deadweight capacity, as well as being able to provide the stability to enable the CC2800 to slew with the bridge truss once lifted off the pile headstocks.

Paul Muller has been with Borger Cranes since 2012 and looks after the Demag CC2800 600t crawler crane. He operated the CC2800 throughout the project.

“We put the crane’s car body and tracks together on Harwood Marine Slipway and then walked the machine onto the barge. Grillage had been put down and welded on the barge and we walked the crane onto the grillage and finished building the crane,” he said. “A lot of logistics were involved and a lead time of around a week was required to build the crane before it arrived on site at Lawrence.

“The barge and crane sailed under the Harwood Bridge on the Clarence River. The optimal time to open the bridge was discussed between Borger Cranes, the Barge Master and Roads and Maritime Services,” said Muller.

The traffic on the Pacific Highway had to stop for ten minutes so the deck could be lifted and the bridge opened. The only time the highway could stop was before 8.00am and between 9.30am and 2.30 pm and after 5.00pm. The tide flow had to be slack to enable effective steering by the tugs through the narrow clearance between the bridge piers, and the barge could only move during daylight hours.

“A number of elements were out of our control to enable us to travel to site we had to align these elements and meet the small windows of opportunity a number of times during the project. The barge was brought up to the side of the site and anchored and we put our rigging gear on the hook the total weight we were pulling was 76t including the rigging equipment,” said Muller.

“Two trusses were removed – one on each visit. We lifted the first truss and slowly brought it onto the barge and sailed it back to Harwood and unloaded it at the marine slipway and repeated the process for the second. The whole project took close to five days and it was a sensitive lift with a high degree of difficulty,” he said.

The Demag CC 2800-1 is a crawler crane with a maximum lifting capacity of 600t. The maximum boom length is 138m with a maximum jib length of 96m.

The tracks of the Demag CC 2800-1 are powered by two hydraulic motors, each through closed planetary gear reduction units running in oil baths. The gear units were designed to fit inside of the width of the crawler. The four hydraulic assembly-jacking cylinders are found on the car body for easy assembly of the crawlers and fold to a 3m width.

Matt Steain is a supervisor at Borger Cranes responsible for planning the lift.

“We engaged Ausbarge to provide the barge for the lift and we also engaged a naval architect who calculated the tides as well as calculating how much ballast was needed in the tanks for us to walk the crane on,” he said.

“We ballast the back of the barge opposite to where we planned to walk the crane on which allows for the weight once the crane is walking on. It was a 30-minute process to get the crane completely on the barge. We put the toe of the tracks onto the barge, waited and transferred more ballast, moved the crane half on and transferred more ballast, then three quarters of the way on and

Paul Muller operates the DEMAG CC2800.

transferred more ballast, and then drove the crane completely on,” said Steain.

The barge chosen for the project was a 3,000t deadweight barge with an overall length of 180ft and a beam of 70ft. This required approximately 300t of water to be loaded into the barge ballast tanks to compensate for the changes in barge freeboard, list, trim and tidal compensation as the crane was walking onto the barge. This ballast was also required for the bridge lift operations and was transferred by four ballast pumps with a capacity of 100 tonnes per hour each pump. The crane walked on with just car body and tracks then dressed with counter weight and boom after positioning on steel load share mats to distribute the overall weight. The barge deck had a point loading of 20t per square metre. All stability, roll on and deck strength calculations for the barge were carried out by accredited Naval Architects ASO Marine Consultants as were the stability calculations for the crane lifts at the Sportmans Creek Bridge.

“We established the crane on steel grillage, and welded it down in the right position and built the crane on the barge. Once the crane was ready to go we had two tugs, one pushing and one pulling but we had to wait for slack water until the tide changed. We also had a representative from the port authority on board,” said Steain.

“They had to close the Pacific Highway and open the Harwood Bridge, which we had to book obviously, and then the tugs pushed us through, under the Pacific Highway and all the way down the river to the bridge.”

As part of the approval process, Ausbarge Marine Services developed a Marine Works Management Plan for NSW Roads and Maritimes Services review and approval. The towage from Harwood to Sportmans Creek at the township of Lawrence required passage through the opening span of Harwood Bridge on the Pacific Highway. Given the beam of the barge being 70 feet, and the height of the crane on the barge the bridge had to be opened, highway traffic stopped and the bridge opened to a vertical height of 36 metres. This particular part of the passage had to be carried out in daylight hours only, and at slack water, which is the period where the tidal current stops between the ebb and flood tidal stream.

The barge with the crane, ballast and all of the equipment on board had a total displacement of 1,500t. Once towed to site, the barge was moored in position for the bridge lift operation by 4 x 2.5t anchors.

“We used the naval architect for the lift itself. We designed the location and provided him with our slew angles, radiuses, weights, where we were picking the trusses from, as well as track pressures for the crane,” said Steain.

“When we had the crane in the position, we had the right amount of ballast in the back of the barge. We lifted and took the weight of the truss. We then had to luff it up and slew it around over the side,” he said.

“But before we were able to slew it around, we had to transfer ballast to one corner to allow for the weight. We picked the truss up, luffed it up, transferred the ballast slewed around 180 degrees and luffed it down straight behind the crane. They then transferred the ballast back over so the barge was level and ready for travel,” said Steain.

Each individual lift required approximately 150t of ballast water to be transferred from the port to starboard ballast tanks on the barge to enable the CC2800 to slew from over the stern of the barge and place each truss on the deck to maintain an acceptable stability condition. Individual trusses were transported on the barge back to Harwood Marine and unloaded. On completion of the project, the boom and counterweight were removed from the crane and the car body and tracks walked off the barge while again transferring ballast.