The Mthatha River bridge project in the Eastern Cape is the maiden project for the heavy-lift capabilities of the new 750t hydraulic crane from Concord Cranes, a crane hire and specialised transport service company in the Industrial Services Holdings (InServe) stable.
The project for main client Haw & Inglis involved construction of a 90-m-long bridge comprising three 32m-long spans, with an average height from ground level of 8m. The substructure comprised two abutments and two piers. All foundations were founded on 1 050mm piles augered and socketed into bedrock with an average depth of 7m.
The superstructure comprised 18 precast beams, each 29.9m long and weighing about 60t. These beams were constructed on a site adjacent to the bridge, from where they were transported and placed in position. An in-situ concrete slab covered the beams in order to cater for two lanes crossing the river. The superstructure was completed by F-shape Type A parapets.
The civil engineering company contacted Concord Cranes regarding the transportation and placing of the precast beams to a radius of about 20m. The height from the platform to the top of the deck was between 9m to 10m.
The 750t crane required for this project was sourced from group company Concord Castle, Concord Cranes CEO, Herman van Staden, points out. “The original quote was based on a 550t crane, the largest available in our fleet at the time, which would have necessitated construction of large platforms in order to extend the reach of the 550t crane. These platforms required stabilisation on the 3-m-deep silt riverbed.
“We therefore proposed that our new 750t crane be deployed on the project, which was still in Germany at the time. However, its delivery to South Africa was well in advance of the date when it would be needed,” he explains. “This is a seriously impressive piece of machinery that is able to work with great accuracy.”
In two days
The contract with Concord Castle was based on the site establishment of all required cranes, equipment, and trucks to complete the transportation and placement of the precast beams. Equipment supplied included all lifting slings, guide ropes, shackles, and chains needed to carry out the work safely.
In addition, the company provided trained riggers and staff and submitted the required lifting and rigging studies, method statements, and occupational health and safety file to the satisfaction of the main contractor and engineer. Lastly, the company oversaw the mechanical, maintenance, and back-up support for all the machinery.
A qualified rigger supervised the lifting process at the precast yard, where the 60t beams were lifted in tandem by the 90t and 110t cranes onto an extendable trailer. Two 32mm-diameter steel lifting hooks were cast into each end of a beam. The cranes were positioned at each end with the trailer parked next to the beam.
Once the beam was placed onto the truck, it was tied down with chains. The 40m-long truck drove to the bridge, which was about 300m away from the precast yard. The main rigger then assumed charge of the operation, and supervised the lifting and placement of each beam onto the bridge.
The truck stopped at a predetermined position, from where special slings were connected to the lifting hooks on each beam. Guide ropes were also tied to each end of the beam. Each rope was handled by a team of about five workers, and a leader employed by Concord Castle.
Guide ropes were used to stabilise and steer the elements when these were up in the air. This was critical, as any wind or other external forces could cause the elements to rotate or swing out of control.
The rigger communicated with the 750t crane operator by means of a two-way radio, and supervised the guide-rope teams in securely lifting and placing the beams into position. Separate teams were positioned on top of the bridge to receive the beams and steer them onto the bridge bearings.
Before the crane released the load completely, the beams were secured to the bridge by the main contractor in order to prevent them from falling over. Once secured, the load was released and the slings untied. During the placement process, the extendable trailer travelled back to the precast yard, and the process was repeated for the next beam.
“The service and supervision provided by Concord Castle was professional and safety-conscious,” concludes Johan Ehlers of Haw & Inglis.
Herman van Staden
Tel: (011) 805-8071