Visitors to the Dubai Expo 2020 were welcomed through three gates or entry portals inspired by the traditional lattice pattern ‘Mashrabiya’ in Islamic architecture.
The 21m x 30m gates were made of carbon fibre to reduce weight, and and they were installed on top of bridges connecting the expo site to the access roads.
During construction of the Expo site, the gates needed modification, which required dismantling of the existing structure, lashing of the carbon-fibre frames and then reinstalling them after the modification. The contractor Besix-Orascom chose Johnson Arabia, having had a long-standing working relationship of around 20 years in delivering several infrastructure and civil construction projects.
The complex lifting operation would require a special rigging arrangement using two mobile cranes working in tandem and executing a tailing lift from roads below either side of the bridge on which the gate was installed.
Johnson Arabia created the lifting plan and supplied a 300-tonne Grove GMK6300L and 100-tonne Demag AC100-4L all-terrain cranes for the job. Each mobile crane was positioned 10m below the bridge.
Sreethu Thulaseedharan, lead engineer for the project, explains how Johnson Arabia’s team of engineers addressed the jobsite challenges: “The gates needed to be lifted over the bridge without full operator visibility; so, each crane was positioned and operated carefully on either side below the bridge, and our riggers and operators relied on radio communication for both lifting accuracy and avoiding damage to the carbon-fibre structure. An initial risk assessment of the job site revealed that the roads were not wide enough for the crane outriggers; so, we made provisions to spread the outrigger load on curb stones. We applied a safety margin of 25% for the tandem and tailing lifts, and we used two spreader bars to stabilise the loads. There were no risks for offloading as we had enough open space below the bridge.”
The Grove GMK6300L and Demag AC100-4L cranes were operated with boom lengths of 52.5m and 50.4m, respectively. The maximum loads handled by the GMK6300L and AC100-4L were 3.9 tonnes and 1.95 tonnes, respectively. Each gate required one day for dismantling the structure, followed by two weeks for modification and one day for reinstallation.
Sreethu Thulaseedharan, says: “This project was a milestone for Johnson Arabia because not only did it require careful planning but it also required great communication, skill and coordination for the entire team to be able to lift all the three carbon-fibre gates.”