Construction World February 2016

HEAVY PRECAST elements resurges

One of the trends within the construction sector relative to cranage and heavy lifting is the resurgence of the use of heavy precast elements in construction projects. This, according to Quentin van Breda, technical director of Torre Lifting Solutions and founder of SA French, will require much larger tower cranes than those typically used on a construction site. over the years. “Originally tower cranes were seen as general materials handling tools. They handled almost everything that needed to be lifted and moved, and this included large skips with concrete. In the past, slabs were most commonly poured using tower cranes,” he says. Fast track projects This, however, changed as more and more projects became fast track. “Fast track project schedules meant that concrete needed to be placed faster and where the bulk of concrete being used was for slabs, pumping became more common place,” Van Breda says. “This meant that tower cranes were > Commenting on the role of tower cranes on construction sites, Van Breda says that their use in terms of material being handled has varied

and the load chart is ideal for lifting heavy precast panels at increased radii, while providing the construction site with the addi- tional flexibility and convenience that a tower brings to a project. Even though this is a big tower crane, the individual components never exceed 10 t and this, according to van Breda, ensures that erection and disassembly fall within the parameters of normal mobile cranes. “This is particularly important where space constraints exist and this is, as all contractors know, always a factor with urban construction projects.” It was designed jointly by Manitowoc engineers in Europe and Asia to serve several types of markets, and offers a 2 metre mast with a maximum free standing height of 64,9 metres. This compact mast, along with a compact jib design and a streamlined counter jib, make the tower crane easy to assemble and transport. “This is a major advantage on crowded urban projects,” Van Breda says. Telescoping the crane is made easier as the hook height can be 50 metres above the last anchor points, and in addition, the design allows for internal climbing on high- rise applications. With a 20 t maximum capacity, the Potain MCT 385 is equipped with frequency-con- trolled mechanisms for hoisting, trolleying and slewing, facilitating smooth movement and precise positioning. This is an important feature when handling and placing such large precast elements. Van Breda says that servicing the mechanisms is straightfor- ward as they are conveniently located and easily accessible. “The larger Potain towers will be supported through the same infrastructure as all Potain tower cranes, and this includes technical input and support from the time of specifying the crane through to erection by skilled technical teams. Ongoing mainte-

handling general materials and when it came to concrete placement the cranes were used only for the pouring of columns.” Van Breda says that with this move towards precast solutions, Torre Lifting Solutions has seen an increasing number of enquiries for tower cranes capable of handling heavy precast elements such as flooring slabs on new construction projects. He says it is significant because this type of lifting requirement doubles the lifting capacity of the tower crane required. “In the normal construction environment everything is equated to cubic metres of concrete, and the equation for lifting would then be, say 2,5 t to be lifted at the required maximum radius of 50, 60 or 70 metres,” Van Breda explains. “The entire scenario changes in the case of heavy precast elements as these could be as heavy as 4 t to 6 t but would still need to be lifted at the same radii.” Good for using cranes This move towards precast elements is a good one for industry as the utilisation of much larger cranes will inevitably result in quicker cycle times on site even when moving other materials. Van Breda says that this will make for greater productivity with the subsequent cost savings in labour and time. “What is however noticeable is that few contractors in South Africa own this size tower crane, with the population in this category probably no more than10 in the country,” van Breda says. He says that a standard run-of- the-mill tower crane used at the top end on a construction site for traditional materials handling would be a 200 mt machine, but in the case of handling heavy precast elements the bottom end tower crane would need to be 385 mt. The Potain MCT 385 is a topless crane which is easily erected with a mobile crane,

40

CONSTRUCTION WORLD FEBRUARY 2016