Gantry cranes: A leg up for loads27 March 2023
Gantry cranes are quite simply lifting devices on legs. Julian Champkin looks at this most useful of concepts.
Gantry cranes are instantly recognisable as a type: they are, quite simply, a horizontal girder on legs. The girder carries a trolley and hoist, and the legs can generally move, on rails, tyres or casters depending on the function and the size of the crane.
Sizes can range from the ultra-light and portable – as used in a host of auto repair shops for lifting engines from their chassis – to some of the very largest and heaviest cranes in the world. Typically, these latter are installed in shipyards and go by the name of Goliath cranes. What is claimed as the world’s largest was installed by Konecranes at the Meyer Turku shipyard in Finland and weighs 6,500t, spans 210m and can lift 2,000t.
They have been in use, almost unchanged in general outline, for more than 2,000 years; the Romans used man-powered gantry cranes. That, and the fact that it is so scalable, points to a machine that is fit for purpose. Indeed, no fundamental change in the design has happened until very recently (for that, see nearer the end of the article). But we will start with more standard designs of the larger gantry cranes.
Typical applications for these are in metal or timber stockyards and hydro power station turbine halls. An example is an installation currently under way for the New York Power Authority (NYPA). The authority is the largest state public power organisation in the US, and more than 80% of the power it produces is sourced renewably. This is in no small part due to the hydro power produced by some of the 3,000 tons of water that plummet over the edge of the Niagara Falls every second.
The first electrical generators at Niagara opened in 1881, and the current station, known as the Robert Moses Niagara power plant, has had since its inception a gantry crane 18m wide and standing 21m high in the main turbine hall. Affectionately known by the staff as ‘Big Red’, the crane’s functions include lifting rotors and other major components for maintenance and repair. It is now, however, nearing the end of its useful life.
Its replacement was ordered in the summer of 2022 from REEL COH of Canada. It will have a capacity of 680 tons, which is some 50 tons greater than its predecessor. It will serve the 13 generating units that make up the plant.
The contract for fabrication, delivery and installation is part of a 15-year $1.1bn modernisation and digitisation programme with the title Next Generation Niagara and is worth around $38m.
“The Niagara Power Project’s overhead gantry crane is the workhorse that makes possible all the of the plant’s mechanical upgrades, especially those related to our effort to modernise and extend the life of New York’s flagship clean energy plant,” says NYPA interim president and CEO Justin E. Driscoll. Among its tasks will be assembling and disassembling the generating units. “Many of the efforts to digitise the project are already under way, but a new crane is essential,” he says. A new 15-ton monorail hoist and a 5.0-ton maintenance hoist are also part of the development programme. Construction of the gantry crane is expected be complete by 2026.
Waste-to-power is another generating application well suited to gantries. The Riikinvoima waste incineration plant in southern Finland can take 145,000 tons of refuse a year, from which it generates 150GW of district heating and 90GW of electricity. The entire flow of waste, from arrival to transfer to the furnace and then incineration, is handled automatically. The cranes in particular are in full automatic mode almost all of the time.
“The gantry cranes have a very high utilisation rate, and that tells us that the system works well. Few interventions are needed,” says Juha Räsänen, managing director of the plant. “You can really leave the crane in the waste storage bunker alone, to work by itself picking up and transporting the waste.”
A crab grab claw on the gantry crane’s hoist picks up the rubbish and transfers it; target positioning of the load over the delivery chute into which it is released has manual, semi-automatic and fully automatic modes. A remote operating station (ROS) gives multi-screen views of the bunker from the many video cameras in the bunker and on the crane. The station is located not by the bunker and crane but in the central control room for the whole facility, where all the staff have access to it and can use it.
“The fact that all the staff members can and do use the ROS for the crane shows that the interface is very successful and intuitive,” says Räsänen. “The staff gladly adopt it and the information is easy to find.”
There is actually a dedicated control room for the crane, with an operator’s chair and windows looking down on the bunker, but it gets very little usage. “If we were to build the plant again now I would consider leaving it out completely,” says Räsänen.
As feeder cranes transferring loads from rail, road or barge to factory floor is one common use for gantries, transferring from rail, road or barge to barge, road or rail – that is, intermodal lifting – is another. Again, the wide spans over unobstructed ground space is an obvious reason to use them.
The rugged nature of their construction that makes them able to cope with bad weather is another.
Thus, for the end of 2022, the Intermodal Eurotransit Group of Companies (Eurotransit) in Kazakhstan scheduled delivery of two Konecranes rail-mounted gantry (RMG) cranes for the intermodal terminal it is constructing at Dostyk, near the border with China. They will trans-ship containers on trains running between Kazakhstan and China.
Erlan Dikhanbaev, director, Eurotransit, says: “The Konecranes RMGs are central to our ambitious growth plans. We have very demanding environmental requirements – we often have to deal with strong winds and very low temperatures. We also had very demanding requirements for container handling productivity and reliability.”
The Konecranes gantry cranes run on rails 32m apart and will serve six train tracks, lifting containers 1-over-2.
They come equipped with graphical user interface (GUI), and extra visibility is provided by video cameras on the spreader and under the trolley. They also come with a skew control system and auto-positioning.
Tunnelling projects frequently use gantry cranes. Installed over the top of a shaft they are typically used for lowering the components of the tunnel boring machine. Since these machines can have sections weighing hundreds of tonnes apiece, a crane of very high capacity is a requirement, and gantry cranes are usually the default solution in practice. Even for tunnels constructed by other methods gantry cranes are the norm.
Acconia is building a new line for the São Paulo metro system in Brazil. It will have 15 stations and will serve an estimated 600,000 people each day. In April 2022, Spanish crane makers GH installed a gantry crane to serve the extension works. It was constructed in GH’s factory in Cabreúva, which GH established in 2011, and was installed at the PUC Cardoso Station in the centre of São Paulo.
Cabreúva is some 50km from the city centre. The girder for the crane is 35m long, and transporting it and the other crane components took two days. Installation at the site took nine days, with a further day for testing.
The crane has a capacity of 30t and is 14m high. Its hook and cable can reach a depth of 80m below ground level. The entire interior of the enclosure has been covered with acoustic material to minimise the noise that escapes to the outside – a greatly beneficial development that was used also, for example, around gantry cranes on London’s Crossrail project.
A more unusual, indeed possibly unique, application of gantry cranes was demonstrated by Graham Construction & Engineering in Canada, which used two of them to reconstruct a bridge. Originally built in the 1950s, the Groat road bridge is a seven span, four-lane structure that carries traffic and pedestrians 1,000ft across the North Saskatchewan River and provides a critical link between downtown Edmonton and the university area. Approaching the end of its service life, it was decided that the bridge should undergo a substantial structural rehabilitation rather than replacement. A full superstructure replacement and a fairly extensive rehabilitation of the substructure were called for, and most of the abutments were to be replaced. Some 13,000t of concrete needed to be removed. Graham’s won the $45.6m contract.
A traditional approach, of using a succession of berms to perform the work would have been problematical: traffic lanes needed to be kept open. Only 60% of the river could be blocked at a time, and the need to protect fish habitat imposed timing restrictions as well. Using the gantry cranes circumvented all these problems.
The idea resulted from a chance meeting between a Graham Construction employee and a colleague from Cowi North America, the civil, structural and geotechnical engineers specialising in the design and maintenance of bridges, tunnels and marine structures. “The process amounted to sawing the old bridge down the middle, repairing one half of the bridge, keeping two-way traffic open on the other side, then flipping the process and repeating,” says Jim Murray, project manager for the City of Edmonton. The construction team installed two 40t lift gantry cranes, one on each side of the bridge.
“The gantry crane idea allowed us to do all the work from above,” says Stephanie Grundke, project manager for Graham. But it called for ingenuity in execution.
Getting the runway beam, truss and bracket system installed and running was a large part of the overall project. There were many technical constraints as well as critical tolerances for the rails and gantries, anchorage of the pier brackets and runway beam without conflicting with existing rebar, plus concerns about the bridge’s deficient shear strength. And, of course, it had to remain open to traffic. The design package analysing the impacts of the runway beam on the existing bridge ran to 1,000 pages.
Melissa Jennings of Cowi performed that design work. “It’s a simple concept to understand,” she says, “but there were all these different pieces involved, and designing it to handle the large loads during demolition was quite complicated. It became a weirdly elegant solution that was quite challenging to carry out.”
On the interior half of the bridge the gantries travelled on a temporary I-beam connected to the bridge. “We attached a truss to the side of the bridge using brackets each side of the bridge anchored and tensioned to the piers, and these were what supported the outer edge of the crane,” says Grundke. The team used the gantries to systematically remove large swathes of decking.
“We would go and cut the sections of the bridge deck between the girders and those sections were light enough for a single crane to go and pick them out. Once all the deck panels were removed in a section, we would bring both of the cranes and do tandem lifts to take out the girder pieces. These were quite heavy, sometimes close to 80 tons, and quite near the capacity of the cranes.”
The novel nature of using the gantries took some time to get used to, she says: “There was definitely a lot of learning in the beginning, ironing out all of those kinks because it was something even new to us. But I felt it was a well-oiled machine by the end.”
And she believes that it is a good technique that could be used elsewhere for bridge rehabilitation: “If you’re doing a new bridge build it doesn’t work well because you have no structure to attach it to. But in this type of situation, if you’re keeping the bridge and if they are close enough together it makes sense.”
One difficulty was that the bridge piers were actually hinged at their lower ends, to allow for thermal expansion of the bridge. “So, when the bridge expanded and contracted, it actually rocked the pier slightly,” says Grundke.
“We had to go into the river and cast a concrete collar around that section to stop it from rocking. Then we installed a bearing on the top to allow for the movement.”
Using the gantry gave a much less invasive approach to the river and allowed scheduling unaffected by the needs of its wildlife. “I think it’s a really good solution,” says Grundke.
At the start of this article we mentioned a design change for gantry cranes. It is crane makers Künz, based in Germany, which has come up with it. A common use for gantries is as in stockyards, to feed bulk raw material arriving by rail, barge or truck into the plant for processing. Metal, timber and raw material for waste-to-power are typical applications, and Künz, recently completed the commissioning of a log yard for its customer Schwaiger Holzindustrie in Bavaria. Since the beginning of last year two large gantry cranes have been operating there. Their main girders are 115m long – the trolleys can travel along 105m of it – and the cranes run on 380m of trackway, with 57m between the tracks – the result is an area of 22,000m2 covered by the cranes. Each crane has a lifting capacity of 21.5t, and they can handle between them around 1.2 million metres cubed of log wood each year.
Each hoist has 160kW of drive power – lift speed is up to 60m/min, while maximum travel speed, for both crane and trolley, is 150m/min.
The cranes unload the logs and stack them in the yard until needed, at which point they lift the logs again and feed them into the sawmill. Both cranes can cover the entire unloading and stacking area. To prevent accidents, an anti-collision system is in place. “The crane design has been optimised to reduce noise as well,” says Johann Niedermeier of Schwaiger Holzindustrie.
Dietmar Nußbaumer is head of technical sales at Künz. “The cranes are equipped with anti-sway technology and much of their operation is automated,” he says.
For example, the logs are taken out of the containers under manual control, but a single push of a button then drives crane and load to the selected storage area where the loads are unloaded. From the log pile onwards to the saw infeed is entirely automatic. “This automation of processes results in an increase in productivity. We have been nominated for the Austrian State Prize for Innovations for our patented single-girder gantry crane,” says Nußbaumer with visible pride.
The nomination came in October 2022. The reason lies in the cross-section of the girders of the crane: the tradition is for these to be either I-beams or, if composite, rectangular – basically box-shaped. Künz has a unique selling point in that the bridge girders of their cranes are shaped aerodynamically: they are ovals.
It is a patented structure for girder cranes. “The starting point for the new development of the aerodynamic main girder was that we had reached technical limits with the traditional design of container cranes. We could no longer guarantee ever-faster cranes, in combination with higher wind speeds at which the cranes are operated,” explains David Moosbrugger, CTO of Künz. “With the aerodynamic main girder, we have solved this problem, and we have also managed to significantly improve the manufacturing costs as well as the operating costs for the cranes in operation. And the gantry crane system can be operated even at wind speeds of up to 105km/hr.” Wear and energy consumption are also significantly reduced.
The aerodynamic steel structures consist of only a few components; the design reduces the amount of steel used by around 15%. Since a crane girder weighs in at some 300t, this means that each crane is about 45t lighter. This is turn brings significant savings in wear and operating costs. The improved aerodynamics reduces the wind resistance of the main beam by 75%, which reduces the power requirement of the trolleys by around 30% – an annual saving of around 80,000kWh per crane system.
If an aerodynamic cross-section seems, with hindsight, an obvious change, it is. (All the best new ideas seem obvious once someone else has thought of them.) If it seems a small and simple change to implement, it is not. “Cooperation with universities and other scientific institutions was indispensable to bring about our ideas,” says Moosbrugger. “There were cooperations with independent companies Bionic Surface Technologies, for computer simulated flow behaviour, and Frindt, for the procurement and production of the shell elements. RWTH Aachen University worked on optimisation of the beam cross-sections and the Vienna University of Technology studied the driving behaviour and the intrinsic stiffness of the crane portals.”
It seems that even a mature and well settled technology can evolve further, given a little ingenuity, imagination and hard work. For what happens to gantry cranes next, watch this space.