Since the Brooklyn Bridge became the first bridge to use a steel suspension cable design, suspension bridges have been the main technology in bridge building architecture. The increasing size of prefabricated elements used in the construction of suspension and cable-stayed bridges has led to a demand for bigger cranes with greater lifting capacity, on projects already challenging enough due to the very nature of their construction.
Carsten Bohnenkamp, director of sales for Manitowoc’s heavy lifting special application tower cranes explains, "most suspension bridges are made of two main supporting piles. The suspension cables are joined in the middle of the bridge. The span of the bridge generates different heights of the bridge piles so as the span gets bigger and bigger, the piles grow proportionally. It’s now becoming possible to build bridges with longer spans than ever, so consequently the lifting requirements of cranes is greater."
Prefabricated bridge elements and systems offer significant advantages in terms of construction time, safety, environmental impact and cost. Bridge designers and builders are finding ways to prefabricate entire segments of a superstructure. Transporting prefabricated elements to bridge sites is one solution to address the challenges of tight construction schedules, particularly on projects where weather conditions may only allow brief periods of construction. However while prefabrication is solution to one problem, it throws up a whole new challenge for crane operators and contractors.
"The tendering process for these kind of projects is lengthy, costly and can cause construction time to be squeezed," says Bohnenkamp, "And high performing lifting equipment can help keep construction times to a minimum. For the most recent Potain bridge projects, the cranes were designed to withstand wind speeds up to 250km/h. This has a strong impact on tower crane mast structure, the number of anchorages to the bridge and the climbing sequences. In some cases we had to consider the "vortex" effects of the tower crane in the wind shadow of the bridge pile, due to turbulent storm wind. It’s critical to evaluate these type of risks and design the cranes accordingly. Only major tower crane manufacturers are able to do this."
The recently completed bridge to Russky Island is now the world’s longest cable-stayed bridge and commanded the use of the world’s biggest cranes. With a central span of 1104 metres, the bridge also has the second highest pylons after the Millau Viaduct and the longest cable stays. Bohnenkamp explains, "the Russky bridge project was realized with two hammerhead cranes, the MD1100 and MDT368. During the build, cranes lifted a variety of equipment and construction materials, including concrete, formed work, steel reinforcement, steel structures and temporary bracing beams. Prefabricated elements on this project weighed up to 30 tonnes."
Among the most challenging lifts undertaken by the MD 1100 was placing metallic blocks to connect cable stays to the top of the pylon. Each 22t block was lifted more than 325m at a radius of 36m.
"As the bridge piles were made of concrete, we used the MD1100. This is a heavy lift tower crane that can pick up loads of up to 19 tonnes out to a radius as far as 60 metres", continues Bohnenkamp. "Both cranes were climbed to the top of the bridge pile. The positioning of the cranes on this type of bridges was of capital importance, as the dismantling of the cranes at the end of the job site was strongly restricted by the stay cables of the finished bridge. For this particular project the MD1100 was positioned in a way that it was able to dismantle the MDT368 at the end of the project.
Denmark-based Krøll provided one of its mighty K1000s for the Vladivostok project. "The cranes for Russky Island were placed extremely close to the pylons and it wasn’t possible to use the counter jib", says Neils Peter Sorenson, sales manager at Krøll. "To dismantle the ties, we designed a derrick to be placed on the side of the slewing of K1000.
"We faced a similar challenge on the Industrial Ring Road bridge project in Bangkok. Again, the cranes were located close to the pylons and it wasn’t possible to remove the ties with the front jib of the crane. We reversed the crane by adding a trolley and hook system to the counter jib. With the shorter counter jib it was possible to remove the ties. The same principle was used with the K400 on the CanTho bridge in Vietnam.
"The issue with the construction of pylons is height and designing hoist rope winches which can carry the sufficient amount of hoist rope for the height. We, and our sister company Favelle Favco, have made cranes for buildings of 800m in height and have both been designing winches with big wire rope capacity for many years.
Growing demand
Manitowoc expects to see an increase in bridge projects from developing countries. "The number of projects in developed countries is decreasing as it’s mainly dedicated to replacement projects but we’re seeing a rise in demand for big cranes on bridge projects in developing countries", says Bohnenkamp. "This means the number of projects on a global scale staying about the same".
Hans-Martin Frech, marketing manager at Liebherr says, "the demand for larger cranes can be observed all over the world and does not only concern bridge projects but also building construction projects, residential construction projects, industrial construction projects as well as dam sites and dockyards.
"We’ve noticed an increasing demand for larger cranes which can be erected and dismantled easily and can also be shipped in ship containers. Cranes of this size category travel around the world. To meet this demand, we presented our largest EC-H tower crane, the 1000 EC H 50, at this year’s bauma. This crane has been specially developed for high lifting capacities, simple erection, easy container transport and large working radii. Special attention was paid to a high lifting capacity at the jib head at maximum working radius. At present, the 1000 EC H is the largest EC H crane from Liebherr in the EC-H series.
Zoomlion recently developed the D5200, now the world’s largest tower crane. This giant can lift 240 tonnes to a height of 210 metres. Lekang Yu, vice general manager of the tower crane branch for Zoomlion says, "we are currently using the D5200 on large-scale bridge construction in China are meeting the needs of customers who require lifting of heavy weights in excess of 160 tonnes. In addition to large bridges, we expect to use it in the large-scale construction of energy facilities, shipyards, ports and other areas.
The Middle East is just beginning a building boom of large ports as well as planning the construction of Turkey’s Black Sea bridge, the third Bosphorus Bridge.
The third Bosphorous Bridge is a €2.3 billion project linking Asia and Europe in the north of Istanbul. At a width of 59m carrying 10 lanes of road and rail traffic, it’s expected to be the world’s widest suspension bridge. "We hope the D5200 will also have the opportunity to contribute to this project", says Yu.
Here’s one we made earlier
Whether it’s a brand new construction or a replacement bridge, maximising prefabrication and minimising onsite construction can reduce costs in time and materials, permit safer work access and keep traffic disruption to a minimum.
The Hardanger Bridge on Norway’s west coast is currently under construction and, when completed, will become the ninth longest suspension bridge in the world. Scandinavian construction company, Veidekke , is providing the concrete, reinforcements and castings on the project. Halvard Leren, project manager at Veidekke says, "We cast all the concrete onsite but the tower saddles were manufactured by Goodwin Steel Castings in the UK and brought to site. These two huge steel structures weighed 13t each and we lifted them in place at 185m. We spent a lot of time choosing the right crane for this. Because of the cost of having to get a bigger crane, we ended up with just one crane that could take this load directly into place for one pylon, but we had to slide the other saddle into place. We landed the remote saddle on the upper riegel, then we made a steel arrangement to slide and lift it into place. We rented a Liebherr 280 EC-H to take the saddle to the top of the pylon." Construction began in 2011 and is scheduled for completion this year.
The Forth Crossing Bridge Constructors (FCBC) joint venture in Rosyth, Scotland sees the design and delivery of a cable stayed road bridge and will replace the existing Forth Road Bridge as the main route for traffic across the Forth.
Streif Baulogistik GmbH, international construction logistics experts, supplied three Liebherr 630 EC-H 40 Litronic cranes for the project. "We have already erected one crane at the position of the central tower in the Firth of Forth", says Christoph Brandenburg, project manager at Streif. "We are planning to climb the crane in eight phases and it will reach the final hook height of 226 metres in 2016. We will install the other two cranes in mid July and at the end of August 2013. They will also be climbed in eight phases at the base of the pylons."
"These cranes have a maximum lifting capacity of 40t" says Liebherr’s Frech. "Due to the short jibs of 36m, it is possible to move loads of 18t at 36m. This tower crane configuration has deliberately been chosen so that very high loads can be transported with a very high handling capacity.
"The biggest problem of dismantling the crane is the lengths of the tie in to the building", says Brandenburg. "The easiest way will be to remove the ties will be to put a small derrick on the top of the pylons. We’re currently working with Liebherr and the FCBC to solve this issue." The bridge is expected to open to traffic in 2016
Linden Comansa’s biggest range is the LC3000 series with two different models — 30LC1100 and 30LC1450 — and three versions each, with 32, 48, and 64t maximum loads. While the LC3000 series was developed to work on big projects such as dams, industrial plants, shipyards and nuclear plants, the company mainly uses the LC2100 series for its bridge projects.
"In our current bridge projects we are using 21LC290, 21LC400 and 21LC550, with maximum capacities of 18 or 24t", says Mariano Echávarri, marketing manager at Linden Comansa. "These are used to move the materials around the site and also to build the pillars of the bridges with prefabricated blocks. When the pillar gets particularly high, the cranes are jacked-up using a hydraulic jacking cage so the pillar can be built higher.
"There are five 21LC290 tower cranes on the Marão viaduct project in Portugal right now, and all of them lift heavy material up to 18t, machinery, steel or iron structures, formwork structures, concrete blocks and concrete buckets. Their jib length is 74m, the maximum of this model, so the cranes can move the material in a wide space of the jobsite.
"As the cranes reach a maximum final height of 149 metres, the hoist speed is very important. For this kind of project, we have optional mechanisms with a maximum hoist speed of 228 metres per minute so the crane can work as fast as possible. And for projects where the cranes have to work at even higher heights, we can offer mechanisms with drums with capacity for more hoisting rope up to 1280 metres, so the crane could work at a height of 320 meters with double reeving. Without such drum capacity, the crane could not work this high, or could only work with simple reeving, which means that could only lift half of its maximum capacity."
How high can they go With advancements in technology making it possible for bridges to be constructed across an even wider span at unprecedented heights, crane manufacturers are wondering where the limits lie.
"It’s difficult to say where the limits will be", says Bohnenkamp. "For tower cranes the technical challenges grow in proportion with the height of the bridges and the weight of the prefabricated elements. The span of the bridges is increasing and the height of the bridge piles grows proportionally. It all brings new challenges to be overcome.
"There is a visible trend to use high performance tower cranes for big infrastructural projects. The erection and dismantling time for a tower cranes is similar to lattice boom crawler cranes, but the ground preparation is much easier for a tower crane. Another growing interest to use tower cranes is for wind mill erection and especially in remote, difficult to access, high wind areas. To catch higher wind speeds, the wind mills itself and the generators get bigger and heavier. For those reasons, plus in general terms, we are anticipating that the number of high performance cranes in the range above 600mt should double in the next five years and double again in the following five years."
"For crane usage worldwide there is increasingly high demand to lift more than the traditional 80 – 120t. The D5200 goes beyond the conventional large-scale projects and we anticipate infrastructure projects in emerging regions", says Zoomlion’s Yu. "We expect cranes with lifting power even greater than the D5200 tower crane to be an inevitable trend. We are currently in the process of pre-research for a 8000tm tower to ensure we can meet this demand"