Big wheels

20 March 2008

The engineering skill required to reach working heights of 100 m is important, of course, but the current divide in opinion is not about how to get to these heights, it's about what truck carrier to use.

In the blue corner we have Bronto of Finland, which exclusively chooses modified commercial trucks. (It has built 144 units with working heights60 m and above.) Most recently it has built threeof its HLA 101, currently the world's tallest aerialplatform at 101 m working height, onchassis modified to handle the 60–odd theof GVW.

Further down the continent, in the redcorner, is WUMAG, preparing to take the ‘world's tallest’ title with the three +100 mmachines it is currently building. However, the WT1000s are on all–terrain chassis built by Faun, themanufacturer of carriers for Tadano Faun's allterrainmobile cranes.

Although the figures indicate that recent marketactivity is evenly split between truck and cranecarriers, the historical split is about 90/10 in favourof commercial trucks, according to Jerry Kist, salesmanager with Italy's OP Pagliero. That company'stallest model is an 85 m machine, two of which itis building this year, said Mr Kist, on trucks and forgeneral applications.

One explanation for WUMAG's crane–carrierchoice is the growing popularity of wind turbinesin Europe “The considerable gain in cross–countrymobility…is indispensable for reaching windturbines placed in the open countryside, the mainfield of application of [WUMAG's] WT 850 and WT1000,” says Oliver Schroeder, marketing specialistfor the company.

Wolfgang Latton, managing director of Germanrental company Eisele and buyer of one of the WT1000s, anticipates other uses, too. He told AccessInternational that “a crane chassis [is] also highlymanoeuvrable and permits operations in tight, inner city conditions.” However, “Its rental ratesremain the same as with similar lifts of this workingheight and reach.”

Jan Denks, regional sales manager for Bronto, offers a different explanation for these cranechassis platform sales: “Crane carriers havebecome slightly more popular recently because ofnecessity, not sensibility.” His explanation is that some national road laws allow higher maximumaxle loads for crane chassis. France, for example, allows registration of 5– or 6–axle cranes, but nottrucks. Mr Denks believes this inconsistency isbecause the crane industry has more lobbyingpower than the access business.

Chassis running gear is a good starting point forunderstanding the differences between the chassistypes. Platforms offering working heights above90 m, according to Mr Denks, require carrierswith five or six axles to carry their weight. No truc kmanufacturer, such as Mercedes, MAN, and Volvomakes such chassis, so specialty manufacturersbecome part of the production process (see boxstory). Most frequently they add standard runninggear to meet road load limits.

Although modifications are necessary formounting large booms on a commercial truck, one advantage is their availability, and also theavailability of service resources around the world. On the other hand, only a few manufacturers, including Grove, Liebherr, Tadano Faun, Marchetti,Terex Demag –build crane chassis, and theytypically use different, more robust running gear. While running gear supports the large aerialplatforms on the road, outriggers support thebooms while working. The two different chassistypes accommodate these critical components infundamentally different ways.

Outrigger mechanisms on crane carriers areintegrated into the chassis, and Bronto's MrDenks feels that, as a result, the “access platformmanufacturer has limited possibilities to control hisdesign. This restricts, for example, variable jackingoptions, automatic levelling and extended outriggeroptions.”

Outriggers for trucks attach to the frame ofthe platform assembly, allowing greater designflexibility. “We can vary the distance between frontand rear outriggers”, says Mr Denks, “and we canmount them at the top or bottom of the frame. Wecan also adapt the height of the slew ring to fitcabin height.”

Of course, it is the all–terrain travel abilitythat is one of the main benefits of the cranecarrier. These are benefits that are well understoodby the crane manufacturers. Take Liehberr, forexample. Wolfgang Beringer, sales promotor forthe crane manufacturer, says “Users want shortand compact cranes, and crane designers wantshort axle distances”.

Evenly distributed, lower loads minimise thelikelihood of any one set of wheels breaking thoughsoft surfaces and losing traction. Even distributionof weight also helps maintain the traction of torqueequally distributed to wheel sets, more likely foundin crane carriers.

Ground clearance is a matter of tyre radius, andMr Beringer points out that truck chassis cannot fitthe larger wheel hubs and tyres (20.5 R25) of mostall–terrain chassis. Their greater ground clearanceis primarily due to be able to fit 20.5 in (520 mm)radius tyres, while the maximum on a truck is 16in (400 mm).

Trucks and cranes differ little in engine power, but crane chassis usually have wider tyres withprofiles that better transmit torque from powertrains. Crane chassis deliver power train torquemore effectively and consistently to the ground onuneven surfaces.

Steering to negotiate around or between obstacles can be important in some settings, and cranechassis usually have all–wheel and multi–modesteering, again superior to a typical truck.

There are trade offs, as well, between the twotypes of carriers and boom designs themselves. Bronto's Mr Denks points out that crane chassis, which are higher than truck chassis, make it moredifficult to keep booms below the 4 m transportheight limit of European Directive 96/53EC. Brontoalways folds the cage boom alongside the mainboom in order to minimise height of the boompackage.

WUMAG's sales director, Stefan Kulawik, says the telescopic/articulated design of its 85 and 100 m booms has advantages. It allows the fly boom to store at the rear of the carrier, making “easy entrance to the cage and ‘climbing experience’ to the platform decking of the chassis not necessary.”

Flexibility and choice, in Mr Denks’ opinion, are considerations for large platforms as a whole, as is after sale service: “[Crane chassis] integration also limits owner's choice of chassis; he must accept the one chosen for him by the manufacturer.

“The decision might be made based upon the availability of one local, competent service facility and not maximising the owner's benefit. Also, the platform manufacturer probably buys the carrier in his country; the local dealer for the crane carrier may be reluctant to service that chassis.”

That comment introduces the subject of costs. Mr Denks told AI that a 5–axle truck costs about I€150000, and the cost of a 5–axle crane chassis is about twice that. Operating costs are also significantly different.

According to Mr Denks, complying with the 4 m height restriction of European Directive 96/53EC for a boom designed for folding during transport sometimes requires lowering the truck's cab. This costs about €40000 and also reduces clearance at the vehicle's front, negatively affecting rough terrain and ramp negotiation ability. He says that Bronto is the only company able to mount 90 m platforms on a truck chassis without the need to incur this cost.

WUMAG told Access International that the cost differences between the two types of carriers are minimal. “The use of a mobile crane chassis results in a compact design with less overall length and no necessity to add stabilisers, lengthen the [truck] chassis, lower a standard driving cab, or do other price–raising modifications. Taking this into consideration, [perceived price differences vanish if you consider all factors].”

Resale is part of the financial analysis, too. “Usually when you have a special chassis, the machine has its own life, it has only one purpose. It is hard to re–sell it. A work platform on a crane chassis is even more difficult,” says Pagliero's Jerry Kist.

Mr Denks agrees and points out its truckmount booms “…are often remounted onto new chassis at some point in their life…This would be impossible with the crane carrier.”

Other manufacturers

Bison Palfinger, which makes the 61 m working height TKA 61, says it has never built for crane chassis mounting. The German company prefers the Scania 8x4 chassis for its truck–mounts because, says European sales manager Alexander Lukas, of “…its lowest cabin profile on standard truck.” It is not planning a taller platform model, instead focusing its product development on other market segments. It sees “little demand [and a] growing number of players.”

Germany's Anton Ruthmann made the 100 m working height breakthrough a few years ago with a trailer–mounted machine, but produced only two units. It also has no plans for a new, tall platform. A company spokesman told AI that ”when it did, it I would be a completely different design.”

OP Pagliero was “…probably one of first to build on a crane chassis, a 55 m machine, and we built 55 and 65 m units for [access rental company] Maes in Belgium,” says Mr Kist. However, it built its last crane chassis unit probably 15 years ago. The two 85 m machines it will build this year are truck–mounts and for the general access market, he says.

Given the preponderance of trucks in the big boom market segment, will demand for higher capability platforms change the mix between truck and crane chassis? Mr Kist doesn't think so. “Truck manufacturers will have to increase truck capability. Demand for heavier off–road capability is increasing, for concrete pump trucks and dumpers, for example. This market segment will increase and get a lot more development.”

This also begs the question, if crane–type chassis become more common, could their use spread to aerial platforms in the 50 to 80 m sector?

WUMAG doesn't think so. Although it put the single 85 m machine that it built a few years ago for Spanish rental company Umesa on a crane chassis, its next smaller platform, at 70 m working height and 35 t GVW, mounts on a 4–axle truck chassis. “These types of chassis are available in 8x8 execution as well as 8x6,” says Mr Kulawik.

Bronto certainly thinks that most large platforms will continue to provide access from the back of trucks. “This topic [cranes vs. trucks] pops up every few years,” says Mr Denks, “but trucks are 98 to 99% of the market. There are just too many positive things for trucks.”

However, positive too are the greater manoeuvrability and accessibility of crane chassis for getting to some sites. Buyers' choices depend on where users need the high access, how they plan to get there, and, perhaps most importantly, determining if all–terrain capability is worth any anticipated greater cost.

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