The popularity of self-erecting tower cranes in different countries is hard to explain, beyond attributing it to differences in “construction culture”. Where there is a lot of prefabrication of building components a mobile crane, which lifts more and can be brought in just for when it is needed, is more popular. Where housebuilding follows more traditional lines, a small tower crane which can be quickly erected and simply used, becomes attractive – especially if labour costs make the economics viable.
For those opting for self-erecting tower cranes, or fast erectors as they are also known, the huge range of models on offer can make purchasing decisions difficult.
Major markets for self-erectors include Germany, France and Italy. Perhaps unsurprisingly, these countries are home to most of the major manufacturers, with Potain of France claiming to be the world’s largest manufacturer and offering the most hydraulic models.
Germany has been the world’s dominant market for self-erecting cranes in recent years, with sales peaking at 5,100 units in 1994. A dramatic decline saw this figure tumble to under 780 in 1997 and early industry estimates suggest that sales were about the same in 1998. A slight improvement is forecasted for 1999, with sales expected to rise slightly to 850 units.
For most of the 1990s self-erectors accounted for between 80% and 85% of all tower cranes sold in Germany. Though sales tumbled in 1997, the ratio increased to 93%.
Potain claims more than 50% of the German market, with its GMR HD 32 proving to be its most popular model.
Illustrating the collapse of the German market, Liebherr’s production in 1995 was 75% self-erecting models and 25% top slewing. Today these figures are reversed.
In 1997 Italy overtook Germany in sales of self-erecting towers, hitting about 1,00 units, though here the models are typically smaller.
High labour costs in countries like Germany for example, enhance the popularity of self-erecting cranes, making them a cheaper option. The UK has a similar housing structure but construction methods are different and so a self-erecting crane is less often used.
McCarthy & Stone Construction Services, with a fleet of nearly 30 from various manufacturers including Liebherr, Munsters and Potain, claims to be the UK’s largest operator of self-erecting tower cranes. McCarthy & Stone’s fleet ranges from a small Liebherr 38 K up to the 8t-capacity Potain 386. The company also has a crawler mounted Munsters A30 which plant manager Peter Johnson says is a good alternative to a rail mounted crane. McCarthy & Stone specialises in building sheltered retirement housing, usually of between 35 and 120 units, but its cranes are also available for hire.
There is also competition from other lifting methods and this varies widely from country to country. Though truck loader type cranes may have a shorter horizontal reach or inferior lifting capacity at maximum reach than self-erecting tower cranes, they do present a potential alternative, particularly the larger models with jibs and perhaps as many as eight extensions, because they can be used to unload building materials from a delivery vehicle and place them directly, ready for use, in a single operation, thereby obviating the need for further handling by a site crane.
Telehandlers are a further source of competition, particularly in the UK and USA where, it seems, wheeled machines are preferred, and to a lesser extent so is short-term rental of a mobile crane. Unsurprisingly, according to one manufacturer of self-erecting cranes, one of its cranes on site can complete the work otherwise carried out by a telehandler, truck-mounted loader type crane or an occasionally rented mobile crane.
Loader cranes and telehandlers have added appeal in countries where charges are made for, or it is not possible to, oversail adjoining property, which a self-erecting crane may have to do in order to operate. However, when a site crane is required, self-erecting models are easily transported by towing as a trailer or a semi trailer at up to 80km/h, erection is simple, often taking less than two hours and the jib can often be luffed.
On larger construction sites the choice between a bottom slewing self-erecting model and a small top slewing saddle jib tower crane can be a difficult one. It may be preferable to select a top slewing crane because although erection takes longer, the purchase price of the crane itself may be only about half that of a comparable 45m jib self-erecting model. About 10 years ago there was a trend towards these larger self-erecting models but now users often find top slewing tower cranes cost-effective where the job will run for at least two months.
Having said that, another tower crane manufacturer claims only a marginal purchase price premium on a self-erecting crane over a top slewing tower type. Additional penalties such as the need to close roads while a mobile crane is used to erect the tower crane could be enough to swing the decision.
Height restrictions can be a problem for both top slewing and self-erecting tower cranes so Comansa, a leading exponent of the flat-top principle on tower cranes, incorporates a similar idea on its self-erecting models in that there is no tower head and no jib ties that can be difficult to see. The increased height of these components could be a problem in applications where a self-erecting crane is working underneath a tower crane for example.
Having decided on a self-erecting crane as the best option, the purchaser can then choose between two basic types – hydraulic or rope-mounted erection. Hydraulic models have become popular in the last 10 years and a common size is about 1t capacity at 30m or 35m jib. For larger models however, a rope and winch design remains the preferred solution and is better suited to the commonly employed telescoping lattice tower configuration. The hydraulic type is said by some to be safer because more care and attention needs to be given to a rope that may be less reliable than an (albeit heavier and perhaps 10% or 20% costlier) hydraulic system. Some older hydraulic designs mount the mast erection cylinder on the jib side of the tower which, because it can weigh as much as 1t, means that extra counterweight must be added to compensate.
Another disadvantage of some small designs is that they are not self contained and the counterweight must be transported separately and then mounted either by a separate crane or by an on-board derrick. It often takes two hours or more to mount the counterweight, a problem overcome by Comansa. Its HT-30, launched at the Bauma show in March is a self-contained design featuring a patented folding counterweight system. The load is sufficiently evenly distributed for road transport but the counterweight can be removed if erection is on a difficult jobsite. Large self-erecting cranes need more counterweight than can be carried on board, perhaps as much as 20t, so the need for a separate truck is not an issue.
Aside from erection methods, there are also two basic tower designs – lattice or a single hollow section, each of which may have either rope or hydraulic mounting. The single hollow section design may be considered more “modern” and appears neater, particularly if cabling is routed inside. The main disadvantage of this type is that usually, only a single, fixed mast height is possible, whereas at least the larger lattice models tend to be telescopic and adjustable.
Manufacturers offering models to overcome this include Gru Comedil, with its CBR, and Potain. Potain’s largest hydraulically erected model, the HDT 70, was first presented in 1997 and full production began this year. The ‘T’ designates that this model has a telescopic mast. There are three hydraulically adjustable height positions to give 13.6m, 22.9m or 32.2m under hook. The jib can also be luffed to give a maximum hook height of 53.7m. Tip load at its maximum 45m is 1.1t and the operator cabin can be positioned at various points on the mast.
Potain continues to extend and refine its HD range to accommodate customer demand for a different model for every 5m increase in jib length. To this end, the new HD 30 replaced the HD 26 last month.
This year has also seen Potain expanding its range at the bottom as well as the top. Its HDM 2, launched at the Bauma show in March, is unusual because of its small size and weight (less than 3t). It is intended for projects where lifts only involve lightweight roofing and framework components for example. The crane can lift 150kg all along the 13m jib, the maximum height under hook is 12m, and unfolding takes less than 10 minutes. It needs only a 2kW power supply and features radio controlled stepless motors on all mechanisms.
Italian manufacturer Alfa’s smallest model, the recently introduced A22 Super, has a 22m jib and 600kg tip load. The company says that currently 75% of its sales are made directly to contractors but the majority of this business is city-type tower cranes rather than self-erectors.
FM Gru’s most popular self-erectors are in the 28m to 30m jib length range but it has two new models above and below this range: the RB 10.35I, which has a 35m jib, a maximum lifting capacity of 4t and a 1t tip load; and the RB 6.22I, which has a 22m jib, 600kg tip load and 1.5t maximum capacity.
FM showed the RB 10.35I at the SAIE exhibition in Bologna, Italy in October alongside its smaller RB 6.18 model, which has an 18m jib, 600kg tip load and 1t maximum capacity.
Also in Italy, Gru Comedil (now part of Terex Towers – see News) is adapting its product line by focusing on a limited number of larger models with 32m to 36m jibs because it finds the smaller end of the market too competitive. It has an arrangement with fellow Italian manufacturer Cattaneo which sells its self-erecting cranes through the same dealer network as Comedil and the two ranges complement each other.
From Germany, recent additions to Liebherr’s range include the 34K, designed to be as short as possible when folded for road transport and to need only 12m of erection space. Three different jib lengths are possible between 25.5m and 33m, and standard hook heights are between 11.7m and 20m. Hook height can be increased to 26m by the addition of 2.2m tower sections and with the jib luffed to 30o the maximum height under hook is 39m.
Based on the same system as the 34K, Liebherr’s larger 71K model, launched at Bauma, is claimed to offer advantages in terms of transport, ballasting, different extensions, hook heights and minimal space requirements for erection. At maximum 45m reach the 71K two-rope version can lift 1.2t and the maximum load is 6t. With the jib in the steep angle position maximum height under hook is 53.2m.