When Linden produced the 8000 series, in 1975, its sophisticated modular design astonished many in the crane industry. Despite the groundbreaking design, the Scandinavian crane manufacturer ran into financial trouble in the late 70s, when the oil crisis hit demand for high capacity tower cranes.

Comansa took over the design rights and expanded the crane range, focussing more on smaller 100-200t class cranes, for which there was broader demand. It was Franc Jost who rediscovered the flat-top saddle jib crane concept, realising it in 1990 with BKT in an erection and transport friendly manner as the 80tm city crane. During his time with Terex-Comedil of Italy, and later on at his own Germany-based company Jost set further milestones in the development of flat-top cranes, extending their capacity range into the 700tm class.

Now nearly every major tower crane manufacturer provides flat-top models somewhere in their range. Some traditional market leaders, like Liebherr and Wolff of Germany and Potain of France, see this crane breed as an addition to their traditional saddle jib crane line. For them, flat-tops are increasingly important, particularly in the city class range and up to the 300tm class.

Others, like Comansa of Spain, and Terex-Comedil and Raimondi of Italy, have replaced more and more of their classic saddle jib crane range by flat-top cranes. Some newcomers, like Jost, RDLift of Italy and Vilniaus Kranai of Lithuania, have gone so far as to use flat-top designs for all of their top slewing saddle jib tower cranes. Many successful crane manufacturers from the Far East are relying on the flat-top design entirely.

A number of manufacturers, including Liebherr, Potain, Raimondi, San Marco of Italy, Wolff, Wilbert of Germany, and China-based Zhongsheng Construction Machinery (ZS) have developed the concept in their own ways. However, the two main structural lay outs of flat-top upper crane design come from either the original Comansa LC1000 and LC2000 series, or on Franc Jost’s first designs. While most cranes of the Yongmao STT range and the QLP range of Sichuan Quiangli Construction Machinery follow the Comansa design, cranes from DKT of Malaysia and Shenyang Peter’s Machinery Co. Ltd of China show their inheritance of Jost’s ideas.

Big flat-tops

Some manufacturers see declining benefits in the flat-top crane design when it is applied to high capacity cranes, arguing that an overall jib section profile above 2.80m and the high weight of the jib cause logistical problems in many countries. Other companies though point out that sectional upper crane rigging is far more flexible than conventional high capacity crane design.

For example ZS, based in Nanjing, China, is delivering real giants for the domestic power station construction industry. The ZSC60300 boasts a maximum capacity of 80t at 25m radius in 8 fall operation mode. Even at a radius of 60m, the 2,000tm class flat-top crane can still lift 30t. The ZSC70240 even provides a tip load of 24t at 70m radius.

In Europe, the Linden 8000s delivered to Poland in 1978 are still among the biggest flat-top cranes ever built. At the moment one unit is operated by crane rental specialist Sarens at the Belchatów power station construction site in Poland, where it is working with a 58m jib. On a 5.8m x 5.8m mast the crane reaches a free standing height of 148m and can lift 50t at 16.6m radius.

The Linden 8000s at Belchatów was used first on the construction of a stair tower for the plant’s boiler house. The crane has now been transferred to the cooling tower site, where it will reach an under hook height of 198m, only anchored two times at 108m and 160m height using a guying system. The Linden self jib dismantling device will climb down the crane inside the finished hyperbolic concrete structure.

Latest trends

The growing success of the new Liebherr EC-B range is based on the crane’s sophisticated assembling technology and the 20% greater load capacity available on the Litronic version at the touch of a button. The youngest member of the new light weight flat-top crane series is the 30EC-B2.5, following the 30LC city crane. At 30m jib-end 1t can be handled. While the counterjib of the small city crane only carries the ballast plates, the trolley winch is unusually located aside the jib foot, along with the hoisting winch. This facilitates aerial rigging by helicopter. No module is heavier than 1.5t.

In the medium capacity class, the Terex-Comedil CTT231 moves away from the original Jost design features in the traditional Terex-Comedil flat-top crane line. Instead of the massive hammerhead-like first jib section on the top of the tower, only a compact tower head is used as the connection point for the flat counterjib, which is fitted with pendants. The compact hoisting unit can be left in place on the counterjib during transportation. Depending on the assistant crane’s capacity, the complete upper crane with maximum 70m jib and 10t or 12t maximum load can be installed in four lifts.

With the MDT 268 Potain is creating a new flat-top upper crane design with 65m maximum jib length. Just carrying the ballast, the compact counterjib can be folded for reducing transport length. At the back of the slewing unit the machinery platform is located under the counterjib, in the same way as on the ancient Peiner KL series cranes, providing direct access by the cabin platform.

Raimondi has a long tradition in flat-top city cranes. It extended its line into the higher capacity class by introducing the MRT243. Its extraordinary trapezoidal boom foot shape permits reduction of wind force and gives the long pendant free 78m boom the required rigidity and torsion fluidity. Tip load is 2t while maximum capacity is 16t. The crane can be installed in a 95m free standing version. A minimum boom length of only 24m demonstrates the flexibility of the crane design to cope with narrow site conditions.

With the export market in mind, Spain-based Saez has some long jib flat-top cranes in the pipeline. The TLS8024 will be available in a 24t version with 80m boom and 2.6t tip load capacity in September 2008, while the smaller TLS7516 with 16t maximum capacity and 3t at 75m is said to have been on the testing ground in March 2008.

Following Jost’s flat-top crane design principle, DKT recently manufactured the massive DT912-40 with 40t maximum capacity and 7.5t maximum load at 80m radius. Like the modern Jost tower cranes, the DT912-40 is equipped with a side mounted control unit made up of a comfortable cabin and a walk-in electric cabinet.

The latest compact flat-top crane concept developed by Jost is the JT132.8. This has a side mounted retractable cabin unit which can be left in place for transportation. A licensed copy of the crane, the JT140-8, is manufactured by Shenyang Peter’s in China, delivering flat-top cranes in Jost design to the Asian market.

Meanwhile, in Europe, the first fruits of the Jost’s co-operation with Netherlands-based Kranenbouw are visible. According to Frank Crombe, the Dutch company is specialising their manufacturing capacity on the middle size class M series Jost flat-top cranes.

At the time of writing a JT312 with 64kW hoist (instead of the standard 45kW unit) was assembled at Kranenbouw for a high rise construction project in the UK. The crane has a maximum jib length of 80m with 1.8t tip load. In one year, already about 25 units of the 300tm class crane have been delivered.

Growing building activities have supported the development of BCT (Baltic Cranes Technologies), based in Vilnius, Lithuania. Besides many second hand Zeppelin flat-top tower cranes, new BCT80 cranes are to be found in the booming construction market of Lithuania. Besides minor updates, the BCT80 follows the design principle of the Zeppelin ZBK80. The 80tm version representing the roots of Franc Jost’s flat-top crane development. BCT offers a BCT140 with 60m jib and 8t maximum capacity, showing substantial design improvements on the Zeppelin ZBK132.

San Marco International of Italy offers a flat-top city crane range up to 67.5m radius with 1.6t tip load. The cranes follow the Italian city crane design with the trolley and reeved hook parked at the so-called ‘trolley jib’ on the complete tower head. This means the complete upper crane can be installed in two lifts without needing to reeve the hoist rope.

With the ‘clear’ models, Wolff of Germany entered the flat-top crane market in the 200tm class in 2007. in early 2008 a 140tm unit named the 6015clear was added to the 224tm Wolff 6031clear and the 180tm 6023clear. The crane comes in two versions with 6.2t or 8.5t maximum capacity. In both cases two fall operation is possible for all loads. Thanks to the optional 45kW frequency regulated winch 1.6t can be lifted at an impressive 115m/min. As typical for the range, the arrangement of the electric cabinet behind the drivers cabin allows free slewing of the tower top during erection procedure. The counterjib with hoisting winch forms one containerised transport unit.

Wilbert of Germany began manufacturing tower cranes four years ago, taking advantage of 15 years of rental experience. Today its saddle jib crane range comprises flat-top models from 150tm-420tm with a extraordinarily transport-friendly design. The cranes’ unique jib system has two different cross-sectional profiles. The jib section with the smaller diameter can be easily inserted into the jib section with the bigger diameter, cutting transport requirements in two. For example, the complete upper of the WT150e.tronic with 60m jib can be transported in two truck loads in two containers.

In the middle sized crane class another Chinese manufacturer is entering the international scene. Sichuan Qiangli Construction Machinery (QLCM) already exports the QLP125A (QLP6015) flat-top crane to the Ukraine and UAE. This crane has a 10t maximum capacity and lifts 1.5t tip load at 60m radius. At the time of writing, larger models, with 3t capacity at 80m radius and 5t at 70m radius called QLP8030 and QLP7050 are under development.

Why so popular?

In contrast to conventional saddle jib cranes with pendants and tower head, flat-top cranes can easily be adapted to very special site requirements demonstrated.

Since 1959 Pingon tower cranes have been fabricated under licence in Brazil. Today Pingon Elevadores & Gruas provides a complete range of flat-top cranes, from the City Crane TL30-3 with 1t capacity at 30m, to the large TL600-16 with 2.9t tip load at 85m radius. The firm builds 10-12 flat-top each year. The biggest one so far was a 1000tm unit.

The cranes find a ready market beyond just the construction industry. Specially adapted Pingon flat-top cranes are used for industrial rigging work, like chimney construction and flare tower renovation work. Thanks to the pendant free construction principle these cranes are equipped with short boom and counterjib combinations, demonstrated by the custom built Pingon TL crane. This is based on the TL300-8 series model with 110m hook height and 8t capacity at the 15m boom.

A unique design feature of all of the ZSC series cranes built by ZS, is the hoisting rope that leads directly from the winch unit. The winch unit is located on top of the lattice, box-shaped, counterjib above the jib to the jib end. This means that reeving on top of the standing crane is simplified. The hoisting winch platform can be fixed at different location of the counterjib, to adapt the crane to special site requirements.

ZS was involved in recent prestigious Chinese bridge construction projects. At the 306m high North Pylon of the Sutong Bridge one ZSC flat-top crane was working under the massive Potain MD3600 umbrella crane. When removing the flat-top tower crane after topping out of the bridge tower , a number of bracings had to be deinstalled as well. So it was decided to enable the ZSC series crane to do this work, while climbing down alongside the pylon with only limited modification of the standard crane.

The hoisting unit was replaced from the back of the counterjib, to a position next to the flat tower head section. This meant that the sectioned counterjib could be reduced to about 6m, while at the same time the pendant free jib was shortened to the jib base section at the standing crane. The crane worked in extreme compact upper crane configuration, letting it slew freely and dismantle the complex bracing to the pylon. It climbed down by taking tower sections out of the climbing cage in conventional manner.

In a similar way SCJC has just delivered an all new JCP7427 topless tower crane with de-rigging derricks for the construction of the 181.8m high Zhongxiang transmission tower. Main hoisting of the 18t maximum load crane, trolleying and slewing mechanism are controlled by converting and speed-adjusting technology. Stepless and low speed regulation helps to improve working efficiency for the 955t steel structure that is being built.

With its wide crane range and modern flat-top crane line up to 24t capacity, SCJC is due to enter the international market. Its first cranes in this range have been delivered to Vietnam and UAE. CE certification has already been received for some models. Equipment suppliers such as Schneider Electric (of France) and Flender drive units (from Germany) for example, will soon open up other export markets for SCJC.

In Italy the Gulliver VR35/100 represents another sophisticated adaptation of flat-top tower crane design to special site conditions. Space is very restricted in historic European inner cities. Sometimes there is not enough room even to install a suitable mobile crane or to pre-rig the jib of a tower crane on the ground. Italian crane manufacturers TGM and RDLIFT provide the VR35 city crane for such cramped sites.

The crane offers 35m jib with 1t tip load on a 34.6m high free standing tower. A forklift helps to rig the top slewing climbing crane, using self rigging devices. After the upper crane with counterjib is installed, a derrick on the counterjib lifts jib sections on the counterjib platform. From there the sections are slid to the front by a hydraulic cylinder. The jib can be extended in 2.5m steps to the required length. New jib sections are added safely on the counterjib platform to the existing jib. For climbing procedure in conventional manner only the outer jib section have to be slid over the counterjib. Hence the crane can climb in very narrow back yards before the jib is extended over the roofs.