China’s custom-builder

The Chinese tower crane market will not remain unaffected by the global economic crisis and the decline of the construction boom after the Beijing Olympic games in 2008.

However, large-scale governmental infrastructure programmes and prestigious projects like Expo 2010 in Shanghai still provide healthy demand, especially for large capacity tower cranes. With enhanced emphasis on environmental pro­­tection, the generators of modern coal-fired power plants get larger and more complex. The boiler houses of the 300MW–600MW power stations had an elevation of 80m and required cranes with capacities of 80t–120t. For today’s 1,000MW power stations, cranes are required to raise 80t–140t to 100m–130m height.

This high capacity crane market is one of the domestic core markets served by Zhongsheng Machinery (Nanjing) Heavy Industry Co. Ltd (Jiangsu province). The company specialises in the production, sales and leasing of tower cranes, floating cranes, special cranes, drill rigs, static press-in pile drivers and special machines for bridge erection and fabrication. Since its establishment in 1993, it has delivered about 100 tower cranes with capacities greater than 300tm, and 40 tower cranes with capacities over 1,000tm capacity.

Although at the moment concentrating on the domestic market, the company has some unusual features. Cranes Today understands that Taiwanese investors have a stake in the company, but it is not known how large that stake is. Perhaps as a result, the company has advanced Taiwanese management methods, intensive use of CNC and NC (computer numerical control) fabrication equipment for quality management and some international-level features. These features include hydraulic stepless speed regulation system for smooth load placement, and PLC and touch screen technologies for operational safety and comfort.

While super skyscraper projects are generally dominated by Favelle Favco luffing jib cranes, Zhongsheng luffing jib cranes are gaining in China. Recent examples are the 430m high Nanjing Green Square Building and the 309m Guangzhou Pearl River Tower. Cranes in the company’s standard livery of dark blue masts and jibs, and yellow drivers’ cabins, have also worked on the 230m high Third Nanjing Yangtze River Bridge tower and the Chinese Pavilion at the Shanghai World Exposition Center.

The biggest flat top crane in the world is the company’s ZSC2800 series, with a maximum lifting capacity of 140t at 19.5m radius. Zhongsheng’s crane series numbers appear to refer to its maximum load moment (2,800tm). Individual models within the series each have a different model number. The model number refers to the crane’s maximum lifting capacity at maximum jib length, so a model in the ZSC2800 series is named the ZSC70360 because at the end of its 70m jib it can lift a tip load of 36t. Despite the crane’s size, 3.2m square, 6m high, monoblock tower sections are used for up to 60m free standing height. Extraordinary large ZSC series models are suitable for heavy steel erection work, like boiler house construction.

Apart from their size, the most unusual aspect of Zhongsheng flat tops is their upside-down jib. Many tower crane jibs are triangular in cross-section, with the top of the triangle upward. Zhongsheng’s design turns the triangle upside down. Its base chord is designed as an I-beam, on which the double-monorail trolleys of the big ZSC cranes roll.

According to Danny Shu, representative of ZS, the modular pendant free jib and counter jib design allows the basic cranes to be assembled by relatively small mobile cranes. The size of the modules to be installed can be easily adapted to the available assisting crane capacity. For simple erection and maintenance the winch platform is bolted on top of the box-shaped modular counterjib. The hoist rope runs completely outside the jib, simplifying reeving. The crane can be reconfigured relatively quickly into a special short-tail design by shifting the winch platform on to the counterjib foot section and dismantling the outer counterjib section.

As far as possible, pin connections are used for fast set-up procedures. For example, the H-shaped rail undercarriages designed by ZS consist only of a central frame supporting the tower that is pinned to two side beams. The beams’ length can vary to cope with conditions on the actual construction site.

The company’s most popular luffing-jib crane is the ZSL750 with maximum 50t capacity. It is about the same capacity as the Favelle Favco M600D. Zhongsheng’s largest luffing-jib crane is the ZSL2000 series with 100t maximum capacity up to 20m. It is built in three different versions with jib lengths of 40m, 45m and 50m. The ZSL40445, for example, has a tip load of 40.4t at 40m radius. It fills the gap between the Favelle Favco M900D and M1280D in the Chinese market.

Unlike Favelle Favco luffers, the Zhongsheng cranes can be specified with either diesel engine or electric (DC) drive. Steel or concrete ballast is installed as fixed counterweight into the edge of the machinery deck, speeding up crane erection. Optionally, the machinery deck can be ordered in a split deck version (connected by pins) in order to reduce erection weight. The boom retaining rope, used during reeving of the luffing rope, is kept in place after erection, to shorten derigging time.

A number of special tower and climbing systems have been designed. For example, the internally-climbing ZSL750 (ZSL5099) was modified to externally climb to a height under hook of 430m on the Nanjing Greenland Square Zifeng Building. To minimise interference with ongoing construction work at the lower building set back, the crane climbed up outside the core to the very top of the building with special wall-bracket climbing collars.

For an October 2008 bridge construction project, two ZSL750s climbed to freestanding heights of 100m using a special large-diameter external tower with the standard 2.7m x 2.7m tower, normally suitable only for a maximum height of 54m. The extraordinary freestanding height was essential for the bridge pylon design, which did not allow anchorage of the large capacity cranes. The luffing-jib cranes installed 50t steel segments at 15m radius.