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Mini Sky City, a skyscraper built in 19 days

J57 Mini Sky City was built in a combined construction time of only 19 days, which is almost at a pace of 3 completed floors per day. The tower was developed by Broad Sustainable Building (BSB), which is a construction company specialising in prefabricated buildings. The tower was built with energy-efficient, factory-produced elements, using the BSB prefabricated construction method, which won the 2013 Council on Tall Buildings and Urban Habitat (CTBUH) Innovation Award. Using this construction method reduced the use of up to 15, 000 concrete trucks and avoided the release of dust associated with conventional Chinese construction processes. J57 includes 19 ten-meter tall atriums, 800 apartments and office space for 4 000 people, which highlights the flexibility of the building use, even if it uses this construction method.

ArcelorMittal Solutions Fire 
Heavies High strengh 
Bracing pre-fabricated steel frames HISTAR® 460    sprayed
Columns   sprayed
Floor solutions     modular construction sprayed


Steel Structure

90% of the tower is made of manufactured block that are developed offsite. The block can simply be locked together and secured with high strength ribs and bolts. This provides adequate structure, increases the rate of construction, and simplifies the construction process. The flexibility of the spaces, strength of the structure, rate of construction, and the accuracy and precision of each module can only be achieved by using steel elements.

ArcelorMittal Steel Sections

ArcelorMittal provided 10 345 tonnes of HISTAR® steel sections from Differdange to build the frame of J57 Tower. The team of ArcelorMittal Europe – Long Products was selected by BSB, due to the accuracy of the size and strength of their steel sections; this is the most crucial element to ensure that prefabricated buildings are built according to the construction schedule.


According to the Architect of J57, Xian Min, in addition to significantly reducing the amount of concrete required and eliminating the dust on the construction site, this construction method is so energy efficient that it will save 12 000 metric tonnes of CO2 emissions compared to conventional buildings with a similar function. Furthermore, another reason for which ArcelorMittal was specifically selected was the fact that the majority of the steel from Differdange was derived from recycled scrap steel elements.

Height: 207,8m (682ft)
Number of Floors: 57
Gross floor area: 179 600m2
Building Function: Residential; Office
Structural material: Steel
Completion: 2015
Architect: Broad Sustainable Building Co., Ltd
Structural Engineer: Sky City Investment Co., LTD 
General Contractor: Sky City Investment Co., LTD
ArcelorMittal Steel: 10 345 tonnes of prefabricated sections in HISTAR® 460
Fabricator: Yuanda Keijian