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SLJ900/32: China’s Mega Bridge Building Machine

A labyrinthine network of land-and-sea based transport routes is being built to connect China’s booming economy with those of various African, European, and Asian countries. And the Chinese government is leaving no stone unturned to ensure that President Xi Jinping’s Belt and Road Initiative (BRI) – an ambitious project to connect 70 countries or two-thirds of the world’s population through various land and maritime routes – is a success. 

Launched in 2013, the Belt and Road Initiative is an infrastructure development strategy which aims to increase trade between various countries, stimulate economic growth, and enhance regional integration. The Initiative was inspired, in part, by the Silk Road established by the Han Dynasty of China over 2,000 years ago. This elaborate network of trade routes was central to the economic, political, religious, and cultural interactions between Asia and Europe from the 2nd century BCE up until the 18th century.  

While critics have dismissed the BRI as a projection of Chinese foreign policy and criticized it for burdening poorer countries with billions of dollars of Chinese debt, the program has already led to the development of some incredible new technology. To ensure the success of the Initiative (often referred to as China’s modern Silk Road), the country is designing some state-of-the-art, custom-made machinery that will speed up the construction process and improve the durability of the newly-constructed routes. 

One such pioneering piece of bespoke construction technology is known as the SLJ900/32, locally nicknamed the Iron Monster. This gigantic Segmental Bridge Launching Machine has fascinated industry watchers around the world and might one day supplant the traditional method of building bridges with cranes. 

The SLJ900/32 – An Overview

The SLJ900/32, also known as the Iron Monster, was designed by the Shijiazhuang Railway Institute and manufactured by the Beijing Wowjoint Machinery Company. It is 91.8 meters long, 7.4 meters wide, and weighs about 580 tonnes. It is 9 meters high and has a loaded speed of 5km/h, with an impressive unloaded speed of 8km/h. It offers a completely new way of building large bridges, without the need for complex and expensive scaffolding or framework structures. 

Simple and functional, the Iron Monster is very different from traditional bridge construction devices. A casual observer, seeing it away from the construction environment, might think that it is simply a vehicle meant to transport heavy materials and structures via road. This is because it doesn’t feature any of the conventional crane technology. 

It is used to build high-speed railway tracks quickly and efficiently, in areas where large sections of the route need to be suspended over canyons and valleys in order to avoid bends. Having a total of 64 wheels, it is an all-in-one bridge building machine capable of lifting, carrying, and placing sections of track on bridge pillars. It uses heavy stone blocks to connect one pillar with another. The 64 wheels are divided into fully rotating blocks of 16, allowing the machine to maneuver deftly and move sideways to easily pick up large beams and pillars when needed. 

How the SLJ900/32 Works

The Iron Monster operates by picking up a beam from its point of origin and driving to the pillars of the bridge, before lowering a pneumatic support structure that will anchor the machine to the first pillar. This allows the machine to extend itself out to the second pillar, then the third, and so on, depositing the next beam as it does so. This makes for an efficient and fuss-free operation that is much less time-consuming than the traditional, crane-centric bridge building methods.

During the construction process, the machine travels to the very edge of the installed segments of the bridge and then uses a temporary track to reach out to the beams that are yet to be connected. Once the track is stable, the SLJ900/32 moves forward with a new segment of the bridge in tow. It then lowers this segment into place, allowing the construction crew to begin their work. Once the segment has been secured, the process can be repeated once again.

Building a bridge using cranes makes it impossible to use full-sized beams or pillars, as these are difficult to lift and transport. Therefore, the beams and other materials have to come in sections that are no more than a few meters in length. These sections are then fixed together during the process of construction. However, these extra steps have been rendered redundant by the Iron Monster, as it allows for the use of beams and pillars that were specially designed to be full length. These prefabricated parts are then connected with each other with expansion joints.

The Iron Monster lays one section of the bridge, then returns to collect another block with the help of its 64 wheels segmented into sections of 16. It then rolls forward – over the newly laid segment of the bridge – to place the next section. Moving at the impressive speed of 5km/h even when it is fully loaded, the machine ensures that the entire bridge-building process is quick and efficient. Traditional construction techniques, which required enormous cranes to be put together on the ground, were much slower and more expensive than this method. 

The Iron Monster was designed to construct long bridges comprising numerous spans. The distance between two intermediate supports of a structure – such as the beams of a bridge – is known as a span. The primary function of this machine is to move, install, and secure the finished segments of the bridge to the preinstalled beams or supports. It can build bridges in urban areas as well as through the wilderness. It was used to build one such bridge in the forest between the cities of Guizhou and Chengdu. 


The Iron Monster is capable of laying 700 to 1,000 bridge spans during its estimated lifespan. Usually, such machines (known as launching gantries) can be used for an average of four years before they need to be replaced. Much less manpower is required to build a bridge using this machine than would be necessary for traditional, crane-based construction methods. However, due to its enormous size, the Iron Monster requires a dedicated crew to check, clean, and maintain its various parts. To ensure their safety, extensive harness and height training is provided to the workers hired to operate and maintain it. 

An unexpected benefit of the Iron Monster is that, at 580 tonnes, it is much heavier than any of the railway traffic that is likely to pass over the tracks that it is laying. Hence, the bridges it is building are, by necessity, much larger and stronger than they need to be, to support the rail networks for which they are intended. This creates an extra layer of safety, by ensuring that the bridges connecting China to the world are capable of carrying heavier weight loads than necessary.

The Iron Monster has already been used to complete several high-speed rail projects across China, and is set to propel the country towards its ambitious goal of 30,000km of high-speed rail service within the next few years. A new railway link between the remote region of Inner Mongolia and the rest of the country was recently built with the help of this colossal machine. It is currently in active use for the construction of high (and large) rail viaducts. The most notable of these viaducts was built recently between Wanzhou and Chongqing in Sichuan Province of Southwest China. 

The Yibin Jinsha River Railway Bridge linking the Sinchuan and Guizhou provinces of China was also constructed using the Iron Monster. It is the longest road-rail steel arch bridge in the world with a double-layer structure – having a high-speed rail on the upper layer and a roadway on the lower layer. An arch bridge is one that features abutments shaped like a curved arch at each end. It works by partially transferring the weight of the bridge and its loads onto the abutments at either side. 

The Yibin Jinsha Bridge, constructed by the China Railway Major Bridge Engineering Group, is 1,875 meters long. Its main span is 336 meters in length. This bridge (and the associated rail line) helped shorten travel times between Guiyang (the capital of Guizhou) and Chengdu (the capital of Sichuan) from 12 hours to three.

Some Other Mega Machinery Used by the Chinese

Apart from the SLJ900/32, the Chinese have also built some other innovative pieces of construction technology to facilitate the completion of the Belt and Road Initiative. Two of the most impressive of these are the TBM Slurry and the Track-Laying Machine. 

TBM Slurry

The Tunnel Boring Machine (TBM) Slurry was built by the China Railway Engineering Equipment Group Company, with the help of freelance German engineers, to make the process of drilling underground tunnels faster and more efficient. It is 100m in length, 15.3m in diameter, and weighs about 4,000 tonnes.

In the city of Shantou near Hong Kong, the TBM Slurry was used to drill 5km underground through an earthquake zone, to facilitate the construction of a six-lane motorway. The tunnel helped modernize Shantou’s transport system in time for it to become one of the 15 key ports along the maritime Silk Road. 


Designed by the China Road and Bridge Corp, the Track-Laying Machine specializes in building railway tracks, covering a potential daily distance of more than 700m. It transports and sets down prefabricated lengths of track along a railway line, then rolls along the newly laid track to set down the next section.

This machine has a 2cm margin of error and takes about four minutes to install one section of the railway track. The length of each track section is about 25m. However, creating the prefabricated sections of track, and ensuring the low margin of error, is time-consuming and requires a significant amount of manpower.

Despite their flaws, the efficient, innovative, and cost-effective pieces of construction technology coming out of China might soon change the face of infrastructure development around the planet.

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