Digital Hydraulics Help To Position Railway Bridge

Irene Kremer, Enerpac BV,
Special Collaboration

Local conditions sometimes make it impossible to build a bridge on-site. In those cases, the bridge must be built up on an adjacent site or bank and then moved to the final position.

This is what happened in the Brussels Schaerbeke, where a steel railway bridge with a length of 140 m and a weight of over 1600 t had to be slid across a number of already existing tracks. Enerpac was asked to hydraulically monitor the movement and the forces that occurred during the movement with its digital 'Synchronous Lifting System' and to make corrections if necessary.

The new railway bridge in Brussels was built by order of the Belgian railways by Victor Buyck Steel Construction, a large internationally operating Belgian steel construction company. The bridge was supplied in parts and assembled on one side of the newly built railway viaduct. Because of the intensive use of the railways over which the bridge had to be placed and the fact that the railway traffic had to be stopped during the movement, the builder was given only 48 hours to move the bridge to its proper place.

Complex combined action of forces
A steel construction may be called rigid and inflexible, but this is absolutely not true. Especially not in case of a steel railway bridge of this length and weight. Enormous forces are developed during the movement. Under the influence of these forces the steel construction and in particular the superstructure are subject to high, changing tensions and will certainly bend.

In order to have the combined action of forces develop evenly during the movement of the railway bridge and to prevent these tensions from becoming too high, the occurring pulling and pushing forces had to be measured and reduced if required. Additionally, the vertical position of the bridge had to be monitored, of course.

Manual monitoring and correction of the movement is too inaccurate in these cases. To much variation at the different points of support results in unacceptable tensions that may affect the construction. Besides, manual monitoring and correction takes much time and the builders did not have much time. Therefore Enerpac was asked to guide the movement of the railway bridge with its 'Synchronous Lifting System' that had already proven itself all over the world.

Platform wagons and strand-jacks
For the first phase of the movement a series of hydraulically controlled, multi-axle platform wagons (supertransporters) were used on both sides beneath the bridge as rearmost support points. For the second phase - the wagons could only reach a certain point - use was made of a hydraulic pulling system with 'Strand-Jacks', cable strands that pull the bridge meter by meter over the remaining distance. Apart from that a hydraulic retracting and braking system was provided, because the railway bridge had to be launched under a downward slope with a level difference of 2 m.

Eight temporary steel pillars were built to support the viaduct parts during the movement. Each pillar had been provided with a so-called 'draw beam', a pivoting steel cross with heavy springs to compensate the force, the angular displacement and the bending of the lower beam of the bridge. Beneath each 'draw beam' two hydraulic cylinders were mounted. The primary function of these cylinders was to keep the construction at the correct height. In order to reduce the resistance as much as possible during the movement Teflon gliding plates were applied between the 'draw beam' and the lower beam.

Additionally, a launching nose (beak) was provided on the front side of the bridge for a safer distribution of the forces and to limit the bends and tensions during the movement.

Forces under control
Victor Buyck Steel Construction accurately calculated the forces and tensions that could occur at each support point during the movement beforehand. In order to be able to control this complex combination of forces and to correct it if necessary, Enerpac installed a monitoring system especially built for this. This system consisted of a total of 32 measuring points (28 of which were used) on an equal number of hydraulic cylinders, a central pomp unit with a pressure of 700 bar, plc-control and a computer system showing all movements and forces. Project leader J.P. Vrombaut of Victor Buyck Steel Construction was very satisfied during the implementation already. "Also thanks to Enerpac things are going much faster than we expected," he said.

Both the hydraulics and the electronics of the system were designed and developed by a team of experts in the 'Enerpac Center of Excellence' in Spain. Enerpac itself hired out the equipment to the client, in accordance with the policy pursued with respect to such large projects. The installation and implementation were taken care of by the so-called Heavy Lift Team, experienced Enerpac experts from Great-Britain. The total project period - installation phase, test phase, implementation and completion - covered two weeks.

Synchronous Lifting System: Digital hydraulics
The integrated and automatic 'Synchronous Lifting System' of Enerpac is a combination of hydraulics with digital monitoring and control. No matter whether a bridge or a large building is concerned, this system offers an extremely effective method for both vertical and horizontal movement and positioning.

The total system is built in such a way, that the different measuring points and cylinders are stable and do not influence each other and it checks the measuring way and force. For this the control system receives electronic signals from the movement sensors and the pressure in the cylinders is also electronically transmitted through sensors.

The computer continuously calculates the force on each cylinder using pressure sensors. The system checks the position and movements of the individual cylinders and controls pump and valves if necessary to keep the forces at the correct value. In this way each point of the object is moved automatically and fully synchronically and positioned with millimeter accuracy.

When the force is outside a set value, the pressure is 'adjusted'. Here the speed of the computer is used to quickly send short pulses to the hydraulic valves. The result of this is that the individual cylinder movements can be many times smaller than with manual operation. At the moment that a cylinder movement is outside the tolerance, a warning signal is sent and the entire movement is stopped manually or automatically.

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