Weightlifting in 10 steps

Weightlifting in 10 steps
Marginal Column
Content

November 2014

 

When building a bascule bridge, the expertise supplied by Bosch Rexroth reduces engineering effort and optimizes safety.

 

When you mention machine safety, many people think only about factories. The European Machinery Directive, however, also covers large scale equipment. Safely moving several hundreds of tons is what it’s all about in bascule bridges. The new bridge crossing the Hollandse IJssel river, in the South Holland province of the Netherlands, is one of Europe’s first bascule bridges featuring a hydraulic system as per the specifications in the Machinery Directive. Auxiliary to standards for the safe engineering of movable bridges, the Netherlands has also adopted national standards covering the hydraulic systems in used in civil engineering. Specific regulations on the functional safety of hydraulic drive systems used in bascule bridges, by contrast, have not been adopted. And until now, most general contractors have only limited experience with the safe design and implementation of such projects on the basis of the Machinery Directive.

Implementation as per standards

To ensure that the safety concept for the drive system was fully in line with standards and when subcontracting for the entire hydraulic system, the general contractor for the Hollandse IJssel Bridge turned to Bosch Rexroth. The experts for machine safety there have decades of experience with custom-engineered hydraulic systems for major projects like the Tower Bridge in London. And they have the necessary tools, too. “Working in close cooperation with the customer, we worked our way through the original risk analysis,” recalls Wouter Leusden, application engineer and safety specialist at Bosch Rexroth in Benelux. The Rexroth system known as "10 Steps to Performance Level" subdivided the complex assignment into easy-to handle “packages” – beginning with risk assessment and continuing through to verification and validation. When engineering the drive hydraulics, a team of specialists headed by Wouter Leusden first defined the required performance level. This takes into account, for example, the potential frequency and duration of exposure to hazards as well as possibilities for hazard avoidance.

Carefully monitored weight

When opening the bascule bridge, the powerful hydraulic system has to move the counterbalance weights – about 750 tons. To move this weight safely and reliably, the system uses redundant components and monitors the motions. If an anticipated deceleration does not take place while the two spans are being lowered, then the cylinders will safely bring the motion to a standstill. The spans are then hydraulically locked. In the case of excessive speed, the hydraulic valves close immediately and the system is placed in a safe state. The required safety equipment is a part of the standard control concept and thus offers Safety on Board.

Reality confirms simulation

Bosch Rexroth examines the safety functions right from the conceptualization phase, using simulation programs the company developed in-house. They are used to calculate the behavior of the safety controls on the cylinders, under full load, and the response of the entire bridge under unfavorable wind conditions. “Our system worked perfectly from the very beginning and, for the operator, is the new benchmark for hydraulic systems designed for complete safety,” emphasizes Leusden.