Cable-stayed bridges span roads, valleys, rivers and straits all over the world. They carry countless vehicles around the clock, every day. Their stability depends, crucially, on the permanent load-bearing capacity of the stay cables. Their tension must therefore be monitored continuously. For a customer, WIKA has developed a special force transducer for cable-stayed bridges. The marketable solution works with high precision, is extremely temperature-resistant – and also contributes to sustainable bridge operation.
The construction of a cable-stayed bridge often appears almost delicate. Diagonal, tensioned cables, which support the carriageway, run from the bridge deck to the towers or pylons. These transfer the load via the towers to the bridge’s foundations. The tensile force acting in the cables is therefore one of the fundamental parameters for the construction and operation of such bridges. This means that tension monitoring begins as early as the construction phase.
Each stay cable consists of a bundle of wire ropes that are grouped together in strands. The tensile force of the stay cable is monitored on one of these strands using a ring force transducer. The measuring instrument is installed between the fastening elements and the anchor plate in the bridge deck.
Force transducers for cable-stayed bridges also serve as a reference
The force transducer initially serves as the reference while a hydraulic jack brings the individual wire ropes to the defined tension. It then takes over the continuous monitoring. A change in tension outside the tolerance could be due to corrosion or other negative influences. Following a corresponding signal, the bridge operator can immediately initiate an inspection and thus prevent serious consequences – in extreme cases a collapse of the bridge.
WIKA solution offers high performance and is suitable for all climates
Ring force transducer with signal amplifier for cable-stayed bridges – both parts of the measuring system form a separable unit.
Such monitoring is a challenging task. At the customer’s request, tecsis, the WIKA Group’s centre of excellence for force measurement, developed a ring force transducer for cable-stayed bridges with high performance and a signal amplifier for reliable transmission of the measured values. The force transducer is ring-shaped and is designed for a nominal load of 160 kN. Both the dimensions and the load-bearing capacity can be adapted to customer-specific requirements.
The force transducer for cable-stayed bridges, which transmits measured values with a 4 … 20 mA signal output, can be operated continuously over a wide temperature range. It is therefore suitable for any climate. In the rated temperature range of -40 °C to 70 °C the instrument has a measurement uncertainty of 1.5 per cent, and an external laboratory has confirmed the measuring behaviour of the force transducer over the entire temperature range.
The force transducers for cable-stayed bridges and their signal amplifiers are connected via a cable connector. After installation, the maintenance-free sensor remains in its position in the stranded wire housing, which is filled with paraffin to protect it from moisture. The signal amplifier, and consequently the electronics of the measuring system, on the other hand, are located away from the actual measuring location.
Measuring system as a separable unit supports sustainable bridge operation
The WIKA measurement solution, as a separable unit, means an additional advantage – in the event of potential damage, the amplifier can be replaced without the time-consuming and costly dismounting of the force transducer. The operator then receives a new instrument with a calibrated signal that is matched to the sensor and can be connected and commissioned immediately using the plug-and-play principle. In this way, the WIKA measuring system supports the sustainable, long-term operation of the bridge.
Note
Ring force transducers are suitable for a wide range of applications. A detailed overview of the different models and versions in the WIKA portfolio can be found on the WIKA website. There, we also present further products and solutions for force measurement. Should you have any further questions, your contact will gladly help you.
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