Cable damper systems
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MAURER Cable damper systems

Products and Technical Information List of Content 1 2

1 Introduction The growth of bridge spans also leads to an increasing length of required stay cables or suspensions. As longer the steel cables, as more sensitive they are to dynamic excitation – be it from the supported structure, be it from weather conditions. The very small value of inherent damping capacity is not sufficient to eliminate cable vibrations. Moreover, with increasing cable length, also the number of possibly excited eigenmodes is growing. The capacity of passive damping systems may not be sufficient to protect the cables over the whole range of occurring vibrational modes....

2 Theoretical overview Modern bridge design meanwhile covers spans which were not even conceivable some decades ago. The employment of high strength materials leads to very slender structures, which forces the designer to consider the dynamic behaviour of the structure. In case of cable-stayed bridges, the increasing cable length leads to vibrations with higher amplitudes. Apart from the micro-vibrations produced by the traffic load on the bridge deck and induced into the stay-cables, the most frequent type of vibration origins from aero-elastical turbulences. The following types of...

2.2 Rain-wind induced galloping The occurrence of rain-wind induced galloping requires specific conditions regarding wind velocity and rainfall-intensity. However, considerable amplitudes of stay-cables can be traced back to this phenomenon. Rain-wind galloping at stay-cab les occurs when: • Wind occurs in direction of the stay-cable (case 1) • Wind occurs in transverse direction to the cable (case 2) As long as no wind is blowing, the rain collected on one cable drains down in a rill on the underside of the cable. Occurring wind forces the rain rill to move up around the cable. That way,...

2.3 Gust-induced excitation As many bridges are very exposed to the weather due to their location high above land- or sea level, high wind velocities can occur. Stochastical variations of the wind velocity lead to variations of the flow pressure on the cables which may start to vibrate. 2.4 Sudden dropping of ice-/glazed frost-/snow film Due to a sudden dropping of an existing snow- or ice layer around the cable, stay cables may shoot up as a reaction to the considerable mass reduction. The occurring vibration frequency usually is low while the amplitudes are high.

3 Damping Systems 3.1 SDI-R: Integrated elastomeric or friction damper A very esthetical cable- or hanger damping system is the integration of the damping device type SDI-R in the vandalism-tube at the cable- or hanger bottom end. The damper is entirely enclosed into this cover tube. However, it has to be checked whether the damper can be accommodated within the tube and whether the displacement at the damping location is sufficient to activate the damper. For this damper type, high damping elastomers (20-30% damping), cured in special geometries and cut to special shapes are applied....

3.2 SDI-H: Integrated hydraulic damper Alternatively to the application of elastomeric damping bodies, the installation of hydraulic dampers in the cable protection tube leads to an increase of the damping capacity (equivalent viscous damping up to 55% possible). Viscous elements show a higher efficiency compared to elastomeric elements as the dissipation capacity is bigger. These devices are applied e.g. in case of strong cable- or hanger vibrations, or cables longer than 70 m. Damper connector to cable Section B-B: Flange with bolt connection Existing cable protection tube Possible...

3.3 SDE-R: External elastomeric or friction damper The SDE-R-Damper is externally mounted with clamps to the cable or hanger in a sufficient distance to the fixing of the cable or hanger. This solution is used when a cover tube is not suitable for an integration of the damper type SDI-R. Depending on the structure, elastomeric-, frictionor viscous damping elements are applied. The SDE-R type is fitted with special elastomeric or friction damping elements. All dampers are individually adapted and designed according to the structural requirements (damping, space conditions, etc.). K r a f t -...

3.4 SDE-V: External viscous damper The external damper SDE-V, arranged rectangular to the cable, offers a highly efficient viscous damping element instead of the elastomeric or friction element. The fixing to the cables can be realised by means of clamps. The viscous damping elements are designed in various versions, depending on the individual project requirements. SDE-V: sketch application example: Eilandbrug Kampen / Neherlands Externally arranged cable damper – principle SDE-V fixing clamp for connection damper - cable SDE-V testing at Munich University of Technology

3.5 ACD – Adaptive Cable Dampers The efficiency of a cable damper is better as closer the damper is placed to the cables’ antinode. Due to practical and optical reasons, external dampers are located close to the root point of the cables, e.g. in a distance of app. 26% of the cable length. To still achieve a sufficient cable damping, the damping device has to be tuned to the occurring eigenmode, vibration intensity and cable properties. Constant variation of these values lead to a reduction of the effectiveness of a conventional damping device. The application of adaptive damping devices...

4 Testing of cable and hanger dampers The tests of the various damper types are continuously carried out with regard to the required quality control for specific projects and with regards to product development. The specific project testing is to confirm the devices requirements, e.g. damping function, displacement and efficiency respectively. For all cable and hanger dampers a permanent d [mm] product development is safeguarded in the company headquarters in Munich, at the Munich University of Technology and at the EMPA (Material Testing Institute) in Dübendorf/Switzerland. At the EMPA...