4. Anti-seismic measures using a vibration control damper

  • A design method for a vibration control device has been developed for work on difficult structures, such as bridge piers constructed in rivers.
  • Using the proposed design drawing, the effectiveness of the vibration control can be estimated to within an error margin of approximately 10% .
  • Guidelines including some numerical examples have been proposed to assist application of the vibration control device in design work.

Given the environmental constraints on bridge piers in rivers, ordinary reinforcement measures such as concrete jacketing are relatively difficult to apply. By using a vibration control damper however, it is possible to significantly improve the seismic resistance of the bridge pier by reinforcement the upper part of the structure alone.

Given that structural design methods have not been devised to integrate the use of vibration control devices however, incorporating such devices would require numerous complicated dynamic analyses, requiring significant investment of time and labour.

Consequently, a design drawing has been proposed by which structural damage and design loads for the vibration control device can be estimated, avoiding the need for detailed dynamic analyses (Fig. 1). The design drawings can be used to estimate the characteristics of the vibration control device required to contain structural damage to a level that would allow the structure to remain intact, considering the basic design characteristics of the structure, such as natural period, yield seismic intensity, ground conditions and maximum acceleration of seismic motion.

In order to verify the accuracy of this design drawing, the vibration control device was applied to an actual bridge. The vibration control damper loads required to contain damage to the bridge to a level that would allow the structure to remain intact were estimated, and dynamic analyses were conducted. Results showed that the bridge pier response (Fig. 2) was 0.90 times the yielding limit. This demonstrated that the design drawing could be used to design the vibration damper for an actual structure, and that the margin of error in damage prediction was approximately 10%.

Following this, a set of guidelines and examples to help this method were drawn up bringing together the design drawing itself, control methods to verify members and the basic impact of the vibration control reinforcement, and other design related points. Following this, a proposal was made to disseminate the vibration control device as one of the possible anti-seismic measured for bridges and/or viaducts.

Fig.1 Design drawing for vibration control device (L2 earthquake spectrum II/ G3 ground conditions)
Fig. 2 Verification of the design drawing through dynamic analyses
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