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Projects : CUREE-Kajima Joint Research Program
PHASE I RESEARCH REPORT

CKI-14: PASSIVE CONTROL OF HIGHWAY STRUCTURES

The objective of this project is to introduce recent development, in seismic-counter measure techniques to assess analytical and experimental effectiveness, feasibility and limitations of damping augmentation devices, such as lead rubber bearings, elastometric bearings and damped resonant appendages, with respect to the seismic performance of cable-stayed bridges. To achieve this objective, emphasis was placed on: (1) the results of the USC two shake tables (4 ft x4 ft with separating distance 12 ft center-to-center) tests of a 1:100 reduced scale model of an existing Japanese cable-stayed bridge; (the Yobuko Bridge) tests were carried out without the energy absorption device and with the hysteric energy dissipation device, (2) the results of damped resonant (tuned) appendages with relatively small mass and high damping ratio using a pair of small shaking tables (at UCI) to longitudinally shake the 12-ft long bridge model of the same cable stayed in Part 1, and (3) the results of computational analysis of the prototype by the Kajima research team to improve the earthquake resistance of floating type prestressed concrete cable-stayed bridges by introducing passive vibration systems such hysteretic type devices and tuned mass damper devices.

This report includes the following:

Use of Damped Responant Appendages To Augment Damping in Cable-Stayed Bridges: A Feasibility Study

Roberto Villaverde and Scott C. Martin

A study is carried out to investigate how effective tuned appendages with a relatively small mass and a high damping ratio can be to increase the inherent damping in cable-stayed bridges and reduce, thus, their response to earthquake excitations. The study involves the review of a theoretical formulation that explains why the addition of these appendages may improve the damping characteristics of a structure, and numerical and experimental tests conducted to assess the
validity of this theoretical formulation and the extent to which they can reduce the seismic response of cable-stayed bridges. In the numerical study, an actual cable-stayed bridge is modeled with finite elements and analyzed with and without the proposed appendages under different earthquake ground motions. Appendages with damping ratios of 10, 15, 20, and 30 per cent and weights that respectively represent 0.67, 1.5, 2.7, and 6.0 per cent of the total weight of the bridge are considered. In the experimental test, a 12-foot long cable-stayed bridge and an appendage consisting of a small mass, a small spring, and a small viscous damper are built and tested, without and with the appendage, on a pair of shaking tables set to reproduce specified ground acceleration records from past earthquakes. The damping ratio of the appendage in this test is 32 per cent and its weight represents 8 per cent of the weight of the bridge model. In the numerical test, it is found that the appendages reduce the longitudinal response of the bridge deck of the analyzed bridge up to about 86 per cent. Similarly, in the experimental test the appendage reduces the longitudinal bridge deck response about 41 per cent. It is concluded, thus, that the suggested appendages may indeed be effective in reducing the response of cable-stayed bridges to seismic disturbances, and that they have the potential to become a competitive alternative for their seismic design.

CONTENTS

1. INTRODUCTION
- Background
- Historical Review
- Object and Scope
- Organization

2. THEORETICAL BASIS
- Introduction
- Natural Frequencies and Damping Ratios of Systems Without Classical Damping
- Damping Ratios and Natural Frequencies of Structure-Appendage Systems
- Parameters of Effective Resonant Appendages

3. NUNERICAL STUDY
- Introductory Remarks
- Analyzed Bridge
- Finite Element Model
- Bridge Dynamic Properties
- Parameters and Location of Resonant Appendage
- Dynamic Properties of Bridge-Appendage System
- Earthquake Ground Motions
- Results

4. EXPERIMENTAL STUDY
- Introduction
- Model Description
- Equipment
- Experimental Dynamic Properties
- Experimental Set-Up
- Base Acceleration Time Histories
- Experimental Results

5. SUMMARY AND CONCLUSIONS
- Summary
- Conclusions
- Feasibility Assessment
- Recommendations for Future Research

REFERENCES

ACKNOWLEDGMENTS

File Download Type Size
CKI-15 PDF 14.6 MB

Also listed as Report No.: 1992.8



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Consortium of Universities for Research in Earthquake Engineering
last updated 02.20.15