structural control using hybrid spring -damper isolator

Structural Control Using Hybrid Spring-Damper Isolator

with Integral Gapping Function

The Sutong Yangtze River Bridge2008

BRIDGES:POTENTIAL SHOCK AND VIBRATION INPUTS

1. Windstorms

2. Hurricanes / Typhoons

3. Earthquakes

4. Impact shock to support piers or deck

5. Truck / car braking loads or accident loads

6. Traffic vibration

7. Synchronous traffic or pedestrian vibration

The Sutong Bridge The World’s Largest Cable-Stayed BridgeNantong, China

Total Length = 4.7 MilesTower Height = 980 FeetCenter Span = .67 Miles

200 Ft Navigation ClearanceExpected Ship Traffic = 3,000 / Day

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What the Isolators Must Do: Axial Direction

• Allow the bridge deck to freely expand/contract with ambient temperature change.

• Protect the 53,000-ton center span against earthquake and typhoon inputs.

• Reduce motions under synchronized truck/car braking loads – or a massive traffic accident.

Idealized Isolator Response:SPRING OUTPUT PER UNIT

Idealized Isolator Response:DAMPING OUTPUT PER UNIT

DESIGNISSUES

1. Gapping required for spring element.

2. Peak spring forces roughly 3.3 times higher than peak damping forces.

3. Large spring forces limited the choice of spring elements.

• Mechanical Wound Coil Spring: Could not be made.• Stacked Steel Belleville Washers: Material fabrication

issues, physical size=large.• Liquid Spring: Too large in force to package within damper,

cannot be manufactured easily with a tubular cross section. • Pneumatic Spring: Non-linear output, low pressure yielded

large package. • Elastomer Spring: Difficult to manufacture. This spring type

was selected for the design, using multiple elastomer sections.

Mechanical Design:DAMPER ELEMENT

Mechanical Design:ADD SPRING ELEMENT

Mechanical Design:ADD GAPPING MECHANISM

COMPRESSION ENGAGEMENT OF SPRING

EXTENSION ENGAGEMENT OF SPRING

Assembly and Testing:SUTONG BRIDGE HYBRID ISOLATOR

Proof Pressure Test – Pressurized internally to 200% of the damping pressure equal to maximum rateddamper force.This pressure was held for 3 minutes on each isolator and for 24 hours on the first test article.

Velocity Testing – Cycle at various displacements with peak velocities of 50%, 75% and 100% seismicvelocity, plus a thermal creep velocity test. End of travel tests performed to verify spring output.

Wind Fatigue Test – The first test article subjected to a 50,000-cycle test at plus or minus 0.2 inchesamplitude to simulate wind gusts applied to the bridge structure.

DAMPER CARTRIDGE ASSEMBLY

SUB-ASSEMBLY WITH SPRING ELEMENTS

COMPLETED ISOLATORS

DYNAMICTESTING

100% SPEED DAMPER

SINE WAVE TESTS

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END OF TRAVEL SPRING

FORCE TEST

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WIND FATIGUE

TEST

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PRODUCTION DAMPING FUNCTION TEST DATA

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ISOLATORS INSTALLED ON SUTONG BRIDGE

CONCLUSIONS:

1. Single component spring-damper isolators can combine dissimilar spring and damping elements.

2. Optimization of any specific design is driven by:• Absolute values of spring force and damping force.• Available package envelope.• Material availability for spring elements.• Required suite of output requirements.

3. Sutong Bridge Isolators optimized with fluid damping and elastomer springs. 23

Taylor Devices, Inc.90 Taylor DrivePO Box 748North Tonawanda, NY 14120-0748

(716) 694-0800 Phone(716) 695-6015 Fax

www.taylordevices.comwww.shockandvibration.comwww.seismicdamper.com