1. GW Rodgers, C Denmead, N Leach, JG Chase & John B Mander
Experimental Development and Analysis of a High Force / Volume Extrusion Damper
GW Rodgers, C Denmead, N Leach, JG Chase & John B Mander
‘Energy Dissipation Without Damage’

2. Problem:
Damage to concrete and yielding of re-bar
Requires expensive repair or retrofit
Putty
Solution:
Does not require expensive repair
Must be small enough to fit where traditional dampers do not!
And deliver forces just as large!
Device fixed to re-bar cage at each end and embedded in concrete for containment
Objectives: - To eliminate yielding in the critical reinforcing bars
- To absorb more energy than a ductile concrete system

3. Other Possible Applications
Seismically Vulnerable Bridge Piers
Direct Placement into Steel Joints
Dissipative rocking with no damage
Single or double bulge extrusion damper fixed to column
Steel Beam
Steel joints
Reinforced concrete joints
Bridge decks
Tuned mass dampers
Base isolation
Steel Beam
Gap transmits joint rotation to damper instead of damage
Steel Column

4. Requirements High force capacity = High dissipation
Only 3-10 large response cycles per big earthquake
Small device volume
Tight constraints for typical structural connections - Universal column sections nominally 350mm deep – W14 in American Codes
Maximum energy dissipation per cycle
“Square” hysteresis loop
Goal: Dissipate energy in the device every cycle rather than by damage to structural connections

5. Test Method 500kN compression testing device Quasi-Static
DARTEC 10,000kN dynamic test system
Fixed in Place
Lead
Sinusoidal Input

6. Results without pre-stress
40mm bulge
Quasi-static test
100kN peak force, 50kN average
Not repeatable
Trailing void formation ~10%
Peak force only in “new” material
Device coring trailing void

7. Results with pre-stress
40mm Bulge Diameter
Air voids decreased by 3-5x
‘Squarer’ hysteresis loops
for max energy dissipation
Repeatable results
Small decrease in force still
due to air voids, but much less
Air voids same ~2-3% volume
40mm bulge has longer void as
smaller bulge than 50mm as it
is about void volume
50mm Bulge Diameter

8. Experimental Relationships
Variation in reported and experimental relationships
– linear and polynomial
Linear relationship in tested region
Likely the relationship would become exponential
Force/Bulge Diameter Relationship
Friction
Shaft Yield

9. Can be readily used for new device designs
Experimental Relationships
Relationship between ratio of bulge area
to cylinder area and Force
Ratio makes relationship device
independent
Linear relationship
Wider variety of devices
Relationship used to estimate
design force
Exhibits Mohr-Coulomb Behaviour
Can be readily used for new device designs

10. Spectral Response decreases with increasing damper size
Structural Impact
Spectral Response decreases with increasing damper size
Reduced magnitude of structural response and damage
Multiple earthquake suites (3x20=60) of probabilistically scaled
earthquake records – near field and far field ground motions
El Centro Response Spectra
Reduction in response with increasing damper size
Reduction in response with increasing damper size

11. Reduction factors increase with increasing damper size
Structural Impact
Reduction Factors
Design spectra divided by the spectra with added extrusion damping
Indicates the magnitude of the achieved reduction in response
Reduction factors increase with increasing damper size

12. Structural Design Impact
Multiple Equation Regression Analysis
Split the spectra into 3 regions based upon existing bifurcation points
Use linear regression analysis and linear interpolation
Obtain equations to estimate damping reduction factors
Enable use in structural design analyses

13. Conclusions
Importance of pre-stress in repeatable device behaviour and maximum energy dissipation identified
Full-scale 300kN+ prototype created and tested
Final device design underwent proof-of-concept testing over entire speed range
Analytical design space characterised and device independent
Results not same compared to studies reported in the literature
Comprehensive theoretical simulation of device placement in a structure shows significant impact on response
Future work requires some minor modifications but the concept is proven for multiple devices