GW Rodgers, C Denmead, N Leach, JG Chase & John B Mander

Damage to concrete and yielding of re-bar
Requires expensive repair or retrofit
Putty
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 rebar 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

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

 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

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

150
100
50
0
-20
-50
-100
-150
• 40mm bulge
• Quasi-static test
• 100kN peak force, 50kN average
• Not repeatable
• Trailing void formation ~10%
Peak force only in
“new” material
40 mm diameter bulge with un-pre-stressed lead
Device coring trailing void
-10 0 10 20 30
Displacement (mm)

300
200
100
0
-5
-100
-200
-300
200
150
100
-100
-150
-200
50
0
-5
-50
5
5
15
15
25
25
Displacement (mm)
35
35
Displacement (mm)
45
45 55
• Air voids decreased by 3-5x
• ‘Squarer’ hysteresis loops for max energy dissipation
• Repeatable results
55
• 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

• Variation in reported and experimental relationships
– linear and polynomial
• Linear relationship in tested region
• Likely the relationship would become exponential
Force/Bulge diameter relationship
Force/Bulge Diameter Relationship
1000
900
800
700
600
500
400
300
200
100
0
30
Friction
35 40 60
Shaft Yield
65 70 45 50 55
Bulge diameter (mm)
Reported relationship
Least square fit

350
300
250
200
150
100
50
0
0
Relationship between ratio of bulge area to cylinder area and Force
0.05
0.1
Exhibits Mohr-Coulomb Behaviour
D
D
 
D
A shaft
  o
A bu lg e
0.15
0.2
0.25
Face Area bulge/Area cylinder
0.3
0.35
0.4
• Ratio makes relationship device independent
• Linear relationship
• Wider variety of devices
• Relationship used to estimate design force
Can be readily used for new device designs

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

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

Multiple Equation Regression Analysis
• Spl it 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

 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