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’

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

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

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

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

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

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

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

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

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

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

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

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