Chase, J.G.

Dhakal, R.P.

Mander, J.B.

Rodgers, G.W.

Solberg, K.M.

UC Research Repository

DAD Post-Tensioned Concrete Connections with Lead Dampers: Analytical Models and Experimental ValidationGeoffrey Rodgers1, J Geoffrey Chase1, John Mander2, Rajesh Dhakal3, Kevin Solberg31 Dept. Of Mechanical Engineering, University of Canterbury2 Zachry Dept. of Civil Engineering, Texas A&M University3 Dept. of Civil Engineering, University of CanterburyDamage to concrete and yielding of re-barSignificantly reduce yielding of the critical reinforcing bar.This will also absorb more energy– particularly after 1-2 cycles.Problem:Solution:Requires expensive repairDoes not require expensive repairArmoured rocking interfaceDevice fixed to re-bar cage and embedded in concrete for containmentAxial PrestressPossible ApplicationsSeismically Vulnerable Bridge Piers Steel joints Reinforced concrete joints Bridge decks Tuned mass dampers Base isolationSingle or double bulge extrusion damper fixed to columnSteel BeamSteel BeamSteel ColumnDissipative rocking with no damageGap transmits joint rotation to damper instead of damageDirect Placement into Steel JointsMain Goals 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 connectionsDevice MechanicsPlastic extrusion of working material through an annular restrictionBulged-shaft design chosen for low manufacturing cost and repeatable resultsBulged-shaft type extrusion damperConstricted-tube type extrusion damperSource: Robinson and GreenbankStructural ImplementationPlacement of lead extrusion dampers into the rocking interface of a reinforced concrete joint.Structural ImplementationRecent research has focused on damage-free jointed pre-cast connectionsBeams and columns are completely separate entities, held together by post-tensioned tendons running through the joint regionStructural ImplementationNon-linear response is achieved by joint-opening at the connection in place of structural damage and the formation of a plastic hingeGap opening elongates tendon, increasing the tendon force that pulls the joint closed, providing an elastic resistance, with hysteretic energy absorption due to friction alone.Bare JointBare JointDamper Hysteresis+Overall Joint=Large amounts of energy absorbed in a damage-free manner, with overall recentring abilityExperimental Joint TestingA near full-scale 3D joint configuration was constructed using Damage-Avoidance Design principles.This joint utilised a bend tendon profileTendon ProfileExternally Mounted DampersDamage-Avoidance-Design (DAD) joint have very low inherent damping, so another form of energy dissipation is provided.By mounting lead extrusion dampers across the joint region, joint opening leads to large amounts of energy being absorbed directly in the joint.Experimental ResultsResponse is a combination of initial linear elastic deflection of members, followed by non-linear response due to gap opening.Hysteretic area is a combination of extrusion damping and friction of the tendons within the duct.Initial linear stiffness(elastic member deflection)Post gap-opening stiffness(further elastic member deflection and gap-opening)Rocking EdgeGap OpeningCorner JointThe original joint has only most amounts of added damping, kept low to ensure ready recentring of the overall joint.In reality, much more damping could be provided without the loss of recentring.Therefore, one of the seismic beams was removed, and both extrusion dampers mounted onto one beam to double the amount of damping providedCorner Joint ResultsMuch larger hysteretic area – much larger dissipationAsymmetry of force due to eccentric tendon profileAsymmetry of inherent hysteresis due also to tendon profileHigh Force-to-Volume Experiment and Overall Summary• Significant added force capacity• “Weak” joint with device can outperform sacrificial designs in first and every cycle – by design!• Easily fit inside of existing typical structural connections• Large amounts of energy dissipated, without damage, and ready joint recentring• Design equations derived for devices and for application (spectral analysis) – we can make any “size” for any applicationConclusions• Novel devices can enable significant new applications• Open several new design avenues not previously available• Large amounts of energy can be absorbed reliably and repeatably• Damage can be significantly reduced or eliminated• Full or large scale validation of all concepts• Several further applications show promise in analysis (using validated models) and/or hybrid experimental testing

DAD Post-Tensioned Concrete Connections with Lead Dampers: Analytical Models and Experimental Validation

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DAD Post-Tensioned Concrete Connections with Lead Dampers: Analytical Models and Experimental Validation

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