Reference Textbook CONTENT LOW DAMAGE SELF-CENTERING SYSTEMS. 1. Introduction. 2. Behavior of Self-centering Systems

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1 Reference Textbook CIE 580 Emerging Technologies for Bridges André Filiatrault, Ph.D., Eng. LOW DAMAGE SELF-CENTERING SYSTEMS Christopoulos, C. and Filiatrault, A Principles of Passive Supplemental Damping and Seismic Isolation, IUSS Press, University of Pavia, Italy, Can be ordered online at: or Passive Supplemental Damping Isolation/dp/ /ref=sr_1_3?ie=UTF8&s=books&qid= &sr=1 3 1 Also available at the UB Bookstore CONTENT 1. Introduction 2. Behavior of Self-centering Systems SDOF Self-centering Systems 4. Ancient Applications of Self-centering Systems 5. Early Modern Applications of Self-centering Systems 7. The Energy Dissipating Restraint (EDR) 1. Introduction Current Seismic Design Philosophy Introduction Current Seismic Design Philosophy Performance of a structure typically assessed based on maximum deformations Most structures designed according to current codes will sustain residual deformations in the event of a design basis earthquake (DBE) Residual deformations can result in partial or total loss of a building: static incipient collapse is reached structure appears unsafe to occupants response of the system to a subsequent earthquake or aftershock is impaired by the new at rest position Residual deformations can result in increased cost of repair or replacement of nonstructural elements Residual deformations not explicitly reflected in current performance assessment approaches. Framework for including residual deformations in performance-based seismic design and assessment proposed by Christopoulos et al. (2003) (see Chapter 2) Lecture presents structural self-centering systems possessing characteristics that minimize residual deformations and are economically viable alternatives to current lateral force resisting systems 5 2. Behavior of Self-centering Systems 6 1

2 Normalized Equations of Motion Normalized Equations of Motion 7 8 Normalized Equations of Motion Ground Motions Considered in Parametric Study 9 10 Ground Motions Considered in Parametric Study Range of Key System and Hysteretic Parameters

3 Comparative Response of Flag-Shaped and Elastoplastic Hysteretic Systems Comparative Response of Flag-Shaped and Elastoplastic Hysteretic Systems Ancient Applications of Self-centering Systems 5. Early Modern Applications of Self-centering Systems South Rangitikei River Railroad Bridge, New Zealand, built in 1981 Piers: 70 m tall, six spans prestressed concrete hollow-box girder, overall span: 315 m Rocking of piers combined with energy dissipation devices (torsional dampers) Gravity provides self-centering force Superelasticity Shape Memory Alloys (SMAs): class of materials able to develop superelastic behavior SMAs are made of two or three different metals Nitinol: 49% of Nickel and 51% of Titanium. Copper and zinc can also be alloyed to produce superelastic properties. Depending on temperature of alloying, several molecular rearrangements of crystalline structure of alloy are possible Low alloying temperatures: martensitic microstructure High alloying temperatures austenitic microstructure Superelasticity

4 Intermediate Allowing Temperatures: Superelasticity Superelasticity Advantages for supplemental damping purposes: Exhibits high stiffness and strength for small strains It becomes more flexible for larger strains. Practically no residual strain and Dissipate energy Disadvantages: Sensitive to fatigue: after large number of loading cycles, SMAs deteriorate into classical plastic behavior with residual strains Cost Experimental Studies Attanasi and Auricchio (2011): Superelastic Seismic Isolation System Flat slider device & SMA coil springs restraining devices Structural Implementations Seismic retrofit of historical San Giorgio bell tower, San Martino, Italy Damaged after 1996 Modena and Reggio earthquake Nitinol wires introduced and prestressed through masonry walls of bell tower to prevent tensile stresses The Energy Dissipating Restraint (EDR) Hysteretic Behavior Manufactured by Fluor Daniel, Inc. Originally developed for support of piping systems Principal components: internal spring, steel compression wedges, bronze friction wedges, stops at both ends of internal spring, external cylinder 7. The Energy Dissipating Restraint (EDR) Hysteretic Behavior

5 7. The Energy Dissipating Restraint (EDR) Hysteretic Behavior No gap gp No gap No spring preload Spring preload Description of Ring Springs (Friction Springs) Outer and inner stainless steel rings with tapered mating surfaces When spring column loaded in compression, axial displacement and sliding of rings on conical friction surfaces Outer rings subjected to circumferential tension (hoop stress) Inner rings experience compression Special lubricant applied to tapered surfaces Small amount of pre-compression p applied to align rings axially as column stack Flag-shaped hysteresis in compression only Compression Force, F Axial Displacement SHAPIA Damper Manufactured by Spectrum Engineering, Canada Ring spring stack restrained at ends by cup flanges Tension and compression in damper induces compression in ring spring stack: symmetric flag-shaped hysteresis Experimental Studies with SHAPIA Damper Filiatrault et al (2000) 200-kN capacity prototype damper Characterization Tests Experimental Studies with SHAPIA Damper Characterization Tests Experimental Studies with SHAPIA Damper Characterization Tests

6 Concrete Frames PRESSS (PREcast Seismic Structural Systems) program Use of unbonded post-tensioning elements to develop selfcentering hybrid precast concrete building systems Concrete Frames PRESSS (PREcast Seismic Structural Systems) program Concrete Frames PRESSS (PREcast Seismic Structural Systems) program Hysteretic Characteristics of Post-Tensioned Energy Dissipating (PTED) Connections Self-centering conditions: k 2 = Elastic axial stiffness of ED elements k 3 = Post-yield axial stiffness of ED elements B = Gap opening angle at first yield of ED elements (textbook p ) Cyclic Modeling of PTED Connections with Equivalent Nonlinear Rotational Springs Extension of PTED Model to Constrained Beams

7 Extension of PTED Model to Constrained Beams Model Accounting for Beam Depth Concrete Walls Post-Tensioned Rocking Wall System (Stanton et al. 1993) Concrete Walls Jointed Cantilever Wall System (Restrepo 2002) Concrete Walls Jointed Cantilever Wall System (Restrepo 2002) Extent of damage at 6% drift Propped Rocking Walls Afsoon Nicknam Ph.D. Dissertation Propped Rocking Walls

8 Strong Wall Load Cell Test Column, typ m Pin, typ. Test Beam, typ. Sha ke Table PT Load Cell 2.025m Self-centering Systems for Confined Masonry Walls Self-centering Systems for Confined Masonry Walls Toranzo1 Toranzo Self-Centering Systems for Steel Structures PTED Connection (Christopoulos et al. 2002a, 2002b) Self-Centering Systems for Steel Structures PTED Connection (Christopoulos et al. 2002a, 2002b) Strong Wall System Testing Load Cell Pin, typ. PT Load Cell Test Column, typ. Test Beam, typ. C1 C2 C3 C m Sha ke Table 7.390m Self-Centering Systems for Steel Structures PTED Connection (Christopoulos et al. 2002a, 2002b) Self-Centering Systems for Steel Structures Friction Damped PT Frame (Kim and Christopoulos 2008) ED bars replaced by Friction Energy Dissipating (FED) connections made of Non Asbestos Organic (NAO) brake lining pads on stainless steel C1 C2 C3 C

9 Self-Centering Systems for Steel Structures Self-Centering Energy Dissipating Bracing System (Christopoulos et al. 2008) Two bracing members, tensioning system, energy dissipating system, guiding elements Application to wood structures Beam-to-column subassemblies using Laminated Veneer Lumber (LVL) Unbonded post-tensioned tendons and either external or internal energy dissipaters 49 Palermo, A., Pampanin, S., Fragiacomo, M., Buchanan, A.H. and Deam, B.L. (2006) Innovative Seismic Solutions for Multi-Storey LVL Timber Buildings. Portland, OR, USA: 9th World Conference on Timber Engineering (WCTE 2006), 6-10 Aug I 50 Shape Memory Allow Restrainers Rocking Piers with Energy Dissipation Devices Accelerated Bridge Construction: Uses discrete precast concrete elements stressed together by continuous tendons to form the bridge s superstructure and/or substructure. Reduces on-site construction time; minimizes traffic impacts and community disruption; improves work zone safety; decreases environmental disruption; increases product quality. Unbonded post-tensioned segmental members with Hybrid Sliding- Rocking (HSR) joints. P. Sideris PhD Dissertation (2012) HSR Joint Type 1: Rocking-dominant Joints Resistance and re-centering by PT tendon axial forces. Minimal energy dissipation. Intended for bridge superstructure elements (deck)... x gv Left Bottom Duct adaptor Right Top Tendon Duct Tendon.. x gv 9

10 S HSR Joint Type 2: Slip-dominant joints Energy dissipation by friction at segments interface. Resistance and re-centering by tendon bearing forces (dowel effect). Rocking initiated i i after sliding capacity is reached. Intended for bridge substructure elements (piers). Cyclic Testing of Bridge Pier with HSR Joints Test Specimen Half-scale bridge pier made of five segments and 8 PT tendons. PT force = 720 kn (90 kn/tendon); gravity load = 200 kn. Joint silicone to achieve friction coefficient i of Threaded rods Tendon restoring force (Dowel effect) Joint 5 PS5 Joint 4 Actuator Top Tendon Duct 0.6 m PS4 PS3 Joint 3 Joint 2 Gravity Tendon (For safety reasons, PVC tubing is used as PT Tendon a cover) Duct & Duct 15.2 Adaptor mm 2 1/2" Sandwich steel plates Steel tubes Bottom Duct adaptor.. x gh PS2 PS1 Joint 1 Joint 0 2'-1" 635 mm 2 1/2" October 2'-1" 635 mm 8, " 10" 10" Tendon for gravity loa ds Cyclic Testing of Bridge Pier with HSR Joints Cyclic Testing of Bridge Pier with HSR Joints Drift Ratio (%) 100 Test Results Lateral Force (kips s) Lateral Drift Ratio (%) Global Hysteretic Response Secant stiffness (kips/in) Secant Stiffness Variation Note: 1 kip = 4.45 kn Damping Ratio Equivalent Viscous Damping Ratio Variation Cyclic Testing of Bridge Pier with HSR Joints Test Observations Negligible structural damage for drift ratios <3%. Sliding-dominant response. Concrete spalling for drift ratios >5%. Rocking-dominant response. Concrete crushing for drift ratios > 6%. Stabilize for drift ratios >10%. PT system behavior: Negligible or no yielding negligible dowel deformations. Lost of 50% of initial PT in some tendons for drift ratios >8%. No structural failure at ultimate drift ~15%. Seismic Testing of HSR Bridge System Test Specimen Half-scale, single-span single-cell bridge system with overhangs 19 m long by 5 m high Superstructure: 8- HSR rocking-dominant segments with mm unbonded PT tendons WEST SIDE Suspension Substructure: Safety System Similar to cyclic test specimen Superstructure Design: AASHTO LRFD (2007) PCI Bridge Design Manual (2003) Cap Beam Larger force reduction factors Pier Dual shake table testing Foundation Block EAST SIDE 10

11 Seismic Testing of HSR Bridge System 100% MCE Horizontally + 240% MCE Vertically Seismic Testing of HSR Bridge System 100% MCE Horizontally + 240% MCE Vertically Total Accel. - Longit. Dir. (g) ( Longitudinal Absolute Acceleration Limited to ~0.5g West Table Superstructure - West Side Time (sec) (g) Total Accel. - Lateral Dir Transverse Absolute Acceleration Limited to ~0.55g West Table Time (sec) Superstructure - West Side Seismic Testing of HSR Bridge System 100% MCE Horizontally + 240% MCE Vertically Total Base Shear (kip ps) Global Transverse Hysteretic Response Superstructure Substructure 40 Mid-span Base Shear (kips) y 20 East West Questions/Discussions Relat. Displ. u supy (in) Relat. Displ. u cby (in) Note: 1 kip = 4.45 kn; 1 in = 25.4 mm 64 11