3rd Annual EHKS Retreat March 10, 2007 Allerton Park Controlled Rocking Steel Frames with Replaceable Energy-Dissipating Fuses Matt Eatherton, MS SE University of Illinois at Urbana-Champaign

3rd Annual EHKS Retreat March 10, 2007 Allerton Park My Background Born in Kansas City, 1975Born in Kansas City, 1975 BS in CE - University of Missouri at Columbia, 1997BS in CE - University of Missouri at Columbia, 1997 MS in CE - University of Missouri at Columbia, 1999MS in CE - University of Missouri at Columbia, 1999 –Master’s research involved instrumenting and monitoring four prestressed bridge girders with over 150 gages during construction and for one year in service. 2 years structural design experience in Kansas City2 years structural design experience in Kansas City 5 years structural design experience in San Francisco5 years structural design experience in San Francisco Volunteer Structural Engineering ActivitiesVolunteer Structural Engineering Activities –Build Change – improving seismic resistance of housing in developing countries –SEAONC subcommittee – investigated diaphragm forces –Steel Plate Shear Walls – several projects, conference articles, design examples, and other involvement Began PhD program at UIUC in fall 2006 with the goal of getting an academic position afterwardBegan PhD program at UIUC in fall 2006 with the goal of getting an academic position afterward

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Organization 1.Introduction 2.Controlled Rocking System 3.Parametric Study & Prototype Building 4.UIUC Half-Scale Test Program 5.Conclusions

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Two story steel-framed office building in Santa Clarita suffered residual drift in the first story due to the Northridge Earthquake. From EERI Earthquake Recon. Report, Jan & May 1990 Building with a Red Tag restricting access after the Northridge Earthquake Industrial Structure that experienced brace buckling and residual drift during Loma Prieta Expected Building Performance

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Component 1 – Stiff braced frame, designed to remain essentially elastic - not tied down to the foundation. Component 2 – Post- tensioning strands bring frame back down during rocking Component 3 – Replaceable energy dissipating fuses take majority of damage Bumper or Trough Controlled Rocking System

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Corner of frame is allowed to uplift. Fuses absorb seismic energy Post-tensioning brings the structure back to center. Result is a building where the structural damage is concentrated in replaceable fuses and virtually no residual drift! Rocked Configuration

3rd Annual EHKS Retreat March 10, 2007 Allerton Park F PT = Initial post-tension force V p = Fuse yield strength in shear Overturning moment = Resistance comes from Post-Tensioning and Fuses: In an LRFD context use a resistance factor to design: Can also include gravity loads Design Equations - Overturning Resistance

3rd Annual EHKS Retreat March 10, 2007 Allerton Park In the rocked configuration, the fuses resist self-centering. The restoring moment due to P/T must overcome the restoring resistance: Other sources of resistance not considered in this equation include: Stiffness of gravity system Stiffness of interior partitions that have undergone inelastic damage P-delta effect Can also include effect of gravity load in restoring force. Design Equations - Self-Centering Mechanism

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Fuse Shear Strain,  = Shear strain in the fuses is amplified compared to the roof drift ratio (RDR). Using small angle assumption: Example: Fuse Shear Strain Demand

3rd Annual EHKS Retreat March 10, 2007 Allerton Park FLAG SHAPED HYSTERESIS 1.Begin Loading 2.Frame Uplifts 3.Fuses Yield 4.Load reversal. If pushed far enough P/T would yield 5.Zero force in fuses 6.Fuses yield in other direction 7.Frame sets back down and forces in the frame relax. 8.Elastic strain energy remains in frame and fuses 7 8 Controlled Rocking – Hysteretic Response

3rd Annual EHKS Retreat March 10, 2007 Allerton Park 1.Global Overturning (F PT > V p ) 2.Initial P/T stress: Stressing the P/T strands 0.4 F u may require special procedures to anchor post-tensioning (post-blocking). 3.P/T strain capacity: If performance criteria includes not replacing P/T after a severe earthquake then ensure adequate strain capacity. Preventing Global Overturning Other Design Considerations

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Use prototype structure to apply controlled rocking to a realistic structure Based on SAC Building configuration Tests and analysis simulate the controlled rocking frames in this structure. Prototype Structure

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Prototype – Controlled Rocking Frames

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Goals: 1.To test and improve details – post-tensioning and base connections are not typical to steel structures. 2.Study the forces realized in the fuses and distribution of force between fuses. Geometric nonlinearity and indeterminacy creates complexity. 3.Examine effect of out-of-plane motion while rocking. 4.Determine whether typical P/T strands and anchorage can be stressed to yield without fracturing or slipping. 5.Establish whether there is inelasticity or relaxation in the P/T that would require replacement or re-stressing. 6.Investigate whether inelasticity occurs in the frame. VERIFY THE PERFORMANCE OF THE SYSTEM FOR IMPLEMENTATION IN PRACTICE UIUC Half Scale Tests

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Front ViewSide View UIUC Half Scale Tests

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Test Matrix Test ID Dim “B” 1 A/B Ratio OT Ratio Initial P/T Stress 2 and Force Fuse Type and Fuse Strength Time Req’d Testing Protocol Reason for Test A13.09’ (R=8) Fu (103.9 kips) Steel Slit 1 (82.6 kips) 4 weeks Quasi- Static 3 This configuration should produce the least amount of demands on the fuses. If there are problems with the fuses, we may be able to reconfigure. A23.09’ (R=8) Fu (103.9 kips) ECC 1 (82.6 kips) 1 week Quasi- Static 3 If the system works in the first test, try an ECC fuse in this best- case configuration. A33.09’ (R=8) Fu (103.9 kips) Steel Slit 3 (82.6 kips) 2 week Hybrid Simu- lation 4 Now that we know how well this configuration responds, conduct a hybrid simulation to find out how the system will perform in a real building. One of the main objectives is to examine effect of out-of- plane rotation. A43.09’ (R=5.3) Fu (155.8 kips) Steel Slit 2 (123.9 kips) 1 week Quasi- Static 4 Increase the OT to 1.5. The higher OT would result in lower ductility demands, so if it works, this would be the configuration proposed for better performance in a PBD. This configuration will also cause P/T yielding before the fuses are completely destroyed. B12.16’2.51.5(R=5.3) Fu (155.8 kips) Steel Slit 4 (139.1 kips) 4 weeks Quasi- Static 3 Now that we have an idea how well the system works, push the A/B to 2.5, but with an OT of 1.5. This configuration still produced reasonable fuse shear strain demands in the parametric study. B22.16’2.51.0(R=8) Fu (103.9 kips) Steel Slit 5 (92.7 kips) 1 week Quasi- Static 3 Drop the OT back to 1.0. This configuration pushes the envelope with regards to fuse shear strain demand predicted by the parametric study. B32.16’2.51.0(R=8) Fu (103.9 kips) ECC 2 (92.7 kips) 1 weeks Quasi- Static 3 If the previous test with A/B = 2.5 and OT = 1.0 works, try an ECC fuse. *We will cast another set of ECC fuses based on OT=1.5 and A/B = 2.5, in case system isn’t performing as well as expected. B42.16’2.51.0(R=8) Fu (103.9 kips) Steel Slit 6 (92.7 kips) 2 week Hybrid Simu- lation 4 For the finale, try a hybrid simulation at A/B = 2.5. Along with other hybrid simulation, this will tell us how well the system might perform in a real building.

3rd Annual EHKS Retreat March 10, 2007 Allerton Park Degree of Freedom Left LBCB Right LBCB ForceMovementForceMovement U - horizontal Free USE THIS AS CONTROL Constrain to Match Force of left LBCB Free U - vertical Gravity Load Specified Free Free U - out-of-plane Free Constrain to be 0 Free θ - in-plane As necessary to simulate applying gravity load to exterior columns Free Free θ - out-of-plane Free Constrain to be 0 Free θ - torsion Free Constrain to be 0 Free The horizontal movement of the Left LBCB would be used to control the test. The Right LBCB will match the horizontal force in the left LBCB. This will apply the same amount of load to both frames, but allow differential rocking between the frames. Mixed Mode Control

3rd Annual EHKS Retreat March 10, 2007 Allerton Park 1.Seismic loads prescribed in current building codes assume considerable inelasticity in the structure during a severe earthquake. This can result in structural damage and residual drift that cannot be economically repaired. 2.To provide a building that is relatively easy to repair after an earthquake, two attractive performance criteria are: a)Eliminate residual drift. b)Concentrate bulk of structural damage in replaceable fuses. 3.The controlled rocking system satisfies these performance goals. 4.The controlled rocking system consists of three major components: a)Stiff steel braced frame designed to remain essentially elastic, but not tied down to the foundation. b)Post-tensioning that provides self-centering capability. c)Highly ductile energy dissipating fuses. 5.A multi-institution, international research project is underway to examine, improve, and validate the performance of this innovative system. Summary

3rd Annual EHKS Retreat March 10, 2007 Allerton Park 6.A parametric study was conducted to optimize A/B ratio, OT ratio, and SC ratio. 7.Some considerations in the design of the controlled rocking system include: a)Proportioning fuses and P/T to resist overturning, but still self- center. b)Insuring enough P/T strain capacity. c)Using fuses with enough shear strain capacity based on frame geometry (fuse shear strain is amplified compared to roof drift ratio). d)Preclude global overturning. 8.Half-scale tests will be conducted later this year at the UIUC MUST-SIM Facility to improve details and validate the performance of the controlled rocking system for implementation in practice. 9.Hybrid simulation tests will further validate the system performance and demonstrate the self-centering and repairability of the controlled rocking system when subjected to a realistic ground motion. Summary

3rd Annual EHKS Retreat March 10, 2007 Allerton Park PI Greg Deierlein – Project Manager, Stanford University Co-PI Sarah Billington – ECC & HPFRCC Fuses, Stanford Unviersity Co-PI Jerome Hajjar – Simulation and Half-Scale Tests, University of Illinois Helmut Krawinkler, Stanford University Mitsumasa Midorikawa – E-Defense, Building Research institute in Japan David Mar - Industry Collaborator, Tipping and Mar Engineers Current Graduate Students: Xiang Ma (Stanford), Matt Eatherton (UIUC) Past Graduate Students: Paul Cordova (Post-Doc at Stanford), Eric Borchers (Stanford), Kerry Hall (UIUC), Project is funded by a grant from NSF - NEESR-SG E- DEFENSE JAPAN Research Team