NEESR-SG: Controlled Rocking of Steel- Framed Buildings with Replaceable Energy Dissipating Fuses Greg Deierlein, Paul Cordova, Eric Borchers, Xiang Ma, Alex Pena, Sarah Billington, & Helmut Krawinkler, Stanford University Jerome Hajjar, Kerry Hall, Matt Eatherton, University of Illinois Mitsumasa Midorikawa, Hokkaido University Toko Hitaka, Kyoto University David Mar, Tipping & Mar Associates and Greg Luth, GPLA

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

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 with little or no residual drift Rocked Configuration

Controlled-Rocking System

Base Shear Drift a bc d f g Combined System Origin-a – frame strain + small distortions in fuse a – frame lift off, elongation of PT b – fuse yield (+) c – load reversal (PT yields if continued) d – zero force in fuse e – fuse yield (-) f – frame contact f-g – frame relaxation g – strain energy left in frame and fuse, small residual displacement Fuse System Base Shear Drift a bc d efg Fuse Strength Eff. Fuse Stiffness PT Strength PT – Fuse Strength Pretension/Brace System Base Shear Drift a,f b c d e g PT Strength Frame Stiffness e 2x Fuse Strength

Shear Fuse Testing - Stanford Panel Size: 400 x 900 mm Attributes of Fuse ­ high initial stiffness ­ large strain capacity ­ energy dissipation Candidate Fuse Designs ­ ductile fiber cementitious composites ­ steel panels with slits ­ low-yield steel ­ mixed sandwich panels ­ damping devices

Trial Steel Fuse Configurations Rectangular Link Panel Butterfly Panel B L b thickness t h a KEY PARAMETERS: Slit configuration b/t and L/t ratios Butterfly – b/a ratio Out of plane bracing

Similar Deformation Mode ABAQUS Modeling of Fuse

Prototype Structure

1.A/B ratio – geometry of frame 2.Overturning Ratio (OT) – ratio of resisting moment to design overturning moment. OT=1.0 corresponds to R=8.0, OT=1.5 means R=5.3 3.Self-Centering Ratio (SC) – ratio of restoring moment to restoring resistance. 4.Initial P/T stress 5.Frame Stiffness 6.Fuse type including degradation Parametric Study – Parameters Studied

OT=1.0 SC=1.0 A/B=2.3 SC=1.0 A/B=2.3 OT=1.0 Sample of Parametric Study Results: Mean Values of Peaks from Time Histories

UIUC Half Scale Tests

UIUC Half Scale Tests Typical Alternative Configuration: Six Fuses

UIUC Half Scale Tests Elevation of Post Tensioning Column Base

Test Matrix Test ID Dim “B” 1 A/B Ratio OT Ratio SC Ratio Num. of 0.5” P/T Strands Initial P/T Stress 2 and Force Fuse Type and Fuse Strength Fuse ConfigurationTesting Protocol A12.06’ (R=8) Fu (94.8 kips) Steel Butterfly 1 (84.7 kips) Six – 1/4” thick fuses 3F-025-AB2.5-OT1.0 Quasi- Static A22.06’ (R=8) Fu (94.8 kips) Steel Butterfly 2 (84.7 kips) Two – 5/8” thick Fuses 1F-0625-AB2.5-OT1.0 Quasi- Static A32.06’ (R=8) Fu (142.3 kips) Steel Butterfly 3 (84.7 kips) Two – 5/8” thick Fuses 1F-0625-AB2.5-OT1.5 Hybrid Simu- lation 3 A42.06’ (R= 5.3) Fu (142.3 kips) Steel Butterfly 3 (127.0 kips) Two – 1” thick Fuses 1F-1-AB2.5-OT1.5 Quasi- Static B13.06’ (R=8) Fu (94.8 kips) Steel Butterfly 4 (75.4 kips) Six – 1/4” thick fuses 3F-025-AB1.69-OT1.0 Quasi- Static B23.06’ (R=8) Fu (94.8 kips) Steel Butterfly 5 (75.4 kips) Two – 5/8” thick Fuses 1F-0625-AB1.69- OT1.0 Quasi- Static B33.06’ (R=8) Fu (94.8 kips) Steel Butterfly 4a (75.4 kips) Six – 1/4” thick fuses 3F-025-AB1.69-OT1.0 Hybrid Simu- lation 3 B43.06’ (R= 5.3) Fu (142.3 kips) Steel Butterfly 6 (113.2 kips) Two – 1” thick Fuses 1F-1-AB1.69-OT1.5 Quasi- Static

System Test at E-Defense (2009) Large (2/3 scale) frame assembly Validation of dynamic response and simulation Proof-of-Concept ­ construction details ­ re-centering behavior ­ fuse replacement Collaboration & Payload Projects Special thanks to Profs. Takeuchi, Kasai, Nakashima and all those involved in the testbed development and E-Defense operations

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.The controlled rocking system satisfies two key performance goals: a)Minimize residual drift. b)Concentrate bulk of structural damage in replaceable fuses. 3.Experimental and analytical work has been carried out at Stanford to optimize fuses. 4.A parametric study was conducted at UIUC to optimize A/B ratio, OT ratio, and SC ratio. 5.Half-scale tests will be conducted at the UIUC MUST-SIM Facility to improve details and validate the performance of the controlled rocking system for implementation in practice. 6.Tests will be carried out at E-Defense to further validate the system performance and demonstrate the self-centering and repairability of the controlled rocking system when subjected to a realistic ground motion. Conclusion

Controlled Rocking Project

Extra Slides

Organization 1.Context for System Development 2.Controlled Rocking System 3.Fuse Tests at Stanford 4.Brief Overview of Parametric Study 5.UIUC Half-Scale Test Program 6.Tests at E-Defense 7.Conclusions

Two story steel-framed office building in Santa Clarita suffered residual drift in the first story due to the Northridge Earthquake. From EERI Earthquake Reconnaissance Reports, 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

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

Fuse Tests at Stanford

Trial Fuse Designs: Rectangular Slits #3 R56-10 #4 R56-10BR #3 R56-10 #4 R56-10BR

Parametric Study 1.Reduction in the A/B ratio resulted in a decrease in the fuse shear strains, but requires steeper bracing in the braced frames, and yields slightly higher displacements. 2.Higher OT factors minimize displacement response, including residual displacements and fuse shear strain demands. The advantages of increasing OT must be tempered by the cost of larger forces that must be transmitted through the frame and foundation, and slightly larger accelerations. 3.The system exhibited excellent self-centering capability. The SC ratio does not need to be larger than 1.0 to self-center the system, but configuration must be checked to preclude global overturning. Also, it is expected that upon removal of the fuses (for replacement), any residual uplift or roof drift would be eliminated. 4.The system has to rock to work. None of the configurations considered eliminated uplift for even the smaller event considered (50% in 50 years). The OT ratio had the most effect in limiting peak uplift. 5.Peak roof drift ratios and peak uplifts were in acceptable ranges even for OT = 0.75 (R=10). 6.Based on median for 2% in 50 year event, the following are limits that might be imposed on fuse design: For A/B ratio = 1.5, use fuses with shear strain capacity of 0.08 For A/B ratio = 2.0, use fuses with shear strain capacity of 0.10 For A/B ratio = 2.5, use fuses with shear strain capacity of 0.11 For A/B ratio = 3.0, use fuses with shear strain capacity of 0.13

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 Half Scale Tests at UIUC

UIUC Half Scale Tests – Instrumentation 1

UIUC Half Scale Tests – Instrumentation 2

Tests at E-Defense