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Self-Centering Steel Frame Systems NEESR-SG: Self-Centering Damage-Free Seismic- Resistant Steel Frame Systems Project Team Richard Sause, James Ricles,

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Presentation on theme: "Self-Centering Steel Frame Systems NEESR-SG: Self-Centering Damage-Free Seismic- Resistant Steel Frame Systems Project Team Richard Sause, James Ricles,"— Presentation transcript:

1 Self-Centering Steel Frame Systems NEESR-SG: Self-Centering Damage-Free Seismic- Resistant Steel Frame Systems Project Team Richard Sause, James Ricles, David Roke, Choung-Yeol Seo, Michael Wolski, Geoff Madrazo ATLSS Center, Lehigh University Maria Garlock, Erik VanMarcke, Li-Shiuan Peh Princeton University Judy Liu Purdue University Keh-Chyuan Tsai NCREE, National Taiwan University

2 Current NEESR Project NEESR-SG: Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems This material is based on work supported by the National Science Foundation, Award No. CMS , in the George E. Brown, Jr. Network for Earthquake Engineering Simulation Research (NEESR) program, and Award No. CMS NEES Consortium Operation.

3 Motivation: Expected Damage for Conventional Steel Frames Conventional Moment Resisting Frame System Reduced beam section (RBS) beam-column test specimen with slab: (a) at 3% drift, (b) at 4% drift.

4 Self Centering (SC) Seismic- Resistant System Concepts Discrete structural members are post-tensioned to pre-compress joints. Gap opening at joints at selected earthquake load levels provides softening of lateral force-drift behavior without damage to members. PT forces close joints and permanent lateral drift is avoided. M

5 3660 to 4120 mm 6100 to 8540 mm W24x62 (Fy 248 MPa), or W36x150 (Fy 350 MPa) W14x311, W14x398 (Fy 350 MPa) or CFT406x406x13 (Fy 345 MPa) PT Strands Previous Work on SC Steel Moment Resisting (MRF) Connections MRF Subassembly with PT Connections

6 Stiffness with welded connection Initial Stiffness Is Similar to Stiffness of Conventional Systems H PT Steel MRF MRF subassembly with post-tensioned connections

7 Steel MRF subassembly with post-tensioned connections and angles at 3% drift Lateral Force-Drift Behavior Softens Due to Gap Opening

8 Lateral Force-Drift Behavior Softens Without Significant Damage Conventional steel MRFs soften by inelastic deformation, which damages main structural members and results in residual drift SC steel MRF softens by gap opening and reduced contact area at joints Post- Tensioned Connection Welded Connection

9 Energy Dissipation from Energy Dissipation (ED) Elements Specimen PC2 L6x6x5/16, g/t = 4 Specimen PC4 L8x8x5/8, g/t = 4 Steel MRF subassemblies with post- tensioned connections with different size ED elements. H Steel MRF

10 Limited, Repairable 4% DriftBefore testingAfter testing Angle fracture

11 Summary of SC Seismic-Resistant Structural System Behavior Initial lateral stiffness is similar to that of conventional seismic-resistant systems. Lateral force-drift behavior softens due to gap opening at selected joints and without significant damage to main structural members. Lateral force-drift behavior softening due to gap opening controls force demands. Energy dissipation provided by energy dissipation (ED) elements, not from damage to main structural members.

12 NEESR-SG: Self-Centering Damage-Free Seismic- Resistant Steel Frame Systems Project Scope. Project Goals. Status of Selected Research Tasks. Summary.

13 NEESR-SG: SC Steel Frame Systems Project Scope Develop two SC steel frame systems: –Moment-resisting frames (SC-MRFs). –Concentrically-braced frames (SC-CBFs). Conduct large-scale experiments utilizing: –NEES ES (RTMD facility) at Lehigh. –non-NEES laboratory (Purdue). –international collaborating laboratory (NCREE) Conduct analytical and design studies of prototype buildings. Develop design criteria and design procedures.

14 NEESR-SG: SC Steel Frame Systems Project Goals Overall: self-centering steel systems that are constructible, economical, and structurally damage-free under design earthquake. Specific: –Fundamental knowledge of seismic behavior of SC- MRF systems and SC-CBF systems. –Integrated design, analysis, and experimental research using NEES facilities. –Performance-based, reliability-based seismic design procedures.

15 NEESR-SG: Self-Centering Damage-Free Seismic- Resistant Steel Frame Systems Project Scope. Project Goals. Status of Selected Research Tasks. Summary.

16 NEESR-SG: SC Steel Frame Systems Project Research Tasks 1.Develop reliability-based seismic design and assessment procedures. 2.Develop SC-CBF systems. 3.Further develop SC-MRF systems. 4.Develop energy dissipation elements for SC-MRFs and SC-CBFs. 5.Develop sensor networks for damage monitoring and integrity assessment. 6.Design prototype buildings. 7.Perform nonlinear analyses of prototype buildings. 8.Conduct large-scale laboratory tests of SC-MRFs and SC-CBFs. 9.Collaborate on 3-D large-scale laboratory tests on SC-MRF and SC- CBF systems.

17 Task 2. Develop SC-CBF Systems: SC-CBF System Concept Rocking behavior of simple SC-CBF system.

18 More Complex SC-CBF Configurations Being Considered

19 SC-CBF Design Criteria Δ gap PT steel yields Member yields Column Decompression PT Yielding Significant Yielding of Frame Members Failure of Frame Members DBE MCE Lateral Force Roof Drift IOCPLS

20 Current Work on SC-CBF Systems Evaluate frame configurations. Evaluate effect of energy dissipation (ED) elements. Develop and evaluate performance- based design approach.

21 SC-CBF Configurations Studied Frame AFrame B12Frame B12ED PT ED PT ED

22 Dynamic Analysis Results (DBE) Roof drift: –Effect of frame configuration. –Effect of ED elements. 2.4% 2.7% 1.4% 2.7%

23 Pushover Analysis Results PT Yield Decompression Roof Drift (%) Base Shear (V/V des )

24 Preliminary Results for SC-CBF Dynamic analysis results indicate self- centering behavior is achieved under DBE. Frame A has lower drift capacity before PT yielding than Frame B: –PT steel is at column lines rather than mid-bay. Frame A also has lower drift demand. Energy dissipation helps to reduce drift demand and improve response.

25 Task 3. Further Develop SC-MRF Systems: Current Work Study of interaction between SC-MRFs and floor diaphragms by Princeton and Purdue. SC column base connections for SC- MRFs being studied by Purdue.

26 Interaction of SC-MRFs and Floor Diaphragms (Princeton) Approach 1. Transmit inertial forces from floor diaphragm without excessive restraint of connection regions using flexible collectors. gap r Collector Beams

27 Interaction of SC-MRFs and Floor Diaphragms (Purdue) Approach 2. Transmit inertial forces from floor diaphragm within one (composite) bay for each frame.

28 SC Column Base Connections for SC-MRFs (Purdue) Reinforcing Plate Slotted Keeper Angle Post-Tensioned Bars Energy Dissipation Plate Beam at Grade

29 Moment-Rotation Response at Column Base Identifying appropriate level of column base moment capacity and connection details, leading to laboratory experiments.

30 Task 4. Develop Energy Dissipation Elements for SC-MRFs SC systems have no significant energy dissipation from main structural elements: –Behavior of energy dissipation elements determined SC system energy dissipation. Energy dissipation elements may be damaged during earthquake and replaced. For SC-MRFs, energy dissipation elements are located at beam-column connections.

31 Quantifying Energy Dissipation Define relative hysteretic ED ratio E E : Relative ED capacity For SC systems: 0 E 50% Target value: E = 25% E = x 100(%) Area of yellow Area of blue Hysteresis Loop

32 ED Element Assessment Consider several ED elements: –Metallic yielding, friction, viscoelastic, elastomeric, and viscous fluid. Evaluation criteria: –Behavior, force capacity versus size, constructability, and life-cycle maintenance. Friction ED elements selected for further study.

33 Bottom Flange Friction Device Col. angle bolts Friction bolts Column angle Slotted plate Friction PL W36x300

34 BFFD Moment Contribution BFFD contribution to connection moment capacity M Ff = F f r M Ff + = F fr + M Ff - = F fr - |M Ff + | > |M Ff - | COR+ COR-

35 Test Setup Test setup elevation Test setup Bracing BFFD Beam PT Strands Column 3/5 Scale W21x111

36 Test Matrix CS: Cyclic SymmetricEQ: Chi-Chi MCE Level Earthquake Response Test No. Loading Protocol r,max (rads) Experimental Parameter 1CS0.035Reduced Friction Force 2CS0.030Design Friction Force 3CS0.030Fillet Weld Repair 4EQ0.025Response to EQ Loading 5CS0.065Effect of Bolt Bearing 6CS0.035Assess Column L Flex., CJP 7CS0.065Effect of Bolt Bearing, CJP

37 Test 2: Design Friction Force Beginning of Test 2 r = rads r = rads

38 Test 2: Response

39 Test 2: Comparison with Simplified Model M d + M + Ff 2M - Ff 2M + Ff 1 Axial stiffness of PT strands & beam M d + M - Ff

40 Results for ED Elements for SC-MRFs Friction ED element: –Reliable with repeatable and predictable behavior. –Large force capacity in modest size. BFFD: –Provides needed energy dissipation for SC-MRF connections. –When anticipated connection rotation demand is exceeded, friction bolts can be designed to fail in shear without damage to other components.

41 Task 8. Conduct Large-Scale Laboratory Tests Two specimens, one SC-MRF and one SC-CBF, tested at Lehigh NEES ES (RTMD facility). 2/3-scale 4 story frame. Utilize hybrid test method (pseudo dynamic with analytical and laboratory substructures). Utilize real-time hybrid test method, if energy dissipation elements are rate-sensitive.

42 9. Collaborate on 3-D Large- Scale Laboratory Tests Large-scale 3-D SC steel frame system tests at NCREE in Taiwan under direction of Dr. K.C. Tsai. Interaction of SC frame systems with floor diaphragms and gravity frames will be studied. 3-D tests are part of Taiwan program on SC systems. Project team is collaborating with Taiwan researchers: –US-Taiwan Workshop on Self-Centering Structural Systems, June 6-7, 2005, at NCREE. –2 nd workshop planned for October 2006 at NCREE.

43 Summary Two types of SC steel frame systems are being developed: –Moment-resisting frames (SC-MRFs). –Concentrically-braced frames (SC-CBFs). Research plan includes 9 major tasks: –Significant work completed on 7 tasks. –Numerous conference publications available from current project. Large-scale experiments utilizing NEES ES at Lehigh are being conducted. Ongoing collaboration with NCREE in Taiwan.

44 Self-Centering Steel Frame Systems Thank you.

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