Japan's Key Technologies for Seismic Protection of New and Existing Buildings

Transcription

1 Keynote Speech: Seminar: Steel Design in Chile Intercontinental Hotel, Santiago, May 27, 214 Japan's Key Technologies for Seismic Protection of New and Existing Buildings Kazuhiko Kasai Professor and Director Structural Engineering Research Center Tokyo Institute of Technology, Japan Summary of Experiences & Findings from 3.11 (Building Structures) Acceleration-induced failures and falling of ceiling, electrical & mechanical systems, and loss of building functions. Large displacements of super-tall bldgs. even at long epicentral distance, due to long period ground motions. Difficulty of quick evaluations of damage and functionality in judging continued use of major buildings. Strong motion records of major bldgs. & super-tall bldgs. in Tohoku (>.4g) and Tokyo (.1g), clarifying many issues. Protective systems (base isolation & added damping systems) performed well at various epicentral distances. Japan's Key Technologies for Seismic Protection of New and Existing Buildings 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions Tokyo Institute of Technology Kasai Lab. Coventional System vs. Two Protective Systems Conventional Structure : Dissipates seismic energy by sacrificing main components such as columns, beams, and walls. Base-Isolated Structure : Isolates building from ground shaking. Damped Structure : Mitigates damage and vibration by dissipating seismic energy using dampers installed at building floors or top. Tokyo Institute of Technology Kasai Lab. 1

2 Tokyo Institute of Technology Kasai Lab. Conventional Structure vs. Two New Structures Isolator Demonstration of Added Damping Systems and Base Isolation Systems Damping Systems for Houses Conventional Structure: Damage Caused by Seismic Energy Base-Isolated Structure: Structure Isolated from Ground Motion Added-Damping Structure: s Absorb and Dissipate Seismic Energy Tokyo Institute of Technology Kasai Lab. Our patented techniques were commercialized by two companies. These damping systems are displayed in our campus. L.A. City Hall Originally Built in 1928 Retrofitted in 21, the Largest Retrofit Project Using Base Isolation Historical Super-Tall Building (137m tall) 575 Japanese Isolators Adopted (High-Damping Rubber + Sliding) 2

3 Devices for Base-Isolation Systems March 11 Performance: Structural Concept Isolator Steel Oil No foundation girders to connect footings 1 Movement of Lead Rubber Bearing 3 章一質点制振構造の力学原理と性能曲線 Amplifier Type 11 JSSI パッシブ制振構造設計 施工マニュアル 3

4 Buckling-restrained Brace Brace type damper with core steel member whose buckling is restrained by concrete/steel member Core steel member Conventional Brace Buckling Buckling-restrained Brace Load Load Bucklingrestrained member Tension Compression Displacement. Tension Compression Displacement. Configuration of Buckling-restrained Brace Comparison of mechanical behavior between Bucklingrestrained Brace and Conventional Brace Japan's Key Technologies for Seismic Protection of New and Existing Buildings 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions VALUE-ADDED 5-STORY STEEL FRAME AND ITS COMPONENTS: PART 1 FULL-SCALE DAMPER TESTS AND ANALYSES Major Types Used in Japan Manual by JSSI (Japan Society for Seismic Isolation) 1st, 2nd, and 3rd Editions, 22, 25, 27, and 213 The 14th World Conference on Earthquake Engineering October 12-17, 28, Beijing, China 4

5 15,835 1, 2,985 3, 3, 3, 5, 5, 15 G2 G3 C1 G13 G13 G2 G1 C1 G2 C1 G2 C1 7, Roof 5, 12, G3 G1 5th fl. G3 4th fl. G3 3rd fl. G3 2nd fl. G1 G1 G1 B A 15,835 Full-Scale 5-Story Building with s Seismically Active Wt.: 4,734 kn Frame Period:.74s (x),.79s(y) With Elast. Steel :.53s (x),.56s(y) 2,985 3, 3, 3, 15 C1 C1 C1 Roof 5th fl. 4th fl. 3rd fl. C1 2nd fl. 3,85 G3 1st fl. G1 3,85 C1 1st fl. G3 G1 7, 5, 12, 5, 5, 1, Full-Scale 5-story Steel building with Steel 5

6 Steel Viscous Oil Viscoelastic 6

7 Summary The 5-story building with dampers kept the story drift angle below the target limit of 1% rad against the catastrophic motion of unscaled Takatori record. It was so for all four cases of using steel, viscous, oil, and viscoelastic dampers, respectively. Main frame was kept almost elastic. Peak displacements were.45 ~.65 times, and peak accelerations were.6 ~.85 times those of the case of undamped building. These indicate good seismic protection of both building and its contents. Japan's Key Technologies for Seismic Protection of New and Existing Buildings 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions 29-Story Building (No s) Guest Professorship Presentation, Tongji Univ., Shanghai Damage to Nonstructural Components (From Prof.Hisada) Name Kogakuin University Completion 1989 Number of Floors 29 floors above ground 6 floors below ground 1 floor penthouse Aspect Ratio EW(X): 3.73; NS(Y): 5.59 Frame Type Steel frame with brace Period (s) (obtained by Kasai lab.) EW (X): 2.96s, 1.s NS (Y) : 3.9s,.94s Movement of copy machine(25f) Falling of books(25f) (From Prof. Hisada) Falling of ceiling:28f(21f, 14F, etc.) Elevator cable damage (another tall bldg., repaired in 3 weeks) Guest Professorship Presentation, Tongji Univ., Shanghai 7

8 Acc. of 29th level and base Top acceleration Base acceleration 29-Story Bldg. (No s), Y-direction Modal Contributions to Disp. and Acc. High Frequency Low Frequency 29th Floor Dispt. 1st The 2nd mode dominated at 16th floor. 29th Floor Acc. 3rd 2nd 1st Modal contribution and manner of vibration depend on story level. The vibration continued for more than 6 min. The recorded responses are well explained based on the modes and modal responses. 1 st mode 2 nd mode (Y-direction) 16th Floor Acc. X-Direction(Finding Good Locations) shown by red color: (Zero-stiffness assigned in the eigenvalue analysis) Against March 11 Base Motion (Recorded): Actual Case vs. Retrofitted Case (Oil dampers) With damper Story No. No damper Displacement (cm) Story drift (rad) Absolute Acc. (cm/s 2 ) Story Shear (kn) 1 次モード 2 次モード 8

9 Japan's Key Technologies for Seismic Protection of New and Existing Buildings 21-Story Bldg. with 336 Steel s & 284 Viscous s 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions 21-story Steel Frame X Y Viscous damper (284) Steel damper (336) 41-Story Bldg. with 688 Oil s Steel Core Frame 41-story Steel Frame + Oil damper (688) 54-Story Bldg. Retrofitted by 288 Oil s. 54-story Building: Steel Frame Oil s ( ) Oil 42m Y X 63m Oil 9

10 21-story Building: Steel Frame Steel s Viscous s 41-story Building: Steel Frame Oil s 45.4m 45.4m 54-story Building: Steel Frame Oil s 63m 42m Black: With damper, actual recorded acc. and disp. (double integration). Gray: No damper, modal analysis by assuming 1% damping ratio. 96m 52m 186.9m 223m Top Floor Acc. 99.6m Top Floor Disp. Steel Y X (a) Viscous Y Oil X (b) Y X Oil (c) 54-Story Bldg. (continued): Without damper, the acc. and disp. will increase considerably. Japan's Key Technologies for Seismic Protection of New and Existing Buildings 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions Tokyo Institute of Technology Kasai Lab. Steel frame is the easiest one to connect dampers! uˆ d Steel 鋼材ダンパー û d Viscous 粘性ダンパー û d û d オイルダンパー Oil Viscoelastic 粘弾性ダンパー û a ûd u ˆ d û a = u ˆ d+ û d (sum of deformation at both side only for steel damper) û a = û d + stiffness of supporting member Tokyo Institute of Technology Kasai Lab. 1

11 Steel Products and Joining Technology for Construction of Steel-frame Buildings Circular steel tube Production Method of Square Tubes Cold roll-formed square tube Cold press-formed square tube High-strength bolt Square steel tube Section Weld Weld Weld Wide-flange Plate Roll forming + Electric resistance welding Weld Press forming + Arc welding (2 seams) Press forming+ Arc welding (1 seam) Welding Size (mm) -2 6~ ~ -1 4 Built-up Column welded by large heat-input welding method Submerged arc welding Heat input 2~6 kj/mm Corner weld Electro-slag welding Heat input 5~1 kj/mm Diaphragm plate weld New Steel Products for Building Structures Stress (N/mm 2 ) 1, N/mm 2 steel 59 N/mm 2 steel SN49 SN4 LY1 LY Strain (%) <Directions of Development of Steel Products for Building Structures> Higher strength 59N/mm 2 steel 78N/mm 2 steel Higher performance Heavier thickness and larger cross section TMCP plate TMCP extra-heavy wide-flange Lower yield point - LY1, LY225 SN, BCR, BCP - Weldability - Lower yield ratio, narrower-range yield point - Higher dimensional accuracy New performances High-temperature property Fire-resistant steel Durability Weathering steel Stainless steel 11

12 - Concrete-Filled Steel Tube (CFT) - Compensates for demerits of the RC and steel structures, realizing higher seismic and fire resistance. (MN) Comparison of Axial Strength Fc 6 t=5 t=5 t=5 Fc 9 RC S355J SA44 SA44 Note: This means that RC columns requires CFT much larger cross section for the same strength. SA44(Tensile Strength 59N/mm 2 ) Japan s Tallest Bldg. Landmark Tower in Yokohama (296.m, 7-story, Built in 1993) Roppongi-Hills Tower (238.1m, 54-story, Built in 23) 12

13 CURRENT STATUS OF BUILDING PASSIVE CONTROL IN JAPAN Stress σ(mpa) 1, YS65 HSA Development of Damage-Free Structure & Design Specifications by ANUHT HT62 SN49 SN4 HT44 Level of σ y to Achieve θ y = 1/6 1/75 1/1 1/ ε(%) Strain Fig. 8 Super High Strength Steel Considered Acceleration (cm/s 2 ) K-NET Oshika 23 (6.3) K-NET Hiroo 23 (6.) K-NET Chokubetsu 23 (6.3) K-NET Tokamachi 24 (6.2) K-NET Nagaoka-shisho 24 (6.1) K-NET Anamizu 27 (6.3) K-NET Kashiwazaki 27 (6.3) JMA Kobe 1995 (6.4) JMA Ojiya 24 (6.3) JMA Kawaguchi 24 (6.3) Tokyo-Koenji (6.6),Artif. Tokyo Bay -Nihonbashi (6.5),Artif. 1.5 Design Basis Eq.Level,Artif. ξ = Period (sec) Fig. 9 Catastrophic Earthquakes Considered The 14th World Conference on Earthquake Engineering October 12-17, 28, Beijing, China Tokyo Institute of Technology Kasai Lab. Direct Design Method for Required Performance: E-Defense 5-Story Bldg Using the Performance Curve, -Choose balance among damper and frame S pa (cm/s 2 ) Steel = T f =.35H T f =.45H T f =.55H.25.5 K a /K f (rad) F a Frame K f K d F Brace K b Added Comp. K a K a u d u max Tokyo Institute of Technology Kasai Lab. u u Performance curve gives a variety of solutions for damper stiffness and frame stiffness satisfying the story drift limit. For example, Solution 1. Relatively stiff damper and flexible frame. Solution 2. Relatively flexible damper and stiff frame. Solution 1 can lead to smaller response acc. But the frame s restoring capability will be less, meaning increased potential of residual deform. and nonuniform story drifts over the height of the building. Solution 2, if acc. is well-controlled, would be a good choice by the above reasons, and the rectangular square tube section is suited best to provide adequate frame stiffness in both x- and y-directions. Japan's Key Technologies for Seismic Protection of New and Existing Buildings 1. Introduction to Protective Systems 2. Largest Shake Table Test of Building with s 3.Conventional Tall Building Retrofit by s 4.Damped Tall Building Performance During Scopes for Tall Buildings with Protective System 6. Conclusions 13

14 Conclusions Seismic base isolation systems and added damping systems have become the standard technology to protect human lives, building functionality, and assets against major earthquakes. Such protective systems are discussed, with emphasis on added damping which most new tall buildings in Japan utilize now. Full-scale tests results using the world s largest shake table (E-Defense), as well as response records of major buildings at the 211 Tohoku earthquake indicate beneficial effects of dampers for existing or new buildings. Supplemental damping technology and steel frame match well, since; 1) dampers are most securely and easily connected to the steel members through welds or bolts; 2) a steel frame, below the yield limit, has a clear undamaged state warranting continued post-quake use of the building, and; 3) a steel frame with square tube columns provides sufficient stiffness for any lateral direction. 14