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1 Normalized stress σ/g Breaking test Theory 1 2 Shear tests Failure tests Compressive tests Fig.1. Relation between normalized stress and shear strain. 2)A.N.Gent Elastic Stability of Rubber Compression Springs,Journal Mechanical Engineering Science, pp318pp 326, 1964.

2 ( FAILURE INTERACTION CURVE OF NATURAL RUBBER BEARINGS ) Ryuichi Kato, Kurashikikako Co, Ltd., katoh@kuraka.co.jp 1 Kenjiro Oka, Kurashikikako Co, Ltd., okaken@kuraka.co.jp 2 Mineo Takayama, Dept. of Architecture, Faculty of Engineering, Fukuoka University, mineot@fukuoka-u.ac.jp SUMMARY The application of seismic isolation technology is spread to various structures, and the most of them use laminated rubber bearings. The research of ultimate characteristics of laminated rubber bearings has been advanced theoretically and experimentally, but there are no standard testing methods for estimating them. In this paper, several testing methods for estimating the ultimate capacity of the Natural Rubber Bearings were present and the failure interaction curve of them is clarified according to proposed methods. : Key words: Natural Rubber Bearings, Failure Interaction Curve, Buckling Stress 1

3 Fig.1. Feature of Natural Rubber Bearings. Table1: Specification of NRB Diameter of a rubber sheet D (mm) Thickness of a rubber sheet t R (mm) Numbers of rubber sheets n Total thickness nt R (mm) Shape factor S1 33 Shape factor S2 5.1 Inner rubber Inner plate Connecting p late Connecting bolt Flange p late Surface rubber Table2: Test conditions of shearing tests Compressive stress σ (N/mm 2 ) Vertical stiffness K v Vertical load P 5 K vmax.9 K vmax φ9 φ7 φ5 φ1 φ8 V ertical stiffness vs displacem ent buckling stress V ertical load vs disp. 1 V ertical displacem 2 ent y 3 Fig.2. Evaluation of compressive tests.

4 Fig.3. Evaluation of shearing tests. 8 Shear strain % 1 15% 2% 7 % 25% 6 Horizontal s tiffness K H 1.2 K H K H K H=1- (σ σ Η cr) σ Hcr Compressive stress σ Comressive s tress σ (N/mm 2 ) 1 Fig.4. Vertical characteristics by compressive tests (G.34) Fig.5. Relation between buckling stress and shear strain (G.34) Vertical displacement y (mm) Non-buckling Compressive tests 3% 35% 4%

5 .5. Tensil e stress σt (N/mm 2 ) ε = 5% % 75 % 5 % 25 % 1 % Fig.6. Tensile stress-strain curves under shear strain 1% (G.44)..5. σ = Shear strain % 1 % 2 % 3 % σ = 29.4 N/mm Tensile strain ε t (%) Fig.7. Tensile stress-strain curves under shear strain,1,2 and 3% (G.44). Fig.9. Horizontal load-displacement curves (G.34) Design range Non-failure Shear strain 1% Failure 2% % 35% % Fig.8. Results for tensile tests and failure interaction curve. Fig.1. Relation between K H and σ (G.34). Tensile stress σt (N/mm 2 ) Tensile strain εt (%) Tensile strain ε t (%) σ = 19.6 γ = 3% γ = 35% γ = 4% Ratio of horizontal stiffness

6 Fig.11. Relation between buckling stress and shear strain (G.34). 15 Shear stress τ (N /m m 2 ) Fig.12. Shear stress-strain curves by failure tests (G.34) φ5 φ7 φ1 theoretical value Shear strain γ () Compressive stress 9.8 N /mm N /mm N /mm 2 Failure tests 29.4 N /mm Fig.13. Relation between compressive stress and buckling strain by failure tests (G.34). σ Normalized stress σ/g 1 5 Breaking test Theory 1 2 Shear tests Failure tests Compressive tests Fig.14. Relation between normalized stress and shear strain.

7 Compressive load Tensile deformation 6)Buckle,I.G.andLiu,H Stability of Elastomeric Seismic Isolation, Passive Energy Dissipation and Active Control, ATC-17-1, Vol.1, 1993 ε t σ cr Design range Stable ultimate range Fig.15. Concept of failure interaction curve. D Shear deformation 2)A.N.Gent Elastic Stability of Rubber Compression Springs,Journal Mechanical Engineering Science, pp318pp 326, 1964.