HIGH DAMPING RUBBER BEARING

HIGH DAMPING RUBBER BEARINGS

Base isolation of a structure requires an interface with the following characteristics between the
foundation and the superstructure:

• low horizontal stiffness at design displacement;

• high vertical stiffness;

• capability to support the gravity load of structure over long term;

• capacity to accomodate large horizontal displacements during earthquakes and at same time support vertical load including seismic loads;

• moderate level of damping (10-15% for buildings);

• capability to re-centre structure after the earthquake;

• stable stiffness and damping properties over long term;

• high initial horizontal stiffness to provide wind restraint;

• ability to function again after the design earthquake.

SIMPLE, COST-EFFECTIVE AND MAINTENANCE FREE

High Damping Rubber Bearings (HDRBs) are a simple, cost-effective and maintenance-free means of providing the isolation interface. They can be designed to withstand the design earthquakes without signi cant damage.

The HDRB consists of alternative layers of rubber and steel. The steel plates can greatly increase the vertical stiffness of the bearing; a ratio of around 800:1 between vertical and horizontal stiffness is typical. The plates enables the bearing to support the vertical load even under a large shear displacement. The bearing is supporting the design vertical load even with a shear deformation suf cient to produce no overlap between the top and bottom bearing endplates. A strong bond between the rubber and steel is critically important to the correct functioning of the bearing. The rubber (usually a compound based on natural rubber) is specially formulated to give the damping required.

The use of high damping rubber avoids the need for auxiliary dampers such as viscous or elasto-plastic steel dampers in the isolation system.

DOSHIN “HIGH DAMPING RUBBER BEARINGS” (HDRBS)

DOSHIN RUBBER’s HDRBs are steel laminated rubber bearings made on specially formulated high damping rubber compounds.

The rubber compounds used for the production of DOSHIN RUBBER’s HDRBs are characterized by a dynamic shear modulus G variable from 0,6 to 1,3 MPa and an equivalent viscous damping coef cient (at shear strain, y=1) varying from 10 to 20%. The non-linear behavior of the compounds means at low strains the modulus is higher, allowing only slight movement due to forces such as wind. The steel lamination ensures a high compression stiffness to support the vertical load.

Three different rubber compound are available as standard:

• soft compound (S), with a low modulus (G= 0,6 MPa);

• normal compound (N), with a medium modulus (G=0,9 MPa);

• hard compound (H), with a high modulus (G=1,3 MPa).

THREE STANDARD COMPOUNDS

DOSHIN RUBBER’s HDRBs are identi ed by the mark DSH followed by a letter (S, N or H to indicate the type of compound – soft, normal or hard) and 2 numbers; the rst representing the diameter in millimeters while the second indicates the total thickness of rubber in millimeters.
DOSHIN RUBBER can develop alternative rubber compounds to satisfy different design requirements and can design seismic isolators to all the international standards.

The information provided is intended for preliminary calculations. DOSHIN RUBBER would discuss with its clients their application and would be happy to consider any adjustments to the geometry and connection details of the bearings to suit the project requirements.

COMPOUNDS FOR EVERY NEEDS

DOSHIN RUBBER can develop alternative rubber compounds to satisfy different design requirements and can design seismic isolators to all international standards.