Superior Natural Rubber Bearing for Residential & Commercial Buildings

Natural rubber bearing, short for NRB, is a kind of seismic isolation bearing with alternately piled up multi-layer natural rubbers and multi-layer steel plates. This bearing offers a higher vertical load capacity and a greater horizontal flexibility. It has been widely used in the seismic isolation design of residential buildings, office buildings, hospitals and other buildings, and has achieved great economic and social benefits.

As the NRB has a low energy dissipation capacity, therefore, it often forms a seismic isolation system together with dampers.

Working Principle
Structure
Features
Production Flow
Category
Specification

Working Principle

By installing natural rubber bearings between the superstructure and the foundation, a seismic isolation layer is formed, achieving a soft connection with the ground to turn the violent shaking of the building into a slow horizontal movement, thereby reducing the input of seismic energy.

At the same time, the NRB separates the superstructure from the lower foundation. When the earthquake occurs, the vibration energy of the lower foundation will be transferred to the natural rubber bearing first. By taking advantage of the characteristics of the combination of rigidity and flexibility of the NRB, the transmission of seismic energy to the upper structure can be effectively avoided or reduced, thereby ensuring the safety of the superstructure and appurtenances inside.

The difference results of buildings with or without natural rubber bearing when earthquake occurs.

Structure

Natural rubber bearing consists of a top and a bottom connecting steel plates, a top and a bottom sealing plates, internal natural rubber layers, internal steel plates and a rubber cover.

When the NRB is subject to a vertical pressure, rubber sheets and steel plates are radial deformed. However, the deformation of steel plates is much smaller than that of rubber sheets, therefore, rubber sheets are constrained by steel plates, thus limiting the vertical compression deformation of rubber sheets to ensure that the bearing has a higher vertical bearing capacity and provides a stable support to the building.

When the NRB is subject to a horizontal pressure, laminated steel plates cannot restrain the shear deformation of rubber sheets. At that time, the horizontal deformation of the bearing is approximately the sum of the horizontal deformation of all rubber sheets. As a result, the bearing has a large horizontal deformation capacity.

The comparison of single-layer rubber bearing and multi-layer rubber bearing under pressure

Features

The strong adhesion between the rubber layer and the steel plate allows the bearing maintaining a higher vertical bearing capacity and providing a stable support for the building when a large horizontal displacement occurs.
It prolongs the natural vibration period of the building and turns the violent shaking of the building into a slow horizontal movement.
It has great linearity and a stable restoring force, which allows the NBR can restore the normal position quickly when it is subject to a wind-induced vibration and an earthquake.
It requires to be used together with dampers. However, combining with different types of dampers offers great design flexibility.
It maintains a stable performance after going through repeated earthquakes, offering an exceptional durability.
Easy to install, maintain and replace, bringing great social and economic benefits.

The relationship between the shear displacement and shear force of natural rubber bearing

The great linearity of the hysteresis curve reveals the excellent horizontal flexibility and stable resorting force the natural rubber bearing can offer.

Production Flow

Rubber production line for natural rubber bearing

1

Rubber material preparation

Natural rubber and other auxiliary materials are processed into rubber compound by adopting internal mixing technology.

Steel plate surface treatment production line for natural rubber bearing

2

Metal part surface treatment

Sandblast the surface of the steel plate inside the natural rubber bearing. Spray rubber-to-metal adhesive on the bonding interface to ensure the integrity of the NRB.

3

Vulcanization

Vulcanization is required to integrate the rubber compound and treated internal steel plates into a whole unit. Generally, a large flat vulcanizer with special molds is required for vulcanization. The whole process takes about 8 to 48 hours. Specifically, it depends on the size of the NRB. Continuous monitoring is required during vulcanization to ensure that the rubber cures uniformly throughout the process.

Workers are assembling all parts of the natural rubber bearing into a whole unit.

4

Assembly

The pre-embedded steel plate, pre-buried sleeve, anchor bolts and the support body are assembled into a whole to finish the manufacturing of a full set of natural rubber bearing.

Category

Natural rubber bearings are divided into round and rectangular natural rubber bearings by shape.

Round natural rubber bearing

Rectangular natural rubber bearing

Specification

Table 1: Natural Rubber Bearing Specification (G4)
Item	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)	NRB (G4)
Item	Φ300	Φ400	Φ500	Φ600	Φ700	Φ800	Φ900	Φ1000	Φ1100	Φ1200
Shear modulus of elasticity N/mm²	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39	0.39
1st shape factor	23.3	24.3	24.0	28.5	33.3	38.0	35.6	39.6	41.9	45.7
2nd shape factor	5.17	5.84	5.10	5.45	6.36	5.00	5.56	6.17	6.65	7.21
Effective size cm²	700	1250	1879	2820	3839	5014	6346	7834	9326	11116
Datum level pressure N/mm²	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0
Ultimate deformation (at datum level pressure) %	400	400	400	400	400	400	400	400	400	400
Horizontal equivalent stiffness kN/m	470	710	710	990	1350	1210	1510	1870	2229	2641
Vertical compression stiffness kN/mm	844	1384	1420	2282	3632	3664	4339	5839	7347	9095
Notes: Other specifications are available upon request.

Table 2: Natural Rubber Bearing Specification (G6)
Item	NRB (G6)	NRB (G6)	NRB (G6)	NRB (G6)	NR B(G6)	NRB (G6)	NRB (G6)	NRB (G6)	NRB (G6)	NRB (G6)
Item	Φ300	Φ400	Φ500	Φ600	Φ700	Φ800	Φ900	Φ1000	Φ1100	Φ1200
Shear modulus of elasticity N/mm²	0.55	0.55	0.55	0.55	0.55	0.55	o.55	0.55	0.55	0.55
1st shape factor	23.3	24.3	24.0	28.5	33.3	38.0	35.6	39.6	41.9	45.7
2nd shape factor	5.17	5.84	5.10	5.45	6.36	5.00	5.56	6.17	6.65	7.21
Effective size cm²	700	1250	1879	2820	3839	5014	6346	7834	9326	11116
Datum level pressure N/mm²	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0
Ultimate deformation (at datum level pressure) %	400	400	400	400	400	400	400	400	400	400
Horizontal equivalent stiffness kN/m	720	1090	1170	1540	2090	1880	2350	2900	3108	3705
Vertical compression stiffness kN/mm	1027	1628	1720	2688	4173	4124	4932	6532	7461	9095
Notes: Other specifications are available upon request.

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