LRB lead-rubber bearing

Building rubber isolation bearings: principle and types

An isolation layer at the building base or another designed level separates the upper structure from the lower foundation. By isolating or dissipating seismic energy, it reduces transmission to the occupied structure and helps protect occupants, equipment and continued operation. Conventional earthquake resistance primarily relies on the connected structure carrying seismic action; isolation introduces a flexible layer to reduce that action.

The product specification states indicative reductions of 70%–90% in seismic response, equivalent to 1–2 intensity degrees, and 5%–20% construction-cost savings. These indicative benefits depend on the building design and site conditions. The listed applications include lifeline facilities, major projects, ordinary buildings and retrofit strengthening.

Rubber isolators use shear deformation of rubber/steel laminations; friction pendulum bearings dissipate energy by sliding friction and use pendulum geometry for restoring action. Example product sizes include LNR-1000 and LRB-1100.

Building isolation testing

Building isolation bearing evaluation covers vertical compression, horizontal shear stiffness, equivalent damping, cyclic behaviour and rubber material properties. The test documentation includes rubber isolation bearing inspection reports, performance-result tables, force–displacement curves and test-machine records.

Rubber-property evaluation covers hardness, tensile strength, elongation at break, brittleness, compression set, ageing and rubber-to-steel adhesion. Mechanical tests assess the complete bearing under its specified load and displacement conditions.

Building isolation: principle, applications and benefits

An isolation system at the building base converts much of the structure’s lateral shaking into movement of the isolation layer, reducing the seismic energy transmitted to the upper structure. The presentation describes applications in housing, schools, hospitals, public venues, precision-instrument rooms and lifeline facilities in areas of high seismic demand.

• Potential construction savings: reduced design earthquake action can permit smaller member sections and less reinforcement, subject to the actual structural design.
• Vertical support: carries the building weight.
• Restoring function: rubber elasticity supports recovery after wind or earthquake movement.
• Damping: limits isolated-structure response, particularly horizontal displacement.

Building isolation: types and design benefits

Rubber bearings and elastic sliding bearings can be used independently or together in a combined isolation system. Rubber bearings are available in Type I, Type II and Type III construction forms.

Construction cost and use of land

Under the appropriate structural design conditions, isolation can allow the superstructure seismic design intensity to be reduced by 1–1.5 degrees, optimising reinforcement and wall construction and reducing civil construction cost. In medium- and high-intensity regions, controlled design conditions can permit 1–2 additional storeys, improving floor-area utilisation.

Seismic performance objectives

The company’s design presentation describes a reduction in upper-structure seismic response of 1/4–1/8 compared with conventional earthquake-resistant structures, together with a one-level increase in protection. Actual performance depends on the building and isolation-system design.

Hainan Provincial Childcare Comprehensive Service Centre

Building isolation bearings supplied for the Hainan Provincial Childcare Comprehensive Service Centre include natural-rubber LNR1000 bearings and lead-rubber isolation bearings in the 1100 size class.

Jinshan Middle School library reconstruction

LNR natural-rubber and LRB lead-rubber building isolation bearings were supplied for the post-disaster demolition and reconstruction of the Jinshan Middle School library in Wenchang, Hainan.