Base IsolatorsBase isolators consist of a laminated rubber and steel bearing with steel flange plates for mounting to the structure. Ninety percent of our isolators have an energy dissipating lead core.New construction or retrofitsFor more than two and a half decades Dynamic IsolationSystems has been helping architects, engineers, businessesand institutions match the right earthquake protection technology to the specific needs and requirements of their individual structures.

Isolator Function The rubber in the isolator acts as a spring. It is very soft laterally but very stiffvertically. The high vertical stiffness is achieved by having thin layers of rubberreinforced by steel shims. These two characteristics allow the isolator to movelaterally with relatively low stiffness yet carry significant axial load due to their highvertical stiffness. The lead core provides damping by deforming plastically when theisolator moves laterally in an earthquake. Rubber

The rubber provides flexibility through its ability to move but return to its original position. At the end of an earthquake, if a building hasn’t returned to its original position, the rubber bearings will slowly bring it back. This might take months, but it will return to its original position.

Image: Lead rubber bearings

Lead

Lead was chosen because of its plastic property – while it maydeform with the movement of the earthquake, it will revert to its original shape, and it is capable of deforming many times without losing strength. During an earthquake, the kinetic energy of the earthquake is absorbed into heat energy as the lead is deformed.

Steel

Using layers of steel with the rubber means the bearing can move in a horizontal direction but is stiff in a vertical direction.

Size RangesIsolators from 12 to 60 inches in diameter with capacities of up to 4,000 tons aremanufactured. Custom dimensions are available for special applications.

FabricationThe shims for isolators are cut to exacting tolerances by laser. The steel mountingplates are machined by computer-controlled milling machines thatgive high production throughputand accuracy. Molding eachbearing takes 8 to 48 hoursdepending on the size of thebearing. The curing phase iscontinuously monitored to ensurethat the rubber is uniformly curedthroughout the bearing.

Sliding Isolators

A sliding isolator consists of a PTFE (Teflon) disc that slides on a stainless steel plate. A slider may be manufactured with or without an elastomeric backing. The most common slider has the same construction as an isolator with a Teflon disc substituted for the flange plate.

Slider FunctionSliders support vertical loads and have low lateral resistance. They are typically used in conjunction with isolators and enable the designer to optimize the performanceof the isolation system. In some applications they are placed under lighter parts of the structure such as stairs and lightly-loaded columns. The elastomeric backing isused to accommodate rotations in the structure. An added benefit of sliders is that they provide damping from sliding friction.

Size RangeSliding isolators havebeen made from 12 to41 inches in diameter. 

Slider ManufacturingSliders are fabricatedwith a Teflon disc thatmates with a stainlesssteel sliding surface.

Base isolation, also known as seismic base isolation[2] or base isolation system,[3] is one of the

most popular means of protecting a structure against earthquake forces.[4] It is a collection of

structural elements which should substantially decouple[disambiguation needed] asuperstructure from its

substructure resting on a shaking ground thus protecting a building or non-building structure's

integrity.[5]

Base isolation is one of the most powerful tools of earthquake engineering pertaining to the passive

structural vibration control technologies. It is meant to enable a building or non-building structure to

survive a potentially devastating seismic impact through a proper initial design or subsequent

modifications. In some cases, application of base isolation can raise both a structure's seismic

performance and its seismic sustainability  considerably. Contrary to popular belief base isolation

does not make a building earthquake proof.

Base isolation system consists of isolation units with or without isolation components, where:

1. Isolation units are the basic elements of a base isolation system which are intended to

provide the aforementioneddecoupling[disambiguation needed] effect to a building or non-building

structure.

2. Isolation components are the connections between isolation units and their parts having no

decoupling effect of their own.

By their response to an earthquake impact, all isolation units may be divided into two basic

categories: shear units[6] and sliding units.[7] The first evidence of architects using the principle of base

isolation for earthquake protection was discovered in Pasargadae,[8] a city in ancientPersia, now Iran:

it goes back to 6th century BC. It works by having a wide and deep stone and mortar foundation,

smoothed at the top, upon which a second foundation is built of wide, smoothed stones which are

linked together, forming a plate that slides back and forth over the lower foundation in case of an

earthquake, leaving the structure intact.[citation needed]

This technology can be used for both new structural design [9]  and seismic retrofit. In process

of seismic retrofit, some of the most prominent U.S. monuments, e.g. Pasadena City Hall, San

Francisco City Hall, Salt Lake City and County Building or LA City Hall were mounted onBase

Isolation Systems. It required creating rigidity diaphragms and moats around the buildings, as well

as making provisions against overturning and P-Delta Effect.

Base isolation is also used on a smaller scale - sometimes down to a single room in a building.

Isolated raised-floor systems are used to safeguard essential equipment against earthquakes. The

technique has been incorporated to protect statues and other works of art - see, for

instance, Rodin's Gates of Hell at the National Museum of Western Art in Tokyo's Ueno Park.[10]

Base isolation demonstration at The Field Museum in Chicago

Research on base isolation[edit]

Through the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES),

researchers are studying the performance of base isolation systems.[11] The project, a collaboration

among researchers at University of Nevada, Reno; University of California, Berkeley; University of

Wisconsin, Green Bay; and the University at Buffalo is conducting a strategic assessment of the

economic, technical, and procedural barriers to the widespread adoption of seismic isolation in the

United States. NEES resources have been used for experimental and numerical simulation, data

mining, networking and collaboration to understand the complex interrelationship among the factors

controlling the overall performance of an isolated structural system. This project involves shaking

table and hybrid tests at the NEES experimental facilities at the University of California, Berkeley,

and the University at Buffalo, aimed at understanding ultimate performance limits to examine the

propagation of local isolation failures (e.g., bumping against stops, bearing failures, uplift) to the

system level response. These tests, including a full-scale, three-dimensional test of an isolated 5-

story steel building on the E-Defense shake table in Miki, Hyogo, Japan, will help fill critical

knowledge gaps, validate assumptions regarding behavior and modeling, and provide essential

proof-of-concept evidence regarding the importance of isolation technology.[12]