LRB vs FPS: Which Seismic Isolator Should You Choose?

At some point in every isolation project, the conversation narrows to two candidates: lead rubber bearings (LRB) and friction pendulum systems (FPS). Together they account for the large majority of isolators installed worldwide, and both have decades of earthquake performance behind them. Neither is "the better isolator." They solve the same problem with different physics, and the right choice depends on your building, your site, and your procurement options.

This article compares the two systems the way we do in a consultation: working principle first, then the practical differences that actually drive the decision. If you are still at the "what is this technology" stage, read our primer on seismic isolation or the complete guide first.

How each system works

LRB: a rubber spring with a lead damper inside

A lead rubber bearing is a stack of thin rubber layers bonded to steel shim plates, with a cylindrical lead core through the center. The rubber layers give the bearing low horizontal stiffness, which lengthens the building's period, while the steel shims keep it stiff vertically so it can carry the column load.

The lead core is the damper. When the bearing shears sideways in an earthquake, the lead yields plastically and turns kinetic energy into heat, cycle after cycle. After the shaking stops, the elasticity of the rubber pushes the bearing back toward center. The technology was developed in New Zealand in the 1970s and has been in commercial use since the 1980s, which makes it the most field-proven isolator type available.

One physical detail matters for design: the lead core heats up as it works. Full-scale tests have measured large temperature rises in the core during long-duration cyclic loading, and the bearing's characteristic strength drops as the lead gets hotter. Modern design codes and manufacturer models account for this, but it means LRB properties are not constant through a long earthquake. They soften somewhat as energy accumulates.

FPS: a building standing on pendulums

A friction pendulum bearing takes a completely different route. It is a sliding bearing: an articulated slider, faced with a PTFE-type composite liner, rests on a polished stainless steel surface that is machined into a concave sphere. When the ground moves, the slider travels along the curved surface. Friction at the sliding interface dissipates energy, and because the slider has to travel uphill along the curve, gravity itself supplies the restoring force that brings the building back to center.

The elegant part is the period equation. An FPS bearing's isolation period is T = 2π√(R/g), where R is the effective radius of the curved surface and g is gravitational acceleration. Mass does not appear in the formula. The period is a property of the geometry, not of the building sitting on it. The original Friction Pendulum bearing was developed by Victor Zayas, who founded Earthquake Protection Systems in California in 1985; the concept was validated in shake-table tests at UC Berkeley in 1987. Later generations added a second and then a third sliding surface. Triple pendulum bearings behave differently at different shaking intensities and extend the displacement capacity well beyond what a single surface offers.

Comparison table

The differences that actually matter

Period and mass

An LRB's period depends on the ratio of supported weight to bearing stiffness. If the building mass changes, or if mass is distributed unevenly across the footprint, each bearing has to be sized so the system still hits the target period. FPS sidesteps this entirely. Every bearing on the same radius delivers the same period regardless of the load on it, which also means the center of stiffness naturally tracks the center of mass, reducing torsion in irregular buildings. For structures with uncertain or changing mass, think storage facilities, tanks, or buildings with heavy variable contents, this property is a genuine advantage.

Damping and long-duration shaking

The lead core gives LRB strong, reliable hysteretic damping, and this is a big reason the type became the global default. The trade-off is the heating effect described above: in long or repeated shaking, the effective strength of the system decreases. FPS damping comes from friction, and the designer selects it directly by specifying the friction coefficient of the liner. Friction is not constant either. Test programs show it varies with sliding velocity, contact pressure, and interface temperature, so a proper FPS design models those dependencies. Comparative studies land where you would expect: LRB systems tend to show excellent base shear and drift control across common ground motions, while pendulum systems hold their behavior well at very high intensities and large displacements. Neither dominates every scenario.

Re-centering

Both systems are designed to return to center, and codes such as ASCE 7 explicitly require adequate restoring capability so the building does not end up permanently offset after the event. LRB re-centers through rubber elasticity, and it does this well. FPS re-centers geometrically: as long as the restoring force from the curve exceeds the residual friction, gravity pulls the slider home. In near-fault sites with pulse-like motion, where a single large displacement excursion is likely, that geometric re-centering and the large displacement capacity of pendulum bearings are frequently the deciding factors.

Vertical load and physical size

This one is practical rather than theoretical. An LRB carrying a very heavy column becomes a very large bearing, because capacity scales with rubber area. FPS bearings carry high pressures on the steel and composite-liner interface, so they handle very large vertical loads in a low-height unit; note that the compactness is vertical, since the sliding dish still needs enough plan diameter for the full design displacement. On bridges, LNG tanks, and heavy industrial structures, that low profile often settles the argument by itself. It reduces pedestal size, moat depth, and installation complexity.

Environment, aging, and maintenance

Rubber is an organic material. It stiffens in sustained low temperatures and its properties drift slowly over decades, which is why LRB programs include periodic visual inspection. The lead core also raises handling and disposal questions at end of life. An FPS bearing is steel and composite liner: no rubber aging, no lead, and consistent behavior across a wide temperature range, though the friction interface has its own temperature sensitivity during sliding and the surfaces must stay protected from contamination. On durability the two families are held to the same bar: standards do not assign a service life in years, and both types are qualified through accelerated aging tests to serve for the structure's design life, with periodic inspection rather than scheduled replacement. How the inspection programs affect total cost of ownership is covered in our cost guide.

Cost

Unit prices for both families are set by tender: bearing size, displacement capacity, testing scope, and order volume all move the number, and no credible universal price range exists for either system. At project level, isolation adds roughly 5 to 10 percent to the structural shell cost, and the isolator hardware is only a fraction of that, so a unit-price gap between the two families shrinks further once the whole system is priced. The gap is also market-dependent: domestic production in Türkiye, for example, has made both families more competitive locally. Get quotes for both systems from multiple manufacturers before you let price steer the design. The full cost framework, including installation and lifecycle items, is in our 2026 cost guide.

Friction pendulum bearing cost: what drives the price

Because friction pendulum bearing cost is the number owners ask about most often, it is worth breaking down on its own. There is no credible universal price for a single FPS unit; every quote is set by tender, and where a specific bearing lands comes down to a short list of drivers:

• Vertical load. A bearing under a heavily loaded column needs a larger slider and thicker plates. Load capacity is the single biggest price input, the same tiering logic that applies to LRBs.
• Displacement capacity. The design displacement sets the diameter of the concave surface. A near-fault site that demands 700 mm of travel means a physically bigger, more expensive dish than a 400 mm design.
• Configuration. A single pendulum is the simplest and cheapest build. Double and triple pendulum bearings add machined surfaces and internal sliders, and triple pendulum units, the usual pick for critical facilities, sit at the top of the range.
• Machining and liner quality. The concave surfaces are precision-machined and the slider runs on an engineered composite liner. Tight tolerances and liner qualification are a real share of the manufacturing cost, and they are not the place to economize.
• Testing. Prototype and production testing under ASCE 7 Section 17.8 is priced into the procurement. Full-scale dynamic testing of large bearings requires rigs that few labs have, which shows up in the quote.

Two budgeting notes soften the sticker price. First, the hardware is only part of the system: at project level, isolation adds roughly 5 to 10 percent to the structural shell cost, and our cost guide's breakdown shows where FPS hardware sits inside that. Second, lifecycle cost is not a tiebreaker: both families are qualified through aging tests for the structure's design life, and neither has a scheduled replacement, only periodic inspection. For heavy structures the comparison can even flip at purchase, since one compact FPS unit can replace an oversized LRB and shrink the pedestal and moat around it.

Which should you choose?

There is no universal winner, but the decision usually falls out of the project profile.

LRB tends to be the right call when:

• The building is a regular mid-rise with well-defined, stable mass, such as housing, offices, or schools.
• Displacement demand is moderate and the site is not near-fault.
• You want the longest track record and the widest manufacturer pool, which helps competitive bidding.
• Your market has a strong pool of elastomeric bearing suppliers, which sharpens tender competition.
• The service environment is wet, humid, or dirty, where the sealed rubber package is naturally robust and a polished sliding interface would need extra protection against contamination and corrosion.

FPS tends to be the right call when:

• Column loads are very heavy or vary widely, as in bridges, tanks, and heavy industrial plants.
• The site is near-fault or the design displacement is large, where triple pendulum capacity and geometric re-centering earn their premium.
• The structure is a critical facility, such as a hospital or emergency center, where predictable behavior at extreme intensity matters most.
• Building mass is uncertain or its distribution is irregular, and the mass-independent period simplifies the design.
• Physical height is constrained and a low-height bearing simplifies the isolation plane; keep in mind the dish still needs its plan footprint for the design displacement.

In practice, many projects run a preliminary design with both systems and let the numbers decide. Displacement demand, pedestal cost, procurement lead times, and testing logistics differ enough between the two that the comparison is worth the engineering hours. And before any of this, confirm that isolation itself is justified for your building; our checklist on when a building needs seismic isolation covers that decision.

One more option worth knowing: the two systems are not always rivals. Some projects combine elastomeric and sliding bearings in one isolation plane, using sliders under lightly loaded columns and LRBs elsewhere. That is a design-stage decision your isolation engineer should evaluate.