What Is a Friction Pendulum Bearing?
A friction pendulum bearing is a seismic isolator that lets a building slide on a curved stainless-steel dish — the building's weight on the curved surface creates a pendulum action, gravity pulling the building back to center after each earthquake push. Friction in the sliding interface dissipates the earthquake's energy. Simpler and more compact than elastomeric bearings, friction pendulums are the modern default for base-isolated structures.
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How it works
The bearing has an articulated slider moving on a spherical concave surface: lateral earthquake motion lifts the building slightly up the dish's curve, and gravity restores it — the effective period set by the dish radius (larger radius, longer period, less force transmitted). The friction coefficient (PTFE composite on polished stainless steel) controls the energy dissipation and the force transmitted. Triple-pendulum variants stack multiple sliding surfaces for adaptive behavior across earthquake intensities.
Advantages over elastomeric bearings
Compact (lower profile — less moat depth and structural height consumed), the period is independent of the building's weight (the dish radius sets it — useful where mass varies), and high displacement capacity (30+ inches in large bearings). No rubber to age or degrade. Trade-offs: the friction coefficient must remain stable over decades (material qualification and testing), and the bearings need inspection access — the sliding surfaces are precision components.
Design and testing
ASCE 7 Chapter 17 governs: prototype testing of the bearing design (full-scale cyclic tests verifying the force-displacement behavior and friction stability), production testing of every bearing, and the moat design for the maximum displacement. The structural engineer models the bilinear hysteretic behavior; the displacement demands come from response-history analysis. Bearings are manufactured to order (12-24 week lead times) — procure early.
The bottom line
Friction pendulum bearings isolate buildings on curved sliding surfaces — gravity recentering, friction damping, compact profile. Design per ASCE 7 Ch. 17 with prototype-tested bearings.
Torch Engineering PLLC · (480) 490-0064 · info@torchengineering.com — PE stamping backed by Apex Grid Engineering.