Friction Pendulum Bearing Base Isolation: Saving Money and LivesBrett Ford and Andrew Westpy

Isolating a Natural Disaster

Friction Pendulum Bearings (FPBs) are a modern earthquake damage-preventing system gaining popularity in the last decade. The first official model was designed by Victor Zayas in 1985, and FPBs have slowly been evolving into a more complex and safety-assuring system for modern infrastructure. FPBs are located below the ground floor of a structure, and essentially allow the ground to move underneath while the structure stays in the same place, resting on the FPBs. The system consists of two outer concave surfaces, two inner concave surfaces, and a sliding mechanism as the very center.

Variables and Mechanics

Each system has its own individual set of design specifications to optimize its functionality. There are three main variables for each mechanism: radius, coefficient of friction, and displacement capacity. These variables will effect a system’s performance greatly when altered. The coefficient of friction allows a certain force that an earthquake must impose on a system to set it in motion. The radius is a measure of the curvature of each plate, allowing the bearing to glide either with ease or difficulty. The displacement capacity is how far each plate can move horizontally.When seismic activity begins, the bottom plates

begin to slide along with the ground motion, while the top plates stay attached to the bottom of the structure. After activity stops, the motion begins to die down, and the bearing returns to the center of the plate.

Effectiveness

FPBs have the potential to greatly reduce the harmful effects of seismic activity on structures. The figure to the left shows how a fixed-base building performs during an earthquake (left), as opposed to a FPB equipped building (right). Generally speaking, a fixed-base building twists around a central axis, causing shear forces toward the bottom of the building, which can lead to structural damage. FPBs allow the building to move as an entire unit. This way, there is no twisting or unnatural movement that the building was not designed to withstand.Not only are FPBs effective on

buildings, but they can be used for bridges, oil rigs, and other large structures. FPBs are measured to reduce elastic base shear on bridges by a factor of three to seven. This all leads to reduced costs on repair, labor, and time.

• Reduced interior effects felt by observers• Reduces structural damage• Can keep necessary buildings like hospitals open during times of

crisis

Safety and Security

• Avoids costly repair jobs• Fixed-base repairs roughly 15% of initial construction costs

• Low implementation cost• 9.5% of initial construction costs

Economically Friendly

Variable Name VariableRadius (Curvature) Reff1, Reff2

Coefficient of Friction µ1, µ23, µ4Displacement Capacity d1, d2