How Are Shocks Used in Houses to Prevent Earthquakes?

Significance

• Earthquakes can impart a tremendous amount of force onto structures and buildings on the land. According to an article in Terra Daily, seismic activity can transfer raw energy in two forms: kinetic energy and strain energy. Kinetic energy moves buildings from side to side, whereas strain energy deforms the building's structural integrity. Either form of energy transfer can lead to catastrophic damage to homes and businesses. Most buildings are designed to withstand their own weight, but not all are built to accommodate the added stresses of seismic activity.

Seismic Dampers

• Seismic dampers are meant to function as shock absorbers, preventing the total collapse of buildings undergoing seismic stress. These dampers are designed to absorb most of an earthquake's energy, much like a car's shocks and struts absorb the bumps of a countryside road. Most seismic dampers are modeled after hydraulic systems, where a fluid-filled shock absorber is integrated into the walls and frame of a building. Seismic dampers attempt to minimize the amount of raw energy an earthquake exerts by redirecting that power or by providing a building with increased flexibility to withstand extreme force.

Wood-Frame Structures

• Most of the buildings in underdeveloped areas are constructed with wooden frames. Yet there is a lack of understanding by civil engineers on how to build wood-frame structures to withstand earthquake forces. According to an article in Terra Daily, wood structures were associated with about half of the $40 billion in losses caused by the 1994 Northridge earthquake in the Los Angeles region. This problem has led civil engineers at the Rensselaer Polytechnic Institute to embark on a project that will test seismic dampers on wood frame structures. The NEESWood system is a $1.24 million international project that will install seismic shock absorbers inside the walls of a full-scale, 1,800-square-foot townhouse to absorb the energy produced from a typical seismic event.

Seismic Slide Plate System

• The seismic slide plate, or SSP, is a shock absorber designed by MM Systems Corp. The SSP system is used for load-bearing structures like parking garages and stadiums. The system employs 10-foot lengths of aluminum extrusion paired with a seismic centering device, which allows a building to effectively flex and move during a seismic event. The device is placed flush against a flexible concrete form, and the seismic centering device acts as a joint that uses a ball and spring system to absorb weight and movement. A special feature of slide plate systems is that they also work as sound, water and fire barriers in most applications.

Magnetorheological Damper

• A recent article in Science Daily reports on a revolutionary shock absorber called the magnetorheological (MR) damper. Civil engineers at Washington University's School of Engineering and Applied Science boast that the MR dampers can reduce the effects of an earthquake by as much as 50 percent. The device itself consists of three horizontal metal plates that are sandwiched together, with the outer two plates connected at either end of the building. A sophisticated array of sensors relay seismic intensity to a central computer, and the MR damper responds accordingly. It features a unique fluid that turns into a solid once an electrical charge is introduced from a battery. The electrical current produces a magnetic field in the fluid's iron particles that causes the plates to stick together. The entire process takes place in just fractions of a second and effectively dampens the vibrations of a seismic event.