Operation of Elevators during the Earthquake

Elevators are among the most important mechanical systems in building structures that are quite open to earthquake-induced damage. In this Article I mentioned the countermeasures to mitigate the related risks.

In 1971 San Fernando earthquake with a magnitude of 6.6 on the Richter Scale resulted in significant damage to buildings and vertical transportation systems in the Los Angeles area. Counterweights came out of their guide rails, and control panels, motors, and traction machines were tipped over. As a result, California developed seismic provisions to its elevator code in 1975, and seismic provisions were added to the National Elevator Code in 1981.

When an earthquake occurs, it releases in the form of waves. The different types of waves shake the ground in different ways and travel through the earth at different velocities. The wave motion consists of both longitudinal and transverse waves.  The first wave that arrives is called P wave is a longitudinal wave with little vibration but with high transmission velocity. The secondary wave is S wave. It travels slowly but with high vibrational energy. The interval between P wave and S wave is not less than 7 seconds. When the P wave is detected the elevator car is brought with the Earthquake emergency landing device to the nearest possible floor and a display panel informs the passenger that earth quake has been detected and asks the passenger to get out of the elevator immediately. The elevator waits at that floor with an open door until the S wave is detected. After the detection of S wave, the elevator door closed automatically, and the elevator service is suspended.

There are different seismic provisions/countermeasures adopted in different countries with different Elevator Safety codes.

In the American ANSI/ASME code below requirements/ equipment are recommended:

1. At least one seismic switch.
2. A counterweight displacement switch
3. Rope Retainer guards on sheaves
4. Securing Beams and supports
5. Fastening to building structure
6. Bracket Fastening and support
7. Guarding of snag points

According to the ANSI/ASME code:

1. Upon activation of a seismic switch, all elevators with traction machines, counterweights, and selective, collective, or group automatic operation that are in motion shall proceed to the nearest available floor, open their doors, and shut down; except where Phase II Emergency In-Car Operation is in effect.
2. When the counterweight displacement switch is activated, the elevator if in motion, shall initiate an emergency stop and then proceed away from the counterweight at a speed of not more than 0.75 m/s (150 ft/min) to the nearest available floor, open the doors, and shut down; except that where Phase II Emergency In-Car Operation is in effect,
3. Elevators with power-operated doors, upon reaching a landing shall cause their doors to open and remain open; except where Phase II Emergency In-Car Operation is in effect, door operation.
4. Upon activation of an earthquake protective device, an elevator standing on a floor with its doors open shall remain on the floor. If its doors are closed, it shall open its doors. Where Phase II Emergency In-Car Operation is in effect.
5. An elevator not in operation when an earthquake protective device is activated shall remain at the landing. (f) An elevator shall be permitted to be operated at a speed of not more than 0.75m/s(150ft/min), provided the counterweight displacement switch is of the continuous monitoring type and is not activated.