We may all be aware of smart buildings that can automatically control lighting, water, heating and ventilation to reduce operational costs and maintain a comfortable working environment. Increasingly, smart building technology is also used to safeguard building occupants and limit building damage from seismic events.
Early warning
The earthquake pre-alert sensor technology that has been available in a number of countries for a few years is now available in New Zealand with the technology developed both in Japan and Taiwan.
The technology works by sensing the higher frequency primary wave triggered by a seismic event that travels through the ground at around twice the speed of the potentially damaging secondary wave. This can provide up to 30 seconds warning or more depending on variables such as the nature of the seismic event, the terrain geology and distance from the epicentre. The 14 November 2016 Kaikoura earthquake event had a primary wave detection of around 20 seconds before the shaking started in Wellington. With the right technology those vital seconds can be a game changer for automatically preparing a building and the people inside for what is coming.
Building systems can be readied by shutting down gas and water supplies, lifts and machinery and warning people to take cover. This can reduce potential for injuries, building damage and business disruption.
Fire spread following earthquake has been identified as a potential concern if Wellington suffered a significant earthquake because of the close proximity of buildings to each other and location of gas, so the shutdown of gas supplies triggered by a seismic prewarning system reduces that risk.
Building structure active dampers
Active dampers are another system to reduce losses from earthquakes. Active dampers can absorb the high shock loads imposed by a seismic event on the buildings structure as well as allowing the building to move in a controlled manner to reduce damage to structural connections. The Insurance Council is not aware if this technology has been used in New Zealand so far, however it is used extensively in Japan.
Passive structural damper systems are more common in newer buildings in New Zealand. Passive structural dampers are used in a buildings structure bracing to absorb movement shocks to a predetermined limit to protect structural connections. Passive structure dampers will need to be checked or replaced after a large seismic event. Often, they are sacrificial elements.
Active structural dampers have the advantage of allowing variability of damping depending on the type of seismic event, its direction and the movement of the building, particularly the upper levels in relation to the lower levels and foundations. They are not designed to be sacrificial.
The active structural dampers found in many new buildings in Japan use large hydraulic rams connected to links and cranks to inverted “K” frames connecting the floor above to the floor below to control movement or the drift between floors. These dampers can be located on each of the sides of the building and sometimes at every level.
The hydraulic rams provide variable resistance to movement. This is controlled by valving connected to a central building computer that is programmed with seismic event logarithms tuned to the buildings structural design. More recent systems use hydraulic rams that use electromagnetic fluid, much like the active shock absorber systems used in luxury motor vehicles. These can be less complex, more responsive and require much less power to operate which can be important if the electricity supply is lost and the building is relying on backup power.
Active structural dampers systems use many sensors located around the building measuring movement and accelerations, all feeding back information to the control computer.
The active structural dampers systems as used in Japan, require vast earthquake modelling knowledge to be able to programme the control computer to effectively react to all likely earthquake events parameters.
Installation of this technology in New Zealand buildings would make them more attractive to insurers as well as making them safer and better able to function after a large earthquake.
