Qualities of Seismic Expansion Joints

New Zealand is sometimes called the shaky isles - and for good reason. Christchurch earthquakes were devastating events, but almost every day earthquakes are experienced somewhere in New Zealand.

Between 1960 and 2021, there have been over 23,000 earthquakes recorded in New Zealand of over 4.0 magnitude (source:www.geonet.org.nz). This equates to over ONE EARTHQUAKE GREATER THAN MAGNITUDE 4.0, PER DAY!

For this reason, many of the joints we supply are classed as 'Seismic joints.'

What makes a joint a "seismic joint?"
Typically, this type of joint can handle larger movements caused by other factors, apart from normal cyclic temperature related, shrinking and expanding of structures. Normally, this is dynamic loads cause from ground settlement or seismic events (Earthquakes). Most often, these 'Seismic Joints' remain undamaged, but always serviceable following such an event. This is extremely critical when it comes to building access for emergency personal, and tenant evacuations etc.

The unique features of a seismic joint are:
  • Can handle the rapid acceleration related to a seismic event.
  • It must be multi-directional (i.e. can accommodate vertical movement or lateral shear). 
  • Has much wider movement range than regular joints. Almost all seismic joints have a range of +/- 50% for a total of 100% movement. 
  • It should return to normal after the seismic event - self centering bars are very often used for this purpose.

BAS Expansion Joints (NZ)® have non-seismic joints available also, but considering our environment in New Zealand, structures should be built for New Zealand conditions. 

Seismic Devices for Bridges

For the bridge structure market, we have a range of seismic devices called Shock Transfer Units (STU's) or sometimes referred to as Lock-up devices (LUD's). These are a specialty item that needs further discussion earlier on in the structures designing phase. Please contact us for more information on these and to discuss if they may be suitable for your structure design requirements..
Each expansion joint job is unique so please contact us on 0800 SPAN-IT​ for a system demonstration