The February 2011 Christchurch earthquake was a powerful
natural event that severely damaged New Zealands second
largest city. The earthquake caused widespread damage across
Christchurch, especially in the central city and eastern suburbs,
with damage exacerbated by buildings and infrastructure already
being weakened by 4 September 2010 earthquake and its
- More than 70% of CBD buildings severely damaged
- 124 km of water mains and 300 km of sewer pipes damaged
- 500,000 tonnes of liquefaction silt removed
- 600 km of roads seriously damaged
- 50,000 road surface defects
- 55% of secondary students sharing with other schools
- 13 out of 36 hotels operating
- NZ$ 40 billion estimated cost
- 185 lives tragically lost
- 459,000 EQC claims
In reality tested:
Earthquake protection by RINGFEDER®
Surely not all of the damage could have been avoided, but with RINGFEDER® Friction Springs you have a great possibility that your building survives an earthquake like the ones in 2010/11 and is still habitable. There already are buildings in New Zealand which are equipped with RINGFEDER® Friction Springs, for example Te Puni Village Student Accommodation with 340 dwelling units, 24 Taranaki Street, One Market Lane (all Wellington) and Tait Communication Campus (Christchurch). Te Puni Village was already completed when the earthquake on July 21st 2013 occurred, measuring 6.5 on the Moment Magnitude Scale and the following aftershock measuring 5.8 on the MMS. The building withstood the earthquake without nameable damage.
Description of a RINGFEDER® Friction Spring
A RINGFEDER® Friction Spring consists of outer and inner rings with conical contact surfaces. Figure 1 shows a cross section through a spring. When the spring column is axially loaded the tapered surfaces overlap causing the outer rings to expand and the inner rings get smaller in diameter. 2/3 of the introduced energy will be absorbed due to friction between the tapered surfaces of the mating rings.
How a RINGFEDER® Friction Spring works
Valid for vertical application
Diagrams 1 to 3 explain how a RINGFEDER® Friction Spring absorbs up to 66% of the introduced energy, depending on the type of grease used.
Figure 2: Friction spring type 20000, which consists of 8 outer rings, 7 inner rings and 2 half inner rings. It is preloaded with 200 kN to a length of 334 mm. With these values it has a maximum stroke of 38 mm and a capacity of 13400 Joule. The requirement is to absorb a maximum energy of 6000 Joule.
Diagram 1: When the Friction Spring receives the impact force, it compresses 21 mm and absorbs 6000 Joule from which 66% respectively 4000 Joule are converted to heat. After the compression, the friction spring discharges back by the same 21 mm due to a reaction force and there are 2000 Joule which has to be absorbed.
Diagram 2: The impacting body strikes again on the friction spring with the remaining 2000 Joule and compress it by 8,5 mm. After the compression, the buffer springs back by the same 8,5 mm due to the reaction force.
Diagram 3: It remains a theoretical energy of 680 Joule at a spring travel of 3 mm. Based on the fact that the friction not only occurs between the rings of the friction spring but in the whole system, the complete 6000 Joule are now absorbed and the system comes to rest.
Advantages of a RINGFEDER® Friction Spring
1. Long life – RINGFEDER® Friction Springs are designed to last through many cycles and are reusable. If one of the rings in a RINGFEDER® Friction Spring assembly breaks, the spring will still work but lose a little travel and become slightly stiffer. The end force and the dampening remain unaffected. As a comparison, if a coil spring or a Belleville spring breaks, there will be a total failure and you have no protection any more.
2. Damping – Using our standard RINGFEDER® F-S1 grease, our friction springs will damp 2/3 of the introduced energy. If you need less damping, we can easily design a customized solution that is tailored to your needs to achieve a reduced damping of about 1/3 of the introduced energy. This is a simple solution that can change the properties of the friction spring. In certain seismic designs you may require the friction spring to have a higher force when the spring is unloaded to help to push the building structure back to its vertical position.
3. Fire and high temperatures – Friction springs are made of special spring-steel. They are coated with grease. In case of a fire, rubber products will be destroyed but our friction springs will endure the fire. It is only needed to regrease the springs.
4. Return force – You can discuss your application with us to determine the best return force of the spring for your specific design. This is not possible with other conventional spring types. We can change the grease, increase the outside diameter or change the taper angle to achieve the results you need.
5. Re-Usability – Friction springs can be re-used after a seismic event. They are designed to withstand many cycles and remain stable. Friction springs are maintenance-free.
6. Speed – Friction springs react faster to applied forces than any other spring type.
7. Space – Friction springs give you the highest forces at a given diameter.
So the essence from all these advantages is:
If you buy a RINGFEDER® Friction Spring, you assemble it and never have to think about it again. And you can rest assured to have chosen a long-time proven, solid and reliable protection system from the RINGFEDER® damping technology.
For more information please download our RINGFEDER® Flyer Earthquake Protection or contact us.
Video Experimental Testing RINGFEDER® Friction Springs
download PDF Description