Frequently Asked Questions

All structures will have some energy dissipation due to entropy however what is important is the rate at which the energy is dissipated. In traditional concrete buildings, the energy is stored in concrete members with very little dissipation. Once the earthquake energy exceeds the storage capacity you get ductility of the steel rebar and eventually rupture and collapse (releasing the energy). Analogous behavior occurs in structural steel structures. The more flexible a structure the more energy

In the case of yielding or ductile technologies (e.g. BRBs), the earthquake energy is used to deform the yielding core and the energy is partially stored (through elasticity and strain hardening) and partially dissipated through entropy (heats up). That heat is then transferred throughout the BRB through mostly through convection. This will occur in any material and you can see it yourself if you bend a paperclip back and forth rapidly.

A viscous damper will generate heat as all the energy is transferred into the fluid and the fluid heats up. This can in turn affect the viscosity and so the selection of the working fluid is important in order to manage these changes.  The total increase in temperature will depend on the total thermal mass (mass of damper, fluid and the specific heat of the materials) and the energy input by the earthquake.

A friction damper which is essentially a coulomb damper transfers the energy directly into the surfaces which dissipate the heat through the entire damper mostly through conductive heat transfer. The amount of temperature change will ultimately depend on the thermal mass of the damper and conductivity of its elements.  If the damper has insufficient thermal mass or poor conduction it will heat up excessively.

In our case we have carefully developed the friction interfaces to ensure conductive heat transfer, minimal thermal expansion and corrosion resistance. This is important because certain materials will actually become velocity dependent as they heat up. For example, friction sliding isolation bearings will sometimes use composites or PTFE which is a polymer (plastic). As plastics approach their glass transition temperatures they behave more similarly to fluids. This abrupt change in the behavior of plastics creates challenges in modelling and predictability of the elements’ performance. Further complicating the use of plastics in friction interfaces is poor heat conduction. Since friction dampers convert earthquake energy into heat it’s important that the heat be conducted away from the friction interface quickly, which is not the case with plastics and many other materials resulting in excessive heat generation especially at high velocities.

Therefore, when it comes to friction seismic dampers is better to have bigger friction surfaces and thus, bigger mass.