Base isolation is a pretty effective measure against structural quake damage. However , it isn’t an inexpensive approach as the entire building or structure must be briefly moved for the sliding bearings or elastomeric to be installed, thus concerning pricey building alterations.

So a less expensive, yet similarly effective earthquake mitigation methodology appeared – use of liquid viscous dampers which does not need building isolation.

So as to build a baseline for the main topic of this article (viscous damping vs base isolation) I'm going to provide a tiny discussion of each one of these two structural seismic mitigation strategies.

Let’s start with their definitions.

What is fluid viscous damping?

This is a technique of adding energy dissipation to lateral methods of building structures. A viscous fluid damper dissipates seismic energy by filling up the orifice with fluids, making a damping pressure which then produces a certain force to neutralize the damaging energy of earthquake vibrations.

This viscous liquid damping system can lessen lateral deformations and horizontal floor accelerations of structures by as much as 50 % (sometimes more).

What is base isolation?

This is sometimes referred to as seismic base isolation and is one of the most common ways of protecting a structure from possible earthquake forces damage. Contrary to what many think base isolation does not make a structure tremor proof.

After defining the two terms, shall we now proceed in comparing the techniques they employ in diffusing quake power from a building.

Fluid viscous damping in comparison to seismic base isolation

Both these strategies aim to noticeably evaporate quake and seismic energy in structures; enable the structure to remain in the safe elastic region, forestalling long-lived damage from a seismic activity.

Though their objectives are the same, the implementation of their systems considerably varies. Below is a quick rundown of each:

Base isolation methods

Seismic base isolation decreases seismic energy by physically decoupling structures from the ground. Elastomeric pads or sliding bearings are placed at the base of the buildings and are then connected right to the foundation. In earthquake, these pads and bearing deflects in the place of the structure.

In technical terms, the installation of base isolation at length increases the structure’s period of natural vibration, making it seriously longer than the earthquake’s period of vibration.

Base isolation methodology requires that the structure be removed and cut loose from the main foundation casted in the supporting soil structure. In a redevelop, this technique involves the cutting of all vertical columns in the structure to be able to supply a gap of 18 inches between the foundation system and the bottom of the columns. Pads and bearings are then inserted in the openings.

Liquid damping techniques

Viscous liquid damping methodology adds, as the name says, fluid damping to a structure. The increased damping noticeably lowers the effect of an earthquake to structures. Unlike base isolation, the extra fluid dampers don't extend the natural vibration period of the structure, what it does is to significantly increase the damping level from the regular 5%of critical to about 20% to 30%.

Fluid viscous dampers can be installed in both new structures and existing buildings. Furthermore, they're relatively tiny so their addition will not cause any noticeable change of appearance in the structure, thus they're ideally useful for reconditioning historical building and structures.

To find out more about a viscous damper, go check out the Magnetorheological Damper Lab. Read more about the pros and cons by clicking here.