Earthquake Barrier Technology (EQB)

In all of physical science there are only three (3) Technology Options for ridding a moving body, such as a car or building, of the energy it possesses once in motion. There may be thousand of ways to impart energy, both man-made and Nature-made, but only three ways to dissipate it; namely hydraulics, sliding-friction and inelastic stretching of steel.

The oldest energy dissipating Technology Option to be mathematized (Bernoulli: 1650) was chosen by automotive engineers at the turn of 20th Century to suspend vehicles, absorbing pothole impact without disturbing passengers.

The 2nd oldest energy dissipating Technology Option to be mathematized (Coulomb: 1790) was chosen by automotive engineers 100-years ago to stop vehicles, absorbing the energy of a car’s forward motion with sliding-friction brake shoes engaged at the driver’s pedal control.

The 3rd and most recent energy dissipating Technology Option to be mathematized (Lehigh University: 1960) was the inelastic bending of steel frames and fenders, permanently bending them out of shape. The ability of steel frames or reinforced concrete frames to heat up on extreme bending, by molecular rubbing of one steel molecule against another, provides un-calibrated energy dissipation by “hysteresis.”

That’s it! Those are the only three choices known to science at start of the 3rd-Millennium for stopping motion in building or bridge structures, once earthquake excitation starts. Sliding-friction Isolation (SFI) technology provides inexpensive protection against structural damage during the strongest of earthquakes, both for new buildings and bridges as well as the rapid retrofit of existing buildings and bridges. Installed at the basement or lobby level, SFI decouples buildings from their foundations and dissipates enormous amounts of energy, protecting against damaging structural deformations during earthquakes as strong as 1906 San Francisco’s Richter Magnitude 8.3.

Building and bridge superstructures protected with SFI can never be subjected to a greater horizontal shear force than that “shop-calibrated” into the separate energy dissipating sliding-friction bearings [relative velocity dependent] and re-centering spring force [relative displacement dependent]. Both shop calibrated and prototype-tested values would of course be set quite low, preventing structural damage during an earthquake but not sliding at all during the strongest of anticipated windstorms.

SFI technology can be installed very inexpensively at each building’s lobby level or basement level, but the lobby is usually less costly when retrofitting existing buildings. Applied in the upper basement of new construction, SFI usually uses small square special polymer lined steel sole plates under columns and walls, positioned above enlarged stainless steel surfaced plates that entirely cover footings. By constructing the enlarged stainless steel bottom plates to fit over the footing, column can have lots of sliding room once the footing accelerates rapidly enough during an earthquake and the base shear force exceeds that of the shop-calibrated coefficient-of-friction (as low as 0.04 with a 10 RMS finish on the stainless steel) times the building or bridge’s weight.

All columns and walls can be made to deform elastically, thereby protecting against both flexural damage as well as shear fracture. The smaller rectangular special polymer lined steel plates simply slide about over the enlarged stainless steel bearing plates, in a random fashion that tracks an earthquake’s ground motion at every instant of time. Random is better!

Before inserting prefabricated SFI bearings, all bearings will have been exercised in the shop to assure their calibration. Once sliding begins, the sliding-friction force causes superstructure acceleration in the precise direction of the ground motion. The superstructure thereby follows after and tracks the randomly moving foundation during the earthquake, but may lag a few inches behind. The sliding friction force is a vector always acting in the direction of relative velocity between the foundation and superstructure. The non-bearing spring always acts as a vector in the direction of relative displacement between the foundation and superstructure. Hence they’re rarely additive contributions to base shear, and the springs constantly act to re-center the building during an earthquake.

Steel or elastomeric springs can be added both in series and in parallel with SFI Polymer-lined steel bearings. These non-bearing springs placed “in parallel”, don’t support any vertical weight but are attached to the superstructure at one end and substructure at the other. They serve as low stiffness re-centering springs, acting to resist off-center alignment at the end of each earthquake’s duration.

Steel spring bearing pads placed “in series” beneath the small special polymer lined steel plates, uniquely modify vertical spring stiffness of each slide-bearing connection. This enables the epoxy filled permanent Freyssi flat jacks to gradually transfer loads from the reusable temporary jacks.

Total control of performance for a passive SFI system stems from shop-calibration control of 2-elements. These are the calibrated sliding-friction shear force bearings and non-bearing recentering shear springs acting “in parallel.” Both these shop fabricated and shop-calibrated elements provide the structural engineer with total quality control over horizontal force transfer of any earthquake ground motion, even during near-fault right-lateral motion.

Once horizontal base shear reaches the reliably shop-calibrated coefficient-of-friction, set as low as 0.04, the foundation begins to slide a few inches beneath the columns and piers of the structure while dissipating vast amounts of energy as heat. Only then do the otherwise dormant “in-parallel” non-bearing springs begin exerting their re-centering forces at the building’s perimeter. Very low stiffness “biasing springs” can be effective in re-centering a large structure.

Installation of the system in new construction is obviously easy, costing only $3,000 per column plus $1,500 per linear foot of bearing wall. Retrofit construction for existing columns and walls is far less costly than any other retrofit option available, costing only $40,000 per column plus $2,500 per linear foot of bearing wall.

Combined with the advantage of low cost is the very high seismic performance standard attainable, especially for very old existing buildings built before the year 2000. Even very brittle heritage buildings can be protected against seismic damage as they have significant elastic strength but little inelastic ductility.

By limiting the horizontal base shear during the strongest of earthquakes to one-half a building’s elastic strength, if permitted by wind resistance, a safety factor of two can be established against structural damage. This can inexpensively enhance life safety for people and create millions of new jobs, as well as protecting vulnerable assets to the highest possible seismic performance standard.