DESIGN

IBC


The EQ-Force process is the only earthquake process which
reduces the seismic force on a footing and decreases damage to the structure.


This pencils model captures
the EQ-Force™ design.


With new studies of seismic protection being added to from re-analysis of earthquakes which have occurred during the last twenty years, the idea of a Unified Building Design system has emerged. We have added some information and thoughts about the concept. We believe you should look into the idea, as it can help optimize the structural elements you need to consider. Such an analysis often can reduce the overall cost of a project.


The design of an EQ-Force mini-pile array is based on a few easily stated principles and rules:

You leave the mini-piles unattached to the footing at the top. This leaves the dense shallow soil or rock immediately below the footing with the ability to shift a little without shaking the structure apart. That layer acts as a shock absorber.

You use long, slender, flexible piles which can bend to absorb more high frequency energy.

You do not embed the pile tips into hard and stable sub-strata, but leave them so they can shift, which will lower direct shock transmittal.

By intercepting the seismic shock waves coming from deep in the ground or horizontally near its surface, the velocity and force of the waves are reduced as they enter an interference pattern and are partly nullified. The system is designed mostly for the interception of the vertical force recognizing that the epicenter of most earthquakes is 2 to 5 miles below ground.

The force of secondary shock waves is reduced as they are dispersed as after-shock effects are always less than those created in the primary quake.

As an example of additive effects, a pile array created by using compaction piles proceeds along conventional lines using standard procedures for grout piles, with only the spatial arrangement of the piles being different. The compaction grouting will provide at least some densification of the soil, the amount dependent on the soil nature. That, in it-self, will eliminate some settlement. Then the forces of vibration that the area sees become less so the net result is an additive benefit with a substantial increase in the safety factor.


Unified Building Design Return to prior text

There is always a growing transformation of the design methods applied to structures. But it is changing more rapidly than it has in the past, and it has become formal enough to have a name, the Unified Building Design method. Elements of the idea have always been in use, but they have been nudged into prominence in design of large buildings and bridges. They are, however, applicable to small structures as well. The idea is to treat an entire structure as a single item reacting to intermittent loadings such as vibration, wind, and seismic events looked at as a whole.

The soil or rock, the underpinning and anchoring, the footing, and the superstructure are dealt with as one rather than as separate items which were previously worked in their own geotechnical, structural or materials isolation. As one element is changed, the reaction of other elements is also changed. That, in turn, may change the nature of the pilings or footings, and the type of materials used for construction. Using stronger and lighter materials can then affect the isolation dampers, use of mini-piles in place of caissons, and the methods of soil compaction or soil of rock modification. Such considerations can then recycle around the loop to further change the underpinning.

A few homely examples will illustrate the idea. A tall skyscraper reacts to wind by bending and going with the flow. The wind variation is low frequency, which is relatively easy to design against. There are two initial ways of dealing with the wind loading: build a strong footing, and then provide some method of damping or isolating the structure from the footing. Or, one may design so that more flexible underground pilings connect directly to the above ground piles and beams so the building will sway as a unit.

Another example is the footing for an electric wind generator. The damage and wear to such a windmill is in the bearings of the generator section. They are precision mechanisms and very expensive to construct, not to mention the expensive downtime for maintenance. One of the first designs, which came about as the ancient types of windmills were made larger, was to anchor the legs deeply in the soil or rock. But today, those legs are a single tapering strut made in the form of an airfoil, pointing in the direction of the prevailing wind. Aeronautical efficiency dictates larger diameter blades meaning taller support towers. Then if you design the footing innovatively, you can absorb most of the high frequency shaking and vibration in the soil directly below, alongside, and above the footing. The tower will then slowly sway but not vibrate, reducing wear dramatically.

Large bridge design requires suspended spans of great length. This means the deck must be thick. It also must be lightweight. Bridge decks are now being designed as airfoil shapes oriented to the prevailing direction of the wind. That airfoil will provide lift (either upward or downward) with that added force being absorbed by the piers. The result is a steady lift upward, or a steady force downward, but little vibration. Then super lightweight and composite materials are introduced, and the design effort cycles back to even lighter footing requirements.

So it is with earthquake forces. Very high frequency and very powerful waves deliver the seismic force. Such forces can break up the buildings, from their underpinnings and footings to their superstructures. Through integrated design though, a structure can be made to react as a whole. And with proper design, it can become lighter and less fragile. One thing which will reduce the seismic energy is the use of long, flexible mini-piles and isolation zones to reduce the direct transmission of shock by providing flexible mini-piles and isolation zones top and bottom; in essence the EQ-Force array.

Keeping the Unified Building Design method in mind will keep you focused on the least cost structure (or least cost upgrade of an existing structure) with the highest safety factor at the least cost. Whether you actually use EQ-Force system or not, the methods and analysis fit right in with state of the art and IBC design requirements.


10410 Cogdill RdKnoxville, TN 37932
Ph 865-671-2925Fax 865-671-2895		 Covered by US Patent 6,659,691. View it at The United States Patent and Trademark Office's website.
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