The Anatomy of an Isolator — An Integral Component to the Overall Seismic Protection System

Behind that black inner tube like material is a magical “EPS” system. EPS stands for Earthquake Protection System and is the company that invented the “Friction Pendulum seismic isolation concept in 1985.”¹ The company manufactured 126 isolators for the Loma Linda University Campus Transformation Project (LLUCTP). The isolators arrived on site in late August of 2017, and provided some curiosity as they were wrapped in a plastic sheathing.

Upon returning from a short vacation, I noticed a few of the isolators had been lowered onto a few of the bases. I was rather disappointed that the plastic covering was still on the isolators (little did I know

One of the wrapped Isolators.

that the covering had been removed upon lowering the isolators and recovered). I was really curious as to what they looked like. A few days later, I noticed the plastic covering had come off or been removed from an isolator. There the in all of its glory was an isolator enclosed in all of its black tubing. At first glance it did look like a black inner tube with a blue plate on the top and a blue plate on the bottom. At first blush it appeared that it was held together by four plates, one at each of the corners of the compass.  As I was accessing the isolator, one of the ironworkers walked by and commented that the isolator looked like a “giant Oriole Cookie.” Within a few weeks the wrapping had been removed from all of the isolators. Every time thereafter, I walked by the Isolators, I wondered what was behind the black tube. Could it be a thick spring? I mused. Shortly after the unveiling, the isolators were rewrapped to keep out the elements, I suppose. By the time the structural support beams were lowered onto the isolators, the covering was off again. They would not be wrapped again until the MONOKOTE fireproofing was sprayed on the beams. Today they stand unwrapped.

An unwrapped Isolator: “The Oriole Cookie.”

Today, I learned what is inside. With the permission of the company that invented and fabricated the isolator for the LLUCTP project, I will divulge in this blog what is actually behind the black tube. In the feature photo, introducing this blog, the EPS illustrative image is positioned on top of an actual isolator (after the keeper plates had been removed), which is down in the basement of the structure. The isolator is known as a Triple Pendulum™ Bearing, which according to the website: “Incorporates three pendulums in one bearing, each with properties selected to optimize the structure’s response for different earthquake strengths and frequencies.” ²

For illustrative purposes an illustration from the EPS website is provided below. Click on the link below the illustration to watch how the bearing system works during an earthquake. The link provided below is courtesy of and used by permission of EPS.

http://www.earthquakeprotection.com/popup_bearing_works291007.html

~ CLICK THE ABOVE LINK ~

Just imagine the video if the components in following illustration were included 

One of my favorite shots is of the existing Children’s Hospital and Medical Center. Under azure skies over looking the pit that will give birth to two new structures that will not only rise above them but replace them as the new improved towers of healing. With the camera resting on top of an isolator the scene captures the massive steel support beams mounted and bolted to the isolators in a the arduous journey to the east foundation wall. From this perspective it appears that the hospitals in the background are being supported by the steel in the foreground.  Within a matter of days, the first vertical column will be set. Just think, this is a view from this angle will never be captured again.

The above illustrations are not to scale seismic elements (relating only to the isolator and the isolator base) that portray how the isolator (cross section) would appear sans the black tubing. The top illustration (1) depicts the spline beam node centered above the isolator in a pre-earthquake mode. The bottom illustration (2) provides an example of how the isolator and the components above shift during a seismic event. Please note that the illustration is not to scale but it is how it would appear if a single photograph comprised all of the sections including an actual EPS isolator. 

By way of disclosure: I was down in the basement today (08.08.18) taking photos of the last few keeper plates being removed.  I heard nary a creak from the steel building!

EPS is continually making improvements on how the concept responds to seismic events. EPS’s Friction Pendulum solutions are engineered for eacch application considering seismic performance criteria, structure requirements, seismic hazards, and construction costs.” ³

End Notes: No’s 1 – 3 the Earthquake Protection Website.