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Earthquake Protection Systems

Buildings, Bridges Withstand Earthquakes with the Help of Eaton Products

"We needed to develop a machine that could simulate the vertical load, as well as the dynamic horizontal movement experienced during seismic activity in real time.”

Victor Zayas
President of Earthquake Protection Systems (EPS)

Background

Eaton is playing an important support role in protecting buildings, bridges, storage tanks, drilling platforms, and other vulnerable structures in earthquake- prone regions of the world.

Earthquake Protection Systems (EPS) is relying on cylinders, pumps, and valves from Eaton’s Hydraulics Operations to test its Friction Pendulum™ seismic isolation bearings that decouple structures from their foundations during seismic events, thereby preventing catastrophic damage. Eaton products are being supplied to EPS by Berendsen Fluid Power, an Eaton distributor located in Hayward, California.

The bearings are structural joints consisting of a large concave surface on which rides an articulated slider. When activated by an earthquake, the slider moves along the concave surface, causing the supported structure to move with small pendulumlike motions. The dynamic friction force generated provides dampening to help absorb the earthquake’s energy and reduce structural shaking.

Due to their design, the seismic bearings are designed into new construction projects, as well as retrofitted to existing structures as a cost-effective solution to meeting changing building code
regulations.

The massive bearings are tested on an equally massive test structure at EPS’ Vallejo, California, facility, where earthquake tremors are literally brought indoors. The Eaton-product equipped fixture simulates both the vertical load of a structure weighing up to 15 million pounds, as well as the horizontal movement of the ground at realistic seismic velocities.

Challenges

In operation for 23 years, EPS previously tested its largest bearings at a seismic lab operated by the University of California at San Diego. As orders increased, so did test scheduling conflicts, which prompted EPS to look into building its own test stand.

“Previous testing was done at much slower velocities, which didn’t simulate real world seismic conditions,” says Victor Zayas, president of EPS.

“We needed to develop a machine that could simulate the vertical load, as well as the dynamic horizontal movement experienced during seismic activity in real time. Therefore, we contacted Eaton and Berendsen Fluid Power for assistance in designing the stand’s hydraulic system.”

The project was indeed a challenge, says John Kostyal, Eaton area sales manager.

“Building a hydraulic system for what amounts to a 7,500-ton press with a shaker table that can move up to 14 feet horizontally under full load, while simulating a magnitude 8 earthquake, was no small challenge,” Kostyal says.

“We learned that the test stand would be equipped with a unique control system that would open valves sequentially as needed to simulate increasing wave strength. This meant that cylinders in the system needed an extremely high-flow capacity and that the valve circuitry would have to be precise in order to regulate the flow.”

Solution

Kostyal and Zayas worked with Eaton engineer and the staff at Berendsen Fluid Power in Northern California for over two years to develop a robust, hydraulic system solution capable of withstanding the demands of the testing environment. By determining the configuration of the hydraulic system, calculating the maximum flow requirement, and incorporating other design requirements, they were able to design and implement the system that features numerous Eaton custom cylinders and valves, including:

  • Fifteen 20-inch bore x 48-inch stroke Eaton Large Bore cylinders
    -Generate a vertical load
  • Five 20-inch bore x 180-inch stroke Eaton Large Bore cylinders
    -Generate horizontal motion
  • Eaton’s Vickers® DG valves and slip-in cartridge valves
    -Control oil flow to the cylinders
  • Eaton’s Vickers PVM pump
    -Assists in charging a bank of accumulators, used to maintain constant pressure as the vertical cylinders traverse the concave surface of the bearing, while supplying oil to the horizontal cylinders

Results

Fitted with load cells and displacement transducers, the test fixture is being used around the clock for production testing, as well as to qualify bearings for the most demanding certification specifications. Its hardworking hydraulic system was made possible by Eaton’s technical expertise, collaboration with a key distribution partner, manufacturing capability, and extensive cylinder and valve product lines that offer both broad style and flow ranges. EPS’ riction Pendulum™ bearing design has been employed in some of the largest seismic isolation projects in the world. Among them are the International Terminal at the San Francisco International Airport, the Benicia- Martinez Bridge in Northern California, the I-40 Mississippi River Bridge, the trussed roof on Seattle’s Qwest Field football stadium, and the Sakhalin LUNA, Russia’s first offshore gasproducing platform.