The researchers recently developed and successfully tested the first seismic design methodology for bridge towers that respond to ground motions by literally jumping a few inches off the ground.
The new methodology allows steel truss towers that support bridge decks to be built or retrofitted at far less expense than conventional approaches, where each leg of a bridge tower is strongly anchored to its footing.
The research is funded by the U.S. Federal Highway Administration.
The design recently underwent successful testing on a model truss tower that is 20 feet high and weighs nine tons.
Testing was conducted on a six-degrees-of-freedom shake table in UB's Structural Engineering and Earthquake Simulation Laboratory (SEESL). One of the world's most versatile earthquake engineering laboratories, it is a facility within the UB School of Engineering and Applied Sciences.
"Our approach is unconventional, counterintuitive," admits Michel Bruneau, Ph.D., director of MCEER and UB professor of civil, structural and environmental engineering, who developed the new approach with Michael Pollino, a doctoral candidate in the UB Department of Civil, Structural and Environmental Engineering.
"With an earthquake, conventional wisdom dictates that the most important thing is to anchor the bridge tower," explained Bruneau. "The mass wants to overturn, so you have to tie it down."
To do that, he explained, the tower must be anchored with a very expensive foundation system, which in turn, subjects it to the full force of the earthquake.
"In this scenario, something usually has to yield," he says. "Here, we're standing that concept on its head. By letting the tower rock, we're significantly reducing the overturning force."
The UB engineers developed a design procedure in which the legs of the truss tower are disconnected from their base and briefly uplifted by a small amount if significant ground motions occur.
One of the options they evaluated includes using specialized devices to control the structure's uplift. The devices, called hysteretic or viscous dampers, some of which were provided by Taylor Devices, Inc., were inserted at the base of the towers to allow the tower to rock while absorbing part of the earthquake's energy and helping to control the amount of uplift to the structure.
During the series of tests at UB on SEESL's state-of-the-art shake table, the experimental truss tower fitted with these devices was subjected to ground motions simulating the 1994 Northridge, California earthquake; testing also was conducted without any devices attached, as the design procedure was developed to generally address performance both with and without dampers.
Typically, during testing, the tower's legs uplifted nearly two inches in the air for less than a second. For some of the free-rocking cases, the tower legs lifted nearly four inches.
"All of the tests were successful," said Bruneau. "The damper systems typically reduced the magnitude of uplift and the velocity upon impact, which may be important, in some conditions."
The methodology will not allow uplifts to exceed limits considered safe by the design procedure and dictated by the tower design, local conditions and the need for the tower to return safely to its original position, according to Bruneau. The UB methodology is the first to be established for this application, but Bruneau notes that engineers previously have employed the concept, such as in the approach spans of the Lions Gate Bridge in Vancouver, British Columbia.
"Professional engineers are starting to recognize that it is economical to allow this type of rocking in their designs, as long as the structure remains stable and the speed with which the legs come down is carefully controlled to minimize the forces that develop during the rocking," said Bruneau.
In addition to the cost savings in construction, this design also saves money if seismic retrofit needs to be done, he added.
"It's much easier to fix a tower to enhance its seismic resistance if the crew only has to work at the base, instead of having to climb 60, 80 or 120 feet to strengthen individual members along the height of those towers," he said.
MCEER, headquartered at the University at Buffalo, was founded in 1986 as a national center of excellence in advanced technology applications dedicated to reducing losses from earthquake and other hazards nationwide. MCEER has been funded principally over the past 19 years with $68 million from NSF; $36 million from the State of New York and $26 million from the Federal Highway Administration. Additional support comes from the Federal Emergency Management Agency, other state governments, academic institutions, foreign governments and private industry.
The University at Buffalo is a premier research-intensive public university, the largest and most comprehensive campus in the State University of New York.
Ellen Goldbaum | EurekAlert!
Flexible protection for "smart" building and façade components
30.11.2016 | Fraunhofer-Institut für Silicatforschung ISC
Healthy living without damp and mold
16.11.2016 | Fraunhofer-Gesellschaft
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
08.12.2016 | Materials Sciences
08.12.2016 | Materials Sciences
08.12.2016 | Physics and Astronomy