Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

‘Shakers’ Help Engineers Develop Inexpensive System for Testing Condition of Bridges

31.10.2013
Research employs popular devices used in home entertainment systems

Engineering researchers at the University of Arkansas have developed a new and inexpensive system to test the structural condition of short- to medium-span bridges.


Three hundred and fifty feet above the East River, Kirk Grimmelsman inspects the Throgs Neck Bridge in New York City.

The system employs a network of tactile transducers – small-scale, inexpensive and off-the-shelf devices that create the sensation of shaking through feedback of low-frequency sound waves. These devices, known as “shakers,” are normally used in home entertainment systems and amusement park rides to enhance user experience.

“The compact size of the tactile transducers and their supporting electronics makes them ideal for executing controlled vibration testing of bridges without disrupting the traffic on the structures,” said Kirk Grimmelsman, assistant professor of civil engineering. “These devices can replicate practically any type of dynamic excitation, including random noise, impulses and harmonic signals.”

There are roughly 600,000 bridges in the United States, the overwhelming majority of which are 300 feet or shorter. The Federal Highway Administration maintains the National Bridge Inventory, a database containing safety and structural information on all U.S. bridges that carry vehicles. The data are used to analyze and judge the condition of bridges. As part of the requirements of the inventory, specially trained engineers must visually inspect each bridge every two years. Many bridge engineers consider the qualitative data provided by visual inspections to be less than optimal for cost-effective and reliable maintenance of the nation’s inventory of aging bridges. In recent years there has been a greater effort to use modern technology to provide more quantitative data for assessing the condition and safety of deteriorating bridges.

Grimmelsman’s work is part of this effort. He has performed a variety of full-scale testing programs on numerous bridges, including the Brooklyn Bridge and New York City’s heavily traveled Throgs Neck Bridge. His research focuses on investigating scientific, quantitative methods for testing the safety and structural integrity of bridges. The method he uses is called dynamic testing, an experimental approach that quantitatively characterizes and evaluates bridges. The two main approaches for dynamic testing are experimental modal analysis, also called forced-vibration testing, and operational modal analysis, frequently referred to as ambient vibration testing.

With forced vibration testing, the bridge is dynamically excited by a controlled and measurable source, such as shakers and impact hammers. This allows engineers to control the inputs used for testing. The relationship between the dynamic inputs and structural response provides a meaningful description of how the bridge is currently behaving. However, this approach has depended on a single vibration-inducing device, which is large, heavy and expensive, costing a minimum of $20,000. The device and its supporting equipment also interfere with traffic on bridges and are not practical for long-term measurements to track the condition of bridges as they age and deteriorate.

Ambient vibration testing, by far the most popular form of dynamic testing for bridges, relies on natural environmental sources such as wind, microtremors, waves and operating traffic on and near the structure, all of which make the bridge vibrate. Although it has the important advantages of being inexpensive and not disruptive to traffic, ambient vibration testing is more uncertain because researchers cannot control or measure the forces that are making the structure vibrate.

In recent years, Grimmelsman has sought to develop a more reliable, practical and less expensive way to perform forced vibration testing. He considered using small and inexpensive shakers to vibrate a bridge from many input locations spread out across the structure. He originally planned to modify subwoofer speakers to serve as shakers, until a graduate student in his laboratory mentioned “bass shakers,” devices that create the sensation of shaking with low frequency audio signals.

Grimmelsman and students Jessica Carreiro and Eric Fernstrom modified and experimented with a variety of available types of bass shakers, also known as tactile transducers. The devices they studied were all small and portable – weighing less than 10 pounds. Grimmelsman designed and built a bridge-testing system with these devices that cost less than $500 per shaker.

The researchers later installed 12 tactile transducers on the underside of a rural highway bridge to evaluate how the shakers would operate. As a network, the system produced vibrations with reasonable force over a broad range of frequencies. The bridge vibrations induced by the shakers were also much larger than those due to wind and other natural sources.

“The bridge test demonstrated that a system of these devices could dynamically excite a full-scale structure in a controlled manner to produce vibration responses with less uncertainty and more uniformity than those resulting from natural sources and traffic,” Grimmelsman said.

The testing was the first attempt by any researchers to dynamically excite a full-scale bridge in the field using a large number of controlled inputs at the same time.

Grimmelsman recently presented the research at the 2013 American Society of Civil Engineers Structures Congress. He and his team are conducting further bridge tests with their system and preparing their results for publication.

CONTACTS:
Kirk Grimmelsman, assistant professor, civil engineering
College of Engineering
479-575-4182, kgrimmel@uark.edu
Matt McGowan, science and research communications officer
University Relations
479-575-4246, dmcgowa@uark.edu

Matt McGowan | Newswise
Further information:
http://www.uark.edu

More articles from Architecture and Construction:

nachricht Modular storage tank for tight spaces
16.03.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH

nachricht Smart homes will “LISTEN” to your voice
17.01.2017 | EML European Media Laboratory GmbH

All articles from Architecture and Construction >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>