An SHM system for the new Minnesota Bridge

The St. Anthony Falls Bridge is already under the microscope as construction continues at breakneck speed to replace the collapsed I-35W bridge—and it’s already pushing new boundaries in intelligent design. But by turning the lens on itself, America’s smartest bridge could have an even bigger impact. 

A new high-tech structural health monitoring system equipped with 240 sensors should inform how we monitor other bridges and, eventually, determine how we build them. For all the details and an exclusive animation of the accelerometer-laden fiber-optic rig, we sat down with Figg Engineer Group CEO Linda Figg, who’s heading up St. Anthony Falls' design, before she appeared at the PM-NSF Bridge to the Future summit today. 

Some details of the sensing system have been ironed out, but most are being determined as the bridge goes up—much like its entire design and construction, which occurred almost simultaneously. The importance of the sensors, Figg insisted, is that all the information they collect will funnel into a database, eventually helping other engineers determine how best to design and build a bridge. 

To round up that data, the system—a collaboration between the University of Minnesota and the Minnesota Department of Transportation—will employ at least four different kinds of sensors: accelerometers (red), chloride penetration sensors (magenta), linear potentiometers (blue) and wire strain gauges (green). "The accelerometers will measure vertical deflections [or deformation] with traffic loads," Figg said. The chloride penetrating sensors will evaluate the condition of surface wear and tear by measuring whether or not salt is penetrating the pavement on the bridge deck. Repair and replacement are pricey, so early monitoring should make up for the initial cost of the sensors. 

Meanwhile, linear potentiometers will measure pressure to keep track of St. Anthony Falls’ expansion joints and bearings; Figg said UMinn and Mn/DOT would correlate that data with design codes to analyze how the bridge performs over its lifespan. Finally, the wire strain gauges will measure temperature as well as the amount of force per sq. in. placed on the concrete—all important in assessing a bridge's condition. 

The four sensors will be hardwired using fiber optics through the bridge, then wirelessly transmitted for analysis. They will account for about 100 of the sensors on the bridge; the University of Minnesota will outfit 140 more for research purposes. 

[Erin McCarthy via Popular Mechanics.com]

German Institute to Develop SHM

Several Fraunhofer institutes and various industrial partners are currently working on an SHM system that will use ultrasound to detect any damage to the technical structures of aircraft, pipelines or wind turbines. The core of the sensors used is made up of ceramic piezo fibers that convert mechanical energy into electrical impulses and vice-versa. Any piezo element can be used as either a transmitter or a receiver. It can excite the structure to produce vibrations, and it can record vibrations in the structure.
The ultrasound waves spread out in certain patterns depending on the type of structure. Cracks and other flaws alter this wave pattern in the same way as a rock changes the pattern of waves in a lake. Even a group of four piezo elements is sufficient to locate flaws accurately to the nearest centimeter – flaws that are often no more than a few millimeters in size.
“Our system is intended to supplement the checks used up to now,” says Bernhard Brunner of the Fraunhofer Institute for Silicate Research ISC, Würzburg. But that is only the first step. If the SHM systems prove successful, the researchers can envisage a status-dependent maintenance and repair system: “to save inspections and therefore time,” adds Brunner’s project partner Bernd Frankenstein of the Fraunhofer Institute for Non-Destructive Testing IZFP in Dresden. He is in no doubt that SHM systems will eventually replace conventional test methods, at least in part. The task of the Fraunhofer Institute for Structural Durability and System Reliability LBF is to create deliberate flaws in structures, which can then be detected during tests.
There are even more reasons for teaching structures to ‘feel’. It helps to make better use of valuable resources, both materials and energy. This is particularly noticeable in the aviation industry, where each gram less in the weight of the aircraft increases its potential payload as well as reducing exhaust fumes.
Continuous monitoring by SHM systems is also expected to yield greater safety, particularly for equipment such as offshore wind farms that are not readily accessible. The artificial nervous system fulfills a dual task in such cases: It monitors the structure and at the same time delivers data about occurrences in the structure during day-to-day operation. Data of this kind, which hardly existed until now, will help to optimize the next generations of components.
[Fraunhofer-Gesellschaft via physorg.com]

Scientists use an old bridge for new tests

Scientists at Britain's National Physical Laboratory say they have saved a 46-year-old foot bridge from demolition and will use it to develop new technology.

Scientists at the facility -- the national measurement standards laboratory for the United Kingdom -- said the 14-ton, 66-foot-long and 16-foot-high bridge had been used to allow access from one side of the NPL site to the other.

With redevelopment of the NPL site the bridge had become redundant. But rather than demolish the bridge, researchers will use it as a demonstrator to try different techniques for maximizing a structure's lifetime while minimizing maintenance costs.

During the three-year project the bridge will be loaded until it cracks, repaired using new composite repair methods and then retested.

NPL officials said the opportunity to have a large scale structure that can be abused while being monitored is a once-in-a-lifetime event and will provide evidence for the cost saving benefits of structural health monitoring.

[United Press International]

SHM on Government Technology

An article on SHM of bridges appeared in "Government Technology "

http://www.govtech.com/gt/261440?topic=117693

Entitled "Wireless Sensors May Help Governments Monitor Health of Aging Infrastructure" it describes the consequences of the 35W bridge collapse and some of the technologies that might prevent similar accidents in the future.
In particular, the article introduces a wireless technology perfected at Clarkson University by the team of prof. Kerop Janoyan:

New York is one of many states re-evaluating bridge inspection methods after the Minneapolis bridge collapse by turning to SHM technologies. The state department of transportation's pilot program uses wireless sensors placed on bridges to transmit data on stress and vibration, and should warn if a bridge is weak or needs repairs. The system, designed by Clarkson University associate professor Kerop Janoyan, is expected to help engineers monitor the state's 17,000 bridges.
"Providing more information is the first step to a feedback system," Janoyan said. "Without information, you can't have any feedback when ultimately you're trying to control potential damage."
A New York bridge between Canton and Potsdam is serving as a test site - 40 wireless channel sensors affixed to the bridge log in real-time data to a base station. Each sensor is about the size of a few decks of playing cards, and cost about $200. The battery-powered sensors are connected to a computer that aggregates sensor data and determines whether to alert inspectors.

The article than describes the work of prof. Farhad Ansari at the University of Chicago on optical fiber sensors:
The Department of Civil and Materials Engineering at the University of Illinois at Chicago is developing a similar bridge monitoring approach, using fiber-optic wires instead of wireless sensors. A research program at the university called - Smart Sensors and NDT Laboratory - develops fiber-optic sensors for monitoring structures during construction and throughout their service lives.
The Illinois Department of Transportation awarded a $55,000 contract in September 2007 to the laboratory - to devise a system that can detect bridge scour - when sediment is washed from the bottom of the river and weakens a bridge's support. The project involves embedding a fiber-optic sensor in a rod and driving the rod into a river base near the piers.
Fiber-optic sensors assess a bridge's overall health by measuring microfractures and vibration frequency. Fiber optics promise many innovations for bridge monitoring since they are smaller and more flexible than electrical wires, are immune to interference from wireless devices, and aren't prone to fires or explosions, said Farhad Ansari, professor and head of the Civil Engineering and Materials Department at the University of Illinois at Chicago.

The article also describes projects at the University of Michigan on "sensing paint" at at Sandia National labs on remote sensing.

35W bridge collapse pictures

In this interesting document, it is possible to observe a large number of pictures of the 35W bridge that collapsed into the Mississippi river.

http://www.ntsb.gov/dockets/Highway/HWY07MH024/387406.pdf

In particular it is interesting to notice that some of the gusset plates appear to be buckled as early as 2003 and the fractured plate show signs of corrosion.

Other related documets and reports can be found here:

http://www.ntsb.gov/dockets/Highway/HWY07MH024/default.htm

SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring

I am currently at the
SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring conference in San Diego.

Several interesting trends emerged in this edition:

• The seems to be a growing interest in aerospace applications, SHM and smart structures for active control.


• The civil engineering and structural monitoring parts are attracting less presentations and little new work. Probably more specific conferences such as SHMII and IABMAS are becoming more relevant in this field.


• A lot of papers as usual on Fiber Optic sensing and a growing number on wireless sensing. This technology is maturing and appears now adapted for field use, but mostly limited to short- and medium-term applications.


• Besides the usual bridges, other structures were also monitored, including aircraft, oil platforms and buildings.

Norhwestern University pubblications

Here is a list of interesting papers and presentations on "Improved Condition Monitoring for Bridge Management / Non-Destructive Evaluation" published by the insfrastructure Technology Institute at northwestern University.

2nd Asia-Pacific Workshop on Structural Health Monitoring

Conference Announcement:

Organiser: Materials Australia
Location: Melbourne, Australia
Date: December 02-04, 2008

This is the second in a series of biennial Asia-Pacific workshops that focuses on the field of Structural Health Monitoring (SHM). This is a particularly promising area that has attracted significant attention in recent years for its wide potential of applications, particularly for civil infrastructures, and maritime and aircraft structures. The purpose of the workshop is to allow a forum where key and emerging technical issues that are critical and unique in structural health monitoring can be discussed and identified, as well as allow current state-of-the-art technologies and R&D activities in the field to be presented. The workshop is also intended to promote exchanges and cross-fertilisation among many disciplines.

The workshop shall focus on, but is not limited to, the following topics:

- Sensor and Actuator Development
- Reliability of Structural Health Monitoring Methodologies
- Bio-inspired sensors
- Damage Identification and Properties/ Integrity Characterisation and Assessment: Intelligent Processing of Materials and Structures
- System Integration
- Applications (particularly in the field of aircraft, automotive, rail and maritime structures, civil and petroleum infrastructure, textiles etc)
- Homeland Security

Website: http://www.materialsaustralia.com.au/SHM2008/

SHM for aeropase structures

In this article you will find an interesting overview about the future of SHM for aircrafts:

Future Inspection Technologies (from avitaion week)

Here are a few interesting quotes:

Posit for a moment the airplane of the future, a flying machine all but freed from scheduled inspections, able to keep flying because of sets of sophisticated sensors imbedded within it.
Behold, the monitored machine.
In perhaps a decade or so, a mechanic might do a walk around inspection, much as the first officer does at pre-flight, just before departure. But this walkaround would be far more probing. Armed with a wireless ultrasound device, "your technician walks past the airplane and a little chip beeps at him," envisions Michael Moles, senior technology manager for Olympus NDT. "He knows then and there whether there's a problem." This, contends the veteran NDT executive, "will tend to be the future," a future predicated not so much on periodic inspection, as on structural health monitoring.

The irreducible criteria regulators will consider whether the in-situ sensor "works as [well] or better than my current hand-held inspection technique," said Roach. That's step one, a step that conceivably could lead to what Roach and Rackow write terms, "Condition-based maintenance practices ... substituted for the current time-based maintenance approach." At the very least, the Sandia researchers contend in-situ sensors render it "possible to produce an aircraft prognostic health architecture that can assist in maintenance scheduling and tracking."

Bridge Inspection and Conditions Maps

MSMBC has created a nice tool to map the conditions and inspection record of all US bridges in the national inventory.

You can find it here.