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There are several factors stimulating modern bridge design, specifically structural health monitoring (SHM) and the methodology of intelligent infrastructure. Making the move from an initiative purely examined by way of academic research to practical application, SHM technologies are — without doubt — gaining momentum. But although the momentum is real, and experts throughout the industry agree on the potential advantages of SHM, there are differing views regarding its present status.
Domestically, the demand for SHM of bridges is starting to rise, says Mark Sereci, president and CEO of Digitexx Data Systems, a provider of data acquisition and control products.
“However, there are still a lot of questions and schools of thought,” he notes. “On one side of the country, seismic activity is calling for a global approach to monitoring and measuring the overall performance of the bridge through a predominant use of accelerometers. On the other side of the country, more challenge and focus is around aging infrastructure, hence more use of strain gages. Both schools of thought are correct, so there is need for a system that can adjust to the demands of the region, bridge type, and potential structural challenges.”
SHM, as an application, is starting to gain adherents, explains Peter Vanderzee, president and CEO of LifeSpan Technologies, a developer of structural-health-monitoring solutions. “However, it is being used primarily with older structures, particularly to safely extend operating life,” he adds. “The world of SHM is divided into two halves: academic (projects used to support grad students) and commercial service providers (who develop applications for structure owners). More and more, structure owners are gravitating to commercial service providers from academics.”
SHM technology, offered by a number of providers, is fully commercial, according to Vanderzee. “Academic providers typically do not have the same project objectives as the structure owners, but there are a few non-academic providers which meet the needs of structure owners quite effectively,” he says.
Because of the increase in accessibility of monitoring systems today, there is a strong trend of employing such technology in new and existing construction, says Chris Kavars, president of SENSR, which provides dynamic monitoring solutions for structural engineers.
“The objective is to measure the response of the structure in an unusual event,” he states. “Although the technology has existed for a few years, with advances in instrumentation and real-world experience, the industry now has real data to compare to the models. Further, the advances in instrumentation allow users to test their models, and from there, predictions can be made. With today’s equipment, users have the ability to measure the subtlest of disturbances that excite the structure in order to see how the structure will respond. The trend is best summarized by linking real-world and design performance, enabling users [with] the ability to assess the capability of a structure to withstand a future hazard.”
The biggest factor the industry is aware of is that bridges need to last 100 years, saysKen Stevens, industrial group manager for Campbell Scientific, Inc.
“To really have a cost-effective design to meet this requirement, one needs better data. Bridge designers are instrumenting bridges at construction time to better understand bridge behavior,” he points out. “More and more universities and DOTs are performing long-term bridge monitoring to create a better understanding [of] how the health of a bridge changes with time.”
To really understand the health of a bridge, one must have more and better data than visual inspections provide, Stevens states. “To determine whether a bridge is structurally deficient, you need to install strain gauges, accelerometers, load cells, tilt meters, and even weather sensors to determine the behavior of a bridge today and what has changed months or years later,” he says. “The FHWA (Federal Highway Administration) has started a 20-year plan to determine the health of our 600,000 bridges by first studying seven bridges for five years and determining the critical factors needed to characterize the health of a bridge.”
Responding to the SHM market
Suppliers are responding to the current SHM market in several ways, including research and development and new-product development.
“Unlike other companies in this space, we aren’t a sensor manufacturer, so we aren’t trying to develop a system to cater to the response of our own sensors,” Sereci says. “Instead, we started more than a decade ago by looking at the challenge and designing a solution accordingly. Our bridge-monitoring systems perform in real-time (no buffer time) and can incorporate just about any third party sensor: accelerometers, strain (traditional, fibre, vibrating wire), environmental, displacement, weigh-in-motion, and even video.”
Sereci added that Digitexx can easily incorporate structural algorithms to perform analysis in real-time, making a “smart bridge” even smarter. “Our architecture is flexible so that the system can evolve as the SHM industry evolves, enhancing the value of a customer’s capital investment,” he says. To date, most Digitexx solutions have been geared toward more permanent installations for continuous monitoring, Sereci explains.
“In our discussions with customers, we saw a need for a portable solution for short-term testing, research and monitoring,” he notes. “To answer that need, we recently introduced the PDAQ line of products. One example — our PDAQ Premium — is a 16-channel system that offers both local and remote real-time monitoring capabilities. We have a client that is currently using a PDAQ during the construction of a bridge in Europe. The real-time data is helping validate their design estimations.”
Although there are some systems that have been running continuously for more than a decade, overall, the industry is still in its infancy, Sereci adds. “As solution providers, it is our duty to help educate, provide information, and support the continued evolution and growth of the industry,” he says. “Some of what we provide are tools such as our SHM product guide, informational videos, web demonstrations, and an interactive blog.”
To that end, Vanderzee says LifeSpan Technologies has an almost continuous upgrading effort underway, both for its sensors and software.
Kavars adds that SENSR launched two new products this spring that respond to the needs of the marketplace.
“Both SENSRnet and the CX1 platforms are easy to place and more cost-effective than many of the traditional solutions found in the industry,” he says. “The CX1 combines three technology platforms into one solution, which results in fewer components and less wiring. Capable of being installed on a variety of structures for both indoor and outdoor environments, the CX1 can measure the sway of a highrise building, the vibration caused by construction, or the angle of a bridge pier during a flood.”
SENSRnet automatically measures responses and notifies engineers when responses change. “Unique sensors can detect more than 16 different hazardous states and conditions, which provides advanced detection capabilities aiding in avoiding disasters and triggers the early responses that can minimize property and casualty losses,” Kavars says.
Stevens says Campbell Scientific manufactures rugged, battery-powered dataloggers that provide long-term stand-alone bridge monitoring.
“Our systems are compatible with most available sensors and multiple telemetry options, including radio, cell phone, telephone, satellite, and ethernet,” he says, adding that this allows data from remote sites to be sent right to the office.
“We recently released our AVW200 vibrating-wire interface that virtually eliminates external noise that commonly interferes with vibrating-wire measurements,” Stevens points out. “This is significant because many sensors used for bridge monitoring use vibrating-wire technology. We have also released wireless measurement peripherals that make it easier and less expensive to instrument bridges by eliminating long runs of cable.”
Stevens says the Campbell Scientific is working closely with Virginia Tech and Utah State University, who are instrumenting the first seven pilot bridges for the FHWA. “We are helping them with the programming of our dataloggers and with sensor integration for this project,” he says. “Our goal is to ensure that they get meaningful, accurate, and reliable data.”
In terms of resources, what is needed at this point is for the firms that supply solutions in the marketplace to come together to create industry standards, Kavars explains. “An unbiased resource that builds on practice — not purely academic theory — and experience is needed to help guide the industry,” he says.
Pamela Accetta Smith is a freelance writer based in Albuquerque, N.M.
