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NDE/NDT – Structural Materials Technology
for Highways and Bridges
Sense and Cents from Sensors
Peter J. Vanderzee, President and CEO
Structural health monitoring (SHM) technology, as a commercial service, has been available for over a decade, yet very few US State DOTs have adopted the technology for deployment on a routine basis. When asked why, some DOT engineers often cite lack of budget. Others cite uncertainty about how to procure the services effectively. Several engineers have voiced concern over application appropriateness, in other words, how and when to best deploy technology solutions for assessment of specific structural issues. It is rare that State DOT engineers express concern for return on investment (ROI), although that should be of primary interest to them.
For purposes of this paper, it’s worthwhile to define what full-scale adoption of SHM means to users and service providers. This author believes it can be defined by a combination of the following situations: (1) Owners routinely consider its use for deficient structures; (2) Owners’ procurement practices for SHM are defined; (3) Owners can describe what system functionality they need for most situations; (4) SHM is discussed in the context of providing financial benefits, e.g. an expected ROI; and (5) Owners can readily identify the most reliable and cost-effective SHM commercial suppliers.
Given the current and expected future Federal, State and local government transportation funding challenges and the continued deterioration of bridges large and small, it’s no surprise that bridge preservation has become a hot topic for practitioners. Yet this hot topic has not led to vigorous SHM adoption and deployment. The key question all State DOTs should be asking is this: “If we can’t afford to repair or replace a bridge, how can we ensure its continued safe use?” This paper will explore the practical issues surrounding the use of SHM technology as an answer to that question and provide specific recommendations for accelerating its adoption and deployment.
Historical Context for SHM Technology
SHM was conceptualized in academia nearly 25 years ago, probably on a white board in a structural engineering classroom. Credit is due to those academics that pioneered the SHM concept, but after ten years of effort, they were only able to inch toward commercialization, probably the result of competing interests they had to consider, such as PhD student research, obtaining research grants, their State DOT research agenda, and teaching load.
As a result, early use of SHM was research oriented which influenced the number and type of sensors used, data capture frequency, and reduction of data captured into an acceptable PhD thesis. Suffice it to say, several DOTs, who were early pilot project pioneers, now affirm that overly complex systems led to high costs, data overload, and difficulty in reducing the captured data into actionable intelligence, in essence a poor return on investment.
Entrepreneurs entered the fledgling SHM market about fifteen years ago and were unduly influenced by the path academia paved, principally use of a plethora of sensors, high frequency data capture and difficulty interpreting the data. In a rush to sell hardware, some commercial salesmen told DOT engineers and executives that “…you should ‘sensorize’ every bridge”, or “…you can pay for SHM technology by terminating all your bridge inspectors”, or “…only my sensor provides sufficient data to diagnose every potential issue with your bridge” – all preposterous statements which were rightly brushed off by DOT engineers and executives as if these salesmen were selling used cars instead of SHM technology.
So, SHM technology meandered from academic promise to broken commercial promises as various SHM-focused firms came and went. There’s little wonder why State DOT bridge engineers cycled between confused, annoyed, and non-interested as SHM technology salesmen made visit after visit. However, some entrepreneurs persevered and made it a priority to deliver value to every customer for the long-term benefit of their firm and the taxpayers. The SHM market today can still be described as emerging, but continued successes are piling up as more state and local bridge owners are taking note that judiciously applied, the technology does work as intended and can provide substantial relief from expected funding shortfalls in the context of a quality asset management program.
NBIS Condition Assessment and SHM Technology
The Federal Highway Administration (FHWA) mandates biennial visual inspection of bridges, known as the National Bridge Inspection Standards (NBIS), which have been in place for over 40 years. NBIS provides bridge owners with a first-line-of-defense to ensure user safety while providing both FHWA and Congress with an estimate of how much money will be needed for future bridge repair and replacement projects. NBIS data helped shape the early practices of bridge management and undoubtedly had a net positive impact on maintenance actions (deck washing), bridge design (fracture critical details), and construction techniques (bolts vs. rivets).
After 30 years of implementation, FHWA decided to study the reliability of visual inspection in terms of its accuracy and overall impact on bridge management. In early 2001, FHWA published the results of that study in Public Roads Magazine (1,2). Study conclusions were somewhat startling to practitioners – that NBIS visual inspections were “subjective” and “significantly variable”, making its use problematic for financial optimization of repair and replacement decisions and by deduction, predicting funding need in future Transportation Legislation. That study and a subsequent Transportation Research Board Committee Paper, co-authored by a private sector consultant and FHWA engineer (3), provided eye-popping conclusions and an incentive for SHM technology entrepreneurs to re-define the value SHM technology could and should deliver to cash-strapped owners.
FHWA, AASHTO and MAP-21
All bridge owners, whether State or local, know that the FHWA and Association of American State Highway and Transportation Officials (AASHTO) are important policy and standards-setting organizations, affecting how bridge management processes are defined and implemented. To its credit, FHWA has been responsible for improving NBIS techniques since inception, which includes upgraded training courses and even relaxing biennial inspection requirements in certain situations, improving its cost-effectiveness. As FHWA and State DOTs start implementation of more comprehensive element level inspections, one has to wonder if this enhanced protocol will just provide more of the same subjective information, further deferring adoption and deployment of SHM technology.
The FHWA has not, to this date, actively encouraged the use of SHM by bridge owners to objectively and more accurately assess bridge condition in a global sense or even its use to monitor known, visible defects that add a layer of safety for users. FHWA’s neutral stance has clearly hindered SHM technology adoption and deployment. However, FHWA has recently brought SHM technology use into the spotlight for two unique situations: (1) load ratings for old bridges without plans or calculations and (2) State DOT bridge preservation programs. FHWA and AASHTO have both long recognized the importance of bridge preservation, but have not yet “married” difficult bridge preservation decisions with more objective and precise condition assessments. That tie is critical for SHM.
In certain AASHTO Technical Committees, such as T-9 (Bridge Preservation), there has been some discussion on use of SHM technology, but there have been no recommendations for its use in assessing overall bridge condition – specifically bridge superstructure. AASHTO’s lack of support on this issue has also hindered SHM adoption and deployment for the past decade. When you belong to an organization that promulgates specific standards, it’s not easy for practitioners to waver from those standards or pioneer a modified approach for certain aspects of bridge management. Yet some DOTs have pushed beyond this conundrum and implemented meaningful pilot projects.
In its 2011 Manual for Bridge Evaluation (MBE), AASHTO included a Chapter (8) on non-destructive load testing that discussed use of sensing devices to capture maximum strain values or frequency data using known live loads. The MBE also included an important statement that confirmed what most structural engineers intuitively know: “…..the actual performance of most bridges is more favorable than conventional theory dictates”. To most practitioners, this is an admission that conventional methods of bridge condition evaluation are very conservative. In essence, this statement is a tacit acknowledgment that certainty regarding actual bridge condition will likely result in a different decision for repair or replacement than what could be presumed from a subjective and highly variable NBIS visual inspection. This conclusion assuredly supports more recent emphasis on asset management and SHM.
When the current Transportation Bill (MAP-21) was finally signed into law two years ago, some DOT engineers and executives were surprised to see so much emphasis on asset management. While this management paradigm has been discussed for years, it took a Congressional mandate to reduce the concept to daily practice. FHWA has been tasked to provide State DOTs with implementation guidance for this MAP-21 requirement, yet a number of DOTs have already started building on their bridge management programs in scope and impact across all transportation asset classes, e.g., roadways, tunnels, guardrails, etc.
Over the past few years, several DOTs have conducted pilot projects with SHM technology to see if it was able to provide them with what commercial technology providers have been claiming – that objective, accurate and timely performance data can be effectively used to assess overall superstructure condition and monitor known defects to enhance safety. It is generally accepted that Transportation Asset Management (TAM), as it evolves and improves with time, especially when coupled with SHM technology, will support more effective prioritization of increasingly scarce Federal and local funding, enhance safe operations, and drive improved major project planning.
Current Status of SHM Adoption and Deployment
At this writing, full-scale SHM adoption and deployment still remains an elusive goal for commercial service providers that should, however, be achieved over the next five years. Experience over the past ten years confirms there remains a wide gap of interest, knowledge, and experience about SHM technology across all State DOTs. Recent State DOT comments to this author have ranged from very positive: “We’d like to conduct a pilot project to verify the usefulness of SHM technology for an upgraded Asset Management Program” to very puzzling: “We don’t believe in use of SHM technology” (despite the published evidence and before ever conducting a pilot project).
Also, there are still DOTs who rely on their state research University to provide SHM, thinking that SHM technology remains a semi-mysterious research-related curiosity. While there will always be a role for research in the SHM field, full-scale commercial deployment of SHM in a state, as envisioned by this author, is not feasible for a University. Full-scale deployment of SHM by State DOTs requires a project management organization (engineers, technicians, and administrators), field installation expertise, proven suppliers, insurance, working capital, reliable data storage, etc. that University professors and PhD students do not have or know how to manage. Suffice it to say that conducting one project over three years for a State DOT is vastly different than designing, selling, building, installing, operating, and warranting an SHM program for 100+ structures across a vast swath of real estate.
The current status of SHM adoption suggests there remains a crucial role for FHWA and AASHTO to actively support use of SHM in the context of enhancing safe operations, reducing long term bridge repair and replacement funding demand, and making more accurate load posting decisions. Importantly, FHWA support must be visible, consistent and at a sufficiently high level for State DOTs to take notice and for AASHTO to join the chorus. FHWA might consider publishing a policy guide, or conducting Workshops and Webinars, or work with AASHTO to publish a joint White Paper on the benefits derived from judicious use of SHM technology.
No matter what method of support FHWA and AASHTO finally decide to implement, the timing for this action is LONG OVERDUE. When considering the technical and financial disconnect between press releases and articles from various interest groups that advocate tens of billions more in taxpayer spending for bridge repair/replacement with the promise that SHM holds to reduce overall funding demand, Congressional staff must be totally confused.
Key Issues with Adoption and Deployment
There are three key issues at this time that are affecting full-scale SHM adoption and deployment: SENSE; CENTS; and SENSORS. These issues are explored in more detail in the following paragraphs.
SENSE in this context means exactly what it implies – SHM technology adoption and deployment must make sense to both the bridge engineering practitioners and their DOT leadership who rightly expect that full-scale SHM adoption and deployment will bring significant value to bridge management protocols already in place. There must be a compelling technical reason why SHM is considered for deployment on any given structure. Perhaps a third party NBIS inspection resulted in a recommendation for a substantial superstructure repair or even replacement based on observed section loss. Or, the latest NBIS inspection reduced the superstructure rating from six to four in one cycle. Or, the latest NBIS inspection suggested the structure be evaluated for a restrictive load posting. There are many other situations where SHM deployment should be considered, but most importantly, bridge engineers should be able to offer confident assurance to DOT management that SHM will provide actionable information when the monitoring and data analysis have been completed.
CENTS in this context means that deployment has a high probability of providing the owner with an ROI. When an SHM technology project is provided by a University, there is typically no expectation of a quantifiable return on investment in the ensuing five to ten years. However, when SHM technology is provided by a commercial supplier, there must be an expectation of an ROI, or there is no value delivery and no business viability. Commercial use of SHM is not research; it has to provide results for the owner and taxpayer, who fund SHM deployment. It can be concluded at this point that State DOTs will inevitably adopt SHM when a series of projects proves the financial value of its use. While that adoption and deployment decision will necessarily include some engineering judgment, DOTs cannot ignore the financial benefits of a safe deferral of major repair or replacement projects or avoiding restrictive load postings that provide immediate economic benefits for major employers in their state.
SENSORS is this context means that the right sensors for the right reasons in the right quantities are essential if commercial SHM suppliers expect State and local DOTs to routinely specify, purchase and utilize SHM technology. In the past, too many sensors led to data overload and expensive/lengthy analysis, which is not in the owner’s best interest. Also, using the wrong sensors leads to non-actionable information, making an ROI impossible to achieve. As full-scale adoption and deployment of SHM technology gains momentum over the next five years, the following five “that matters” points are made with total confidence:
It’s not the manufacturer of an installed sensor that matters; rather whether that sensor produces actionable intelligence for the owner.
It’s not how many sensors are installed that matters; rather how few sensors it takes to meet the owner’s need.
It’s not how much data can be captured that matters; rather whether the right data is captured at the lowest reasonable frequency.
It’s not how long SHM data analysis takes that matters; rather how quickly actionable intelligence can be extracted from SHM captured data.
It’s not how much SHM technology costs that matters; rather how much value SHM technology delivers.
Overcoming Slow Adoption and Deployment
This paper concludes with some hard-hitting recommendations that will speed the adoption and deployment of SHM technologies. First, FHWA and AASHTO need to provide unwavering support for SHM technology in the context of a comprehensive Transportation Asset Management Plan; through policies, information exchanges, speeches, testimonies, and reports to Congress. Second, Congress should consider providing modest funding incentives for rapid adoption and deployment in the next Transportation Bill. Third, commercial providers must only promote the judicious use of SHM technology, not as a replacement for NBIS bridge inspection or inspectors. Fourth, both commercial suppliers and owners must have a laser-like focus on achieving an ROI for every structure where SHM technology is used. Fifth; owners, commercial suppliers, FHWA and AASHTO must be willing to publicize results from SHM deployment, both good and bad. The more positive results that are publicized, the faster the adoption rate will be, but everyone will benefit from lessons learned on projects that were technically unsuccessful or did not provide an adequate return on investment.
In closing, it may be enlightening to consider the ramifications of continued delay for SHM technology adoption and deployment. As new technologies are developed and commercialized, they take a well-worn path that has significant implications for liability exposure, especially in the public sector, which has always relied on the liability protection offered by state sovereign immunity statutes. As this author and a colleague explained six years ago in Professional Engineer Magazine (4), there comes a time when civil engineering technology advancements become standard of care for professional engineers. After nearly twenty years of conferences, articles, papers, speeches, presentations and pilot projects, continued delay in adopting and deploying SHM technology will assuredly expose jurisdictions and practitioners to liability that may not be defensible, even under well-established state sovereign immunity laws.
(1) Phares B.M., et.al., “Reliability of Visual Bridge Inspection”, Public Roads Magazine, March/April 2001.
(2) Phares B.M., et.al., “Studying the Reliability of Bridge Inspection”, Public Roads Magazine, November/December, 2000.
(3) Walther, R.A. and Chase, S.B., “Condition Assessment of Highway Structures”, Dynamics and Field Testing of Bridges Committee, TRB Annual Meeting, Washington, D.C., 2005.
(4) Vanderzee, P.J. and Loulakis, M.B. Esq., “Technology Adoption and the Standard of Care”, Professional Engineer Magazine, 2008.