Bridge Monitoring Systems

By: Christopher Huck, Abigail Browder, Phillip Sutter

For: CHA Consulting, Inc. – Transportation Structures

8/5/2014

Abstract

With steel bridges representing approximately 34 percent of the over 600,000 highway bridges in

the United States, continual monitoring and early detection of deterioration in these structures is

vital to prevent expensive repairs or catastrophic failures. As one may be aware over two

hundred million trips are taken across deficient bridges each year. In total, one in nine of the

nation’s bridges are rated as structurally deficient, and the average age of the 607,380 bridges in

America is 42 years. The Federal Highway Administration estimates that to eliminate the

nation’s bridge deficient backlog by 2028, the government would need to invest $20.5 billion

annually, while only $12.8 billion is being spent currently.

Typically structures at risk for catastrophic failure are susceptible to scouring, fatigue,

progressive cracking or any other progressive structural deficiency. Bridge monitoring system(s)

(herein referred to as BMS) can determine structural integrity and warn of excessive and sudden

impact loading. Additionally, monitoring systems can provide overall bridge health information

such as wind speed, three-axis acceleration, humidity and strain loading. These systems provide

the advantage of having the ability to locate damage in areas where access is limited or

impossible. The data collected on a daily basis will help owners and maintenance authorities

make rational decisions in allocating maintenance and repair of bridges.

The goal of this study is to determine if/ how CHA may use BMS to improve and expand our

bridge inspection/evaluation capabilities and services we can offer. The research looks into the

various technologies that are on the market, limitations BMS might have, how others are

currently using it and its possible advantages to bridge owners and CHA. The primary

deliverable will include determining the feasibility of CHA using BMS to expand market share,

up-front/ development costs that CHA would need to expand and the potential benefit to CHA.

Table of Contents

Introduction 1

Bridge Monitoring Technologies 1

BMS Services by other Consulting Firms 2

Case Studies 4

URS 4

IIS, Pennoni 5

Advantages to the Owner 7

Services CHA can provide 7

Cost 8

How are Bridge Owners Using BMS 8

Research and Development Use 9

Conclusion 9

Appendix

Table of Figures

Figure 1: Sensors Required per Span 8

Figure 2: Real world application and layout 8

(Performance Monitoring, Gangone, Whelan, Fuchs, Janoyan)

1

Introduction

Metal fatigue in bridges begins with tiny fatigue cracks caused by the constant movement of car

and truck traffic. These cracks usually initiate at the fatigue prone areas of the bridge and grow

under repetitive loads until they can reach a critical size and eventually cause structural failure.

To tackle this problem, engineers require the ability to determine the presence of fatigue cracks,

calculate the rate of growth, and identify at what stage of fatigue the structure is in. They also

need to track many other things that can contribute to failure. Currently most companies and

agencies use only visual inspection as a means of making sure the bridges are safe and

adequately aging with no/minimal signs of deterioration. Sreenivas Alampalli of NYSDOT says,

“Bridge Monitoring using instrumentation is only used occasionally, on a bridge-by-bridge basis,

when there is a need for such monitoring to supplement visual inspection data. “

Bridge Monitoring Technologies

Bridge failures are typically monitored through visual inspections and nondestructive testing, but

now new technologies are being used to help improve the accuracy and preventive techniques for

bridge monitoring. The typical BMS available are the sensors presented for smart bridges. This

wired system monitors the possible bridge failures as well as the overall structural health of the

bridge. This can be seen on the 1-35W Saint Anthony Falls Bridge, which allows for the

maintenance to occur sooner before bridge maintenance issues become costly. The sensors are

connected through a network of cables to transmit the data, which creates high initial installation

costs, and can limit the placement of some of the sensors. The I-35W Saint Anthony Falls Bridge

contains a total of 62 sensors, which include 26 accelerometers, 12 linear potentiometers, and 24

strain gauges spread over the 1,200 foot span of the bridge.

The accelerometer uses vibrations to account for the vertical movement of the bridge, the linear

potentiometers are used to account for the movement associated with the expansion or

displacement of the joints. The strain gages were embedded in the concrete to measure the tensile

and compressive stresses. They were inserted while the concrete was curing. The sensors were

synced with the data acquisition systems that had to be placed at each of the eight nodes on the

bridge. A node is an area of the bridge that is a major stress point, such as at each of the piers as

well as the worst loading case, which is the center point between any given set of piers and

abutments. All the nodes are then synced to a timer for accurate data retrieval. This technology

can total also be seen on the Bill Emerson Memorial Bridge in Missouri which totaled a typical

cost of $1.3 million dollars, but this bridge was 2,086 ft long, nearly doubling the span of the I-

35W bridge.

An alternative to the expensive wired sensor system would be the new low cost wireless smart

sensors on the market. This is a cheaper alternative and can be more easily applied to the

thousands of aging bridges currently in the US. This technology was first implemented on the

Jindo Bridge in Korea in 2009, in a joint venture with University of Illinois-Urban Champaign.

This bridge contains 71 nodes and 427 sensors. Sensor boards were added to measure

accelerations, temperature, humidity, and light. (University of Illinois) Accelerometers and ultra-

sonic anemometers were added later. This increased the number of nodes to 113. This type of

monitoring system measures the modal properties of the bridge to monitor structural

performance and damage conditions. The system, can also monitor the tension force in the cables

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using a vibration method. The cost of the wireless sensors is significantly lower, $100 versus

$15,000 per sensor. This allows for more sensors to be added to a given structure for improved

data collection of bridge monitoring information. With improvements in data retrieval, small and

large engineering firms are entering the market of BMS services.

BMS Services by other Consulting Firms

There are two different consulting firms that will be presented here.

URS is a global consulting firm of more than 50,000 employees. At the time of this paper,

AECOM has announced the acquisition of URS. Based out of Maryland, URS has complete in-

house capabilities. They “own multiple state-of-the-art test control and data acquisition systems

with wireless communication and solar capabilities, plus a suite of sensors and transducers for

the measurement of strain, displacement, crack movement, tilt, acceleration, and temperature.”

“Since 1994, URS has evaluated over 80 bridges of different structural types across the United

States using a variety of instrumentation and/or analysis techniques.” URS’s division of bridge

instrumentation and evaluation was started by a PhD in 1994.

URS offers the following applications through their division of bridge instrumentation and

evaluation:

Load Rating for Strength Evaluation: Helps understand actual structural behavior to

identify and quantify inherent load carrying mechanisms that are not considered in

conventional analysis. Usually results in improved load ratings.

Fatigue Life Assessment and Crack Repairs for Steel Bridges: Field measurement of

stress histograms at areas of concern quantify live load and temperature effects for

evaluation and retrofit of fatigue cracks, or assessment of remaining fatigue lives.

Tension Assessment in Cables or Post-Tensioning (P-T) Bars: Nondestructive Taut Cable

Vibration Measurement (TCVM) method for accurate determination of existing tension

in cables or Post-Tension bars.

Diagnosis/Retrofit of Structural Problems: Field measurements of key strains, movements

of aged/dysfunctional expansion bearings/joints, opening/closing of existing cracks, or

structural vibration characteristics are used to diagnose and develop effective retrofit

solutions.

(Continuous) Structural Health Monitoring: Provides value to bridge maintenance and

repair decisions using strains in and displacements/tilt of key elements, movement of

expansion bearings, and vibrations of flexible members reflect actual structural behavior

as well as magnitudes and distribution of loads including vehicles, temperature, and

winds.

Balancing, Performance Evaluation, and Problem Diagnosis of Movable Spans:

Balancing of trunnion-type bascules, lift, rolling lift, or swing spans can be evaluated

3

through field instrumentation by continuously recording the torque in the driving shafts

and/or hydraulic pressures in the driving cylinders as well as the motion of the leaves

during opening and closing.

Courtesy: URS Literature by

Y. Edward Zhou, PhD, PE

National Practice Leader - Bridge Instrumentation & Evaluation

Intelligent Infrastructure Systems (IIS) got its start in Philadelphia from two PhD’s from Drexel

University and they are still principals in the company today. At some point IIS became a

subsidiary of Pennoni Associates also based out of Philadelphia through an acquisition. Pennoni

Associates now employs more than 950 people. IIS’s goal is to be their own company in order to

better market their services to a wide range of companies instead of just Pennoni Associates.

Today, IIS uses PhD’s and PE’s to analyze a bridge and work with the bridge engineer to

develop a solution.

IIS offers the following applications:

Structural Testing

o Emergency Assessment Response (Fire, impact, etc.)

o Assessment of Overload Vulnerability

o Advanced Load Rating

o Prognosis of Deterioration & Structural Damage

o Seismic Vulnerability Assessment

o Vibration Diagnosis & Mitigation

o Identification of Critical Members

Structural Health

o Structural Health Monitoring

o Continuous Performance Monitoring

o Fatigue Assessment & Monitoring

o Construction & Retrofit Monitoring

Asset Management

o Asset Management

o Clustering & Stratification to Guide Maintenance

o Development of Custom Inspection Procedures

o Operation Management

o Risk-Based Prioritization for Maintenance & Replacement

o Support for Maintenance & Capital Improvement Programs

Courtesy: iisengineering.com, pennoni.com &

Andrew Katz, CPSM

IIS Marketing Manager

4

Case Studies

A few case studies from each firm are presented below.

URS:

North Carolina (2008-2010) – 9 bridges statewide:

o Finite Element Analysis and Diagnostic Load Testing for Load Rating: Bridges

constructed between 1930’s and 1950’s including steel beams with non-

composite RC deck, reinforced concrete (RC) slab, RC box culvert, and RC T-

beams. Previous analysis based on conventional methods resulted in weight

postings. Analysis resulted in weight postings being removed with specific repair

actions recommended for identified deteriorations.

Allegheny County, PA (2012-2013):

o Continuous remote wireless monitoring and performance evaluation of steel deck

truss:, A 12-month analysis was performed on this three span continuous,

riveted steel deck truss with a pin connected suspended span built in 1940.

Powered by solar energy the testing included displacements at truss expansion

bearings and pins, tilt of a pier and rocker bearings, and strains in select truss

members due to daily and seasonal temperature changes. A 3-D finite element

model was also established for correlation. Results provided guidance to load

rating and rehab alternatives.

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Maryland (2006-2011) – I-68 over MD Route 55:

o Field instrumentation/monitoring and fatigue evaluation and retrofit of welded

steel girder bridge: Previously repaired connections had reoccurring distortion

induced fatigue cracks between the main girders and floor beams. Scope

included special inspections, finite element analysis, field instrumentation and

wireless monitoring, development of fatigue retrofit concept, and verification

load test using multiple test trucks upon completion of retrofit construction.

Courtesy: URS Literature by

Y. Edward Zhou, PhD, PE

National Practice Leader - Bridge Instrumentation & Evaluation

Intelligent Infrastructure Systems (IIS):

Throgs Neck Bridge, NY

o Seismic Study & Suspended Span Deck Replacement Feasibility Study: Pennoni

provided engineering services and field instrumentation testing for the ambient

vibration monitoring and modal characterization of the Throgs Neck Bridge. This

identified 3D model shapes for the towers and main suspended span

superstructure. The instrumentation plan was designed based on previous

experiences with long-span bridges in order to best mitigate the uncertainty in

field testing of large constructed systems.

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Easton-Phillipsburgh Toll Bridge

o Rehabilitation Concept/Scoping Study: Opened to traffic in 1938. The main river

bridge consists of a 540-foot Petit through-truss span over the river, a 430-foot

five-span plate-girder viaduct at the New Jersey approach, and a 40 foot pre-

stressed concrete box beam span over Pennsylvania Route 611 on the

Pennsylvania approach. In 2010, the Delaware River Joint Toll Bridge Commission hired Pennoni Associates to evaluate the condition, vulnerabilities and

performance of the bridge through a comprehensive approach that merged

conventional engineering practices with advanced sensing and simulation

technologies. High speed strain gages were used to capture live load response,

vibrating wire gages to capture temperature induced response, and a suite of

accelerometers to capture ambient vibration response. Each of these sensing

applications were developed to inform the most uncertain aspects of the

bridge’s performance and were designed based on the results of a series of

simulations from a detailed 3D finite element model. These sensing and

simulation studies were able to demonstrate that the live load stresses in the

critical tension members were quite small and that the bridge (under current

operating conditions) can be expected to have infinite fatigue life. Additionally, it

was demonstrated that the floor system and wind braces were acting

redundantly with the bottom chord, so significant reserve capacity was available.

Given the desirable performance observed, no major retrofit was required.

However, to ensure that the bottom chord redundancy was maintained, some

repairs to deteriorated connections within the wind-bracing system were

recommended.

Courtesy: Pennoni.com

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Advantages to the Owner

BMS “help owners to assess aging infrastructure using advances in information, sensing and

communication technologies that have developed over the past decade.” “Given the very high

concentration of aging transportation and water infrastructure in the Northeastern US, many

infrastructure owners find themselves with extensive maintenance and preservation needs but

limited funding.” Through integrated simulation, sensor and information technology approach,

BMS can provide detailed and reliable information on the actual integrity of specific bridges.

This can directly aid clients in making sound business decisions on how to best spend their

limited financial resources. In addition, BMS can also assist in providing detailed maintenance

and/or renewal plans that focus resources where the largest benefit is possible. This allows

bridge owners to focus their rehabilitation, renewal and presentation efforts, as well as their

valued funding, on the precise areas of the inventory that need it the most. Applying continuous

bridge monitoring can possibly reduce the amount of inspections as well as the ability to flag

something that is not right. It is a great supplement to visual inspections and can allow the visual

inspections to be focused on a certain issue that was flagged by the system. Given these benefits

how can CHA get involved?

Courtesy: pennoni.com & campbellssci.com

Services CHA can provide

CHA expansion into new markets is critical for future growth as well as a more widely known

brand. BMS can provide the opportunity for the transportation structures group to expand and

become more diverse. Using BMS as a base, it is also possible to develop systems for other

sectors within CHA. Some of these markets include Gas and Utilities, Rail and Aviation.

Since CHA currently does bridge work in Colonie, Buffalo, Indianapolis, Rocky Hill, Evansville,

Atlanta, Scranton, South Bend, Nashville and Columbus it would be fairly easy to expand and

get these systems into those locations. The main contingency that controls this whole operation is

whether or not CHA can partner with a software engineering or development firm to design and

build a central database system. Assuming this can be developed; all regional and mobile offices

can communicate with this database and share information regarding the network of national

bridges.

Another service CHA can provide with this system is consulting. This would mean going after

existing clients with new services as well as new services to new clients. (Courtesy to Mark

Tebbano for the business building outline). CHA would provide: program formulation and

planning, design of a system, implementation, and analysis. Professional engineers and project

engineers would oversee the first three items of that list and technicians would handle the

analysis and going out to the bridge and gathering other information/checking sensors for

damage and wear. This lowers the cost per person working on the project in hopes of complying

with the Pareto Principle or 80/20 rule and keeping project costs down.. If this cannot be

achieved in-house, CHA would need to subcontract it out to another firm or acquire a firm that

has this technology already and let them run it

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Cost

It is hard to gather a figure for what all this would cost but a rough estimate would be 0.1%-0.3%

of construction cost for a new bridge (Sétra) and to retrofit would be the total cost of all the

sensors needed plus 20% contingency. This percentage comes from odds and ends needed to

complete the system in which we don’t know the quantities yet. Additionally, the cost of

developing the database, training people and labor costs cannot be determined because the

quantities are not yet known. One thing is for certain; a wireless system is a lot cheaper than a

wired system, which as one can probably deduce, has wires that run the length of the span.

Fig. 1

From the Fig. 1, one can see that in general a BMS system has a fairly linear relationship

between number of sensors and spans in the bridge. However, this can change according to the

job and what the bridge owner wants to monitor.

How are Bridge Owners Using BMS?

As stated above, the number of sensors directly depends on what the owner(s) want to measure.

Generally standard practice on smaller bridges, one to two pans, is to measure 3-axis acceleration

and strain. On larger bridges such as cable stays and greater span lengths, temperature (both

ambient and of the structure), humidity, wind speed/direction, vehicle weights/heights, corrosion

activity, joint movements, vibrations, tilt, and fatigue are also measured. Right now BMS is not

widely used except on large bridges, which is not feasible for CHA to take on at this time. In

talking with more people about the topic, it is becoming apparent that this technology needs

more time in R&D before becoming widely used.

Fig. 2

0

200

400

600

800

1 2 3 4 5 6 7 8 9 10

Sen

sors

Spans

Sensors Required per Span

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Research and Development Use

Michael Brown of the Virginia Center for Transportation Innovation and Research said they are

“Using such a system to monitor structural stability and movement during the re-decking of a

pair of large delta-frame steel bridges. We have also used such systems (selectively) in the past

to assist in load rating of structures.” He also went on to say, “We conduct research, evaluations,

provide technical assistance, and provide training within those agencies. We evaluate emerging

technologies and look for ways that they may be applied to VDOT operations.” As far as any

concerns he may have, he said he doesn’t have any particular concerns about bridge monitoring

as a practice, so long as it is applied in a rational and targeted manner to answer specific

questions or concerns. He does not believe that a general practice of putting a suite of sensors on

every bridge would be helpful or practical.

The FHWA (Federal Highway Administration) has a program called NDE (Non-Destructive

Examination). Here they use BMS and modify its usage to capture different aspects of bridge

design and wear. They are testing a system to better detect and evaluate fatigue cracks in steel

highway bridges. They are also trying different ways to integrate nondestructive evaluation more

fully into bridge management systems. Some of these techniques include: Development of Dual-

Band Infrared Thermography Imaging System for Bridge Deck Inspection, Ground-Penetrating

Radar Imaging for Bridge Deck Inspection, Acoustic emission monitor, thermo-graphic imaging

for fatigue cracks. Specifically for fatigue loading they have modified BMS to include forced

vibration responses and electromagnetic acoustic transducers.

Conclusion

The fact is that the existing methods are not good enough to make sure that our nation’s bridges

are safe for the millions of people that use them every day. There needs to be a way to inspect

bridges on a more regular basis so that when the government does start closing the gap on

funding, that money won’t be going to waste. The BMS fills that void and can provide real time

data to owners and operators all over the world. The potential to expand the global market and

presence means more money and more business.

BMS needs more time in R&D before CHA becomes involved. There are a lot of good

technological advances that have been made thus far but there are too many unknown factors that

still need to be determined before any investment is to be made. It seems feasible to do but CHA

needs more data and market research. Up-front development costs cannot be accurately

determined at this time but development and construction of a central database would be one

large cost. CHA would also need to consider expanding offices with bridge groups

and/or acquiring a firm which does this already and has all their own equipment and has a proven

track record. In the latter case, most of the what-ifs would be nullified and the question would be

what it would cost to acquire such a firm.

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Appendix

Central CHA Database

County Bridges

State Bridges City Bridges

Regional CHA Databases