Center Identifying Number

A491

Project Title

Bridge Asset Management Based on Life Cycle Cost Considerations

Principal Investigator
Institution
Telephone Number
Email Address

Raymond J. Krizek
Northwestern University
847-491-4040
rjkrizek@northwestern.edu

Ahmad Hadavi
Northwestern University
847-467-3219
a-hadavi@northwestern.edu

Pablo L. Durango-Cohen
Northwestern University
847-491-4008
pdc@northwestern.edu

David A. Novick
Professional Consultant

Yingchun Zhang
Northwestern University (Research Analyst)

External Project Contact
Address
Telephone Number

Project Objective

The main objectives of this project are to:

• Determine the achievable useful life for a bridge
• Develop guidelines for optimizing useful life
• Determine life cycle cost of a bridge
• Formulate a cost model for bridge life cycle cost
• Determine the design practice that leads to the lowest bridge life cycle cost
• Determine MRR practices that lead to the lowest bridge life cycle

Project Abstract

This is a continuation of the 2004 project to use historical cost data from a variety of geographically distributed bridges of different structural designs to (a) formulate a cost model for bridge life cycle cost, (b) assess the impact of deferred maintenance on bridge total life cycle cost, and (c) develop a supporting rationale for projecting the useful life of a bridge. The results of this work will provide critically needed supplemental input information for PONTIS and Bridge Life Cycle Cost Analysis (BLCCA), which both rely heavily on expert elicitation and engineering judgment, such as the cost and timing for various maintenance, repair, and rehabilitation actions, the probability of a condition changing from one status to another, the total life cycle cost, and the achievable useful life for bridge deck, superstructure, substructure, and bridge as a whole.

In the first twelve months, historical cost information for 21 Chicago movable bridges, 26 different types of bridges in California, and 4 bridges and 2 tunnels administered by the Port Authority of New York and New Jersey have been collected; the initial cost, MRR (maintenance, repair, and rehabilitation) costs, and the total life cycle costs for all of these structures have been determined; the selection of an appropriate cost index has been rationalized; most factors which may impact the total life cycle costs for the Chicago bridges have been analyzed; the distribution of annual maintenance cost for the Chicago bridges has been determined; the impact of delayed MRR actions on the total life cycle cost was also captured for two Chicago bridges; and a preliminary life cycle cost comparison has been conducted for 4 bridges and 2 tunnels of the Port Authority of New York and New Jersey.

Task Descriptions

Generate Cost Models for Bridges and Tunnels Studied by this Research

The original proposal described our intent to analyze the factors impacting total life cycle cost, quantify the relationships, and formulate a bridge life cycle cost model, which may be similar to the cost model for pavements.  Recognizing that the total cost for a bridge is more complicated than that for a segment of pavement, we will attempt to determine the relationship between initial cost and MRR cost, as well as the distribution of MRR costs among major items, including deck and structural repair, painting, machinery system, and electrical equipment.  We also will try to determine the relationships between cost items and internal features, such as length of the longest span, design load capacity, and so forth, as well as external conditions, such as traffic volume, bridge openings, etc.  Because such analyses require detail information regarding design and operation history, the first stage of this research will simply use regression technology to curve-fit the historical life cycle cost pattern and generate the cost model for the first 70 years or so of service life.

Summarize Design and MRR Practices that Reduce Total Life Cycle Cost

The initial proposal planned to determine the design and MRR (maintenance, repair, and rehabilitation) practices that lead to the lowest total life cycle cost, and further provide guidelines for bridge asset management based on life cycle cost considerations.  Based on historical data, the first stage of such research will summarize good design and MRR practices that obviously reduce bridge life cycle cost.

Milestones, Dates
(inc. Project Start & End Dates)

Period October 1, 2004– September 30, 2005

1. Oct. 2004 – Feb. 2005: Generate cost models for Chicago bridges
2. Dec. 2004 - Apr. 2005: Generate cost models for Caltrans bridges
3. Feb. – June 2005: Generate cost models for New York bridges and tunnels
4. June – July 2005: Summarize design practices that reduce total life cycle cost
5. July – Aug. 2005: Summarize MRR practices that reduce total life cycle cost
6. Aug. – Sept. 2005: Final report

Yearly and Total Budget

Total Costs - Current Year: $125,960
- Federal Share:           $60,000        6-Year Federal Share Total: $253,624
- Matching Share:        $65,960

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Undergraduate student: 8 hrs/wk

Graduate student: Yingchun Zhang, PhD

Relationship to Other Research Projects

This is the second twelve months of a two-year research project.

Technology Transfer Activities

Four abstracts have been accepted by three conferences held in 2005, which are the 4^th International Workshop on Life Cycle Cost Analysis and Design of Civil Infrastructure Systems, ACSE Construction Research Congress 2005, and AACE 2005 conference.  The final papers are going to be prepared and submitted on schedule in early 2005.

Potential Benefits of the Project

One of the major requirements for effective Asset Management is having the facts to identify potential problems before they develop, and the importance of Asset Management for transportation facilities cannot be overstated. America has invested more than $1 trillion in its highway system during the past 100 years. Without proper management of this critically important asset, it will not meet future structural and functional needs. Nationwide, there are nearly 577,000 bridges, the majority of which were built during two major bridge building periods – immediately before and during the recession (1920s and 1930s) and in the first two decades of the Cold War (1950s and 1960s). Hence, a large portion of this bridge system is aging and in need of maintenance, repair, rehabilitation, or reconstruction. Asset Management provides a framework for identifying the investment needed to operate and manage these facilities systematically and cost-effectively.

The most commonly used bridge management system in the U.S., PONTIS, is basically a data information system. Bridge Life Cycle Cost Analysis (BLCCA) is a framework of life cycle cost analysis methodology. PONTIS and BLCCA rely heavily on expert elicitation and engineering judgment, such as the costs for different MRR actions, the probability of a condition changing from one status to another, the total life cycle cost, and the achievable useful life for bridge deck, superstructure, substructure, and bridge as a whole. This type of data is critical to bridge life cycle asset management. To build a new bridge or preserve and improve an existing bridge cost effectively, either within a network or for an individual bridge, it is necessary to know the economic conditions that prevail, that is: how long will it last, and how much will it cost initially and over time. If we defer MRR, how much more might it cost eventually? This research is aimed toward answering these fundamental questions, as well as supplying background data to support the implementation of existing bridge management systems and economic analyses for investment decision-making.

This research is aimed toward (a) determining the asset value or total life cycle cost, as well as the achievable useful life, of bridges and (b) suggesting design, preservation, and improvement practices that lead to lowest life cycle cost. Such results are critical to bridge asset management and form the basis for economic decision-making. The results of this study will provide critically needed information for input to currently used bridge management systems such as PONTIS and bridge life cycle cost analysis such as that advanced in the recent NCHRP study.

TRB Keywords

Bridge management systems, Life cycle analysis, Life cycle costing, Asset management, useful life, Maintenance, Repair, Rehabilitation (maintenance), Reconstruction

Center Identifying Number

A499

Project Title

Development of Highly Fragmentable Concrete Using a No Fines Aggregate Grading Strategy

Principal Investigator
Institution
Telephone Number
Email Address

Hamlin M. Jennings
Northwestern University
847-491-4858
h-jennings@northwestern.edu

Jeffrey J. Thomas
Northwestern University
847-491-3201
jthomas@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

The goal of this project is to continue to develop and commercialize a new type of concrete that will disintegrate into small fragments (rather than fracture into large chunks) when subjected to sudden and severe loading. Because of the emphasis on preventing damage to buildings and people, this material has been dubbed "safety concrete."

Project Abstract

The project will focus on a new approach to the design of Safety Concrete with significant potential to improve the performance, which is based on the existing (but little used) technology of ‘no fines’ concrete, which consists of monosized aggregate particles coated with a layer of cementitious binder and held together only at interparticle contacts.  Initial experiments using the approach, with Safety Concrete binders and various gradings of aggregate, have been very promising.  The project will continue development of hollow Safety Concrete blocks by refining the new ‘no fines’ aggregate grading strategy.

Task Descriptions

Research for this year of the project will focus on the following:

1) Development of mix designs and processing methods that will allow hollow safety concrete blocks with the desired properties to be manufactured in bulk.  The basic ingredients for success are currently in place.

2) Regular large scale blast tests of full scale Safety Concrete walls at the Engineer Research and Development Center (ERDC)’s of the Army Corps of Engineers’ test site, and smaller scale blast experiments at the ERDC local test site may also be performed to determine the behavior of various designs.

Milestones, Dates
(inc. Project Start & End Dates)

October 1, 2004 to September 30, 2005

1. Q1: Source and order materials
2. Q1: Analyze results of statistical experiment to optimize aggregate grading. Conduct additional experiments as needed. Identify key variables.
3. Q1-2: Conduct experiments related to the formation of hollow blocks. Identify best procedure for mixing, molding, and curing to achieve rapid and reproducible results.
4. Q2-3: Conduct and intermediate-scale blast test at the ERDC using blocks made with the no-fines aggregate grading approach.  Correlate results to drop impact results.
5. Q2-Q4: Continued experiments on properties of hollow blocks, including stability of properties over time, ability to withstand shipping and handling, etc.
6. Q2-Q4: Research the cost of manufacturing, delivering, and installing safety concrete block walls.  Identify partner or contractor for commercial manufacturing.
7. Q3-4: Large scale blast test of a wall made from best available mix design safety concrete blocks. Create final report.

Yearly and Total Budget

Total Costs- Current Year: $148,000    
- Federal Share:         $74,000              6-Year Federal Share Total: $227,073
- Matching Share:      $74,000

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Graduate students: Julie Gevrenov, MS student from the Department of Materials Science and Engineering; Bentley Bradley, MS student; recruiting another graduate student for the project.

Undergraduate students: one undergraduate student. 

A group of undergraduate students are also involved in developing and performing a statistically designed experiment on the use of no-fines aggregate grading Safety Concrete as part of a required class project on Engineering Process Design.

Relationship to Other Research Projects

Continuation of "Safety Concrete" - A New Impact-absorbing Concrete for Protecting Buildings, Structures, and People", and "Safety Concrete" – A New Impact-absorbing Concrete for Protecting Buildings, Structures, and Vehicles project"

Technology Transfer Activities

For the purpose of this proposal, commercial success means that the results of the research are put into practice, not necessarily that a company take a license or some other money-making proposition. The ERDC will take the lead on the implementation of safety concrete.

Potential Benefits of the Project

This type of concrete that disintegrates into small fragments rather than fracturing into large chunks or cracks when subjected to impact loading will prevent or reduce damage to people and property.

TRB Keywords

Concrete, Barriers (Roads), Safety, Infrastructure

Center Identifying Number

A497

Project Title

Introducing Size Effect Into Design Practice and Codes for Concrete Infrastructure

Principal Investigator
Institution
Telephone Number
Email Address

Zdenek P. Bazant
Northwestern University
847-491-4025
z-bazant@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

The overall objectives of the project are:

1. Capitalizing on two decades of basic research funding of the writer's research of size effect at Northwestern University, demonstrate in journals and at conferences practical applications to design and testing.
2. Translate existing material models for quasibrittle fracture, capable of capturing the size effect, into subroutines suitable for use in computer codes in design, including commercial codes (which at present generally miss the size effect).
3. Formulate standard test procedures for concrete strength and fracture taking the size effect into account, and propose improved testing standards to ASTM, ACI and RILEM.
4. Based on the general theory already developed, construct simple design formulae for the size effect in various basic types of failure, suitable for use in design firms.
5. Work in engineering societies, particularly ACI, RILEM, ASTM and FIB (the specifications or recommendations of which are generally co-opted by AASHTO), and in the committees of ASCE which influence decisions, to introduce improvements in the respective code articles, one by one, beginning with design code specifications for shear failures of reinforced concrete structures and flexural failures of unreinforced concrete structures.
6. Formulate a statistically correct system of load factors for the code, suitable for use after the size effect is taken into account in code provisions.
7. Articulate the reasons and promulgate the necessary changes by tutorial presentations at conferences.

Project Abstract

The objective of the project is to improve the reliability, durability and structural efficiency of infrastructure by transferring the results of previous basic research on fracture mechanics of size effects in concrete structures into: (1) design practice, (2) design codes, (3) standardized materials testing, and (4) commercial computer programs. This is important for large-span box girders of prestressed concrete bridges and cable-stayed bridges, supporting piers, column footings and foundation plinths, as well as for road and airport pavements, earth-retaining walls, dams (which often carry highways) and tunnel linings. The design practices for ductile failures are not affected, but those guarding against brittle failures, which are currently still based on the plasticity-based theory of limit states, need to be updated for size effect according to fracture mechanics and random strength statistics. Furthermore, this goal requires introduction of a standard for fracture testing, which is not yet included among ASTM standards. The commercial computer programs for simulating concrete structures are generally still not yet based on fracture mechanics and do not take the size effect into account. Although the basic theory is now ripe, however, simple design formulas for particular design problems need to be developed, proper material testing procedures instituted, and simple ways of implementation in commercial computer codes proposed and promulgated. Moreover, the relevant committees of ACI, ASTM, RILEM and FIB, the specifications of which are generally followed by AASHTO, need to be convinced.

This is the third phase a three and one-half year project that will focus on conducting detailed analyses of some famous structural disasters which were blamed on other errors, and demonstrate that the size effect must have been a significant contributing factor.  A new design method that can capture the statistical part of size effect on the basis of standard deterministic finite element analysis.  Similarities with the failure of foundation plinth of Schoharie Creek Bridge on the New York Thruway, and failures of retaining walls, will be examined.  Second, a detailed computer analysis of the failure of the Koror-Babeldaob bridge in Palau, a prestressed box girder of world record span, will be initiated.  Efforts in ACI committees 445, 446 and 318, involving oral and written discussions, presentations at meetings, critical studies, etc., will continue.

Task Descriptions

Major tasks for this twelve-month period are:

1. Demonstrate the role of size effect in certain major structural disasters, which have so far been blamed exclusively on other mistakes.
• Search for precise information on material properties, structural dimensions, reinforcement, prestress level, loading, etc.
• Prepare a mesh and, using previous results obtained under NSF and ONR support, prepare a nonlocal finite element code capable of simulating distributed fracturing and cohesive fracture propagation
• Generalize the code for randomness of material properties, to capture the statistical part of size effect
• Evaluate the size effect, by comparing the nominal strengths predicted for the actual structures and scaled down structures of laboratory size.
• Interpret the results in a suitably simplified form that would appeal to the design oriented committees of ACI, RILEM and FIB.
• Compare the results to proposed design formulas for the size and articulate the consequences for adopting a proper formula for the design code.
• Study analogies, such as the failure of foundation plinth of the pier of Schoharie Creek Bridge
2. Based on previous research, prepare a proposal for a code specification on shear design of reinforced concrete beams without stirrups including the size effect and publish it in a design-oriented journal of ACI or ASCE.
3. To capitalize on successful voting and publication of the state-of-art report on size effect by the RILEM Committee QFS, "Quasibrittle Fracture Scaling" (chaired by Bazant), continue to push within RILEM for backing proposals for introducing a sound size effect formulation into the American and European design codes.
4. As member of ACI Committee 445, Shear and Torsion, persevere in arguing for the adoption of a realistic code formula for size effect in shear failure of reinforced concrete beams without stirrups, and expand the argument to code formulas for shear failure of beams with stirrups and for torsional failure.
5. In collaboration with ACI Committee 445, Shear and Torsion, analyze the size effect in beams without stirrups and demonstrate that even if stirrups are used, there still exists size effect – quite significant albeit reduced and pushed to higher sizes.
6. As member (and former founding chairman) of ACI Committee 446, Fracture of Concrete, prepare in collaboration with subcommittee 2 an unsolicited proposal for size effect in beam shear, competing with the proposal of ACI 445, and submit it to ACI 318 (code committee).
7. Argue within ACI that size effect needs to be introduced into all the ultimate load formulas for all brittle failures, the number of which is about twenty (including torsion, punching shear, prestressed beam flexure, retrofitted beams, columns, etc.), and promote establishment of a general task force for this purpose – by committee presentations, critical discussions, letter to editor, etc. Explore the possibility of getting a push by forming a committee of National Research Council (run by NAS and NAE) are coming up with a report advocating positive change.
8. As a member of the strength subcommittee of ASTM Committee C-09 (Concrete), update and improve the proposal (submitted last year) for a revision of the ASTM standard on the modulus of rupture (i.e., flexural strength), incorporating the size effect, and push it to the voting stage.
9. As member (and former founding chairman) of ACI Committee 446, Fracture of Concrete, articulate the advantages and disadvantages of various proposed methods for the standard fracture energy test, with a special attention to size effect, and prepare arguments for ASTM Committee C-09.
10. Continue the analysis of the necessary confining reinforcement of concrete columns (tied, spiral and tubular, including bridge columns) needed to suppress or minimize the strain softening response of concrete and thus to suppress or minimize the size effect, and report to ACI and in a journal on this problem.
11. Analyze the problem of reliability of design of quasibrittle structures of different sizes from the viewpoint of the shape of the far-off tail of the probability density distribution of structural resistance, based on the previous finding that the tail strongly depends on structure size; prepare a journal article on this subject and present the results at design conferences and in seminars with design and construction oriented audience.
12. Complete the study (begun in previous year) of the effect of boundary layer at the far side of the ligament of fracture test specimen, with the objective of compensating for the deleterious effect in the standard fracture test concrete, and argue adoption of the standard test.
13. Prepare a paper for the quadrennial 8th International Conference on Structural Safety in Rome, June 2005, to make the capacity reduction factors in design codes dependent on the degree of brittleness, as a function of structure size, and to introduce a design method based on failure probability and tail of probability density distribution of structure resistance (which depends on structure size).
14. As member of ACI Committee 447, Finite Element Analysis of Concrete Structures, promulgate improvements in standard finite element codes making it possible to capture the size effect (which means nonlocal modeling or incorporation of energetic concepts of fracture mechanics), and prepare a paper on this subject for an ACI Special Publication planned by the committee.
15. As member of the Scientific Committee, collaborate on the program themes for the 3^rd International Conferences on Bridge Management and Maintenance (IABMAS).
16. Prepare a paper for the 7th International Conference on Concrete Creep and Durability Mechanics, France, Sept. 2005, to present an improved formulation for creep and cracking problems in design. This work will also represent a continuation of the efforts under the writer’s preceding ITI grant, the objective of which was to introduce new advances in creep and shrinkage of concrete into design and codes.

Milestones, Dates
(inc. Project Start & End Dates)

October 1, 2004 to September 30, 2005

Task 1:   Q1 – Q4
Task 2:   Q1 & Q2
Task 3.   Q2 & Q3
Task 4.   Q1 & Q2
Task 5.   Q2 – Q4
Task 6.   Q2
Task 7.   Q1
Task 8.   Q1, Q3 & Q4
Task 9.   Q2 & Q3
Task 10. Q3 & Q4
Task 11. Q4
Task 12. Q2 - Q4
Task 13. Q1 & Q4
Task 14. Q3
Task 15. Q4
Task 16. Q4

Yearly and Total Budget

Total Costs - Current Year: $152,599
- Federal Share:         $81,000            6-Year Federal Share Total: $297,436
- Matching Share:      $71,599

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Graduate Students: Qiang Yu and/or V. Parik and/or Sze-Dai Pang. Both are graduate research assistants, working on their doctorates.

Postdoctoral fellows: Dr. D. Novak, Dr. G. Cusatis, and/or Dr. G. Grassl

Relationship to Other Research Projects

This is the last year of a three and one-half year project.

Technology Transfer Activities

Much of the focus of this project is on technology transfer through advancing updates to codes, advancement of new design and testing methods, and presentations at conferences.  The PI will be active in the relevant committees of ASTM, ACI and RILEM. Activities include promoting new and updated codes, design recommendations and testing methods as part of the ASTM Committee C-04 (Concrete) and subcommittee on strength testing; ACI Committee 447 (Shear and Torsion); ACI Committee 446 (Fracture of Concrete); RILEM Committee QFS (Quasibrittle Fracture Scaling). Additional transfer activities include writing journal articles and presenting papers at international conferences, such as for the 3^rd International Conferences on Bridge Management and Maintenance (IABMAS) and the 7th International Conference on Concrete Creep and Durability Mechanics, France, Sept. 2005.

Potential Benefits of the Project

According to the classical theories of failure such as elasticity with a strength limit of plastic limit analysis, a structure fails when the maximum stress reaches a certain critical value that is independent of structure size.  This simple concept is valid for many situations, for example the bending failure of a steel girder or the failure of tensile reinforcement in a reinforced concrete beam.  In modern concrete structures, however, there are many situations where this simple concept breaks down and the apparent material strength (or nominal strength) decreases with increasing structure size.  This is called the size effect.

There are two physical causes of size effect: 1) the statistical cause, consisting in the randomness of material strength; and 2) the deterministic cause, consisting in the release of strain energy stored in the structure into the front of a propagating crack. 

The basic theory of the statistical size effect, formulated by Weibull in 1939, was universally believed to be the only explanation of the size effects observed experimentally in concrete structures until the 1980s.  The belief is no longer universal.  A theory is now generally accepted by the leading researchers that deterministic size effect exists and is in fact dominant for all quasibrittle materials, not only concrete, but also rocks, ice, tough ceramics and fiber composites.  However, the theory has not yet penetrated general concrete practice, design codes, materials testing, or the commercial computer programs for structural design. 

The basic theory of the deterministic size effect was developed largely at Northwestern by the PI, under a series of grants from NSF, AFOSR and ONR.  It was presented in a recent textbook (Bazant and J. Planas, Fracture and Size Effect, CRC Press, Boca Raton 1998), and the advanced aspects in a monograph just published (Bazant, Size Effect on Structural Strength, Hermes-Penton, London 2002). The present project is aimed at bringing this new theory into practice.

TRB Keywords

Concrete, Infrastructure, Fracture mechanics, Design standards

Center Identifying Number

A486

Project Title

Improved Condition Monitoring for Bridge Management

Principal Investigator
Institution
Telephone Number
Email Address

David Prine
Infrastructure Technology Institute
847-491-2873
dprine@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

The objective of this program is to provide bridge owners with a set of advanced NDE tools so that they may better (more quantitatively and with improved repeatability) determine bridge condition, which is the primary input to a bridge management system.  These tools will consist of both equipment and procedures to aid in the inspection of critical bridge components.

Project Abstract

This project will continue the development of active monitoring technology for our remote monitoring sites, student / faculty support, and large structure instrumentation and testing. Our current student / faculty activities continue to represent a major portion of the total staff time. Growth of the remote monitoring technology that was started during Year 3 with the Michigan Street Bridge in Sturgeon Bay, Wisconsin continued. Major efforts included equipment upgrades for the Michigan Street Bridge for Wisconsin DoT. Remote monitoring will continue to be a major activity during the coming year. The web page for our remote site in Sturgeon Bay, WI is now active and represents the model for future remote monitoring efforts. Installation of the new instrumentation system was completed in July 2002 and the automated website is up and running. Software has been developed and tested in the laboratory that will detect and alarm on pre-selected data thresholds. When a pre-set alarm condition is detected, the system sends an E-mail or page to selected recipients. This software is installed at the local server that hosts the Michigan Street bridge web site.

The user group development effort maintains a strong involvement with the user community through meetings. Electronic communications via the Internet have also been very effective. Many of our new customers and potential deployment partners contact us because of our Internet presence. We are closely coordinating our user group efforts with the Mid-West Bridge Maintenance and Inspection (BMI) working group.

The field tests and demonstrations allow for development and refinement of the bridge monitoring technology. It also helps to forge working relationships with practitioners and provides a vehicle for strengthening the integration of the ITI staff/NU faculty team members by providing opportunity for field verification of newly emerging technology. The increased student involvement in this activity exploits the educational opportunities offered by providing hands-on experience by students under real field conditions and is becoming a major growth area. Both of these tasks (Users Group and Field Tests) also are the main marketing vehicles for additional commercialization efforts in the service area.

The emphasis for this funding period will be on expansion of the autonomous web-based active remote monitoring technology. This will be accomplished primarily through demonstrations to infrastructure owners. Additionally, a considerable amount of acoustic emission testing is anticipated.

Task Descriptions

Task 1. Field Tests and Demonstrations

This task is a continuation and expansion of the ongoing efforts in this area. A major portion of the effort will be focused on the continuation of the demonstration and evaluation of the remote monitoring technology that emerged in previous years' work. The automated internet-based approach will be demonstrated to both state and municipal DoT's.

The Bryte Bend retrofit project is under contract and work will be completed by the end of 2004.  We are assisting Caltrans in their evaluation and monitoring of this retrofit.  Our efforts in this program consist of applying and further refining the AE technique we developed during the earlier retrofit design and evaluation. During this year we evaluated 6 cross-frame connection sites prior to the application of the retrofit. We will complete the second phase of this effort during 2005 by re-monitoring the previously tested sites to confirm retrofit performance.  Also during this second set of tests we plan to monitor and record additional sites to provide baseline data for future reference 

We anticipate doing two field jobs on Kentucky bridges during 2005.

We also anticipate additional field work with Fish Testing and Inspection involving both strain gages and AE.

An area of increased interest among bridge owners is the automatic detection of potentially damaging impacts.  Inquires from both KY Dot and the Union Pacific Railroad will be followed upon and hopefully result in projects.

The revenue picture remains fairly bleak.  Most of the above field tests and demonstrations will be done for in-kind match with the exception of work with consultants like Fish Testing.  Hopefully sometime during the coming year Congress will finally pass the transportation Authorization Bill and the economic conditions will improve with state and local Infrastructure owners.

Task 2. User Group Development

The user group development work that was started in Year 1 and continues through the subsequent years is a vital part of this program.  It continues to provide guidance to the NU researchers and a valuable source of information exchange between bridge engineers from the various states as well as keeping the bridge engineers informed of the developments of our NU researchers.  The ever increasing restrictions to interstate travel that are imposed on State and Municipal DoT personnel have caused us to increasingly emphasize forms of communications other than the traditional topical meeting.  Specific activities will include the continued application of the H.323 teleconferencing technology to special topical meetings between NU researchers and various deployment partners, participation in various committees and working groups that are organized by other infrastructure and NDE groups, and Internet activities.  We will also continue to support the BMIWG meetings with this technology where appropriate.

Task 3. Educational Activities

This task will aid the development and growth of the educational activities started in previous years.  We will continue to organize and support educational tours to various infrastructure-related locations (fabrication facilities, historical bridges, construction sites, etc.).  Students and faculty are invited to participate in our field test efforts on a regular basis.  We have successfully worked with the freshman engineering design course participants and we plan to continue to utilize this valuable resource.  Both ITI and the students receive considerable benefit from these projects.  The EDC projects provide these students with valuable hands on project experience with the potential of greatly expanding the capabilities of our small bridge team staff.   Additionally, we also attempt to employ students (either work study or as temporary part-time employees) wherever possible.  We will also continue to provide support for graduate students who are involved with research activities under the direction of our faculty partners.

Milestones, Dates
(inc. Project Start & End Dates)

October 1, 2004 to September 30, 2005

Yearly and Total Budget

Total Costs- Current Year: $664,072
- Federal Share:       $395,000              6-Year Federal Share Total: $1,810,496
- Matching Share:    $269,072

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

We will continue to organize and support educational tours to various infrastructure-related locations (fabrication facilities, historical bridges, construction sites, etc.).  Students and faculty are invited to participate in our field test efforts on a regular basis. 

We also expect to continue to provide support for graduate students who are involved with research activities under the direction of our faculty partners.

Relationship to Other Research Projects

This is a continuation of prior years’ projects. 

We also expect to continue to provide support for graduate students who are involved with research activities under the direction of our faculty partners.

Technology Transfer Activities

Several marketable products have emerged from this work.  They include an improved acoustic emission bridge monitor (AEBM), and test services.  The test services include application of advanced NDE such as AE, Impact Echo, TDR, and strain gages as well as the installation and maintenance of remote monitoring systems.  In year five a new approach to scour monitoring emerged which has achieved acceptance at Caltrans and resulted in a major change in their approach to solving this problem based on the ITI developed technique.  This is an excellent example of successful technology transfer.

The feasibility of marketing these products has been shown by the response of the DOT NDE practitioners to the demo/field tests.  The first service commercialization was achieved in Year 2 with a $60,000 task order test services contract from Wisconsin DOT.  This was expanded in Year 3 to over $100,000 and included the remote monitoring system developed for the Sturgeon Bay Bridge.  An additional $150,000 two-year contract was added in 1997.  Another two-year $183,000 master contract from WI-Dot was finalized early in 2000.

The current economic downturn has had an adverse impact on the budgets of state transportation agencies, which in turn will negatively impact our revenue.  Out of state funding has become increasingly difficult to attain.  Furthermore decentralization with the accompanying demise of the central DoT office hasn’t helped matters.  The decentralization has been accompanied by an increasing dependence on consultants.  We have successfully worked with major consulting firms such as Hazlet and Erdal, Wiss Janey Elstner, Michael Baker, Lichtenstein, and recently Hardesty and Hanover.  We anticipate work in the coming year with Fish Testing Services.  Phil Fish, a long time associate is the founder of this growing business that provides testing services and consulting to infrastructure owners and construction firms.  We will continue to pursue and strengthen relationships with these organizations as well as actively pursue new state and municipal partners.  A high and growing level of user community involvement is key to maintaining and expanding the market and insuring relevance. We have demonstrated to this community our willingness to tackle new and challenging problems posed by them, and the resulting practical results have been enthusiastically received.  Our willingness to go out and climb on the bridges and struggle with the difficult conditions encountered there has placed us in a unique position of respect with the user community.

Potential Benefits of the Project

A major contribution to improved condition monitoring of critical infrastructure has been made through the development of remote monitoring technology under this program.  The first application occurred in 1995 in Sturgeon Bay, WI.  Since then great strides have been made in system complexity and improved reliability.  The numbers of long term sites and applications have continued to expand primarily because this technology addresses a need that is readily recognized by the infrastructure owners.  Safe economically practical life extension of critical portions of the infrastructure demands improved condition monitoring and the remote technology provides a solution to this growing need particularly when one considers the added problem of downsizing imposed on the owners and operators by budget shrinkage.  The ability to interrogate a remote site without actually sending an inspector out to the site is an obvious improvement over present methods.

TRB Keywords

Bridge management systems, Infrastructure, Monitoring

Center Identifying Number

A496

Project Title

Nondestructive Determination of Early-Age Concrete Properties with an Ultrasonic Wave Reflection Method

Principal Investigator
Institution
Telephone Number
Email Address

Surendra P. Shah
Center for Advanced Cement-Based Material
Northwestern University
847-491-7878
s-shah@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

The general objective of the research is to make the wave reflection method attractive for industrial application. This requires fulfilling two important requirements: (1) the WR-method must be capable of predicting the properties of concrete mixtures without calibration and (2) the equipment used for the WR-measurements has to be as portable and as inexpensive as possible.

The elimination of the need for calibration will be pursued by developing a material model that relates the reflection loss measurements and the mix design of the concrete to its compressive strength. The modification of the technical equipment for the WR-measurements will be done on the basis of commercially available test devices. A detailed description on how these two issues will be addressed by the proposed research is given in the following sections.

Project Abstract

The nondestructive, in-situ testing of early-age concrete properties is a crucial tool for monitoring the progress of many construction projects in the building sector. The application of such techniques can establish the earliest possible form removal from concrete construction elements, thereby opening highways to traffic, releasing prestress from steel reinforcement, or applying post-tensioning with greatest efficiency.

A nondestructive, ultrasonic technique, which measures the reflection loss of ultrasonic shear wave reflections from the concrete surface, was developed at the Center for Advanced Cement-Based Materials (ACBM). The focus of this research project is to develop a nondestructive field sensor for in-situ monitoring of the setting, hardening, and strength gain of cementitious materials.

The research here will immediately tie in with the results of the previous funding period. Special attention will be given to determining the need of the test method to be calibrated for different mix designs. It is our aim to merge the results of experimental studies and numerical modeling to create a model for predicting early-age concrete properties from in-situ wave reflection measurements.

The research will focus on the following:

I. Constitutive Model
- model for evolution of early age properties on basis of wave reflection measurements
- linking results of fundamental parameter study with numerical modeling
- eliminating need for calibration

II. Practical Application
- develop procedure to combine wave reflection method and temperature measurements
- full scale test on massive concrete structure
- further field tests

Task Descriptions

Part I. Development of Constitutive Material Model

The first part of the research is aimed at developing a constitutive model for the evolution of early-age concrete properties on the basis of the wave reflection measurements by interrelating the results of the studies on fundamental material parameters and the numerical modeling. For this constitutive model, the input parameters will be concrete mix design (w/c-ratio, cement type, additives), and the reflection loss measured in-situ on the structure. We will evaluate the potential of this type of model to predict the elastic modulus or compressive strength of early-age concrete without further calibration.

The aim of this part of the research is to develop a constitutive material model that can determine early age concrete properties based on the mix design of the concrete and the reflection loss measured in-situ at the structure. The final goal is to develop the model in a form that requires no further experimental calibration. The basis of the model will be the results of the study on the fundamental relationships between reflection loss and basic concrete properties and the results of the numerical simulation.

The model will be based on relationships originating from two different concepts. One important component will be the results obtained from experimental studies. The previous experiments investigating the relationship between the reflection loss and fundamental material parameters have shown that the reflection loss has a unique relationship to the gel-space ratio of the cement paste. This relationship was not found to depend on the w/c-ratio.

The second component is a set of fundamental relationships obtained from the numerical simulation of cement hydration and their relationship to the reflection loss. The simulations have shown that the reflection loss and the contact area of cement particles have a unique relationship independent from the w/c ratio. It was also found that compressive strength and contact area have the same unique relationship.

These two basic relationships will be incorporated into a model that will have the ability to predict early-age concrete properties, e.g. compressive strength. This part of the research will also determine if the identified relationships among reflection loss, gel-space ratio, and contact area are universal enough to be used for different cement types, curing conditions, admixtures, and aggregate types. Most likely, the model will have to be applied in combination with a database that provides the necessary information related to the individual applications.

Part II. Practical Application of Wave Reflection Method

In the second part of the research, the practical application of the wave reflection method will be given special emphasis. A concept will be developed that provides a procedure for relating reflection loss measurements taken at the near surface of a structure to the properties of other more critical locations. The key to this procedure will be temperature measurements on the structure in conjunction with a suitable maturity function. A large-scale experiment will be conducted to verify this concept. This experiment will be performed outdoors.

To more accurately investigate this phenomenon, experiments will be conducted to determine the influence of fine aggregates on the reflection loss behavior. The mortars tested previously contained mono-sized silica sand with a very small aggregate size. Additional experiments will be conducted with mortars containing different types of sand (larger aggregate sizes, lightweight sand, etc.), and the appropriate cement paste. The results of this part of the research is of particular importance for further development of the test method, since the influence of different sand types used in field concrete mixtures must be understood.

To facilitate the transition of the wave reflection method to field application, it is necessary to have reliable information about the ability of the test method to predict the bulk properties of a concrete structure from measurements conducted near the surface. In order to obtain this information, a large-scale laboratory test will be conducted. The concrete structure to be tested will consist of a massive and a slender section. The massive section will resemble concrete curing conditions of a massive structure with high heat of hydration, while the slender section will simulate concrete curing conditions of a slab with lower heat development (such as used for highway pavements or floors).

Part III. Field Testing

Within the frame of this research, field testing is considered as a continuation of the Parts I and II. The existing collaboration with Rocky Mountain Prestress, Denver, Colorado will be continued. A main focus of the field testing will be to solve questions regarding the need of the test method to be calibrated for certain concrete mixture compositions. The constitutive model to be developed in Part I of the research will be applied for the field measurements. Usually precast plants are using a range of concrete mixes for their applications and it will be the goal to determine if the test method can predict properties of this range of mixes without calibration. Because it might be necessary to calibrate the method for a certain range of concrete mixes, calibration experiments for certain mixes will be conducted in the ACBM lab before the actual field tests.

Another direction is to focus on highway paving mixes, which vary less than construction mixes do. ACBM will work within the Midwest Concrete Consortium to determine the number of different mixes used by various state DOT's in their paving and bridge construction. We will also continue to promote the wave reflection technology to these potential customers.

A third possibility is cast-in-place concrete construction, where depending on the application a broad range of concrete mixes are used. However, there is a trend on large projects, to establish a local batching plant to more closely control mix design. It seems logical, given the stage of wave reflection technology development, to establish a collaboration with a construction firm that undertakes such major projects, in order to limit the range of mix designs across which a calibration matrix must be developed.

The on-site field testing will yield information about the degree of calibration that is needed to monitor concrete properties with the wave reflection method, being used in conjunction with the developed material model.

Milestones, Dates
(inc. Project Start & End Dates)

October 1, 2004 to September 30, 2005

I. Material Model for Concrete
- 3^rd Q. 2004 - 1^st Q. 2005: experimental work
     * Selecting concrete mix designs
     * Determination of shear modulus and compressive strength
- 2^nd Q. 2005: formulation of material model
     * Determination of parameters for composite theory model
     * Implementing model data in spreadsheet software
- 3^rd Q. 2005: applicability: verification
     * Experimental work to verify strength determination with the material model

II. Selection and Adaptation of Test Equipment
- 3^rd Q. 2004 - 1^st Q. 2005: purchase of handheld device
     * Survey of market of ultrasonic testing equipment
     * Talking to manufacturers and obtaining quotes
     * Selecting suitable device
- 2^nd Q. – 3^rd Q. 2005: measurements with handheld device
     * Experimental work using new test device
     * Adapting measurement protocols to new test equipment

III. Field Testing
- after completion of first two phases, possibly end of funding period

Yearly and Total Budget

Total Costs- Current Year: $180,003    
- Federal Share:       $90,003              6-Year Federal Share Total: $315,458       
- Matching Share:    $90,000

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Graduate student: one

Post-doctoral fellow: Thomas Voigt

Relationship to Other Research Projects

This project builds on a prior research project, "Nondestructive Testing of Early-Age Concrete Properties with an Ultrasonic Wave Reflection Method".

Technology Transfer Activities

Once the material model for a small set of concrete materials is developed a more comprehensive field trial will be conducted. For these tests we will primarily focus on highway paving mixes, which vary less than construction mixes do.  ACBM will work within the Midwest Concrete Consortium to determine the number of different mixes used by various state DOT’s in their paving and bridge construction.  We will also continue to promote the wave reflection technology to these potential customers.

Another possibility is cast-in-place concrete construction, where depending on the application a broad range of concrete mixes are used.  However, there is a trend on large projects, to establish a local batching plant to more closely control mix design.  It seems logical, given the stage of wave reflection technology development, to establish a collaboration with a construction firm that undertakes such major projects, in order to limit the range of mix designs across which a calibration matrix must be developed.

In the organization of the field tests we will work closely with our industrial partners from the cement industry. The companies Holcim, Inc. and Lafarge Cement have good relationships to precast plants and construction companies, which will allow us to effectively approach potential partners for the field tests.

The results of the research will be published in appropriate journals to ensure the national and international outreach of the test method. The research work will also be presented at conferences dealing with testing and evaluation in civil engineering. Besides the presentation on national conferences or seminars organized by the Center for ACBM it is planned to attend one international conference to introduce the results to the international research community.

Results of the research conducted in the previous funding period include two separate presentations that were given at the RILEM International Symposium on Advances in Concrete through Science and Engineering, Evanston, USA, in March 2004. One of the contributions is part of the proceedings of this conference [1] and the other presentation was given within the meeting of the RILEM Committee ATC-185 on the advanced testing of cementitious materials during setting and hardening. ACBM is also involved in the preparation of a State-of-the-Art-Report on the wave reflection method for testing early age cement-based materials. This report will be published by RILEM in early 2005.

An overview about the research conducted on the field of the wave reflection measurements was given in a keynote talk at the conference on "Concrete under Severe Conditions: Environment and Loading, CONSEC’04 in Seoul, Korea. The keynote paper was published in the conference proceedings [2].

Details about the relationship between the cementitious microstructure and the results of the wave reflection measurements were published in the proceedings of the 5th International PhD Symposium in Civil Engineering that was held in June 2004, Delft, The Netherlands [3].

One refereed journal paper was published in June 2004 [4], and two papers were accepted for publication [5,6]. Several journal papers and conference proceedings article that cover the results of the entire research conducted so far have been published [7-10].

A great extend of the research conducted so far is subject of Thomas Voigt’s PhD thesis [11], which was submitted to University of Leipzig, Germany and successfully defended in September 2004. The thesis will be published shortly and will be provided to ITI as soon as it becomes available.

A number of five research papers were submitted to various journals and are currently under review.

Potential Benefits of the Project

The nondestructive, in-situ testing of early-age concrete properties is a crucial tool for the progress of many construction projects in the building sector.  The application of such techniques can establish the earliest possible form removal from concrete construction elements, thereby opening highways to traffic, releasing prestress from steel reinforcement, or applying post-tensioning with greatest efficiency.

TRB Keywords

Concrete tests, Nondestructive tests, Ultrasonic tests, Infrastructure, Construction

Center Identifying Number

A494

Project Title

Automated Deformation Monitoring – Autonomous In-place Inclinometers

Principal Investigator
Institution
Telephone Number
Email Address

Richard J. Finno
Northwestern University
847-491-5885
r-finno@northwestern.edu

External Project Contact
Address
Telephone Number

Advisory Board consisting of a number of professionals, representing contractors, engineers and owner representatives, including:

• Dr. Jerry Parola, Case Foundation
• Mr. David Weatherby, Schnabel Foundation Company
• Mr. William Hansmire, Parsons Brinckerhoff, New York
• Mr. Dimitrious Koutsoftas, Arup, San Francisco
• Dr. Robert Bachus, GeoSyntec Consultants
• Mr. Zenon Stuck, Department of Transportation of the City of Chicago
• Mr. Manoher Chawla, Department of Transportation of the City of Chicago
• Mr. Michael Wysockey, Thatcher Engineering (the support system subcontractor for the Ford Engineering Design Center)
• Dr. Bryan Sweeney, Haley & Aldrich, Boston

Project Objective

Work funded last year by ITI focused on developing an autonomous total station for measuring ground surface movements.  We propose herein to extend this concept to inclinometers – a labor intensive instrument used to measure lateral movements in a soil mass adjacent to an excavation.  To improve the state-of-the-art and practice of predicting and controlling ground movements associated with supported excavations and tunneling operations, and the consequent deformations of adjacent structures and utilities, we propose to automate the data collection, data transmission and interpretation of deformations associated with construction operations.  In particular, lateral movements in a horizontal plane at any depth can be obtained and processed automatically so that the results can be interpreted in a timely fashion and be input to a numerical procedure that is used to compute ground movements.

These improvements will be checked, and ultimately verified, in the field in real time during excavation for a project in Chicago, likely the Block 37 project in downtown Chicago. The successful deployment of such a system will supplement the capabilities of an automated total station.  This capability will remove more of the impediments that prevent the use of intelligent updating of performance data to control construction operations. These techniques will have application to any project where deformations must be measured to verify performance or control construction operations. 

Project Abstract

Many transportation projects require detailed performance monitoring as they are constructed. When optical survey points are used, this operation becomes labor intensive and time consuming, and the transmission of the data to interested parties is slow. Consequently, the information cannot be used during construction in a timely fashion.

One example where such data are routinely used is when making deep excavations or when tunneling in urban environments. A major concern in these projects is the impact of construction-related ground movements on adjacent buildings and utilities. The ground movements cause any structures within the affected zone to deform and possibly sustain damage. It is critically important to predict and control the magnitude and distribution of the ground movements that result from creating the underground space.

However, it is quite difficult, if not impossible, to use the observed movements for these purposes in a typical project where time is of the essence to a contractor. To obtain optical survey data, process it, and use it to "calibrate" the results of a finite element model is a time-consuming, and here-to-fore a trial-and-error, process. This updating process presently can be done with the commitment of a significant number of personnel, but cannot be accomplished in a time frame that provides useful feedback to a contractor during the normal pace of excavation activities.

Work funded last year by ITI focused on developing an autonomous total station for measuring ground surface movements, that involved developing a system that allows one to use a total station to automatically sense the lateral and vertical movements of optical survey points, to transmit the data to a remote location where it can be automatically processed, and to present the data in such a way that meaningful interpretations can be easily made. This capability will remove some of the impediments that prevent the use of intelligent updating of performance data to control construction operations.  This project will extend this concept to inclinometers – a labor intensive instrument used to measure lateral movements in a soil mass adjacent to an excavation.

Task Descriptions

Purchase an in-place inclinometer system manufactured by GEODAQ, Inc.

Test an inclinometer developed by Prof. Michael Mooney from the Colorado School of Mines.  This system uses a low-cost MEMS based sensor for measuring tilt.

Develop software needed to acquire and process the measured data from a remote site (design office) and test the system under field operating conditions at the excavation for the Block 37 development.  Software must be developed to obtain a traverse of an inclinometer, to transmit and store the data in a remote host computer program and to develop a graphical representation of the data so that an interpretation of the results can be quickly made.  Data processing includes conversion of the proprietary GSI data format to universal ASCII format.

We will develop a remote host program which will initiate the reading cycle, obtain the tilts of each transducer in the case of fixed transducers or to obtain the data from a traverse of the winched-driven inclinometer, and send the data back to the host program.  This data can be processed by evaluating relative movements between an initial set of data or an initial traverse to compute the lateral movements at each elevation sensed by the system.  We plan to do this by transmitting the data over a phone line, which in many urban construction sites is the best way to accomplish this task, and to use wireless data transmission, which is better for remotely located sites, such as highway or railroad bridges.

We will use a geographical information system to store the data and to present it in a graphical form.  This data conversion and plot creation will allow for the displacement data to be used in several applications and analyses and to be accessible to multiple users.  Within the program at the host computer, we will compare results of the autonomous inclinometer with conventional inclinometer results taken at the site as part of the monitoring program for the project. 

Test System in Field

Once the system has been tested in the laboratory to check the coding, we will install GEODAQ system in the field at the Block 37 project site.  Costs associated with installing the autonomous inclinometer are included in the budget.  This system will be placed within several feet of a conventional inclinometer so that direct comparisons can be made.  This will allow us to evaluate the accuracy of the data within the context of conventional measurements at a construction site.

The scheduled start of the Block 37 project is March 2005 and the excavation portion of the work should last for about 1 year.  We plan to have the coding for the inclinometer within the first two months of the project so that the inclinometer can be deployed very close to the start of significant construction activities.

Milestones, Dates
(inc. Project Start & End Dates)

The scheduled duration of this work is from October 1, 2003 through September 30, 2004. Construction for the Ford Motor Company Engineering Design Center is scheduled to begin in mid-October with the excavation and backfilling operations to last approximately 9 months. We plan to have the coding for the total station done within the first month of the project so that the total station can be deployed very close to the start of significant construction activities.

Data will be collected throughout the excavation and backfilling period, and adjustments to the coding will be made as necessary. We will work initially to establish the phone link as the interface between the total station and the host computer, and we expect that that will be accomplished before start of construction. We estimate that it will take about 3 months to establish a wireless link. It will be important to maintain the system through the winter months to evaluate its robustness and develop, if necessary, means to "harden" the device to the elements.

Yearly and Total Budget

Total Costs - Current Year: $1,085,000
- Federal Share:            $85,000              6-Year Federal Share Total: $169,363
- Matching Share:     $1,000,000

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Graduate student: one

Relationship to Other Research Projects

Continuation of "Automated Deformation Monitoring" project.

Technology Transfer Activities

We propose to present our results to an advisory board consisting of practicing engineers, contractors and owner's representatives to provide review for the results of the research and to assure that the results are relevant to engineering practice. This board has been formed as part of the PI's National Science Foundation grant entitled "Objective updating of design predictions for supported excavations using construction monitoring data." This board meets annually, and the results of this work will be presented to them as part of the annual meeting scheduled in October of each year.

The principal investigator will present the results of the study to professional societies both locally and nationally. Papers will be submitted to journals and future conferences to further disseminate the findings.

Potential Benefits of the Project

When designers are faced with an excavation where ground movements are an important issue, they can estimate movements using either semi-empirical methods based in part on past performance data or results of finite element analyses.  The latter approach has become much more common for excavations in urban environments.  For example, designers and contractors conducted finite element analyses of excavations for many sections of the Central Artery/Tunnel project in Boston.  However, such predictions contain uncertainties related to soil properties, support system details and construction procedures.  In many instances, contracting practices dictate that the contractor is responsible for temporary support systems, and designers usually do not have sufficient control over important details in the construction process.  Given these uncertainties, it is usual to include a monitoring program during construction to record the ground movements and, in some cases, adjacent building movements.  These observations can be used to evaluate how well the actual construction process is proceeding in relation to the predicted movements.  Ideally, these observations also can be used to control the construction process and update predictions of movements given the measured deformations at early stages of constructions.

However, it is quite difficult to use the observed movements for these purposes in a typical project where time is of the essence to a contractor.  To obtain optical survey or inclinometer data, process it, and use it to "calibrate" the results of a finite element model is a time-consuming, and heretofore a trial-and-error, process.  This updating process presently can be done with the commitment of a significant number of personnel, but cannot be accomplished in a time frame that provides useful feedback to a contractor during the normal pace of excavation activities.   Developing an autonomous total station for measuring ground surface movements will be highly beneficial in monitoring movements.  We propose herein to extend this concept to inclinometers – a labor intensive instrument used to measure lateral movements in a soil mass adjacent to an excavation.  To improve the state-of-the-art and practice of predicting and controlling ground movements associated with supported excavations and tunneling operations, and the consequent deformations of adjacent structures and utilities, we propose to automate the data collection, data transmission and interpretation of deformations associated with construction operations.  In particular, lateral movements in a horizontal plane at any depth can be obtained and processed automatically so that the results can be interpreted in a timely fashion and be input to a numerical procedure that is used to compute ground movements. 

TRB Keywords

Deformation, Monitoring, Inclinometers, Excavation, Construction, Automatic data collection systems, Infrastructure

Center Identifying Number

A495

Project Title

Experimental Verification of Guided Wave Solutions for NDE of Concrete

Principal Investigator
Institution
Telephone Number
Email Address

Richard J. Finno
Northwestern University
847-491-5885
r-finno@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

To extend non-destructive techniques to allow application of higher frequencies, and hence create the ability to sense smaller defects, it is proposed herein to experimentally verify the recently-published numerical solutions for flexural wave propagation in cylinders and plates and for longitudinal propagation in plates.

Project Abstract

The purpose of this project is to experimentally verify guided wave methods to non-destructively evaluate the condition of concrete components of bridges, including columns, foundation elements and bridge piers.  Many times one cannot access the top of a cylindrical element, but can only place instruments on the sides of the member, for example, at a pier for a bent of a bridge.  When energy is added at the side of a column, one can generate flexural waves that have different propagation characteristics than longitudinal waves.  Flexural waves in general are dispersive, i.e., their propagation velocity depends on frequency.  Furthermore, the displacements associated with flexural waves also depend on frequency.  Hence to use these waves to non-destructively evaluate a member, one must have the dispersion relation in hand to know how fast the waves travel and to locate the optimal position of a transducer to measure the response.

This work is a continuation of the project funded last year by ITI wherein numerical solutions for guided wave theory describing the relation between frequency and group velocity for longitudinal and flexural wave propagation in plate (cast-in-place and soil-mixed walls) and cylindrical elements (columns, bridge piers, piles and drilled shafts) were developed by Wang (2004).  Wang’s work is a further extension of Hanifah’s (2002) work wherein he developed numerical solutions for longitudinal wave propagation in embedded cylinders.  These guided wave methods are capable of inducing higher frequencies that conventional sonic echo or impulse response tests.  Consequently, use of these methods will allow one to identify smaller defects than possible with conventional techniques. 

Task Descriptions

The work for this year will focus on two main areas, (1) experimental verification of the guided wave theory, and (2) continued development of the prototype system to induce guided waves.

1.  Experimental verification

We propose to experimentally verify the guided wave theory for flexural wave propagation in concrete cylinders and piles and longitudinal and flexural wave propagation in embedded walls and plates.  The latter is needed to apply these techniques to in situ walls, such as structural slurry or soil-mixed walls, which comprise part of many excavation support systems.  The question of integrity of these wall systems arose a number of times during construction of the Central Artery / Tunnel project in Boston and during construction of the secant pile wall at the Chicago-State Subway Renovation project.  During our work on these projects, we found that the conventional techniques based on 1-dimensional wave propagation in a cylindrical structural element were inadequate to provide answers regarding integrity of the as-built walls. 

2. Continued development of the prototype system to induce flexural guided waves

As we conduct verification tests of the theory, there are a number of issues that require further study.  In particular, when conducting a controlled frequency test, we must find the best orientation for the shaker so that flexural waves can be efficiently induced into a pile or plate.   Two cases must be evaluated: when only the top of a shaft or plate is accessible and when only the side of a shaft is accessible.  In the former case, a single shaker can be mounted in the center of the structural element with incident angles of 45° and 90°, as shown in Figure 10.  In these cases, multi-axial accelerometers will be mounted on the top surface of the concrete to measure the response and verify the mode of the received signals.

Milestones, Dates
(inc. Project Start & End Dates)

Duration is one year, and will begin on January 1, 2005.

Yearly and Total Budget

Total Costs- Current Year: $200,000
- Federal Share:         $100,000              6-Year Federal Share Total: $594,477
- Matching Share:      $100,000

Student Involvement (e.g., Thesis, Assistantships, Paid Employment)

Post-doctoral scholar: Helsin Wang

Relationship to Other Research Projects

Continuation of earlier projects "Nondestructive Evaluation of Concrete with Guided Waves" and "Improved Condition Monitoring of Bridges: Nondestructive Evaluation of Foundations"

Technology Transfer Activities

In 1996, 1997 and 1999, the P.I. taught "Foundation Evaluation with NDE Techniques," part of a wider course entitled "Nondestructive Evaluation of Bridge Conditions," for the University of Wisconsin-Madison Department of Engineering Professional Development.  He expects to teach the class again as the opportunity arises.

The PI will continue to participate in the User’s Group meetings for the Bridge Project.

Publication of results in journals and conference proceedings also will continue.

Potential Benefits of the Project

Longitudinal and flexural stress waves in concrete are dispersive in nature, that is their propagation velocity and displacements depend on frequency. This feature is not taken advantage of in conventional NDE tests, such as impulse response, that rely solely on identifying reflections of low frequency, one-dimensional compression waves. Drilled shafts that are relatively long or embedded in dense soil lose a significant amount of stress wave energy, owing to leakage into the surrounding medium, and cannot be reliably tested with these techniques beyond a certain limit, which we have defined in the past several years of this project. The use of frequency-controlled, guided stress waves offers an approach that may overcome this limitation. Guided stress waves have been successfully used for non-destructive flaw detection and characterization of structures, such as bounded metal hollow cylindrical tubing. We are the first research group to take advantage of guided waves when non-destructively testing concrete piles and shafts.

Whereas the longitudinal wave propagation solutions are useful, we can further extend the method to cover other conditions commonly encountered in the field. When the top of a concrete column or pile is inaccessible, one can attach transducers to its side, induce a flexural wave, and observe the response. Alternately, quality control of a cast-in-place concrete wall cannot be accomplished with conventional techniques. Thus we seek to extend the method to consider embedded plate-like structures.

TRB Keywords

Bridge, Infrastructure, Monitoring, Nondestructive testing, Concrete, Longitudinal waves, Flexure, Foundations

Center Identifying Number

A490

Project Title

Autonomous Crack Monitoring Continuation (continuation of Commercialization of Instrument for Micro-Inch Measurement of Crack Width in Support of Thrust in Remote Monitoring for Bridge Management)

Principal Investigator
Institution
Telephone Number
Email Address

Charles Dowding
Northwestern University
847-491-4338
c-dowding@northwestern.edu

External Project Contact
Address
Telephone Number

Project Objective

There are two main divisions of this project: 1) autonomous measurement of micro-inch vibratory and long-term crack movement and 2) autonomous graphical display of the results via the Internet. Its successes in 2) autonomous graphical display compliment and support other ITI Bridge Monitoring projects. For instance, instrumentation of the Sturgeon Bay Bridge is built around the concept of Internet display with the server software developed through this project.  With regard to micro-inch sensing, the ultimate goal is to cooperatively develop with GeoSonics and other manufacturers of vibration instruments a remotely operable and accessible instrument to measure micro-inch changes in crack width.

Project Abstract

There are two main divisions of this work: 1) autonomous measurement of micro-inch vibratory and long-term crack movement and 2) autonomous graphical display of the results via the Internet. Successes in 2) has lead to the decision by ITI to incubate a spin-off company to commercialize autonomous graphical display called Civil Data Systems. With regard to micro-inch sensing, the ultimate goal is to cooperatively develop with GeoSonics and other manufacturers of vibration instruments such as Instantel a remotely operable and accessible instrument to measure micro-inch changes in crack width.

Specifically, the micro-inch instrument allows comparison of changes in crack width from weather and environmental effects (long term) with those from construction vibration (short term). Such a simple comparison is urgently needed as the general public has too little ability to understand the abstract complexity of the current system of control by measurement of ground motion. The public is interested in cracking, not abstract comparison of time histories of ground motion. They feel vibration but do not sense the long-term weather response. Thus some mechanism is needed to allow the neighbors of traffic and construction vibration to compare these two phenomena, both of which produce strains that can lead to cracking.

Industrial and regulatory interest in this concept is strong. Formal coordination of parallel codeployment efforts with GeoSonics, a world leader in the manufacture of vibration monitoring instrumentation, demonstrates the potential for its immediate application. For instance, a beta test model for on-site polling has already been deployed by GeoSonics for one of their clients. Vulcan Materials Corp. has loaned ITI the use of a home (adjacent to one of its quarries) for use in the development of the ACM system. ACM on site polling equipment was integrated with White Industrial Seismographs in a nation-wide study of the response of atypical structures. Plans are underway at Instantel to develop ACM capability in conjunction with ITI.

Task Descriptions