A435

Analysis of the Performance of the Rehabilitation of the Chicago-State Subway Station and its Effects on Adjacent Structures

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

An advisory committee has been established to assure the relevance of the research results. The following people have participated in this committee.

Dr. Andy Longinow (Wiss Janney Elstner & Associates) - Dr. Longinow is the project director for WJE for this work.

Manoher S. S. Chawla (Department of Transportation, City of Chicago) - Mr. Chawla is the geotechnical engineer responsible for approving all building projects in Chicago.

John Yohan (Department of Transportation, City of Chicago) - Mr. Yonan is the Department of Transportation’s representative for the project.

Robert Staiton (Baker Engineering, Inc.) - Mr. Staiton is the project engineer for the construction manager of the project

This project uses data obtained from the monitoring effort conducted during the subway station reconstruction to check methods of predicting ground movements arising from supported excavations in soft clay, and to evaluate the soil-structure interaction between the adjacent buildings and the deforming soils. Damage to the nearby Warde School occurred, and an analysis of the detailed soil-structure interaction will provide information concerning levels of movement and onset of damage. Furthermore, a method of automatic updating of finite element predictions based on observed data will be developed so that updated predictions of ground movements in movement-sensitive excavations can be made quickly enough to provide input to contractors and engineers responsible for the performance of the excavation.

The Department of Transportation of the City of Chicago extensively rebuilt and expanded the circa 1940 subway station located at State Street and Chicago Avenue. As part of the work, a 44 ft deep excavation was made adjacent to the foundations of the Frances Xavier Warde School and within about 80 ft of Holy Name Cathedral. Both structures are founded on shallow foundations. The excavation support walls were located within one foot of the edge of continuous wall footings at the Warde School.

Wiss, Janney, Elstner & Associates (WJE) was the City of Chicago's Field Instrumentation Specialist for this project, and monitored the structural response of the Frances Xavier Warde School and Holy Name Cathedral. Northwestern University had a subcontract with WJE to monitor the ground deformations during and after excavation. The excavation support system consisted of a stiff, reinforced cast-in-place wall, constructed by the secant pile method, supported by one level of cross-lot bracing and two levels of inclined tiebacks. The excavation was made through fill, and soft clay, and bottoms out in medium stiff clay. The foundations for the exterior walls of the Warde School are continuous footings founded on the upper stiff clay. The wall was supported at three levels, near the top by a cross-lot brace and by two deeper levels of tiebacks. The tiebacks are angled at 45° below the Warde School and are founded in very stiff to hard glacial till. The presence of the existing subway tubes in the excavation necessitated the use of the angled tiebacks.

The field performance data collected by Northwestern University were processed daily during construction, and used to verify that the contractor’s excavation and support procedures adequately restricted associated ground movement such that damage to the Warde School was minimized and damage to the Cathedral was prevented. However, a great deal more usefulness can be obtained from the data if additional analyses are conducted.

There are two main tasks in the current scope of work: finite element studies and developing guidelines for onset of damage to structures adjacent to deep excavations.

Finite element studies

The finite element studies have three purposes. First, studies were conducted prior to start of construction to better predict ground movements associated with construction. The semi-empirical approaches that were used to estimate the magnitudes of movements are based on methods that consider either cross-lot bracing or tieback support, but not both in the same system. Additionally, there are a number of considerations unique to this project that warrant study, especially in relation to urban reconstruction, including the effects of the nearby subway tubes, the steeply dipping tiebacks, and the secant pile wall installation in soft and

Medium clays

Additional laboratory testing is underway and will be completed by a graduate research assistant.

Additional finite element analyses will be conducted to allow the soil model parameters to be calibrated to the observed performance using the actual construction sequence. The exact excavation sequence can be input to the analyses, as can be the exact amount of preload for the tiebacks. Both sides of the wall will be modeled since the deformations and tieback loads were different for both sides.

Lastly, parametric studies will be conducted to define the limits of behavior for other construction scenarios that were not followed by the contractor.

Guidelines for onset of damage to structures

Based on the observed performance of the ground and the adjacent Warde School, coupled with the results of the parametric finite element studies, guidelines for onset of damage to structures will be developed for stiff retaining systems in soft ground. Existing damage criteria relate ground deformation, as reflected in angular distortions of the ground and ground horizontal strain, to building damage.

The contract for the subway reconstruction was awarded on June 1, 1999, and the excavation was backfilled in May 2000. Work on the interior of the station will continue through July 2001.

Current Year = $73,500     2-Year Total = $187,404 

Three graduate students will work on the project this year. Jill Roboski will soon finish her MS thesis that completes the laboratory evaluation of the compressible glacial clays. Sebastian Bryson is working on his PhD and is focusing on the evaluation of the field data and the structural response of the adjacent school. Michele Calvello is working on his PhD and is focusing on the finite element studies, especially the automatic updating of parameters based on observed field responses.

This is the second year of a two year project to be conducted from January 1 through December 31, 2001.

Regular construction meetings took place weekly during construction to ensure coordination among the owner (CDOT), the contractor and the instrumentation specialists (WJE and Northwestern University). The results of much of the completed work was presented and discussed at these meetings.

The principal investigator presented the results to the Chicago geotechnical community in an invited lecture to the Geotechnical Group of the Illinois Section of ASCE in February 2001. He also presented the results to the profession in May 2001 as an invited speaker in a series of lectures sponsored by Hayward Baker, a geotechnical specialty contractor.

Kristi Kawamura completed her MS thesis entitled "Hardening Soil Parameters for Compressible Chicago Glacial Clays." Gilles Marchadier, from the Institute of Science and Technology at Grenoble, France, completed an internship at Northwestern University and wrote the report "Instrumentation and Numerical Simulation of the Chicago-State Excavation" (in French).

A paper, "Design and Performance of a Stiff Support System in Soft Clay," summarizing the performance of the supported excavation has been submitted to the ASCE Journal of Geotechnical and Geoenvironmental Engineering. Papers will be submitted to Journals and the results will be presented in upcoming conferences to further disseminate the findings.

While one cannot expect to develop comprehensive guidelines based on one case study that concerns only one stratigraphic condition and one building type, one can develop guidelines for the soft clay condition and a structural system consisting of a reinforced concrete frame with exterior masonry bearing walls, like the Warde School. This is a fairly common structural type and hence the guidelines will have ample applicability. Furthermore, the monitoring system can serve as a model for similar projects with different structural systems.

The field performance data collected by Northwestern University have been processed daily and been used to verify that the contractor’s excavation and support procedures adequately restrict associated ground movement such that damage to the Warde School was minimized and damage to the Cathedral was prevented. However, a great deal more usefulness can be obtained from the data if additional analyses are conducted.

Rehabilitation (Maintenance), Infrastructure, Structures, Subways, Subway Stations

A437

Improved Condition Monitoring of Bridges: Nondestructive Evaluation of Foundations

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

The objectives of this work are to develop an experimental system for guided wave evaluation of deep foundations, and to continue refinement and field verification of the existing nondestructive testing methods for deep foundations.

The purpose of this project is to develop methods to non-destructively evaluate the condition of existing deep foundations and bridge piers. With previous support, a drilled shaft test section for non-destructive evaluation has been established at the National Geotechnical Experimentation Site (NGES) at Northwestern University. Experimentation at this test section and subsequent analysis and numerical simulation have defined the limits of the ability of the impulse response technique to evaluate damage to drilled shafts in both accessible and inaccessible head conditions.

The work for this year will focus on two main areas, (1) continued development of the prototype system to induce and measure guided waves, and, (2) field testing of guided wave and conventional non-destructive testing methods.

Continued development of the prototype experimental system

With a theoretical solution to the guided wave problem for wave propagation along a cylindrical pile in hand and a prototype experimental system for inducing high frequencies bursts of energy available, to successfully apply the guided wave approach for evaluation of drilled shafts and unknown bridge foundations, the following tasks must be performed:

1. Conduct laboratory verification tests of the system. We will continue to test the prototypes piles in the laboratory in a free condition to verify the theory for higher modes of vibration. We are in the process of simultaneously measuring response with multiple accelerometers to help identify the mode of vibration. We also will explore the using a triaxial accelerometer for the same purpose. We will test the prototype piles installed at the Northwestern NGES in an embedded condition. We will explore in the laboratory and the field the use of synchronized shakers to increase the amount of energy input to a pile.
2. Trial and optimization of the developed technique to actual in situ deep foundations in both the accessible and inaccessible head condition. Depending on the outcome of the laboratory and prototype pile experiments, we will take the device to the field to test full-scale drilled shafts. Candidate sites include the National Geotechnical Experimentation Sites at Northwestern, in Houston, and at Texas AM, as well as ad hoc test sites in the Chicago area. We also propose to try the guided wave methodology at several bridge sites in Wisconsin. At this time, we plan to test the piers at the Sturgeon Bay Bridge. We expect that the guided wave approach could be successfully applied at this site because the piers have large cross-sectional areas, and conventional surface reflection techniques are not well suited for large diameter members.

The work for this project is broken into two main tasks:

(1) Develop guided wave approach for evaluating existing concrete foundations: work will continue throughout the year on both laboratory and field testing of the system

Duration: January 1 to December 31, 2001

(2) Field work at the Sturgeon Bay Bridge and other sites in Wisconsin. We expect the field work to be conducted weather permitting throughout the year.

Duration: January 1 to December 31, 2001

Current Year = $89,180     2-Year Total = $169,134

The principal investigator for this project is Professor Richard Finno. Hsiao-Chao Chou has assisted him and is expected to complete his PhD dissertation this summer. Helsin Wang has joined the team, and will pursue a PhD degree.

Continuation of earlier project

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 in 2001, and will continue to do so 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.

In the past year, several technical articles were published, including:

Gassman, S.L. and Finno, R.J., "Cutoff Frequencies for Impulse Response Tests of Existing Foundations," Journal of Performance of Constructed Facilities, ASCE, Vol. 14, No. 1, February, 2000, p. 11-21.

Finno, R.J., and Chao, H.-S., "Nondestructive Evaluation of Drilled Shafts at the Central Artery/Tunnel Project, Proceedings, Structural Materials Technology IV: an NDT Conference, Atlantic City, New Jersey, Feb. 2000, 81-88.

Gassman, S.L. and Finno, R.J., "Anomaly Detection in Drilled Shafts," Proceedings, National Geotechnical Experimentation Sites, Geotechnical Special Publication 93 , ASCE, J. Benoit and A.J. Lutenegger, eds. , 2000, p. 221-234

One paper has been accepted for publication in an Archival Journal:

Finno, R.J., Popovics, J.S., Hanifah, A.A., Kath, W.L., Chao, H.-C., and Hu, Y.H., "Guided Wave Interpretation of Surface Reflection Techniques for Deep Foundations," Italian Geotechnical Journal

In addition, one paper has been submitted to an archival Journal:

Finno, R.J., Popovics, J.S., Kath, W.L. and Hanifah, A.A., "Frequency Equation for Cylindrical Piles Embedded in Soil," Journal of Engineering Mechanics, ASCE.

The following abstract for a paper has been accepted for the 2002 International Deep Foundation Congress sponsored by the GeoInstitute of ASCE:

Finno, R.J., Chou, H.-C., and Gassman, S.L., "Non-destructive Evaluation of Drilled Shafts at the Amherst NGES Test Section."

A multiple geophone method has been developed which minimizes the effects of the surface wave reflections from intervening pile caps at the NDE test section. The impulse response technique with and without multiple geophone arrays has been used in the field at a number of bridge sites. A theory based on guided waves, describing the relation between frequency and group velocity of frequency-controlled excitations, has been developed to allow higher frequencies to be used to evaluate shafts, and, consequently, to identify smaller defects than possible with conventional techniques.

Bridge Management Systems, Infrastructure, Monitoring, Nondestructive Testing, Infrastructure

A438

Evaluation of Capacity of Micropiles Embedded in Rock

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

TCDI
Steven Scherer
Linconshire, Illinois
847-634-8580

While the load transfer along the length of the four piles has been determined from the results of the axial load tests, it is not clear as to which interface controls the magnitudes of mobilized friction along the length of the pile. The data suggests that it is the pile-grout interface and not the grout-rock interface as one might expect. Futhermore, there are grout-pile interfaces both inside and outside the steel pipe, and the nature of the responses at these locations are not necessarily the same. The objective of the work is to define the mechanisms of load transfer along the length of the micropile, so that rational design criteria can be established for this type of foundation element.

Micropiles socketed in rock are extensively used in rehabilitation work for infrastructure systems. They differ from the other micropiles in that they are founded in rock instead of developing high interface capacity, like traditional micropiles. There are no specially-created procedures for designing micropiles socketed in rock. Their load capacities are conservatively determined by current codes or conventional design methods for drilled shafts. Typically, the capacity of a micropile socketed in rock is approximated by the bearing capacity of its tip, neglecting the shearing resistance along its side. Results of a number of field axial load tests indicate that the load deflection responses are essentially linear to code-specified design loads, suggesting that the true capacity of the piles are significantly higher than currently-allowed values.

The work consists of collecting additional load tests conducted on full-sized micropiles in the Chicago area and conducting finite element studies of the detailed load transfer mechanisms.

TCDI occasionally conducts axial load test on full-sized micropiles as part of their normal project work. As they do so, the database concerning full-scale response will be enhanced. Northwestern will have access to the data as it accumulates. We will analyze the data, particularly in light of the deformations that develop during the test. Typically the load tests are not conducted to failure, but rather to loads equal to two times the design values.

Finite element analyses of each of the axial load tests conducted at the Vulcan quarry will be made using the program PLAXIS. This code is licensed to the principal investigator and was specifically designed for analyses of geotechnical engineering problems.

The steel pipe, the grout inside and outside the steel pipe, and the rock will be explicitly modeled in the analyses. Rock and grout properties used in the analyses will be based on the laboratory testing done on the grout samples collected during the construction of the micropiles and the rock cores collected from each pile location. A key factor in the study will be the interfaced behavior. We will explicitly model the interfaces between (1) the inside diameter of the steel pipe and the grout, (2) the outside diameter of the steel pipe and the grout, and, (3) the grout and the surrounding rock. The interface behavior will be modeled based on responses calculated from numerous plain steel bar- concrete pullout tests reported in literature (e.g., Gilkey, H.J., Chamberlain, S.J. and Beal, R.W., "Bond between steel and concrete, Bulletin 147, Iowa Engineering Experiment Station, 1940).

The interfacial behavior will be varied until the axial load transfer data matches that recorded during the load tests. The results of these analyses will allow a complete interpretation of the load tests. Given these interpretations, guidelines will be developed for calculating capacities of micropiles in competent rock. It is expected that the most important factor will be the interface friction, and not the end bearing capacity. In addition to developing more appropriate design guidelines, it may be possible to improve the micropile per se so that higher capacities can be achieved.

The field work at the quarry was completed during the fall of 2000. The finite element studies can be completed during the 2001 calendar year.

Current Year = $23,520     2-Year Total = $51,320

Benoit Paineau, a research assistant at Northwestern, was heavily involved in the instrumentation and field testing. He completed his MS thesis in December 2000. A graduate student in geotechnical engineering will assist the principal investigator in conducting the finite element studies.

This is an extension of the ITI funded project wherein Northwestern University, in conjunction with TCDI, a specialty geotechnical contractor, tested four micropiles embedded in rock.

The technology transfer for this project is enhanced by the participation of TCDI, a leading geotechnical specialty contractor. TCDI is a division of Hayward Baker Inc., a Keller Company. Hayward Baker has an international reputation and results of the work accomplished to date have already been discussed and transmitted to TCDI.

A MS thesis has already been published, "Capacity of Micropiles in Dolomite." An abstract for a paper, "Load Transfer Characteristics of Micropiles in Dolomite," has been accepted for the 2002 International Deep Foundations Congress sponsored by the GeoInstitute of ASCE. Additional publications are planned upon completion of the analysis and collection of additional full-scale axial load tests.

The results of these analyses will allow a complete interpretation of the load tests. Given these interpretations, guidelines will be developed for calculating capacities of micropiles in competent rock. It is expected that the most important factor will be the interface friction, and not the end bearing capacity. In addition to developing more appropriate design guidelines, it may be possible to improve the micropile per se so that higher capacities can be achieved.

Infrastructure, Rock

A440

Improved Condition Monitoring for Bridge Management

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

Wisconsin Department of Transportation
Phil Fish
4802 Sheboygan Avenue, Rm. 601
Madison, WI 53707
608-266-8165

The objective of this program is to provide bridge owners with a set of advanced nondestructive testing and evaluation (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.

The bridge NDE staff working with an undergraduate computer science student succeeded in developing our first fully automated web page for Professor Dowding’s crack monitoring project during 2000. We plan to implement this approach on our remote site in Sturgeon Bay, WI during this coming year. A major activity during the first quarter of 2001 was assisting Lichtenstein Associates in their efforts to conduct load tests on the Hoan Bridge in Milwaukee, WI. This structure experienced a major failure in one of the approach spans during December 2000. Approximately 40 strain gages and a mini-weather station with three Somat data loggers were installed in a wireless network. Strain, temperature and wind data were recorded for an extended period (1 to 2 weeks) in addition to the controlled load test data.

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.

Task 1. Field Tests and Demonstrations

This task is a continuation and expansion of the previous year’s effort. 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 efforts. Major effort will continue to focus on improvements in remote system reliability, communications, and power supply. We plan to explore the utilization of the Internet for communication purposes and plan on having the Sturgeon Bay lift bridge on the net during the coming year. We expect to get at least one acoustic emission monitoring project during the coming year. Additionally, we will continue to respond to emergency and special testing requests from our deployment partners.

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. Specific activities will include the 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 as well as a trade show booth.

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. ITI staff also actively supports student activities such as the AISC/ASCE Steel Bridge Competition. During 2000 we made use of the freshman engineering design course participants to develop a web page for Prof. Dowding’s remote crack monitoring project. This effort was very successful and we will utilize this resource to develop the Sturgeon Bay web page that will display "live" data as well as pictures of the bridge obtained from a web controllable video camera. 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.

January 1^st to December 31^st, 2001

Remote monitoring will continue to be the major activity during the coming year. Development efforts on communications software suitable for application to the active mode are under way as is a project to implement remote monitoring on the Internet.

Current Year = $281,611     2-Year Total = $518,227

We anticipate that both faculty and student involvement in the field test program will continue to increase dramatically. This effort has been aided by publishing notices of impending fieldwork and inviting both faculty and student participation.

Additionally, we also attempt to employ students (either work study or as temporary part-time employees) wherever possible. We also expect to continue to provide support for graduate students who are involved with research activities under the direction of our faculty partners.

During the last year’s effort the emphasis was on reliability improvement for our remote monitoring sites, student/faculty support and user group activities. These activities will continue during the coming year. Our current student/ faculty activities represent over half 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. This year’s efforts have further solidified ITI’s leadership position in this area.

The Western Bridge Engineers Seminar will be held in Sacramento during September of 2001 and we plan on having our booth included in the exhibits. Additionally we will present a one-day seminar/short course on remote monitoring with plans to broadcast it over the Internet or at least direct it to several deployment partners using the H.323 technology.

Two marketable products have emerged from this work. They are 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 produced considerable interest at Caltrans and resulted in a major change in their approach to solving this problem based on the ITI developed technique. Three bridges have been instrumented and Caltrans is planning to extend this approach to several hundred structures using the services of outside contractors. This is an excellent example of successful technology transfer.

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. Overall system reliability has made order of magnitude improvements since the early days of the Sturgeon Bay system. It is now possible because of improvements in software to perform some diagnostics and maintenance of the monitoring system without dispatching an engineer to the site. As the technology evolves and our experience increases, system reliability will continue to improve but it still has a long way to go before the smart structure becomes a widely accepted reality.

We are closely coordinating our user group efforts with the Mid-West Bridge Maintenance and Inspection (BMI) working group. At the November meeting of the BMI group we introduced new technology (H.323) that allows low cost multi-point teleconferencing over the Internet. The response to this technology was very positive and we are currently planning a teleconference topical meeting with Ohio DoT on the subject of scour monitoring to take place in late spring of 2001. We see H.323 technology as a potential solution to the travel problems that typically plague state dot workers and greatly hinder the timely interchange of information and ideas. The equipment is easy to use and relatively low cost ($4,000). The use of the Internet eliminates the high connect time costs that are part of the current DSL technology and allows much greater flexibility.

Bridge management systems, Infrastructure, Monitoring

A442

Further Commercialization of 70-KSI NUCu Steel

Prof. Morris E. Fine
Northwestern University
847.491.4322
m-fine@northwestern.edu

Semyon Vaynman
Northwestern University
No Phone
Svaynman@northwestern.edu

1. Illinois Department of Transportation
2. Office of Naval Research
3. AISI/FHWA/US Navy HPS Steering Committee

The main objective of the follow-on ITI-sponsored work is to increase commercialization and acceptance of NUCu 70W HP steel for use in bridges. The steel’s commercialization will proceed through our collaboration with FHWA, IDOT, other state DOT’s, steel companies, etc.

Several years ago the FHWA and the Navy identified a need for a high performance weatherable structural steel that would have a 70 Ksi yield strength (compared to 50 Ksi yield as in the micro-alloyed steels in common use). Lower C content for improved welding and high fracture energy at cryogenic temperatures was desired for this steel. A Steering Committee was formed with the American Iron and Steel Institute to achieve this development. Under the auspices of this Committee the participating steel companies developed new steel, designated ASTM HPS 70W. This steel requires rapid cooling to form martensite and then the steel is tempered. Initially this steel required re-heating and quenching after it came off the hot rolls. This limited the length of plates that could be manufactured to 45 ft. Subsequently, the processing was refined for continuous direct quenching and tempering after hot rolling (thermo-mechanically-controlled processing, TMCP). This steel in the Q&T form has already been used in more than 10 bridges in the United States.

At Northwestern several years after the development described above began, a different approach was taken to meet the target steel. Our approach was to meet the requirements by a combination of Cu precipitation hardening and grain refinement by niobium carbides. NUCu 70W steel resulted. It has a number of advantages over the ASTM HPS 70W. The processing is simpler because a quench is not required. It has a lower equivalent carbon content and, therefore, has better weldability. It has a remarkably high fracture energy at cryogenic temperatures. It has substantially better weathering resistance than HPS 70 W steel or other weathering steels. Our current and proposed efforts are toward further marketing of NUCu 70 W steel.

Proposed Use of NUCu Steel for the New LaSalle, IL Bridge

A new bridge at LaSalle, IL has been designed and contracts are expected to be let in June 2001. The consultant has specified girders with 3-inch-thick flanges and 1-inch-thick webs 2.7 to 3 ft. wide. The girders are to be fabricated with 70W steel. Chris Hahin of IDOT, who has been involved in the development of NUCu steel almost from the beginning, has recommended ASTM A709 HPS70W Q&T steel for the flanges and our, NUCu 70W, steel for the webs.

Proposal to Include NUCu Steel in ASTM A709 Specification

At this time the major barrier to use of NUCu steel is that it is regarded as an experimental steel and is not included yet in the ASTM A709 specification for bridge steels. Chris Hahin is now on the ASTM sub-committee and he plans to propose inclusion of our steel in the ASTM A709 specification since two commercial heats have been already produced at Oregon Steel Mills. He has volunteered to draft and submit a proposal for ASTM sub-committee meeting in May 2001. Since there is much interest in an improved 50W steel, he has recommended preparing a dual proposal for 50 and 70-Ksi yield steels. We already prepared a data set listing producers, compositions and mechanical properties of our steel. This data set includes three manufacturers (Inland Steel, USS and OSM) and 8 steel heats with several different heat treatments.

We will discuss NUCu steel with other state DOT engineers for infrastructure applications and to other agencies for other than infrastructure applications.

We will participate in further modifications and other studies of NUCu steel that are currently underway or hoped to be sponsored by the steering Committee or IDOT. These include weathering resistance (painted and unpainted), welding, machining, and promotion of a low cryogenic temperature high toughness 50W-grade version of NUCu steel. These studies should broaden the interest and possible infrastructure applications of NUCu steel.

1^st Quarter

• Work with IDOT and AISI/FHWA/Navy Committee to include NUCu steel into ASTM Standard
• Prepare steel, paint, and equipment for corrosion tests. Start testing
• If NUCu steel modification proposals are approved by AISI/FHWA/Navy Committee, order steel from USS Company
• Contact State DOT's, discuss the use of NUCu steel
• Participate in AISI/FHWA/Navy Committee

2^nd Quarter

• Finish corrosion tests of painted steel/analyze data
• Prepare marketing brochure
• Contact steel producer and fabricator for LaSalle bridge. Discuss details for steel production
• Analyze data from welding and machining studies sponsored by IDOT
• Continue steel marketing to State DOT's, to other agencies for non-infrastructure application
• Start testing of modified NUCu steel (if proposed projects are funded by AISI/FHWA/Navy Committee)
• Study effects of temperature on NUCu steel (if project is funded by IDOT)
• Participate in AISI/FHWA/Navy Committee

3^rd Quarter

• Work with steel producer and fabricator for LaSalle bridge on steel production
• Continue steel marketing to State DOT's, to other agencies for non-infrastructure application
• Finish testing of modified NUCuu steel (if proposed projects were funded by AISI/FHWA/Navy Committee). Prepare report. Use data for NUCu steel marketing
• Evaluate the results of the long-term weathering tests (with Bethlehem Steel Co.)
• Participate in AISI/FHWA/Navy Committee

4^th Quarter

• Work with steel producer and fabricator for LaSalle bridge on steel production, and bridge component fabrication
• Continue steel marketing to State DOT's, to other agencies for non-infrastructure application
• Participate in AISI/FHWA/Navy Committee

Current Year = $51,156     2-Year Total = $116,731

Our work for 2001 fiscal year is a continuation of that done during the prior year. Everything we propose follows from work during the year prior.

We are in discussions with Chicago DOT engineers about using our steel for painted girders in bascule bridges instead of A36 steel. There should be less salt corrosion under the paint and we have begun planning corrosion tests to demonstrate this effect. We have been in contact with DOT engineers in several other states and some have shown interest. Other applications besides bridges are being explored.

The technology transfer will continue through publications, reports, presentations and personal contacts. We will continue to collaborate with IDOT and participate in the FHWA/AISI/US Navy HPS Steering Committee. This Committee includes steel producers, bridge engineers and representatives from FHWA and the Navy in its membership. We will work to expand the group of potential users that we are in contact with.

We plan to prepare a brochure that describes the properties of NUCu steel, its advantages over other high-performance steels and its use in the bridges. This brochure will be distributed to the steel producers, fabricators and to the users community.

There is interest in high-performance steels for navy ships, tank cars, pipes, pressure vessels, construction, etc. We will continue to target these markets through presentation of papers at conferences and through the direct contacts with different companies. We have been invited to present a paper at an Iron and Steel Society Conference in a session concerned with railroad tank cars.

NUCu steel is attractive to steel companies because of its excellent mechanical and weathering properties combined with simpler processing than for ASTM A709 HPS 70W. This gives our steel a competing edge.

Since the bridge steel market is considered a small one, use of NUCu steel for applications besides bridges increases the interest of the steel manufacturers to market our steel. There is interest in high-performance steels for navy ships, tank cars, pipes, pressure vessels, construction, etc. We will continue to target these markets through presentation of papers at conferences and through the direct contacts with different companies. We have been invited to present a paper at an Iron and Steel Society Conference in a session concerned with railroad tank cars. A current problem is brittle fracture at low temperatures.

Steel, Bridges, Infrastructure

A439

Life-Cycle Management of Steel Bridges Based on Non-Destructive Testing and Failure Analysis

Prof. Brian Moran
Northwestern University
847-491-8793
b-moran@northwestern.edu

Prof. Jan Achenbach
Northwestern University
847-491-5527
achenbach@northwestern.edu

Prof. Ed Rossow
Northwestern University
847-492-3453
e-rossow@northwestern.edu

The thrust of the project is to develop an understanding of failure mechanisms in pin-hanger connections in steel bridges and to develop guidelines for the assessment of the structural integrity of the connections.

During the first two years of the project, a variety of finite element stress analysis and fracture mechanics templates were developed and/or customized for this task. Two failure mechanisms are being investigated: 1) locking of the free rotation of the pin and failure due to plastic collapse or overload, 2) fatigue crack propagation due to thermal stressing with the eventual attainment of a critical flaw. Preliminary results for the first of these cases were obtained for prototype bridge and pin-hanger geometries and dimensions. These results indicate that the contact algorithms and the thermal stress aspects of the modeling have been correctly implemented and that they give accurate results in benchmark tests. While such analyses on prototypes are useful in developing the methodologies, it has become apparent that meaningful assessment of likely failure mechanisms requires a faithful representation of the actual bridge in question. Using such a model of a girder and pin-hanger connection in the Wisconsin Dells bridge, preliminary results indicate that stress levels approaching the yield strength are attained in the pin (with yield strength of 115 ksi). The hanger plate appears to exceed yield. In the coming year, we will complete this analysis. We will also carry out an elastic-plastic analysis and consider a range of pin "freeze-up" scenarios. Finally we will carry out an analysis of fatigue crack growth in the pin and carry out risk assessments to determine failure probabilities with and without NDE inspection.

1. Complete the stress analysis of pin-hanger assembly and explore range of "freeze-up" conditions

The assessment of "freeze-up" due to corrosion in the Dells bridge pin/hanger assembly will be completed. Results obtained to date for the freely-rotating and fully frozen conditions will be examined and refined meshes used to assure convergence. These analyses will be supplemented with an elastic-plastic analysis as there are indications of yielding in the hanger plate for the fully frozen case.

2. Carry out assessment of fatigue crack growth in pin –- Use of X_FEM

A preliminary analysis of cracks at safety critical locations in the pin will be carried out using standard three-dimensional finite element analysis, including detailed meshing of the crack surfaces. This will provide us with an initial estimate of fatigue crack growth characteristics in the pin.

2.3. Carry out risk assessment

A probabilistic fracture analysis of fatigue crack growth in the pin will be carried out using the computational fracture methodologies mentioned above along with First Order Reliability Methods or the Limit State Surface Element Method developed by the PIs. The POD curves used will be guided by measurement models. The outcome will be a probability of failure (due to fatigue) with and without inspections. This will permit us to assess the likelihood that pins fail in fatigue.

Quarter 1: In the first quarter, the three-dimensional finite element stress analysis of the Dells bridge pin/hanger assembly will be completed and an elastic-plastic analysis carried out. Begin implementation of "freeze-up" eigenstrain/friction model.

Quarter 2: Complete analysis of "freeze-up" model. Begin implementation of substructuring procedure for crack growth modeling using X-FEM.

Quarter 3: Complete assessment of cracks in pin using standard FEM and X-FEM. Begin implementation of probabilistic fracture model.

Quarter 4: Complete risk assessment (probabilistic fracture) modeling. David Houcque should be at final stage of thesis at this point.

Current Year = $51,156     2-Year Total = $147,729

Graduate student: David Houcque

The research is a continuation of the current ITI funded project "Life-Cycle Management of Steel Bridges Based on Non-Destructive Testing and Failure Analysis" (Moran and Achenbach). The project will enter its third and final year.

A high level of interest has been expressed in the work with pin-hanger assemblies. Contacts are being maintained with representatives of State Transportation Agencies, particularly with Frank Reed (Cal Tran), Phil Fish and Finn Hubbard (Wisconsin Department of Transportation), Duane P. Carlson and Burt R. Thakar (Illinois Department of Transportation) and Mark Grunert (Nevada Department of Transportation). Ed Rossow will provide guidance in the presentation and communication of this work to the bridge engineering community.

The research is on the important topic of life-cycle maintenance of safety critical components in bridges. The work addresses issues pertaining to broad capabilities for general application as well as specific issues pertaining to the development of a further understanding of the failure of bridge pins and, ultimately, how these pins can best be monitored and failures avoided.

The research is based both on our original vision of the development of a methodology for life-cycle maintenance based on QNDE.

Types of bridges by material, Bridges, Infrastructure, Bridge management systems, Nondestructive testing, Steel, Failure analysis

A441

Ultrasonic Technique for In-situ Monitoring of the Setting, Hardening, and Strength Gain of Concrete

Prof. Surendra Shah
Northwestern University
847-491-3858
s-shah@northwestern.edu

K.V. Subramaniam, Assistant Professor
City University of New York

The primary focus of this work is to develop a nondestructive field sensor for in-situ monitoring of the setting, hardening, and strength gain of concrete.

The results obtained so far indicate that the WRF technique can sensitively and accurately predict the trend of strength gain in concrete structures. However, prior to undertaking further development of the technique, we propose to conduct a thorough investigation of the influence of temperature and humidity on the WRF response under carefully controlled laboratory conditions. In addition, we propose to develop a quantitative relationship between the observed WRF values and the strength of concrete that will help in developing applications where the strength gain in structures is assessed from the WRF response. Further, a predictive approach for the time required to attain the design strength will be developed.

The ultrasonic WRF method shows sufficient promise to be further developed for field applications. To be accepted as a field device, the test procedure should be easy to implement, and the results obtained using the technique should be easy to interpret. A part of this study will be devoted to developing reliable and robust field instrumentation with the capability of real-time analysis and display of results.

Development of Field Applicable Test Device

We will develop computer subroutines that collect data and provide real-time analysis and display of processed data. The existing test setup will be modified to receive and process input from multiple sensors thereby permitting multiple-point sampling of a structure. In addition, a graphic user interface will be designed for display of results.

Laboratory Experiments

• Influence of Temperature

We will investigate the influence of temperature on the hydration process and the resulting strength gain in concrete. WRF measurements will be recorded continuously for each mixture composition up to 14 days after casting. In addition, the specimens will be instrumented to obtain the temperature profiles as a function of time. Compressive strength gain and the development of elastic modulus will be determined by testing standard 3inch by 6inch cylinders at different ages.

• Influence of Humidity

We willinvestigate the influence of humidity on the hydration process and the corresponding strength gain in concrete. Three different concrete compositions will be evaluated at each humidity condition. The instrumentation and test program will be similar to that for the temperature study.

• Establishing Analytical Procedures for Strength Prediction

Based on the results of the experimental program, analytical procedures for estimating the compressive strength and the rate of gain in compressive strength will be developed. Decision criteria for demolding a structure will be developed. In addition, the decision criteria will be implemented in the graphic user interface computer program for the WRF technique.

Quarter 1

• Material and Equipment Preparation
• Software Development
• Laboratory Development
• Data Analysis

Quarter 2

• Software Development
• Laboratory Development
• Data Analysis
• Instrumentation
• Predictive Model Development

Quarter 3

• Data Analysis
• Instrumentation
• Lab scale in-situ experiments
• Predictive Model Development

Quarter 4

• Lab scale in-situ experiments
• Field in-situ experiments
• Predictive model development

Current Year = $73,500     2-Year Total = $88,493

Results of a preliminary investigation indicated that the ultrasonic WRF method shows promise sufficient to be further developed for field use. Subsequently projects to demonstrate the field applicability of the WRF technique and to assess the market potential of a field device based on the WRF technique were funded by the Infrastructure Technology Institute, located at Northwestern University.

Previous ITI-funded work had two objectives: (1) to demonstrate the field applicability of the WRF technique in predicting the rate of strength gain in a structure and (2) to perform a feasibility study to assess the market potential of a field device based on the WRF technique.

Upon completion of the project, a standardized test method for in-situ monitoring of the hardening and setting of concrete will be developed. The New York Department of Transportation has expressed interest in evaluating the field performance of the proposed technique and to compare its performance against existing methods that are in use. Additionally Prairie Materials has committed to assist in a test of the WRF technique on an industrial scale.

A technique that monitors the setting and hardening of concrete was recently developed by the principal investigators and successfully tested in the laboratory. The procedure is based on monitoring the wave reflection factor (WRF) at the interface between a steel plate and concrete surface. The changes in ultrasonic WRF were shown to correspond well with the observed trends in the hydration process of cement that leads to strength gain in concrete. The WRF technique can therefore be utilized for monitoring in-place properties of concrete from an early age and assessing the strength gain with time. A market survey performed as a part of an earlier study revealed that there is a critical need for field devices that can accurately assess the in-situ strength gain in structures.

Concrete, Monitoring, Infrastructure

A436

Commercialization of Instrument for Micro-Inch Measurement of Crack Width in Support of Thrust in Remote Monitoring for Bridge Management (continuation of Triggered, Real Time Display of Infrastructure)

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

MNDOT, Materials and Research Laboratory
Chuck Howe
Maplewood, MN 55109
612-779-5602

GeoSonics-Instrument Manufacturer
Alvin L. Budd
Warrendale, Pennsylvania 15095
724-934-2900

There are two goals of this project. The first is to implement and commercialize seismographic instruments that can measure micro-inch changes in crack width produced by both transient, construction vibrations and long-term environmental effects. The second is to provide via the internet these data in real time to the public in a form that allows direct visual comparison. This new approach has the potential to be a cost effective means of informing the lay public of and controlling that which is of concern, crack movement, during vibration producing construction. The detailed objectives of this project are to:

• Determine the optimal micro-inch proximity measurement system for measuring crack movement

• Integrate proximity measurement and environmental observation with traditional vibration measurement

• Display the comparisons of long-term and vibratory crack deformation in real time via the internet;

• Demonstrate the robustness, reliability, cost effectiveness, and limitations of micro-inch proximity measurement within structures;

• Assess the commercial potential by soliciting comments form the GeoSonics clients around the world;

• Report the results of field trials of this equipment

Public concern over construction and traffic vibration-induced cracking has led to the search for a radically new approach to vibration control. This project is to develop equipment and software for real-time monitoring and internet display of crack response and weather supports development of such a new approach to monitor and control construction induced vibration. The new instrument, the Autonomous Crack Comparometer (ACC), will automatically record changes inc rack width produced by ground motion to allow direct comparison with those induced by long-term, environmental effects. Internet based, real-time public access to these data is fundamental to this new approach.

Time histories of ground motion and past correlations are simply too difficult for most jurors and village and county regulatory boards to understand. Since these public bodies control the manner in which construction activity is adjudicated and regulated, information must be provided in a form that they can understand. Measurement of micro-inch changes in crack width provides information in a visual form that can be understood by these lay bodies, and allows direct comparison of vibration and environmental effects on the same crack with the same device. Use of the ACC system will allow an understanding of this relationship not now possible and potentially may avoid payment of 10's of millions of dollars in illegitimate claims and construction delays each year.

Deployment of this system compliments other instruments which sense and report singular incidents. For example, the Internet software being developed can be employed with other bridge monitoring devices for display and dissemination of information.

1.Install and Render Operable MNDOT Equipment

2.Write Software to Discriminate Household from Construction Vibrations

3.Plan to Integrate Stage II Equipment with Commercial Equipment

4.Rework Back End Server Software to Eliminate Automate

5.Document Server Side Software

6.Bring the Sheridan Rd House Back on Line

The pace and pulse of the project is affected primarily by availability of students and timing of field activity. The MNDOT installation will no doubt become very active in the summer. The programming and documentation will peak in the summer when Kosnic is most available for programming. The next thesis will not be written until early 2002.

1st Quarter

• Plan MNDOT installation.

2nd Quarter

• Employ additional hardware to render Sheridan Rd. house operable.

3rd Quarter

• Install MNDOT equipment as MNDOT will fund through its construction account the infrastructure for the ACC as well as other equipment for comparative monitoring.

4th Quarter

• Develop logic to trigger off both excitation by household activity induced vibration as well as that produced by construction activity.

5th Quarter

• Test new hardware and software to eliminate automate step.

6th Quarter

• Begin plans to document server side software.

Current Year = $95,550     2-Year Total = $157,284

Graduate Students

• Laureen McKenna, MS Student. Will focus on the final development of the Stage II prototype

Undergraduate Students

• David Kosnik, Sophomore at Northwestern University will be developing the server software

• Matt Kotowsky, Sophomore at the University of Illinois works part-time on the graphing software

Continuation of "Triggered, Real Time Display of Infrastructure Response"

The technology transfer process will begin with a market analysis of GeoSonics country-wide data base as well as an assessment of world-wide market potential. Additionally, ownership of any intellectual property that results from this cooperative project will be obtained for the instrumentation. Essentially it is in GeoSonics’ best interest to continue to bring new products to market. This need will drive all of the commercialization activities.

Commercialization of micro-inch crack measurement products will be conducted by advertisement through the following channels: (1) technical journal articles, (2) instrumentation, vibration, civil, geological, explosives, quarrying, mining, and construction magazines, (3) direct marketing to operators through the codeployment partner, GeoSonics, (4) GeoSonics and Northwestern University www sites, and (5) short courses and seminars.

Development of this instrument allows comparison of changes in crack width from weather and environmental effects (long term) with those from construction vibration (short term). This comparison has the capability of showing that current regulatory controls permit less distortion than that which occurs from natural and habitation effects. 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.

Cracking, Types of cracking, Width, Traffic, Vibration, Construction, Remote, Internet, Education, Public, Awareness, Instrumentation, Response, Access

A443

Commercialization of TDR Measurement of Soil Deformation in Support of ITI Thrust Area for Improved Condition Monitoring for Bridge Management

Prof. Charles Dowding
Northwestern University
847.491.4338
c-dowding@northwestern.edu

Clark Landfill - STS
Ted Buschell, Principal Engineer
Deerfield, IL 60015
847.279.2473

INDOT Division of Materials and Tests
Dan Chase
Indianapolis, IN 46219
317.232.5280 ext 229

PennDOT District 12-0 Geotechnical Engineer
David Whitlach
Uniontown, PA 15401
274.439.7357

F1DOT District Materials Engineer Dist 6
John Barker
Bataw, FL
800.292.3368

Field measurement of TDR cable sensitivity in soft soils can be accomplished by installation and monitoring of the response of unique field sites. Continued potential of misapplication of the technology also points out the need for positive case studies that demonstrate the importance of the use of appropriately compliant cables.

TDR techniques replace other manual methods for assessing lateral movement of bridge abutments and piers. TDR's remote operability and its inherently digital nature provide an appropriate and remotely operable method for monitoring stability of critical bridges while they await repair. Occurrence of excessive bridge pier and abutment movement is large. For instance scour-induced deformation was responsible for some 40 bridge failures during the Mississippi and Missouri flooding of 1993.

Compliant cable-grout composites are necessary to maximize the use of TDR technology in soft soils. To date, TDR cables have been extensively deployed in rock and stiff soils. Recently, stiff, commercial cables installed with weak grout have been deformed with movements of 0.01 m (0.5 in) in soft lake clays. This observation has caused a shift in development emphasis from the cable itself to the reaction of the grouted hole-cable composite.

It is important to further develop these special cables-grout composites for soft soils as State DOT’s are beginning to experiment independently and will require assistance to ensure that the technology is evaluated properly. Furthermore, exploratory field work with State DOT's has revealed an overly simplistic view of installation requirements, which makes publicity of the importance of the composite view all the more critical.

Successful monitoring of mine-induced subsidence of I 70 with TDR-Tiltmeter technology for Pennsylvania DOT has lead to an increasing awareness at TRB of the advantages of infrastructure monitoring with TDR technology. This next year there is a potential to transfer TDR technology to monitoring of sinkhole induced highway subsidence for Florida and/or Maryland DOT’s. The planned TDR 2001 Symposium this coming September is optimally timed to take advantage of this increased interest.

1.Interpretation of Cable-Grout Composite Sensitivity with Finite Element Modeling.

2.Continued Observation of Already In-Place Cables

3.Install Sinkhole Monitoring System

4.Organize and Administer the TDR 2001 Symposium

5.Remote Operation and Internet Observation of SR 62 Installation.

Three different activities are being undertaken for year 2001: Finite Element Modeling with new software, installation of TDR field equipment to monitor sinkhole subsidence, and holding TDR symposium.

Quarter 1

• Begin Finite Element modeling with new software and plan installation of F1DOT TDR Equipment.

Quarter 2

• Assist FIDOT by installing combination TDR and tiltmeter system as it copes with the necessity to instrument facilities built over known, active sink holes.

Quarter 3

• Hold TDR 2001 symposium on September 5, 6 & 7 2001 to provide a forum for the researchers, practitioners, manufacturers, and owners (DOT’s) to meet and discuss TDR technology.

Quarter 4

• Finish initial phase of Finite element modeling of the cable-grout- soil system to validate the process of matching grout and soil stiffness.

Current Year = $67,771     2-Year Total = $198,397

Graduate Students

• William Bergeson, MS student. Gathered last data from field sites and began to develop finite element model of cable-grout-soil composite interaction.

• James Blackburn, MS/PhD student. Will be assuming responsibility for operating Indiana State Road 62 TDR site and will finish finite element modeling.

Undergraduate Students

• Michael Babik, Senior. Is assisting with the planning and administration of the TDR 2001 Symposium.

Continuation of Geotech/TDR component of Condition Monitoring Thrust

TDR specific user community involvement was fostered through five mechanisms: papers at workshops and specialty sessions, demonstration projects, TDR-L Email listserve, development of the TDR 2001 Symposium, and installations and consulting by Dr. O’Connor of Geo TDR. Last year ITI and GeoTDR personnel have made presentations at the following conferences: 1) The DOT Structural Materials Technology IV (NDT) Conference in Atlantic City in March 2000. 2) The ASCE Geo-Institute Specialty Sessions on Field Instrumentation in Denver in August 2000. 3) The Midwest Bridge Inspector’s Meeting in Indianapolis in November. 4) FHWA Specialty Conference on Geophysical Instrumentation in St. Louis in December 2000.

Demonstration projects have been summarized elsewhere. They have mainly involved rock or stiff soils and therefore soil sites are a high priority. The PennDOT and FIDOT sites and some horizons in the INDOT sites represent unique opportunities.

The TDR listserve, operated by ITI, continues to serve some 150 to 200 TDR suppliers and consumers. Provision of this communication channel maintains ITI’s preeminence in TDR technology.

Indirect support of Dr. O’Connor’s efforts to build a TDR, a company that specializes in TDR instrumentation has been instrumental in developing ITI sponsored demonstration projects.

Finally, the user community has been engaged by the interaction necessary to organize and plan for the TDR 2001, the Second International TDR Workshop and Symposium at Northwestern University. So far some 60 papers have been received for publication in the proceedings. In addition, three practical short courses are currently being planned for the gathering.

In addition to bridge monitoring, development of a TDR system to detect deformation in soil will allow further understanding of the localized shearing. Heretofore, deformation could only be measured with a resolution of 60 cm with slope indicators. When fully developed TDR technology will allow a resolution of 2 to 5 mm, which is a 100-fold increase in resolution.

Time Domain Reflectometry, Deformation, Soft Soil, Bridge Management Systems, Monitoring, Monitoring Systems, Infrastructure

A447

Minimizing Shrinkage, Creep and Cracking Damage to Concrete Bridges

The objective of the project is to build on the theoretical results of previous 25 years of theoretical investigations of creep, shrinkage and fracturing of concrete funded by NSF, EPRI and DoE, and introduce these results into the practice of the design of bridges, as well as into their maintenance and rehabilitation.

The ultimate goal is to achieve a significant revision of a number of specifications of AASHTO and other appropriate societies, particularly ACI and (to a lesser degree) RILEM (AASHTO usually co-opts the ACI recommendations, as far as creep, shrinkage and cracking are concerned).

This project will translate the existing theoretical results of 25 years of theoretical investigations of creep, shrinkage and fracturing of concrete into simple user-friendly algorithms or simple formulae, working out typical practical examples of calculations, presenting convincing comparisons with experiments, reducing sophisticated theoretical considerations to simple arguments preferably relying on graphical illustrations, analyzing the competing models and demonstrating their shortcomings or lack of agreement with test data, etc.

Efforts will continue toward achieving significant revisions of design codes and recommendations for creep, shrinkage and cracking in concrete bridges.

1. Continue efforts in ACI Committee 209 towards the approval of the B3 Model and rejection of the competing obsolete and simplistic, and for adoption of scientifically sound criteria and guidelines for concrete prediction models

2. Create a study of excessive deflection and cracking of concrete bridges on the basis of the latest research, with preparation of a draft recommendation

3. Defend the submitted proposal of a new proposed standard on the modulus of rupture test (flexural strength) submitted to ASTM-C04

4. Defend the proposal submitted to ASTM-C04 of a new testing procedure for concrete creep and shrinkage

5. Promote in ACI Committee 446 and in AST C-04 the adoption of a sound test standard for fracture properties of concrete, based on the writer’s previous research at NU

6. Pprepare for Conference Concreep-6 to be held in August 2001, which will feature a scientifically based discussion of standard recommendations for design and transfer to practice

7. Study ways to remove the size effect hidden in an excessive current dead load safety factor, and replacing the code provisions with a sound model for size effect.

April 1, 2001 to March 31, 2002

Current Year = $62,851     2-Year Total = $143,578

Postdoctoral: Dr. V. Kristek or Dr. D. Novak

Graduate Research Assistant: G. Zi or Y. Zhou

Continuation of "Minimizing Shrinkage, Creep and Cracking Damages to Concrete Bridges"

Much of the focus of this project is on technology transfer through updates to standards and information dissemination to practicing engineers.  The PI will be active in the relevant committees of ACI and RILEM, attracting as members well educated young researchers, writing critical evaluation reports for various meetings and workshops, etc. Activities include continuing efforts in ACI Committee 209, ACI Committee 446, ASTM C-04 Committee, and AASHTO committees for updating standards and guidelines; writing a report for the RILEM creep committee; submitting a study of fracture energy and test standard to a leading journal (e.g., ACI Materials Journal, Engineering of Fracture Mechanics); working on the organization of the 6^th International Conference CONCREEP-6 to be held at MIT in August 2001, to transfer theoretical research into practice; and collaborating with V. Kristek on improvements of the web site that provides an automatic prediction of creep and shrinkage of concrete. 

If the creep and shrinkage effects in concrete structures are mis-predicted, the result is long time fracturing (or cracking), which may grossly affect the durability of a bridge.  Excessive deflections due to creep may cause the loss of serviceability.  Both phenomena lead to costly repairs, shortening of lifetime, and may also cause structural collapse due to the phenomenon of creep buckling.  There are now many examples of such problems, for instance the Koblenz Bridge and Worms Bridge in Germany, or the Parrot Creek Bridge in California, a prestressed box girder of a span over 300 ft. which deflected two feet more than calculated in design.  The resulting financial losses are enormous on the national scale.  An even greater and more costly problem is the cracking of concrete induced by misprediction of restrained shrinkage and nonuniform creep.

During the last 25 years, very significant progress has been achieved in basic research.  The concrete creep, shrinkage and cracking prediction methods that have been developed up to now are much superior to those embodied in the current codes, standards and standard recommendations of ACI, ASTM, AASHTO, and RILEM and are used in practice only sparingly, doubtless for lack of information by practicing engineers.   To this end, it is necessary to update the design codes and recommendations, and make other efforts to disseminate the improved methods.

Concrete Bridges, Shrinkage, Creep, Cracking, Deflection, Standards, Infrastructure