NORTHWESTERN UNIVERSITY
Infrastructure Technology Institute
2003 Research Progress Report
January 23, 2004

2133 Sheridan Road
Evanston, Illinois 60208
Phone: (847) 491-8165
Fax: (847) 467-2056

dschulz@northwestern.edu
www.iti.northwestern.edu

Contents

Introduction

Introducing Size Effect into Design Practice & Codes for Concrete Infrastructure Principal Investigator: Prof. Zdenek P. Bazant

Commercialization of Instrument for Micro-Inch Measurement of Crack Width in Support of Continuous Remote Monitoring for Bridge Management Principal Investigator: Prof. Charles Dowding

Commercialization of Time-Domain Reflectometry (TDR) Measurement of Soil Deformation in Support of Improved Condition Monitoring for Bridge Management Principal Investigator: Prof. Charles Dowding

Improved Condition Monitoring of Bridges: Nondestructive Evaluation of Foundations Principal Investigator: Prof. Richard Finno

Allowable Deformations of Gas Mains Adjacent to Deep Excavations Principal Investigator: Prof. Richard Finno

Bridge Asset Management Based on Life-Cycle Cost Considerations Principal Investigator: Prof. Raymond J. Krizek

The Infrastructure Construction & Condition Monitoring Laboratory (ICCML) as a Novel Teaching Tool to Improve Undergraduate Education & Student Learning of Civil Engineering Prof. Roberta Massabo, Principal Investigator

Nondestructive Testing & Evaluation of Bridges Principal Investigator: David Prine, Institute Chief Research Engineer

Feasibility Study for Commercialization of a Nondestructive Ultrasonic Technique for Monitoring the Setting & Hardening of Concrete Principal Investigator: Prof. Surendra P. Shah

Safety Concrete – A New Impact-Absorbing Concrete for Protecting Buildings, Structures, & People Principal Investigators: Prof. Hamlin Jennings and Prof. Jeffrey Thomas

Development of Templates to Facilitate Mitigation of the Impact of Transportation System Disruptions Principal Investigators: Prof. Joseph L. Schofer, David Schulz, & Richard Raub

INTRODUCTION

Northwestern University's Infrastructure Technology Institute supports research projects on an annual cycle, through proposals solicited from principal investigators currently funded by the Institute. Proposals from other Northwestern researchers are accepted and evaluated throughout the year. Researchers report monthly on their progress at meetings of the Institute’s Research Associates group. In addition, the Infrastructure Knowledge Manager works with each researcher to put news about research projects and research end-products on the Institute’s Web site. This report constitutes a summary of progress for each Institute-funded research project for calendar 2003.

INTRODUCING SIZE EFFECT INTO DESIGN PRACTICE AND CODES FOR CONCRETE INFRASTRUCTURE

Principal Investigator: Prof. Zdenek P. Bazant

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 American Society of Testing and Materials (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 (which earned Prof. Bazant his election to National Academy of Sciences) is now ripe, simple design formulas for particular design problems still 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 code-making societies (American Concrete Institute (ACI), ASTM, the International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM) and the International Federation for Structural Concrete (FIB), the specifications of which are generally followed by the American Association of State Highway and Transportation Officials (AASHTO), the standard-setting organization in the United States, need to be convinced of the need for a change. This is not only a problem of a sound technical argument but also a difficult and time-consuming political problem.

Project accomplishments during 2003 were:

1) A proposal for a standard fracture test exploiting the size effect was prepared and submitted to ACI, and an explanatory article was written.

2) A state-of-art report on size effect was completed by a RILEM committee chaired by Prof. Bazant.

3) A draft proposal for a new standard modulus of rupture test of concrete incorporating a correction for size effect was prepared and submitted to ASTM.

4) A size effect formula for shear design of reinforced concrete beams was set up and proposed to ACI committee.

5) A proposal for restructuring of the load factors in view of size effect was developed.

6) A study on loads of extremely small failure probability was undertaken and submitted for publication.

7) A paper on the handling the size effect in compression failure of concrete columns was written.

8) The papers from the National Science Foundation (NSF) Workshop on Durability chaired by Prof. Bazant were assembled into a special issue.

9) As a member of US National Committee on Theoretical and Applied Mechanics, Prof. Bazant collaborated on the Committee's efforts to improve the transfer of theoretical results into practice.

10) The RILEM state-of-art report of committee QFS that Prof. Bazant chairs was completed and approved by the editorial committee. It awaits final approval.

COMMERCIALIZATION OF INSTRUMENT FOR MICRO-INCH MEASUREMENT OF CRACK WIDTH IN SUPPORT OF CONTINUOUS REMOTE MONITORING FOR BRIDGE MANAGEMENT

Principal Investigator: Prof. Charles Dowding

First-Ever Commercial Instrument for Autonomous Crack Monitoring

During the fall of 2003, researchers on this project installed and began a two-year test program of the first commercial instrument developed specifically for autonomous crack monitoring. GeoSonics of Warrendale, Pennsylvania, has produced the beta test model (Figure 1) for validation under this project as GeoSonics also pursues additional validation.

Figure 1. First-Ever Commercial Instrument for Autonomous Crack Monitoring, Developed in Partnership with GeoSonics

This parallel deployment scheme was utilized by Prof. Dowding under this project and GeoSonics to enable GeoSonics to maintain clear ownership of any independently developed hardware or software. The system of parallel codeployment has allowed significant synergism as GeoSonics and project researchers can trade experience without GeoSonics fear of issues of ownership of intellectual property.

Both systems have been installed in the test house (Figure 2), which has been loaned to the project by Vulcan Materials Company, another co-deployment partner. The test house is a significant research asset as it is close to Northwestern and it subjected to blasting vibrations. Construction of such a test structure and artificially subjecting it to vibration would be a prohibitively expensive proposition. Response of the GeoSonics system will be compared to that of the project-developed system.

Figure 2. Installation of Beta Test Model of First Commercial Autonomous Monitoring Device New Berlin, Wisconsin

Papers and Articles Published

"Electromagnetic Wave Propagation Model for Differentiation of Geotechnical Disturbances along Buried Cables," Dowding CH, Summers JA, Taflove A, Kath WL, ASTM Geotechnical Testing Journal, 2002; 25 (4): 449-458, 2002

"Monitoring Deformation in Rock and Soil with TDR Sensor Cables," Dowding, C. H., Dussud, M.L., Kane, W.F. & O'Connor, K.M., Geotechnical News, BiTech Pub. Ltd., Richmond, BC, Canada, Vol. 21, No. 2, PP 51-59

(This magazine article was featured on the front cover with Northwestern and ITI attributions), 2003

"New Developments in TDR Cable Surveillance of Potential Instability," Dowding, C., Dussud, M, and O’Connor, K. Field Measurements in Geomechanics, F. Myrvoll Ed. Swets and Zeitlinger, Lisse, PP 459-468

Graduate Students Supervised

Dussud, Matthew, Graduated with MS, June 2003, Thesis title "TDR Monitoring of Soil Deformation: Case Histories and Field Techniques"

Lectures/Talks Given

"TDR Surveillance of Construction," University of Illinois, Chicago, 4/2003

"New Developments in TDR Cable Surveillance of Potential Instability," Oslo, Norway, 9/2003

COMMERCIALIZATION OF TIME-DOMAIN REFLECTOMETRY (TDR) MEASUREMENT OF SOIL DEFORMATION IN SUPPORT OF IMPROVED CONDITION MONITORING FOR BRIDGE MANAGEMENT

Principal Investigator: Prof. Charles Dowding

Design & Installation of Inexpensive Radio Communication for Florida Sink Hole TDR Demonstration Site

In the summer of 2003, continuous communication was established between the Northwestern University data polling computer and the previously-installed TDR-tiltmeter site on state road 66 near Sebring, Florida (Figure 3). This site has been chosen as a permanent demonstration site for both TDR instrumentation and autonomous monitoring of site data (see 2002 annual research report). The site was a pioneer in the autonomous monitoring and Internet-based display of data which led to the launch of the Computer Data Systems business (see below).

Communication was accomplished by 900 Mz radio connection to bridge site from a station hard wired to land line telephone. A radio based system was necessary in this location because of poor cellular connection. Poor cellular phone communication is commonplace in the United States, because of both poor coverage at remote sites and the analog rather than digital nature of US cellular communication systems. Digital systems are necessary for reliable communication of data, since date requires far higher packet transfer success rates than does voice communication.

Figure 3. Location of TDR Test Site near Sebring, FL

Engineers from the Infrastructure Technology Institute upgraded the communications system at the TDR site in June of 2003. The original installation used a cellular telephone for transmitting data to our web server. The cellular signal proved to be unreliable. The nearest land line telephone connection to the site was over a quarter of a mile away. Extending the line would have been prohibitively expensive. ITI engineers developed a wireless solution using point to point spread spectrum data radios. A modem and data radio were installed on a pole off site where telephone service was available. Another data radio was installed at the main instrumentation site to complete the link. Both sites are completely powered by solar panels. This method of communications has proven to be very reliable and FLDOT is planning to install a similar system at a TDR site in the median of a divided highway in early 2004.

The installation is on a land bridge that spans a possible sink hole (Figure 4). Included inside the solar/battery powered communication box are a TDR pulser, battery, data logger, and radio modem communication device (Figure 5).

Figure 4. Land Bridge over Sinkhole, Sebring, FL

Figure 5. Exterior and Interior of Equipment Installation at TDR Site, Sebring, FL

Launch of Civil Data Systems

For the last three years, recently-graduated NU student David Kosnik has worked with Prof. Dowding on the TDR and ACM projects. For the last twenty-four months, Dave and recent University of Illinois Graduate Matt Kotowsky have developed a family of applications to collect, process, archive, and display data from infrastructure remote-monitoring sites over the Internet. This innovative technology will allow infrastructure owners, consultants and contractors, and neighbors to obtain both real-time data on infrastructure facilities, but will also allow them to easily design customized data reports including graphs and charts, to optimize the use of the data.

Messrs. Kosnik and Kotowsky have decided to take this technology and use it to launch a company, Civil Data Systems (CDS):

http://www.civildata.com/demo.html

CDS offers infrastructure owners custom-designed services in data collection, processing, archiving, and display, relieving public agency staff, who too often have neither the time not the technical training for this sort of information processing. In doing so, CDS will facilitate the more rapid and widespread adoption of remote monitoring as a standard part of the infrastructure engineer’s "toolbox," since information processing is a major barrier to large-scale remote monitoring.

The Infrastructure Technology Institute is pleased to be helpful to these two young entrepreneurs in their business launch, through an innovative labor-sharing agreement whereby they each work half-time through the Institute as research engineers, and spend the other half of their time on their new business. The Institute is also providing CDS with office, clerical, equipment, and business planning support, in cooperation with Northwestern’s Illinois Technology Enterprise Center.

Draft Paper "Response of Cracks to Construction Vibrations and Environmental Effects"

This paper, by Professor Dowding and graduate student Mickey Snider, summarized below, describes the results of the project’s installation and operation of an ACM testing site in Las Vegas, Nevada (Figure 6):

The installation measured micro-inch response of cosmetic cracks in a typical slab on grade ranch style house to both construction equipment-induced vibration and environmental (weather) effects. ACM systems are intended to record -- with a single sensor -- micro-inch crack displacements from both long-term environmental changes and transient construction vibrations for comparison in an understandable fashion. Ground motions were measured with velocity transducers, and micro-inch crack displacements were measured with LVDT displacement gages. Construction within 14 m (45 ft) of the house involved trackhoe excavation for a 10x12 ft. reinforced concrete box culvert, chain trencher excavation for an 8-inch water service line, and vibratory compaction of trench backfill and granular sub-grade. As with many other studies of this nature, it was found that the weather induced crack response far exceeded that produced by construction vibrations even when produced by vibratory rolling within 3 m (10 ft) of the structure. More details and the full copy of the thesis behind this study can be found at www.iti.northwestern.edu/acm/.

Figure 6. Automated Crack-Monitoring Installation, Las Vegas, Nevada

Synthesis of measurements and calculations of response from the Las Vegas, Nevada site structure led to the following conclusions:

• Trackhoe, trencher, and vibratory roller construction (Figure 7) in the vicinity of the structure (<50 ft) did not create significant (>0.5 ips) ground motions.

Figure 7. Trencher & Vibratory Roller, ACM Installation, Las Vegas, NV.

• Long-term environmental and weather-induced crack displacement was 30 to 150 times greater than the crack displacement caused by the largest measured construction-induced ground motion (0.435 ips) (Figure 8).

Figure 8. Comparison of Weather and Vibratory Induced Crack Response Showing the Small Vibratory Response Compared to Weather Effects, ACM Installation, Las Vegas, NV.

• Cracks in Las Vegas site structure appear to displace in a stick-slip fashion, rather than evenly over time. Further examination of this phenomenon is needed.
• One hour of typical weather-induced Crack 2 displacement was twice as large as that produced by the largest vibratory event (0.435 ips) occurring during the same time period.
• For excitation frequencies between 20 and 30 Hz, crack displacement correlated best with peak particle velocity.
• Localized in time, component responses may have been accentuated by the small radii of curvature of the excitation vibrations.
• Cracks reacted to changes in humidity with different sensitivities, which may be the result of differences in construction as well as differences in inside and outside temperature and humidity.

Papers and Articles Published

"New Approach to Control Vibrations Generated by Construction in Rock and Soil," Dowding, C.H. Snider, M.L., Soil and Rock America, Proc. 12th Pan Am. Conf. and 39th U.S. Rock Mech. Symp. At MIT, Cambridge MA. Culligan, P.J. et al Eds., VGE Essen Gr., ISBN 3773959850, pgs 2683-2690,, 2003

"Micro-Meter Measurement of Cracks to Compare Blast and Environmental Effects," Dowding, C. and Lewis, M., Proceedings, 29th Conference on Explosives and Blasting Technique International Society of Explosives. Engineers, Cleveland, OH, Vol. II, pp 245-269, 2003.

"Blasting Complaints: Old Problem, New Approach, Just for the Record," Dowding, C.H, Instantel Co. News letter, Vol. 2, Q 3, 2002

"Effect of Blast Design on Crack Response," Dowding, C. and Snider, M. Explosives and Blasting Technique, Proceedings of the EFEE 2^nd World Conference on Explosives and Blasting Technique, Prague, CZ. Balkema, PP 573-582.

Graduate Students Supervised

Snider, Mickey, Graduated with MS, June 2003, Thesis title, "Crack Response to Weather Effects, Blasting, and Construction Vibrations"

Sullivan, Laura, Second Year student, beginning thesis work on methods for measuring the age of a crack.

Lectures/Talks Given

"New Approach to Control of Vibrations Generated by Construction in Rock and Soil," MIT, Cambridge MA, 6/2003

"Micro-Meter Measurement of Cracks to Compare Blast and Environmental Effects," ISEE, Nashville, TN, February 2003

"Effect of Blast Design on Crack Response," EFEE, Prague, Czech Republic, September 2003

Undergraduates Supervised

Chok, Ker Min: Graduating Senior: Rewrote NUVIB for graphical user interface. Software given away on ITI – ACM website

Kosnik, David: Graduating Senior: Wrote software for Autonomous Monitoring and has started own enterprise, Civil Data Systems.

Griffiths, Luke: Junior, Deploying the software written by Chok, maintaining CHD records and assisting with publication work.

IMPROVED CONDITION MONITORING OF BRIDGES: NONDESTRUCTIVE EVALUATION OF FOUNDATIONS

Principal Investigator: Prof. Richard Finno

The purpose of this project is to develop methods to non-destructively evaluate the condition of existing deep foundations and bridge piers.  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.  After developing an experimental system for inducing high frequencies bursts of energy, we conducted the laboratory tests on concrete piles in a free condition, i.e., no soil surrounding the concrete (Figure 9), and field tests on prototype piles installed at the Northwestern NGES to verify the theoretical solution and evaluate the test equipment.

Figure 9. Freestanding "Prototype" Concrete Pile, Vibrator & Accelerometers

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. Whereas the theoretical solution for flexural wave propagation in a concrete cylinder has been published, to use the information, one must numerically evaluate the solution to find propagation velocities and displacements. The solution for embedded cylinders that represent concrete piles has not been published for flexural wave propagation. Hence to extend non-destructive techniques to allow application of higher frequencies, and hence create the ability to sense smaller defects, we have developed numerical solutions for flexural wave propagation in cylinders.

Summary of progress

The work this past year focused on development of numerical solutions for flexural wave propagation in concrete cylindrical elements, and development of an experimental system that utilizes the guided wave approach for both flexural and longitudinal wave excitations.

The results of numerical calculations for flexural wave propagation are shown in Figure 10 for the first three branches of flexural wave modes. The calculations are for a concrete pile embedded in relatively soft soil, although the same trends will occur for other soil stiffness. Plots of non-dimensional frequency versus real and imaginary parts of the wave number are shown on Figures 10a and 10b, respectively. Results shown on Figure 10a can be used to compute the propagation velocity at a particular frequency. The imaginary part of the wave number in Figure 10b is proportional to the geometrical attenuation and can be used to evaluate how far a given mode will travel along a pile. As shown in (10a), the first branch has the lowest geometric attenuation at non-dimensional frequencies less that 3.5, and the third branch has the lowest values at non-dimensional frequencies greater than 3.5. On this basis, our field verification will focus on these two branches.

(10a) (10b)

Figure 10. Numerical Solutions for Flexural Wave Propagation in a Cylindrical Pile

Figure 11 shows the results of the numerical solution in terms of group velocity ratio, C_g, versus non-dimensional frequency. The propagation velocity is computed by multiplying C_g by the shear wave velocity. The dispersive nature of the flexural wave is clearly seen, especially at the lower non-dimensional frequencies for each branch.

We have begun to conduct laboratory verification tests of the flexural wave system. In tests wherein flexural waves are to be induced, a single shaker is mounted in the center of a cylinder with incident angles of 45° and 90°, as shown in Figure 12. In these cases, multi-axial accelerometers are mounted on the top surface of the concrete to measure the response and verify the mode of the received signals.

Figure 11. Group Velocities for Flexural Waves

Figure 12. Shaker and Transducer Arrangement for Flexural Wave Tests

We have also used a simple impact method to generate flexural waves with frequencies less that 2000 Hz. We use an impact hammer that we have long used for longitudinal tests at relatively low frequencies to strike the side of the cylinder and measure the responses along the length of the pile with two transducers. We have performed such tests at the Advanced Waterfront Technology Test Site (AWTTS) dock facility at Port Heuneme, California, for the US Navy in 2002. We recently have reinterpreted these results and have found that the surface waves we measured on the sides of the piles propagated at velocities of flexural waves as predicted by the results of the theory in Figure 10. A more complete verification of the flexural wave theory will be conducted in laboratory and NGES field tests at frequencies as high as 25 kHz.

Personnel

Prof. Richard Finno has been assisted by post-doctoral fellow Dr. Hsiao-Chou Chao and two PhD candidates in Geotechnical Engineering, James Lynch and Helsin Wang.

Publications

Wang, H. and Finno, R.J., "A Modified Impulse Response Method to Evaluate Foundations of Overwater Structures," Proceedings, The 10^th Taiwan Geotechnical Conference, Taipei County, Taiwan, Oct., 2003

Chao, H.-C. and Finno, R.J., "Non-destructive guided wave approach and cylindrical concrete," ACI Materials Journal, ACI International, submitted

Chao, H.-C. and Finno, R.J., "Guided Wave Experiments for Cylindrical Piles," Geotechnical Testing Journal, ASTM, submitted.

Finno, R.J. and Chao, H.-C., "Guided Waves in Embedded Concrete Piles," Journal of Geotechnical and Geoenvironmental Engineering, ASCE, submitted

Finno, R.J. and Chao, H.-C., "Shear Wave Velocity in Concrete Cylinders and the Universal Mode Method," ACI Materials Journal, ACI International, submitted

ALLOWABLE DEFORMATIONS OF GAS MAINS ADJACENT TO DEEP EXCAVATIONS

Principal Investigator: Prof. Richard Finno

Many deep excavations are made as part of projects that modernize existing urban infrastructure. Because many utilities, including gas mains, are located under the streets, they deform with the ground as the ground adjacent to an excavation moves in response to the attendant stress relief. Surprisingly, there are no universal guidelines for allowable deformations for buried gas mains or other utilities adjacent to excavations. This lack of standards leads to either ignoring the possibility of damage to gas mains when an excavation is made, or arbitrarily selecting a movement criterion for an excavation project, the purpose of which is to prevent damage to utilities. For example, the City of Chicago requires in some projects that settlements in the street caused by an excavation be limited to two inches. This criteria is imposed regardless of the utility being protected, proximity of the utility to an excavation, and the type of pipe being protected. Furthermore, if a gas main were to uniformly settle two inches, no additional stress would be imposed in the pipe. It is distortions that will induce stresses in a pipe that can lead to damage.

Northwestern University is constructing the Lurie Research Center on its Chicago campus. As part of the work, a 42 ft. deep excavation has being made, as shown in Figure 13. Construction started on April 1, 2002, and superstructure construction continues at the time of this writing.

Figure 13. Lurie Research Center Site as Excavation Neared Final Grade, Chicago, IL

The excavation support system consisted of a PZ27 sheet-pile wall supported by 3 levels of tieback anchors. From the ground surface, the stratigraphy generally consists of 15 ft of rubble fill, 15 ft of medium dense beach sand, 13 ft of soft to medium stiff clay, 40 ft of stiff to very stiff clay overlying hard glacial till, known locally as hardpan. The excavation bottomed out in the soft to medium clay. The water table is located about 15 ft from the ground surface. The upper two tieback anchors are founded in the medium dense sand, and the lower tieback anchor is located in the very stiff clay and hardpan.

Figure 14 shows a plan view of the excavation, adjacent utilities and the surrounding area. Gas mains and other utilities run parallel to three sides of the excavation. There are four gas mains that bound the excavation, two under Huron Street and one each under Superior Street and Fairbanks Court. The Prentice Women’s Hospital lies to the east of the excavation. The hospital is supported on deep foundations, so the design criteria for movements associated with the excavation are intended to limit damage to the utilities.

Figure 14. Plan View of Lurie Center Excavation & Adjacent Gas Mains, Chicago, IL

Also shown in Figure 14 are the locations of the instrumentation installed at the site to monitor the ground deformations associated with the excavation. This instrumentation consists of 149 ground surface survey points, 16 ground anchors set about 2 ft below ground surface, 30 utility settlement indicators, and 8 slope inclinometers. This extremely detailed array of observation points allowed one to determine the three-dimensional response of the ground to the excavation process, and allowed us to develop an empirical method to predict magnitudes and distribution of ground movements around an excavation that can be used as an input to stress and rotation analyses of pipes. This method was found to be valid for reported movements at other excavations.

The objectives of this research was to use the extensive monitoring data from the Lurie Research Center excavation to evaluate the effects of the deformations of gas main pipes and other utilities on the stresses in the pipes, to conduct a comprehensive stress analysis of the gas mains including the connections, and to develop rational methods to define the allowable deformations of such buried pipes when impacted by excavations in urban areas.

Summary of Progress

This research project was completed during 2003. The following procedure was developed to determine the magnitudes of stresses and rotations in a pipeline caused by excavation-induced ground movements:

1. Determine the maximum lateral ground movements from semi-empirical or finite element methods. Estimate the maximum vertical movement from the value of the lateral movement, and develop a proposed ground surface settlement profile at the pipeline location based on:

(1)

where d(x) is the settlement or lateral movement at distance x from the corner of the wall, d_max is the maximum movement, A is the distance to the inflection point of the function to the corner of the wall, and B is an empirical shape factor. Positive values of settlement should be used and lateral movement should be considered positive towards the excavation. The value of A is determined from a relationship with the ratio of the depth of the excavation to the length of the wall, H_e/L. The value of B can be calculated from the value of A from the following expression:

(2)

2. The maximum stresses and rotations in the pipeline are determined from two limiting conditions:

a. First, the pipeline is assumed flexible and a bending analysis is conducted to determine the maximum tensile stress occurring in the pipe. Bending is of greatest concern at the location of the displacement profiles where the curvature is the largest. The curvature is calculated at a point j from the lateral and vertical displacement profiles causing a differential movement of point j with respect to two adjacent points along the pipeline by the following equations:

(3)

(4)

where ε_ji = X_j-X_i is the differential lateral movement between points i and j (i,j = 1,2,3,..n), L_ji = Y_j-Y_i is a characteristic length defined as the distance along pipe between points i and j, and ρ_ji = Z_j-Z_i is the differential settlement between points i and j. The displacements are defined in the local coordinate system as X_i and Z_i representing the total lateral and vertical movements at point i, respectively, and Y_i is defined as the distance from the origin along the pipeline to point i. In defining a characteristic length, L_ji, for the curvature calculations, the distance should be large enough to reasonably reflect the curvature in the pipeline.

For a pipe subjected to bending, there is a distribution of tensile and compressive stresses within the cross section. An equation for stress at a point i along the pipeline was derived in terms of the pipe radius, r, and the angle from the positive x-axis, θ:

(5)

To calculate the maximum tensile stress within the cross section, this expression has to be maximized. By taking the derivative of the stress with respect θ, the expression for the angle of the principal plane can be found as:

(6)

The value of the maximum tensile stress is determined by substituting the results of (6) into (5).

b. The pipeline is then assumed to behave rigidly, and a joint rotation analysis made to determine the largest possible rotation along the pipeline. The pipe sections can be represented as vectors that intersect at the joint. The angle between them, or the distortion at the joint, can be calculated if the differential movements are known. The differential lateral and vertical displacements, e_ji and r_ji, are as previously defined for the bending stress analysis. The characteristic length, L_ji, is defined by the pipe section length of the pipeline. The rotation at joint j, α_j, can be calculated using the following expression:

(7)

For buried pipelines, the locations of the joints may be unknown. In this case, in order to determine the maximum potential joint rotation along a pipeline, a joint should be assumed at one end of the displacement profile. The next joint should be located on the displacement profile a distance of a pipe section length along the pipeline. The line connecting these two points represents the pipe section between these two points. This should be continued to the other end of the profile. Once the rotations are calculated, the same procedure should be repeated after offsetting the location of the first joint. Multiple analyses should be completed with the offset increasing until it is as long as the length of a pipe section. From these analyses, the maximum potential joint rotation can be determined.

3. The maximum tensile stress and joint rotation values should then be compared to the allowable values given in Tables 1 and 2, respectively. If the values predicted fall below the minimum allowable values, the pipeline should be safe under the imposed ground deformations.

Table 1. Allowable Bending Stresses from Excavation-Induced Movements

Table 2. Allowable Joint Rotations for Cast Iron and Ductile Iron Joints

Personnel

The principal investigator for this work was Professor Richard Finno. One graduate student, Kristin Molnar, an MS student specializing in structural engineering has focused on the analyses of the gas mains and the parametric studies. She completed her MS degree this year. Prof. Ed Rossow helped develop the procedures for the structural analysis of buried pipes. Other students funded in part from different sources also worked on this project, including Jill Roboski, a PhD student, is responsible for the evaluation of the field data, Terence Holman, a PhD student, who is working on defining the small strain behavior of the compressible glacial clays, and John Glatt, Jeff Hoffman and Matt Weil, undergraduates who participated in the project under the auspices of the National Science Foundation’s Research Experience for Undergraduates (REU) program.

Publications

Finno, R.J. and Roboski, J.F., (2004) "Three-dimensional Responses of a Tied-back Excavation through Clay," Journal of Geotechnical and Geoenvironmental Engineering, ASCE. Submitted for publication.

Molnar, K.M., Finno, R.J. and Rossow, E.C., (2004) "Analysis of Effects of Deep Braced Excavations on Adjacent Buried Utilities," Final report to the Infrastructure Technology Institute, Northwestern University.

R. J. Finno, J. Roboski, and J. Hoffman, "Ground movements caused by caisson installation at the Lurie Excavation Project," Proceedings, Geotrans, 2004, ASCE, Los Angeles, CA, 2004

R. J. Finno, J. Roboski, and J. Glatt, "Sheetpile-induced vibrations at the Lurie Excavation Project," Proceedings, Geotrans, 2004, ASCE, Los Angeles, CA, 2004

A paper describing the procedure presented in this summary is currently being prepared.

BRIDGE ASSET MANAGEMENT BASED ON LIFE-CYCLE COST CONSIDERATIONS

Principal Investigator: Prof. Raymond J. Krizek

Associate Investigators: David Novick, Prof. Ahmad Hadavi, Prof. Pablo Durango-Cohen

Bridge asset management based on life cycle cost considerations provides a resource allocation framework for cost-effective decision-making on how to build, preserve, and improve a bridge to minimize its life cycle cost while achieving a satisfactory level of service over the useful life of the bridge. This research uses actual historical cost data from a variety of geographically distributed bridges of different structural designs to formulate a cost model for bridge life cycle cost, assess the impact of deferred maintenance on bridge total life cycle cost, and develop a supporting rationale for projecting the useful life of a bridge. Guidelines are being prepared to suggest the actions that must be implemented to achieve the target useful life. The results of this study will provide critically needed supplemental input information for currently used bridge management systems, such as PONTIS, and more recent bridge life cycle cost analysis tools, such as BLCCA; input to these systems is currently obtained primarily from expert elicitation.

Chicago Movable Bridges

Chicago has more movable bridges than any other city in the world. Evolved from earlier types of movable bridges, including swing bridges and rolling lift bridges, the double-leaf trunnion bascule type most satisfactorily met the existing conditions and became most popular in Chicago. Among the 63 original movable bridges, 32 are double-leaf trunnion bascules. It is proposed to concentrate on this bascule type and collect all available historical data from the city public library and the city bridge bureau. Thus far, we have identified 21 double-leaf trunnion bascules built before 1940 to have the most complete cost data, including initial construction cost, annual MRR cost for years before 1980, and capital improvement (major repair, rehabilitation, and reconstruction or MRR) costs for years from 1980 to 2001.

The total life cycle cost or asset value of a bridge consists of its initial construction cost and MRR costs accumulated over its life-time. By using the Engineering News Record (ENR) Building Cost Index (BCI), these historical costs have been adjusted to year 2002, and typical total life cycle cost versus time curves, such as shown in Figure 15, have been plotted to indicate the basic pattern of total cost distributed over time.

Various statistical analyses can be conducted to illustrate the relationships among total cost, initial cost, MRR costs, structure size, number of major improvement, bridge age, latest bridge condition, latest traffic volume on bridge, predicted growth of traffic volume on bridge, and frequency of bridge opening. Using the ratio of total life cycle cost to initial cost as the dependent parameter, Figure 16 shows example of how this varies as a function of bridge age. Other more complex relationships will, of course, be studied, but have not yet as of this time.

Figure 15. Sample Life Cycle Cost Curves for Chicago Bridges

Figure 16. Ratio of Total Life-Cycle Cost to Initial Cost
vs. Bridge Age for Chicago Bridges

The historical data and preliminary analyses suggest the following basic findings for Chicago double-leaf trunnion bascules:

• Useful life can be more than 100 years
• Older bridges have higher TLCC/IC ratios, as expected
• Bridges in better condition have higher TLCC/IC ratios
• Major MRR cost items are deck overlays, structural repairs, painting, sidewalks, bridge house, machinery, and electrical equipment
• Major MRR cost items are deck overlays, structural repairs, painting, sidewalks, bridge house, machinery, and electrical equipment
• Initial costs and MRR costs - For these Chicago bascules, many factors may influence MRR costs, so it is inappropriate to conclude that higher initial costs should result in lower MRR costs, because higher initial costs might be attributed to various other causes, such as traffic volume or the frequency of bridge opening. However, in general, if the initial design is conservative or designed to facilitate future MRR, the higher initial cost will result in lower MRR costs, so that eventually the total life cycle cost is lower.
• Distribution of MRR costs - Attempts are currently being made to determine the distribution of MRR costs among structural, painting, machinery system, and electrical equipment.

An attempt was made to collect historical cost data for highway bridges from the Illinois Department of Transportation (IDOT). From the IDOT data base, the oldest bridges (built before 1930) with a total length greater than 100 feet and a main span constructed of steel were identified. In addition, four truss bridges over major rivers were selected. The basic relevant data for these bridges were obtained from IDOT headquarters in Springfield and some supplemental data were gotten from Schaumburg (IDOT District One). In general, the initial cost information is limited and routine maintenance costs are not readily available. No analyses have yet been conducted.

Some preliminary data from four bridges and two tunnels in New York City have been obtained, but we are still seeking detailed maintenance and rehabilitation cost data. We are in the early stage of evaluating the impact of design, maintenance, and rehabilitation practice on the total life cycle cost of the Chicago bridges for which data have been collected. Finally, a sensitivity analysis is being conducted to assess the variations involved in the use of various cost indices to adjust the cost data temporally.

Prof. Hadavi presented a talk titled "Empirical Study of Life Cycle Cost for Bridges" to the Chicago Midwest Section of AACE International (formerly American Association of Cost Engineers) on December 4, 2003.  An abstract titled "Whole Life Costing Study for Chicago Movable Bridges" was submitted for the inclusion in the program of the Second International Conference on Bridge Maintenance, Safety and Management (IABMAS04 in Kyoto - Japan) and has been accepted; the full paper is due April 1, 2004.

THE INFRATRUCTURE CONSTRUCTION AND CONDITION MONITORING LABORATORY (ICCML) AS A NOVEL TEACHING TOOL TO IMPROVE UNDERGRADUATE EDUCATION AND STUDENT LEARNING OF CIVIL ENGINEERING

Prof. Roberta Massabò, Principal Investigator

The project deals with the development of multimedia supported case-study material for undergraduate civil engineering courses. The project aims at using the Infrastructure Construction and Condition Monitoring Laboratory (ICCML) of the Infrastructure Technology Institute, its web site and remotely operated web-cameras as a novel teaching tool to enhance undergraduate education.

Teaching material (courseware) has been developed using the case study method and new technologies. The courseware is incorporated into a highly structured and expandable web site and deals with an in-depth analysis and presentation of the 11th Street Pedestrian Bridge, a project of the City of Chicago that has been recently completed at the south-west end of Grant Park. Real time view of the operations during construction has been made possible through a remotely-operated web camera that overlooked the construction site.

The main educational goal of the project is to bring knowledge from the infrastructure/building industry to university curricula. The web site allows active monitoring of construction sites that would otherwise be restricted and incorporates information on the history of the projects, construction plans, design drawings, calculations and other material that would otherwise be confidential and restricted to the design team and contractors. The courseware is intended to be a tool to synthesize and apply knowledge acquired in different undergraduate civil engineering courses through interactive activities, quizzes and open-ended problems.

The project has been executed by the graduate student Randy Herbstman under the supervision of the PI. Brian Nielsen, manager of Learning Support Systems, and Jonathan Smith, Distributed Learning Architect, of the Academic Technologies Department of Northwestern University have guided the team in the design and development of the web site, navigational paths and interactive activities.

The first year of the program has been devoted to six activities:

Activity #1 - Bibliographical investigation on the use of the case study method, new media and new technologies in teaching at high level institutions

Activity #2 - Bibliographical investigation of prior experiences in educational projects based on the use of new technologies in teaching

These preliminary cognitive phases enabled the definition of the main requirements that the civil engineering projects used as case studies and the courseware should satisfy. The civil engineering projects used as case studies should:

(1) Involve different aspects of civil and environmental engineering – the courseware is a tool to synthesize and apply knowledge from different civil engineering courses;

(2) Be large scale, with a high visibility and a high level of public involvement – the courseware explores all aspects and phases of a project, including project history, environmental issues and public involvement, project criteria, alternatives, selection processes; and

(3) Have a long duration (lifecycle of the construction) to allow real time view of the construction operations using the remotely operated web camera – the web camera overlooks the construction site allowing for: creation of time-lapse short videos covering project progress and individual processes, extraction of still images of structural details to manipulate and annotate, real life interviews to engage students in discussions with project managers, practitioners, …

The main features of the courseware (web site, educational paths, interactive activities) are:

(1) The civil engineering project is presented as a case history with an accurate review of the different phases of the project, successful and unsuccessful events, design, construction processes, equipment, materials;

(2) The material is organized in a hierarchical structure with an expandable modular approach integrating basic media: text, graphics, video, simple animation;

(3) A highly structured package is generated for effective learning, allowing for individual item viewing (to support specific classes and lectures) and sequential learning (to proceed chronologically through the project) and avoiding the possibility of loosing track of the navigational path;

(4) The possibility that different amounts of knowledge can be reached if the students follow different navigational paths is accounted for and suggested paths are created with progressive assessment of level of knowledge acquired to move to the next step;

(5) Information is organized into small units and additional printable documentation from books, original documents, plans, etc. is included, along with links and references, to allow further study and investigation;

(6) A project glossary is included to help students with interpretation of legal documents and professional acronyms;

(7) A limited level of interactivity is included through interactive problem solving, electronic quizzes, open ended problems;

(8) Usage outside of classroom (e.g. homework) is allowed and properly organized to give students the time to think and understand;

(9) Project managers, practitioners, structural engineers are brought into the classroom with recorded and real life interviews to engage students in discussions; and

(10) Different educational paths for different levels of instruction are generated (beginner, intermediate, advanced).

Activity #3 - Preliminary analysis of two civil engineering projects, the Hoover Dam Bypass (Arizona/Nevada border) and the 11th Street Pedestrian Bridge (Chicago, IL), that have been selected as possible case studies; final selection of the 11th Street Pedestrian Bridge project in Chicago as exemplary case study

Two civil engineering projects have been examined for the selection of the exemplary case study. The first project is the Hover Dam Bypass, a composite bridge under construction in front of the Hover Dam that connects the Arizona and Nevada sides of the canyon. The material available at the Hover Dam Bypass web site (www.hooverdambypass.org) has been examined. The material included information on the history of the project, environmental issues, public involvement, project criteria, project alternatives and selection processes, surveys and mapping, geotechnical, seismic and wind investigations, bridge preliminary design and bridge type selection.

The second project is the 11^th Street Pedestrian Bridge, a project of the City of Chicago under construction at the south-west end of Grant Park. The material available at the offices of the City of Chicago included information on the history of the project, project criteria, bridge preliminary design.

Following this preliminary analysis, the 11th Street Pedestrian Bridge project has been chosen as exemplary case study. The choice has been motivated mainly by the accessibility of information and material and the interest shown by the engineers and managers of the City of Chicago to collaborate in the educational project. Furthermore, for its importance in the current activities of redevelopment and revitalization of Grant Park and since it deals with different aspects of civil engineering, the project satisfies all requirements set up in the first phase of the work. In the summer 2003 a web-camera was placed on the roof of a high-rise building on Michigan Avenue overlooking the construction site.

Activity #4 - Analysis of the project material (specifications for bid, drawings, Calculations, etc.) produced by the City of Chicago and its consultant.

A highly structured web site was designed to allow effective learning following the requirements set up in the first phase of the work. The web site can be accessed at the URL http://www.iti.northwestern.edu/iccml/

The web site has a hierarchical structure with an expandable modular approach allowing for individual item viewing and sequential learning. The material is organized into small units and additional printable documentation is included from books, design drawings, plans, original documents, along with links and references to allow further study and investigation (Figures 17 and 18).

Figure 17. Project Web Site Home Page

The homepage of the project website (Figure 17) allows users access to the different civil engineering projects that have been considered. The tabs across the top of the screen provide direct links to the projects, e.g. the 11th Street Pedestrian Bridge, Hoover Dam or any other future endeavor. The buttons down the left side of the screen allow users to access the projects through subject areas or disciplines, e.g. Structural Engineering and Mechanics, Environmental Engineering, Geotechnical Engineering, Transportation Engineering. Using these buttons a student/user wishing to learn about only one topic area will have access to information available on all projects on that specific discipline. The Interactive Activities link provides a portal to all of the teaching/learning activities that have been created for the different projects. The Teaching Philosophy button gives the visitors an understanding of the educational goals behind the creation of the site.

Different teaching/learning modules are currently under development that deal with structural engineering aspects. A limited level of interactivity is currently been included through interactive homework assignments and electronic quizzes.

Suggested methods to convey the material are presented in the section Teaching Philosophy of the web site.

Figure 18. 11^th Street Pedestrian Bridge Web Page

When the 11th Street Pedestrian Bridge Project tab is clicked from the website, the project page appears (Figure 18). From this page the users still have access to the other projects of the website. The section outlines the design and construction of the bridge. Introduction and History gives background information about Grant Park, where the bridge is located, and some information about the area and its recent redevelopment. The Project Site section describes the layout of the area where the construction is located. Major Structure Selection deals with the design decision process and examines the different options considered. Project Design provides information about how the design was accomplished and illustrates some of the resulting plans. Project Construction and Project Management provide some of the documentation produced by the City of Chicago during the construction process. A link to the web camera overlooking the website and timelapse photography is available at the button Web cam. An example of the photos collected is shown above. The Teaching Tools section contains the Interactive teaching/learning modules created for the project. The Current Progress button chronicles the construction using photographs taken on the site.

Activity #5 - Design and development of the basic structure of the web site that contains the courseware and progressive incorporation of teaching material

Portions of the design material related to the 11th Street Pedestrian Bridge was obtained from the City of Chicago and its consultant, H.W. Lochner, in the summer 2003. The material consists of: Project Specifications for Bid, Design Drawings and Design Calculations. The material has been analyzed and checked in order to be used for the presentation of the case study as a case history and for the development of the interactive activities dealing with structural engineering aspects.

Activity #6 - Layout of the first module of interactive activities dealing with the design of the prestressed reinforced concrete beams of the bridge

A first module of interactive activities is currently been developed under the supervision of Jonathan Smith of the Academic Technologies Department of Northwestern. The module deals with the design of the prestressed concrete beams and examines different design issues: choice and characterization of the structural materials, selection of the design parameters and safety factors from the building codes, calculations and review of the structural components. The general structure of the module is presented in Figure 19.

The Teaching Tools page (Figure 19) created for the 11th Street Pedestrian Bridge takes users through designing the prestressed concrete beams of the bridge. The tabs across the top illustrate the eight major steps/areas that are involved in the design and a brief description of the content is given in the vertical tab on the left.

Design Philosophies introduces the students to the building codes and specifications used for the project. It also explains the design philosophies behind the specifications and the limit states that are considered for the design.

Structural Materials is a brief introduction to the building materials that are used in the beams as well as the prestressing techniques. In Design Parameters the students calculate the parameters necessary for the service load design and the limit state design. The Loads section calculates the load acting on the structure as well as the relevant load combinations. Structural Models describes the structural schematics used to analyze the beams. Strength Limit States illustrates the strength design of the beams. Serviceability Limit States illustrate the design of the beams for serviceability conditions. The Design Summary is a wrap up of all the sections where the safety and usability of the structure is verified. The interactive sections of the Teaching Tools were created using Flash.

Figure 19. Teaching Tools Web Page

An example of interactive activity under the section Design Parameters is shown in Figure 20. The example deals with the calculation of the allowable stresses for concrete and steel for the different loading stages. This is one of the interactive modules created in the Design Parameters area. It deals with finding the allowable stresses for the beam cross sections as specified in the AASHTO Specifications. On the left is background information written to help the student understand the theory before they perform any calculations. The tables in the center of the module are copies of the tables in the Specifications where the allowable stress factors are given. The student will move through each of the parameters provided selecting the correct entry. This will automatically input the resulting factors into the equation on top. The students must then choose and input the appropriate nominal strengths to get the allowable stress. Once the student is ready to move to the next section he/she can check the answers using the Check and Proceed button. If any of the answers are incorrect a box will pop up identifying the mistake and suggesting proper solutions.

Figure 20. Allowable Stresses Teaching Tools Web Page

NONDESTRUCTIVE TESTING AND EVALUATION OF BRIDGES

Principal Investigator: David Prine, Institute Chief Research Engineer

Miller Park

In 2003 engineers from the Institute conducted additional acoustic emission (AE) tests on components of the segmental moveable roof at the Miller Park baseball stadium, Milwaukee, Wisconsin, building on the work undertaken in 2002 which helped support a redesign of the roof segment pivot bearings. After the damaged pivot bearings were replaced with the new design over the winter of 2002/2003, three more tests were run on the moveable roof and its associated equipment. The roof segments are moved by electric locomotives, called "bogies", attached to the outfield end of the stadium roof segments. These bogies have been emitting strange noises during use. The engineers working for the Miller Park authority were unable to identify the source or mechanism generating these noises. ITI was invited to return and apply acoustic emission techniques to localize the noise source(s).

Figure 21. Acoustic Emission System Mounted on Roof Segment
Miller Park, Milwaukee, WI

Three roof segments were tested during two separate sessions. The need to monitor a large piece of machinery which rolls, rotates, and translates presented a unique AE challenge. Our solution was to affix the entire AE system and one ITI engineer to the catwalk of the moving roof segment (Figure 21). A custom rotating interface was fabricated by ITI engineers to allow AE measurements on the rotating axle. We were able to successfully determine that the bearing/ housing area on either side of the idler wheel axle was the source of the noise. The bogies are scheduled to be completely replaced in order to address this and several other deficiencies. Our third visit to Miller Park was to record baseline acoustic emission readings on the newly installed pivot bearings. The baseline tests detected no AE, a marked improvement over the original bearings.

Michigan Street Bridge

The Michigan Street Bridge is a rolling bascule type moveable bridge located in downtown Sturgeon Bay Wisconsin (Figure 22). This 1930 vintage structure is one of only two active bridges providing access to the Northern Door County peninsula. The bridge serves as a vital physical and economic link to the city. Wisconsin Department of Transportation (WisDOT) inspections from 1994 to the present have documented the ongoing deterioration of the structure.

Figure 22. Rack and Pinion Support Structure,
Michigan Street Bridge, Sturgeon Bay, WI

The Institute has been continuously monitoring the condition of the bridge for WisDOT since 1995. The original monitoring system consisted of an onsite PC, two Somat 2100 data loggers, eight strain gages, and four tilt meters. Institute engineers periodically called the on site PC via modem, downloaded the data, reviewed and then archived it. This system worked well, but depended entirely on the engineer or technician downloading the data. Recent advances in sensors and data acquisition technology combined with an increase in the number of remotely monitored sites maintained by ITI prompted a proposal to WisDOT to upgrade the Michigan Street Bridge monitoring system in 2002.

This system with further 2003 upgrades is now operating with autonomous data acquisition. These upgrades include a new on site PC in order to take advantage of new data acquisition software. Hardware and software upgrades addressed stability and reliability issues. While onsite, ITI engineers performed a complete system check and sensor inventory. The most important sensor additions were the motor current probes and new strain gages on the underside of the racks of the rack and pinion drive system (Figure 20). These new sensors will provide more indications and information on overall changes in the structure. ITI requested a survey and quotation for bringing high speed internet access to the bridge. Unfortunately, the provider determined several thousand dollars worth of excavation would be required to bring service to our site. We are currently pursuing an agreement to share service over a wireless connection with a nearby hotel. Since late July, the system has been automatically gathering data and sending it to the ITI web server for archiving and display. We are now providing user specified notification (email, pager, fax, etc) and complex data reduction techniques to the Michigan Street website.

I-94 and SR-100 Bridges Milwaukee WI

Wisconsin department of Transportation engineers contacted ITI to perform strain gage testing on two freeway overpass bridges in Milwaukee under our task order contract. Testing initiated in 2002 was concluded in 2003. Both bridges exhibited cracks in welded details and the WisDoT engineers wanted to know if the cracks were being driven by large live loads. ITI engineers used medium term (months) strain gage monitoring to determine that significant traffic live loads were not present at either bridge.

Automated Internet-Based Remote Monitoring

ITI continues to use Automated Internet Based Remote Monitoring as its primary data display and archiving method. As indicated above, in 2003, two former ITI student employees have formed a private company, Civil Data Systems, providing automated internet based remote monitoring services. ITI has committed to incubating this new company for the next year by providing space in a corner of our lab, limited access to certain ITI resources, and guidance from ITI senior staff.

AEWG 46

David Prine, the Institute’s Chief Research Engineer attended the 46^th meeting of the Acoustic Emission Working Group in Portland, Oregon, in August of 2003. Mr. Prine gave a two hour invited lecture covering the application of AE to the NDE of large civil structures. This lecture was part of a one day tutorial on AE basics. He also presented a paper during the regular technical session entitled, "Application of AE to the Localization of Noise Sources in Large Civil Structures." Mr. Prine also received the Joseph Kaiser Achievement Award in recognition of his extensive work in developing application techniques and advancing the state of the art of AE.

ASCE/AISC Steel Bridge Competition

Sixteen students participated in this year’s competition with Dan Hogan acting as staff advisor. They designed a twenty-four foot bridge that spans a simulated river with an island in the middle. The team designed the bridge and fabricated the bridge, under Mr. Hogan’s supervision, in the Mechanical Engineering Prototype Shop. The students spent many hours on the design and fabrication. After fabricating the bridge, they were able to analyze the problems that they discovered and devise solutions. The competition was held on May 3^rd in Evansville, Indiana. The team was in third place when a connector failed and the bridge was disqualified. Overall, this year’s effort was very good. Professor Hadavi coached the team on project management and they were able to keep to the schedule that they set for themselves. The students gained considerable experience in solving engineering problems and managing a project while at the same time enjoying the camaraderie and finally the excitement of the competition with other mid-west engineering schools.

Computer-Aided Design

The Institute purchased a computer and set up a self-teaching program so that students can learn the newest CAD software for civil engineers. ITI acquired a network license for twenty-five seats of the complete Autodesk package, including AutoCAD, Land Desktop, Civil Design Series, Raster Image, Autodesk Map and Inventor. As of December 31, 2003, we have AutoCAD 2004 and Inventor release 7 and Land Desktop 2004. We are awaiting publication of a new book on Land Desktop.

ITI also purchased instructional materials on Land Desktop R3 in the form of two sets of instructional DVD’s which have proven successful in teaching this powerful Civil Engineering tool to engineering students.

A Civil Engineering senior used the two sets of DVD’s, which contain over twelve hours of instruction on Land desktop and Civil Design, to teach herself these two very powerful programs. She was able to learn both programs by going through those tutorials and by watching the DVD’s.

Using Land Desktop and Civil Design, the student was able to take available data from the Illinois Railway Museum and additional data from the National Geologic Survey and develop two possible scenarios for a project at the Illinois Railway Museum at Union, Illinois. Using this software, she was able to create solid models of the site, a proposed bridge installation at the site, and a box culvert design. She did this project under the guidance of Professor Robert Gemmell and was awarded C-99 credit for it.

AUGI World, a magazine that is read worldwide by over 200,000 AutoCAD users, interviewed this student for an article on self-teaching programs. The article will appear in the May issue of AUGI World. As a direct result of this student’s success, other students are now interested in this method of learning these highly specialized CAD programs for civil engineers. There is renewed interest in the project at Union, Illinois. Learning these highly productive tools greatly increases a graduate’s marketable skills.

Faculty Support

The Institute notifies the faculty whenever field engineering work is planned. The faculty and their students are invited to participate.

Institute research engineers are currently providing assistance to graduate students who are conducting research efforts under Professors Dowding and Finno. The efforts under Professor Dowding are focused on development and commercialization of his remote crack monitoring technology. Assistance to Professor Finno focuses on his efforts to monitor potential movement of the Northwestern Technological Institute resulting from the excavation work currently underway for construction of the new Ford Design Center.

Streaming Video

ITI has continued to keep video records of notable events and presentations. A unique CD utilizing video was created to promote several recent NU Civil Engineering graduates, and distributed to potential employers. ITI has chosen to implement technology from Real Networks for our streaming content. A full version of the Real Helix server has been purchased and installed on the ITI web server. We are closely monitoring the available technologies in this still evolving field.

Midwest Bridge Working Group

In 1996, the Infrastructure Technology Institute formed and (and continues to sponsor) the Midwest Bridge Inspection and Maintenance Technology Sharing Consortium. This group facilitates sharing of information on current practices and research relating to bridge inspection and maintenance among state transportation engineers and university researchers.

Two meetings were held in 2003. In May the first meeting was held in Kansas City and the second meeting was held in Nashville in early December. Attendance at both meetings included over 50 representatives from various highway departments. While initially aimed at the midwest states of Illinois, Indiana, Kentucky, Michigan, Ohio, and Wisconsin, the group has expanded to include California, Iowa, Kansas, Missouri, Nebraska, New York, Pennsylvania, Tennessee and Virginia and West Virginia. Representatives from consulting firms and the FHWA also participate in these meetings. The meeting agendas are primarily driven by suggestion from the practitioners and considerable discussion takes place during the technical presentations.

Solar Powered Race Car

Institute Research Engineer Dan Hogan has over twenty-five years of experience as a prototype specialist and a welding researcher. Mr. Hogan provides consultations to the faculty and students who are designing the 2003 solar powered race car (Figure 23). Mr. Hogan was able to outline the steps needed to fabricate and weld this complex space frame and meet the requirement that total distortion be no more than one millimeter. Mr. Hogan supervised the students who fabricated the individual components and Mr. Hogan welded the space frame. The frame is made of aircraft quality Chrome-Molly tubing. Mr. Hogan assisted faculty members and other staff in portions of the analysis and design. The finished frame weights forty-five pounds and can resist a 5-G side impact.

Figure 23. Dan Hogan welding solar race car frame

FEASIBILITY STUDY FOR COMMERCIALIZATION OF A NONDESTRUCTIVE, ULTRASONIC TECHNIQUE FOR MONITORING THE SETTING AND HARDENING OF CONCRETE

Principal Investigator: Prof. Surendra P. Shah

Introduction

The ultrasonic wave reflection technique was developed in the Center for Advanced Cement-Based Materials (ACBM) to monitor the properties and strength gain of cementitious materials at early age. The principle of this test method consists of monitoring the reflection coefficient of ultrasonic waves with a frequency of about 2 megahertz or higher at an interface formed by a buffer material and the cementitious material to be tested. When shear waves are used for the measurements and the test material (e.g. cement paste) is in liquid state, the entire wave energy, which is approaching the interface, is reflected, since shear waves cannot propagate in liquids. Thus, the reflection coefficient is unity. With proceeding hydration the cement grains percolate and build up a skeleton allowing the shear waves to propagate. This allows the shear waves to pass the interface resulting in reflection losses at the interface. These two different states are illustrated in Figure 24. The test setup used in laboratory study is presented in Figure 25.

Figure 24. Ultrasonic Reflection Process
at Steel-Concrete Interface

a) For fresh concrete: The pulse is entirely reflected at the steel-concrete interface (T-waves do not propagate in liquids)

b)     For hardened concrete: The pulse is partially reflected and transmitted at the steel-concrete interface

Figure 25. Experimental Setup

Research Objective

The conducted research was aimed at studying the fundamental relationship among evolving microstructure, mechanical properties, and ultrasonic wave reflection measurements. The reflection loss measured with shear waves can theoretically be related to shear modulus. The development of shear modulus with time is related to how the microstructure of hydrating cement evolves as a result of curing. Experiments are designed to elicit this fundamental understanding. The hydration behaviour of different cement mortar mixtures will be investigated by the wave reflection method and alternate test methods. The comparison of the test results will yield the material parameters that govern the measured reflection loss. The final goal is the development of a field sensor for the in-situ assessment of the early age properties of concrete.

Experimental Program

The experimental study was conducted on cement mortars containing Portland cement type I and silica sand as fine aggregates. The cement mortar was tested in three different w/c- ratios: 0.35, 0.5, 0.6. The mixture composition of the mortars is given in Table 3.

Table 3. Mixture Proportions by Weight of Cement for Tested Mortars

To determine the hydration behaviour of the mortars, the reflection loss and three alternate material parameters were measured: compressive strength (ASTM C109), dynamic shear modulus (ASTM C215) and degree of hydration (TGA). The tested materials were cured at a constant temperature of 25°C throughout the duration of the experiments.

Reflection Loss vs. Compressive Strength

As shown in Figure 26, the S–R_L relationship exhibits a strong bilinear pattern, dividing the relationship into two parts. The first part at very early ages has a clearly lower slope compared to the second part of the relationship at later ages. The slope changes at a certain time, which is 10.5 hours for the shown mortar with w/c = 0.5. It was observed, that the time of transition (t_trans) between the two slopes changes with the kinetics of the strength gain.

Reflection Loss vs. Degree of Hydration

The relationship between degree of hydration and reflection loss for the mortars with different w/c ratios is given in Figure 27. The presented data show a very strong linear trend over the entire period of time that is plotted. It was also found that the slope of the relationship changes with w/c-ratio, where a low w/c-ratio corresponds to a high slope. This variation is due to the different microstructural properties of the mortars caused by the different w/c-ratios.

The relationship between the reflection loss and the gel-space ratio for the tested mortars is given in Figure 28. The relation between reflection loss and gel-space ratio for all three mortars can be described by a single trend line, which follows a power law. The uniqueness of the relationship between reflection loss and gel-space ratio leads one to conclude that the reflection loss measured with shear waves is governed by physico-chemical parameters of the cement paste, namely degree of hydration, porosity, and w/c-ratio.

Figure. 27. Correlation of Reflection Loss & Degree of Hydration	Figure 28. Correlation of Reflection Loss & Gel-Space Ratio

Numerical Modeling of Wave Reflection Measurements

A numerical model for simulating the three-dimensional microstructure of hydrating cement has been developed at Technical University of Delft, The Netherlands. The great advantage of this kind of numerical modeling is that it gives information about the cement microstructure that cannot be obtained (or only with great difficulty) by experiments. The model was developed by Prof. Klaas van Breugel in 1991 and has been considerably extended and validated with many experimental results within a Ph.D. study by Guang Ye. Mr. Ye worked in ACBM as a visiting scholar for two months to support our work with the model and assure an optimal output from this part of the research during the summer of 2003.

With this simulation model, the cement particles are assumed to be spherical. The simulation starts from a random distribution of cement particles in a cubic cell. As hydration progresses, the growing particles become more and more connected. Thus a porous structure is formed. In this model, the hydration products are considered as solid phases. The capillary pores are considered as the space between the hydration products. The development of the microstructure of cement paste during its hydration are shown in Figure 29 for a sample with w/c=0.6.

In the model, the percolation phenomena of solid/pore phases can be obtained from the serial section algorithm and the overlap criterion. 2D section images are shown in Figure 30 for convenience of description. The critical degree of hydration, when the solid phases become percolated from unpercolated is considered as the percolation threshold.

Figure 31. Correlation of Reflection Loss & Growing Solid Phase

The development of reflection loss and evolution of the solid phase for mortar with w/c-ratio=0.6 are plotted in Figure 31 as an example. The reflection losses at the percolation threshold of the solid phases and the time when the solid particles are almost connected with each other (t_e) are plotted as solid dots in the figure. From the three figures it can be seen that the time of the percolation threshold and the time of increase of the reflection loss are very similar for all three tested w/c-ratios. This indicates that the initial stage of the reflection loss development is governed by the connectivity of the cement particles. After the occurrence of the percolation threshold the volume fraction of the connected solid phase increases rapidly, which results in a steep rise of the reflection loss.

Another main focus of computational simulation is the contact area of hydrated cement grains. The contact area of the solid phase can provide a measure of the degree of interparticle bonding. The correlation of wave reflection loss and contact area is under probating. It is assumed that contact area can serve as a bridge that links reflection loss and strength gain of the material. It also provides with a stronger theory backbone that explain the feasibility of using wave reflection technique to predict the strength gain.

Field Application of the Wave Reflection Technique

To evaluate the industrial applicability of the wave reflection method, a field trial in collaboration with a precast production plant, Rocky Mountain Prestress, Denver, Colorado, was conducted. The objective of this first field trial was to assess the general suitability of the test method to monitor the curing process of full-scale concrete structures during the production process. The field measurements also gave information about how the test arrangement performs under field conditions with respect to measuring location, equipment reliability, and preparation efforts. This field trial can be considered as a first step towards commercial application of the wave reflection method.

To conduct the field measurements it was necessary to make the test equipment portable. This was achieved by placing the different electronic devices into a portable case. The arrangement of the equipment for the wave reflection test and in-situ temperature measurements in a durable and portable case is shown in Figure 32. All components are connected ready for use, and the case features a main power switch and a main power inlet for all components. The case can easily be moved on the construction site and allows for minimal setup times during field testing.

To assess the applicability of the wave reflection method for monitoring the hardening process of concrete under field conditions, the production of prestressed box girders (Figure 33) was chosen. The production schedule of the precast plant required the removal of the girders from the steel bed as soon as the concrete has reached the critical strength that allows lifting the girders with a crane. To evaluate the ability of the wave reflection method to determine the time when the critical concrete strength is reached, a girder was instrumented with two separate transducer-steel plate combinations located on the top-surface of the girder. The steel plates where put in place after the concrete was completely placed and the top surface was finished with the rake.

Figure 32. Equipment for Wave Reflection Measurements for Field Testing	Figure 33. Finished Box Girder

Additionally, the girder was instrumented with thermocouples at different locations (see Figure 34) to track the temperature rise in the girder during hydration. A data logger, which was part of the portable test setup, recorded the temperature in regular time intervals throughout the hardening process.

The results of the wave reflection and temperature measurements are given in Figure 34. It can be seen that the reflection loss measured at the points A and B shows differences after approx. six hours. These differences can be explained by the different temperature histories of the measurement points A and B. Since measurement point A is located above the massive end block of the girder, the temperature increases earlier and to a higher level at the end of the measurement period. It can also be noted that the concrete temperature measured at the bottom and the side of the girder is higher than at the top surface. These temperature differences indicate that the compressive strength at a given time varies with the location. To account for these differences, the comparison between the compressive strength predicted from the reflection loss measurements at points A and B and the cylinder strength determined in the lab and the precast plant will be done on the basis of equivalent age.

The comparison between the in-situ strength predicted from the reflection loss measurements and the cylinder strength determined in the ACBM lab and the precast plant is given in Figure 35. To calculate the compressive strength from the measured reflection loss (symbol: u), the relationship between reflection loss and compressive strength as determined in the laboratory has been used. It can be seen that at an equivalent age of about 25 °C-hours the strength calculated from the reflection loss measurements is very close to the strength obtained from cylinders tested in the precast plant (symbol: o, These cylinders were cured at the same temperature as measured in the girder at location ƒ.)

Conclusions

From investigations to date, the following conclusions can be drawn:

1. The relationship between reflection loss and compressive strength has a bilinear character for the tested mortar mixtures at early ages (70 to 90 hours). The time of the transition point depends on the kinetics of the strength gain.

2. Degree of hydration and reflection loss are linear related at early ages. This demonstrates the high sensitivity of the presented wave reflection method to changes in the microstructure of cementitious materials due to hydration.

3. The reflection loss of the mortar mixtures was found to be related to the development of the volume fraction of the total and connected solid phase of the cement paste obtained from numerical simulation. The time of increase of the reflection loss and the time of the percolation threshold of the solid phase are very similar. After the percolation of the solid phase the reflection loss is governed by the volume fraction of the connected solid phase. At later ages the reflection loss develops according to the total solid phase.

4. The ultrasonic wave reflection technique can be used as an in-situ NDT method to predict the strength gain of cement based materials.

Publications and Conference Presentations

Akkaya, Y., Voigt, T., Subramaniam, K. V., and Shah, S. P. (2003). "Nondestructive measurement of concrete strength gain by an ultrasonic wave reflection method." Materials and Structures, 36(262), 507-514.

Voigt, T., Akkaya, Y., Shah, S.P. (2003). "Determination of early age mortar and concrete strength by ultrasonic wave reflections." ASCE Journal of Materials in Civil Engineering, Vol.15, No.3, pp. 247-254.

Voigt, T., Shah, S. P. (2003). "Nondestructive monitoring of setting and hardening of Portland cement mortar with sonic methods." Proceedings of the Sixth International Symposium on Non-Destructive Testing in Civil Engineering (NDT-CE 2003), .

Voigt, T., Shah, S. P. (2003). "Nondestructive testing of early age concrete." Cementing the Future, Newsletter of the Center for Advanced Cement-Based Materials, Winter 2002-2003, 14(1), 4-5.

Voigt, T., Shah, S.P. "Properties of Early Age Portland Cement Mortar monitored with A Shear Wave Reflection Method" submitted to ACI Materials Journal

"A Better Maturity Meter?" ACBM Update, Concrete International, Vol. 25, No. 10, 2003, pp. 98-99.

ACI Spring Convention 2003, Vancouver, Canada. Session "Hydration Kinetics, Maturity and Early-Age Properties of Concrete" organized by the ACI Committee 231 "Properties of Concrete at Early Ages." Sixth International Symposium on Non-Destructive Testing in Civil Engineering, September 2003, Berlin, Germany.

SAFETY CONCRETE – A NEW IMPACT-ABSORBING CONCRETE FOR PROTECTING BUILDINGS, STRUCTUREs, AND PEOPLE

Principal Investigators: Prof. Hamlin Jennings and Prof. Jeffrey Thomas

Project Overview

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." A standard strategy for increasing the security of sensitive buildings such as embassies is a concrete perimeter wall intended to keep unauthorized persons and vehicles from approaching too closely. However, an unintended consequence is that a powerful explosion set off just outside the security wall can cause it to break into large pieces that become projectiles and cause considerable damage and loss of life. An unfortunate example of this phenomenon occurred when the U.S. embassy in Beirut was bombed. The specific application of safety concrete is thus to form security perimeters or walls around buildings that will fragment into small particles that cause a minimum amount of damage in the event of an explosion.

The technical strategy for making safety concrete, developed at Northwestern University by the PIs, is to process a cement-based material so that it has microcracks distributed throughout its volume and a state of internal tensile stress. Under static loading, the material behaves like a normal (although low-strength) concrete, but under impact or explosive loading the cracks all propagate and connect, causing fragmentation into small particles. To generate this type of microstructure, the binder contains a significant proportion of blast furnace slag, a cementitious material with a strong tendency to form shrinkage cracks when dried at an early age. The process of forming safety concrete includes a controlled drying treatment which generates the internal stress state and the microcracks.

This project was motivated by the Engineering Research and Development Center (ERDC) of the Army Corps of Engineers, Vicksburg, Mississippi. The ERDC is a cost sharing partner and is conducting blast testing of safety concrete.

Significant progress was made on this project during 2003:

• The disintegration properties of safety concrete were successfully demonstrated in a blast test conducted by the ERDC. This important milestone not only verifies the desired properties of safety concrete, but also demonstrates the ability to perform successful blast tests.

• The relative performance of safety concrete specimens in the blast test was very similar to the relative performance in drop impact testing. This confirms the usefulness of the simple drop impact test as predictor of blast performance.

• Experiments at Northwestern University demonstrated the properties of sodium silicate accelerator and cement kiln dust on the properties of safety concrete. While neither variable provided a dramatic improvement in properties, they provide the ability to shorten the time required for curing and to control the amount of shrinkage to prevent macrocracking.

• A new mix design strategy centered around high sand-to-binder ratios (s/b = 5-7) gives significantly improved fragmentation as measured by impact testing.

• In discussions with the ERDC we have reached a mutual decision for the final configuration of the product. Instead of large panels that would be placed end to end to form a wall, the goal is to form much smaller hollow blocks that would be stacked to form a wall.

Effects of Sodium Silicate and Cement Kiln Dust

Previous research indicated that mix designs using a very high proportion of slag as the binder gave superior results. However, pure slag hydrates quite slowly unless it is accelerated. An effective method of accelerating the hydration of slag is to add a solution of sodium silicate, or "water glass", to the mix water. The sodium raises the pH of the pore solution, increasing the rate at which the slag dissolves, while the silica reacts with dissolved calcium to form calcium-silicate-hydrate (C-S-H) gel binder phase. For these experiments an aqueous sodium silicate solution with a SiO₂/NaOH ratio of 1.9 by weight and a total solids content of 41% by weight (Fisher Scientific) was used.

Cement kiln dust (CKD) is a byproduct of the manufacture of cement. It consists of fine particles that pass through the kiln without reacting and are then trapped on electrostatic precipitators to prevent their release into the environment. These particles are surrounded by a layer of condensed volatiles such as alkali oxides and chlorides. CKD is considered a nuisance material because of the costs of collecting and storing it, and finding applications for CKD is of significant interest to cement manufacturers. CKD is of potential interest for use in conjunction with slag because its relatively high alkali content can provide an accelerating effect on the hydration. For the experiments reported here, a CKD from a Lafarge cement plant in Illinois was used. This CKD has an alkali content (Na₂O +K₂O) of 3.7% by weight and a mean particle size of 50 µm.

The use of sodium silicate and CKD was investigated, along with other variables such as cure temperature, sand content, and cure time, using statistically designed experiments. Each mix design was analyzed for both compressive strength and fragmentation in the drop impact test. To be successful, safety concrete must have a moderate strength while also exhibiting a high degree of fragmentation. Therefore, each experimental mix design was evaluated against both of these parameters simultaneously by generating a "quality factor" that combines the dry compressive st