Browsing by Author "Shield, Carol K."
Now showing 1 - 10 of 10
- Results Per Page
- Sort Options
Item Acoustic Emission Equipment for Infrastructure Monitoring(Minnesota Department of Transportation, 1999-01) Shield, Carol K.This system consists of acoustic emissions sensors, preamplifiers, filers, an AE monitor, and a digital oscilloscope. The system has been applied successfully to both steel and concrete structures and used to detect brittle fracture and low-cycle fatigue failures in welded steel joints and crack propagation in cover-plated rolled bridge girders, in the field and in the laboratory. The AE system detected initial cracking during the flexural crack testing of two high-strength concrete prestressed bridge girders. The acoustic emission monitoring of bond tests also provided insight into the behavior of the bond between glass fiber reinforced polymer rebar and concrete.Item Acoustic Emission Monitoring of Fatigue Cracks in Steel Bridge Girders(Minnesota Department of Transportation, 1999-09) McKeefry, Jay A.; Shield, Carol K.This report presents results from a laboratory study and field implementation of acoustic emission monitoring of fatigue cracks in cover-plated steel bridge girders. The acoustic monitoring successfully detected growing fatigue cracks in the lab when using both source location and a state of stress criteria. Application of this methodology on three field bridges also proved successful by detecting a propagating crack in two of the bridges and an extinguished crack in a third bridge. Researchers tested a double angle retrofit, designed by the Minnesota Department of Transportation, both in the lab and in the field of girder with fatigue cracks in the top flange. This retrofit does not require removal of concrete deck, and only involves bolting the retrofit to the bridge girder web. The double angle retrofit applied to laboratory test girder resulted in a reduction of flange stresses by 42 percent. Field implementation of the retrofit had mixed success. On one bridge, stress ranges in the cracked flange was reduced by 43 percent. However, on a second test bridge, the reduction was only 8 percent, likely due to the inadequate space for proper installation of the retrofit.Item Development Length of GFRP Reinforcement in Concrete Bridge Decks(Minnesota Department of Transportation, 2000-07-01) Hanus, Joe; Shield, Carol K.; French, Catherine E.This report summarizes an experimental program that investigated the developement length and variability in bond of glass-fiber-reinforced-polymer (GFRP) reinforcement in concrete. The variables in the study were manufacturer (Marshall Industries Composites, Inc. [M1] and Corrosion Proof Products/Hughes Brothers [M2]), bar size (No. 5 and 6), cover (2 and 3 bar diameters), and embedment length (10 through 47 in.). Eighty-four inverted half-beam bond specimens were tested while monitoring load, loaded-end slip, free-end slip, cracking, and acoustic emissions on the embedded bar and concrete. Neither bar was recommended for immediate use as reinforcement in bridge decks. The M1 rebar exhibited cracking and splitting along the outer coating of the bar which damaged bar deformations. Additionally these bars exhibited larger COVs for bar failures with average ultimate loads below the reported manufacturer's value. The M2 rebar exhibited a smaller COV for tensile test bar failures and a similar ultimate load average when compared to the manufacturer's reported strength. However, both GFRP rebar had 47.0 in. embedment length bond tests which exhibited bar failures with ultimate loads less than the tensile test average minus two standard deviations. Keywords: Bond, GFRP Rebar, Bridge DecksItem Feasibility of Vibration-Based Long-Term Bridge Monitoring Using the I-35W St. Anthony Falls Bridge(Minnesota Department of Transportation, 2017-01) Gaebler, Karl O.; Shield, Carol K.; Linderman, Lauren E.Vibration based structural health monitoring has become more common in recent years as the required data acquisition and analysis systems become more affordable to deploy. It has been proposed that by monitoring changes in the dynamic signature of a structure, primarily the natural frequency, one can detect damage. This approach to damage detection is made difficult by the fact that environmental factors, such as temperature, have been shown to cause variation in the dynamic signature in a structure, effectively masking those changes due to damage. For future vibration based structural health monitoring systems to be effective, the relationship between environmental factors and natural frequency must be understood such that variation in the dynamic signature due to environmental noise can be removed. A monitoring system on the I-35W St. Anthony Falls Bridge, which crosses the Mississippi River in Minneapolis, MN, has been collecting vibration and temperature data since the structures opening in 2008. This provides a uniquely large data set, in a climate that sees extreme variation in temperature, to test the relationship between the dynamic signature of a concrete structure and temperature. A system identification routine utilizing NExT-ERA/DC is proposed to effectively analyze this large data set, and the relationship between structural temperature and natural frequency is investigated.Item Instrumentation and Fabrication of Two High-Strength Concrete Prestressed Bridge Girders(Minnesota Department of Transportation, 1998-01) Kielb, Jeffrey; French, Catherine E.; Leon, Roberto T.; Shield, Carol K.This report describes the design, instrumentation, construction, and test set-up of two high-strength concrete prestressed bridge girders. The girder specimens were constructed to evaluate prestress transfer length, prestress losses, flexural fatigue, ultimate flexural strength, and ultimate shear strength. Each test girder was a 132.75-foot long, 46-inch deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with 46 0.6-inch diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi. Each girder was made composite with a 9-inch thick, 48-inch wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi. Girder I used a concrete mix incorporating crushed limestone aggregate while Girder II utilized round glacial gravel aggregate in the mix with the addition of microsilica. In addition, the two test girders incorporated two different end patterns of prestressing--draping versus a combination of draping and debonding--and two different stirrup configurations--standard Mn/DOT U versus a modified U with leg extensions. More than 200 strain gages were imbedded in each girder during construction. Other reports present flexural and shear testing results.Item Instrumentation, Monitoring, and Modeling of the I-35W Bridge(Minnesota Department of Transportation, 2012-08) French, Catherine E.W.; Shield, Carol K.; Stolarski, Henryk K; Hedegaard, Brock D.; Jilk, Ben J.The new I-35W Bridge was instrumented incorporating "smart bridge technology" by Figg Engineering Group in conjunction with Flatiron-Manson. The purpose of the instrumentation was to monitor the structure during service, and to use this information to investigate the design and performance of the bridge. Instrumentation included static sensors (vibrating wire strain gages, resistive strain gages and thermistors in the foundation, bridge piers, and superstructure, as well as fiber optic sensors and string potentiometers in the superstructure) and dynamic sensors (accelerometers in the superstructure). Finite element models were constructed, taking into account measured material properties, to further explore the behavior of the bridge. The bridge was tested using static and dynamic truck load tests, which were used, along with continually collected ambient data under changing environmental conditions, to validate the finite element models. These models were applied to gain a better understanding of the structural behavior, and to evaluate the design assumptions presented in the Load Rating Manual for the structure. This report documents the bridge instrumentation scheme, the material testing, finite element model construction methodology, the methodology and results of the truck tests, validation of the models with respect to gravity loads and thermal effects, measured and modeled dynamic modal characteristics of the structure, and documentation of the investigated assumptions from the Load Rating Manual. It was found that the models accurately recreated the response from the instrumented bridge, and that the bridge had behaved as expected during the monitoring period.Item Modeling and Monitoring the Long-Term Behavior of Post-Tensioned Concrete Bridges(Minnesota Department of Transportation, 2014-11) French, Catherine E.W.; Shield, Carol K.; Hedegaard, Brock D.The time-dependent and temperature-dependent behavior of post-tensioned concrete bridges were investigated through a case study of the St. Anthony Falls Bridge, consisting of laboratory testing of concrete time-dependent behaviors (i.e., creep and shrinkage), examination of data from the in situ instrumented bridge, and time-dependent finite element models. Laboratory results for creep and shrinkage were measured for 3.5 years after casting, and the data were best predicted by the 1978 CEB/FIP Model Code provisions. To compare the in situ readings to constant-temperature finite element models, the time-dependent behavior was extracted from the measurements using linear regression. The creep and shrinkage rates of the in situ bridge were found to depend on temperature. An adjusted age using the Arrhenius equation was used to account for the interactions between temperature and time-dependent behavior in the measured data. Results from the time-dependent finite element models incorporating the full construction sequence revealed that the 1990 CEB/FIP Model Code and ACI-209 models best predicted the in situ behavior. Finite element analysis also revealed that problems associated with excessive deflections or development of tension over the lifetime of the bridge would be unlikely. The interactions between temperature and time-dependent behavior were further investigated using a simplified finite element model, which indicated that vertical deflections and stresses can be affected by the cyclic application of thermal gradients. The findings from this study were used to develop an anomaly detection routine for the linear potentiometer data, which was successfully used to identify short-term and long-term artificial anomalies in the data.Item Self-Compacting Concrete (SCC) for Prestressed Bridge Girders(Minnesota Department of Transportation, 2008-10) Erkmen, Bulent; Shield, Carol K.; French, Catherine E.Researchers conducted an experimental program to investigate the viability of producing self-consolidating concrete (SCC) using locally available aggregate, and the viability of its use in the production of precast prestressed concrete bridge girders for the State of Minnesota. Six precast prestressed bridge girders were cast using four SCC and two conventional concrete mixes. Variations in the mixes included cementitious materials (ASTM Type I and III cement and Class C fly ash), natural gravel and crushed stone as coarse aggregate, and several admixtures. The girders were instrumented to monitor transfer length, camber, and prestress losses. In addition, companion cylinders were cast to measure the compressive strength and modulus of elasticity, and to monitor the creep and shrinkage over time. The viability of using several test methods to evaluate SCC fresh properties was also investigated. The test results indicated that the overall performance of the SCC girders was comparable to that of the conventional concrete girders. The measured, predicted, and calculated prestress losses were generally in good agreement. The study indicated that creep and shrinkage material models developed based on companion cylinder creep and shrinkage data can be used to reasonably predict measured prestress losses of both conventional and SCC prestressed bridge girders.Item Shear Capacity of High-Strength Concrete Prestressed Girders(Minnesota Department of Transportation, 1998-05) Cumming, David A.; French, Catherine E.; Shield, Carol K.As part of a project at the University of Minnesota to investigate the application of high-strength concrete in prestressed girders, four shear tests were performed on high-strength concrete prestressed girders. Originally constructed in August 1993, the girders, Minnesota Department of Transportation (Mn/DOT) 45M sections were 45 inches deep. Each girder utilized 46 0.6-inch diameter prestressing strands on 2-inch centers. The girders were designed assuming a 28-day compressive strength of 10,500 psi. Later, a 4-foot-wide and 9-inch-thick composite concrete deck was added to each girder using unshored construction techniques. The shear test results were compared with predicted results from ACI 318-95 Simplified Method, ACI 318-95 Detailed Method (AASHTO 1989), Modified ACI 318-95 Procedure, Modified Compression Field Theory (AASHTO LRFD 1994), Modified Truss Theory, Truss Theory, Horizontal Shear Design (AASHTO 1989), and Shear Friction (AASHTO LRFD 1994). The calculated shear capacities were in all cases conservative compared to the actual shear capacity.Item Ten-Year Review of Monitoring System on I-35W Saint Anthony Falls Bridge(Minnesota Department of Transportation, 2020-06) Brown, Riley J.; McCoy, Rebekka; Shield, Carol K.; Linderman, Lauren E.; Hedegaard, Brock D.The I-35W St. Anthony Falls bridge was highly instrumented with over 500 sensors to verify design assumptions, serve as a testbed to examine bridge sensing techniques, and evaluate the effectiveness of different bridge monitoring strategies. The instrumentation deployed on the bridge to investigate the structural behavior included vibrating wire strain gages (VWSGs), thermistors, fiber optic sensors (SOFO), resistance strain gages, linear potentiometers, accelerometers, and corrosion monitoring sensors. This report documented the successes and challenges of the monitoring program over the first ten years of the bridge’s life. In particular, the effectiveness of different strain measurement techniques and sensor distributions were addressed. Previous investigations of temperature-dependent and time-dependent behavior were also expanded with the larger data set to better understand the behavior of post-tensioned concrete box girder structures with the potential to impact future designs.