Catherine French | University of Minnesota - Twin Cities (original) (raw)

Papers by Catherine French

Journal of Structural Engineering-asce, Nov 1, 2020

There are three potential options to reduce end stresses in prestressed concrete bridge girders: ... more There are three potential options to reduce end stresses in prestressed concrete bridge girders: drape strands, debond strands, or a combination of the two. In the draping option, a portion of the strands are raised from harp points within the girder to reduce the strand eccentricity at the girder ends. Large vertical reactions are required at the hold down points within the girder to resist the uplift of the draped strands. In addition, end cracking that follows the draped strand pattern is often observed, particularly in deeper sections. In the debonding option, a portion of the strands are debonded toward the girder ends to reduce the resultant prestress force. Concerns with debonding are its potential to reduce shear strength and to cause corrosion issues if moisture and deicing chemicals make their way into the girder ends along the debonded path. Due to potential corrosion concerns, MnDOT has prohibited strand debonding. However, as a means to eliminate some of the end cracking observed during fabrication with draped strands, this study was conducted to explore the use of debonded strands and to develop design recommendations. To this end, an extensive literature review was conducted regarding debonded strand research, and state Departments of Transportation with similar climates and fabricators were queried to learn from their experiences. Design recommendations and potential material specifications to protect debonded strands from corrosion are presented in this report.

... of MN Matthew Smith, Engineer, Meyer, Borgman and Johnson, Mpls., MN Whitney Eriksson, Engine... more ... of MN Matthew Smith, Engineer, Meyer, Borgman and Johnson, Mpls., MN Whitney Eriksson, Engineer, Barr Engineers, Mpls., MN Dave Klaseus, Graduate ... Typical crane capacities can readily handle the 80 kip (350 kN) capacity (this value could be as high as 130 kips (580 kN ...

Methods for mitigating corrosion in reinforced concrete structures were investigated on the subst... more Methods for mitigating corrosion in reinforced concrete structures were investigated on the substructure of a bridge in Minneapolis, Minnesota. Several corrosion-damaged columns and pier caps were treated with electrochemical chloride extraction (ECE), and then selected ECE-treated and untreated structures were wrapped with FRP wraps or sealed with concrete sealers to prevent future chloride ingression. Embeddable corrosion monitoring instrumentation was installed in the field structures to evaluate the effectiveness of ECE treatment. Although the ECE process reduced average chloride levels in the treated structures by approximately 50%, several locations still had chloride concentrations in excess of the established corrosion threshold following ECE treatment. Resistivity probe failures that occurred at some of these locations indicated corrosion within the treated structures could still occur, despite re-passivation of the reinforcing steel following ECE treatment. Continued monitoring of the installed instrumentation is required to evaluate the long-term effectiveness of ECE treatment and concrete wrapping/sealing as a corrosion mitigation technique.

This report describes the design, instrumentation, construction, and test set-up of two high-stre... more 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-ft (40.46-m) long, 46-in. (117-cm) deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with forty-six 0.6-in. (1.5-cm) diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi (72,398 kPa). Each girder was made composite with a 9-in. (23-cm) thick, 48-in. (122-cm) wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi (27,580 kPa). 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.

The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a ... more The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a problem. A number of manufacturers have developed GFRP rebar for this application. Because the production of the material is relatively new, there is a great deal of variability among the products from different manufacturers. In addition, as the manufacturers continue to develop their own product, variations in GFRP from single manufacturers have been observed. The objective of this study was to investigate the bond between GFRP reinforcement and concrete using inverted half-beam specimen. The inverted half-beam specimen were designed to simulate the conditions likely to be found in a bridge deck (no transverse reinforcement and small concrete cover). Products from two different manufacturers were chosen for the study because of the widely varying characteristics of the product. One manufacturer produced reinforcement with surface deformations created by a helical wrap of glass fibers around the GFRP bar; the other manufacturer developed a ceramic coating that emulated the surface texture of a deformed steel bar. The two different bar types exhibited different bond behaviors. The bond for the bars with the ceramic deformations relied most heavily on mechanical interlock, as was evident from cracking patterns. The bond for the bars with the helical wrap deformations relied most heavily on friction. Both bar types demonstrated large variability for the bond specimen that failed in bar fracture, with some bar failure loads more than two standard deviations below the average bar tensile strength.

Engineering Structures, May 1, 2021

Abstract Two large-scale structural assemblages, which had equivalent PreWEC (Precast Wall with E... more Abstract Two large-scale structural assemblages, which had equivalent PreWEC (Precast Wall with End Columns) rocking-wall systems but different surrounding structures, were tested under quasi-static cyclic loading to study the impact of wall-floor interaction on the performance of rocking-wall buildings. The first specimen (PFS1) included cast-in-place (CIP) edge columns and a CIP unbonded post-tensioned slab with rigid wall-floor connections, which maximized wall-floor interaction. The second specimen (PFS2) included precast edge columns and a precast slab with special vertical-isolation wall-floor connectors, which minimized wall-floor interaction. Test results showed that both structural assemblages demonstrated great seismic performance with limited damage and self-centering behavior. The strength of PFS1 was more than twice that of PFS2; PFS2 encountered less damage and had better self-centering performance than PFS1, but it possessed less energy-dissipation capacity. The difference in the performance of the two assemblages was mainly attributed to the different gravity load transfer paths and constraint effects of the surrounding structures. Contributions to the strength and the self-centering behavior of the two assemblages from different structural elements were quantified and compared.

This report summarizes an experimental program that investigated the development length and varia... more This report summarizes an experimental program that investigated the development 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 inc.). 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 a 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.

Concrete Bond 6 7. Author(s) 8. Performing Organization Report No.

The Minnesota Department of Transportation (Mn/DOT) Precast Slab Span System was initially design... more The Minnesota Department of Transportation (Mn/DOT) Precast Slab Span System was initially designed by Mn/DOT with input from University of Minnesota researchers and local fabricators. The bridge system consisted of a series of precast, prestressed concrete inverted tee bridge elements which also served as stay-in-place formwork for the cast-in-place portion of the deck placed in the field. One of the Mn/DOT implementations, located in Center City, MN, was instrumented. The bridge has been monitored for reflective cracking and continuity over the piers since the deck was cast. Transverse load distribution was evaluated with a static truck test. In addition, a two-span test specimen was constructed to investigate effects of variations in flange thickness, bursting reinforcement, horizontal shear reinforcement, and flange surface treatment. The data obtained from the field study indicated that cracking had initiated in the bridge at the locations of some of the gages at midspan and near the support. The cracking was determined to be the result of environmental loads and shrinkage rather than due to vehicular loads. The data from the truck tests indicated that the design assumption of a monolithic slab system was valid for the determination of load distribution factors. The results of the laboratory study showed that positive restraint moments developed in the precast system for which continuity was made at a young age (i.e., seven days), and that these moments could be reasonably well predicted by existing models. It has also been found that current American Association of State Highway and Transportation Officials bursting requirements require unnecessary transverse reinforcement in the end zones of slab span systems.

The shear provisions of the American Association of State Highway and Transportation Officials br... more The shear provisions of the American Association of State Highway and Transportation Officials bridge design code have changed significantly in recent years. The 2004 Load and Resistance Factor Design (LRFD) and 2002 Standard shear provisions for the design of prestressed concrete bridge girders typically require more shear reinforcement than the 1979 Interim shear provisions. The purpose of this research was to determine whether or not bridge girders designed according to the 1979 interim shear provisions were underdesigned for shear and develop a method to identify potentially underdesigned girders. Two shear capacity tests were performed on opposite ends of a bridge girder removed from Mn/DOT Bridge No. 73023. The stirrup spacing in the girder suggested it was designed according to the 1979 Interim shear provisions. The results from the shear tests indicated the girder was capable of holding the required shear demand because the applied shear at failure for both tests was larger than the factored shear strength required by the 2004 LRFD HL-93 and 2002 Standard HS20-44 loading. The results of a parametric study showed that girders designed using the 1979 Interim were most likely to be underdesigned for shear near the support and that the girders most likely to be underdesigned in this region had smaller length to girder spacing ratios.

Any increase in legal truck weight would shorten the time for repair or replacement of many bridg... more Any increase in legal truck weight would shorten the time for repair or replacement of many bridges. Five steel girder bridges and three prestressed concrete I-girder bridges were instrumented, load tested, and modeled. The results were used to assess the effects of a 10 or 20% increase in truck weight on bridges on a few key routes through the state. Essentially all prestressed girders, modern steel girders, and most bridge decks could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately, most Minnesota steel girder bridges were designed before fatigue-design specifications were improved in the 1970's and 1980's. Typically, an increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life). Bridge decks are affected by axle weights rather than overall truck weights. Transverse cracks in bridge decks are primarily caused by shri...

This study sought to determine the dominant parameters that lead to premature transverse cracking... more This study sought to determine the dominant parameters that lead to premature transverse cracking in bridge decks and to make recommendations that help reduce cracking tendency in bridge decks. The project includes two main parts: a field study and a parametric study. The field study identified 72 bridges in the Minneapolis/St. Paul area and explored the correlation between the observed cracking of those bridges and available design, material, and construction-related data. The parametric study investigated the relative influence of the factors that affect transverse deck cracking through a controlled nonlinear analysis study. Variables included: shrinkage, end restraint, girder stiffness, supplemental steel bar cutoff, cross frames, splices, deck concrete modulus of elasticity, and temperature history. In addition, four bridges from the companion field study were modeled to compare the analytical results with the actual crack patterns. Based on these results and correlation with other research, the study identified the following dominant factors affecting transfer cracking: shrinkage, longitudinal restraint, deck thickness, top transverse bar size, cement content, aggregate type and quantity, air content, and ambient air temperature at deck placement. Recommended practical improvements to bridge deck construction, in order of importance, include: using additives to reduce shrinkage of the deck concrete, using better curing practices, and minimizing continuity over interior spans.

Advances in Structural Engineering, 2000

The use of high-strength concrete is becoming popular around the world. The american code, ACI 31... more The use of high-strength concrete is becoming popular around the world. The american code, ACI 318–95 is used in many countries to calculate the development length of deformed bars in tension. However, current design provisions of ACI 318–95 are based on empirical relationships developed from tests on normal strength concrete. The results of a series of tests on high-strength concrete, reported in the literature, from six research studies are used to review the existing recommendations in ACI 318–95 for design of splices and anchorage of reinforcement. It is shown that ACI 318–95 equations may be unconservative for some cases beyond 62 MPa (9 ksi).

The work chronicled within this thesis was largely a team effort. I would like to especially than... more The work chronicled within this thesis was largely a team effort. I would like to especially thank my advisors, Cathy French and Carol Shield, for their help and guidance. I would also like to thank Charles M. Bell for his efforts during the design of the system and the instrumentation of the Center City Bridge. I would also like to thank

The 2005 Mid-Continent Transportation Research SymposiumIowa Department of TransportationIowa State University, AmesMidwest Transportation Consortium, 2005

Self-consolidating concrete (SCC) has been developed for use in precast prestressed concrete brid... more Self-consolidating concrete (SCC) has been developed for use in precast prestressed concrete bridge girders in the state of Minnesota. Locally available materials were used with a number of cementitious and filler materials, including ASTM Type III cement, Class C fly ash, and blast furnace slag. SCC was successfully proportioned with both natural river gravels and crushed stone as coarse aggregates. Moreover, for the mix incorporating natural river gravels, air-entrained SCC was successfully developed without using a viscosity enhancing admixture. The effect of a number of parameters on the fresh properties of SCC, including but not limited to temperature, cement, type of coarse aggregates (natural and crushed), were studied. A number of test methods (e.g., slump flow, L-box, and U-box) have been under development to evaluate the fresh properties of SCC. However, none of these test methods has been integrated into any American standards. A vertical column segregation test has been used to evaluate vertical segregation of SCC mixes. The slump flow test was employed to evaluate the flowability, while self-leveling and passing abilities of the mixes were investigated using a U-box. The L-box test procedure was modified to evaluate, not only flowability and passing ability, but also horizontal segregation resistance of SCC mixes. Although, in general, at least three to four test methods are typically used to evaluate fresh properties, the slump flow test and modified L-box test may be adequate to evaluate the fresh properties of SCC properly.

The I35W St. Anthony Falls Bridge, constructed to replace the steel truss bridge that collapsed i... more The I35W St. Anthony Falls Bridge, constructed to replace the steel truss bridge that collapsed in 2007, contains over 500 instruments to monitor the structural behavior. Numerical models of the bridge are being developed and calibrated to the collected data obtained during truck load testing and environmental loading. The data obtained over the first few years of monitoring will be correlated with the calibrated models and used to develop the baseline bridge behavior. This information will be used to develop a system to monitor and interpret the long-term behavior of the bridge. This paper describes the instrumentation, preliminary results from the data and model calibration, and plan for developing the long-term monitoring capabilities.

Structural health monitoring of in situ concrete structures is complicated by variations in the b... more Structural health monitoring of in situ concrete structures is complicated by variations in the behavior of the structure due to ambient environmental conditions, transient loads, and time-dependent effects (e.g., creep and shrinkage of concrete, prestress losses). As a case study, the I-35W St. Anthony Falls Bridge, a post-tensioned concrete box girder bridge instrumented with over 500 sensors to monitor structural behavior, was studied over the first five years of operation. A data normalization scheme was developed to extract the time-dependent behavior of the bridge from long-term data, removing the instantaneous response due to thermal variations and adjusting the timescale with the Arrhenius equation to account for the temperature-dependent rate of time-dependent behavior. The resulting time-dependent behavior followed a line in log time, and served as the baseline for anomaly detection. Short-term and long-term checks were developed to identify anomalous, and thus potentially damage-related, changes in the time-dependent behavior. The efficacy of these checks was investigated by introducing perturbations into the monitoring data from the St. Anthony Falls Bridge, assumed to contain no damage, to simulate instantaneous bearing lockup and a slow degradation process through introduction of a two-year drift in the data. The proposed method succeeded in successfully identifying the perturbations while minimizing false positives.

Journal of Structural Engineering-asce, Nov 1, 2020

There are three potential options to reduce end stresses in prestressed concrete bridge girders: ... more There are three potential options to reduce end stresses in prestressed concrete bridge girders: drape strands, debond strands, or a combination of the two. In the draping option, a portion of the strands are raised from harp points within the girder to reduce the strand eccentricity at the girder ends. Large vertical reactions are required at the hold down points within the girder to resist the uplift of the draped strands. In addition, end cracking that follows the draped strand pattern is often observed, particularly in deeper sections. In the debonding option, a portion of the strands are debonded toward the girder ends to reduce the resultant prestress force. Concerns with debonding are its potential to reduce shear strength and to cause corrosion issues if moisture and deicing chemicals make their way into the girder ends along the debonded path. Due to potential corrosion concerns, MnDOT has prohibited strand debonding. However, as a means to eliminate some of the end cracking observed during fabrication with draped strands, this study was conducted to explore the use of debonded strands and to develop design recommendations. To this end, an extensive literature review was conducted regarding debonded strand research, and state Departments of Transportation with similar climates and fabricators were queried to learn from their experiences. Design recommendations and potential material specifications to protect debonded strands from corrosion are presented in this report.

... of MN Matthew Smith, Engineer, Meyer, Borgman and Johnson, Mpls., MN Whitney Eriksson, Engine... more ... of MN Matthew Smith, Engineer, Meyer, Borgman and Johnson, Mpls., MN Whitney Eriksson, Engineer, Barr Engineers, Mpls., MN Dave Klaseus, Graduate ... Typical crane capacities can readily handle the 80 kip (350 kN) capacity (this value could be as high as 130 kips (580 kN ...

Methods for mitigating corrosion in reinforced concrete structures were investigated on the subst... more Methods for mitigating corrosion in reinforced concrete structures were investigated on the substructure of a bridge in Minneapolis, Minnesota. Several corrosion-damaged columns and pier caps were treated with electrochemical chloride extraction (ECE), and then selected ECE-treated and untreated structures were wrapped with FRP wraps or sealed with concrete sealers to prevent future chloride ingression. Embeddable corrosion monitoring instrumentation was installed in the field structures to evaluate the effectiveness of ECE treatment. Although the ECE process reduced average chloride levels in the treated structures by approximately 50%, several locations still had chloride concentrations in excess of the established corrosion threshold following ECE treatment. Resistivity probe failures that occurred at some of these locations indicated corrosion within the treated structures could still occur, despite re-passivation of the reinforcing steel following ECE treatment. Continued monitoring of the installed instrumentation is required to evaluate the long-term effectiveness of ECE treatment and concrete wrapping/sealing as a corrosion mitigation technique.

This report describes the design, instrumentation, construction, and test set-up of two high-stre... more 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-ft (40.46-m) long, 46-in. (117-cm) deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with forty-six 0.6-in. (1.5-cm) diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi (72,398 kPa). Each girder was made composite with a 9-in. (23-cm) thick, 48-in. (122-cm) wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi (27,580 kPa). 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.

The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a ... more The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a problem. A number of manufacturers have developed GFRP rebar for this application. Because the production of the material is relatively new, there is a great deal of variability among the products from different manufacturers. In addition, as the manufacturers continue to develop their own product, variations in GFRP from single manufacturers have been observed. The objective of this study was to investigate the bond between GFRP reinforcement and concrete using inverted half-beam specimen. The inverted half-beam specimen were designed to simulate the conditions likely to be found in a bridge deck (no transverse reinforcement and small concrete cover). Products from two different manufacturers were chosen for the study because of the widely varying characteristics of the product. One manufacturer produced reinforcement with surface deformations created by a helical wrap of glass fibers around the GFRP bar; the other manufacturer developed a ceramic coating that emulated the surface texture of a deformed steel bar. The two different bar types exhibited different bond behaviors. The bond for the bars with the ceramic deformations relied most heavily on mechanical interlock, as was evident from cracking patterns. The bond for the bars with the helical wrap deformations relied most heavily on friction. Both bar types demonstrated large variability for the bond specimen that failed in bar fracture, with some bar failure loads more than two standard deviations below the average bar tensile strength.

Engineering Structures, May 1, 2021

Abstract Two large-scale structural assemblages, which had equivalent PreWEC (Precast Wall with E... more Abstract Two large-scale structural assemblages, which had equivalent PreWEC (Precast Wall with End Columns) rocking-wall systems but different surrounding structures, were tested under quasi-static cyclic loading to study the impact of wall-floor interaction on the performance of rocking-wall buildings. The first specimen (PFS1) included cast-in-place (CIP) edge columns and a CIP unbonded post-tensioned slab with rigid wall-floor connections, which maximized wall-floor interaction. The second specimen (PFS2) included precast edge columns and a precast slab with special vertical-isolation wall-floor connectors, which minimized wall-floor interaction. Test results showed that both structural assemblages demonstrated great seismic performance with limited damage and self-centering behavior. The strength of PFS1 was more than twice that of PFS2; PFS2 encountered less damage and had better self-centering performance than PFS1, but it possessed less energy-dissipation capacity. The difference in the performance of the two assemblages was mainly attributed to the different gravity load transfer paths and constraint effects of the surrounding structures. Contributions to the strength and the self-centering behavior of the two assemblages from different structural elements were quantified and compared.

This report summarizes an experimental program that investigated the development length and varia... more This report summarizes an experimental program that investigated the development 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 inc.). 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 a 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.

Concrete Bond 6 7. Author(s) 8. Performing Organization Report No.

The Minnesota Department of Transportation (Mn/DOT) Precast Slab Span System was initially design... more The Minnesota Department of Transportation (Mn/DOT) Precast Slab Span System was initially designed by Mn/DOT with input from University of Minnesota researchers and local fabricators. The bridge system consisted of a series of precast, prestressed concrete inverted tee bridge elements which also served as stay-in-place formwork for the cast-in-place portion of the deck placed in the field. One of the Mn/DOT implementations, located in Center City, MN, was instrumented. The bridge has been monitored for reflective cracking and continuity over the piers since the deck was cast. Transverse load distribution was evaluated with a static truck test. In addition, a two-span test specimen was constructed to investigate effects of variations in flange thickness, bursting reinforcement, horizontal shear reinforcement, and flange surface treatment. The data obtained from the field study indicated that cracking had initiated in the bridge at the locations of some of the gages at midspan and near the support. The cracking was determined to be the result of environmental loads and shrinkage rather than due to vehicular loads. The data from the truck tests indicated that the design assumption of a monolithic slab system was valid for the determination of load distribution factors. The results of the laboratory study showed that positive restraint moments developed in the precast system for which continuity was made at a young age (i.e., seven days), and that these moments could be reasonably well predicted by existing models. It has also been found that current American Association of State Highway and Transportation Officials bursting requirements require unnecessary transverse reinforcement in the end zones of slab span systems.

The shear provisions of the American Association of State Highway and Transportation Officials br... more The shear provisions of the American Association of State Highway and Transportation Officials bridge design code have changed significantly in recent years. The 2004 Load and Resistance Factor Design (LRFD) and 2002 Standard shear provisions for the design of prestressed concrete bridge girders typically require more shear reinforcement than the 1979 Interim shear provisions. The purpose of this research was to determine whether or not bridge girders designed according to the 1979 interim shear provisions were underdesigned for shear and develop a method to identify potentially underdesigned girders. Two shear capacity tests were performed on opposite ends of a bridge girder removed from Mn/DOT Bridge No. 73023. The stirrup spacing in the girder suggested it was designed according to the 1979 Interim shear provisions. The results from the shear tests indicated the girder was capable of holding the required shear demand because the applied shear at failure for both tests was larger than the factored shear strength required by the 2004 LRFD HL-93 and 2002 Standard HS20-44 loading. The results of a parametric study showed that girders designed using the 1979 Interim were most likely to be underdesigned for shear near the support and that the girders most likely to be underdesigned in this region had smaller length to girder spacing ratios.

Any increase in legal truck weight would shorten the time for repair or replacement of many bridg... more Any increase in legal truck weight would shorten the time for repair or replacement of many bridges. Five steel girder bridges and three prestressed concrete I-girder bridges were instrumented, load tested, and modeled. The results were used to assess the effects of a 10 or 20% increase in truck weight on bridges on a few key routes through the state. Essentially all prestressed girders, modern steel girders, and most bridge decks could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately, most Minnesota steel girder bridges were designed before fatigue-design specifications were improved in the 1970's and 1980's. Typically, an increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life). Bridge decks are affected by axle weights rather than overall truck weights. Transverse cracks in bridge decks are primarily caused by shri...

This study sought to determine the dominant parameters that lead to premature transverse cracking... more This study sought to determine the dominant parameters that lead to premature transverse cracking in bridge decks and to make recommendations that help reduce cracking tendency in bridge decks. The project includes two main parts: a field study and a parametric study. The field study identified 72 bridges in the Minneapolis/St. Paul area and explored the correlation between the observed cracking of those bridges and available design, material, and construction-related data. The parametric study investigated the relative influence of the factors that affect transverse deck cracking through a controlled nonlinear analysis study. Variables included: shrinkage, end restraint, girder stiffness, supplemental steel bar cutoff, cross frames, splices, deck concrete modulus of elasticity, and temperature history. In addition, four bridges from the companion field study were modeled to compare the analytical results with the actual crack patterns. Based on these results and correlation with other research, the study identified the following dominant factors affecting transfer cracking: shrinkage, longitudinal restraint, deck thickness, top transverse bar size, cement content, aggregate type and quantity, air content, and ambient air temperature at deck placement. Recommended practical improvements to bridge deck construction, in order of importance, include: using additives to reduce shrinkage of the deck concrete, using better curing practices, and minimizing continuity over interior spans.

Advances in Structural Engineering, 2000

The use of high-strength concrete is becoming popular around the world. The american code, ACI 31... more The use of high-strength concrete is becoming popular around the world. The american code, ACI 318–95 is used in many countries to calculate the development length of deformed bars in tension. However, current design provisions of ACI 318–95 are based on empirical relationships developed from tests on normal strength concrete. The results of a series of tests on high-strength concrete, reported in the literature, from six research studies are used to review the existing recommendations in ACI 318–95 for design of splices and anchorage of reinforcement. It is shown that ACI 318–95 equations may be unconservative for some cases beyond 62 MPa (9 ksi).

The work chronicled within this thesis was largely a team effort. I would like to especially than... more The work chronicled within this thesis was largely a team effort. I would like to especially thank my advisors, Cathy French and Carol Shield, for their help and guidance. I would also like to thank Charles M. Bell for his efforts during the design of the system and the instrumentation of the Center City Bridge. I would also like to thank

The 2005 Mid-Continent Transportation Research SymposiumIowa Department of TransportationIowa State University, AmesMidwest Transportation Consortium, 2005

Self-consolidating concrete (SCC) has been developed for use in precast prestressed concrete brid... more Self-consolidating concrete (SCC) has been developed for use in precast prestressed concrete bridge girders in the state of Minnesota. Locally available materials were used with a number of cementitious and filler materials, including ASTM Type III cement, Class C fly ash, and blast furnace slag. SCC was successfully proportioned with both natural river gravels and crushed stone as coarse aggregates. Moreover, for the mix incorporating natural river gravels, air-entrained SCC was successfully developed without using a viscosity enhancing admixture. The effect of a number of parameters on the fresh properties of SCC, including but not limited to temperature, cement, type of coarse aggregates (natural and crushed), were studied. A number of test methods (e.g., slump flow, L-box, and U-box) have been under development to evaluate the fresh properties of SCC. However, none of these test methods has been integrated into any American standards. A vertical column segregation test has been used to evaluate vertical segregation of SCC mixes. The slump flow test was employed to evaluate the flowability, while self-leveling and passing abilities of the mixes were investigated using a U-box. The L-box test procedure was modified to evaluate, not only flowability and passing ability, but also horizontal segregation resistance of SCC mixes. Although, in general, at least three to four test methods are typically used to evaluate fresh properties, the slump flow test and modified L-box test may be adequate to evaluate the fresh properties of SCC properly.

The I35W St. Anthony Falls Bridge, constructed to replace the steel truss bridge that collapsed i... more The I35W St. Anthony Falls Bridge, constructed to replace the steel truss bridge that collapsed in 2007, contains over 500 instruments to monitor the structural behavior. Numerical models of the bridge are being developed and calibrated to the collected data obtained during truck load testing and environmental loading. The data obtained over the first few years of monitoring will be correlated with the calibrated models and used to develop the baseline bridge behavior. This information will be used to develop a system to monitor and interpret the long-term behavior of the bridge. This paper describes the instrumentation, preliminary results from the data and model calibration, and plan for developing the long-term monitoring capabilities.

Structural health monitoring of in situ concrete structures is complicated by variations in the b... more Structural health monitoring of in situ concrete structures is complicated by variations in the behavior of the structure due to ambient environmental conditions, transient loads, and time-dependent effects (e.g., creep and shrinkage of concrete, prestress losses). As a case study, the I-35W St. Anthony Falls Bridge, a post-tensioned concrete box girder bridge instrumented with over 500 sensors to monitor structural behavior, was studied over the first five years of operation. A data normalization scheme was developed to extract the time-dependent behavior of the bridge from long-term data, removing the instantaneous response due to thermal variations and adjusting the timescale with the Arrhenius equation to account for the temperature-dependent rate of time-dependent behavior. The resulting time-dependent behavior followed a line in log time, and served as the baseline for anomaly detection. Short-term and long-term checks were developed to identify anomalous, and thus potentially damage-related, changes in the time-dependent behavior. The efficacy of these checks was investigated by introducing perturbations into the monitoring data from the St. Anthony Falls Bridge, assumed to contain no damage, to simulate instantaneous bearing lockup and a slow degradation process through introduction of a two-year drift in the data. The proposed method succeeded in successfully identifying the perturbations while minimizing false positives.