Browsing by Author "French, Catherine E"

Now showing 1 - 10 of 10
  • Thumbnail Image
    Item
    Aerodynamics of highway sign structures: from laboratory tests and field monitoring to structural design guidelines
    (American Society of Civil Engineers, 2020-08-20) Heisel, Michael; Daugherty, Carly; Finley, Nicole; Linderman, Lauren; Schillinger, Dominik; French, Catherine E; Guala, Michele
    Field- and model-scale experiments were conducted to quantitatively assess the effects of wind loading on Rural Intersection Conflict Warning System (RICWS) highway sign structures. A field-scale RICWS was instrumented with acceleration and linear displacement sensors to monitor unsteady loads, dynamics, and displacement of the sign under various wind events classified by cup and vane wind velocity measurements. To complement the field-scale results, tests on a 1:18-scale model were conducted under controlled laboratory conditions in the St. Anthony Falls Laboratory towing tank and wind tunnel facilities. Aerodynamic effects on the sign structure were identified through analysis of the mean and oscillating drag and lift forces. Vortices periodically shed by the structure induced forces at a frequency governed by the Strouhal number. The shedding frequency overlapped with the estimated natural frequency during strong wind events, leading to possible resonance. Amplified oscillations were additionally observed when the wind direction was parallel to the structure, possibly due to an aeroelastic instability. The findings highlight the relevance of aerodynamic effects on roadside signs or similar complex planar geometries under unsteady wind loading.
  • Thumbnail Image
    Item
    Application of Precast Decks and Other Elements to Bridge Structures
    (2006-09-01) Bell, Charles M; French, Catherine E; Shield, Carol K
    A number of countries have incorporated precast components in bridge superstructures and substructures. Precast components include deck, abutment, and wall elements. Benefits of using precast elements in bridge construction include the high level of quality control that can be achieved in plant cast production compared to field cast operations and speed of construction afforded by the assembly of precast elements at the site rather than the time consuming on site forming and casting required in cast-in-place construction. Key components in the application of precast concrete to bridge structures are the connection elements. Connection details include the use of posttensioning systems, and various connection details such as weld plates, studs in grout pockets, and shear keys. The Minnesota Department of Transportation (Mn/DOT) constructed a bridge incorporating precast elements to enable rapid construction. The objective of this study was to develop an instrumentation plan to enable investigation of the performance of this bridge. Researchers developed an instrumentation plan based on information provided by the Mn/DOT bridge office regarding the specific bridge details and behaviors to be investigated. The instrumentation plan included the types and locations of the instruments.
  • Thumbnail Image
    Item
    Behavior of Concrete Integral Abutment Bridges
    (2004-11-01) Huang, Jimin; French, Catherine E; Shield, Carol K
    Integral abutment bridges have been increasing in popularity over the past 30 years due to low construction and maintenance cost and good earthquake resistance. However, their behavior is not fully understood with respect to thermal movements, time-dependent response, soil-structure interaction, and skew effects. In order to quantify--and predict--those conditions, researchers monitored a prestressed concrete Integral Abutment bridge from initial fabrication through seven seasonal cycles.
  • Thumbnail Image
    Item
    Effect of Vertical Pre-Release Cracks on Prestressed Bridge Girders
    (2002-10-01) Baran, Eray; French, Catherine E; Shield, Carol K
    Vertical cracks near the midspan of large-sized prestressed concrete bridge girders may develop during the curing process and can extend through the depth of the girder. The cracking is attributed to restrained shrinkage and thermal effects prior to release of the prestressing strands. Eighteen full-scale Mn/DOT Type 28M prestressed concrete beams were tested to investigate the effects of the cracks on the performance of the beams. Thirteen beams tested in this study incorporated manmade pre-release cracks. All of the beams were tested under static loading to investigate the effects of pre-release cracks on concrete strains, flexural crack initiation and re-opening loads, overall beam stiffness, and ultimate flexural capacity. Three of the beams were subjected to cyclic testing to evaluate possible effects of the pre-release cracks on the strand stress ranges and fatigue life of the beams. Unlike the field observations, the pre-release cracks in the test beams did not close completely under the beam's weight and pre-stressing force. The pre-release cracks were found to cause changes in beam strains around the crack locations. The overall stiffnesses of the beams were also affected by the reduction in the moment of inertia of the pre-release crack section. Following pre-release crack closure, the beams recover the stiffness comparable to that of the uncracked beams. No significant effect of pre-release cracks was observed on the behavior of the beams near the ultimate capacity. Results from the cyclic testing of three beams indicated that a beam that develops pre-release cracks is more likely to experience fatigue problems and tend to cause a reduction in the beam's fatigue life. Guidelines are proposed for the assessment of girders that develop pre-release cracks during production.
  • Thumbnail Image
    Item
    Effects of Increasing Truck Weight on Steel & Prestressed Bridges
    (2003-03-01) Altay, Altan; Arabbo, Diego; Dexter, Robert; French, Catherine E; Corwin, Eric
    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 shrinkage soon after construction and are not affected by increasing axle weight. However, decks with thickness less than 9 inches or with girder spacing greater than 10 ft may be susceptible to longitudinal flexural cracking which could decrease life.
  • Thumbnail Image
    Item
    Effects of Pre-Release Cracks in High-Strength Prestressed Girders
    (2000-01-01) Wyffels, Tina; French, Catherine E; Shield, Carol K
    Pre-release cracks have been observed during the fabrication process of some prestressed concrete girders. The pre-release cracks were observed to begin at the top flange and extend into the depth of the section, sometimes penetrating through the entire depth. The cracks close due to the effects of prestressing and girder self-weight when the prestressing strands are released. The objective of this report was to determine the effects these pre-release cracks have on girder camber, flexural cracking capacity, and steel stress ranges. The research included a parametric study investigating stress ranges in the prestressing strands in uncracked, cracked, and partially cracked girder sections to determine if steel fatigue was a concern. An analytical study was also performed which modeled several pre-release cracks, including models of two experimental girders that developed pre-release cracks, to determine the effect of various cracks on girder stress and camber. It was found that steel fatigue in the prestressing strand is a concern in girders that become cracked in service. Fatigue of the steel strands has typically not been a concern in prestressed girders because the girders are designed so the section remains uncracked under service load. However, a loss of compressive stress is believed to occur in the bottom fiber of the girder due to pre-release cracks, which may result in the section cracking at a lower applied load. The loss of compressive stress in the bottom fiber of girders with pre-release cracks was determined using finite element modeling. Additional results of the analytical models were that pre-release cracks result in a loss of girder camber, the effects of the pre-release cracks remained local to the crack location, non-linear stress distributions occurred during the process of crack closure, and the magnitude of the pre-release crack effects was dependent on the number of cracks, the crack width, and the crack depth. Keywords: pre-release cracks, prestressed concrete girders, flexural cracking, fatigue
  • Thumbnail Image
    Item
    Evaluation of Electrochemical Chloride Extraction (ECE) and Fiber Reinforced Polymer (FRP) Wrap Technology
    (Minnesota Department of Transportation, 2000-06-01) Chauvin, Mark; Shield, Carol K; French, Catherine E; Smyrl, William
    Methods for mitigating corrosion in reinforced concrete structures were investigated on the substructure of a bridge in Minneapolis, Minnesota. The structures chosen for this investigation constituted a portion of the substructure of I-394, Bridge #27831, over Dunwoody Blvd. in Minneapolis, MN.
  • Thumbnail Image
    Item
    High-Strength Concrete Prestressed Bridge Girders: Long Term and Flexural Behavior
    (2000-11-01) Ahlborn, Theresa M; French, Catherine E; Shield, Carol K
    This project involved the construction of two long-span, high-strength composite prestressed bridge girders to investigate their structural behavior and the adequacy of American Association of State Highway and Transportation Officials (AASHTO) 1993 provisions for their design. The scope of the research included examining prestress losses, transfer length, cyclic load response, and ultimate flexural strength. The research revealed that prestress losses could not be determined solely from strain gage instrumentation. Foil strain gages attached to the strand cannot measure losses caused by relaxation and drift over time. Vibrating wire strain gages embedded in the concrete cannot account for losses in the prestressing strand before the concrete hardens. Researchers used vibrating wire gage data to measure the prestress losses incurred since the time of strand release. To back-calculate the losses that occur before release, researchers used total prestress losses determined from flexural cracking and crack reopening loads. The measured prestress losses were found to be much higher than those predicted by analytical methods. Prestress losses predicted by AASHTO not only ignore concrete stress before release but also overestimate the high-strength concrete modulus, leading to lower initial losses, and overpredict the creep and shrinkage, leading to higher long-term losses.
  • Thumbnail Image
    Item
    Release Methodology of Prestressing Strands
    (1998-05-01) Kannel, Jeffrey J; French, Catherine E; Stolarski, Henryk K
    This report presents the results of numerical and experimental investigations to determine the causes of prestressed concrete girder end cracks. The cracks, which develop during the flame-cutting release process, result from the restraining effect of unreleased strands as the girder shortens from the partially transferred prestress and from shear stresses generated by the cutting order of the strands. Researchers examined several methods to elimate the cracks, such as making changes to the strand cutting pattern, debonding some of the strands in the end regions, and increasing the slope of the top surface of the bottom flange. Implementation of the first two of these methods in the field proved successful.
  • Thumbnail Image
    Item
    Retrofitting Shear Cracks in Reinforced Concrete Pier Caps Using Carbon Fiber Reinforced Polymers
    (2005-04-01) Milde, Emily; Shield, Carol K; French, Catherine E; Wacker, Jon
    The Minnesota Department of Transportation (Mn/DOT) documented the appearance of excessive cracks in the reinforced concrete pier cap overhangs of State Highway Bridges 19855 and 19856. As a part of this study, the ultimate capacity of the pier cap overhangs was estimated by comparing predicted capacities calculated using standard design specifications to experimental results published in the worldwide literature. It was determined that the ultimate capacity of the pier cap overhangs was more than sufficient to assure that a cracked, but undeteriorated, pier cap is not prone to structural failure. An estimate of the initial cracking load of the pier cap overhangs was also created to determine what changes to pier cap design would be required to prevent future overhangs from cracking.