Browsing by Author "Shield, Carol K"

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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.
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.
Displacement Monitoring of I-35W Saint Anthony Falls Bridge with Current Vibration-Based System
(Minnesota Department of Transportation, 2019-01) Brown, Riley J; Gaebler, Karl O; Shield, Carol K; Linderman, Lauren E
Since the opening of the I-35W Saint Anthony Falls Bridge in 2008, over 500 sensors have been collecting data to better understand the behavior of post-tensioned concrete box girder structures. Recent research in the accelerometers installed on the bridge indicates they can be effectively used in a vibration-based structural health monitoring system, but previous studies have shown that natural frequency alone may not be sufficient to determine the performance of the structure. Vertical displacements were believed to be a simpler performance measure as direct comparisons can be made with design calculations and maintenance guidelines. To avoid the shortcomings of conventional displacement measurement options, this study focuses on using the currently installed accelerometers to estimate the vertical displacements of the southbound bridge. The proposed technique utilizes up-to-date modal parameters within a dual Kalman filter to estimate the vertical displacements of the structure from noisy acceleration measurements. When applied to the I-35W Saint Anthony Falls Bridge, it was found that the dual Kalman filter approach captures only dynamic displacements due to relatively slow loading (e.g., traffic loading and thermal loading) and the corresponding low-frequency static displacements are likely too small for GPS measurements due to the high stiffness of the structure.
The Effect of Transverse Stiffener Beams on Shear Transfer
(2003-01-01) Shield, Carol K; Stolarski, Henryk K; Bergson, Paul; Obeidat, Khalid
There are many wooden bridges in the United States. Their decks are often built of timber beams nailed together and covered with asphalt. The asphalt plays a mechanical role, and it provides environmental protection for the wood deck. The asphalt layer deteriorates and requires replacement. That leads to a faster deterioration of the deck, increased maintenance, and shorter bridge life. The flexibility of the deck is a probable cause of the fast deterioration of the asphalt. Low temperatures lead to deformations of the deck and may lead to cracks, which are propagated by mechanical and environmental effects. This project investigates stiffening the bridge deck by connecting a beam perpendicularly to the deck planks with metal bolts to reduce deformations of the deck. The additional beam is called a Transverse Stiffener Beam (or TSB). It can be incorporated as a part of new bridges or be attached to existing bridges. The investigations show the TSB significantly reduces deformations of the deck in most cases. The study indicates the positive effects of the TSB's should be expected in other applications. The magnitude of the effects can be analyzed with the computer program developed during this project. An investigation of the use of Transverse Stiffener Beams (TSB) for use on new and existing wooden bridges to reduce deformations of bridge decks, thus prolonging the life of asphalt bridge coverings, was undertaken. Positive effects of TSBs should be expected in other applications and can be analyzed with a computer program developed by this project.
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.
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
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.
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.
Investigation of Shear Distribution Factors in Prestressed Concrete Girder Bridges
(Minnesota Department of Transportation, 2016-09) Dymond, Benjamin Z; French, Catherine EW; Shield, Carol K
As shear requirements for prestressed concrete girders have changed, some structures designed using older specifications do not rate well with current methods. However, signs of shear distress have not been observed in these bridge girders and they are often deemed to be in good condition. The primary objective of this research program was to investigate the accuracy of existing shear distribution factors, which are used to estimate bridge system live load effects on individual girders, and provide recommendations on shear distribution to be used in Minnesota with four components: a full-scale laboratory bridge subjected to elastic and inelastic behavior, field testing of bridges, a numerical parametric study, and integration of results to develop a screening tool to determine which structures benefitted from refined analysis. Laboratory bridge inelastic testing indicated shear force redistribution after cracking and before ultimate failure. Use of elastic distribution factors is conservative for shear distribution at ultimate capacity. Elastic laboratory testing was used to validate the finite element modeling technique and study the behavior of a barrier and end diaphragm, which affected shear distribution; ignoring their effects was conservative. Parametric study results indicated that a ratio of longitudinal stiffness to transverse stiffness could be used as a screening tool. If the stiffness ratio was less than 1.5, shear demand from a simple, conservative grillage analysis may be more accurate than shear demand from AASHTO distribution factor methods. Grillage analysis shear demand results due to permit trucks may also be more accurate, regardless of the screening tool ratio.
Repair of Fatigued Steel Bridge Girders with Carbon Fiber Strips
(2003-12-01) Shield, Carol K; Hajjar, Jerome F; Nozaka, Katsuyoshi
This report investigates a method of repairing fatigued steel bridge girders using carbon fiber reinforced polymer (CFRP) strips. This type of repair would be used to prevent the propagation of cracks which could lead to failure of the bridge girders. The main advantages of using CFRP are it is lightweight and durable, resulting in ease of handling and maintenance. Therefore, it would not require the closing of traffic on the bridge during rehabilitation. Effective bond length was determined by a series of experimental tests with actual materials, as well as through the use of analytical equations. Finally, tests were conducted on full-scale cracked girders; the application of the CFRP strips to the steel girders resulted in significant strain reduction, except in the case of small cracks where it was difficult to clearly identify the benefits.
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.
Use of Adhesives to Retrofit Out-of-Plane Distortion Induced Fatigue Cracks
(2006-02-01) Hu, Yuying; Shield, Carol K; Dexter, Robert
Prior to 1985, it was common practice to avoid welding the connection plates to the tension flange of the girders of steel bridges. However, extensive fatigue cracking has developed in the unstiffened web gaps because of out-of-plane distortion. A new retrofit option was investigated that uses a room-temperature-cured two-part epoxy (3M Adhesive DP460-NS) to join a small length of ??-inch thick steel angle to the tension flange and the connection plate. A field test on two skewed bridges showed that the adhesive-angle retrofit system decreased the out-of-plane strain range by 40 to 50% when the original strain range was more than 50 microstrains. The ten adhesive-angle retrofits remained in place and were in good condition after three and a half years, suggesting that the chosen adhesive had good environmental durability. A laboratory large-scale specimen test with 8 web gaps showed that the retrofit system stopped or retarded most cracks even without stop holes when the measured out-of-plane strains were approximately 600 microstrains. Coupon tests conducted to investigate the environmental durability of the chosen adhesive showed that the chosen adhesive is suitable for applications at room or low temperature, even with high relative humidity.

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