The present book is compiled from the notes of lectures given by Professor
Parks in the winter semester 1979-SO when he was a guest Professor at the
Ruhr University in Bochum. These lectures were aimed at studenU of control
engineering with some knowledge of dynamical systems described by means
of differential equations. Although the stability of dynamical systems is
portrayed from a technical point of view, the book is also aimed at readers
with interests in dynamical processes in other technical fields, for example
biocybernetics, meteorology, etc. Apart from an understanding of the
description of dynamical processes, the book requires no previous knowledge
from its readers and is suitable as an introduction to the topic. On the other
hand, an overview of so many methods of stability analysis is given that it
is suitable as a 'reference book' for instant information about any particular
method. Additional value lies not only in the application of a particular method
but also in the description of its derivation and context. In this respect, the
book is a significant supplement to existing texts in the field of stability of
dynamic systems. I hope that this book will be of practical interest and will
provide the motivation for further application of the methods described.
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Application of Precast Decks and Other Elements to Bridge Structures
Author: Bell II, Charles M French, Catherine E Shield, Carol K | Size: 6.29 MB | Format:PDF | Quality:Original preprint | Publisher: University of Minnesota, Twin Cities | Year: 2006 | pages: 271
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.
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Posted by: mahyarov - 11-13-2012, 10:37 AM - Forum: Steel
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Effects of Fabrication Procedures and Weld Melt-Through on Fatigue Resistance of Orthotropic Steel Deck Welds
Author: Uang, Chia-Ming | Size: 6.09 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2007 | pages: 168
Orthotropic bridge decks are commonly fabricated using 80% partial-joint-penetration groove welds (PJP) to join closed ribs to a deck plate. Because a tight fit may not always be achievable, weld melt-through is difficult to avoid and fatigue resistance may result. This report presents a study in which six 2-span, full-scale orthotropic steel deck specimens were built and tested to study the effects of weld melt-through and distortion control measures on the fatigue resistance of closed rib-to-deck PJP welds. Three of the specimens were heat straightened, while the other three were pre-cambered to minimize the need for subsequent heat straightening. Based upon test results, it was determined that effective pre-cambering is beneficial to mitigate the crack potential in rib-to-deck PJP welds.
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Laser Welded Steel Sandwich Panel Bridge Deck Development: Finite Element Analysis and Stake Weld Strength Tests
Author: Caccese, Vincent | Size: 4.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Maine, Orono | Year: 2009 | pages: 108
This report summarizes the analysis of laser welded steel sandwich panels for use in bridge structures and static testing of laser stake welded lap shear coupons. Steel sandwich panels consist of two face sheets connected by a relatively low-density core resulting in high strength and stiffness, which leads to promising design advantages. Steel sandwich panels offer substantial resistance to static and dynamic loads due to their high stiffness and substantial energy absorbing capacity. Panels of this kind are of interest for potential use in bridges for deck replacement. They are especially efficient in resisting dynamic events such as fatigue, impact or shock loading. A verification study is performed comparing finite element analysis and an analytical model to an experimental study documented in the literature. Results demonstrate good agreement between the approaches. Modeling techniques are developed from the verification study. Finite element analyses are subsequently employed to study the response of a laser welded steel sandwich panel case study of a deck replacement for a steel bridge located in Gardiner, Maine. The deck design results in a stiff structure that has a deflection of 1/1500 of the span at a depth of 7.25 inches. Structural response of stake welds was also investigated experimentally in a single lap shear configuration. Multiple pass welds consisting of 2 and 4 stake weld passes were fabricated and tested to assess the process of using multi-passes to increase weld resistance.
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Posted by: mahyarov - 11-13-2012, 10:24 AM - Forum: Steel
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Fatigue Life of Steel Base Plate to Pole Connections for Traffic Structures
Author: Stam, Andrew Richman, Nicholas Pool, Charles Rios, Craig Anderson, Thomas Frank, Karl | Size: 3.77 MB | Format:PDF | Quality:Original preprint | Publisher: University of Texas, Austin | Year: 2011 | pages: 165
This is a final report of an extensive experimental and analytical examination of the fatigue behavior of the welded end connection used on high-mast light structures and traffic signal masts. The weld details commonly used for these connections produce very poor fatigue performance. Their performance is a function of base plate stiffness, weld type and geometry, and number of anchor bolts. Older connection designs produced very poor fatigue performance far below the lowest American Association of State Highway and Transportation Officials (AASHTO) fatigue category. These connections can be improved by increasing the base or end plate thickness, improving weld details, and other geometric considerations. Due to the interaction of the overall connection geometry upon fatigue performance, the fatigue performance of the connection cannot be classified by simply the type of connection. The fatigue life can be improved to fatigue performance comparable to Category B but a similar connection with a thinner base plate can produce fatigue life of Category E. Recommended connections and their corresponding fatigue strength are given as well as recommended fabrication and welding specifications.
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Posted by: mahyarov - 11-13-2012, 10:21 AM - Forum: Steel
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Fatigue Failure and Cracking in High Mast Poles
Author: Goyal, Raka Dhonde, Hemant B Dawood, Mina | Size: 2.71 MB | Format:PDF | Quality:Original preprint | Publisher: University of Houston | Year: 2012 | pages: 272
This report presents the findings of a comprehensive research project to investigate the fatigue cracking and failure of galvanized high mast illumination poles (HMIP). Ultrasonic inspection of poles throughout the state has revealed the presence of weld toe cracks at the shaft-to-base-plate connections of some galvanized poles that the Texas Department of Transportation (TxDOT) owns. However, the effect of these galvanization-induced cracks on the fatigue life of the poles has not been clearly defined. The first phase of this research involved extensive review of published and unpublished data, to identify key factors that contribute to galvanization-induced cracking. Best fabrication practices to minimize such cracking are recommended. In the second phase, a comprehensive reliability analysis of several TxDOT pole configurations was conducted for different regions in Texas to predict the fatigue lives of the cracked poles. Critical pole configurations and locations are identified to facilitate cost-effective decisions related to inspection, repair, and replacement of poles.
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Posted by: mahyarov - 11-13-2012, 09:09 AM - Forum: Concrete
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Validation and Practical Procedure for Vibrational Evaluation of Tendons
Author: Sagues, Alberto A | Size: 1.62 MB | Format:PDF | Quality:Original preprint | Publisher: University of South Florida, Tampa | Year: 2008 | pages: 189
Vibrational testing of tension to identify potentially distressed external tendons of post-tensioned segments and columns has been successfully used in major Florida Department of Transportation (FDOT) bridges. This investigation provided validation of basic assumptions and verification of tension obtained by the vibration method against independent load cell measurements with tendon segments of size, length, and tension levels comparable to those used in actual structures. Measurements were conducted in a specially built tendon test facility with 12-strand tendons up to nearly 10 m (400 in.) long, some including a deviation block. Tension estimated from vibration tests was on average within ~6% of load cell measurements, after correction for the effect of metal pipe ends in some cases. Upon simulated strand failures at the anchorage area there was tension loss that was tracked adequately in nearly all cases by the vibration tests. Advanced data processing methods were developed to perform rapid evaluation of data from large populations (thousands) of tendons in actual bridges. Vibration test field equipment was developed for simplified operation and analysis procedures. A portable field equipment prototype was designed and constructed to permit testing by a single operator. Extensive vibration tests of tendons were conducted in the segmental approaches of the Sunshine Skyway Bridge, revealing generally normal tension levels but flagging specific tendons with fringe performance for subsequent inspection. A user-oriented summary of findings and applications is provided.
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Posted by: mahyarov - 11-13-2012, 09:06 AM - Forum: Concrete
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Flexural and Tensile Properties of Thin, Very High-Strength, Fiber-Reinforced Concrete Panels
Author: Roth, Michael J | Size: 4.85 MB | Format:PDF | Quality:Original preprint | Publisher: U.S. Army Engineer Research and Development Center | Year: 2008 | pages: 191
This research was conducted to characterize the flexural and tensile characteristics of thin, very high-strength, discontinuously reinforced concrete panels jointly developed by the U.S. Army Engineer Research and Development Center and U.S. Gypsum Corporation. Panels were produced from a unique blend of cementitious material and fiberglass reinforcing fibers, achieving compressive strength and fracture toughness levels that far exceeded those of typical concrete. The research program included third-point flexural experiments, novel direct tension experiments, implementation of micromechanically based analytical models, and development of finite element numerical models. The experimental, analytical, and numerical efforts were used conjunctively to determine parameters such as elastic modulus, first-crack strength, post-crack modulus and fiber/matrix interfacial bond strength. Furthermore, analytical and numerical models implemented in the work showed potential for use as design tools in future engineered material improvements.
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Post-tensioned (PT) bridges are major structures that carry significant traffic. These bridges are designed and constructed because they are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT structures: mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some comprehensive inspections of their PT bridges. A consultant’s report recommended that all ducts be re-grouted. However, the environment in Texas is very different than the environments in which the corrosion of the PT strands were observed. The objective of this research was to evaluate the corrosion activity of strands for PT structures and to correlate this corrosion activity with general environmental and void conditions. To achieve this objective, time-variant probabilistic models were developed to predict the tension capacity of PT strands subjected to different environmental and void conditions. Using these probabilistic models, time-variant structural reliability models were developed. The probability of failure of a simplified PT structure subjected to HS20 and HL93 loading conditions was assessed. Both flexural failure and serviceability were assessed. Results indicate that the presence of water and chlorides can lead to significant corrosion rates and failure is dependent on this corrosion activity and the number of strands exposed to these conditions. These results are presented in Volume 1 of this report. To assist TxDOT with developing a plan to mitigate this corrosion, studies were performed to assess repair grout materials, inspection methods, and repair methods. In addition, a general methodology is presented on optimizing repairs. These topics are presented in Volume 2 of this report. An Inspection and Repair Manual was also developed from this research and is presented in a separate report. Results indicate that TxDOT should prevent water and chlorides from infiltrating the tendons — this can be achieved in part by repairing drain lines, ducts, and protecting anchor heads as these conditions can lead to early failure of PT bridges. Recommendations on inspections, repairs, and materials are provided, however, further research on the potential formation of galvanic coupling of strands embedded in both existing and new repair grouts need to be assessed.
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Post-tensioned (PT) bridges are major structures that carry significant traffic. PT bridges are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT structures, mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some comprehensive inspections of its PT bridges. A consultant’s report recommended that all ducts be re-grouted. However, the environment in Texas is very different than the environments in which the corrosion of the PT strands were observed. The objective of this research was to evaluate the corrosion activity of strands for PT structures and to correlate this corrosion activity with general environmental and void conditions. To achieve this objective, time-variant probabilistic models were developed to predict the tension capacity of PT strands subjected to different environmental and void conditions. Using these probabilistic models, time-variant structural reliability models were developed. The probability of failure of a simplified PT structure subjected to HS20 and HL93 loading conditions was assessed. Both flexural failure and serviceability were assessed. Results indicate that the presence of water and chlorides can lead to significant corrosion rates and failure is dependent on this corrosion activity and the number of strands exposed to these conditions. Volume 1 of this report presents these results. To assist TxDOT with developing a plan to mitigate this corrosion, studies were performed to assess repair grout materials, inspection methods, and repair methods. In addition, a general methodology is presented on optimizing repairs. These topics are presented in Volume 2 of this report. An Inspection and Repair Manual was also developed from this research and is presented in a separate report. Results indicate that TxDOT should prevent water and chlorides from infiltrating the tendons; this can be achieved in part by repairing drain lines and ducts and protecting anchor heads, as these conditions can lead to early failure of PT bridges. Recommendations on inspections, repairs, and materials are provided; however, further research on the potential formation of galvanic coupling of strands embedded in both existing and new repair grouts needs to be assessed.
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