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It is important to develop and incorporate the knowledge needed to design, construct, and maintain bridges to have the longest service life as possible. Consequently, the fatigue effects on bridges need to be considered and more accurately reflected within the proper bridge design specifications. This thesis describes the calibration process used to select the load and resistance factors for the fatigue limit states of steel bridge members within the AASHTO LRFD Bridge Design Specifications. The process presented within this thesis builds upon work completed as part of the Strategic Highway Research Program No. 2 including the determination of the fatigue load model. The resistance model was developed using available fatigue test data and statistically analyzed using specially developed techniques. Load and resistance factors were finally chosen for both Fatigue I and Fatigue II service limit states. We expect the new load and resistance factors for the fatigue service limit states to more accurately capture the fatigue effects of steel bridges and thus increase their service life.
"TRB's National Cooperative Highway Research Program (NCHRP) Report 796: Development and Calibration of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals provides specifications for structural supports of highway signs, luminaires, and traffic signals for consideration and inclusion in the American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) methodology. The report includes the Research Report, which documents the entire research effort, and the Appendix A: Calibration Report. Appendix B: AASHTO LRFD Specifications will be published by AASHTO. Other appendices are available on the TRB website, including: Appendix C: Design Examples, Appendix D: Survey Results, Appendix E: Fatigue Resistance Comparisons."--Publisher's description.
TRB's National Cooperative Highway Research Program (NCHRP) Research Report 851: Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads provides proposed specifications for bridges carrying light rail transit loading, including those subjected to both light rail and highway traffic loading. The proposed specifications and design examples are based on comprehensive response monitoring of five bridges carrying light rail transit vehicles in Denver, Colorado, and analytical programs for investigating the behavior of light rail bridges, live loads and associated forces, rail-train-structure interaction, and load factor calibration to implement the Load and Resistance Factor Design (LRFD) method. A standard live load model generates uniform design outcomes for any transit agency. Load factors are calibrated, particularly for the strength and fatigue limit states of light rail bridges.
The Load and Resistant Factor Design (LRFD) approach is based on the concept of structural reliability. The approach is more rational than the former design approaches such as Load Factor Design or Allowable Stress Design. The LRFD Specification for Bridge Design has been developed through 1990s and 2000s. In the development process, many factors were carefully calibrated such that a structure designed with LRFD can achieve a reliability index of 3.5 for a single bridge girder (probability of failure of about 2 in 10,000). As the initial development of the factors in the LRFD Specification was intended to be applied to the entire nation, state-specific traffic conditions or bridge configuration were not considered in the development process. In addition, due to lack of reliable truck weigh data in the early 1990s in the U.S., the truck weights from Ontario, Canada measured in the 1970s were used for the calibration. Hence, the reliability of bridges designed with the current LRFD specification needs to be evaluated based on the Missouri-specific data and the load factor needs to be re-calibrated for optimal design of bridges. The objective of the study presented in this report is to calibrate the live load factor in the Strength I Limit State in the AASHTO LRFD Bridge Design Specification. The calibration is based on the Missouri-specific data such as typical bridge configurations, traffic volume, and truck weights. The typical bridge configurations and the average daily truck traffic of the bridges in Missouri are identified from statistical analyses of 2007 National Bridge Inventory. The Weigh-In-Motion (WIM) data from 24 WIM stations in Missouri are used to simulate realistic truck loads. Updated material and geometric parameters are also used to update the resistance distributions. From this study, it was found that most representative bridges in Missouri have reliability indices slightly lower than 3.5 mainly due to the adopted projection method to predict 75 year load. For many bridges in rural areas with Average Daily Truck Traffic (ADTT) of 1,000 or less, the average reliability indices are higher than the average reliability index of bridges with ADTT of 5,000. This study proposes a table of calibration factors which can be applied to the current live load factor of 1.75. The calibration factor is developed as a function of ADTT such that bridge design practitioners can select a calibration factor considering the expected ADTTs of a bridge throughout its life span. Impact of the calibration factor on the up-front bridge construction cost is also presented.
TRB's National Cooperative Highway Research Program (NCHRP) Report 683: Protocols for Collecting and Using Traffic Data in Bridge Design explores a set of protocols and methodologies for using available recent truck traffic data to develop and calibrate vehicular loads for superstructure design, fatigue design, deck design, and design for overload permits. The protocols are geared to address the collection, processing, and use of national weigh-in-motion (WIM) data. The report also gives practical examples of implementing these protocols with recent national WIM data drawn from states/sites around the country with different traffic exposures, load spectra, and truck configurations. The material in this report will be of immediate interest to bridge engineers. This report replaces NCHRP Web-Only Document 135: Protocols for Collecting and Using Traffic Data in Bridge Design. Appendices A through F for NCHRP Report 683 are available only online.
Up-to-date coverage of bridge design and analysis revised to reflect the fifth edition of the AASHTO LRFD specifications Design of Highway Bridges, Third Edition offers detailed coverage of engineering basics for the design of short- and medium-span bridges. Revised to conform with the latest fifth edition of the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications, it is an excellent engineering resource for both professionals and students. This updated edition has been reorganized throughout, spreading the material into twenty shorter, more focused chapters that make information even easier to find and navigate. It also features: Expanded coverage of computer modeling, calibration of service limit states, rigid method system analysis, and concrete shear Information on key bridge types, selection principles, and aesthetic issues Dozens of worked problems that allow techniques to be applied to real-world problems and design specifications A new color insert of bridge photographs, including examples of historical and aesthetic significance New coverage of the "green" aspects of recycled steel Selected references for further study From gaining a quick familiarity with the AASHTO LRFD specifications to seeking broader guidance on highway bridge design Design of Highway Bridges is the one-stop, ready reference that puts information at your fingertips, while also serving as an excellent study guide and reference for the U.S. Professional Engineering Examination.