In recent years, serious efforts have been undertaken to develop the concept of energy dissipation or supplemental damping into a workable technology, and a number of these devices have been installed in structures throughout the world. This monograph introduces the basic concepts of passive energy dissipation, and discusses current research, development, design and code-related activities in this exciting and fast expanding field.
Topics
The authors provide basic definitions for passive energy dissipation systems, and provide basic design principles governing their use. Mathematical modeling, recent developments, and modern applications of the following devices are covered in depth:
Metallic Dampers
Viscoelastic Dampers
Tuned Mass Dampers
Friction Dampers
Viscous Fluid Dampers
Tuned Liquid Dampers
The final chapter in the monograph discusses semi-active control systems. Semi-active mass dampers and semi-active fluid dampers have been installed in buildings in Japan, and are discussed in some detail, along with current research in the field.
Tables are provided in the appendices that detail application of passive energy dissipation systems in North America, and active and semi-active systems in Japan.
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Safety Impacts and Other Implications of Raised Speed Limits on High-Speed Roads
Author: Kockelman, Kara M | Size: 1.49 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2006 | pages: 197 | ISBN: -
This report describes the analyses performed and results obtained by a study of safety and other impacts of speed limit changes on high-speed roads. Safety-related analyses were based on a comprehensive framework of the disaggregate relationships between speed limits, driver speed choices, crash occurrence and crash severity. Using a variety of datasets, the project conducted numerous statistical analyses to elucidate and quantify these relationships. It was found that a speed limit increase on a high-speed road is generally associated with a less-than-equivalent increase in average vehicle speed: a 10 mi/h speed limit increase, for example, corresponds to average speeds around 3 mi/h higher. The project identified a relatively small but statistically significant correspondence between speed limits and total crash rates: a speed limit increase from 55 to 65 mi/h on an "average" high-speed road section would be associated with a crash rate increase of around 3%. Finally, the project found a statistically significant association between speed limits and the distribution of injury severities following a crash. For example, the project's models predict that a speed limit increase from 55 to 65 mi/h on the average section would be associated with a 24% increase in the probability of an occupant being fatally injured, once a crash has occurred. Considering that the crash rate itself increases slightly with a speed limit increase, overall fatality rates are predicted to rise by slightly higher percentages. However, the association between speed limit and injury severity dominates the overall fatality rate result. The magnitude of some of these relations between speed limit changes and safety factors is subject to uncertainty because of data limitations. Nonetheless, even after making allowances for such effects, the relationship between typical speed limit changes on high-speed roads and the injury severity distribution would in many cases remain statistically and practically significant. The investigation of non-safety impacts relied on published literature, unpublished reports by state departments of transportation (DOTs) of speed limit change impacts, and results of surveys of state DOT and police officials. The study considered economic, environmental, and other non-safety impacts of speed limit changes. The higher speeds resulting from a speed limit increase lead to travel time savings that have an economic value. The vehicles most likely to experience such savings are those making long-distance trips primarily in rural areas, where vehicle speeds are not significantly constrained by congestion. On the other hand, vehicles have higher operating costs at higher speeds; for a typical passenger car trip, the operating cost increase associated with a speed limit increase of 55 to 65 mi/h is roughly half the value of the reduced travel time. Approaches for determining the economic costs of injuries and fatalities were also reviewed. Little is known regarding the air quality and noise impacts of speed limit changes; the few available studies suggest that these impacts are very small to negligible. No reliable information was found regarding possible impacts of speed limit changes on business and commerce. Similarly, available data do not allow definite conclusions to be drawn regarding the impacts of differential light/heavy vehicle speed limits.
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This report documents and presents the results of a research effort to develop a decision tool for selecting either a one- or two-dimensional hydraulic model when examining flow through bridge crossings. The research began with a literature search and survey of the state of the practice to identify and characterize the site conditions and design requirements that may affect model selection. From this list of factors that influence model selection, a series of “desktop” experiments were constructed that compared one- and two-dimensional model results over a wide range of possible configurations. This research also examined several design criteria to discern their sensitivity to possible inaccuracy in numerical modeling results. From these results, a decision tool in the form of a decision matrix was developed as well as guidelines for its application. This tool provides a formal procedure for selecting the most appropriate model for a particular application incorporating site conditions, design elements, available resources and project constraints.
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The US currently has over 60,000 bridges over water with unknown foundations. This report presents a risk-based approach to managing these bridges in the absence of foundation information. The general framework in this report, which is primarily applied to scour failure, can easily be applied to other hazards such as earthquakes and tsunamis. The guidelines illustrate how to collect appropriate data, estimate risk of failure from an estimated failure probability and associated economic losses, and use risk in a structured approach to select an appropriate management plan. Risk analysis is specifically used to select appropriate performance standards for various bridge classifications and justify the costs of nondestructive testing of foundations, monitoring activities, and countermeasures. The scour guidelines were applied to sixty case studies in the US to validate the management plan that was selected for bridges with known foundations, and to illustrate the specific application of the guidelines in a variety of settings.
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Author: Houston, William N | Size: 2.67 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2009 | pages: 257 | ISBN: -
Performance objectives for achieving durable bridge deck concrete and the properties of locally available concrete raw materials, particularly supplementary cementitious materials (SCMs) like fly ash, GGBFS and silica fume, vary by geographic region. Because of this variation, the optimum concrete mixture proportions for a given application must be determined by experiment. Since durability-related experimental programs investigating the performance of concrete mixtures are expensive and time-consuming, a methodology for designing and conducting an investigation using statistical experimental design concepts has been developed to efficiently identify the optimum concrete mixture proportions for a specific set of conditions. The approach implemented is based on fractional orthogonal experimental design, which supports modeling for a large number of factors (input variables) based on a minimum number of tests. The Methodology, presented in NCHRP Report 566: "Guidelines for Concrete Mixtures Containing Supplementary Cementitious Materials to Enhance Durability of Bridge Decks," consists of six steps: (1) definition of performance requirements, (2) selection of durable raw materials, (3) construction of an experimental design matrix, (4) testing of concrete mixtures, (5) analysis and empirical modeling to determine the Best Tested and Best Predicted Concretes, and (6) confirmation of predictions and selection of the Best Concrete. This Methodology is flexible and may be applied to a range of performance demands. It was developed to identify optimum contents of SCMs but is also able to select between sources of raw materials. A case study was conducted based on a hypothetical set of service conditions and using concrete raw materials from the Midwest. The performance predictions based on the case study experimental design were verified by confirmation testing. Finally, a computational tool (SEDOC) was developed to support the implementation of this Methodology.
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Supplementary Cementitious Materials to Enhance Durability of Concrete Bridge Decks
Author: Houston, William N | Size: 3.64 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2005 | pages: 95 | ISBN: -
Performance objectives for achieving durable bridge deck concrete and the properties of locally available concrete raw materials, particularly supplementary cementitious materials (SCMs) like fly ash, GGBFS and silica fume, vary by geographic region. Because of this variation, the optimum concrete mixture proportions for a given application must be determined by experiment. Since durability-related experimental programs investigating the performance of concrete mixtures are expensive and time-consuming, a methodology for designing and conducting an investigation using statistical experimental design concepts has been developed to efficiently identify the optimum concrete mixture proportions for a specific set of conditions. The approach implemented is based on fractional orthogonal experimental design, which supports modeling for a large number of factors (input variables) based on a minimum number of tests. The Methodology, presented in NCHRP Report 566: "Guidelines for Concrete Mixtures Containing Supplementary Cementitious Materials to Enhance Durability of Bridge Decks," consists of six steps: (1) definition of performance requirements, (2) selection of durable raw materials, (3) construction of an experimental design matrix, (4) testing of concrete mixtures, (5) analysis and empirical modeling to determine the Best Tested and Best Predicted Concretes, and (6) confirmation of predictions and selection of the Best Concrete. This Methodology is flexible and may be applied to a range of performance demands. It was developed to identify optimum contents of SCMs but is also able to select between sources of raw materials. A case study was conducted based on a hypothetical set of service conditions and using concrete raw materials from the Midwest. The performance predictions based on the case study experimental design were verified by confirmation testing. Finally, a computational tool (SEDOC) was developed to support the implementation of this Methodology.
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Environmental Effects in Pavement Mix and Structural Design Systems
Author: Houston, William N | Size: 2.26 MB | Format:PDF | Quality:Original preprint | Publisher: Transportation Research Board | Year: 2005 | pages: 298 | ISBN: -
It is well documented that environmental effects play a significant role in characterizing the material properties, which in turn affect the pavement performance. Studies under the Strategic Highway Research Program (SHRP) were carried out to study the age hardening characteristics of asphalt binders and mixes. As a result of this study, laboratory procedures American Association of State Highway and Transportation Officials, provisional protocols (AASHTO PP1-98 and PP2-99) were developed to study the hardening potential of asphalt binders and mixes. The approaches followed in these procedures are of great value for the ongoing research on pavement aging; however, due to the limited resources and time constraints under the SHRP program, these provisional procedures have certain limitations associated with them. Research study, National Cooperative Highway Research Program (NCHRP) 9-23 was initiated to assess these limitations and if possible, enhance the predictive capabilities of these protocols. Binders and field cores were obtained from LTPP sections and other sites across the United States. Original, laboratory-aged, and field-aged binders were characterized. Based on the findings, an alternate procedure to the AASHTO PP1-98 protocol is suggested and presented. The alternate procedure includes field aging conditions and volumetric properties of the mix. The model developed was calibrated and validated using the data obtained from the field cores. Parametric analysis was performed on the final model to ascertain the practicality of the output. The assessment of the existing PP2-99 test protocol is also presented. Asphalt mix cores aged in the laboratory were tested for complex modulus. These modulus values were then compared to the modulus values of the field cores, the ages of which were known from the construction records. Due to the limited amount of data available, the PP2-99 protocol could not be improved.
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This document explores a methodology designed to predict the safety performance of various elements considered in the planning, design, and operation of nonlimited-access rural multilane highways. Chapter I provides an introduction, covering the background and the research objectives and scope of this project. Chapter II documents the literature review on existing statistical models, Accident Modification Factors (AMFs), and other predictive methodologies relevant to this study. Chapter III summarizes the results of a survey conducted in this study. Chapter IV describes the characteristics of the data collected in this project. Chapter V describes the model development and accident prediction methodology. Chapter VI summarizes the modeling results for estimating the safety performance of rural multilane highways. Chapter VII provides a summary of the work accomplished in this project and proposes recommendations for further work. The appendices document additional models from related research for consideration, Highway Safety Manual Chapter 9, the survey instrument, Cumulative Residuals (CURE plots), crash severity models, a methodology for estimating the variance of the product between baseline models and AMFs, and the Joint NCHRP 17-25/17-29 Expert Panel assessment.
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