Author: Christoph HEINEMEYER Doctor Engineer RWTH Aachen University Aachen, Germany ,Markus FELDMANN Professor RWTH Aachen University Aachen, Germa | Size: 531 KB | Format:PDF | Quality:Unspecified | Year: 2008 | pages: 14
Increasing vibration problems encountered in the last few years show that footbridges should no longer be designed for static loads only but also for the dynamic actions and vibration behaviour of the footbridge due to pedestrian loading.
For this reason European research has been performed to come up with a design concept for footbridges that takes into account different traffic situations and individual demands on vibration comfort. So the elaborated guideline considers different types of pedestrian traffic and the traffic density which can greatly influence comfort requirements of the bridge and the dynamic behaviour. It is important to predict the effect of pedestrian traffic on footbridges at the design stage and in the later verification of serviceability in order to guarantee a comfort level for the user. This guide gives recommendations for designer and client to find relevant design situations as well as methods how to prove if vibration requirements are fulfilled
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A Beginner's Guide to Structural Equation Modeling 3rd ed
Author: Randall E. Schumacker & Richard G. Lomax | Size: 7.8 MB | Format:PDF | Quality:Unspecified | Publisher: Routledge | Year: 2010 | pages: 531 | ISBN: 1841698911
This best-seller introduces readers to structural equation modeling (SEM) so they can conduct their own analysis and critique related research. Noted for its accessible, applied approach, chapters cover basic concepts and practices and computer input/output from the free student version of Lisrel 8.8 in the examples.
Each chapter features an outline, key concepts, a summary, numerous examples from a variety of disciplines, tables, and figures, including path diagrams, to assist with conceptual understanding.
The book first reviews the basics of SEM, data entry/editing, and correlation. Next the authors highlight the basic steps of SEM: model specification, identification, estimation, testing, and modification, followed by issues related to model fit and power and sample size. Chapters 6 through 10 follow the steps of modeling using regression, path, confirmatory factor, and structural equation models. Next readers find a chapter on reporting SEM research including a checklist to guide decision-making, followed by one on model validation. Chapters 13 through 16 provide examples of various SEM model applications. The book concludes with the matrix approach to SEM using examples from previous chapters.
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The advantages of composite materials include a high specific strength and stiffness, formability, and a comparative resistance to fatigue cracking and corrosion. However, not forsaking these advantages, composite materials are prone to a wide range of defects and damage that can significantly reduce the residual strength and stiffness of a structure or result in unfavorable load paths.
Emphasizing defect identification and restitution, Defects and Damage in Composite Materials and Structures explains how defects and damage in composite materials and structures impact composite component performance. Providing ready access to an extensive, descriptive list of defects and damage types, this must-have reference:
• Examines defect criticality in composite structures
• Recommends repair actions to restore structural integrity
• Discusses failure modes and mechanisms of composites due to defects
• Reviews NDI processes for finding and identifying defects in composite materials
Relating defect detection methods to defect type, the author merges his experience in the field of in-service activities for composite airframe maintenance and repair with indispensable reports and articles on defects and damage in advanced composite materials from the last 50 years.
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An Introduction to the Mathematical Theory of Vibrations of Elastic Plates
Author: R. D. Mindlin, Jiashi Yang | Size: 5 MB | Format:PDF | Quality:Unspecified | Publisher: Kingdwarf | Year: 2007 | pages: 212 | ISBN: 9812703810
This book by the late R D Mindlin is destined to become a classic introduction to the mathematical aspects of two-dimensional theories of elastic plates. It systematically derives the two-dimensional theories of anisotropic elastic plates from the variational formulation of the three-dimensional theory of elasticity by power series expansions. The uniqueness of two-dimensional problems is also examined from the variational viewpoint. The accuracy of the two-dimensional equations is judged by comparing the dispersion relations of the waves that the two-dimensional theories can describe with prediction from the three-dimensional theory. Discussing mainly high-frequency dynamic problems, it is also useful in traditional applications in structural engineering as well as provides the theoretical foundation for acoustic wave devic
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Sediments, which constitute the surface of the Earth, start their journey to rivers with the energy obtained from rainfalls, fl oods and other natural processes. Due to transport of sediments, rivers develop with various appearances and functions, and play a crucial role in the activities of human beings and the life cycles of other species.
River sediment, as a conventional topic for river management, has been the topic of continuing research since ancient times, and since then significant progresses in river sediment research has been made. Nowadays, river sediment is much more connected to the activities of mankind and other species, following the increasing awareness of the co-existence of humans and nature.
Advances in River Sediment Research comprises the proceedings of the 12th International Symposium on River Sedimentation (ISRS2013, Kyoto, Japan, 2-5 September 2013). The book contains two keynote papers and 274 peer-reviewed regular contributions from all over the world, and covers recent accomplishments in theoretical developments, numerical simulations, laboratory experiments, field investigations and management methodologies of river sediment related issues. The book may serve as a reference book for graduate students, researchers, engineers and practitioners in disciplines of hydraulic, environmental, agricultural and geological engineering.
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Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures
Author: George Deodatis, Bruce R. Ellingwood, Dan M. Frangopol | Size: 470 MB | Format:PDF | Quality:Unspecified | Year: 2014 | pages: 5732 | ISBN: 1138000868
Safety, Reliability, Risk and Life-Cycle Performance of Structures and Infrastructures contains the plenary lectures and papers presented at the 11th International Conference on STRUCTURAL SAFETY AND RELIABILITY (ICOSSAR2013, New York, NY, USA, 16-20 June 2013), and covers major aspects of safety, reliability, risk and life-cycle performance of structures and infrastructures, with special focus on advanced technologies, analytical and computational methods of risk analysis, probability-based design and regulations, smart systems and materials, life-cycle cost analysis, damage assessment, social aspects, urban planning, and industrial applications. Emerging concepts as well as state-of-the-art and novel applications of reliability principles in all types of structural systems and mechanical components are included. Civil, marine, mechanical, transportation, nuclear and aerospace applications are discussed.
The unique knowledge, ideas and insights make this set of a book of abstracts and searchable, full paper USBdevice must-have literature for researchers and practitioners involved with safety, reliability, risk and life-cycle performance of structures and infrastructures.
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> Presents methodologies for reducing the variability of concrete performance
> Discusses the components of variability (materials, manufacturing, and testing) in terms of quality control
> Examines cost savings and increased business volume due to improved quality practices
> Considers variables such as material handling, mixing, transporting, delivery time, and temperature, and their effects on quality
> Explains how higher quality and lower variability helps with industry sustainability
Summary
Improve the Quality of Concrete, Improve the Quality of Construction
Quality measurement is not prevalent in the concrete industry and quality investment is not seen as potentially generating a positive return. Improving Concrete Quality examines how and why concrete quality should be measured, and includes instruction on developing specifications with the aim of improving concrete quality.
Reduce Concrete Variability: Reduce Costs and Increase Volume
The first part of the book considers the tangible and intangible benefits of improved quality. The later chapters explore concrete strength variability in detail. It provides a greater grasp of the variation in concrete, as well as a deeper understanding of how material variability affects concrete performance. The author discusses the components of variability (material, manufacturing, testing) and provides steps to measuring and reducing variability to improve the quality of concrete. The text also contains a chapter on data analysis for quality monitoring and test results.
Come Away with Practices and Tools That Can Be Applied Immediately:
> Provides techniques and how specifications can improve concrete quality
> Offers a clear understanding of the link between the materials (cement, SCM, aggregate, water, air), manufacturing, testing variability, and concrete quality
> Includes information on analyzing test data to improve quality
Improving Concrete Quality quantifies the benefits of improved quality, and introduces novel ways of measuring concrete quality. This text is an ideal resource for quality personnel in the concrete industry. It also benefits architects, engineers, contractors, and researchers.
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FOOTFALL INDUCED VIBRATION IN LONGSPAN COMPOSITE STEEL BEAMS USED IN TWO PROJECTS AT THE UNIVERSITY OF AUCKLAND
Author: V.N.Patel and R.J.Built | Size: 1.3 MB | Format:PDF | Quality:Unspecified | Publisher: Steel Innovations Conference 2013 Christchurch, New Zealand 21-22 February 2013 | Year: 2013 | pages: 13
Floor vibration due to human activity has become increasingly recognised by structural engineers, architects, and building owners as an inherent issue in long-span steel framed floor systems. In the past, attention was primarily focused on strength and deflection serviceability limits. However, as designers seek to push the limits on structural spans, grid spacings and adopt light-weight, low damping structural steelwork floor systems, more detailed consideration is required of the design tools and processes available to analyse and predict the vibration performance of floor systems.
Selection from published criteria of an “acceptable” vibration limit is sometimes possible depending upon the intended use of the space and the availability of manufacturers’ data for any vibration sensitive equipment. Building Owners and User Groups often have little understanding or quantitative “feel” for what performance the proposed “acceptable vibration limit” actually represents.
The theoretical predication of vibration performance against actual measured performance can sometimes vary significantly. This can lead to dispute post-construction as to whether the floor has an “acceptable” level of vibration. Post construction remediation of a space that is deemed to be “too lively” is often difficult, therefore, it is important that the vibration design criteria proposed are discussed and agreed and the limits of theoretical predications of vibration performance are clearly understood by all parties at the outset.
Beca Carter Hollings and Ferner Ltd (Beca) are currently in the process of designing two projects at the University of Auckland, utilising long-span partial-composite cellular steel beams. Both buildings will utilise existing structural frame layouts and foundations. As the new structure is to be built on the existing foundations, there is a necessity to keep it as lightweight as possible. The question of vibration sensitivity has been raised as a potential issue as both buildings contain research laboratories. An in-depth investigation has been conducted into the factors affecting vibration performance in order to give the Client and User Groups confidence that footfall induced vibration will not be an issue with the proposed floor structure.
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Over the last years, the trend in footbridge design has been towards greater spans
and increased flexibility and lightness. As a consequence, stiffness and mass have
decreased which has lead to smaller natural frequencies and more sensitivity to
dynamic loads. Many footbridges have natural frequencies that coincide with the
dominant frequencies of the pedestrian-induced load and therefore they have a potential
to suffer excessive vibrations under dynamic loads induced by pedestrians.
The main focus of this thesis was on the vertical and horizontal forces that
pedestrians impart to a footbridge and how these loads can be modelled to be used
in the dynamic design of footbridges. The work was divided into four subtasks. A
literature study of dynamic loads induced by pedestrians was performed. Design
criteria and load models proposed by four widely used standards were introduced
and a comparison was made. Dynamic analysis of the London Millennium Bridge
was performed using both an MDOF-model and an SDOF-model. Finally, available
solutions to vibration problems and improvements of design procedures were studied.
The standards studied in this thesis all propose similar serviceability criteria
for vertical vibrations. However, only two of them propose criteria for horizontal
vibrations. Some of these standards introduce load models for pedestrian loads
applicable for simplified structures. Load modelling for more complex structures,
on the other hand, are most often left to the designer.
Dynamic analysis of the London Millennium Bridge according to British and
International standards indicated good serviceability. An attempt to model the
horizontal load imposed by a group or a crowd of pedestrians resulted in accelerations that exceeded serviceability criteria.
The most effective way to solve vibration problems is to increase damping by installing a damping system. Several formulas have been set forth in order to calculate
the amount of damping required to solve vibration problems. However, more
data from existing lively footbridges is needed to verify these formulas.
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