Author: Ronald O. Hamburger Simpson Gumpertz & Heger, Inc. San Francisco, CA Niaz A. Nazir DeSimone Consulting Engineers San Francisco, CA | Size: 3.11 MB | Format:PDF | Quality:Unspecified
In many ways structural steel is an ideal material for the design of earthquake-resistant structures. It is
strong, light weight, ductile, and tough, capable of dissipating extensive energy through yielding when
stressed into the inelastic range. Given the seismic design philosophy of present building codes, which
is to rely on the inherent ability of structures to undergo inelastic deformation without failure, these are
exactly the properties desired for seismic resistance. In fact, other construction materials rely on these
basic properties of steel to assist them in attaining adequate seismic resistance. Modern concrete and
masonry structures, for example, attain their ability to behave in a ductile manner through the presence
and behavior of steel reinforcing. Timber structures derive their ability to withstand strong ground
motion through the ductile behavior of steel connection hardware, including bolts, nails, and various
steel straps and assemblies used to interconnect wood framing.
Steel is a mixture of iron and carbon, with trace amounts of other elements, including principally
manganese, phosphorus, sulfur, and silicon. Steel is differentiated from the earlier cast and wrought irons
by the reduced amounts of carbon relative to these other alloys and the reduced amounts of other trace
elements. These differences make steel both stronger and more ductile than cast and wrought irons, both
of which tend to be quite brittle. Although iron alloys have been in use for centuries, steel is a relatively
modern material. For practical purposes the advent of steel as a construction material can be traced to the mid-19th century, when Sir Henry Bessemer developed the iron-to-steel conversion process that
allowed production of steel in large quantities. Initial uses of steel were in the railroad industry, where
it was used extensively to produce rails, and for armaments, including rifle and gun barrels. Andrew
Carnegie imported the Bessemer process to the United States and constructed his first steel mill in 1870,
initially for rail and machinery production. By the 1890s, however, steel was being applied to building
construction and, with the advent of the elevator and high-rise construction, rapidly became the building
material of choice for the new generation of tall buildings. The same properties that make it a desirable
material for high-rise construction (light weight, strength, ease of fabrication and erection) also make it
a popular construction material for structures involving long, clear spans. Today it is used in a variety
of construction applications ranging from bridges to industrial plants to buildings.
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Seismic design repair and retrofit strategies for steel roof deck diaphragms
Author: John-Edward Franquet | Size: 10 MB | Format:PDF | Quality:Unspecified | Publisher: Department of Civil Engineering and Applied Mechanics McGill University, Montreal, Canada | Year: OCTOBER 2009
Structural engineers will often rely on the roof diaphragm to transfer lateral seismic loads to the bracing system of single-storey structures. The implementation of capacity-based design in the NBCC 2005 has caused an increase in the diaphragm design load due to the need to use theprobable capacity of the bracing system, thus resulting in thicker decks, closer connector patternsand higher construction costs. Previous studies have shown that accounting for the in-plane flexibility of the diaphragm when calculating the overall building period can result in lower seismic forces and a more cost-Efficient design. However, recent studies estimating the fundamental period of single storeystructures using ambient vibration testing showed that the in-situ approximation was much shorter than that obtained using analytical means. The difference lies partially in the diaphragm stiffness characteristics which have been shown to decrease under increasing excitation amplitude. Using the diaphragm as the energy-dissipating element in the seismic force resisting system has also been investigated as this would take advantage of the diaphragm’s ductility and limited overstrength; thus, lower capacity based seismic forces would result. An experimental program on 21.0m by 7.31m diaphragm test specimens was carried out so as to Investigate the dynamic properties of diaphragms including the stiffness, ductility and capacity.The specimens consisted of 20 and 22 gauge panels with nailed frame fasteners and screwed sidelap connections as well a welded and button-punch specimen. Repair strategies for diaphragms that have previously undergone inelastic deformations were devised in an attempt to restitute the original stiffness and strength and were then experimentally evaluated. Strength and stiffness experimental estimations are compared with those predicted with the Steel Deck
Institute (SDI) method.
A building design comparative study was also completed. This study looks at the difference in design and cost yielded by previous and current design practice with EBF braced frames. Two alternate design methodologies, where the period is not restricted by code limitations and where the diaphragm force is limited to the equivalent shear force calculated with RdRo = 1.95, are also used for comparison. This study highlights the importance of incorporating the diaphragm stiffness in design and the potential cost savings.
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Seismic Demands on Steel Braced Frame Buildings with Buckling-Restrained Braces
Author: Rafael Sabelli, Stephen Mahin and Chunho Chang | Size: 0.44 MB | Format:PDF | Quality:Unspecified
This paper highlights research being conducted to identify ground motion and structural
characteristics that control the response of concentrically braced frames, and to identify
improved design procedures and code provisions. The focus of this paper is on the seismic
response of three and six story concentrically braced frames utilizing buckling-restrained
braces. A brief discussion is provided regarding the mechanical properties of such braces and
the benefit of their use. Results of detailed nonlinear dynamic analyses are then examined for
specific cases as well as statistically for several suites of ground motions to characterize the
effect on key response parameters of various structural configurations and proportions.
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Posted by: TAFATNEB - 08-31-2013, 09:44 AM - Forum: Steel
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Seismic Design of Seismic-Resistant Steel Building Structures
Size: 2.1 MB | Format:PDF | Quality:Unspecified
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Posted by: TAFATNEB - 08-31-2013, 09:29 AM - Forum: Steel
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Seismic design of multi-story cold-formed steel buildings: the CFS-NEES archetype building
Author: N. Nakata , B. W. Schafer and R. L. Madsen | Size: 8.57 MB | Format:PDF | Quality:Unspecified | Publisher: Department of Civil Engineering, Johns Hopkins University, Baltimore, | pages: 11
Lightweight cold-formed steel (CFS) framing is an effective building solution for low and mid-rise structures. However, systems level response and component contributions
as well as their interactions such as those from lateral-load resisting systems, floor diaphragms, studs to track connections, etc., are not fully understood. Existing building codes for the CFS frame buildings are based solely on the stiffness of the lateral-load resisting frames and do not explicitly incorporate systems response. This paper presents the first-phase of a multi-year project aimed at generating knowledge
and tools needed to increase the seismic safety of CFS frame buildings. The first phase of the study focuses on the design, instrumentation plan, and preliminary analysis
of full-scale two-story CFS frame buildings that are tested on shake tables at University at Buffalo NEES Facility in the second phase. Design of the two-story CFS buildings incorporates a “state of the practice” ledger framing system that attaches
floor and roof joists to the inside flanges of the load-bearing studs via a combination of track and clip angles. The instrumentation plan for the shake table tests is
developed to capture both systems and component level response of the buildings. The preliminary analysis includes development of new modeling capabilities that incorporate
cross-section limit states (local and distortional buckling) into frame analysis engines such as OpenSees to enable more accurate incremental dynamic analysis.
This paper provides detailed design of a prototype CFS frame building and instrumentation plan for the shake table tests at Buffalo.
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TEST PROCEDURES FOR THE DETERMINATION OF THE DYNAMIC SOIL CHARACTERISTICS
Author: Project coordinator: Bernd Asmussen International Union of Railways (UIC) | Size: 4.9 MB | Format:PDF | Quality:Unspecified | Year: DECEMBRE 2011 | pages: 107
Accurate prediction of railway induced vibration and assessment of the efficiency of vibration mitigation measures within the RIVAS project requires detailed knowledge of the dynamic soil characteristics.
Within the frame of the project, it is assumed that the soil can be modelled as a layered elastic halfspace, where the material properties vary only in the vertical direction, and that small strain behaviour prevails in the case of railway induced vibrations with relatively low amplitude. Within each layer, linear elastic isotropic constitutive behaviour is assumed; anisotropic constitutive behaviour would better represent the formation process, but is not generally used in state-of-the-art numerical models and geophysical prospection methods. Apart from the layer thickness, five parameters need to be determined for each layer: the shear and dilatational wave velocity, the material damping ratios in shear and dilatational deformation, and the mass density. The depth upto which these parameters should be investigated depends on the lowest frequency of interest and on the soil profile (stiffness). After a brief description of wave propagation in elastic media and the dependence of the constitutive soil behaviour on the strain level, the report discusses classical laboratory and in situ tests, which results can be used for soil characterization and a first estimate of dynamic soil characteristics based on empirical relations. Main emphasis is going to a detailed description of small strain dynamic laboratory tests and seismic in situ tests that can be used to determine dynamic soil characteristics.
The report concludes with a recommended course of action to determine dynamic soil characteristics within the frame of the RIVAS project, which is minimally based on a study of geological maps and historical geotechnical investigations, a first estimate of dynamic soil characteristics using empirical relations, soil characterization (e.g. mass density) using classical soil mechanics tests and seismic in situ testing (a combination of surface wave and seismic refraction methods). If budget permits, it is further recommended to perform an intrusive in situ test (cross-hole, up-hole, down-hole or SCPT) in order to enhance profiling depth and resolution, as well as to perform dynamic laboratory tests on undisturbed samples to determine complementary dynamic soil characteristics and to evaluate their strain dependency.
It is emphasized that, within RIVAS, estimations of dynamic soil characteristics based on empirical relations cannot replace their determination by means of in situ or laboratory tests. It is further recommended that impact loads are also measured when performing seismic in situ tests, so that the transfer functions of the soil are available and can be used for validation of the dynamic soil characteristics derived from the test.
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The evaluation of impedance functions in the analysis of foundations vibrations using boundary element method
Author: E. C¸ elebia, *, S. Fıratb , _ I. C¸ ankayac | Size: 2.2 MB | Format:PDF | Quality:Unspecified | Publisher: Applied Mathematics and Computation 173 (2006) 636–667 | Year: 2006 | pages: 32
The basic step in the substructure approach based on discretization of the soil medium
for the soil–structure interaction problems is to determine the impedance functions which are defined as the complex dynamic-stiffness coefficients of the soil-footing system are used in the analysis of foundations vibrations. In this study, the discrete values of impedance functions over wide ranges of frequency-factors are presented for both surface- supported and embedded foundations. The numerical results are obtained by using the substructure approach in the frequency domain which is formulated on basis of the Boundary Element Method derived from the fundamental solution for a homogeneous, isotropic and linear-elastic continuum. To further demonstrate in practical applications and to show the solutions of this type of problems to civil engineers, a comprehensive parametric analysis and systematic calculations are performed with various controlling parameters to evaluate the dynamic response of the vibrating soil–foundation system. In
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DYNAMIC PILE-SOIL-PILE INTERACTION. PART I: ANALYSIS OF AXIAL VIBRATION
Author: National Technical University. Athens. Greece; and Dept Civil Engineering, 212 Kelter Hall, State University of New York, Buffalo, New York 14260. U.S.A | Size: 1 MB | Format:PDF | Quality:Unspecified | Publisher: EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, VOL. 20,115-132 (1991) | Year: 1991 | pages: 18
Simple methods of analysis are developed for computing the dynamic steady-state axial response of floating pile groups
embedded in homogeneous and non-homogeneous soil deposits. Physically-motivated approximations are introduced to
account for the interaction between two individual piles. It is found that such an interaction arises chiefly from the
‘interference’ of wave fields originating along each pile shaft and spreading outward. For homogeneous deposits the wave
fronts originating at an individual pile are cylindrical and the interaction is essentially independent of pile flexibility and
slenderness. For non-homogeneous deposits the wave fronts are non-cylindrical and ray-theory approximations are
invoked to derive pile flexibility-dependent interaction functions.
Results are presented for the dynamic stiffness and damping of several pile groups, as well as for distribution of the
applied load among individual piles. For deposits with modulus proportional to depth, the agreement with the few
rigorous solutions available is encouraging. A comprehensive parameter study focuses on the effects of soil inhomogene-
ity and pile-group configuration. It is demonstrated that the ‘dynamic group efficiency’ may far exceed unity at certain
frequencies. Increasing soil inhomogeneity tends to reduce the respective resonant peaks and lead to smoother
interaction functions, in qualitative agreement with field evidence.
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Machinery Vibration Limits and Dynamic Structural Response
Author: Brian C. Howes, P. Eng., M.Sc. | Size: 0.9 MB | Format:PDF | Quality:Unspecified | pages: 28
Changes in case vibration readings are used to monitor rotating machinery condition. Absolute levels of vibration are indications of condition except where structural resonances (e.g.: bearing
housings, or motor bases) amplify vibrations at certain frequencies (usually integer multiples of shaft speed). Dynamic response at vibration test points can be measured on new installations to assist in establishing standards for absolute vibrations. Also, changes in dynamic response over time can add to understanding of machine condition. Discussion of case history to illustrate points is included.
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- Provides a comprehensive treatment of the behaviour and design of - - FRP-strengthened metallic structures
- Includes descriptions and explanations of basic concepts
- Offers design recommendations and presents design examples
Summary
Repairing or strengthening failing metallic structures traditionally involves using bulky and heavy external steel plates that often pose their own problems. The plates are generally prone to corrosion and overall fatigue. Fibre-reinforced polymer (FRP), a composite material made of a polymer matrix reinforced with fibres, offers a great alternative for strengthening metallic structures, especially steel structures such as bridges, buildings, offshore platforms, pipelines, and crane structures.
FRP-Strengthened Metallic Structures explores the behaviour and design of these structures, from basic concepts to design recommendations. It covers bond behaviour between FRP and steel, and describes improvement of fatigue performance, bending, compression, and bearing forces, strengthening of compression and steel tubular members, strengthening for enhanced fatigue and seismic performance, and strengthening against web crippling of steel sections. It also provides examples of performance improvement by FRP strengthening.
• Summarizes worldwide research on the FRP strengthening of metallic structures
• Contains several topics not generally covered in existing texts
• Presents comprehensive, topical references throughout the book
The book outlines the applications, existing design guidance, and special characteristics of FRP composites within the context of their use in structural strengthening. While the major focus is on steel structures, it also describes others, such as aluminium structures. This book is suitable for structural engineers, researchers, and university students interested in the FRP strengthening technique.
Xiao-Ling Zhao is chair of structural engineering at Monash University, Australia, and is author of Concrete-Filled Tubular Members and Connections, also published by Taylor & Francis.
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