Author: N. S. Potty*, Universiti Teknologi Malaysia, MALAYSIA S. Nambissan, Advanced Defence Laboratory, Bangalore, INDIA | Size: 189 MB | Format:PDF | Quality:Unspecified | Publisher: ICCBT 2008 - C - (09) – pp99-108 | Year: 2008 | pages: 10
The Indian Standard “Criteria for Earthquake Resistant Design of Structures: IS 1893-1984” has been revised. Areas in earthquake zone 1 have been merged to earthquake zone 2 and Killari is now in earthquake zone 3. The seismic zone factors have been also changed. Response spectra are now specified for 3 types of founding soil strata and a response reduction factor has been introduced. Elevated water tanks are vulnerable to earthquake, owing to large mass concentrated at the top of a relatively slender supporting structure. Existing elevated steel water tanks in India designed using IS 1893-1984 is checked for safety as per revised code (IS 1893-2002) by carrying out static and forced dynamic analysis. It is observed that the structure is unsafe due to under-estimation of seismic load as per old code provisions. Retrofit measures such as additional structural elements and passive devices like viscous and friction dampers are modelled and structure analysed again to check for compliance with the revised code. Conclusions drawn from this study are presented.
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As known from very upsetting experiences, elevated water tanks were heavily damages or collapsed during
earthquake. This was might be due to the lack of knowledge regarding the proper behaviour of supporting system of
the tank again dynamic effect and also due to improper geometrical selection of staging patterns. Due to the fluidstructure interactions, the seismic behaviour of elevated tanks has the characteristics of complex phenomena. The
main aim of this study is to understand the behaviour of supporting system which is more effective under different
response spectrum method with SAP 2000 software. In this Paper different supporting systems such as radial
bracing and cross bracing.
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Performance of elevated tanks in Mw 7.7 Bhuj earthquake of January 26th, 2001
Author: Proc. Indian Acad. Sci. (Earth Planet. Sci.), 112, No. 3, September 2003, pp. 421{429 | Size: 988 KB | Format:PDF | Quality:Unspecified | Publisher: Durgesh C Rai Department of Civil Engineering, Indian Institute of Technology, Kanpur 208 016, India. | Year: 2013 | pages: 09
The current designs of supporting structures of elevated water tanks are extremely vulnerable under lateral forces due to an earthquake and the Bhuj earthquake provided another illustration when a great many water tank stagings su ered damage and a few collapsed. The more popular shaft type stagings su er from poor ductility of thin shell sections besides low redundancy and toughness whereas framed stagings consist of weak members and poor brace-column joints. A strength analysis of a few damaged shaft type stagings clearly shows that all of them either met or exceeded the strength requirements of IS:1893{1984, however, they were all found de cient when compared with requirements of the International Building Code. IS:1893{1984 is unjusti ably low for these systems which do not have the advantage of ductility and redundancy and are currently being underestimated at least by a factor of 3 and need an upward revision of forces immediately.
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FEM SEISMIC ANALYSIS OF STEEL TANKS FOR OIL STORAGE IN INDUSTRIAL FACILITIES
Author: A. Di Carluccio , G. Fabbrocino , G. Manfredi | Size: 712 KB | Format:PDF | Quality:Unspecified | Publisher: The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China | Year: 2008 | pages: 08
ABSTRACT :
Structural and seismic engineering are involved in the design of new industrial facilities, but have certainly a
primary role in the evaluation and upgrading of existing plants. Atmospheric steel tanks for oil and other
hazardous material storage are commonly used in power plants, airports, and other critical plants. Their design is
somehow very standardized worldwide and thus they represent a challenging topic in the context of an industrial
risk assessment related to external hazards like earthquakes. In fact, their dynamic response is not trivial, since
fluid/structure interactions are relevant and influence the susceptibility to seismic damage. A full stress analysis
is certainly the more accurate way to design and to evaluate the risk of steel tanks under earthquake loads, but is
generally demanding in terms of computational effort. This approach leads to the direct computation of the
interaction between shell deformations and content motion during earthquakes. In the present paper, seismic
evaluation according to Eurocode 8 is discussed and some global results of Finite Element Analyses (FEM)
analyses are compared with those obtained according to simplified design procedures by Eurocode 8.
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Nonlinear Winkler-based shallow foundation model for performance assessment of seismically loaded structures
Author: Raychowdhury, Prishati | Size: 20.6 MB | Format:PDF | Quality:Original preprint | Publisher: UNIVERSITY OF CALIFORNIA, SAN DIEGO | Year: 2008 | pages: 326
Abstract:
When a structure supported on shallow foundations is subjected to inertial loading due to earthquake ground motion, the foundation may undergo sliding, settling and rocking movements. If the capacity of the foundation is mobilized, the soil-foundation interface will dissipate significant amounts of vibrational energy, resulting in a reduction in structural force demand. This energy dissipation and force demand reduction may enhance the overall performance of the structure, if potential consequences such as excessive tilting, settlement or bearing failure are accounted for.
Despite this potential benefit, building codes, particularly for new construction, discourage designs that allow foundation capacity mobilization. This lack of acceptance to embrace soil- foundation structure interaction (SFSI) as a design inelastic mechanism may stem from the well founded concern that significant uncertainties exist in characterization of soils. More importantly, the lack of well-calibrated modeling tools, coupled with parameter selection protocols cast in a simplistic fashion are lacking. In this work, a numerical model based on the Beam-on-Nonlinear-WinklerFoundation (BNWF) concept is developed to capture the above mentioned foundation behavior.
The BNWF model is selected due to its relative simplicity, ease of calibration, and acceptance in engineering practice. The soil-foundation interface is assumed to be an assembly of discrete, nonlinear elements composed of springs, dashpots and gap elements. Spring backbone curves typically used for modeling soil-pile response are taken as a baseline and further modified for their usefulness in shallow footing modeling. Evaluation of the model and associated parameter selection protocol is conducted using a suite of centrifuge experiments involving square and strip footings, bridge and building models, static and dynamic loading, sand and clay tests, a range of vertical factors of safety and aspect ratios. It is observed that the model can reasonably predict experimentally measured footing response in terms of moment, shear, settlement and
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Providing the main tools used for preliminary design of composites, this concise text covers all design aspects such as fiber and matrix selection, fabrication processes, prediction of material properties, and structural analysis of beams, plates, shells, and other structures.
Powerful preliminary-design tools, such as "carpet plots," are used in examples throughout the book, and software, entitles Computer Aided Design Environment for Composites (CADEC), is provided, which includes all of the design equations.
To download CADEC, visit Dr. Barbero’s book website
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Advanced Modeling and Evaluation of the Response of Base-Isolated Nuclear Facility Structures to Vertical Earthquake Excitation
Author: Eric Scott Keldrauk | Size: 12.9 MB | Format:PDF | Quality:Unspecified | Publisher: University of California, Berkeley | Year: 2012
The commissioning and construction of new nuclear power plants in the United States has dwindled over the past 30 years despite signi cant innovation in reactor technology. This
is partially due to the ever-increasing seismic hazard estimates, which increases the demand on and risk to nuclear power plant structures. Seismic base isolation is a mature technology which introduces a laterally- exible and vertically-sti layer between the foundation and superstructure to signi cantly reduce the
seismic response of the structure, systems, and components therein. Such devices have also been noted to concentrate the displacement response in one plane, reduce higher-mode
participation, and provide damping to protect against excessive displacements, all of which aid in increasing safety margins for seismically-isolated nuclear structures. Despite numerous
studies analyzing the applicability of seismic base isolation to nuclear power plant structures, some of which are discussed herein, no seismically-isolated nuclear plant has been constructed in the United States. This study presents a time-domain procedure for analyzing the performance of seismicallyisolatednuclear structures in response to design-basis earthquake events using ALE3D. The simulations serve as a parametric study to assess the e ects of soil column type, seismic isolation model, superstructure mesh, and ground motion selection on global displacements, rotations, and accelerations, as well as internal oor accelerations. Explicit modeling of the soil columns and superstructures enables detailed analysis of soil-structure interaction. The
soil columns analyzed have constant properties over the height of the nite element soil mesh
and include rock, soft rock, and sti soil sites, as well as a \no soil" case for comparison.
Four separate 3-dimensional seismic isolation bearing models were coded into ALE3D and validated. These include models for friction pendulum, triple friction pendulum, simpli ed lead rubber, and robust lead rubber bearings. Lastly, two superstructure nite element meshes were considered: a cylindrical plant design meant to represent a typical conceptual
design for advanced reactors, and a rectangular plant design meant to represent an advanced
boiling water reactor. The ground motions considered include 30 three-component time his
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Seismic Testing and Analytical Studies for the Development of New Seismic Force Resisting Systems for Metal Buildings /
Author: Smith, Matthew Douglas | Size: 12.8 MB | Format:PDF | Quality:Unspecified | Publisher: UNIVERSITY OF CALIFORNIA, SAN DIEGO | Year: 2013 | pages: 434
Abstract:
Metal buildings (MB) are a prevalent form of low-rise construction in the U.S. They are built in a
variety of geographic locations, including high seismic regions. It is desirable to understand the seismic performance of such a prevalent structural system. There is a general lack of experimental data available concerning the seismic performance of metal buildings and the web-tapered Ishaped
beams of which they are typically composed. In order to improve the seismic performance of the moment resisting frames in these buildings new Seismic Force Resisting Systems (SFRS) need to be developed. But first, several key issues required research. The MB moment frames
are often controlled by lateral-torsional buckling (LTB) and current design methodologies do not provide adequate LTB flexural strength prediction equations for the full range of member geometries commonly used. Single-story MB frames deviate significantly from the buildings used to define approximate fundamental period equations in the current building codes and the applicability of those equations to MB frames is questionable. Partial-floors, called mezzanines, are often attached to MB frames, yet no clear guidance is given in the current building codes to address the seismic analysis and design of these structures. Finally, experimental data for the
dynamic characteristics of MB moment frames at the system level and their cyclic post-buckling behavior at the member level was needed. This research provided experimental data through two testing programs. Shake table testing was performed on two full-scale metal buildings. Results of those tests led to two concepts for new SFRS for MB frames, one of which relies on LTB for inelastic hinging. Experimental data was provided in support of the development of the new SFRS through cyclic tests of ten web-tapered rafter specimens. The cyclic performance of LTB was investigated and results used to outline a new design procedure. In addition, new approximate
period equations and seismic design methods for mezzanines were developed. This research
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The special concentrically steel braced frame (SCBF) system is one of the most effective structural systems to resist lateral forces. Because of its effectiveness and straightforward design,
many SCBFs are incorporated in structures throughout the world. However, the highly nonlinear behavior associated with buckling and non-ductile fracture of braces reduces the ability of the system to dissipate energy resulting in undesirable modes of behavior. While many studies have investigated the cyclic behavior of individual braces or the behavior of subassemblies, the dynamic demands on the structural system under various seismic hazard levels needs additional
study for performance-based earthquake engineering.
Archetype buildings of SCBFs and buckling restrained braced frames (BRBFs) were analyzed using the computer program OpenSees (the Open System for Earthquake Engineering Simulation) to improve the understanding of the seismic behavior of braced frame systems, and to assess
seismic demands for performance-based design. Numerical models were calibrated using test data determined from testing of conventional buckling braces, buckling restrained braces, and the braced frame specimens. In addition, fiber-based OpenSees models were constructed and compared with results of a sophisticated finite-element model that realistically captured local
buckling and local fracture of structural elements. Because the OpenSees models are reasonably accurate and efficient, they were chosen to perform set of parametric computer simulations.
The seismic demands of the system and structural elements were computed and interpreted for 3-,
6-, and 16-story SCBFs and BRBFs under various hazard levels. The analysis results show large seismic demands for the 3-story SCBF, which may result in unexpected damage of structural
and non-structural elements. The median expected probability of a brace buckling at one or more levels in a 3-story SCBF is more than 50% for an earthquake having a 50% probability
of exceedance in 50 years (the service-level event). The possible need to replace braces following such frequent events due to brace buckling should be considered in performance-based earthquake engineering assessments. In addition, brace fracture in SCBFs is likely for an
earthquake having a 2% probability of exceedance in 50 years (the MCE-level event). Analyses show that in general, BRBF models had larger drift demands and residual drifts compared to SCBF systems, because of the BRBF’s longer fundamental period. However, the tendency to
form a weak story in BRBFs is less than that in SCBFs.
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SEISMIC DESIGN, TESTING AND ANALYSIS OF REINFORCED CONCRETE WALL BUILDINGS
Author: Marios Panagiotou | Size: 4.1 MB | Format:PDF | Quality:Unspecified | Publisher: UNIVERSITY OF CALIFORNIA, SAN DIEGO | Year: 2008 | pages: 290
Abstract:
Large investments have recently been made for the construction of new medium- and highrise buildings in California. In many cases performance-based designs have been the preferred method for these buildings. A main consideration in performance-based seismic design is the estimation of the likely development of structural and nonstructural damage limit-states given a hazard level. For this type of buildings efficient modeling techniques are required able to compute
the response at different performance states. A research work was conducted at University of California San Diego (UCSD) on the i) seismic design, ii) experimental response and iii)
computational modeling of medium- and high-rise reinforced concrete wall buildings. In the first part of this work a displacement-based seismic design method for use within performance-based is developed. Capacity design is used to control the mechanism of inelastic deformation. Based on
principles of plastic analysis and structural dynamics the new formulation allows the computation of the effects of system overstrength and of the higher modes of response. Equal emphasis is given to displacement, force and acceleration demand parameters. The ground motion destructiveness potential is also determined. Application of the method to reinforced concrete wall buildings is
discussed. The method is validated with the experimental response of a full-scale 7 story building.
In addition a dual plastic hinge design concept for improving the performance and optimizing the construction of high-rise buildings is presented. The second part presents the experimental research program, with extensive shake table tests, of a full-scale 7-story reinforced concrete wall
building slice, that was conducted at UCSD. The base shear coefficient obtained by the proposed method, of the first part of the research work, described above was 50% of that required by the equivalent static method prescribed by the ASCE-7 code. In spite of the reduced amount of longitudinal reinforcing steel, all performance objectives were met. The response of the building was significantly influenced, as expected, by the interaction of the main lateral force resisting wal
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