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Structural System (structural + system)

Distribution by Scientific Domains

Engineering	95%
2 Other Domains	5%

Selected Abstracts

Identification of Time-Variant Modal Parameters Using Time-Varying Autoregressive with Exogenous Input and Low-Order Polynomial Function

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2009
C. S. Huang
By developing the equivalent relations between the equation of motion of a time-varying structural system and the TVARX model, this work proves that instantaneous modal parameters of a time-varying system can be directly estimated from the TVARX model coefficients established from displacement responses. A moving least-squares technique incorporating polynomial basis functions is adopted to approximate the coefficient functions of the TVARX model. The coefficient functions of the TVARX model are represented by polynomials having time-dependent coefficients, instead of constant coefficients as in traditional basis function expansion approaches, so that only low orders of polynomial basis functions are needed. Numerical studies are carried out to investigate the effects of parameters in the proposed approach on accurately determining instantaneous modal parameters. Numerical analyses also demonstrate that the proposed approach is superior to some published techniques (i.e., recursive technique with a forgetting factor, traditional basis function expansion approach, and weighted basis function expansion approach) in accurately estimating instantaneous modal parameters of a structure. Finally, the proposed approach is applied to process measured data for a frame specimen subjected to a series of base excitations in shaking table tests. The specimen was damaged during testing. The identified instantaneous modal parameters are consistent with observed physical phenomena. [source]

Numerical Treatment of Seismic Accelerograms and of Inelastic Seismic Structural Responses Using Harmonic Wavelets

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2007
Pol D. Spanos
The effectiveness of the harmonic wavelets for capturing the temporal evolution of the frequency content of strong ground motions is demonstrated. In this regard, a detailed study of important earthquake accelerograms is undertaken and smooth joint time-frequency spectra are provided for two near-field and two far-field records; inherent in this analysis is the concept of the mean instantaneous frequency. Furthermore, as a paradigm of usefulness for aseismic structural purposes, a similar analysis is conducted for the response of a 20-story steel frame benchmark building considering one of the four accelerograms scaled by appropriate factors as the excitation to simulate undamaged and severely damaged conditions for the structure. The resulting joint time-frequency representation of the response time histories captures the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event. In this context, the potential of the harmonic wavelet transform as a detection tool for global structural damage is explored in conjunction with the concept of monitoring the mean instantaneous frequency of records of critical structural responses. [source]

A Wavelet-Based Approach to Identifying Structural Modal Parameters from Seismic Response and Free Vibration Data

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2005
C. S. Huang
The wavelet transform with orthonormal wavelets is applied to the measured acceleration responses of a structural system, and to reconstruct the discrete equations of motion in various wavelet subspaces. The accuracy of this procedure is numerically confirmed; the effects of mother wavelet functions and noise on the ability to accurately estimate the dynamic characteristics are also investigated. The feasibility of the present procedure to elucidate real structures is demonstrated through processing the measured responses of steel frames in shaking table tests and the free vibration responses of a five-span arch bridge with a total length of 440 m. [source]

Initialization Strategies in Simulation-Based SFE Eigenvalue Analysis

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2005
Song Du
Poor initializations often result in slow convergence, and in certain instances may lead to an incorrect or irrelevant answer. The problem of selecting an appropriate starting vector becomes even more complicated when the structure involved is characterized by properties that are random in nature. Here, a good initialization for one sample could be poor for another sample. Thus, the proper eigenvector initialization for uncertainty analysis involving Monte Carlo simulations is essential for efficient random eigenvalue analysis. Most simulation procedures to date have been sequential in nature, that is, a random vector to describe the structural system is simulated, a FE analysis is conducted, the response quantities are identified by post-processing, and the process is repeated until the standard error in the response of interest is within desired limits. A different approach is to generate all the sample (random) structures prior to performing any FE analysis, sequentially rank order them according to some appropriate measure of distance between the realizations, and perform the FE analyses in similar rank order, using the results from the previous analysis as the initialization for the current analysis. The sample structures may also be ordered into a tree-type data structure, where each node represents a random sample, the traverse of the tree starts from the root of the tree until every node in the tree is visited exactly once. This approach differs from the sequential ordering approach in that it uses the solution of the "closest" node to initialize the iterative solver. The computational efficiencies that result from such orderings (at a modest expense of additional data storage) are demonstrated through a stability analysis of a system with closely spaced buckling loads and the modal analysis of a simply supported beam. [source]

Seismic performance evaluation of a 34-story steel building retrofitted with response modification elements

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2009
Yuan-Tao Weng
Abstract The original structural design of this case study consisted of five basement floors and a 34-story hotel tower in Kaohsiung, Taiwan. The construction started in 1993, and the erection of the entire steel frame and the pouring of concrete slabs up to the 26th floor were completed before 1996. However, construction of the original hotel was subsequently suspended for 10 years. Recently, this building has been retrofitted for residential purposes. Buckling restrained braces (BRBs) and eccentrically braced frames were incorporated into the seismic design of the new residential tower. This paper presents the seismic resisting structural system, seismic design criteria, full-scale test results of one BRB member and the as-built welded moment connections. Test results confirm that the two side web-plate stiffening details can effectively improve the rotational capacity of welded moment connection. The paper also discusses the analytical models for simulating the experimental responses of the BRB members and the welded moment connections. Nonlinear response history analyses (NLRHA) indicate that the inelastic deformational demands of the original and the redesigned structures induced by the maximum considered earthquakes are less than those found in the seismic building codes or laboratory tests. This paper also proposes a ground motion scaling method considering multi-mode effects for NLRHA of the example building. It is shown that the proposed scaling method worked well in reducing the scatter in estimated peak seismic demands. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Design of passive systems for control of inelastic structures

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2009
Gian Paolo Cimellaro
Abstract A design strategy for control of buildings experiencing inelastic deformations during seismic response is formulated. The strategy is using weakened, and/or softened, elements in a structural system while adding passive energy dissipation devices (e.g. viscous fluid devices, etc.) in order to control simultaneously accelerations and deformations response during seismic events. A design methodology is developed to determine the locations and the magnitude of weakening and/or softening of structural elements and the added damping while insuring structural stability. A two-stage design procedure is suggested: (i) first using a nonlinear active control algorithm, to determine the new structural parameters while insuring stability, then (ii) determine the properties of equivalent structural parameters of passive system, which can be implemented by removing or weakening some structural elements, or connections, and by addition of energy dissipation systems. Passive dampers and weakened elements are designed using an optimization algorithm to obtain a response as close as possible to an actively controlled system. A case study of a five-story building subjected to El Centro ground motion, as well as to an ensemble of simulated ground motions, is presented to illustrate the procedure. The results show that following the design strategy, a control of both peak inter-story drifts and total accelerations can be obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Seismic performance of a 3D full-scale high-ductile steel,concrete composite moment-resisting frame,Part II: Test results and analytical validation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2008
A. Braconi
Abstract This paper presents the results of a multi-level pseudo-dynamic seismic test program that was performed to assess the performance of a full-scale three-bay, two-storey steel,concrete composite moment-resisting frame built with partially encased composite columns and partial-strength beam-to-column joints. The system was designed to develop a ductile response in the joint components of beam-to-column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi-static cyclic test with stepwise increasing displacement,amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam-to-end-plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam-to-column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Dynamic systems with high damping rubber: Nonlinear behaviour and linear approximation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 13 2008
Andrea Dall'Asta
Abstract High damping rubber (HDR) shows a quite complex constitutive behaviour, which is nonlinear with respect to strain and is dependent on the strain rate. In addition, it exhibits a transient response during which the material properties change (scragging or more generally the Mullins effect). A number of recent works were dedicated to analysing and modelling material behaviour. This paper studies the nonlinear dynamics of systems with restoring force produced by HDR-based devices in order to propose a procedure to define equivalent linear models considering both transient and stationary behaviours. The reliability of these linear models is tested by evaluating the upper and lower bounds of the seismic response of a structural system equipped with HDR-based devices (structural system with dissipative bracings and isolated systems). Copyright © 2008 John Wiley & Sons, Ltd. [source]

Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2008
Rabin Tuladhar
Abstract Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full-scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300,mm and a thickness of 60,mm. The test piles were 26,m long. Three-dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load-carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Seismic control of smart base isolated buildings with new semiactive variable damper

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2007
S. Nagarajaiah
Abstract A new semiactive independently variable damper, SAIVD, is developed and shown to be effective in achieving response reductions in smart base isolated buildings in near fault earthquakes. The semiactive device consists of four linear visco-elastic elements, commonly known as Kelvin,Voigt elements, arranged in a rhombus configuration. The magnitude of force in the semiactive device can be adjusted smoothly in real-time by varying the angle of the visco-elastic elements of the device or the aspect ratio of the rhombus configuration. Such a device is essentially linear, simple to construct, and does not present the difficulties commonly associated with modelling and analysing nonlinear devices (e.g. friction devices). The smooth semiactive force variation eliminates the disadvantages associated with rapid switching devices. Experimental results are presented to verify the proposed analytical model of the device. A H, control algorithm is implemented in order to reduce the response of base isolated buildings with variable damping semiactive control systems in near fault earthquakes. The central idea of the control algorithm is to design a H, controller for the structural system that serves as an aid in the determination of the optimum control force in the semiactive device. The relative performance of the SAIVD device is compared to a variable friction device, recently developed by the authors in a separate study, and several key aspects of performance are discussed regarding the use of the two devices for reducing the responses of smart base isolated buildings in near fault earthquakes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Shaking table model test on Shanghai World Financial Center Tower

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2007
Xilin Lu
Abstract The height of 101-storey Shanghai World Financial Center Tower is 492m above ground making it possible the tallest building in the world when completed. Three parallel structural systems including mega-frame structure, reinforced concrete and braced steel services core and outrigger trusses, are combined to resist vertical and lateral loads. The building could be classified as a vertically irregular structure due to a number of stiffened and transfer stories in the building. Complexities related to structural system layout are mainly exhibited in the design of services core, mega-diagonals and outrigger trusses. According to Chinese Code, the height 190 m of the building clearly exceeds the stipulated maximum height of for a composite frame/reinforced concrete core building. The aspect ratio of height to width also exceeds the stipulated limit of 7 for seismic design intensity 7. A 1/50 scaled model is made and tested on shaking table under a series of one and two-dimensional base excitations with gradually increasing acceleration amplitudes. This paper presents the dynamic characteristics, the seismic responses and the failure mechanism of the structure. The test results demonstrate that the structural system is a good solution to withstand earthquakes. The inter-storey drift and the overall behaviour meet the requirements of Chinese Design Code. Furthermore, weak positions under seldom-occurred earthquakes of seismic design intensity 8 are found based on the visible damages on the testing model, and some corresponding suggestions are proposed for the engineering design of the structure under extremely strong earthquake. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Effect of train dynamics on seismic response of steel monorail bridges under moderate ground motion

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2006
Chul-Woo Kim
Abstract This study is intended to investigate the seismic response of steel monorail bridges using three-dimensional dynamic response analysis. We particularly consider monorail bridge,train interaction when subjected to ground motion that occurs with high probability. A monorail train car with two bogies with pneumatic tires for running, steering and stabilizing wheels is assumed to be represented sufficiently by a discrete rigid multi-body system with 15 degrees of freedom (DOFs). Bridges are considered as an assemblage of beam elements with 6 DOFs at each node. Modal analysis is used for dynamic response analysis under moderate earthquakes. The seismic response of an advanced monorail bridge that adopts a simplified structural system and composite girders is investigated through comparison with seismic responses of a conventional bridge. The acceleration response of a monorail train is also calculated to investigate the effect of structural types of bridges on the train's dynamic response during earthquakes. Results show that the seismic responses of the advanced bridges are greater than those of the conventional monorail bridge because of the simplified structural system and increased girder weight that is attributable to composite girders of the advanced bridge. Moreover, the train on the advanced bridge shows greater dynamic response than that on the conventional bridge. Observations reveal that the dynamic monorail train system acts as a damper on the monorail bridge. That fact shows that the existing design, which considers a train as additional mass, yields a conservative result. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Evolutionary aseismic design and retrofit of structures with passive energy dissipation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 13 2005
G. F. Dargush
Abstract A new computational framework is developed for the design and retrofit of building structures by considering aseismic design as a complex adaptive process. For the initial phase of the development within this framework, genetic algorithms are employed for the discrete optimization of passively damped structural systems. The passive elements may include metallic plate dampers, viscous fluid dampers and viscoelastic solid dampers. The primary objective is to determine robust designs, including both the non-linearity of the structural system and the uncertainty of the seismic environment. Within the present paper, this computational design approach is applied to a series of model problems, involving sizing and placement of passive dampers for energy dissipation. In order to facilitate our investigations and provide a baseline for further study, we introduce several simplifications for these initial examples. In particular, we employ deterministic lumped parameter structural models, memoryless fitness function definitions and hypothetical seismic environments. Despite these restrictions, some interesting results are obtained from the simulations and we are able to gain an understanding of the potential for the proposed evolutionary aseismic design methodology. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Forced vibration testing of buildings using the linear shaker seismic simulation (LSSS) testing method

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2005
Eunjong Yu
Abstract This paper describes the development and numerical verification of a test method to realistically simulate the seismic structural response of full-scale buildings. The result is a new field testing procedure referred to as the linear shaker seismic simulation (LSSS) testing method. This test method uses a linear shaker system in which a mass mounted on the structure is commanded a specified acceleration time history, which in turn induces inertial forces in the structure. The inertia force of the moving mass is transferred as dynamic force excitation to the structure. The key issues associated with the LSSS method are (1) determining for a given ground motion displacement, xg, a linear shaker motion which induces a structural response that matches as closely as possible the response of the building if it had been excited at its base by xg (i.e. the motion transformation problem) and (2) correcting the linear shaker motion from Step (1) to compensate for control,structure interaction effects associated with the fact that linear shaker systems cannot impart perfectly to the structure the specified forcing functions (i.e. the CSI problem). The motion transformation problem is solved using filters that modify xg both in the frequency domain using building transfer functions and in the time domain using a least squares approximation. The CSI problem, which is most important near the modal frequencies of the structural system, is solved for the example of a linear shaker system that is part of the NEES@UCLA equipment site. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Simplified non-linear seismic analysis of infilled reinforced concrete frames

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2005
Matja
Abstract The N2 method for simplified non-linear seismic analysis has been extended in order to make it applicable to infilled reinforced concrete frames. Compared to the simple basic variant of the N2 method, two important differences apply. A multi-linear idealization of the pushover curve, which takes into account the strength degradation which occurs after the infill fails, has to be made, and specific reduction factors, developed in a companion paper, have to be used for the determination of inelastic spectra. It is shown that the N2 method can also be used for the determination of approximate summarized IDA curves. The proposed method was applied to two test buildings. The results were compared with the results obtained by non-linear dynamic analyses for three sets of ground motions, and a reasonable accuracy was demonstrated. A similar extension of the N2 method can be made to any structural system, provided that an appropriate specific R,µ,T relation is available. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Studies on seismic reduction of story-incresed buildings with friction layer and energy-dissipated devices

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2003
Hong-Nan Li
Abstract A new type of energy-dissipated structural system for existing buildings with story-increased frames is presented and investigated in this paper. In this system the sliding-friction layer between the lowest increased floor of the outer frame structure and the roof of the original building is applied, and energy-dissipated dampers are used for the connections between the columns of the outer frame and each floor of the original building. A shaking table test is performed on the model of the system and the simplified structural model of this system is given. The theory of the non-classical damping approach is introduced to the calculation analyses and compared with test results. The results show that friction and energy-dissipated devices are very effective in reducing the seismic response and dissipating the input energy of the model structure. Finally, the design scheme and dynamic time-history analyses of an existing engineering project are investigated to illustrate the application and advantages of the given method. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Shake table tests on a mass eccentric model with base isolation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2003
Bijan Samali
Abstract A mass eccentric structure is usually more seismically vulnerable than its concentric counterpart because of the coupled torsional,translational response of such structures. In this work, dynamic characteristics and response of a five-storey benchmark model with moderate mass eccentricity were investigated using a shake table, simulating four different ground motions. The effectiveness of laminated rubber bearings (LRB) and lead-core rubber bearings (LCRB) in protecting eccentric structures was examined and evaluated in relation to translational and torsional responses of the benchmark model. It was observed that both translational and torsional responses were significantly reduced with the addition of either a LRB or LCRB isolated system regardless of the nature of ground motion input. The LRB were identified to be more effective than LCRB in reducing model relative displacements, the relative torsional angle as well as accelerations, and therefore provided a better protection of the superstructure and its contents. On the other hand, LCRB rendered a smaller torsional angle and absolute displacement of the base isolation system, hence a more stable structural system. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Structural damage detection using the optimal weights of the approximating artificial neural networks

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2002
Shih-Lin Hung
Abstract This work presents a novel neural network-based approach to detect structural damage. The proposed approach comprises two steps. The first step, system identification, involves using neural system identification networks (NSINs) to identify the undamaged and damaged states of a structural system. The partial derivatives of the outputs with respect to the inputs of the NSIN, which identifies the system in a certain undamaged or damaged state, have a negligible variation with different system errors. This loosely defined unique property enables these partial derivatives to quantitatively indicate system damage from the model parameters. The second step, structural damage detection, involves using the neural damage detection network (NDDN) to detect the location and extent of the structural damage. The input to the NDDN is taken as the aforementioned partial derivatives of NSIN, and the output of the NDDN identifies the damage level for each member in the structure. Moreover, SDOF and MDOF examples are presented to demonstrate the feasibility of using the proposed method for damage detection of linear structures. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Efficient modal analysis of systems with local stiffness uncertainties

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6-7 2009
S. F. Wojtkiewicz
Abstract The characterization of the uncertainty in modal quantities of an uncertain linear structural system is essential to the rapid determination of its response to arbitrary loadings. Although the size of many computational structural models used is extremely large, i.e. thousands of equations, the uncertainty to be analyzed is oftentimes localized to very small regions of the model. This paper addresses the development of an efficient, computational methodology for the modal analysis of linear structural systems with local stiffness uncertainties. The newly developed methodology utilizes an enriched basis that consists of the sub-spectrum of a nominal structural system augmented with additional basis vectors generated from a knowledge of the structure of the stiffness uncertainty. In addition, methods for determining bounds on the approximate modal frequencies and mode shapes are discussed. Numerical results demonstrate that the algorithm produces highly accurate results with greatly reduced computational effort. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Probabilistic safety analysis of structures under hybrid uncertainty

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2007
Subrata Chakraborty
Abstract The probabilistic and the possibilistic methods of safety evaluation of structure under uncertain parameters have been developed independently. When the structural system is defined with some of the input parameters as possibilistic and others are sufficient enough to model as probabilistic, available literatures normally start with either probabilistic or possibilistic description of all the variables. This may pose restriction on necessary flexibility to the designer at early stage of modelling of the structural system. The primary objective of the present work is to critically examine various emerging methods of transformation of the possibilistic variables to equivalent probabilistic variables so that probabilistic safety evaluation approach becomes compatible with the nature and quality of the input data. Relying on the fundamental concept of equivalent transformations, i.e. the entropy based transformation and the scaling of fuzzy membership function, the reliability analysis is proposed in the framework of second moment format. In doing so, the bounds on the reliability indices based on the evidence theory are also obtained encompassing the first-order reliability analysis for consistent comparison among alternative transformations. Finally, the reliability computation under hybrid uncertainty is elucidated numerically with examples for comparative study on the suitability of the transformation alternatives. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Crack identification of a planar frame structure based on a synthetic artificial intelligence technique

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2003
Mun-Bo Shim
Abstract It has been established that a crack has an important effect on the dynamic behaviour of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a planar frame structure, a method is presented in this paper which uses a synthetic artificial intelligence technique, i.e. adaptive-network-based fuzzy inference system (ANFIS) solved via a hybrid learning algorithm (the backpropagation gradient descent and the least-squares method) and continuous evolutionary algorithms (CEAs) solving single objective optimization problems with a continuous function and continuous search space efficiently are unified. With ANFIS and CEAs it is possible to formulate the inverse problem. ANFIS is used to obtain the input (the location and depth of a crack),output (the structural eigenfrequencies) relation of the structural system. CEAs are used to identify the crack location and depth by minimizing the difference from the measured frequencies. We have tried this idea on 2D beam structures and the results are promising. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Effect of cooling field strength and ferromagnetic shell shape on exchange bias in nanoparticles with inverted ferromagnetic,antiferromagnetic core-shell morphology

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010
Yong Hu
Abstract The dependence of exchange bias (EB) effects on cooling field strength and particle shape in nanoparticles with antiferromagnetic (AFM) interfacial coupling and inverted AFM core with a fixed radius and ferromagnetic (FM) shell with various thicknesses are investigated by using a modified Monte Carlo Metropolis method. It is found that with the increase of cooling field, field-cooled exchange bias field (HE) fluctuates in the range of negative values initially, and then has an abrupt jump from the negative value to the positive value, finally levels off. However, HE decreases as the FM shell shape varies from No. 1 to No. 13 regardless of the strength of cooling field. Coercivity is affected by cooling fields and shapes indicating distinct behaviors. Because the AFM core is almost unaffected by shape and frozen completely during measuring hysteresis loops, the effect of ferromagnets on EB, negligible in most of other systems, is ambiguously manifested in such an unconventionally structural system. Moreover, the phenomena are interpreted well by presenting the snapshots of microscopic spin energy distributions, which make us observe directly and vividly the movement of domains and the competition of energies. This work will shed new light into the microscopic origin of peculiar magnetic properties of nanoparticles with special structures. [source]

Weaving Architecture: Structuring the Spanish Pavilion, Expo 2010, Shanghai

ARCHITECTURAL DESIGN, Issue 4 2010
Julio Martínez Calzón
Abstract A complex basket-like structure woven from lightweight steel and wicker, the Spanish Pavilion for the Expo 2010, in Shanghai, is the site of a unique collaboration between architects EMBT (Enric Miralles and Benedetta Tagliabue) and MC2 Structural Engineers. Here Julio Martínez Calzón and Carlos Castañón Jiménez of MC2 describe how intense dialogue became key to the realisation of the pavilion, as form-finding and the development of the underlying structural system were equally integral to the design process. Copyright © 2010 John Wiley & Sons, Ltd. [source]

The Ecological Facades of Patrick Blanc

ARCHITECTURAL DESIGN, Issue 3 2010
Matthew Gandy
Abstract The urban geographer Matthew Gandy explores the work of French botanist Patrick Blanc, who applies his scientific knowledge and preoccupations to urban design. After his invention of the mur végetal (green wall), a botanical and structural system for greening buildings, in 1988, Blanc's work has gone on to transcend the creation of merely living walls. Through his landscape schemes Blanc has recognised the city's rich potential for verdant metamorphosis, transforming fern- and moss-covered streets and buildings into unlikely ravines or rainforests. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Self-centering structural systems with combination of hysteretic and viscous energy dissipations

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2010
Weng Yuen Kam
Abstract This paper presents an innovative set of high-seismic-resistant structural systems termed Advanced Flag-Shaped (AFS) systems, where self-centering elements are used with combinations of various alternative energy dissipation elements (hysteretic, viscous or visco-elasto-plastic) in series and/or in parallel. AFS systems is developed using the rationale of combining velocity-dependent with displacement-dependent energy dissipation for self-centering systems, particularly to counteract near-fault earthquakes. Non-linear time-history analyses (NLTHA) on a set of four single-degree-of-freedom (SDOF) systems under a suite of 20 far-field and 20 near-fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS systems with a combination in parallel of hysteretic and viscous energy dissipations achieved greater performance in terms of the three performance indices. Furthermore, the use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced base-shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, ,1 and ,2 on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0,s and with various strength levels when subjected to far-field and near-fault earthquakes. For the design of self-centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, ,1 is recommended to be in the range of 0.8,1.6 while ,2 to be between 0.25 and 0.75 to ensure sufficient self-centering and energy dissipation capacities, respectively. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Rigid-plastic models for the seismic design and assessment of steel framed structures

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2009
C. Málaga-Chuquitaype
Abstract This paper demonstrates the applicability of response history analysis based on rigid-plastic models for the seismic assessment and design of steel buildings. The rigid-plastic force,deformation relationship as applied in steel moment-resisting frames (MRF) is re-examined and new rigid-plastic models are developed for concentrically-braced frames and dual structural systems consisting of MRF coupled with braced systems. This paper demonstrates that such rigid-plastic models are able to predict global seismic demands with reasonable accuracy. It is also shown that, the direct relationship that exists between peak displacement and the plastic capacity of rigid-plastic oscillators can be used to define the level of seismic demand for a given performance target. Copyright© 2009 John Wiley & Sons, Ltd. [source]

Real-time hybrid testing using the unconditionally stable explicit CR integration algorithm

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2009
Cheng Chen
Abstract Real-time hybrid testing combines experimental testing and numerical simulation, and provides a viable alternative for the dynamic testing of structural systems. An integration algorithm is used in real-time hybrid testing to compute the structural response based on feedback restoring forces from experimental and analytical substructures. Explicit integration algorithms are usually preferred over implicit algorithms as they do not require iteration and are therefore computationally efficient. The time step size for explicit integration algorithms, which are typically conditionally stable, can be extremely small in order to avoid numerical stability when the number of degree-of-freedom of the structure becomes large. This paper presents the implementation and application of a newly developed unconditionally stable explicit integration algorithm for real-time hybrid testing. The development of the integration algorithm is briefly reviewed. An extrapolation procedure is introduced in the implementation of the algorithm for real-time testing to ensure the continuous movement of the servo-hydraulic actuator. The stability of the implemented integration algorithm is investigated using control theory. Real-time hybrid test results of single-degree-of-freedom and multi-degree-of-freedom structures with a passive elastomeric damper subjected to earthquake ground motion are presented. The explicit integration algorithm is shown to enable the exceptional real-time hybrid test results to be achieved. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Stability analysis for real-time pseudodynamic and hybrid pseudodynamic testing with multiple sources of delay

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2008
Oya Mercan
Abstract Real-time pseudodynamic (PSD) and hybrid PSD test methods are experimental techniques to obtain the response of structures, where restoring force feedback is used by an integration algorithm to generate command displacements. Time delays in the restoring force feedback from the physical test structure and/or the analytical substructure cause inaccuracies and can potentially destabilize the system. In this paper a method for investigating the stability of structural systems involved in real-time PSD and hybrid PSD tests with multiple sources of delay is presented. The method involves the use of the pseudodelay technique to perform an exact mapping of fixed delay terms to determine the stability boundary. The approach described here is intended to be a practical one that enables the requirements for a real-time testing system to be established in terms of system parameters when multiple sources of delay exist. Several real-time testing scenarios with delay that include single degree of freedom (SDOF) and multi-degree of freedom (MDOF) real-time PSD/hybrid PSD tests are analyzed to illustrate the method. From the stability analysis of the real-time hybrid testing of an SDOF test structure, delay-independent stability with respect to either experimental or analytical substructure delay is shown to exist. The conditions that the structural properties must satisfy in order for delay-independent stability to exist are derived. Real-time hybrid PSD testing of an MDOF structure equipped with a passive damper is also investigated, where observations from six different cases related to the stability plane behavior are summarized. Throughout this study, root locus plots are used to provide insight and explanation of the behavior of the stability boundaries. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Shaking table model test on Shanghai World Financial Center Tower

Software framework for distributed experimental,computational simulation of structural systems

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2006
Yoshikazu Takahashi
Abstract Supported by the recent advancement of experimental test methods, numerical simulation, and high-speed communication networks, it is possible to distribute geographically the testing of structural systems using hybrid experimental,computational simulation. One of the barriers for this advanced testing is the lack of flexible software for hybrid simulation using heterogeneous experimental equipment. To address this need, an object-oriented software framework is designed, developed, implemented, and demonstrated for distributed experimental,computational simulation of structural systems. The software computes the imposed displacements for a range of test methods and co-ordinates the control of local and distributed configurations of experimental equipment. The object-oriented design of the software promotes the sharing of modules for experimental equipment, test set-ups, simulation models, and test methods. The communication model for distributed hybrid testing is similar to that used for parallel computing to solve structural simulation problems. As a demonstration, a distributed pseudodynamic test was conducted using a client,server approach, in which the server program controlled the test equipment in Japan and the client program performed the computational simulation in the United States. The distributed hybrid simulation showed that the software framework is flexible and reliable. Copyright © 2005 John Wiley & Sons, Ltd. [source]