bluuebunny/crossref_metadata_2025 huggingface dataset:
Nested case‐control study of occupational chemical exposures and prostate cancer in aerospace and radiation workers
Authors: Krishnadasan Anusha , Kennedy Nola , Zhao Yingxu , Morgenstern Hal , Ritz Beate
Published: April 2007

Background

To date, little is known about the potential contributions of occupational exposure to chemicals to the etiology of prostate cancer. Previous studies examining associations suffered from limitations including the reliance on mortality data and inadequate exposure assessment.

Methods

We conducted a nested case‐control study of 362 cases and 1,805 matched controls to examine the association between occupational chemical exposures and prostate cancer incidence. Workers were employed between 1950 and 1992 at a nuclear energy and rocket engine‐testing facility in Southern California. We obtained cancer‐incidence data from the California Cancer Registry and seven other state cancer registries. Data from company records were used to construct a job exposure matrix (JEM) for occupational exposures to hydrazine, trichloroethylene (TCE), polycyclic aromatic hydrocarbons (PAHs), benzene and mineral oil. Associations between chemical exposures and prostate cancer incidence were assessed in conditional logistic regression models.

Results

With adjustment for occupational confounders, including socioeconomic status, occupational physical activity, and exposure to the other chemicals evaluated, the odds ratio for low/moderate TCE exposure was 1.3; 95%CI = 0.8 to 2.1, and for high TCE exposure was 2.1; 95%CI = 1.2 to 3.9. Furthermore, we noted a positive trend between increasing levels of TCE exposure and prostate cancer (P‐value for trend = 0.02).

Conclusion

Our results suggest that high levels of TCE exposure are associated with prostate cancer among workers in our study population. Am. J. Ind. Med. 50:383–390, 2007. © 2007 Wiley‐Liss, Inc.
Structure‐function analysis of protein complexes involved in the molecular architecture of juxtaparanodal regions of myelinated fibers
Authors: Tzimourakas Alexandros , Giasemi Sevasti , Mouratidou Maria , Karagogeos Domna
Published: April 2007

Demyelinating disorders, including multiple sclerosis (MS), are common causes of neurological disability. One critical step towards the management and therapy of demyelinating diseases is to understand the basic functions of myelinating glia and their relationship with axons. Axons and myelinating glia, oligodendrocytes in the central (CNS) and Schwann cells in the peripheral (PNS) nervous systems, reciprocally influence each other's development and trophism. These interactions are critical for the formation of distinct axonal domains in myelinated fibers that ensure the rapid propagation of action potentials. Macromolecular complexes mediating axo–glial interactions in these domains have been identified, consisting of members of the immunoglobulin superfamily (IgSF) of adhesion molecules and the neurexin/NCP superfamily as well as other proteins. We have investigated the molecular details of axo–glial interactions in the juxtaparanodal region of myelinated fibers by utilizing domain‐specific GFP constructs and immunoprecipitation assays on transfected cells. We have shown that the immunoglobulin domains of the IgSF member TAG‐1/Cnt‐2 are necessary and sufficient for the direct, cis interaction of this protein with Caspr2 and potassium channels.
Relaxometric and Modelling Studies of the Binding of a Lipophilic Gd‐AAZTA Complex to Fatted and Defatted Human Serum Albumin
Authors: Gianolio Eliana , Giovenzana Giovanni B. , Longo Dario , Longo Irene , Menegotto Ivan , Aime Silvio
Published: April 2007

A new lipophilic gadolinium chelate consisting of a long aliphatic chain bound to the AAZTA coordination cage (Gd‐AAZTAC17) has been synthesised. It possesses two coordinated water molecules (q=2) in fast exchange with the solvent (${\tau {{298\hfill \atop {\rm M}\hfill}}}$=67 ns), which yields a relaxivity of 10.2 mM−1 s−1. At concentrations greater than 0.1 mM, it forms micelles (average diameter 5.5 nm) characterised by a relaxivity of approximately 30 mM−1 s−1 at 20 MHz and 298 K. The latter value appears to be “quenched” by magnetic interactions among the GdIII ions on the surface of the micelle that cause a decrease in the electronic relaxation time. A relaxivity of 41 mM−1 s−1 was recorded for this micellar system when 98 % of the GdIII ions were replaced by diamagnetic YIII. Gd‐AAZTAC17 exhibits a better affinity for fatted human serum albumin (HSA) than for defatted HSA, whereas the relaxivities of the supramolecular adducts are reversed. The relaxivity shown by Gd‐AAZTAC17/defatted HSA (${r{{{\rm b}\hfill \atop 1\hfill}}}$(20 MHz, 298 K)=84 mM−1 s−1) is by far the highest relaxivity reported so far for non‐covalent paramagnetic adducts with slow‐moving substrates. As shown by molecular docking calculations, the gadolinium complex enters a hydrophobic pocket present in fatted HSA more extensively than the corresponding adduct with defatted HSA. Interestingly, no marked difference was observed in either the relaxation enhancement or the binding affinity between fatted and defatted HSA when the binding titrations were carried out at a Gd‐AAZTAC17 concentration higher than its critical micellar concentration (cmc). This behaviour has been attributed to the formation of an association between the negatively charged micelle of the lipophilic metal complexes and the positive residues on the surface of the protein.
A Smart Surface in a Microfluidic Chip for Controlled Protein Separation
Authors: Mu Li , Liu Ying , Cai Shaoyu , Kong Jilie
Published: April 2007

The smart surface created in a microfluidic chip has shown the capability of adsorbing and releasing proteins under electrical control. The inner surface of the chip channel was first coated by a thin layer of Au through sputtering and was subsequently modified with loosely packed self‐assembled monolayers (SAMs) of thiols with terminal carboxylic or amino groups. Upon application of an external electric potential to the gold substrate, reversible conformational transformation between “bent” and “straight” states for the anchored mercapto chains could be modulated, through the electrostatic effect between the ionized terminal groups and the charged gold substrate. Thus, a hydrophobic or hydrophilic channel surface was established and could be reversibly switched electrochemically. Accordingly, the microchips prepared in this way can reversibly and selectively adsorb and release differently charged proteins under electrical control. Two model proteins, avidin and streptavidin, were demonstrated to be readily adsorbed by the smart chips under negative and positive potential, respectively. Also, more than 90 % of the adsorbed proteins could be released upon an electrical command. Furthermore, these chips were applied to the controlled separation of avidin and streptavidin mixtures with 1:1 and 1:1000 molar ratios. Under specific applied potentials, the chips adsorbed a certain protein from the mixture whereas the other protein was allowed to flow out, after which the adsorbed protein could be released by switching the applied potential. Thus, two eluted protein fractions were obtained and the separation of the two proteins was achieved. For the former mixture, each eluted fraction contained up to ≈80–90 % avidin or streptavidin. For the latter mixture, the resulting separation efficiency indicated that the molar ratio of avidin and streptavidin could be increased from 1:1000 to about 32:1 after five run separations.
Organogels of 8‐Quinolinol/Metal(II)–Chelate Derivatives That Show Electron‐ and Light‐Emitting Properties
Authors: Shirakawa Michihiro , Fujita Norifumi , Tani Takahiro , Kaneko Kenji , Ojima Masayoshi , Fujii Akihiko , Ozaki Masanori , Shinkai Seiji
Published: April 2007

8‐Quinolinol/copper(II)‐, palladium(II)‐, and platinum(II)‐chelate‐based organogelators (1 M) and their nongelling reference compounds (2 M) were synthesized. Complexes 1 M could gelate various organic solvents at very low concentrations. Electron microscope measurements gave visual images of well‐developed fibrous structures characteristic of low‐molecular‐weight organogels. UV/Vis and FTIR spectroscopy revealed that the good gelation ability of 1 M arises from the π–π interactions of the chelate moieties and the hydrogen‐bond interactions among the amide groups. Very interestingly, field emission performances of the nanofibers prepared from the 1 M gels are evidently different depending on the electronic states of the three kinds of central metals. In addition, the 1 Pt gel shows unique thermo‐ and solvatochromism of visible and phosphorescent color in response to a sol–gel phase transition. Furthermore, the 1 Pt gel possesses an attractive ability to inhibit dioxygen quenching of excited triplet states, which increases the phosphorescence quantum yield of this gel. This effect is attributed to the isolation effect of the phosphorescent chelate moiety from the dioxygen‐containing solution phase.
Microwave Effect in the Fast Synthesis of Microporous Materials: Which Stage Between Nucleation and Crystal Growth is Accelerated by Microwave Irradiation?
Authors: Jhung Sung Hwa , Jin Taihuan , Hwang Young Kyu , Chang Jong‐San
Published: April 2007

Microporous materials, such as silicalite‐1 and VSB‐5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW–MW, MW–CE, CE–MW, and CE–CE (in the order of nucleation‐crystal growth). In the case of synthesis by MW–CE or CE–MW, the heating modes were changed for the second step just after the appearance of X‐ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW–MW<MW–CE≈CE–MW<CE–CE synthesis. The fast crystal growth and small crystal size observed in the synthesis from microwave‐nucleated precursor can be explained in terms of the fact that the microwave‐nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.
SCTP performance evaluation over heterogeneous networks
Authors: Dainotti Alberto , Loreto Salvatore , Pescapé Antonio , Ventre Giorgio
Published: April 2007

Since its definition in 2000, the Stream Control Transmission Protocol (SCTP) has attracted increasing interest. Several research works, often validated through analytical and simulative analysis, have attempted to evaluate the benefits of substituting TCP with SCTP, both for signaling and data transfer. In this work, we present a traffic generation and performance analysis tool to test SCTP on real networks. We study the performance of SCTP on real heterogeneous (wired/wireless) scenarios, providing results in terms of throughput and jitter, and comparing its performance against TCP and UDP over the same conditions. Our experimental analysis shows that the current performance of SCTP (operating on a Linux platform) does not justify the use of SCTP as a simple substitute for TCP. Copyright © 2007 John Wiley & Sons, Ltd.
Automated and accurate cache behavior analysis for codes with irregular access patterns
Authors: Andrade Diego , Arenaz Manuel , Fraguela Basilio B. , Touriño Juan , Doallo Ramón
Published: April 2007

The memory hierarchy plays an essential role in the performance of current computers, so good analysis tools that help in predicting and understanding its behavior are required. Analytical modeling is the ideal base for such tools if its traditional limitations in accuracy and scope of application can be overcome. While there has been extensive research on the modeling of codes with regular access patterns, less attention has been paid to codes with irregular patterns due to the increased difficulty in analyzing them. Nevertheless, many important applications exhibit this kind of pattern, and their lack of locality make them more cache‐demanding, which makes their study more relevant. The focus of this paper is the automation of the Probabilistic Miss Equations (PME) model, an analytical model of the cache behavior that provides fast and accurate predictions for codes with irregular access patterns. The information requirements of the PME model are defined and its integration in the XARK compiler, a research compiler oriented to automatic kernel recognition in scientific codes, is described. We show how to exploit the powerful information‐gathering capabilities provided by this compiler to allow the automated modeling of loop‐oriented scientific codes. Experimental results that validate the correctness of the automated PME model are also presented. Copyright © 2007 John Wiley & Sons, Ltd.
Interactions in virtual customer environments: Implications for product support and customer relationship management
Authors: Nambisan Satish , Baron Robert A.
Published: April 2007

Virtual customer environments (VCE), which provide services ranging from online discussion forums to virtual design toolkits, enable firms to involve their customers in innovation and value creation. Evidently, companies can benefit from operating such VCEs; however, most firms do not seem to attach sufficient importance to the nature of customers’ interactions in the VCE. In this study, we examine two critical implications of customers’ interactions in a product-support focused VCE. First, we suggest that customers’ perceptions of interaction-based benefits will shape their future participation in product support in the VCE. Second, customers’ interactions will also generate changes in their affective states, and these, in turn, influence their attitude towards the firm. Our empirical work provides broad support for the study hypotheses and implies the need for firms to carefully design and implement VCEs that facilitate positive interaction experiences for customers. Implications with respect to customer value co-creation and customer relationship management are discussed.
Efficient time truncation in two‐dimensional bem analysis of transient wave propagation problems
Authors: Mansur W. J. , Delima‐Silva W.
Published: April 2007

An efficient time truncation algorithm for transient two‐dimensional wave propagation analysis by the boundary element method is proposed. First the complete (without any truncation) formulation is reviewed and subsequently time truncation concepts are discussed. Three applications are presented, where the efficiency of complete and truncated algorithms is compared. The most important conclusions inferred from the numerical analyses are: (i) time truncation errors can be controlled and made as small as required and (ii) time truncation algorithms lead to considerable savings in both CPU time and storage area.
Numerical instabilities of a local transmitting boundary
Authors: Liao Z. P. , Liu J. B.
Published: April 2007

A local transmitting boundary is presented in a compact form, which can be directly incorporated into finite elements. The accuracy of the boundary is studied thoroughly for a one‐dimensional model in order to clarify numerical instabilities introduced by the boundary. Discretization of the model and reflection from the boundary are rigorously considered in the study, and the mechanism of the instability is then illuminated in the frequency domain by the amplification of reflection from the boundary and the multi‐reflection of wave motion in a finite computational region. Typical characteristics of the instability in the time domain are illustrated by numerical results of the simple model and explained completely by the mechanism. On the basis of this understanding of the mechanism, a modified transmitting boundary is devised and its stability criterion is given for the one‐dimensional model.
Frequency dependent ritz vectors
Authors: Xia Hong , Humar J. L.
Published: April 2007

In order to reduce the size of problems involving analysis of the dynamic response of structural systems, a transformatio based on appropriately selected Ritz shapes is commonly employed. The lower mode shapes may at times serve a effective Ritz shapes. However, the computation of mode shapes is a time consuming task; in addition, the mode shapes may not form the best basis for representing the spatial distribution of loads. The recently developed load dependent vectors, which are derived from a static solution for the applied loads, address some of the problems inherent in the use of mode shapes. However, both the natural mode shapes and the load dependent vectors fail to account for the frequency content of the loading, a parameter that may influence strongly the response, particularly for loading with a high frequency content. A procedure is presented here for the generation of frequency dependent vectors. A combination of load dependent and frequency dependent vectors will often form a very efficient basis for the representation of the response, as illustrated by several examples presented here.
Pounding of buildings modelled by an impact oscillator
Authors: Davis R. O.
Published: April 2007

Pounding of adjacent buildings is modelled by an impact oscillator subjected to harmonic excitation. Non‐linear impact stiffness is represented by a Hertz‐type relationship. Spectra of impact velocity are presented for a range of model parameters. These spectra are characterized by a strong peak near a period equal to one half the natural period of a similar non‐impacting oscillator. Bands of response are found in which periodic multiple impacts and non‐periodic or chaotic impacts occur.
Earthquake data review and seismic hazard analysis for the Hong Kong region
Authors: Pun W. K. , Ambraseys N. N.
Published: April 2007

This paper presents the results of a review of earthquake data and a study of seismic hazard for Hong Kong. A region of about 660 km × 660 km around Hong Kong was selected for the study. In this study, the earthquake information available for the region was reviewed, and where possible, earthquake magnitudes were calculated. Since there is no strong motion record for any earthquake within the region, Joyner and Boore's attenuation law1 has been used for the analysis. The results show that the seismic hazard in Hong Kong is relatively small, but because of the uncertainty inherent in the assumed attenuation relationship, accurate prediction of peak ground acceleration is not possible.
The uncertainty and ambiguity of isoseismal maps
Authors: de Rubeis V. , Gasparini C. , Maramai A. , Murru M. , Tertulliani A.
Published: April 2007

The problem of defining objective isoseismal maps is as yet unresolved. The aim of the work, here presented, is to show how the studies of different authors and eras can produce contrasting, even contradictory, interpretations of the macroseismic data set for the same earthquake.

At this point in time, the principal macroseismic end (i.e. that which furnishes seismology, seismotectonics and studies of seismic risks with descriptions of the effects of earthquakes, as far as possible exempt from interpretation) is in danger of failing.

Throughout this work, we have sought to bring to light how certain anomalies of macroseismic maps principally reside in the diversity of data interpretation, and how it is possible to put in evidence these by applying appropriate statistical analysis to the macroseismic fields.

The Sicilian earthquake of 11 January 1683 (I0 = XI) was taken as an example, as a sufficient quantity of information was available; a filter procedure was then applied to the macroseismic data. Finally we also show that such procedures are very useful in the treatment of border earthquakes, in an attempt to homogenize macroseismic fields from different countries.
Design of torsionally unbalanced structural systems based on code provisions II: Strength distribution
Authors: Zhu T. J. , Tso W. K.
Published: April 2007

This paper presents the results of an analytical study of the strength distribution of lateral load resisting elements in torsionally unbalanced systems designed based on codified torsional provisions. It is shown that the element strength can be expressed conveniently as the element strength of a similar but torsionally balanced system multiplied by a strength factor. This strength factor depends on three system parameters, namely, the location of the element relative to the centre of rigidity, and the torsional stiffness and eccentricity of the structure. In addition, it depends on the design coefficients of the code specified design eccentricity expressions. The influence of each of these factors on the element strength distribution is discussed. A new set of values for the design coefficients is proposed. By means of examples, it is shown that the proposed torsional provision is an improvement over those suggested in the National Building Code of Canada and the New Zealand code.
The synthesis of strong ground motion accelerograms from existing records
Authors: Westermo Bruce
Published: April 2007

The paper discusses the synthesis of acceleration time histories primarily for use in structural response estimation. A proposed model for the acceleration time history is based on the summation of dispersive wave modes over the range of frequencies of typical interest to structural response. The values of the modal amplitudes and the travel times (or group velocities) are, for cases examined here, extracted from a target earthquake (or an ensemble of them). The synthetic accelerograms are constructed from these parameters with the inclusion of a probabilistic definition of those or other characteristics of the strong ground shaking and, in particular, the modal phase angle. The probability distributions of the peak acceleration and the integral of the square acceleration of the synthetic records are examined along with comparisons of the pseudo spectral velocity (PSV) response.
The masonry arch as a four‐link mechanism under base motion
Authors: Oppenheim Irving J.
Published: April 2007

The dynamic response of an unreinforced masonry arch is examined, modelling the rigid body motions of arch segments under the influence of gravitational and inertial forces. This extends earlier studies of single rocking blocks, stacked blocks, and portal mechanisms of blocks; the masonry arch is analysed as another kinematic form of such a system. In this first effort a part‐circular planar arch ring is studied and excitation is restricted to horizontal ground acceleration of the base. The mechanism kinematics are presented and the governing equation of motion is derived in non‐linear form. The instantaneous form is determined for small rotations about the initial geometry and is used to study the conditions for the onset of mechanism motion. Possible failure conditions are posed and bounding principles are stated. One possible failure condition, direct overturning as a four‐link mechanism, is studied for one simplified base motion. The results show that an arch geometry establishes good resistance to earthquake excitation in that ground acceleration must exceed a rather high threshold before any mechanism motion would develop; however, once that threshold has been passed the arch has relatively modest resistance before failure. Other possible failure conditions are discussed; one emerges from pounding effects between segments at impact, and another develops from sliding of blocks over one another as the internal forces (normal and tangential to the masonry joint) vary with the inertial forces.
Scattering of plane sh waves by a semi‐cylindrical hill
Authors: Yuan Xiaoming , Men Fu‐Lu
Published: April 2007

A new analytical method is presented to study the problem of scattering of plane SH waves by a semi‐cylindrical hill in an otherwise homogeneous, isotropic and elastic two‐dimensional half‐space, using the series of wave functions and a new expansion technique. The results obtained show that (1) the hill has quite considerable effects on ground motions for both the points on the hill and its environs, (2) these effects depend mainly on the frequency, the angle of wave incidence and the ratio of radius of hill to one‐half the wave length of incident waves, and (3) prominent and depression topographies having equal form and radius for the same incident waves would cause quite different mechanisms of wave propagation in both response performance and magnitude. The results, doubtless, would be useful for further deepening knowledge of the effects of prominent topography on seismic ground motion and for testing the accuracy of various approximate methods so far available.
Dynamic response analysis in the frequency domain
Authors: Humar J. L. , Xia Hong
Published: April 2007

Analysis in the frequency domain using discrete Fourier transforms is an efficient means of calculating the dynamic response of linear systems. In fact, for systems with frequency dependent parameters and also in those cases where the complex frequency response functions are more easily determined, frequency domain analysis may be the only effective means of determining the dynamic response. The use of discrete transforms along with finite summation requires that the forcing function and the impulse function be converted into periodic forms. This modification may introduce unacceptable errors in the results of analysis, unless appropriate steps are taken to avoid or minimize the effect of aliasing or overlapping. For single‐degree‐of‐freedom systems, procedures that will eliminate the effect of aliasing have already been developed. However, problems related to frequency domain analysis still exist for multi‐degree‐of‐freedom systems with non‐proportional damping, in analysis through substructuring and in those cases where a continuum solution is involved. A new procedure which addresses these problems and is applicable to both single‐ and multi‐degree‐of‐freedom system as well as to analysis through substructuring is presented here.
On engineering equivalent linear analysis of soils in the frequency domain
Authors: Lin Jeen‐Shang
Published: April 2007

This study investigated the performance, in the frequency domain, of an engineering equivalent linear method that is widely used in soil dynamics. A stochastic linear method using an extended differential equation by Wen and Baber was employed as the base line for evaluation. Stationary responses of single‐degree‐of‐freedom non‐linear systems under filtered white noise from both approaches were compared. For both a smooth nearly elasto‐plastic material and soils, the study found that the engineering equivalent linear analysis underestimated rms displacements, but provided good estimates of rms acceleration responses. Furthermore, the frequency response functions of acceleration from both approaches were close at all levels of response.
Instability due to time delay and its compensation in active control of structures
Authors: Agrawal Anil K. , Fujino Yozo , Bhartia Binod K.
Published: April 2007

Time delay problem and its compensation in active control of civil engineering structures were studied. It has been shown by stability analysis of a SDOF system with time delayed feedback that the maximum allowable time delay depends not only on the natural period of the structure but also on feedback gains. We have demonstrated by numerical simulation that the performance of the control system degrades significantly when the time delay is close to this value and it even becomes unstable when time delay is greater than or equal to this value. The maximum allowable time delay decreases with decrease in natural period of the structure as well as with increase in active damping. The paper presents a technique for compensation by modelling time delay as transportation lag. This method ensures the stability of the controlled system as well as the desired response reduction.
Wave propagation in layered media by time domain BEM
Authors: Cheung Y. K. , Tham L. G. , Lei Z. X.
Published: April 2007

A time domain boundary element in a cylindrical co‐ordinate system is developed for the analysis of wave propagation in a layered half‐space. The field quantities (displacements and tractions) are expressed as products of Fourier series in the circumferential direction and as linear polynomials in the other spatial directions. An integral equation is written for each layer as an independent domain, and these equations are then assembled into a general equation by virtue of compatibility and equilibrium conditions between the interfaces. Examples of three‐dimensional wave propagation in the layered half‐spaces due to various forms of surface and inner‐domain excitations are reported to demonstrate the accuracy and versatility of the method.
Performance of composite steel/concrete members under earthquake loading. Part II: Parametric studies and design considerations
Authors: Elghazouli A. Y. , Elnashai A. S.
Published: April 2007

In this paper, an advanced analytical model proposed and verified in a companion paper (Part I: Analytical model) is used to conduct parametric investigations of ductile partially‐encased composite beam‐columns. Particular attention is given to a new configuration of composite member developed and tested at Imperial College. A detailed account of the analytical results is given, and the most significant observations are highlighted and discussed. Quantitative assessments of plastic moment capacity, rotation and displacement ductility and plastic hinge length are undertaken. The implications of the main findings on the seismic design process are also presented. Finally, a procedure for ductility‐based design according to modern codes of practice is outlined.
Arch responses to correlated multiple excitations
Authors: Hao Hong
Published: April 2007

This paper analyses the in‐plane stochastic responses of incompressible circular arches to spatially correlated multiple excitations. The dynamic, quasi‐static and total structural displacements, moments, shear and axial forces are calculated. The results are compared with those obtained by various simplified excitations. The effects of the ground motion spatial variations on arch responses are examined. The results indicate that the responses may be underestimated or overestimated by neglecting the ground motion spatial variations, depending upon the structure and ground motion properties, the locations where the responses are evaluated, and the response quantity under consideration.
Kinematic soil–structure interaction for long‐span cable‐supported bridges
Authors: Betti R. , Abdel‐Ghaffar A. M. , Niazy A. S.
Published: April 2007

A general procedure is presented to study the dynamic soil–structure interaction effects on the response of long‐span suspension and cable‐stayed bridges subjected to spatially varying ground motion at the supporting foundations. The foundation system is represented by multiple embedded cassion foundations and the frequency‐dependent impedance matrix for the multiple foundations system takes into account also the cross‐interaction among adjacent foundations through the soil. To illustrate the potential implementation of the analysis, a numerical example is presented in which the dynamic response of the Vincent–Thomas suspension bridge (Los Angeles, CA) subjected to the 1987 Whittier earthquake is investigated. Although both kinematic and inertial effects are included in the general procedure, only the kinematic effects of the soil–structure interaction are considered in the analysis of the test case. The results show the importance of the kinematic soil–foundation interaction on the structural response. These effects are related to the type, i.e. SH‐, SV‐, P‐ or Rayleigh waves and to the inclination of the seismic wave excitation. Moreover, rocking components of the foundation motion are emphasized by the embedment of the foundation system and greatly alter the structural response.
A post‐processing technique and an a posteriori error estimate for the newmark method in dynamic analysis
Authors: Wiberg N.‐E. , Li X. D.
Published: April 2007

In this paper, we present a post‐processing technique and an a posteriori error estimate for the Newmark method in structural dynamic analysis. By post‐processing the Newmark solutions, we derive a simple formulation for linearly varied third‐order derivatives. By comparing the Newmark solutions with the exact solutions expanded in the Taylor series, we achieve the local post‐processed solutions which are of fifth‐order accuracy for displacements and fourth‐order accuracy for velocities in one step. Based on the post‐processing technique, a posteriori local error estimates for displacements, velocities and, thus, also the total energy norm error estimate are obtained. If the Newmark solutions are corrected at each step, the post‐processed solutions are of third‐order accuracy in the global sense, i.e. one‐order improvement for the original Newmark solutions is achieved. We also discuss a method for estimating the global time integration error. We find that, when the total energy norm is used, the sum of the local error estimates will give a reasonable estimate for the global error. We present numerical studies on a SDOF and a 2‐DOF example in order to demonstrate the performance of the proposed technique.
Seismic response of heavily damped base isolation systems
Authors: Tsai Hsiang‐Chuan , Kelly James M.
Published: April 2007

The development of an efficient energy‐dissipating mechanism that works in conjunction with laminated elastomeric bearings in order to reduce the lateral deformation of the isolation system has always been a goal of base isolation research. Theoretically, this deformation will be reduced to the minimum if damping augmentation of the isolation system can reach a critical value. However, augmenting the isolation damping may cause some unwanted side effects. The purpose of this paper is to study the influence of isolation damping on the seismic response of heavily damped base‐isolated buildings. The base isolation system is assumed to be linearly viscoelastic and is analysed using the complex mode method. Solutions derived by using perturbation techniques for a two‐degree‐of‐freedom system and the computer simulation for a multiple‐degree‐of‐freedom system reveal that augmenting the isolation damping can reduce efficiently the deformation of the isolation system, but at the price of increasing the high‐frequency vibration in the superstructure. When the damping ratio of the isolation system is beyond some level, increasing the isolation damping will enlarge the extreme values of the base and superstructural accelerations. It is also found that approximate solutions derived from the use of classical damping and classical modes of vibration in the seismic analysis of heavily damped base isolation systems can be substantially in error.
Synchronization of human walking observed during lateral vibration of a congested pedestrian bridge
Authors: Fujino Yozo , Pacheco Benito M. , Nakamura Shun‐Ichi , Warnitchai Pennung
Published: April 2007

Observation of human‐induced large‐amplitude lateral vibration of an actual pedestrian bridge in an extremely congested condition is reported. Walking motions of pedestrians recorded by a video camera are analysed. It is found that walking among 20 per cent or more of the pedestrians on the bridge was synchronized to the girder lateral vibration. With this synchronization, the total lateral force from the pedestrians to the girder is evidently increased and it acts as a resonant force on the girder lateral vibration.
Design formulas for tuned mass dampers based on A perturbation technique
Authors: Fujino Yozo , Abé Masato
Published: April 2007

Modal properties of tuned mass damper (TMD)‐structure two‐degree‐of‐freedom (2DOF) linear systems are studied employing a perturbation technique. Using the perturbation solutions, formulas relevant to designing the TMD for various types of loading are obtained; they are expressed as a function of mass ratio, tuning ratio, damping ratio of the TMD and damping ratio of the structure. Equivalent additional dampings of the structure due to the TMD are derived for random and harmonic forces. Matched expressions of equivalent damping, which are valid for detuned, i.e. non‐optimal, conditions are also presented. The stability boundary of TMD‐structure systems subject to linear self‐excited forces is derived in a closed form. Using the perturbation solutions, procedures for optimizing the TMD parameters for various types of loading are explained and the optimal values are derived. The formulas obtained in this study can be used with good accuracy for mass ratios less than 0.02.
Probabilistic site‐dependent non‐linear spectra
Authors: Miranda Eduardo
Published: April 2007

This paper presents a probabilistic approach to the estimation of lateral strengths required to provide an adequate control of inelastic deformations in structures during severe earthquake ground motions. In contrast to a deterministic approach, the approach presented herein accounts explicitly for the variability of the response of non‐linear systems due to the inherent uncertainties in the intensity and characteristics of the input excitation by considering the probability distribution of maximum inelastic strength demands. This study is based on the computation of non‐linear strength demands of single‐degree‐of‐freedom (SDOF) systems experiencing different levels of inelastic deformation when subjected to 124 recorded earthquake ground motions. Using empirical cumulative distribution functions site‐dependent probabilistic non‐linear spectra were computed for six probabilities of exceedance of different levels of inelastic deformation. It is concluded that the lateral strength required to control displacement ductility demands is significantly affected by the maximum tolerable inelastic deformation, the system's period of vibration, the local site conditions and the level of risk in exceeding the maximum tolerable deformations.
Fluid–foundation interaction in the seismic response of gravity dams
Authors: Chandrashaker R. , Humar J. L.
Published: April 2007

The seismic response of a dam is strongly influenced by its interaction with the water reservoir and the foundation. The hydrodynamic forces in the reservoir are in turn affected by radiation of waves towards infinity, wave absorption at the reservoir bottom, and cross‐coupling between the foundation below the dam and the reservoir bottom. The fluid–foundation interaction effect, i.e. the wave absorption along the reservoir bottom, can be accounted for by using either an approximate one‐dimensional (1D) wave propagation model or a rigorous analysis of interaction between the flexible soil along the base and the water. The rigorous approach requires enormous computational effort because of (a) cross‐coupling between the foundation of the dam and the soil below the reservoir and (b) frequency dependence of the boundary condition along the fluid‐foundation interface. The analysis can be simplified by ignoring the cross‐coupling and by using the approximate 1D wave propagation model. The effects of each of these two simplifications on the accuracy and computational efficiency of the procedure used for the seismic response analysis of a dam are examined. Analytical results are presented for the complex frequency‐response functions as well as the time histories of the response of Pine Flat dam to Taft and E1 Centro ground motions.
Dynamics of structures with uplift and sliding
Authors: Wang Xiao‐Feng , Gould Phillip L.
Published: April 2007

A structure incorporating the mechanism of sliding, as used in seismic isolation, along with the mechanism of uplift, but at a different elevation, is proposed to study the possible beneficial effects on the response of the structure, as compared to allowing partial base uplift only. A two‐mass model of system uplift and sliding is established. The equations of motion for both the phase of full contact and the phase of base uplift are derived. The criteria governing the transformation of these two phases are given. Both the time history and the response spectrum results show that the structure with both uplift and sliding mechanisms is superior to that with only the uplift mechanism. Not only is the response of the structure lessened, but also the amount of uplift is greatly reduced because of the added sliding mechanism.
Accidental torsion in buildings due to stiffness uncertainty
Authors: de la Llera Juan Carlos , Chopra Anil K.
Published: April 2007

Discrepancies between the computed and actual values of the structural element stiffness imply that a building with nominally symmetric plan is actually asymmetric to some unknown degree and will undergo torsional vibration when subjected to purely translational ground motion. Such accidental torsion leads to increase in structural element deformations which is shown to be essentially insensitive to the uncoupled lateral vibration period of the system but is affected strongly by the ratio of uncoupled lateral and torsional vibration periods. The structural deformations increase, in the mean, by at most 10 and 5 per cent for R/C and steel buildings, respectively, and by much smaller amounts for a wide range of system parameters. The increase in structural deformations due to stiffness uncertainty is shown to be much smaller than implied by the accidental torsional provisions in the Uniform Building Code and most other building codes.
Complex‐parameter kelvin model for elastic foundations
Authors: Makris Nicos
Published: April 2007

A new rigorous approach in modelling mechanical behaviour is developed. The dynamic response of a rigid disc resting on an elastic half‐space is approximated by a macroscopic force‐displacement relationship, where not only the coefficients but also the order of time derivatives are complex valued. It is shown that comlex‐parameter constitutive models are not simply an elegant alternative in modelling mechanical behaviour, but are the outcome of rigorous non‐linear regression analysis on complex‐valued functions, like the dynamic stiffness of dissipative systems. Complex‐parameter constitutive models are very attractive since a minimum number of parameters is required to obtain a satisfactory fit of the ‘exact’ response. A two‐parameter generalized Kelvin model reproduces closely the ‘exact’ dynamic stiffness of the disc for all three vertical, horizontal and rocking modes studied herein. Frequency‐ and time‐domain algorithms to solve complex‐order differential equations are developed, validated and used to calculate the foundation–response under earthquake excitation. It is the excellent agreement of results and the economy in number of parameters that make complex‐parameter models so attractive in constitutive modelling.
Uniform reliability safety format for seismic design of reinforced concrete structures
Authors: Economou Spiros N. , Fardis Michael N.
Published: April 2007

A safety format is proposed for the flexural design of reinforced concrete members for the combination of seismic and gravity loads, with load and resistance factors which depend on member type, on the value of the target theoretical probability of failure and on the ratio of the load effect due to gravity loads to that due to the nominal value of the seismic action, both obtained by elastic analysis. Safety factors are computed through an advanced Level II reliability procedure, using a limit state inequality between the member rotation ductility supply under monotonic loading and the peak rotation ductility and cyclic energy dissipation demands. Uncertainties considered are: for resistance, the uncertainty of failure under imposed cyclic deformations, and for action, the maximum peak ductility and energy dissipation demands in the structure's lifetime, as obtained through a series of non‐linear dynamic analyses of multistorey buildings in 3D. using as input ensembles of bidirectional acceleration time‐histories which describe probabilistically the extreme bidirectional seismic action in the structure's lifetime. Computed load and resistance factors are practically independent of the load‐effects ratio. The load factor on the seismic action is found to be independent of member type and to increase with the theoretical probability of failure much faster than the elastic spectral value at the structure's fundamental period with probability of exceedance in the structure's lifetime. Simple rules for the dependence of the resistance modification factors on the theoretical failure probability are also derived. As for the computed values of the load factors the moment due to gravity loads is negligible in comparison to the factored seismic moment, a simplified safety checking inequality between the design flexural capacity and a reduced seismic moment is proposed, in which the ratio of the resistance to the load factor plays the role of a force reduction or effective behaviour factor for the member.
Consistent inelastic design spectra: Strength and displacement
Authors: Vidic Tomaž , Fajfar Peter , Fischinger Matej
Published: April 2007

A procedure for the determination of inelastic design spectra (for strength, displacement, hysteretic and input energy) for systems with a prescribed ductility factor has been developed. All the spectra are consistent (interrelated and based on the same assumptions). This is the first of two companion papers which deals with the ‘classical’ structural parameters: strength and displacement. The input data are the characteristics of the expected ground motion in terms of a smooth elastic pseudo‐acceleration spectrum. Simple, approximate expressions for the strength reduction factor R are proposed. The value of R depends on the natural period of the system, the prescribed ductility factor, the hysteretic behaviour, damping and ground motion. Fairly accurate approximations to the inelastic spectra for strength and displacement can be derived from the elastic spectrum using the proposed values for R.
Inelastic seismic response of torsionally unbalanced systems designed using elastic dynamic analysis
Authors: Wong C. M. , Tso W. K.
Published: April 2007

This paper evaluates the inelastic seismic response of torsionally unbalanced structural systems with strength distributed using elastic response spectrum analysis. The structural model is a single mass torsionally unbalanced system with lateral load resisting elements spanning in two principal directions. The element strength is distributed based on elastic response spectrum analysis and three different approaches to incorporate accidental torsion are considered: (a) without incorporating accidental torsion; (b) by applying static floor torques; (c) by shifting the location of the centre of mass. The seismic input is bidirectionally applied at the base of the model. It is shown that the inelastic responses depend strongly on the torsional stiffness of the system. For a torsionally stiff system, the torsional response leads to a decrease in the stiff edge displacement; however, for a torsionally flexible system, it tends to increase the stiff edge displacement. Using response spectrum analysis without including accidental torsion may lead to excessive additional ductility demand on the stiff edge element. With accidental torsion effect incorporated, the response spectrum analysis will give a strength distribution such that there will be no excessive additional ductility demands on the lateral load resisting elements.