bluuebunny/crossref_metadata_2025 huggingface dataset:
Adventures in Drug Discovery: Potent Agents Based on Ligands for Cell‐Surface Receptors
Authors: Maryanoff Bruce E.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
New Synthetic Methods Utilizing Conjugate Addition of Nucleophiles to 1‐Chlorovinyl p‐Tolyl Sulfoxide
Authors: Satoh Tsuyoshi , Sugiyama Shimpei
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Birch Bark Research and Development
Authors: Krasutsky Pavel A.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Light‐Created Chemiluminescence
Authors: Vasil'ev R. F. , Tsaplev Yu B.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Vascular Disrupting Agents
Authors: Lippert John W. III
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Structural‐Based Engineering for Transferases to Improve the Industrial Production of 5′‐Nucleotides
Authors: Suzuki Ei‐ichiro , Ishikawa Kohki , Mihara Yasuhiro , Shimba Nobuhisa , Asano Yasuhisa
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Dye‐Sensitized Solar Cells Consisting of Ionic Liquid and Solidification
Authors: Ogomi Yuhei , Kato Takehito , Hayase Shuzi
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Biomolecule Sensing with Adaptive Plasmonic Nanostructures
Authors: Drachev Vladimir P. , Shalaev Vladimir M.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Theoretical Analysis of the Rotational Barrier of Ethane
Authors: Mo Yirong , Gao Jiali
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Theoretical Studies on [3 + 2]‐Cycloaddition Reactions
Authors: Kuznetsov M. L.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Molecular Similarity Concept and Its Use for Predicting the Properties of Chemical Compounds
Authors: Skvortsova M. I. , Stankevich I. V. , Palyulin V. A. , Zefirov N. S.
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Multicoordinate Ligands for Actinoid/Lanthanoid Separations
Authors: Dam Henk H. , Reinhoudt David N. , Verboom Willem
Published: April 2007

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Influence of NO on the Reduction of NO2 with CO over Pt/SiO2 in the Presence of O2
Authors: Li Ming‐Shi , Seshan K. , Lefferts Leon
Published: April 2007

Reduction of NO2 with CO in the presence of NO and excess oxygen, a model mixture for flue gas, over a 0.1% Pt/SiO2 catalyst was studied. The related reaction mechanisms, such as oxidation of CO and NO, were discussed. It was found that there was a narrow temperature window (180–190 °C) for the reduction of NO2 by CO. When the temperature was lower than the lower limit of the window, the reduction hardly occurred, while when the temperature was higher than the upper limit of the window, the direct oxidation of CO by O2 occurred and thereby NO2 could not be effectively reduced by CO. The presence of NO shifted the window to higher temperatures owing to the inhibition effect of NO on the activation of O2 on Pt, which made it possible to reduce NO2 by CO in flue gas.
DFT Study on the Origin of the Enantioselectivity of (S)‐4‐Hydroxylproline‐Catalyzed Direct Aldol Reaction between Acetone and 4‐Nitrobenzaldehyde
Authors: Fan Jian‐Fen , Wu Li‐Fen , Sun Yun‐Peng
Published: April 2007

DFT‐B3LYP calculations were carried out to study the enantioselectivity of the (S)‐4‐hydroxylproline‐catalyzed direct aldol reaction between acetone and 4‐nitrobenzaldehyde. Four transition structures associated with the stereo‐controlling step of the reaction have been determined. They are corresponding to the anti and syn arrangements of the methylene moiety related to the carboxylic acid group in enamine intermediate and the si and re attacks to the aldehyde carbonyl carbon. The effect of DMSO solvent on the stereo‐controlling step was investigated with polarized continuum model (PCM). The computed energies of the transition states reveal the moderate enantioselectivity of the reaction.
Catalytic Kinetic Spectrophotometric Method for Determination of Phosphate Ion
Authors: Mitic Snezana , Zivanovic Valentina , Obradovic Mirjana , Tosic Snezana , Pavlovic Aleksandra
Published: April 2007

The kinetic method for the determination of phosphate microamounts was described. The developed method is based on catalytic effect of phosphate on sodium pyrogallol‐5‐sulphonate (PS) by dissolved oxygen. The reaction was followed spectrophotometrically by measuring the rate of change in the values of the absorbance of the oxidation product at 437 nm. The optimum reaction conditions are PS (0.44×10−3 mol·L−1) and HClO4 (3.6×10−6 mol·L−1) at 25 °C. Following this procedure, phosphate can be determined with a linear calibration graph up to 0.23 µg·mL−1. The interference effect of several species was also investigated and it was found that the most common cations and anions did not interfere with the determination. The developed procedure was successfully applied to the determination of phosphate in natural waters and soil.
Synthesis and Structure of a Novel Organic‐Inorganic Hybrid Polyoxovanadate, [Ni(bpp)2]2(V4O12) (bpp=1,3‐bi‐4‐pyridylpropane)
Authors: Zhang Li‐Juan , Hu Zheng‐Jun , Zhang Zhuo , Guo Hong‐You
Published: April 2007

A novel organic‐inorganic hybrid polyoxovanadate, [Ni(bpp)2]2(V4O12) (bpp=1,3‐bi‐4‐pyridylpropane), was hydrothermally synthesized from a mixture of NiCl2·6H2O, NH4VO3, bpp, EtOH and H2O. The crystal structure consists of 2∞[Ni(bpp)2]2+, two‐dimensional networks interpenetrating perpendicularly with each other, and (V4O12)4−, cyclic tetranuclear clusters linking the 2∞[Ni(bpp)2]2+ networks to form a three‐dimensional coordination framework. The crystal belongs to tetragonal space group I41/a with unit cell parameters, a=2.14705 nm, c=1.29293 nm. UV‐Vis‐NIR reflectance spectroscopy study revealed insulator nature for the crystal with an optical energy gap of 2.70 eV.
Flow cytometric CD34+ stem cell enumeration: Lessons from nine years' external quality assessment within the Benelux countries
Authors: Levering Wilfried H. B. M. , Preijers Frank W. M. B. , van Wieringen Wessel N. , Kraan Jaco , van Beers Wil A. M. , Sintnicolaas Kees , van Rhenen Dick J. , Gratama Jan W.
Published: March 2007

Background:

A biannual external quality assurance (EQA) scheme for flow cytometric CD34+ haematopoietic stem cell enumeration has been operational in the Benelux countries since 1996. In an evaluation of the results of 16 send‐outs, we studied the effects of the methods used on assay outcome and whether or not this exercise was effective in reducing between‐laboratory variation.

Methods:

Data were analyzed using robust multivariate regression. This approach is relatively insensitive to outliers and is used to assess the effect of methodological aspects of CD34+ cell counting on the bias and variability.

Results:

Five variables were associated with significant bias of absolute CD34+ cell counts: (i) unique laboratory number (ULN), (ii) gating strategy; (iii) CD34 mAb fluorochrome; (iv) type of flow cytometer, and (v) method of sample preparation. In addition, ULN and platform methodology (i.e., single vs. dual) contributed significantly to the variability of this assay. Overall, the variability in results of CD34+ cell enumeration has declined with time; in particular, after a practical workshop in which participants were trained to use the “single platform ISHAGE protocol.”

Conclusions:

Between‐laboratory variation in CD34+ cell enumeration can be reduced by standardization of methodologies between centres. Our approach, i.e., EQA with targeted training and feedback in response to reported results, has been successful in reducing the variability of CD34+ cell enumeration between participants. © 2007 Clinical Cytometry Society
Injektionsverfahren zur nachträglichen Abdichtung von Mauerwerk – neueste Erkenntnisse
Authors: Balak Michael
Published: April 2007

Im Rahmen des Forschungsprojektes “Hydrophobierende und/oder porenverschließende Injektionsmittel” (gefördert durch die FFG Forschungsförderungsgesellschaft) wurden die Wirksamkeit und die Anwendungsgrenzen von hydrophobierenden und/oder porenverschließenden Injektionsmitteln zur nachträglichen Horizontalabdichtung von Mauerwerk unter besonderer Berücksichtigung der Einbringungsart untersucht. Obwohl Injektionsmittel zur nachträglichen Horizontalabdichtung bereits seit Jahrzehnten eingesetzt werden, zeigt die praktische Erfahrung immer wieder, dass die geforderten Ziele nicht erreicht werden. Im Rahmen einer wissenschaftlichen Arbeit wurde bestätigt, dass in ca. 60 % der gewerblichen Anwendungsfälle die geforderten Wirksamkeitskriterien nach ÖNORM B 3355‐1 nicht eingehalten wurden und dass durch die private Anwendung (Injektionsflaschen) sich dieser Wert noch erheblich erhöht.

In Abhängigkeit des Durchfeuchtungsgrades (gering, mittel, hoch), der Einbringungsart (Injektionsflaschen, Nieder‐ bzw. Hochdruckverfahren, Impuls‐Sprühverfahren, Hohldochtverfahren) und des Wandbildners (Ziegelmauerwerk) wurden an einem Objekt in Wien und im Labor die Anwendungsgrenzen und die Wirksamkeit von acht Injektionsmitteln untersucht.
Baukonjunktur und Mauerwerksbau
Authors: Leuck Hans Georg
Published: April 2007

Haben wir es nun endlich geschafft, seit einem Jahrzehnt wieder positiv über den Bau zu denken? Wer die zahlreichen Konferenzen am Rande der diesjährigen BAU in München und den Messeverlauf selbst verfolgt hat, kommt einerseits zu dem Schluss: Verhaltener Optimismus macht sich in der Tat breit! Ebenso eindeutig ist aber der Ruf zu hören, dass es nun darum geht, den Aufschwung auch wirklich zu verstetigen, damit er nicht nur ein vorübergehendes Gefühl bleibt.
Mikrowellen‐Rasterfeuchtemessungen – morphologische Beschreibung typischer Feuchteschäden in Bauwerken
Authors: Göller Arndt
Published: April 2007

Grundvoraussetzung für die fachgerechte Sanierung von Feuchteschäden in Bauobjekten ist eine Diagnose. Gegenüber den bisher noch weit verbreiteten punktuell arbeitenden Messverfahren bieten Rasterfeuchtemessungen deutlich verbesserte Aussagekraft, liefern sie doch als Ergebnis Bilder der Feuchteverteilung in Bauteilen. Damit lassen sich alle in der Baupraxis auftretenden Feuchteschäden eindeutig klassifizieren und zuordnen. Die Erkennung von Kondensatfeuchten, aufsteigenden Feuchten oder Leckagen, die Detektion von Feuchteschäden aufgrund von Wärmebrücken und die Unterscheidung dieser Schäden von normaler Baurestfeuchte ist damit kein Problem mehr.
DGfM: Mauerwerk 2/2007
Authors: Rast Ronald
Published: April 2007

1. DGfM‐Fachgespräch: Praxistipps und Hinweise aus der Rechtsprechung für die Bewertung von Mauerwerkskonstruktionen

Mauerwerk auch im Nichtwohnbau eine echte Alternative

Deutscher Mauerwerkskongress 2007: Perspektiven für den Mauerwerksbau

DGfM‐Newsletter: Bereich Markt; Bereich Technik; Aktuell; Termine
Adrenal corticosteroids, their receptors and hypertension
Authors: Hu Xiao , Bolten Charles W.
Published: April 2007

Mineralocorticoids and glucocorticoids are primarily synthesized in the adrenal cortex, and play key roles in mediating physiological responses under stressful conditions, such as lack of water or nutrients. Both types of corticosteroid elevate blood pressure and elevated levels of these steroids are found in hypertensive patients. The major mineralocorticoid and glucocorticoid in humans are aldosterone and cortisol, respectively. Aldosterone activates the mineralocorticoid receptor (MR) and cortisol the glucocorticoid receptor (GR). In this overview, the clinical and genetic evidence that both MR and GR are involved in blood pressure regulation is reviewed as are the mechanisms by which MR and GR regulate blood pressure in response to agonists. MR antagonists have been used to treat hypertension. However, GR antagonists have not been fully explored in the clinic. Based on the prevalence of abnormal mineralocorticoid and glucocorticoid signaling in hypertension patients, it is proposed that antagonizing these adrenal corticosteroid receptors will provide benefit in treating hypertension. Drug Dev. Res. 67:871–883, 2006. © 2007 Wiley‐Liss, Inc.
Translating subjective language in letters of recommendation: the case of the sexist professor
Authors: Biernat Monica , Eidelman Scott
Published: April 2007

Letters of recommendation typically use subjective language that is open to interpretation. In three studies, participants “translated” letters of recommendation for female and male applicants written by sexist, anti‐sexist, or “control” professors. Predictions were based on the shifting standards model [Biernat, Manis, & Nelson, 1991], the attributional principle of augmentation [Kelley, 1971, and models of “correction” for contamination [e.g., Wilson & Brekke, 1994]. Participants translated equivalent letters as indicating lesser ability in female than male applicants, particularly when the letter writer was described as sexist, but own impressions of the candidate diverged from those of the sexist writer. Differential standard use and attributional augmentation did not appear to be responsible for these effects. Instead, writer sexism triggered dislike and corrective processes in impression formation. Copyright © 2007 John Wiley & Sons, Ltd.
On the reliability of tower‐shaped structures under seismic excitations
Authors: Zembaty Zbigniew
Published: March 2007

This paper considers the problem of random vibrations and the reliability of slender tower‐shaped structures subjected to seismic excitations. Applying the concept of evolutionary spectra and the uniformly modulated random process as a model of strong ground motion, the response statistics are derived. Peak response values and reliability are then estimated. Results are related to Modified Mercalli and Arias intensities. With the aid of the Fast Fourier Transform technique a numerical analysis of peak response and reliability of a high‐rise reinforced concrete chimney has been carried out. Results indicate the location of seismic failures in the upper half of the shaft of the chimney. Finally, the paper briefly examines the influence of strong motion duration on the peak response and reliability.
Displacement‐proportional friction (DPF) in base isolation
Authors: Tadjbakhsh Iradj , Lin B. C.
Published: March 2007

The theoretical implications of an isolation mechanism that utilizes progressively increasing frictional resistance is investigated. This type of frictional resistance can be provided by the tightening together of a set of friction plates by compressive forces that increase with relative separations of the building and the foundation. The mathematical model of the device is developed and its numerical solutions are obtained. It is shown that in comparison with dry friction alone significant reductions in acceleration transmissibility and relative displacement transmissibility can be obtained.
Stochastic analysis of rigid foundation filtering
Authors: Harichandran Ronald S.
Published: March 2007

The effect of the space–time variation of earthquake ground motion on the translational response of structures supported on large rigid mat foundations is considered. A stochastic space–time ground motion model, based on the analysis of recordings from the SMART‐1 seismograph array in Lotung, Taiwan, is used. Random vibration theory is utilized to obtain an expression for the reduction in the maximum structural response, for a specified probability level and strong motion duration. Numerical computations are performed to examine the sensitivity of the reduction in structural response to various ground motion and structural parameters. The results indicate that spatial correlation and travelling wave effects give rise to significant reductions in structural responses when the seismic waves have low apparent propagation velocities. Utilization of this result in the design of structures on large foundations should yield substantial cost savings.
An error analysis of truncated starting conditions in step‐by‐step time integration: Consequences for structural dynamics
Authors: Hulbert G. M. , Hughes T. J. R.
Published: March 2007

Most of the step‐by‐step time integration algorithms for structural dynamics require an initial acceleration vector to be specified, in addition to displacement and velocity vectors. A consistent initial acceleration vector may be calculated by solving the equations of motion at the initial time, while a truncated initial acceleration vector is obtained by setting the acceleration values to zero. Although the truncated starting procedure decreases computational effort, it is shown to affect accuracy adversely. For the structural dynamics algorithms considered herein, the rate at which the numerical solution converges to the exact solution is O(Δt) when the truncated starting procedure is used, compared to O(Δt2) when consistent initial acceleration values are used.
Analytical models for the rigid body motions of skew bridges
Authors: Maragakis Emmanuel A. , Jennings Paul C.
Published: March 2007

The rigid body motions of the bridge deck, along with the impact between the bridge deck and the abutments, were the source of extensive damage on skew highway bridges during the 1971 San Fernando earthquake. In this paper, a model for the rigid body motions of skew bridges is presented and analysed. The focus of the model is the appropriate representation of the impact between the bridge deck and the abutments and the explanation of the inducement of in‐plane rotational vibrations of the bridge deck as the result of this impact. A simplified model is briefly described first, and the kinematic mechanism of the problem is explained. Then, the analysis of a more detailed and realistic model follows. This model is applied on a short skew bridge located in Riverside, California. The response of this bridge to several earthquake shakings revealed that the planar rigid body rotations of the deck are induced primarily as a result of the skewness of the deck and the impact between the deck and the abutments.
Improved method of generation of artificial time‐histories, rich in all frequencies, from floor spectra
Authors: Khan Mohsin R.
Published: March 2007

A method to generate artificial time‐histories from given floor response spectra is presented in this paper. The original method proposed by Levy and Wilkinson1 is modified. New iterative equations are developed, based on extensive computational experimentation, to speed up and stabilize the convergence process. The present approach, when applied to spectra with peaks in the high frequency range (40 to 100 Hz) along with seismic peaks, converges very closely to the target spectra within eight iterations regardless of damping values. The original computer program for synthetic time‐history generation was developed on the UNIVAC 1100 series computer. This program was converted to work on the IBM PC. The PC based program ‘MICRO‐SEIM’ saves the response spectra generated at each iteration and the final synthetic time‐history on the PC diskette. The post processing program reads those saved data from the diskette and plots the spectra and time‐history.
Reinforced concrete hysteresis model based on the damage concept
Authors: Wang Ming‐Liang , Shah Surendra P.
Published: March 2007

Reinforced concrete members subjected to cyclic inelastic deformation may exhibit both stiffness and strength degradation, depending on the maximum amplitude and the number of cycles experienced by the member. Many of the currently available models do not simulate the cycle‐dependent stiffness loss often observed during the experiments. An analytical model based on a damage parameter which is a function of the cumulative cyclic inelastic deformation is proposed. A small‐scale reinforced concrete beam–column joint was constructed and subjected to cyclic loading to calibrate the damage parameter. The model is able to approximate the complete hysteretic response and is simple to implement. The sensitivity of the analytical model was examined by comparing the model with several experimental results.
Analysis of absorption effects on the dynamic response of dam reservoir systems by boundary element methods
Authors: Antes Heinz , Von Estorff Otto
Published: March 2007

Using reciprocal theorems for dynamic and static boundary value problems, boundary integral equations are presented for wave propagation in elastic, isotropic media and compressible, inviscid fluids in the time domain as well as in the frequency domain. For the analysis of fluid–soil and fluid–structure systems, suitable coupling conditions are prescribed along the interfaces. The numerical treatment of the boundary integral equations consists of a point collocation and of a discretization of the boundary, in which constant and linear approximation functions are assumed. Step‐by‐step integration is applied to the time‐dependent equations, where again the states are taken to be linear and constant over each time interval.

These boundary element procedures are used to analyse the response of dams due to horizontal and vertical ground motions considering dam–water interaction and absorption of hydrodynamic pressure waves at the reservoir bottom or at the far end into the soil medium. Both the frequency response and the impulse generated transient response are investigated.
Non‐classical damping in dynamic analysis of base‐isolated structures with internal equipment
Authors: Tsai Hsiang‐Chuan , Kelly James M.
Published: March 2007

It has been shown that the use of base isolation not only attenuates the response of a primary structural system but also reduces the response of a secondary system mounted on or within the main structure. The isolation system, superstructure and equipment may be made of different materials with significantly different energy dissipation characteristics such that the damping matrix for the combined system is non‐classical and can only be approximately expressed by modal damping ratios if the classical mode method is used for analysis. The object of this paper is to evaluate the accuracy of this procedure in approximating the responses of base‐isolated structures and internal equipment.

The complex mode method can provide exact solutions to problems with non‐classical damping and is used here to find the exact response of the isolation‐superstructure‐equipment system. The entire system is assumed to be linear elastic with viscous damping and the superstructure is assumed to be proportionally damped so that the deformation of the superstructure can be expressed in terms of its classical modes. Recognizing that the ratio of the equipment mass to the structural mass and the ratio of the stiffness of the isolation system to the superstructural stiffness are both small, perturbation methods are used to find the response.

This study shows that the response of base‐isolated structures can be determined by the classical mode method to some degree of accuracy, but the higher frequency content is distorted. The equipment response derived by the classical mode method is much smaller than the exact solution so that the complex mode method should be applied to find equipment response.
Restoring forces on vertical circular cylinders forced by earthquakes
Authors: Tanaka Yoshihiro , Hudspeth Robert T.
Published: March 2007

An eigenfunction solution is presented for the dynamic response of vertical circular cylinders to earthquake excitation in a compressible fluid of finite depth. This single eigenseries expansion eliminates the need for a double summation over both the eigenfunctions and the trial functions as required by Rayleigh‐Ritz methods. Revised definitions for the added mass and hydrodynamic radiation damping coefficients per unit length are derived from the hydrodynamic fluid pressures. Based on comparisons between these newly defined coefficients, the compressibility of the fluid is found to be relatively more important at dimensionless frequencies greater than unity (ω > 1.0) when analysing both rigid and flexible cylinders having relatively large diameter to water depth ratios,r0/h > 0.25 (squatty type). This conclusion regarding the relative importance of the fluid compressibility is derived from a comparison between the relative magnitudes and the vertical distributions over depth of both the added mass and radiation damping coefficients per unit length for both rigid and flexible squatty cylinders. From additional comparisons with Rayleigh‐Ritz solutions that require trial functions, the results for totally immersed flexible slender cylinders (r0/h< 0.10) are shown to be equivalent; but the results for totally immersed flexible squatty cylinders (r0/h > 0.25) are not. The reason for this difference appears to be in the truncation of the trial function series in the Rayleigh‐Ritz methods, which excludes the higher mode shapes, and in the definitions of the added mass coefficients. Comparisons with laboratory data for both rigid and flexible cylinders confirm the accuracy of the solutions obtained by the eigenseries in the limited frequency interval above the highest frequency for surface gravity waves (f > 1.0 Hz) and below the first dimensionless cut‐off frequency for acoustic waves (ω< 1.0).
A test problem for structural systems with discontinuities
Authors: Brown J. M. B. , Borthwick W. K. D.
Published: March 2007

The direct integration method for structural systems having force and/or stiffness discontinuities is known to present considerable numerical difficulties. A non‐linear one‐degree‐of‐freedom test problem having these characteristics is developed and its exact oscillation period determined. The effects on amplitude and phase of small perturbations of the switching point, such as are caused by fixed‐step integration, have been studied. Artificial energy changes introduced at discontinuities by fixed‐step explicit and implicit methods are investigated. For a number of commonly used algorithms orders of convergence in fixed‐step integration of the test problem degrade from design value before, toO(h) after, the first discontinuity traversal.O(h) convergence is maintained for any number of discontinuity traversals thereafter, but design order can be recovered by locating the switching point sufficiently precisely.
Response of tension‐leg platforms to vertical seismic excitations
Authors: Liou Gin‐Show , Penzien Joseph , Yeung Ronald W.
Published: March 2007

Presented is a systematic approach, for analysing the vertical motion, tendon force and foundation uplift of a tension‐leg platform (TLP) when the subsea soil is excited by vertical seismic waves. The complex problem of multiple interactions among the soil, foundation, fluid and platform can be mathematically modelled using the substructure technique. Having obtained the frequency dependent impedance function for each substructure, the total system is then solved in the frequency domain. A specific TLP is analysed to show the application of the procedures developed and the importance of response to vertical seismic excitation.
Seismic vulnerability and risk evaluation for old urban nuclei
Authors: Benedetti Duilio , Benzoni Gianmario , Parisi Maria A.
Published: March 2007

The evaluation of the seismic damageability of existing buildings is a primary element in the planning for mitigation of earthquake effects. To this purpose, the use of the vulnerability index has been recently proposed and adopted in various surveys in Italy. The index results from grading the status of various structural and non‐structural components exposed to damage in a seismic event. The effectiveness of the vulnerability index as a measure of the health status of buildings is discussed on the basis of regional surveys of vulnerability index versus reported damage, carried out in various Italian areas such as Friuli and the city of Gubbio. Also, investigation of the items most effective in describing damageability among those contributing to the index is performed, in view of formulating a reduced survey procedure. A damage versus vulnerability index database collected in these surveys is presented as well. Finally, a vulnerability index based procedure to evaluate the expected damage in a territory is proposed.
Vibrations of beam‐columns on two‐parameter elastic foundations
Authors: Valsangkar A. J. , Pradhanang R.
Published: March 2007

The natural response of a partially supported beam‐column is investigated by idealizing the soil support as a two‐parameter model. The computed natural frequencies are compared when the same problem is solved by idealizing the elastic foundation as a Winkler model.
Convergence and stability of step‐by‐step integration for model with negative‐stiffness
Authors: Cheng Minxian
Published: March 2007

The convergence and stability of step‐by‐step integration schemes used in the inelastic dynamic analysis of structures and their corresponding criteria were studied for a restoring force model with negative‐stiffness. Convergence conditions and stability conditions 1, 2 or 3 were established. The numerical stability of the integration under negative‐stiffness belongs to the category of relative stability; consequently, the concepts and the conclusions concerning numerical stability in the case of positive‐stiffness (which belongs to absolute stability) cannot be used.

Research into several step‐by‐step integration methods usually employed in inelastic dynamic analysis has shown great differences in numerical stability for models with negative‐stiffness as compared with positive‐stiffness models. The central difference method is convergent and unconditionally stable in the case of negative‐stiffness, though it is only conditionally stable in the case of positive‐stiffness. The Houbolt method satisfies the requirement for convergence; its stability, however, depends not only on the integration step size Δt but also on the stiffness ratio β for the model with negative‐stiffness, unlike the unconditional stability for the model with positive‐stiffness. The Newmark constant acceleration method is convergent and unconditionally stable in the case of negative‐stiffness just like it is in the case of positive‐stiffness.
Evaluation of dynamic eccentricities obtained using a probabilistic approach, response spectrum methods and modern building codes
Authors: Rady M. A. , Hutchinson G. L.
Published: March 2007

In this paper a probabilistic approach has been adopted to study both the effects of uncertainty in earthquake frequency content and the correlation between earthquake frequency content and ground motion intensity on the response of a single‐storey torsionally coupled elastic structure. The earthquake ground motion has been assumed to be a Gaussian, zero mean, stationary random process which is fully characterized by a power spectrum. The ground acceleration power spectrum is idealized as a probabilistic normalized power spectrum computed from actual earthquake records. The advantage of such an idealization is that it enables the effect of the natural frequency as a controlling structural parameter in torsional coupling to be assessed. Comparisons of the dynamic amplifications of eccentricity with those obtained from modern codes of practice and conventional response spectrum analyses have been made.

The results of this study have shown that the variation in the frequency content has a significant effect on the response of low frequency structures, while the correlation between the frequency content and the intensity of seismic ground motion is insignificant for the wide range of structures considered.

The structure natural frequency has been shown to be an important controlling parameter in the torsionally coupled response of structures subject to seismic loading. The frequency dependence of the dynamic amplification of eccentricity was found not to be reflected in the response spectrum analysis and the torsional provisions of modern building codes.
An exact component mode synthesis approach
Authors: Suarez L. E. , Singh M. P.
Published: March 2007

The paper presents a method for synthesizing the modal properties of substructures to obtain the exact modal properties of a combined structure. Unlike the currently available modal synthesis approaches, the proposed approach does not require the solution of any transformed eigenvalue problem of the combined structure by conventional means. The substructures are assumed to be coupled by connecting elements and the coupling is done sequentially with one element at a time. The eigenvalues at each stage of coupling are obtained by solving a non‐linear characteristic equation. A simple Newton‐Raphson solution scheme is adequate for this purpose. Once the eigenvalues are determined, the eigenvectors can be calculated in closed form. Several examples demonstrating the applicability of the proposed approach are presented.
Rosenblueth's modal combination rule for systems with non‐classical damping
Authors: Villaverde Roberto
Published: March 2007

A simple rule is derived to combine, within the framework of a complex mode superposition, the maximum modal responses of systems such as soil‐structure and structure‐equipment systems, for which closely spaced natural frequencies are likely, and for which, because of the large difference in the damping values of their various components, the assumption of an orthogonal damping matrix may lead to significant errors. The rule constitutes the generalization of Rosenblueth's rule for systems with closely spaced natural frequencies and classical modes, and is expressed in terms of their complex mode shapes and natural frequencies. Its derivation is based on the theory of a complex modal analysis for systems with non‐classical modes of vibration and on Rosenblueth's original derivation. As in this original derivation, earthquake ground motions are modelled as a stationary white noise process, but the formulae obtained under this assumption are modified later on to account for the transient nature of actual earthquakes. A numerical example is presented to illustrate the application of the rule, and a comparative study with numerical integration solutions is performed to assess its accuracy. In this comparative study, it predicts the numerical integration solutions with an average error of 0.3 per cent.
Dynamic response of vertically excited liquid storage tanks considering liquid‐soil interaction
Authors: Fischer F. D. , Seeber R.
Published: March 2007

The paper presents a dynamic response analysis of vertically excited liquid storage tanks including both liquid‐tank and liquid‐soil interaction. The system considered is a thin‐walled, elastic cylindrical shell entirely filled with an incompressible and inviscid fluid, resting on a flexible foundation over an elastic halfspace with frequency dependent stiffness and damping parameters. The problem is treated analytically by the generalized‐coordinate approach and then solved numerically using the complex frequency response analysis. For one special tank, natural frequencies and equivalent damping ratios are evaluated and compared with those corresponding to a rigid ground. The maximum dynamic pressure is calculated using the response spectra of the 1976 Friuli earthquake. A parameter study is carried out to show the great influence of variable soil stiffness upon the damping ratio of the shell‐liquid‐soil system.
Hydrodynamic‐stiffness matrix based on boundary elements for time‐domain dam‐reservoir‐soil analysis
Authors: Wepf Dieter H. , Wolf John P. , Bachmann H.
Published: March 2007

For a reservoir with an arbitrary shape of the upstream dam face and of the bottom including an adjacent regular part of constant depth extending to infinity, the hydrodynamic‐stiffness matrix in the frequency domain for a displacement formulation is derived using the boundary‐element method. The fundamental solution takes the boundary condition at the free surface into account. The analytical solution of the semi‐infinite reservoir is used to improve the accuracy. To be able to transform the hydrodynamic‐stiffness matrix from the frequency to the time domain, the singular part consisting of its asymptotic value of ω ∞ is split off. It consists of an imaginary linear term in ω which can be interpreted as a damper with a coefficient per unit area equal to the product of the mass density and the wave velocity. This also applies for a reservoir bottom of arbitrary shape. The remaining regular part of the stiffness matrix is transformed numerically. The corresponding interaction force‐displacement relationship involves convolution integrals. This boundary‐element solution agrees well with analytical results and with those of other numerical procedures based on a time‐stepping method. The method is also applied to an actual earthquake acting on a reservoir with an irregular part with an inclined bottom and a regular part extending to infinity. The results of the analysis in the time domain coincide with those determined in the frequency domain.
Dynamic finite strip analysis of surface foundations
Authors: Chow Y. K. , Swaddiwudhipong S. , Lim S. A.
Published: March 2007

The finite strip method is used to study the dynamic response of surface strip foundations. This method is simple to use and versatile. The two‐dimensional problem is effectively reduced to an equivalent one‐dimensional problem. The choice of trigonometric series for the displacement functions results in the uncoupling of the terms of the series and a significant reduction in the semi‐bandwidth of the complex set of equations, making the method well suited to small computers. Non‐homogeneous soil profiles are treated as a matter of course. The finite strip solutions are shown to be in general agreement with other theoretical methods of analysis.
Transient pressures in hydrotechnical tunnels during earthquakes
Authors: Kojic Slobodan B. , Trifunac Mihailo D.
Published: March 2007

Transient pressures generated by earthquake shaking in hydrotechnical tunnels are evaluated by the discrete Fourier transform technique. The effects of the horizontal ground motion accelerating the closed downstream tunnel gate, as well as the upstream dam face, and the influence of the vertical motion of the reservoir floor are considered in this analysis. An example of a typical bottom outlet is analysed by subjecting it to several computed accelerograms. It is shown that high hydrodynamic pressures can be developed, several times larger than the hydrostatic pressure.
The use of optimization to construct critical accelerograms for given structures and sites
Authors: Pirasteh Ali Akbar , Cherry Jeffery L. , Balling Richard J.
Published: March 2007

In this paper a methodology has been presented for constructing the most critical accelerogram from among a be class of candidate accelerograms for a given site and structure. This most critical accelerogram could be used to assess seismic resistance of a structure with a high level of confidence. Specifically, the method superimposes accelerograms recorded at similar sites to create the candidate accelerograms, then uses optimization and approximation techniques find the most critical accelerogram. The most critical accelerogram is defined as the one which maximizes damage is structure, as computed by non‐linear dynamic structural analysis, as well as satisfies constraints on ground parameters to ensure credibility. The damage has been defined as cumulative inelastic energy dissipation or sure of interstorey drifts. The method is applied to ten examples in the paper.
Dynamic analysis of 3‐D flexible embedded foundations by a frequency domain BEM‐FEM
Authors: Gaitanaros Alexandros P. , Karabalis Dimitris L.
Published: March 2007

A study on the dynamic response of three‐dimensional flexible foundations of arbitrary shape, embedded in a homogenous, isotropic and linear elastic half‐space is presented. Both massive and massless foundations are considered. The soil‐foundation system is subjected to externally applied forces, and/or to obliquely incident seismic waves. The numerical method employed is a combination of the frequency domain Boundary Element Method, which is used to simulate the elastic soil medium, and the Finite Element Method, on the basis of which the stiffness matrix of the foundation is obtained. The foundation and soil media are combined by enforcing compatibility and equilibrium conditions at their common interface. Both relaxed and completely bonded boundary conditions are considered. The accuracy of the proposed methodology is partially verified through comparison studies with results reported in the literature for rigid embedded foundations.
Engineering implications of the 1985 nahanni earthquakes
Authors: Heidebrecht Arthur C. , Naumoski Nove
Published: March 2007

A series of strong ground motions was recorded during a set of earthquakes which occurred in the North Nahanni River area of the Northwest Territories of Canada in late 1985. The strongest of these motions were recorded within 10 km of the epicentre of a magnitude 6.9 event; peak accelerations were well above 1g and peak velocities exceeded 0.4 m/s.

This paper describes a study of the engineering characteristics of the Nahanni strong motions, particularly as they affect the response of building structures. The response characteristics are analysed in terms of the response spectra and the unit velocity base shear coefficients for multi‐degree‐of‐freedom elastic frame structures. An analysis of the strong motion durations of the records and several measures of intensity is also included. The characteristics of the Nahanni records are compared with those of typical strong seismic ground motions and an ensemble of epicentral region seismic motions recorded under similar conditions. Comparisons are also made with the equivalent parameters in the 1985 edition of the National Building Code of Canada.

It is concluded that the Nahanni records are very strong seismic ground motion records with relatively unusual response characteristics, even when compared with those of other records obtained within the epicentral region. The impact of these characteristics on engineering design is most significant for low period structures in epicentral regions. The specifications of typical design codes do not adequately describe the response to such records for very low periods.
Dynamic instability of frames having thin‐walled columns
Authors: Sridharan Srinivasan , Ashraf Ali M.
Published: March 2007

Dynamic instability of single storey frames having thin‐walled columns has been investigated. The lateral loads sustained by the frame are dynamic in character, while the axial loads are deemed to be quasi‐statically applied. The analytical model employed by the authors has the capability of modelling the combined action of the two ‘companion’ local modes whose amplitudes are variable along the length of the column and any type of end conditions of the members.

For given levels of axial loads sustained by the columns, the magnitudes of lateral loads causing instability can be significantly smaller than those corresponding to static buckling, provided the dynamic load is of sufficient duration. There exists, however, a threshold value of axial force carried by the columns, below which there is no elastic instability—static or dynamic.

For columns with overall critical loads several times greater than the local critical load, there is no danger of elastic instability, but the deflections under dynamic lateral loads of less than 1 per cent of the axial load may reach such huge values that there is a serious danger of localized plastic collapse. It is also shown that moment frames having thin‐walled columns such as those fabricated out of cold formed steel are extremely vulnerable to moderate seismic excitations.
Seismic damage prediction by deterministic methods: Concepts and procedures
Authors: Powell Graham H. , Allahabadi Rakesh
Published: March 2007

Although the prediction of seismic damage is primarily a probabilistic problem, deterministic analysis can nevertheless be a valuable tool. This paper reviews the concepts which have been used in damage prediction, and identifies and classifies several specific techniques. Techniques of two types are considered, the first based on the balance between some demand on the structure and its corresponding capacity, and the second on the degradation of some structural property. For each technique, one or more damage parameters can be computed, and from these a damage index can be estimated. Several alternative choices for the damage parameters are identified. Procedures for computing values for these parameters, and relating them to damage indices, are suggested.
Non‐stationary spectral moments of base excited MDOF systems
Authors: Borino G. , di Paola M. , Muscolino G.
Published: March 2007

The paper deals with the evaluation of non‐stationary spectral moments of multi‐degree‐of‐freedom (MDOF) line systems subjected to seismic excitations. The spectral moments of the response are evaluated in incremental form solution by means of an unconditionally stable step‐by‐step procedure.

As an application, the statistics of the largest peak of the response are also evaluated.
Stable semi‐explicit algorithms for non‐linear dynamic problems
Authors: Kujawski Jerzy
Published: March 2007

Semi‐explicit iterative algorithms for time integration of large‐scale non‐linear dynamic problems are presented. They use iteratively only forward substitution which allows for the vectorial computation with both consistent and lumped mass matrices. The stability and rate of convergence of the non‐linear iterative solutions can be improved using single or multiparameter acceleration procedures. Numerical results show the stability, accuracy and efficiency of the algorithms.
Stiffness of non‐skew monolithic bridge abutments for seismic analysis
Authors: Wilson John C.
Published: March 2007

A simple analytic model is developed to describe the stiffness of non‐skew monolithic highway bridge abutments for purposes of seismic bridge analysis. The model permits an evaluation of six equivalent discrete spring stiffnesses for three translational and three rotational degrees‐of‐freedom of the abutment and includes effects of the abutment walls, pile foundations and soil. These springs can be incorporated as boundary elements in a more detailed finite element analysis of the dynamic response of the bridge superstructure. A parametric study examines a range of abutment stiffnesses for 2, 4 and 6 lane highway bridges. Application of the model to a single span bridge indicates the importance of including abutment stiffness in the determination of bridge frequencies and mode shapes in the transverse and vertical directions.