Showing papers in "Journal of Engineering Mechanics-asce in 1971"
TL;DR: In this paper, the authors compare the flutter phenomena of the suspension bridge and the airfoil and employ a free-oscillation experimental method to measure model bridge flutter coefficients analogous to air-foil flutter coefficient.
Abstract: The writers compare the flutter phenomena of the suspension bridge and the airfoil and employ a free-oscillation experimental method to measure model bridge flutter coefficients analogous to airfoil flutter coefficients. They employ the airfoil as a check on the experimental method, both as a theoretical backdrop and to test out the nature of aerodynamic oscillatory forces under exponentially modified motion. A short catalogue of bridge deck flutter coefficients is then experimentally obtained and presented covering a range of bridge deck forms. Detailed results are described to account for a number of phenomena observed in the wind tunnel and in the field.
746 citations
TL;DR: In this article, a mathematical material model for granular soils, based on classical plasticity theory, is proposed, which combines a generalized ideally plastic Coulomb-Mohr failure envelope with a moving cap, crossing the hydrostatic loading axis, whose position depends on plastic volumetric strain.
Abstract: A mathematical material model for granular soils, based on classical plasticity theory, is proposed The yield surface combines a generalized ideally plastic Coulomb-Mohr failure envelope with a moving cap, crossing the hydrostatic loading axis, whose position depends on plastic volumetric strain It is shown how this model can fit laboratory test data for a particular sand sample
518 citations
TL;DR: In this paper, the authors present the dynamic compliances of a circular footing resting on an elastic half-space for a wide range of dimensionless frequency, including torsional, vertical, rocking and horizontal oscillations.
Abstract: It is the purpose of the paper to present the dynamic compliances of a circular footing resting on an elastic half-space for a wide range of dimensionless frequency. Numerical results have been presented for the torsional, vertical, rocking and horizontal oscillations of a rigid disc placed on an elastic half-space, as well as for the coupling terms between the rocking and horizontal oscillations. The corresponding compliances, the stress distributions under the disc, and the Rayleigh wave part of the far-field displacements have been evaluated. It is hoped that these results will prove to be useful in the design of foundations for vibrating machinery and in the study of soil structure interaction.
337 citations
TL;DR: In this article, the applicability of Griffith fracture criteria to portland cement systems which are neither elastic nor homogeneous was examined. But it appears that for mortar and concrete the direct application of Griffith criteria is not valid up to a certain length of cracks, depending on the size, volume and type of aggregate.
Abstract: The original Griffith fracture criteria was developed to describe the rapid extension of a crack in a homogeneous elastic body. To check the applicability of the Griffith theory to portland cement systems which are neither elastic nor homogeneous, specimens of hardened cement paste, mortar and concrete made with normal and lightweight aggregates, and with notches of varying lengths were tested in flexure and in tension. While the paste specimens were notch-sensitive, mortar and concrete strengths were independent of notch length. The notch-insensitivity of mortar and concrete appears to be due to their composite nature. Similar behavior occurs in glass-Al²O³, fiberglass-reinforced epoxy and tungsten-reinforced copper composites. It appears that for mortar and concrete the direct application of Griffith criteria is not valid up to a certain length of cracks. This critical length depends on the size, volume, and type of aggregate.
101 citations
TL;DR: In this paper, the benefits derived from the existence of the structure, its initial cost, and the expected losses due to failure are considered in the context of a single load application.
Abstract: Reliability optimization is formulated here in a way that permits dealing explicitly with the benefit derived from the existence of the structure, its initial cost, and the expected losses due to failure. This formulation is adapted to the policies in which the structure is either not rebuilt or systematically rebuilt if it fails. Introduction of the time variable in one-component structures leads to expressions that can be put in the form of those for a single load application. Attention is given to disturbances which are generalized Poisson processes and to criteria for deciding on the advisability of providing defense plateaus in specific cases. The treatment is extended to statically determinate structures having uncorrelated component resistance functions or a certain type of correlation of these variables. An iteration procedure is developed for these cases.
100 citations
TL;DR: In this article, an incremental displacement formulation for the nonlinear finite element analysis of sandwich arches is presented, which permits the analysis of geometrically nonlinear problems with finite rotations but infinitesimal strains.
Abstract: An incremental displacement formulation for the nonlinear finite element analysis of sandwich arches is presented. The formulation permits the analysis of geometrically nonlinear problems with finite rotations but infinitesimal strains. The finite element model employed is a straight beam-column type, and has a three-layered sandwich construction with similar facings. Homogeneous and isotropic material properties are assumed; and flexural, extensional and shear deformations of all three layers are considered. Therefore, it is possible to analyze homogeneous structures by simply assigning the same material properties to all three layers. The method is applicable to investigation of symmetrical and asymmetrical buckling and post-buckling behavior of arches. For the latter, an augmentation scheme has been used to give a positive definite stiffness matrix in the descending branch of the load-deflection curve. Results compare favorably with analytical solutions available in the literature.
76 citations
TL;DR: The finite strip method is used for the flexural vibration analysis of elastic plates as discussed by the authors, which can be isotropic or orthotropic in property, of constant or variable thickness, and with distributed or concentrated masses.
Abstract: The finite strip method is used for the flexural vibration analysis of elastic plates. The plates can be isotropic or orthotropic in property, of constant or variable thickness, and with distributed or concentrated masses. It can have any combination of free, simply-supported and clamped boundary conditions and can also be continuous in one direction. The stiffness matrix of a strip with two opposite ends simply-supported, free or clamped is formed by assuming suitable basic function series in the longitudinal direction which satisfies the end conditions and a simple cubic polynomial in the transverse direction. A consistent mass matrix can also be formed for each strip. The stiffness and mass matrices of all the strips making up a plate are then assembled to form an eigenvalue matrix in the same way as for a beam problem. The method is simple but versatile, and all the natural frequencies and corresponding modal shapes can be obtained rapidly from an intermediate or even small size electronic digital computer.
72 citations
TL;DR: Convergent finite element equations for dynamic stability of plates dependent on vibration and buckling modes were proposed in this paper, where the stability of the plates was evaluated using finite element models.
Abstract: Convergent finite element equations for dynamic stability of plates dependent on vibration and buckling modes
59 citations
TL;DR: In this article, a simple mechanism is proposed to predict ice-structure interaction, where the structure is represented by a spring-mass system and the ice is replaced by a succession of elastic-brittle elements which impinge on the structure at a rate determined by the relative motion between the ice and the structure.
Abstract: In an effort to predict ice-structure interaction, a simple mechanism is proposed. The structure is represented by a spring-mass system and the ice is replaced by a succession of elastic-brittle elements which impinge on the structure at a rate determined by the relative motion between the ice and the structure. A computer program is used to solve for the dynamic response of the structure. A number of test cases and variations have been solved, and the results compared with limited laboratory and field measurements that are available. Interesting agreement has been obtained with observed behavior at various ice velocities. It is believed that the present approach can be used to determine reasonably well the response of a structure to an impinging ice sheet.
48 citations
TL;DR: In this article, an 8-story shear type building with inelastic force-deflection characteristics represented by a bilinear hysteretic model and having various values of stiffness and viscous damping is subjected to twenty samples of the artificial ground acceleration records.
Abstract: Records of strong-motion earthquakes are simulated using a filtered shot noise. Twenty sample records are then used to simulate the response of a structure subjected to earthquake excitation. The stochastic model used to generate the artificial ground acceleration records is designed to produce sample records similar to those of real strong-motion earthquakes of magnitude 8.3 recorded on firm soil at about 45 miles from the epicenter. It is concluded that a filtered shot noise is very suitable for this simulation. An 8-story shear type building with inelastic force-deflection characteristics represented by a bilinear hysteretic model and having various values of stiffness and viscous damping is subjected to twenty samples of the artificial ground acceleration records. Major response parameters are evaluated and Monte-Carlo estimates of the statistics of these parameters are obtained to allow predictions of their values during future earthquakes.
47 citations
TL;DR: In this article, the parametric resonance of a simply supported tube is studied analytically using Galerkin's method, and the equation of motion is reduced to a system of coupled Mathieu-Hill-type equations with multiharmonic coefficients.
Abstract: The parametric resonance of a simply supported tube is studied analytically. By employing Galerkin's method, the equation of motion is reduced to a system of coupled Mathieu-Hill-type equations with multiharmonic coefficients. The stability-instability region boundaries are constructed by the methods of Hsu and Bolotin. The results obtained by Hsu's first approximation show that combination resonance is possible and that the coupling terms do not influence the principal and second instability regions. The higher order approximation is obtained by Bolotin's method which shows that the effect of the coupling terms is to lower, in frequency, the instability regions; they have no effect on the size of the instability regions.
TL;DR: Theoretical and experimental results for the in-plane buckling of shallow circular arches are presented in this article, where the types of end fixity considered are: (1) pinned; (2) clamped; and (3) pinned and clamped.
Abstract: Theoretical and experimental results, with favorable agreement, are presented for the in-plane buckling of shallow circular arches. The types of end fixity considered are: (1) pinned; (2) clamped; and (3) pinned and clamped. Concentrated, uniform radial, and linearly varying radial loading cases are considered.
TL;DR: In this article, a simple approach using a Fast Fourier Transform (FFT) algorithm for obtaining the transient structural response to earthquakes is presented, and two different foundation models are used, a rigid circular plate and a rigid two-dimensional strip bonded to the elastic soil half space.
Abstract: A simple approach using a Fast Fourier Transform (FFT) algorithm for obtaining the transient structural response to earthquakes is presented. Two different foundation models are used, a rigid circular plate and a rigid two-dimensional strip bonded to the elastic soil half space. A numerical procedure is used to obtain all pertinent transfer functions which are subsequently used in conjunction with FFT subroutines to obtain the response time histories. It is shown that over a range of scaled wave numbers which characterize the soil properties, significant base rocking can be expected only when either the slenderness parameter or the mass-ratio parameter is small. The specific advantages of the new approach are: (1) it is computational efficient; (2) it can take into account the frequency-dependent interaction forces; and (3) it is general, readily adaptable in practical applications, and can be used with any linear structure or interaction model.
TL;DR: In this article, the buckling problems of simply supported skew plates with in-plane stresses represented in terms of orthogonal components were considered by using the Rayleigh-Ritz method, employing a double Fourier sine series in oblique coordinates.
Abstract: The buckling problems of simply supported skew plates with in-plane stresses represented in terms of orthogonal components are considered by using the Rayleigh-Ritz method, employing a double Fourier sine series in oblique coordinates. Results for the buckling coefficients for different combinations of side-ratio and skew angle are provided mainly when each of the in-plane stresses is acting singly. Results include buckling coefficients under positive shear which are hitherto unavailable in the literature.
TL;DR: In this article, a modified finite difference technique is used to determine the natural frequencies and mode shapes of hyperbolic cooling tower shells, and the influence of the meridional curvature and the boundary conditions on the vibration characteristics of the tower is investigated.
Abstract: A modified finite difference technique is used to determine the natural frequencies and mode shapes of hyperbolic cooling tower shells. The influence of the meridional curvature and the boundary conditions on the vibration characteristics of the tower is investigated. In all cases, changes in frequency are found to be essentially due to changes in membrane energy. It is shown that, for a fixed-free shell, the increased meridional curvature leads to an increase in the natural frequency. The lack of axial restraint results in a large reduction in the membrane energy and consequently the natural frequency. For simply-supported shells, a critical meridional curvature at which the membrane energy effectively vanishes is shown to exist.
TL;DR: In this article, the relationship between the elastic foundation parameters and the elastic constants of the material is investigated for the case of infinite, semi-infinite, and finite length beams.
Abstract: The representation of an elastic continuum as an elastic foundation for beams is considered. Relationships between the elastic foundation parameters and the elastic constants of the material are developed. One- (Winkler model), two-, and three-parameter foundation models are considered for the cases of infinite, semi-infinite, and finite length beams encased in infinite elastic bodies or supported by semi-infinite elastic bodies. Curves relating the model parameters to the elastic constants are given for a wide range of materials. Comparisons are made of results obtained by representing the supporting material as (1) an elastic foundation and (2) a three-dimensional elastic continuum.
TL;DR: In this paper, a procedure of analysis is presented for determining the elastic-inelastic response of framed structures under dynamic loads, where the material of the structure is assumed to obey the Mises-Hencky yield criterion and the plastic flow is governed by the Reuss-Mises inelastic stress-strain relationship.
Abstract: A procedure of analysis is presented for determining the elastic-inelastic response of framed structures under dynamic loads. Application of Hamilton’s principle in conjunction with the finite-element method leads to the basic dynamical equations of the system incorporating the plastic effects in the form of equivalent nodal forces. This approach also allows the more accurate treatment of the distributed loads and the distributed mass of the element than the usual geometrical method of lumping. In order to take into account stress reversal and strain hardening effects, an incremental theory of plasticity is used and the history of deformation of the entire structure is followed through. The material of the structure is assumed to obey the Mises-Hencky yield criterion and the plastic flow is governed by the Reuss-Mises inelastic stress-strain relationship.
TL;DR: In this paper, the evaluation of earthquake simulation processes relates to the autocovariance function, maximum acceleration response spectra, and nonstationarity of the process, and two previously used and two new processes are examined with respect to these criteria by means of theoretical and simulated results.
Abstract: Criteria presented for the evaluation of earthquake simulation processes relate to the autocovariance function, maximum acceleration response spectra, and nonstationarity of the process. Two previously used and two new processes are examined with respect to these criteria by means of theoretical and simulated results. The previous processes develop a nonstationary white noise for input to a linear filter and take the filter output as the simulated ground acceleration. They are identical except for filter properties. Neither of these processes complies with all the criteria. One fails to provide reasonable response spectra; the other produces an unrealistic ground-velocity variance function that does not disappear with time. The new processes incorporate weighting functions that produce correlated, nonwhite filter inputs. One of these produces response spectra with undesirable irregularities. The other, which employs an exponential decay-type weighting function, complies with all criteria and is recommended as a suitable model for earthquake simulation. Additional relationships are examined for rms and maximum oscillator response spectra.
TL;DR: In this article, an analytical method for determining the effective shear modulus of a multilayered rectangular member in uniform torsion is presented, where the materials in the member are elastic and isotropic, and each layer is perfectly bonded to the adjacent layers.
Abstract: An analytical method for determining the effective shear modulus of a multilayered rectangular member in uniform torsion is presented. The materials in the member are elastic and isotropic, and each layer is perfectly bonded to the adjacent layers. The particular case of a two-layered section is reviewed in detail. Effective shear moduli for the two-layered section are calculated for a range of geometric parameters and modular ratios, and are presented graphically. A simple approximate method of calculating the effective shear modulus for sections with either a large or a small width-to-depth ratio is given. Finally, the position and magnitude of the maximum shear stresses in each of the sections is investigated.
TL;DR: Theoretical and experimental results for the bearing capacity of concrete blocks with an axially or eccentrically located cable duct and axially loaded by two rigid punches are presented in this article.
Abstract: Theoretical and experimental results are presented for the bearing capacity of concrete blocks with an axially or eccentrically located cable duct and axially or eccentrically loaded by two rigid punches. The solutions have been obtained using the concept and the theory developed recently by Chen and Drucker. The problem considered here is closely related to the bearing strength of the anchorage zone of a prestressed concrete beam. More important, these solutions provide additional theoretical and experimental evidence as to the validity and limitations of the theory of perfect plasticity as applied to bearing capacity problems in concrete. In the analysis, it was found that the upper bound theorem of limit analysis may be used to predict the bearing strength of an eccentrically loaded concrete block. However, when the eccentricity ratio of the punch load is large, crack propagation does enter for such a situation. An appropriate fracture mechanics for concrete is needed. Nevertheless, the solutions obtained herein still provide a reasonable upper bound for fractured concrete. The agreement between the theory and experimental results is satisfactory. These solutions should provide a better understanding of the bearing strength of the anchorage zones of post-tensioned concrete members.
TL;DR: In this paper, a macroscopic hydrodynamic approach is used to derive a set of one-dimensional spatially varied unsteady flow equations, that include terms for lateral mass flux, lateral momentum flux, overpressure head due to raindrop impact, and boundary shear.
Abstract: In a macroscopic hydrodynamic approach, a set of one-dimensional spatially varied unsteady flow equations, that include terms for lateral mass flux, lateral momentum flux, overpressure head due to raindrop impact, and boundary shear, are derived from the equation of continuity and the Navier-Stokes equations for the three-dimensional flow of viscous incompressible fluid in cooperation with the kinematic and dynamic boundary conditions on the water and ground surfaces of a watershed. The Darcy-Weisbach equation is employed to evaluate the friction slope, and the laminar uniform flow equation for the Darcy-Weisbach friction coefficient coupled with the Karman-Prandtl logarithmic resistance equation for turbulent flow is used to simulate, as a first approximation, the unknown function of the Darcy-Weisbach friction coefficient for watershed surface flow. The proposed mathematical model for watershed surface flow consists of a set of quasilinear partial differential flow equations of hyperbolic type with the appropriately prescribed initial and boundary conditions.
TL;DR: In this article, the continuous method of analysis of coupled shear walls is reformulated in terms of deflection variables and used to study the dynamic behavior of plane coupled Shear walls.
Abstract: The continuous method of analysis of coupled shear walls is reformulated in terms of deflection variables and used to study the dynamic behavior of plane coupled shear walls. The assumption that mid-points of the connecting beams are points of contraflexure is relaxed so that the resulting theory is applicable to the general case where the lateral loading on the piers can be arbitrarily distributed. The equations of motion with appropriate boundary conditions are given. The free vibration of coupled shear walls is studied and the fundamental frequency determined. Theoretical results are verified by dynamic testing on two models to show the theory is sufficiently accurate to provide information for dynamic analysis in seismic design.
TL;DR: In this paper, a finite element-Ritz method is applied to the extended Hamilton's principle to the non-conservative stability of continuous systems, and the results of the analysis are presented in graphical or tabular form, or both.
Abstract: Nonconservative stability of continuous systems has received considerable theoretical attention in recent years. This class of stability problems is examined herein by application of the finite element—Ritz method to the extended Hamilton's principle. The technique is illustrated by the detailed analysis of two examples. The first is the classical problem concerning the stability of a cantilever under follower force excitation. The principal problem is to determine the follower force at which the column will oscillate in an unstable manner (flutter). The second problem is a cantilevered tube containing an inviscid fluid in slug flow. In this example, primary interest is in the fluid velocity at which dynamic instability occurs. Results of both problems, which are presented in graphical or tabular form, or both, clearly demonstrate the power of the methods.
TL;DR: In this paper, the mean and variance of n th natural frequency of a beam-column are obtained by a perturbation method when the material and geometric properties, the axial load, and the boundary conditions are probabilistic.
Abstract: The mean and variance of n th natural frequency of a beam-column are obtained by a perturbation method when the material and geometric properties, the axial load, and the boundary conditions are probabilistic. The realtive effects of uncertainty in input parameters such as axial load and structural properties with uncertainty in output parameters of natural frequency are studied. It is found that the deviation of the output is great for the small deviation of inputs.
TL;DR: In this paper, the interaction between two types of forces, causing instability of a vertically cantilevered column, is studied. And the effect of the weight on the flutter instability of the column, and of the follower force on its buckling instability, are examined.
Abstract: In this article, the interaction between two types of forces, causing instability of a vertically cantilevered column, is studied. These forces are the conservative force of the column’s own weight, and a nonconservative distributed follower force. The effect of the weight on the flutter instability of the column, and of the follower force on its buckling instability, are examined. It is shown that: (1) the inclusion of the column’s weight lowers the flutter load; (2) it is possible to destabilize certain columns, ordinarily stable under their own weights, by the addition of sufficiently large tensile followers; (3) it is possible to stabilize a column, ordinarily unstable under its own weight, by the addition of sufficiently large compressive followers.
TL;DR: In this article, the authors developed a numerical method for the calculation of first passage time probability of single degree-of-freedom, linear and nonlinear, dynamic oscillators excited by Gaussian white noise.
Abstract: A numerical method is developed for the calculation of first-passage time probability of single degree-of-freedom, linear and nonlinear, dynamic oscillators excited by Gaussian white noise. The random walk model is a difference equation which governs the diffusion of the oscillators response probability in the phase plane and is a discrete analog to the continuous theory Fokker-Planck equation. First-passage is examined by considering the diffusion process when absorbing barriers are superimposed upon the phase plane. Two linear systems are studied for first-passage and compared to results from another numerical approach with good correlation. First-passage is also examined for several nonlinear systems to demonstrate its applicability. It is the study of the latter for which the technique has particular value.
TL;DR: In this article, the elastic-continuum hypothesis is modified by incorporating in the analysis the horizontal displacements in the elastic foundation, thus making the foundation model more general and applicable to foundations of both finite and infinite thickness, and the application of method of initial parameters to beams having general configuration carrying arbitrary external loads and moments is described.
Abstract: Starting from an elastic-continuum hypothesis, the foundation model proposed by Vlasov and Leontev is modified by incorporating in the analysis the horizontal displacements in the elastic foundation, hence making the foundation model more general. Equations derived are applicable to foundations of both finite and infinite thickness. Bending theory of beams on elastic foundations is presented using the proposed foundation model. Method of initial parameters is developed for finite beams on elastic foundations. The application of method of initial parameters to beams having general configuration carrying arbitrary external loads and moments is described. Results are presented in nondimensional form and are compared with existing solutions.
TL;DR: In this article, a bifurcation buckling theory was derived for the case of a tube surrounded by soil with the postulate that outward buckling displacements are prohibited and the inward displacement are retarded by an elastic reduction in external soil pressure.
Abstract: A bifurcation buckling theory was derived for the case of a tube surrounded by soil with the postulate that outward buckling displacements are prohibited and the inward displacements are retarded by an elastic reduction in external soil pressure. A single wave form buckling mode results which matches experimental evidence qualitatively. The proper choice of apparent thickness of the tube to account for imperfections and empirically computing the spring constant of the soil permits a good correlation with published data on the buckling at soil-surrounded tubes. A graphical procedure is presented for solving for the buckling pressure, the subtended angle of the local buckle, and the mode numbers defining the buckled shape. It was found that the effective spring constant of the soil varies with the local effective stress of the soil and, to a lesser degree, the thickness of the surrounding soil cylinder.
TL;DR: Symmetric and asymmetric dynamic buckling of shallow elastic arches under uniform loads, using nonlinear finite difference method, was studied in this paper, showing that the buckling can be achieved under uniform load.
Abstract: Symmetric and asymmetric dynamic buckling of shallow elastic arches under uniform loads, using nonlinear finite difference method