Showing papers in "Journal of Engineering Mechanics-asce in 1980"
TL;DR: In this paper, a crack density tensor describing the averaged geometry of a crack array is introduced and used to study the anisotropy of an effective elastic response due to the presence of cracks.
Abstract: A continuum approach to an elastic medium containing cracks is developed. A crack density tensor describing the averaged geometry of a crack array is introduced and used to study the anisotropy of an effective elastic response due to the presence of cracks. The resulting continuum model turns out to be orthotropic, which is in good agreement with the results given by the small concentration approach and the self-consistent method. Anisotropy of the transport properties (fluid permeability, electric- and heat conductivity) is also considered.
455 citations
TL;DR: In this article, the first three spectral moments of response to white noise and filtered white noise inputs are derived in terms of cross-modal contributions and explicitly account for the correlation between modal responses of multi-degree structures.
Abstract: Stationary responses of single-and multi-degree-of-freedom structures subjected to stationary input excitations are studied. Using a modal superposition prodedure, closed-form solutions for the first three spectral moments of response to white-noise and filtered white-noise inputs are derived. These solutions are in terms of cross-modal contributions and explicitly account for the correlation between modal responses of multi-degree structures; thus, they are applicable to structures with closely spaced frequencies. Speical attention is given a excitations which are typical of earthquake ground motions. Various quantities of response can be obtained in terms of the three spectral moments. These include mean zero-crossing rate and mean, variance, and distribution of peak response over a specified duration. In this regard, improved, semi-empirical relations for the mean and variance of the peak of a stationary Gaussian process are developed. Results from study demonstrate range of applicability of white-noise model as an approximation for wide-band inputs.
330 citations
TL;DR: In this paper, the authors studied the possibility of enhancing TMD effectiveness in structural with added active control capability and showed that an addition of active control forces to TMD systems can lead to significant improvement in displacement and acceleration reductions.
Abstract: Passive tuned mass dampers (TMD) are being using for motion control of tall buildings. The possibility of enhancing TMD effectiveness in structural with added active control capability is studied in this paper. The problem of structural control using active TMD is fromulated using classical feedback control theory. Using simple numerical examples, it is shown that an addition of active control forces to TMD systems can lead to significant improvement in displacement and acceleration reductions. Furthermore, TMD stroke requirement can also be significantly reduced with added active control element.
272 citations
TL;DR: In this paper, the principal stress-strain relations from the tests are transformed into octahedral space, and the material response is expressed in terms of variable bulk and shear moduli.
Abstract: Differences in the observed behavior of concrete under multiaxial stress states can be ascribed to either different materials or different test methods. In order to isolate the effects of these two variables, seven institutions cooperated in a test program in which specimens of indentical material were subjected to variety of biaxial and triaxial stress states common to all participants. Specimen loading conditions ranged from flexible, uniformly-stressed membranes through various intermediate conditions to rigid, rough steel plates providing uniform surface displacements. Stress-strain relations obtained are presented and examined. They indicate that there are some systematic differences in results which depend on the test method used. The principal stress-strain relations from the tests are transformed into octahedral space, and the material response is expressed in terms of variable bulk and shear moduli. A coupling effect relating volume change to stress deviation was also observed. Moduli from the biaxial and triaxial tests are compared to explore the range of validity of a inified formulation.
142 citations
TL;DR: In this paper, an energy criterion for crack band extension in concrete with a dense regular reinforcing grid is formulated and it is shown to be objective, i.e., the results for greatly different element sizes cioncide.
Abstract: The propagation of an element-wide blunt smeared crack band in a finite element mesh is analyzed. The results strongly depend on element size; e.g., a four times reduction in element size causes a 3.5 times reduction in the load to cause further crack propagation in a reinforced concrete planel. An energy criterion for crack band extension in concrete with a dense regular reinforcing grid is formulated and it is shown to be objective, i.e., the results for greatly different element sizes cioncide. This is achieved, however, only if bound slip near the crack band is also taken into account. An approximate formula for the lenght of bond slip of the bars crossing the crack band is derived, and for implementation in finite element programs an expression for an equivalent lenght of free bond slip (slip without bond stresses) is determined. The energy criterion is also generalized for nonlinear material behavior numerical results are given.
139 citations
TL;DR: A general conclusion is that DCM provides remarkably accurate descriptions but that even more detailed characterization of microstructure methodologies is essential for extreme circumstances, such as discrete site interaction or dominance of nicrogeometric connectivity.
Abstract: The basis for the estimates is given in the form of an auxiliary solution characterizing the behavior of a single embedded site. Both classical self-consistent methodologies (SCM) and rationalized differential formulations (DCM) are developed, with emphasis on physical realism, applications to polycrystalline and various composite materials (including porous media and plate bending) are compared favorably with many experimental results. Recent attempts to generate effective plasticity/creep models plus estimates of thermal/electrical/pore-fluid transmissivity, are examined critically. A general conclusion is that DCM provides remarkably accurate descriptions but that even more detailed characterization of microstructure methodologies is essential for extreme circumstances, such as discrete site interaction or dominance of nicrogeometric connectivity. Fully numerical simulation may be avoided by specializations of exact integral equations: among these, only the self-consistent approximation and a few isolated second-order estimates have been explored.
129 citations
TL;DR: In this article, an attempt is made to explore the application of fuzzy sets as an alternative or supplementary approach or both, to assess the damage state of existing structures, which can be used to incorporate the experience, intuition and judgment of various experts, who may be willing to verbalize their valuable knowledge in advancing the state of the art of our profession.
Abstract: Important structures are frequently tested and inspected by structural engineers following the occurence of a hazardous event such as a strong-motion earthquake. Usually, voluminous data are obtained from such an inspection. While it is relatively simple to understand various experimental and analytical procedures in the investigation of any particular structure, the complex decision-making process summarizing the many results of such an investigation into a simple concluding statement remains privileged and specialized knowledge for highly qualified structural engineers. In this report, an attempt is made to explore the application of fuzzy sets as an alternative or supplementary approach or both, to assessing the damage state of existing structures. This proposed methodology can be used to incorporate the experience, intuition, and judgment of various experts, who may be willing to verbalize their valuable knowledge in advancing the state of the art of our profession.
108 citations
TL;DR: In this paper, the authors investigated the seismic response of buried pipelines in both lateral and longitudinal directions using a distributed mass model of the pipe and found that the lack of correlation of the seismic excitation can produce high stresses in the pipe.
Abstract: Seismic response of buried pipelines in both lateral and longitudinal directions is investigated theoretically using a distributed-mass model of the pipe. Soil-pipe interaction is accounted for considering complex soil reactions derived for a viscoelastic continuum. Seismic excitation is considered random and partially correlated. The aim of the study is to find out whether this kind of excitation could produce pipe stresses in excess of those calculated under the usual assumption of full correlation of seismic excitation. It appears that the lack of correlation of the seismic excitation can produce high stresses in the pipe. The level of these stresses depends on the degree of correlation of the excitation and its frequency contents. An extensive parametric study clarifies the effects of main factors such as pipe dimensions, soil properties, etc.
96 citations
TL;DR: In this article, a method is presented to obtain seismic design response of linearly behaving structures with non-proportional damping characteristics using state-vector formulation and is based on random virbration priciples.
Abstract: A method is presented to obtain seismic design response of linearly behaving structures with nonproportional damping characteristics. For such systems, time history analyses are usually performed to obtain accurate seismic response. To obtain design response, such procedures can become expensive and cumbersome as an ensemble of time histories may have to be considered as seismic input. Other procedures have been developed to ascertain appropriate values of modal dampings so that modal analysis approach and thus commonly adopted square-root-of-the-sum-of-the-sqaures (SRSS) procedures can be used. The approach presented here considers nonproportional damping effects exactly in analytical sense. It uses state-vector formulation and is based on random virbration priciples. The approach is similar to conventional SRSS approach and thus ground response spectrum can be directly used to obtain designd respose.
75 citations
TL;DR: A review of the basic work done in this field, for the most part in Italy, and may form the basis for further analysis can be found in this article, where the safety factor for dynamic shakedown is examined.
Abstract: The shakedown problem was first formulated for quasi-static actions, i.e., in absence of inertia forces. In the last 10 yr, with reference to dynamic processes, a more general formulation of the problem has been proposed, introducing the concept of dynamic shakedown. Two basic theorems have been stated: the first corresponds to the Bleich-Melan theorem concerning quasi-static actions; the second is a generalization of Koiter’s kinematic theorem. The definition and the methods for determining the safety factor for dynamic shakedown are examined; in the case of periodic actions, linear and nonlinear programming procedures can be formulated. The influence of damping is also considered. The paper is a review of the basic work done in this field, for the most part in Italy, and may form the basis for further analysis.
71 citations
TL;DR: In this paper, an improved endochronic nonlinear triaxial constitutive relation for concrete is developed, in which in addition to plastic strain increments proportional to stress tensor, fracturing strain increments proportion to strain tensor are used to model strain-softening.
Abstract: An improved endochronic nonlinear triaxial constitutive relation for concrete is developed: (1)In addition to plastic strain increments proportional to stress tensor, fracturing strain increments proportional to strain tensor are used to model strain-softening; (2)the plastic and fracturing inelastic strain increments are characterized by different intrinsic times; (3)degradation of the elastic shear modulus is determined by the intrinsic time for the fracturing strain increments, and degradation of the bulk modulus is related to that of the shear modulus using Budianski-O'Connell's expressions for the elastic moduli of randomly microcracked material; (4)jump-kinematic hardening, in which the center of the loading surface jumps into the current stress and strain point whenever loading reverses to unloading or vice versa, is introduced. The theory also exhibits hydrostatic pressure sensitivity, inelastic dilatancy, initial shear compaction in triaxial loading, and inelastic strain due to hydrostatic pressure.
TL;DR: In this article, the optimal control problem is presented either as a regulator problem or as a tracking problem, where the tracking problem is the most suitable design method and provides the best control response but on the account of an increased cost.
Abstract: The optimal control problem is presented either as a regulator problem or as a tracking problem. If feedback control strategy is desired, the regulator problem provides a closed-loop control and the tracking problem provides a combination of closed-loop and open-loop control. Both problems have been applied to the optimal control of a civil engineering structure. It has been shown that if the disturbance is known a priori, then the tracking problem is the most suitable design method and provides the best control response but on the account of an increased cost. On the other hand, the control law provided by the regulator problem does not depend on the type of the disturbance and since it is a closed-loop type, it is considered a suitable means of controlling against uncertain and unexpected disturbances, because it provides the active stiffness and active damping needed to control the structure properly.
TL;DR: In this article, a general numerical method of solution to the transverse normal stress and longitudinal shear stress distributions in the adhesive layers of bonded stiffener plates, double lap joints, and strap joints, all of dissimilar orthotropic adherends, was presented.
Abstract: The paper presents a general numerical method of solution to the transverse normal stress and longitudinal shear stress distributions in the adhesive layers of bonded stiffener plates, double lap joints, and strap joints, all of dissimilar orthotropic adherends. The bending deformations and the transverse shear deformations are included in the analytical model. The present influence of bending deformations of adherends on both the normal and shear stresses in adhesive layers is discussed in detail for practical cases.
TL;DR: In this article, the probability density function of the response amplitude of a lightly damped linear oscillator subjected to a broad-band nonstationary process with evolutionary spectrum is examined.
Abstract: The probability density function of the response amplitude of a lightly damped linear oscillator subjected to a broad-band nonstationary process with evolutionary spectrum is examined. By using a combination of deterministic and stochastic averaging a one-dimensional diffusion equation is obtained that approximately governs the time evolution of the probability density function of the response amplitude. Based on the diffusion equation it is proved that the nonstationary probability density of the response amplitude can be approximated by a Rayleigh distribution with a time dependent scaling variable. An equation for the analytical determination of the scaling variable is presented.
TL;DR: In this paper, the authors study the shearing flow behavior of granular materials, using a theory based on one proposed by Goodman and Cowin in 1971, and present solutions to the equations of motion for the problem of shear flow between two paralled plates.
Abstract: We study the shearing flow behavior of granular materials, using a theory based on one proposed by Goodman and Cowin in 1971. Solutions to the equations of motion are presented for the problem of shear flow between two paralled plates. The results show in some cases the narrow, dilatant shear zones observed experimentally and in certain geological processes.
TL;DR: In this paper, the authors evaluate existing concrete constitutive relations and failure criteria within the context of their use in the numerical analysis of concrete structures and to determine the range of their applicability, relative merits, and limitations and to identify the specific need for further modifications and developments.
Abstract: With the present state of development of computer programs, inadequate material models are often one of the major factors in limiting the capability of structural analysis. This is especially true for concrete where generally accepted constitutive equations do not exist. Nevertheless, there exists a large variety of models which have been proposed in recent years to characterize the stress-strain and failure behavior of concrete materials. All these models have certain inherent advantages and disadvantages which depend to a large degree on their particular application. The objective of this paper is an attempt to evaluate critically these existing concrete constitutive relations and failure criteria within the context of their use in the numerical analysis of concrete structures and to determine the range of their applicability, relative merits, and limitations and to identify the specific need for further modifications and developments.
TL;DR: In this paper, the authors derived first approximation thin shell and higher order thick shell correction theories for nonhomogeneous anisotropic cylindrical elastic shells by use of the method of asymptotic expansion in terms of a small parameter along with Reissner's variational principle.
Abstract: First approximation thin shell and higher order thick shell correction theories are derived for nonhomogeneous anisotropic cylindrical elastic shells by use of the method of asymptotic expansion in terms of a small parameter along with Reissner's variational principle. The advantages of employing the asymptotic method, in addition to its systematic nature, are that no a priori kinematic or static assumptions need be made or both, that trasverse stresses develop naturally (even in the thin shell analysis) and that thick shell theories follow automatically. Use of the combined method generates various theories based upon different combinations of axial and circumferential length scales introduced in the nondimensionalization of the coordinates. The first approximation theories derived herein for anisotropic materials have their counterparts for isotropic materials. They are: (1)Simplified Donnell theory; (2)simple bending theory; (3)semimembrane theory; and (4)complete Donnell theory.
TL;DR: In this paper, a standard HS-20-44 highway vehicle is represented by a planar, two axle, sprung mass system with a frictional device, and the response equations are derived in terms of the natural modal coordinates of the bridge and of displacement coordinates of vehicle.
Abstract: Single span highway bridges of composite construction are idealized as beams as well as an orthotropic plate. A standard HS-20-44 highway vehicle is represented by a planar, two axle, sprung mass system with a frictional device. The response equations are derived in terms of the natural modal coordinates of the bridge and of displacement coordinates of the vehicle. The bridge dynamic loadings due to the initial bounce of the vehicle and in combination with the braking of the vehicle are investigated for symmetric as well as eccentric loading of the vehicle.
TL;DR: Crisp information is defined as countable data for which moments are available which are used as constraints on the information entropy to obtain an unbiased probability distribution.
Abstract: Crisp information is defined as countable data for which moments are available. These moments are then used as constraints on the information entropy to obtain an unbiased probability distribution. In opposition to this objective viewpoint, subjective information in the form of verbal statements are also available. A quantitative statement of these is obtained by fuzzy support measures. This statement has two parts which refer to the gravity of information and its effect on the objective probability. These two parts are then analyzed by fuzzy set theory and established by a fuzzy conditional relation as a modification of the probability. The modification is obtained by a merging process which allows the subjective support for the objective probability to be detected.
TL;DR: In this article, the response of a lightly damped linear structure to a broad-band nonstationary random process with evolutionary spectral density is considered, and a first-order stochastic differential equation governing the time evolution of the structural energy is derived.
Abstract: The response of a lightly damped linear structure to a broad-band nonstationary random process with evolutionary spectral density is considered. A first-order stochastic differential equation governing the time evolution of the structural energy is derived. Utilizing this equation a readily applicable equation for the determination of the mean energy is obtained. Nonstationary random processes proposed in the literature for the simulation of earthquakes are examined in detail, and equations for the construction of probabilistic energy spectra are presented.
TL;DR: In this paper, a rigorous formal general solution is obtained as a Neumann-type series of multiple integrals which contain the statistical information in terms of n-point correlation functions of increasing order n.
Abstract: The basic problem considered concerns the calculation of effective elastic moduli of a random elastic medium such as a polycrystalline aggregate or a disordered composite, given some statistical information about its microstructure. A rigorous formal general solution is obtained as a Neumann-type series of multiple integrals which contain the statistical information in terms of n-point correlation functions of increasing order n. The integrals can be calculated provided the medium is “highly” disordered. To describe the disorder in a quantitative fashion, the concept of graded and perfect (=maximum) disorder is introduced. Rigorous bounds of nth order are derived for the effective elastic moduli of random media which are classified as disordered of grade n. The effective elastic moduli of the perfectly disordered medium concide in rigor with the well-known self-consistent moduli.
TL;DR: In this article, a numerical formulation for a mathematical model of those soil regions bearing flexible embedded structures of arbitrary geometry was presented for soil-structure analysis in seismic design, where the computational difficulties associated with a strict continuum solution for the unbounded foundation domain with an irregular surface geometry, are alleviated by subtracting the impedance contribution of the embedded region from the impedance matrix of a foundation with a horizontal surface.
Abstract: A numerical formulation is presented for a mathematical model of those soil regions bearing flexible embedded structures of arbitrary geometry. The computational difficulties associated with a strict continuum solution for the unbounded foundation domain with an irregular surface geometry, are alleviated by “subtracting” the impedance contribution of the embedded region from the impedance matrix of a foundation with a horizontal surface. The procedure could be utilized for soil-structure analysis in seismic design.
TL;DR: In this paper, the root mean square responses of linear multidegrees-of-freedom system to nonstationary, nonwhite random excitation are computed analytically using the state space formulation.
Abstract: The root mean square responses of linear multidegrees-of-freedom system to nonstationary, nonwhite random excitation are computed analytically using the state space formulation. Each modal equation is augmented by a filter and the augmented system is driven by evolutionary white noise. Analytical expressions for the evolutionary covariance matrix of the augmented system are given. Modal RMS responses are then superposed to obtain the desired responses; all cross-correlation terms among modes are included. Nonstationary responses are computed for a four-degree-of-freedom system. The effects of nonstationary and nonwhiteness are quantified and examined. Responses are compared with those obtained by using an unfiltered formulation with different white noise intensities driving the modes.
TL;DR: In this paper, it was shown that freestream turbulence has profound effects on the galloping behavior of a square tower and that fine-scale turbulence produced by a thin rod upstream of the stagnation streamline of the tower is sufficient to cause these effects.
Abstract: Galloping is the term used to describe large amplitude single degree-of-freedom motions of a structure associated with a sectional aerodynamic force characteristic which produces a force in the direction of and in phase with the cross-wind motion. Detailed experimental investigations show that freestream turbulence has profound effects on the galloping behavior of a square tower. It is generally believed that increase in freestream turbulence increases the turbulence mixing in the separated shear layers and the rate of entrainment from the wake, and decreases the radius of curvature of the shear layers. These effects significantly alter the transverse force characteristic and thus the galloping behavior of the tower. It is also shown that the fine-scale turbulence produced by a thin rod upstream of the stagnation streamline of the tower is sufficient to cause these effects.
TL;DR: In this article, the nonlinear triaxial behavior of plane concrete that is free of continuous cracks is modeled by an algebraic relation between total strains and stresses, analogous to deformation theory of plasticity.
Abstract: The nonlinear triaxial behavior of plane concrete that is free of continuous cracks is modeled by an algebraic relation between total strains and stresses, analogous to deformation theory of plasticity. Unloading is not modeled. Good agreement with numerous test data is achieved. The formulation implies algebraic expressions for failure envelopes and some stress-strain curves, which make data fitting easier. The model is enhanced by corrective path-dependent terms that vanish for proportional loading so as extend it for highly nonproportional loading. The principal directions of stress and strain then cease to coincide. In contrast to previous models, the present one applies to much largest atrains, gives the peak stress points, failure envelopes, strain softening, inelastic dilatancy, etc. A tangential incremental form for structural analysis is also indicated.
TL;DR: In this article, it was shown that a slightly modified form of the rigid-plastic yield-vertex model for geological materials will contain as a special case both the rigid and non-workhardening forms of the yield-vertices model and the sliding deformation model.
Abstract: It is shown in this paper that a slightly modified form of the rigid-plastic yield-vertex model for geological materials will contain as a special case both the rigid-plastic form of the yield-vertex model and the sliding deformation model. This result is interesting because the yield-vertex model is a prefailure model and the sliding deformation model is a post-failure model. The specific result of interest is that, if the two pairs of localization directions in the nonwork-hardening form of the rigid-plastic yield-vertex model coincide, then the continued deformation in the post-failure regime is that hypothesized in the sliding deformation model. The analysis is confined to two dimensions.
TL;DR: In this paper, simple analytical formulas are presented for approximate computation of the first-passage probabilities for the random response of a linear single-degree-of-freedom system, where the response is taken to be zero-start and the excitation is stationary white noise with a normal probability distribution.
Abstract: Simple analytical formulas are presented for approximate computation of the first-passage probabilities for the random response of a linear single-degree-of-freedom system. The response is taken to be zero-start and the excitation is stationary white noise with a normal probability distribution. Both small-time (nonstationary) and large-time (stationary) responses are included. Certain attractive existing approximate procedures are shown to be sometimes very significantly in error. The new formulas to compute the two parameters of the stationary problem are based on empirical data and the results of an existing approximate procedure which is quite accurate but cumbersome to use. Given the parameters of the stationary problem, a simple procedure is presented for accurately approximating the nonstationary behavior. The limitation on the approximate results is that they do not apply if the crossing level is smaller than the root mean square value of the stationary response.
TL;DR: In this paper, the complex moisture and heat exchange process over the ocean was studied as a strongly coupled system of momentum, heat, moisture, and microwater droplets, which can be naturally explained through the latent heat of evaporation of microwave droplets produced by the breaking waves.
Abstract: The complex moisture and heat exchange process over the ocean was studied as a strongly coupled system of momentum, heat, moisture, and microwater droplets. Many unusual temperature profiles observed over the ocean can be naturally explained through the latent heat of evaporation of microwater droplets produced by the breaking waves. It is hoped that this preliminary analysis will lead to a better understanding of the complex sea-air interface and provide a more accurate means for estimating the rate of evaporation and heat transfer over large bodies of water.
TL;DR: Using a simple structural model which consists of a massless column supporting a concentrated mass at the top, it was shown that the vertical ground motion in an earthquake can amplify the power of the horizontal ground motion, and cause greater horizontal structural displacement response as mentioned in this paper.
Abstract: Using a simple structural model which consists of a massless column supporting a concentrated mass at the top, it is shown that the vertical ground motion in an earthquake can amplify the power of the horizontal ground motion, and cause greater horizontal structural displacement response Furthermore, this amplification effect is greater for greater initial response; ie, the response initally computed without taking the vertical excitation into consideration Although the present analysis is based on a linear structural model, numerical computations have included large deflections so that the general trend can become more visible, and the results so obtained can provide useful guides for future investigation into the nonlinear inelastic regimes
TL;DR: In this paper, the stability of elastic structures under multiple independent loads is examined in terms of stability boundaries, which separate regions of stable and unstable load combinations in the load space, and the convexity properties of these stability boundaries are discussed in general, both for linear and nonlinear systems.
Abstract: The stability of elastic structures under multiple independent loads is considered Interaction effects of the independent loading parameters are examined in terms of stability boundaries, which separate regions of stable and unstable load combinations in the load space The convexity properties of these stability boundaries are discussed in general, both for linear and nonlinear systems A reticulated dome subjected to vertical loads is then analyzed numerically The dome exhibits nonlinear prebuckling deformations Static perturbation and nonlinear programming methods are utilized to compute buckling loads Results are presented for two and three independent load configurations, and the characteristics of the stability boundaries are discussed Finally, the interactions for the reticulated dome are compared to those for shallow arches