Journal of Engineering Mechanics

This paper formulates the derivative of buckling load with respect to intermediate constraint locations. These intermediate constraints include intermediate spring supports and pinned supports. The analysis is based on the generalized energy functional, which includes the product of Lagrange multipliers and boundary conditions. The results show that the derivative of buckling load with respect to the constraint position is proportional to the force between the constraint and the structure as well as to the spatial slope of the associated buckling mode at the constraint position. With the combination of this derivative formula and the Courant maximum-minimum principle, an interesting theorem on the optimal constraint position is proposed.

An experimental and analytical study on pore-water pressure occurring in the prepeak region of concrete due to the external load is performed to investigate the mechanism of water migration in concrete. In the experiment, an apparatus is developed that can measure the pore-water pressure in concrete under fixed lateral displacement. Concrete strain, stress, and pore-water pressure are measured; the experimental parameters are the loading age and water curing period. The effects of each parameter on pore-water pressure generation are discussed. The pore-water pressure occurring in the prepeak region of concrete can be measured due to the development of a cell that is imitated to be completely fixed for the lateral displacement and undrained condition for pore water. The ratio of pore-water pressure to concrete stress is very high. The existence of the inflection point means that negative pore-water pressure exists in the voids formed by the hydration reaction during a curing period.

An experimental and analytical study on pore-water pressure occurring in the postpeak region of concrete due to the external load is performed to investigate the mechanism of water migration in concrete. In the experiment, an apparatus is developed that can measure the pore-water pressure in concrete under the control of lateral pressure. Concrete strain, stress, and pore-water pressure are measured; the experimental parameters are the loading age, lateral pressure, and curing method. The effects of each parameter on pore-water pressure generation are discussed. Further, the main factor that influenced the pore-water pressure is investigated. As a result, it becomes possible to measure the pore-water pressure occurring in concrete under the arbitrary stress state due to the development of a cell that imitates the triaxial, almost undrained condition. The pore-water pressure occurring in concrete due to the external load divides the high rate compared with the concrete stress. In the prepeak region, i.e., volumetric contraction of concrete, the positive pore-water pressure increment occurs, while in the postpeak region, i.e., volumetric expansion of concrete, the negative pore-water pressure increment occurs.

This study deals with the capabilities of artificial neural networks in learning to control water towers of different structural properties that are subjected to earthquakes. To this end, water towers were considered as single-degree-of-freedom systems. First, a number of water towers of different structural properties were controlled by the predictive optimal control method, and then the data collected through this control were used in the training of a general neural network controller, called the general neurocontroller. Capabilities of the general neurocontroller were tested in the control of a number of water towers with structural parameters different from, but in the range of, those used in its training. One of the aims of this study was the introduction of general neurocontrollers as ready-to-use devices that may be used in the design of actively controlled structures, in this case, water towers. Results of this numerical study were promising.

Physically based analytical models capable of describing the behavior of general bilinear hysteretic systems are formulated. The formulation includes the effects of pinching, stiffness degradation, and load deterioration. The type of pinching considered is the one due to unequalness of strengths for loading in opposite directions. This pinching is represented in terms of a strength ratio. Stiffness degradation and load deterioration are described in terms of functions of total absorbed hysteretic energy. All of the system parameters are in terms of definite physical materials or system properties, which can be measured through tests. To show that the proposed analytical model can provide realistic descriptions of the performance of multi-degree-of-freedom systems, examples of a three-degree-of-freedom system subjected to harmonic loads as well as blast loads are presented.

The macrostructure of a granular material is treated as an ensemble of microstates of like spheres where each microstate is identified by a coordination number and a corresponding porosity. The probability of occurrence of these finite numbers of microstates is constrained by measurable information concerning the macrostate and described by maximizing the information entropy subject to these constraints and the axioms of probability theory. The macrostate behavior is then deduced from the probabilities of occurrence of the microstates and their mechanical performance. Existing observations of phenomena in granular media as related to soils and liquids are discussed and explained in light of the proposed entropy maximization scheme. Critical tests to examine the viability of the entropy model are proposed.

Experiments on circular disks supported on a horizontal air table and enclosed in an initially square frame that provides simple shear, constant area, and constant pressure external conditions are reported. Each test was performed on disks of one size; disks of 2.54, 1.27, and 0.64 cm (1, 1/2, and 1/4 in.) diameter were used. The excitation of the system was caused by changing the angle of the frame either monotonically or side to side. The arrangements of the disks were photographed from above at various stages in each experiment. Twenty-one experiments were conducted in which the initial state of the disks, the disk size, the friction between the table and disks, and the external conditions were altered. The number of contacts for each disk was counted, and the frequency of occurrence of states with the same number of contacts was obtained. Similarly, the number of disks about each void was counted, and the frequency of each number was determined. These two counts allowed the contact and void entropies to be calculated. The presentation of these entropies showed that they approached limiting values as excitation increased and that the values depended on the external conditions and not on the friction condition. The behavior of the arrays was random and not chaotic. These results supported the use of information entropy in the geometric description of granular materials and the validity of Jaynes's maximum entropy procedures.

The aim of this work is to investigate the behavior of a 96-m-high gravity dam (the prototype) with a preexisting crack. For this purpose, four different gravity dam models were simulated through the cohesive crack model in mixed-mode conditions. Three of the models (1:40, 1:100, and 1:150 scale) were tested under equivalent dead-weight and hydraulic loads. To obtain correct dead-weight scale ratios, the laboratory tests were performed in an artificial gravity field produced by a system of additional vertical forces and by using a centrifuge. The initial notch in the upstream face served as the starting point of a crack that propagated toward the foundation during the loading process. The structural response and the crack trajectories were reproduced satisfactorily by the cohesive crack model. The behavior of the prototype is discussed on the basis of the behavior of the models.

A predictive optimal control algorithm based on auto-regressive moving average (ARMA) models has been developed. Being a closed loop algorithm, it can be used in the control of structures against any source of random excitation without any special arrangement for measuring the excitation. The algorithm combines two mathematical models: (1) An ARMA model representing the environment and the structure as a single system subjected to the unknown random excitation; and (2) a single-degree-of-freedom system, which represents the structure subjected to a known history of control force only. Unlike some ARMA based control algorithms, which are only for seismic excitations, the proposed algorithm permits the control system to be operational under any type of dynamic load. This results in a large reduction in the standby time of the control system and increases its reliability. In comparison with these algorithms, the proposed algorithm requires less measurements and sensors. The algorithm has the option for reducing or avoiding time delay.

In the field of structural engineering, various analytical procedures have been developed for the analysis of nonlinear structural systems subjected to random dynamic loading. To date, the Monte Carlo simulation (MCS) seems to be the most generally applicable approach for the reliability analysis of large nonlinear multi-degree-of-freedom systems. In this paper, a method that allows for reduction of the computational effort when using the MCS method is presented. First, the method requires the application of digital or analytical techniques (such as equivalent linearization) to obtain the response covariance matrix. Then, by means of the well-known Karhunen-Loéve expansion, the dimension of the system is reduced and MCS is applied. Moreover, in the transformed space the variables with smaller variance are approximated by Gaussian variables. It is shown that this technique allows for a considerable reduction of the computational effort without a significant loss of accuracy. As numerical examples, a 9-degree-of-freedom hysteretic structure and a conservative system (i.e., a 10-degree-of-freedom Duffing structure), respectively, are examined.

The modeling of deteriorating hysteretic behavior is becoming increasingly important, especially in the context of seismic analysis and design. This paper presents the development of a versatile smooth hysteretic model based on internal variables, with stiffness and strength deterioration and with pinching characteristics. The theoretical background, development, and implementation of the model are discussed. Examples are shown to illustrate the features of the model. Many inelastic constitutive models in popular use have been developed independently of each other based on different behavioral, physical, or mathematical motivations. This paper attempts to unify the concepts underlying such models. Such a holistic understanding is essential to realize limitations in application of inelastic models and to extend 1D models to 3D models featuring interaction between various stress resultants.

In this paper, an analytical investigation is made of the frictional damping properties of axially loaded metallic cables made from one layer of wires helically wrapped around a central wire. Our efforts are focused on the quantity of energy dissipated through friction due to the motions between wires when a cable is loaded. Although the local interwire pivoting drives the response of the cables studied, a first linear model is built where pivoting is allowed, but friction is not taken into account. Then, a law of friction is established and linearized to extend the linear model into a tractable piecewise linear hysteretic one. Through a variety of examples, it appears that the energy dissipated in friction over a load cycle is very small compared to other sources of dissipation, because axially loaded simple straight strands do not experience fretting-induced failures, except close to terminations. It is also shown that modifying the design of such cables is not expected to significantly improve their damping properties.

Analytical solutions are obtained for the interior and edge-zone equations of Mindlin-Reissner plate theory in bending of composite circular sector plates laminated of transversely isotropic layers. Circular sector laminates, under various boundary conditions, are considered. It is shown that, depending on the boundary conditions of the laminate, the boundary-layer effect on the response quantities of the laminate will be strong, weak, or nonexistent.

A series solution approach based on the complex Bessel functions is presented in this paper for the analysis of bending of annual sector plates that are simply supported along their straight (or radial) edges, resting on Winkler-type elastic foundations. After a real general solution to a homogeneous differential equation of the bending plates is derived from the complex Bessel functions, the solution to the nonhomogeneous differential equation may be formulated by the general solution. Finally, some numerical examples are given to show the feasibility of this approach.

A sensitivity- and statistical-based method to localize structural damage by direct use of incomplete mode shapes is presented. The method is an extension of the multiple damage location assurance criterion (MDLAC), developed by Messina et al. by using incomplete mode shape instead of modal frequency. This approach makes use of the good sensitivity of mode shape to local damage. The damage detection strategy is to localize the damage sites first by using incomplete measured mode shapes, and then to detect the damage site and extent again by using measured natural frequencies, which have a better accuracy than mode shapes. A plane truss structure is analyzed as a numerical example to compare the performance of the proposed method with the multiple damage location assurance criterion. Results indicate that the new method is more accurate and robust in damage localization with or without noise effect.