General Structural Systems Research Articles

Optimum design of tuned mass damper with pinched hysteresis under nonstationary stochastic seismic ground motion

The optimum design of a recent tuned mass damper with pinched hysteresis (TMD-PH) for seismic protection of structures is here investigated. The considered device consists of mixed NiTiNOL-steel wire ropes undergoing combined tension-flexure cycles. Previous studies demonstrated that concurrent interwire friction and phase transformation of the shape memory material exhibited by these composite wire ropes generate a peculiar pinched hysteretic behavior, which can be well described by means of a modified Bouc–Wen model. A stochastic-based optimum design methodology is here proposed for such TMD-PH, which is tailored to determine the best design parameters for the seismic protection of general structural systems. The seismic ground motion is modeled as a filtered nonstationary random process whereas the inherent pinched hysteresis of the device is dealt with via the stochastic linearization technique. The expressions of the linearization coefficients are obtained ad hoc and the optimum design of the TMD-PH is formulated as box-constrained single-objective optimization problem. Three objective function formulations are considered to reflect alternative design philosophies, namely, displacement-, acceleration- and energy-based design strategies. Unlike most literature studies addressing the optimum design of vibration absorbers via finite difference-based numerical schemes or non-gradient-based metaheuristic methods, the search for the optimal parameters of the TMD-PH is here performed by means of an iterative semi-analytical gradient-based numerical technique in which the derivatives for the covariance matrix of the system response are calculated analytically. A comprehensive numerical campaign is finally presented. First, a parametric study is carried out to evaluate the effects of the protected system characteristics and those of the seismic ground motion duration on the optimal parameters and performance of the device under consideration. The performance of the TMD-PH optimized according to the proposed methodology is also assessed in the context of a practical case study which makes use of synthetic and natural seismic ground motion records.

A Case Study from Istanbul’s Westernization Period: The Technical Documentation of Prinkipo Palace

ABSTRACT The deterioration and the consequent collapse of historic timber structures lead to a significant loss of knowledge transfer of local construction methods and building technics. In this article, based on a case study of an exceptional timber frame structure in Istanbul dating from the end of the 19th century, is an attempt to provide documentation on the structure and materials of the specific building. The main objective is to underline the general structural system and materials as a reference. The case study covers the traditional characteristics such as local timber framework techniques and features of the transition era in construction and materials, with industrialized and standardized construction members.

Improvement of the estimation method of the possibility of progressive destruction of buildings caused by fire

With the progressive destruction of building structures, socioeconomic losses reach the biggest level, especially when the buildings have a high degree of responsibility. For such buildings there is a standardized requirement to carry out a calculated estimation of the possibility of progressive destruction. The article outlines the main provisions of the calculation method as to the estimation of the possibility of progressive destruction, with the failure of one or more compressed elements, that must be removed from the general structural system of the building frame consisting of steel beams, CFST and reinforced concrete columns. The basic principle of the method is the hypothesis about formation plastic joints in beams and columns. The possibility of progressive destruction is estimated according to the energy criterion based on comparison of the work of internal and external forces on the possible displacements of the system, which in such conditions is geometrically variable. The proposed method is productive and cost-effective compared to existing methods that involve complex mathematical models and software complexes.

Identification of average effects under magnitude and sign restrictions on confounding

This paper studies measuring various average effects of X on Y in general structural systems with unobserved confounders U, a potential instrument Z, and a proxy W for U. We do not require X or Z to be exogenous given the covariates or W to be a perfect one‐to‐one mapping of U. We study the identification of coefficients in linear structures as well as covariate‐conditioned average nonparametric discrete and marginal effects (e.g., average treatment effect on the treated), and local and marginal treatment effects. First, we characterize the bias, due to the omitted variables U, of (nonparametric) regression and instrumental variables estimands, thereby generalizing the classic linear regression omitted variable bias formula. We then study the identification of the average effects of X on Y when U may statistically depend on X and Z. These average effects are point identified if the average direct effect of U on Y is zero, in which case exogeneity holds, or if W is a perfect proxy, in which case the ratio (contrast) of the average direct effect of U on Y to the average effect of U on W is also identified. More generally, restricting how the average direct effect of U on Y compares in magnitude and/or sign to the average effect of U on W can partially identify the average effects of X on Y. These restrictions on confounding are weaker than requiring benchmark assumptions, such as exogeneity or a perfect proxy, and enable a sensitivity analysis. After discussing estimation and inference, we apply this framework to study earnings equations.

Applications of higher-order frequency response functions to the detection and damage assessment of general structural systems with breathing cracks

Two types of cracks are often encountered in engineering structural systems and these are the open cracks and the breathing cracks. Existence of open cracks often leads to the loss of physical stiffness, resulting in a mostly linear structure with reduced load bearing capacity and vibration frequencies. The development of breathing cracks not only reduces structural stiffness, but tends to render the otherwise linear structure to become nonlinear, due to their bilinear stiffness characteristics associated with open and closed states. The nonlinear structural vibration responses can then be investigated and potentially employed to detect and identify breathing cracks within a structural system. In the present study, breathing cracks are modeled based on fracture mechanics from which bilinear stiffness values are obtained. These values are then incorporated into finite element models to compute the first- and second-order frequency response functions (FRFs) based on a proposed correlation technique which is both very accurate and resilient against measurement uncertainties. The existence of well-defined second-order FRFs has been firmly established for the bilinear oscillator, as well as a cantilevered beam with breathing cracks. By expressing the bilinear restoring force as a polynomial series, analytical derivation of second-order FRFs of general structural systems such as the GARTEUR AG11 structure with breathing cracks has been established for the first time. Further, a method of identification has been developed to identify the physical parameters of breathing cracks using second-order FRFs. With these new developments that are presented in this paper, a solid foundation has been laid for the potential applications of higher-order FRFs to damage identification and assessment of general real structural systems.

Identification of Average Effects Under Magnitude and Sign Restrictions on Confounding

This paper studies measuring various average effects of X on Y in general structural systems with unobserved confounders U, a potential instrument Z, and a proxy W for U. We do not require X or Z to be exogenous given the covariates or W to be a perfect one-to-one mapping of U. We study the identification of covariate-conditioned average random coefficients, average nonparametric discrete and marginal effects, average treatment effects for the population, treated, and untreated, and local and marginal treatment effects. First, we characterize the bias, due to the omitted variables U, of (nonparametric) regression and instrumental variables estimands, thereby generalizing the classic linear regression omitted variable bias formula. We then study the identification of the average effects of X on Y when U may statistically depend on X and Z. These average effects are point identified if the average direct effect of U on Y is zero, in which case exogeneity holds, or if W is a perfect proxy, in which case the ratio (contrast) of the average direct effect of U on Y to the average effect of U on W is also identified. More generally, restricting how the average direct effect of U on Y compares in magnitude and/or sign to the average effect of U on W can partially identify the average effects of X on Y. These restrictions on confounding are weaker than requiring benchmark assumptions, such as exogeneity or a perfect proxy, and enable a sensitivity analysis. After discussing estimation and inference, we apply this framework to study earning equations and production functions.

Simultaneous optimal design of the structural model for the semi-active control design and the model-based semi-active control

SUMMARY Various semi-active control methods have been proposed for vibration control of civil structures. In contrast to active vibration control systems, all semi-active control systems are essentially asymptotically stable because of the stability of general structural systems with structural damping and the energy dissipative nature of the semi-active control itself. In this study, by utilizing the aforementioned property on the stability of semi-active control systems, a structural model for the semi-active control design and a model-based semi-active control law are simultaneously designed so that the control performance of the resulting semi-active control system becomes good. The model for the control system design is assumed to be a linear parameter varying model with adjustable structural design parameters. The semi-active control law is based on the one step ahead prediction of the structural response of the designed model for the control system design. A genetic algorithm is adopted to obtain design parameters in the model for the control system design and the semi-active control law. Those design parameters are optimized so that the closed-loop system with the detailed dynamic model that accurately approximates the dynamic behavior of the real structural system and the semi-active control law obtained with the model for the control system design. The effectiveness of the present approach is shown with a simulation study. Copyright © 2013 John Wiley & Sons, Ltd.

A one‐dimensional lumped parameter model representing impedance functions in general structural systems with proportional damping

SUMMARYThis paper presents a one‐dimensional lumped parameter model (LPM) that accurately represents the impedance function between two nodes arbitrarily selected in general linear structural systems having proportional damping. Through a procedure based on the modal analysis, the impedance function can be transformed into an equivalent LPM consisting of units arranged in series, with each unit consisting of a spring, a dashpot, and a so‐called gyro mass element arranged in parallel. The gyro mass element generates a reaction force proportional to the relative acceleration of the nodes between where it is placed. Three application examples show that the LPMs accurately simulate the impedance functions in a mass–spring structure, a truss frame structure, and a cantilever plate. For a more efficient representation, a large number of units associated with high‐order modes in the high‐frequency region can be removed from the proposed gyro mass LPM (GLPM) as an approximation of the impedance functions in a target frequency region. The accuracy of the approximated GLPMs is improved by incorporating an additional unit associated with residual stiffness. This approximation greatly reduces the number of degrees of freedom of the GLPMs so that a marked decrease in the computational domain size and time can be expected for solving dynamic problems. Copyright © 2011 John Wiley & Sons, Ltd.

Equivalent One-Dimensional Spring-Dashpot System Representing Impedance Functions of Structural Systems with Non-Classical Damping

This paper describes the transformation of impedance functions in general structural systems with non-classical damping into a one-dimensional spring-dashpot system (1DSD). A transformation procedure based on complex modal analysis is proposed, where the impedance function is transformed into a 1DSD comprising units arranged in series. Each unit is a parallel system composed of a spring, a dashpot, and a unit having a spring and a dashpot arranged in series. Three application examples are presented to verify the applicability of the proposed procedure and the accuracy of the 1DSDs. The results indicate that the 1DSDs accurately simulate the impedance functions for a spring-dashpot-mass structure, a truss frame structure, and a plate structure. The 1DSD transformation offers compatibility with complex modal analysis: a large number of units associated with high modes beyond a target frequency region can be removed from the 1DSDs as an approximate expression of impedance functions. The accuracy of the approximated 1DSDs can be improved by incorporating an additional unit associated with the residual stiffness that compensates for the effect of high modes. A marked decrease in the computational domain size and time with the use of the 1DSDs is of great scientific and engineering importance in diverse technological applications.

DEVELOPMENT OF 3D ELASTODYNAMIC INFINITE ELEMENTS FOR SOIL-STRUCTURE INTERACTION PROBLEMS

This paper presents three-dimensional (3D) infinite elements for the multi-layered elastodynamics problems. There are three types of elements, namely horizontal, vertical and corner elements. They have been developed using wave functions in function spaces that can simulate real wave problems properly. The elements are extended forms of the axisymmetric infinite elements developed previously. Since these elements can simulate multiple layers and multiple wave numbers, the response of a 3D general structural system considering soil-structure interaction effect can be determined effectively. Numerical analyses are carried out for a rigid massless disk and square footings on the surface of various layer conditions for verification purposes. The calculated results are compared with existing analytical and numerical data and they were found to be in good agreement.

Bounds on System Reliability by Linear Programming

Bounds on system probability in terms of marginal or joint component probabilities are of interest when exact solutions cannot be obtained. Currently, bounding formulas employing unicomponent probabilities are available for series and parallel systems, and formulas employing bi- and higher-order component probabilities are available for series systems. No theoretical formulas exist for general systems. It is shown in this paper that linear programming ~LP! can be used to compute bounds for any system for any level of information available on the component probabilities. Unlike the theoretical bicomponent and higher-order bounds, the LP bounds are independent of the ordering of the components and are guaranteed to produce the narrowest possible bounds for the given information. Furthermore, the LP bounds can incorporate any type of information, including an incomplete set of component probabilities or inequality constraints on component probabilities. Numerical examples involving series, parallel and general structural systems are used to demon- strate the methodology.

Structural optimal design of systems with imprecise properties: a possibilistic approach

The optimization problem of structural systems with imprecise properties on the basis of a possibilistic approach is considered. System imprecisions are defined by fuzzy numbers and characterized by membership functions. A methodology for the efficient solution of the optimization process is presented. A two-step method is used to include the imprecision within the optimization, where high quality approximations are used for the evaluation of structural responses. The approximations are constructed using concepts of intermediate response quantities and intermediate variables. The approach is basically an algebraic process which can be implemented very efficiently for the optimal design of general structural systems with imprecise parameters. The method provides more information to the designer than is available using conventional design tools. The effectiveness of the methodology and the interpretation of the results are illustrated by the solution of two example problems.

Fundamentals of Beam Bracing

The purpose of this paper is to provide a fairly comprehensive view of the subject of beam stability bracing. Factors that affect bracing requirements will be discussed and design methods proposed which are illustrated by design examples. The design examples emphasize simplicity. Before going into specific topics related to beam bracing, some important concepts developed for column bracing by Winter (1960) will be presented because these concepts will be extended to beams later. Two general structural systems are available for bracing beams, lateral systems and torsional systems. Torsional bracing is less sensitive than lateral bracing to conditions such as top flange loading, brace location, and number of braces, but more affected by cross-section distortion. In the 1999 AISC-LRFD Specification (AISC, 1999), stability bracing requirements are specified for the first time for frames, columns, and beams. The research and recommendations presented in this paper provide a background and commentary for the beam bracing provisions that were adopted in that Specification.

Bounded-state active control of structures: a set-theoretic approach

The paper presents some results from the application of a set-theoretic bounded-state control strategy to active structural control problems. This particular control strategy, never before applied to structural problems, has many features that are very suited for structural control: among them, the possibility of prescribing and guaranteeing exact bounds on the state and on the control forces, while taking into account the uncertainty on the external forces (in a nonprobabilistic way). After a brief presentation of the control strategy, two examples are discussed, showing the applicability of the proposed control strategy to general structural systems. The interpretation of the results throws light on some limitations of the original approach, and suggests possible extensions of the concept, in view of the application to real problems.

Efficient vibration analysis of general structural systems

An efficient numerical method is described to solve the quadratic eigenvalue problems arising in the dynamic analysis of general structural systems. The method uses a special set of trial vectors to reduce a large eigenvalue problem to a much smaller one. The reduced eigenvalue problem is solved and the solutions are used to construct approximate solutions to the original problem. In the process, the method takes full advantage of the sparseness and symmetry of the system matrices and requires no complex arithmetic, therefore making it very economical for solving large-sized problems.

CONSTRAINTS ON SYSTEMIC TRANSFORMATION AND THEIR POLICY IMPLICATIONS

The purpose of this paper is to provide a general framework for more detailed presentations of the microand macro-economics of the transition of former centrally planned economies under commu nist party states to political democracies and mar ket-oriented economies. Section II describes the problem of the generally disappointing pace and course of transition. Some possible sources of the problem are that sectoral policies might have been decided in too narrow an analytical framework or might have overlooked some significant structural and system constraints on the societies under tran sition. Section III enumerates the main subsets of a structural system which is the target of specific policies formulated for the transition. These sub sets refer to the different ways in which actors in societies interact and for the most part correspond to different areas of expertise, each with its own specialists often making recommendations in isola tion. Section IV describes the typical state of the general structural system of a country in Central or Eastern Europe as a consequence of the last years of communist government and the first year of transi tion. This condition is described as a collection of interacting disequilibria, which are set into motion by the withdrawal of communist authority. Section V describes the main elements of economic policies in the transition, as well as the evidence of the problems of implementing them. Section VI con siders the specific political and moral or value circumstances in which economic policies of tran sition are being decided and executed. Additional constraints on economic policies are identified here. In section VII, the conclusion, consideration is given to the possibility of viewing the political constraints on economic policies as part of an optimum policy design. This appears to be a diffi cult task indeed, yet what now seem to be impeding the transformation of economic institutions are increasingly constraining political conditions.

Use of Lanczos Algorithm in Elastic Stability

The Lanczos algorithm is applied to the eigenvalue problems of elastic stability, wherein the geometric stiffness matrix is used to describe the effect of the stress resultants. This matrix need not be positive or positive definite for a general structural system. Despite this fact, it is found that a simple algorithm, without the use of sophisticated convergence criteria and its concomitant programming, can be employed in stability computations. Even though the procedure exhibits an unusual convergence pattern, it can solve for the important buckling loads without the use of any a priori assumptions concerning the eigenvalues or eigenvectors. The simple algorithm can also be applied to dynamic eigenvalue problems but, as the example considered herein demonstrates, it may not be efficient in computing all required eigenvalues for a given frequency range.

Nonlinear spectral characteristics of large deformation elasticity theory

This paper investigates the spectral properties of general structural systems undergoing large elastic deformations. The governing field equations used in the analysis consist of large deformation elasticity theory wherein the Hookes type constitutive law is defined in terms of the second Piola-Kirchhoff stress and Lagrangian strain tensor combination. Due to the generality of the approach taken, the effects of external loading fields containing a perfusion of harmonics can be handled. In this context, special emphasis is given to ascertaining the various forms of sub/super and combination type harmonics. Overall a wide range of combination behavior is considered. This includes mixed interactions between external harmonics and the various system spectra. Special emphasis is given to dealing with cross talk which may occur between all the various participating system spectral branches.

4 本柱立体骨組の弾塑性挙動に関する実験的研究 : 低層鉄骨造骨組の耐震性に関する研究・その 2

The experimental study was made on the three dimensional elasto-plastic behavior of space frames consisted of two rigid frames in one direction and two tensile braced frames in the other direction which are general structural system of low steel structures. Test specimens were one story-one bay space frames constructed with four columns and four beams of H-shaped members and with four tensile braces of round steels, and were tested under horizontally loading combined with axial load. From these experimental results, the following difference of the elasto-plastic behavior of space frames from plane frames were clarified. 1. Additional axial force in columns caused by deformation of braced frames makes the difference to the restoring forces of two parallel rigid frames, and torsion of frame is accumulated with repetition of loading cycles. 2. The maximum restoring force and plastic deformation capacity in direction of strong axis of H-shaped columns decrease under the influence of the deformation of columns in direction of weak axis.