International Journal of Structural Stability and Dynamics

To implement a safe and reliable design for high-tech industrial buildings, the system response should be accurate enough to include the effect of soil–structure interaction (SSI). This study proposed a simplified building–soil system to analyze the dynamic responses, using parameters that are representative of the practical design values for typical semiconductor fab structures in Taiwan. The responses of the simplified building–soil system subjected to dynamic horizontal loadings are verified in the frequency domain and time domain. The dynamic responses of the simplified building–soil system are found to agree very well with those of the complete system obtained by the half-space theory and by the numerical analysis program. It is shown that the proposed simplified system can effectively analyze the coupled SSI effects in the translational and rotational directions. It is also found that the structural responses may deviate significantly by neglecting the coupling of horizontal and rocking motions as the building has a deeper embedded foundation and a stiffer upper structure. The proposed method can be applied to the vibration analysis of high-tech industrial buildings subjected to dynamic loadings.

Wire loop resistance is critical for microelectronic packaging because it directly influences the reliability of the product. Proposed herein is an effective method for predicting the resistance of a wire loop. A finite element (FE) model is developed for verifying the method. The wire geometry is modeled based on actual wire profiles captured with a high-speed camera. Based on this model, the effects of wire properties, residual stresses, loop shape and loop type on the wire loop resistance are studied. Simulations demonstrated that the shape of the loop could dramatically alter the wire loop resistance. On the other hand, the wire properties, residual stresses and loop type mildly affect the wire loop resistance. The standard loop is the more resistant loop than the N and M loops. By using a large and hard wire, moderately tensioning the wire loop and reducing the loop span, height and number of kinks, one can improve the wire loop resistance. This study should provide useful insights into loop design for modern microelectronic packaging.

Earthquake causes wide and severe damage to building structures, due to not just the great ground motion but also secondary actions, such as impact, blast or fire, occurring after earthquake. The extreme combined loading scenario should be considered for safety of buildings and lives. Taking fire for example, the combined load can be considered as an event in which the structures are first partially damaged under an earthquake and then attacked by fire. In order to investigate the post-earthquake loading scenario, it is important to assess the partial damage caused by earthquake on different components of structures. The behavior of welded steel I-beam to hollow square tubular columns is investigated herein. A detailed experimental study is presented in which two groups of unstiffened welded steel connections, with the same configurations, subjected to static and cyclic loading are considered. The flexibility and strength of the connections are measured, while the damage phenomena and failure modes are explored during the tests. The connection damage is found to be a cumulative fracture developing process which leads to significant gradual degradation of the mechanical properties of the connection. The quantificational evaluations of the cyclic loading induced damage are also carried out to investigate the connection damage level according to different loading intensities. A finite element modeling numerical study is also carried out to validate the experimental results and a good agreement is achieved. The test results and FE modeling provide a benchmark data for the unstiffened welded connections and can be used for further investigations of the connections subjected to combined actions such as post-earthquake fire.

Using the convex model approach, the bounds of uncertain variables are only required rather than the precise probability distributions, based on which it can be made possible to conduct the reliability analysis for many complex engineering problems with limited information. This paper aims to develop a novel nonprobabilistic reliability solution method for structures with interval uncertainty variables. In order to explore the entire domain represented by interval variables, an enhanced optimal Latin hypercube sampling (EOLHS) is used to reduce the computational effort considerably. Through the proposed method, the safety degree of a structure with convex modal uncertainty can be quantitatively evaluated. More importantly, this method can be used to deal with any general problems with nonlinear and black-box performance functions. By introducing the suggested reliability method, a convex-model-based system reliability method is also formulated. Three numerical examples are investigated to demonstrate the efficiency and accuracy of the method.

In this paper, an analytical technique, the so-called Fourier Spectral method (FSM), is extended to the vibration analysis of a rotating Rayleigh beam considering the gyroscopic effect. The model presented can have arbitrary boundary conditions specified in terms of elastic constraints in the translations and rotations or even in terms of attached lumped masses and inertias. Each displacement function is universally expressed as a linear combination of a standard Fourier cosine series and several supplementary functions introduced to ensure and accelerate the convergence of the series expansion. Lagrange's equation is established for all the unknown Fourier coefficients viewed as a set of independent generalized coordinates. A numerical model is constructed for the rotating beam. First, a numerical example considering simply supported boundary conditions at both ends is calculated and the results are compared with those of a published paper to show the accuracy and convergence of the proposed model. Then, the method is applied to one real work piece structure with elastically supported boundary conditions updated from the modal experiment results including both the frequencies and mode shapes using the method of least squares. Several numerical examples of the updated model are studied to show the effects of some parameters on the dynamic characteristics of the work piece subjected to moving loads at different constant velocities.

This paper investigates the dynamic structural behavior of woven-fabric reinforced composites with high matrix–fabric volume fraction as applied in the construction of crash or security barriers typified by the Inflatable Offshore Fender Barrier Structure (IOFBS). Dynamic analysis of the IOFBS comprising of over 98% of the composite under impact loading was carried out using the finite element method employing the Coupled Eulerian–Lagrangian (CEL) formulation. The barriers were inflated to 6 kPa and 7 kPa initial pneumatic fluid pressures and subjected to crash loadings from a high velocity vessel. The enclosed fluid of the structure was modeled based on the Shomate equation and fluid behavior of water on which the structure floats was modeled using Us-Up Hugoniot equation of state. The barriers' membrane stresses distributions, deformations, internal fluid pressure surge and volume variations of the structures after impact as well as vessel's degree of instability and deceleration after impact for different initial inflation pressures were computed and studied. The developed models and numerical results obtained are useful in assessing the performance of the composite as used in the IOFBS and similar structures and in improving the design of the structure.

The vibration reduction for a cantilever beam with an interior sloshing absorber is numerically simulated using an implicit coupling approach of segregated solvers. The sloshing liquid damps the vibration by allowing the sloshing force to lag behind the displacement phase of the beam. The sloshing in the absorber is analyzed both theoretically and numerically. The results show that the impact of free sloshing on the forced sloshing causes the phase to be lagged behind when the free frequency is lower than the frequency of forced vibration. A range of values are considered for the parameters of the absorber and system vibration in the simulations to investigate their effects on the suppression capability of the absorber. In order to explain the effects of the parameters, two new parameters γ and κ are defined to represent the phase lag and magnitude of the sloshing force, respectively. Their applicability is confirmed by a series of numerical simulations. The results reveal the main mechanism of vibration suppression, providing a theoretical basis for optimizing the design of the interior absorber.

Most of the work done for the vibration of composite plates published in the literature is either analytical or numerical studies with few experimental results available on composites with unidirectional fibers. The present study involves extensive experimental works to investigate the free vibration of industry driven woven fiber glass/epoxy composite plates with different boundary conditions including free–free cases. The modern modal testing and subsequent analysis with powerful computer and digital analysis system is an important tool for prediction of behavior of structures. The specimens of woven glass fiber and epoxy matrix composite plates are manufactured by the hand-layup technique. Elastic parameters of the plate are also determined experimentally by tensile testing of specimens using INSTRON 1195. An experimental investigation is carried out using modal analysis technique with Fast Fourier Transform Analyzer, PULSE lab shop, impact hammer and contact accelerometer to obtain the frequency response functions. The computational results are compared with results of previous studies in literature wherever available. The experimental results are also compared with the FEM numerical analysis based on first-order shear deformation theory. The effects of different geometrical parameters including number of layers, aspect ratio, fiber orientation and different boundary conditions of woven fiber composite plates are studied in detail. It is observed that comparisons performed between numerical predictions and experimental tests have a good correlation. The natural frequency is very less for cantilever than simply supported and fully clamped boundary conditions. The prediction of dynamic behavior of laminated composite plates plays a significant role in the future applications of structural composites.

In this paper, buckling analysis of isotropic, orthotropic, laminated composite and sandwich plates utilizing trigonometric shear deformation theory and meshless method based on the finite point formulation using thin plate, polynomial and inverse multiquadric radial basis function is presented. The convergence of the present method is studied for isotropic and laminated composite plates for different radial basis functions with optimal value of shape parameter. Numerical examples of laminated and sandwich plates subjected to various types of in-plane loads are solved to demonstrate accuracy and applicability of present method. Several new results for variety of composite and sandwich plates are presented. The present results are observed to be in good agreement with those available in literature. The effects of orthotropy ratio of material, span to thickness ratio, number of layers, core thickness and lamination scheme on the critical load of plates are also presented.

This paper deals with the application of beam finite element models based on generalized beam theory (GBT) to analyze the buckling behavior of four thin-walled steel structural systems, namely (i) beams belonging to storage rack systems, (ii) pitched-roof industrial frames, (iii) portal frames built from cold-formed rectangular hollow section (RHS) profiles and (iv) roof-supporting trusses, exhibiting different support conditions and subjected to various loadings. In particular, taking advantage of the GBT unique and structurally clarifying modal features, it is possible to assess how different geometries and/or bracing arrangements affect (improve) the local, distortional and/or global buckling behavior of the above structural systems. The accuracy of the GBT-based buckling results is assessed through the comparison with values yielded by rigorous shell finite element analyzes carried out in the code ANSYS. In spite of the disparity between the numbers of degrees of freedom involved, which are orders of magnitude apart, there is a virtual coincidence between the critical loads and mode shapes provided by the GBT (beam) and ANSYS (shell) finite element analyzes.

Cable-stayed bridges have been developing rapidly in the last decade and have become one of the most popular types of long-span bridges. One of the important issues in the design and analysis of cable-stayed bridges is determining the pre-tensioning cable forces that optimize the structural performance of the bridge. Appropriate pre-tensioning cable forces improve the damaging effect of unbalanced loading due to the deck dead load. Because the cable-stayed structure is a highly undetermined system, there is no unique solution for directly calculating the initial cable forces. Numerous studies have been conducted on the specification of cable pre-tensioning forces for cable-stayed bridges. However, most of the proposed methods are limited in their ability to optimize the structural performance. This paper presents an effective multi-constraint optimization strategy for cable-stayed bridges based on the application of an inverse problem through unit load method (ULM). The proposed method results in less stresses in the bridge members, more stability and a shorter simulation time than the existing approaches. The finite element (FE) model of the Tatara Bridge in Japan is considered in this study. The results show that the proposed method successfully restricts the pylon displacement and establishes a uniform deck moment distribution in the simulated cable-stayed bridge; thus, it might be a useful tool for designing other long-span cable-stayed bridges.

Cracks in structural members lead to local changes in their stiffness and consequently their static, dynamic and stability behavior is altered. The influence of cracks on dynamic characteristics like free vibration, buckling and parametric resonance characteristics of a cracked beam with a transverse crack using finite element method (FEM) is investigated in the present work. Modal testing of beams with transverse open crack is conducted using FFT analyzer to verify the frequencies of vibration of beams. The crack is assumed to be open type and the analysis is linear based on small deformation theory neglecting damping. The loading on the beam is considered as axial with a simple harmonic fluctuation with respect to time. A two-noded Timoshenko beam element with provision of crack is used in this study. The equation of motion represents a system of second-order differential equations with periodic coefficients of the Mathieu–Hill type. The development of the regions of instability arises from Floquet's theory and the periodic solution is obtained by Bolotin's approach using FEM. It is observed that the frequencies of vibration and buckling load of the beam are influenced significantly by location and depth of cracks. It is observed that, for a given location of crack, the onset of instability occurs earlier with increase in depth of crack. As the location of crack moves from the fixed end to the free end the excitation frequency increases. The instability occurs later and the width of the instability regions reduces. When the damage is near to the free end, the instability region almost coincides with the instability region for the undamaged beam. This means that the damage near the fixed end is more severe on the dynamic instability behavior than that of the crack located at other positions. The vibration and instability results can be used as a technique for structural health monitoring or testing of structural integrity, performance and safety.