International Journal of Structural Stability and Dynamics

The study investigates the accuracy of analytical solutions to the fundamental anti-symmetric Lamb wave scattering at delamination in multilayered isotropic plates. The analytical models are based on the wave function expansion method and Born approximation within the framework of Mindlin plate theory. The study validates the accuracy of modeling the delamination as an inhomogeneity with reduced bending rigidity in predicting Lamb wave scattering induced by geometry change at the delaminated region. A good agreement is observed between the analytical solutions and results of experimentally verified 3D explicit finite element (FE) simulations. The findings support the inhomogeneity assumption in Lamb wave scattering problems and show the feasibility of employing it in delamination characterization.

This paper introduces a new design of segmented nonbuckling brace member for use in frame structures to resist earthquake loading. The proposed segmented brace member consists of one or more segments connected by either tension-only or compressive force controlled joints. Because it cannot resist or can only resist a limited amount of compressive force, it is effective only under tension, but buckling would not be a failure mechanism of the brace. Its capability of mitigating seismic responses remains effective throughout the entire ground excitation duration. The other advantages of this new design include light weight, easy installation, easy replacement, controlled damage locations, and minimum or no residual structural deformation. The disadvantage is that full energy dissipations can be achieved only when it is in tension. Therefore they will be effective in a frame structure only when cross bracings are used. This paper presents experimental tests and numerical simulation results to examine the effectiveness of this innovative brace member in mitigating seismic responses of frame structures. Laboratory cyclic loading tests on a single brace member and on steel frames without bracing or with cross bracing by conventional brace or segmented brace are carried out. The testing results are analyzed and compared. The effectiveness of segmented brace members in mitigation of seismic loading effects on frame structures is demonstrated. Nonlinear response analyses are then carried out to investigate the performance of this new segmented brace applied to a steel frame structure subjected to ground motions of different amplitudes. The results demonstrate that this new design is effective in mitigating seismic loading effect throughout the entire ground motion duration.

This paper presents an analytical study on the nonlinear vibration of rectangular piezoelectric nanoplates resting on the Winkler foundation. The piezoelectric nanoplate is assumed to be simply supported on all four edges and is subjected to an external electric voltage and a uniform temperature rise. Based on von Karman nonlinear strain–displacement relations and the nonlocal constitutive relations, the nonlinear governing equations and corresponding boundary conditions are derived by employing Hamilton's principle. The Galerkin method is used to obtain the nonlinear ordinary equation, which is then solved by the direct integration method. An extensive parametric study is conducted to examine the effects of the nonlocal parameter, external electric voltage, temperature rise and Winkler parameter on the nonlinear vibration characteristics of piezoelectric nanoplates.

Functionally graded carbon nanotube reinforced nanocomposites have drawn great attention in both research and engineering communities. The weak interfacial bonding between carbon nanotubes and the matrix, which traditionally hinders the application of carbon nanotube reinforced nanocomposites, can be remarkably improved through the graded distribution of carbon nanotubes in the matrix. Within the framework of classical beam theory, this paper investigates the dynamic buckling behavior of functionally graded nanocomposite beams reinforced by single-walled carbon nanotubes and integrated with two surface bonded piezoelectric layers. The governing equations of the beam subjected to an applied voltage, a uniform temperature and an axial periodic force are derived by applying Hamilton's principle. Numerical results are presented for beams with different distribution patterns and volume fractions of carbon nanotubes and end support conditions. The influences of the beam geometry, temperature change, applied voltage, static axial force component, boundary condition, carbon nanotube volume fraction and its distribution on the unstable regions of FG-CNTRC piezoelectric beams are discussed in detail.

This paper describes a numerical study of the effect of vortex induced movement (VIM) on the hull of a paired-column semisubmersible (pc-semi) platform in relation to the column geometric properties. A computational fluid dynamics (CFD) analysis was carried out and vortex shedding was observed. The response of the square and rectangular columns hull configuration was investigated using ANSYS AQWA and the maximum amplitude was observed to be almost the same for both geometry, but it occurred at different range of reduced velocity V_r. The effect of surface wave and flow incidence angle were investigated for extreme and regular weather conditions, and it was found that VIM occurred at 2 ≤ V_r ≤ 12.

This paper reports the results of an investigation on the use of Generalized Beam Theory (GBT) to assess the buckling and vibration behaviors of thin-walled members and frames built from cold-formed steel circular hollow section (CHS) profiles. Initially, the concepts and procedures involved in performing GBT buckling and vibration analyses are presented, paying particular attention to the derivation of the mass tensors that account for the influence of the inertia forces. Then, the formulation, numerical implementation and validation of a GBT-based beam finite element for isolated members are described. Next, the determination of the frame linear stiffness, geometric stiffness and mass matrices, which incorporate the influence of the frame joints, is addressed. Finally, in order to illustrate the application and capabilities of the proposed GBT finite element formulation, numerical results are presented and discussed — they concern the buckling and vibration behaviors of an "L-shaped" frame. For validation purposes, most GBT-based results are compared with values yielded by shell finite element analyses carried out in the code ANSYS.

This paper presents the results of an investigation concerning the free vibration behavior (undamped natural frequencies and vibration mode shapes) of thin-walled beams with rectangular multi-cell cross-section (assemblies of parallel rectangular cells in a single direction). Besides local (plate-type) and global (flexural, torsional and extensional) vibration modes, attention is paid to the relatively less-known distortional vibration modes, which involve cross-section out-of-plane (warping) and in-plane deformation, including displacements of the wall intersections. A computationally efficient semi-analytical Generalized Beam Theory (GBT) approach is employed to obtain insight into the mechanics of the problem. In particular, the intrinsic modal decomposition features of GBT — the fact that the beam is described using a hierarchical set of relevant cross-section deformation modes — are exploited to identify and categorize the most relevant vibration modes and deformation mode couplings.

Cascades have been a prominent feature of many transmission line (TL) accidents around the world. During these events, a localized member failure changes the boundary conditions of the structural system, magnifying member loads over a considerable extension of the line. This results in the progressive failure of successive support structures. Phase conductor breakage is regarded as the most severe cascade triggering event, generating a shock wave that propagates through the conductor and induces large unbalanced longitudinal loads on the transmission line components. Under such an extreme loading event, nonlinear time-history dynamic analysis has to be employed to predict the response of the TL system. In the present work, an explicit dynamic analysis scheme is developed to predict the response of a multi-span TL section. The analysis includes all the main structural components of a TL section. This procedure was used to investigate the response of two types of suspension steel latticed towers, guyed and freestanding, subjected to conductor breakage loading. Results indicate the occurrence of peak dynamic loads (PDLs), that significantly increase the internal forces in system components, exceeding their design capacities, particularly in tower's members. The results also show that the guyed tower accommodates such a loading event more adequately than the freestanding tower.

The identification of railway ballast damage under a concrete sleeper is investigated by following the Bayesian approach. The use of a discrete modeling method to capture the distribution of ballast stiffness under the sleeper introduces artificial stiffness discontinuities between different ballast regions. This increases the effects of modeling errors and reduces the accuracy of the ballast damage detection results. In this paper, a continuous modeling method was developed to overcome this difficulty. The uncertainties induced by modeling error and measurement noise are the major difficulties of vibration-based damage detection methods. In the proposed methodology, Bayesian probabilistic approach is adopted to explicitly address the uncertainties associated with the identified model parameters. In the model updating process, the stiffness of the ballast foundation is assumed to be continuous along the sleeper by using a polynomial of order N. One of the contributions of this paper is to calculate the order N conditional on a given set of measurement utilizing the Bayesian model class selection method. The proposed ballast damage detection methodology was verified with vibration data obtained from a segment of full-scale ballasted track under laboratory conditions, and the experimental verification results are very encouraging showing that it is possible to use the Bayesian approach along with the newly developed continuous modeling method for the purpose of ballast damage detection.

This paper presents an experimental investigation of the bond strength between carbon fiber reinforced polymer (CFRP) and steel substrate by utilizing the pull-off test and scanning electron microscope (SEM) analysis. A series of pull-off experiments was conducted by using three types of CFRP (CFRP sheets and CFRP laminates with/without woven mesh) and two types of epoxy adhesive (ductile and brittle epoxy adhesive) with/without carbon nanotube (CNT) modification. Pull-off samples with CFRP laminates possess higher (about double) bond strength than that of samples with CFRP sheets, due to the good saturation of fibers in the laminates. The steel-CFRP bond with ductile epoxy adhesive (Araldite 2011) is found to have about 16% higher bond strength when compared to that of brittle epoxy (MBrace Saturant), even though the tensile strength of Araldite 2011 is about 40% less than that of MBrace Saturant. Also, it is shown that modified epoxy with CNTs is more efficient than neat epoxy for bonding CFRP to steel at a moderately elevated temperature, and increasing the bond strength about twofold.

Field observations reveal that very long members such as railway tracks and pipelines which are subjected to axial compression, induced usually by temperature and/or pressure increases, experience localized buckling. This paper presents a solution for the antisymmetric post-buckling of such members when restrained by a nonlinear foundation that includes softening effects. The principle of minimum total potential is invoked in order to develop the governing differential equations of buckling, as well as the non-linear equations of equilibrium in the post-buckled range of structural response. In order to solve these equations, a semi-analytical solution is proposed based on a perturbation technique, as well as a numerical technique based on a single shooting procedure for the solution of boundary value problems. The results of the analysis show that the post-buckling configuration of the column changes from a lengthwise periodic mode at the initial stages of loading to an isolated sinusoidal mode at the later stages of post-buckling, which represents a localization in the post-buckling range. This response is typical of that observed often in practice. Comparisons between the results of the perturbation technique and those of the numerical approach indicate that the semi-analytical perturbation solution predicts the initial post-buckling response of a column on a nonlinear foundation quite accurately.

An experimental investigation has been conducted into the degree of shear interaction between cold-formed steel floor joists and wood-based flooring panels and the resulting benefits derived in terms of composite action. A series of four-point bending tests have been carried out to evaluate the overall system behavior, while material tests have been performed to accurately define the material properties of each component of the examined system. Two different shear transfer mechanisms were examined: self-drilling screws with varying spacing and structural adhesive. The bare system was also tested to provide a reference response, against which the stiffness and capacity of the composite system could be bench-marked. The experiments showed that significant benefit could be derived as a result of composite action with as much as a 100% increase in bending capacity and 42% increase in stiffness.

Presented herein is a new method for the analysis of plates with clamped edges. The solutions for the natural frequencies of the plates are found using static analysis. The starting are the equations of motion of an isotropic rectangular plate supported on Winkler elastic foundation, with a positive or negative value. In either case, one can solve the displacements of such a plate under a given concentrated load. This deflection will be infinite if the plate losses its stiffness, or in other words, the generalized foundation is causing the plate to be unstable. The solution for the vibration frequencies of the plate is equivalent to finding the values of the negative elastic foundation that will yield infinite deflection under a point load on the plate. The solution for a clamped plate is decomposed as the sum of three cases of plates resting on elastic foundation: simply supported plate with a concentrated load, and two cases of distributed moments along opposite edges. The solution for simply supported plates with elastic foundation is found using Navier's method. For zero force, the vibration frequencies are found up to the desired accuracy by careful calculations at the neighborhood of the roots.

The end bearing capacity of a rectangular hollow section (RHS) steel tube can be substantially increased through local strengthening using bonded carbon fiber reinforced polymer (CFRP) plates. This paper presents a combined experimental and numerical study into the behavior of such CFRP-strengthened RHS steel tubes with particular attention to debonding failure in such tubes. The results of an experimental study are first presented, which showed that debonding failure occurred in all the CFRP-strengthened steel tubes and the effectiveness of strengthening depended significantly on the slenderness of the webs. A finite element approach for modeling the behavior of such CFRP-strengthened steel tubes is next presented, in which a coupled cohesive zone model is employed to depict the response of FRP-to-steel bonded interfaces with a linear or a nonlinear adhesive. The finite element approach, which is shown to provide close predictions for CFRP-strengthened RHS steel tubes under an end bearing load, offers a valuable tool for understanding the behavior of these CFRP-strengthened steel tubes.