International Journal of Structural Stability and Dynamics

This paper presents a study on optimization of design parameters and positions of single tuned mass damper (STMD) and multiple tuned mass dampers (MTMDs), used as vibration control systems in buildings under seismic excitations aiming to reduce their story drift. As case studies, three buildings are subjected to three real earthquakes and one non-stationary artificial earthquake, and their responses are analyzed. For each building, different control scenarios are proposed and to run the optimizations, the whale optimization algorithm (WOA) was used. The results showed that for Building 1, the Scenario 1-Optimized, with a STMD at the top floor, was the best alternative. In Building 2, the Scenario 1-Optimized, with also a STMD at the top floor, proved to be the best solution. Finally, for Building 3, the Scenario 4-Modified, with 3 TMDs arranged in the building elevation plane was the only one that had effective control of structural response, therefore, it is the best control scenario.

This paper removes the subjective judgment by proposing a technique for automatically identifying the bridge frequencies using singularity spectrum analysis and $K$-means clustering. First, the vehicle-bridge contact-point acceleration newly derived from is used to avoid the adverse effect brought by vehicle’s frequency. Next, the contact signal is processed by singular spectrum analysis to remove the noises. Then, the first several principal components are processed by the FFT to extract peak frequencies. Finally, the $K$-means clustering algorithm is adopted to group the peak frequencies into clusters, with their centroids denoting the bridge frequencies. They are verified against those extrapolated from the 1st bridge frequency. Moreover, the current technique was assessed by studies on factors including pavement roughness, vehicle velocity, ongoing traffic, and vehicle stiffness, along with a field test on a bridge to demonstrate its capability. One feature of the current method is that the errors for higher frequencies predicted are not higher than lower frequencies.

A semi-analytical method is presented to analyze free vibration response of beam-plate-shell combined structures with general boundary conditions. Based on the beam-plate-shell energy theory, the coupled annular plate-conical-cylindrical-spherical shell with stiffened rings and bulkheads regarded as the theoretical model is constructed. The unified displacement admissible functions of each substructure are expanded as modified Fourier series and auxiliary convergence functions along generatrix direction and Fourier series along circumferential direction. Virtual spring technology is adopted to express the energy stored at the junction of adjacent substructures and both boundaries. The energy variational procedure and Ritz method are used to obtain the vibrational governing equation of the combined structure. The present method provides an analytical way for the vibrational response of complicated combined structures. The convergence, accuracy and reliability are validated by comparing the free vibrational response with those of the references and finite element method. Some numerical examples show effects of different boundary conditions on the free vibration. And the influence of stiffened rings and bulkheads treated as Euler-beams and annular plates is also discussed from quantity, size and spatial distribution, offering a feasible way to design the reinforced structures and optimize the bulkheads in engineering problems.

In this study, the vibration suppression effect of a fiber reinforced polymer (FRP) spherical–cylindrical shell coated with the porous graphene platelet (PGP) in a thermal environment is investigated. The dynamic equilibrium equation is derived by combining the first-order shear deformation theory and the Rayleigh–Ritz approach, together with the virtual spring technology and the multi-segment partition technique. After the free and forced vibration responses of this FRP combined shell with PGP coating are solved. The model is validated by the convergence analysis and comparison of the present results and literature or finite element results for different shell structures with and without coating under various boundary conditions. Using the present model, the parametric study is conducted to explore the effects of porosity distribution type, dispersion pattern of volume fraction porosity, nanofiller weight fraction, and thickness ratio of PGP coating on the transient response. This study provides a useful model and some suggestions for better improving the vibration suppression capability of coated shell structures in a thermal environment.

Sensitivity analysis plays an important part in the validation of a sensor layout for the identification of the dynamic response of a system. Although sensitivity analysis has been implemented for this purpose in several civil engineering structures, there are still uncertainties in the case of more complex, nonlinear systems, such as guyed masts, where small changes in mass or stiffness can result in large variations of the general dynamic behavior. This paper describes the influence of antenna masses and initial guy tension variation in the total number and position of sensors required to assess the dynamic response of tall guyed mast telecommunication towers. For the study, the computational models of four different guyed masts were generated and a sensor layout was obtained for each model using a sensitivity analysis. Then, the proposed sensor layouts were verified for different initial guy tensions and total antenna mass of the system, by means of the Modal Assurance Criterion. The principal finding is that initial guy tension presents the highest influence on the variation of correspondence values between mode shapes, with modifications of these values in up to $98\%$. This finding suggests that a preliminary sensor layout based on information provided by a computational model or structural drawings of a guyed mast may be rendered inefficient if there is variation in guy tension due to construction errors or relaxation of cables.

This paper presents the influence of temperature and moisture on the free vibration characteristics of skew laminated composite sandwich (SLCS) panels. The face sheets of the panels are made of graphite–epoxy composite, while the core consists of carbon nanotube-reinforced composite. The coupled hygro-elastic and thermo-elastic relations for the SLCS shells/panels are formulated using first-order shear deformation theory. The nonmechanical stiffness matrices are represented by the initial stress stiffness matrix developed using nonlinear strain–displacement relations. The temperature and moisture-dependent material properties are considered to analyze the laminated composite sandwich spherical, hyperbolic, ellipsoid, cylindrical Shells, and flat plates. Several numerical examples are comprehensively studied to establish the influence of temperature, moisture, the volume fraction of carbon nanotubes in the core material, functional gradation types, skew angle, and edge constraints on the vibration responses of SLCS shells. Further exploration is devoted to studying the combined effect of moisture, temperature, and the geometrical parameters such as length to width ratio, length to thickness ratio, radius-to-length ratio, and the core thickness to face sheet thickness ratios on the natural frequency of the skew laminated composite sandwich panels.

Concrete gravity dams are a common form of dams. The dynamic response analysis of concrete gravity dams under the action of underwater explosions is indispensable for survivability assessments. Due to the constraints of the environment and other conditions, an underwater explosion test of a prototype concrete gravity dam is difficult to achieve. The centrifuge scaled-down test that satisfies similarity theory provides a new way to study the dynamic response of underwater explosions on concrete gravity dams. In a near-field explosion, the shock wave of an underwater explosion will cause direct damage to the gravity dam, and the detonation products after the shock wave will aggravate the damage. Under the premise of verifying the concrete dynamic response material parameters and the fluid–solid coupling model of the underwater explosion, numerical calculations of the scaled underwater explosion model of the centrifuge and the prototype underwater explosion were carried out, and the similarity between the scaled dam response model of the underwater explosion centrifuge and the prototype was discussed. The analysis shows that the scaled-down centrifuge model can better reflect the local damage of the prototype dam subjected to shock waves. The difference between the scaled centrifuge model and the prototype model of underwater explosion damage to the dam is concentrated on the overall damage. The damage effect of detonation products on the prototype dam body is mainly concentrated in the middle and lower parts of the dam body, while the damage effect of detonation products on the dam body in the scaled-down model is mainly concentrated in the middle and upper parts of the dam body.

In this study, the free vibrational behavior of a thin-walled functionally graded conical shell with intermediate ring support is investigated. Theoretical formulations were established based on the first-order shear deformation theory. The governing equations of motion were solved using the Galerkin method. Applying a set of displacement functions, the equations of motion result in an eigenvalue problem, by solving which, the natural frequencies of vibration are determined. Material properties are assumed to be varied in the thickness direction according to the power-law volume fraction function. It has been attempted to examine the effects of ring support position on the natural frequencies of vibration and to introduce the optimal scenarios of the support placement to achieve a higher frequency. In addition, a 3D FE model was built in the ABAQUS CAE software in order to validate the results of the analytical model. The analytical results were in close agreement with the literature and also the numerical ones. Moreover, the effects of some commonly used end conditions, variations in the shell geometrical parameters, changes in the ring support placement have been investigated on the vibrational behavior.

This paper focuses on dynamic buckling of composite structures subjected to impulse loads. Using the Lyapunov exponent, the Budiansky–Hutchinson criterion is improved and its algorithm is constructed. Based on it, the nonlinear dynamic buckling loads are evaluated for typical composite structures such as a fiber-reinforced composite plate, composite laminated cylindrical shells and a laminated plate with delaminations and matrix cracks that are all subjected to impulse loads. The improved criterion of dynamic buckling is validated through comparisons with the results in the published literatures.

In this investigation, the nonlinear dynamic buckling analysis and the failure analysis of laminated composite cylindrical (LCC) panel with different shapes of cutouts under the action of rectangular in-plane pulse loads are performed in the finite element framework. Cross-ply laminates which are balanced symmetric are considered in the investigation. The first ply failure load (FPFL) of the panel is evaluated and checked whether it occurs before the nonlinear dynamic buckling phenomenon considering Tsai–Wu failure criterion. Convergence and validation studies are undertaken, and the results are compared with those from the existing literature. The effects of loading duration, cutout area and cutout geometry on the panel are investigated in detail and results are reported. The results indicate that for the panel with cutout, its dynamic buckling load (DBL), in certain cases, compared to the static buckling load (SBL), can be lower even if the loading duration is half of its first natural period. Additionally, the vibration and the static buckling analyses of the panels are carried out as and when required.

Thermal frequency responses of the hybrid laminated composite panel are theoretically computed using the finite element model and for the first time compared with in-house experimental data. The structural model for hybrid panel is derived using higher-order displacement polynomial functions (to maintain the necessary stress/strain continuity) and discretized through the isoparametric finite elements. Moreover, the elastic properties of the composite are evaluated suitably including thermal and physical parameters of the advanced fibers (Glass/Carbon/Kevlar) with the help of experimentations and numerical tool (via ABAQUS using mean-field homogenization). The variation of modal responses due to the change in temperature increment is computed through a generic computer code generated via the higher-order mathematical model. The numerical frequency values are compared with the earlier published numerical results and the experimentally recorded eigen frequencies. The experimental verifications related to the end boundaries indicate that the incorporation of the clamped boundary for one edge doubles the frequency, whereas the fraction of Kevlar fiber does not influence the stiffness (due to longitudinal modulus) parameter irrespective of the temperature change. Further, the conclusive understandings of the hybrid composite structural panel due to the inclusion of different advanced fibers and other design parameters (geometry, boundary and temperature) are deliberated in detail.

Because structures made of FG material often operate in high temperature environments, it is critical to understand the mechanical behavior of these structures while taking temperature into consideration. As a result, the phase-field model is employed in this work to investigate the thermal buckling of fractured functionally graded material (FGM) plates. Additionally, this study demonstrates the difference between the plate’s static stability response to thermal load in the case of temperature-dependent (TD) material mechanical properties and in the case of temperature-independent (TID) material mechanical properties, illustrating that the calculation for these two cases will appear to be highly skewed. This provides a scientifically valid foundation for scientists to adopt a more realistic computation model. The equations are based on the third-order shear deformation plate theory (TSDT) of Reddy. This work proves that this discrepancy strongly depends on the material, boundary condition, crack length as well as thickness of the crack plate, it has never been explored in published work, the results give very useful and needful information for scientists to choose the best accuracy case to calculate and apply in practice.

In this paper, the nonlinear thermally induced vibration in rectangular plates made of porous functionally graded materials (FGMs) due to thermal shock is studied based on a new numerical approach. The shear deformation influences are taken into consideration via Mindlin’s plate theory. The properties of the materials are also assumed to be temperature- and position-dependent. Moreover, the influence of elastic foundation is captured by the Winkler–Pasternak model. For deriving the governing equations, Hamilton’s principle, transient 1D Fourier-type heat conduction equation and von Kármán hypothesis are utilized. The relations of paper are written in a new matricized format for computational aims. The generalized differential quadarature (GDQ) method and Newmark’s direct integration scheme are used for solving the heat equation. Furthermore, solving motion equations is done based on the variational differential quadrature (VDQ) formulation. The effects of important parameters including material porosity and elastic foundation on the thermal shock response of porous FG plates are investigated in the numerical results.

Damage detection technology based on wavelet packet energy has been widely applied to structural health monitoring, especially for one-dimensional structures. With more complex vibration characteristics than one-dimensional structure, two-dimensional structure is common in ship structure. It is a challenge for using wavelet packet energy methods to detect damage in two-dimensional structures. In this study, based on the wavelet packet energy eigenvector, a novel concept of detection index ratio (DIR) is defined to characterize the damage location ability of the excitation force. Based on the above research, a multi-excitation method of damage location in plate-like structures is proposed. In this method, a series of half-sine pulse excitation forces with different frequencies are applied to the structure, and wavelet packet transform (WPT) is used to decompose the vibration response of the intact structure and the damaged structure. The energy ratio changes in frequency bands on all measuring points are taken as the preliminary damage detection index, and the final detection index is obtained by synthesizing the preliminary indexes under various excitation. Moreover, to verify the effect of the proposed method, several tested damage cases are presented. The results show that the proposed method can locate single and multiple damage more accurately and has better noise robustness than the traditional detection method under single excitation.

In this study, dynamic instability of a sandwich beam made of an isotropic core and functionally graded (FG) graphene platelets-reinforced composite (GPLRC) face sheets is investigated for the first time. A Frostig theory for soft core and third-order shear deformation theory (TSDT) for sheets are used. Hamilton’s principle is used to derive the governing equations of motion, and by applying Bolotin’s approach, the dynamic instability regions (DIRs) are investigated. A comprehensive investigation is conducted to assess the effects of different weight fractions of nanofiller, various GPL patterns, boundary conditions, slenderness ratio, the thickness of face sheet and static load factors on the DIRs of the beam.

State-based peridynamics (SPD) is effective for simulating fracture and damage in different materials. However, the solutions may suffer from numerical instabilities, particularly for strong nonlinearity cases or large displacement cases, leading to inaccurate predictions or oscillation in responses. This paper proposed a novel practical method to solve the instability problem of SPD based on stress equilibrium equation, referred to herein as the stress correction method (SCM). A correction force is applied on each SPD point surrounding the loading points. The correction force is defined as the difference between an internal force obtained by the stress equilibrium equation and that obtained by the force states of the SPD. Four examples are presented herein to verify the accuracy and stability of the proposed method in various conditions, e.g. static and dynamic analyses of elastic and plastic models subjected to force and displacement boundary conditions.