International Journal of Structural Stability and Dynamics

In this paper, buckling of a nanowire column subjected to self-weight and tip load is investigated. One end of the nanowire is free, while the other end is attached to a rotational spring support. Considering the equilibrium equations together with the Euler–Bernoulli beam theory, the governing differential equation describing the behavior of the column can be obtained. Effect of surface stress is also incorporated into the formulations in terms of transverse distributed loading. The differential equation has been solved analytically and the general solution can be presented in the terms of Bessel function of the first kind. Applying the boundary conditions, the characteristic equations influenced by surface stress and stiffness of the rotational spring at the support can be expressed and then the critical load can be determined using the Newton–Raphson iterative scheme. From the results, they reveal that the positive surface stress could strengthen the nanowire against the buckling. Fixity at the base is also influenced to the critical load where the increase of the stiffness of the spring results in the increase of critical load as well.

Under low-speed collision conditions, the thin-walled structures located at the forepart of passenger car act as a significant energy absorber, which can reduce the injury degree of passengers in collision accidents. Therefore, the design of thin-walled structures is particularly important in automobile body development. High stiffness and strength contribute to structural integrity, but the resulting large collision force will be detrimental to occupant safety. To address this issue, the paper proposed a novel negative Poisson ratio thin-walled tube (NPR-TWT). In addition, the second-order sensitivity-based response surface models (SB-RSMs) were established to improve the efficiency of design optimization. Furthermore, the NPR-TWT was optimized by using the non-dominated sorting genetic algorithm (NSGA-II) to enhance its comprehensive performance. The results showed that the optimized NPR-TWT could absorb collision energy by sufficient displacement deformation and reduce the peak impact force. It can provide theoretical and practical guidance for the application of thin-walled structures in automobile body safety.

In this paper, a new finite element for 2D non-prismatic (curved and tapered) elastic beams with narrow rectangular cross-section is proposed. The element is geometrically exact, hence capable of handling large displacements and finite rotations, and allows for cross-section arbitrary warping through the inclusion of additional degrees of freedom (DOFs). These additional DOFs make it possible to capture the non-standard shear stress distributions that are developed in tapered members. All expressions required to implement the proposed finite element are derived and written in a simple vector/matrix form. To assess the accuracy and demonstrate the capabilities of the proposed element, several numerical examples are presented. For comparison purposes, results obtained with refined meshes of standard 2D finite elements are also shown. It is concluded that the proposed element leads to very accurate results with a small computational cost.

Resilience can be treated as an integrated measure to assess the seismic performance of buildings. Available methods to assess the seismic performance of self-centering structures mainly consider inter-story drift ratios, peak floor accelerations, and energy dissipative capacities, however, their seismic resilience is poorly understood. This paper proposes a framework to estimate the seismic resilience of self-centering energy dissipative braced steel frame office buildings. In this context, a new damage ratio assessment model is presented to assess functionality. Unlike the traditional method that only considers the economic loss or repair time in the functionality assessment, the proposed model accounts for the contribution of four performance measures such as downtime. To estimate the repair cost, repair time, casualties, and unsafe placarding, the FEMA P58 methodology is used. Based on the proposed model, the new damage ratios and recovery times of the self-centering structure are estimated. Obtained damage ratios are combined with fragility analysis to calculate the functionality loss. After considering an appropriate recovery model, seismic resilience is assessed. For comparison, the traditional method (i.e. HAZUS) is also used to assess seismic resilience. The whole framework is applied to a three-story self-centering energy dissipative braced steel frame, and the results show that the traditional method often underestimates the seismic resilience, and the proposed method may be more suitable for predicting the seismic resilience of self-centering energy dissipative braced steel frame office building. Sensitivity analysis is performed to identify uncertain parameters to which seismic resilience is most sensitive, and the result indicates that the control time and damage ratio at the extensive damage state have a major influence on seismic resilience. The framework can be modified and extended to assess the seismic resilience of ordinary building structures and other complex structural systems such as isolated structures.

This study examined the transient or dynamic response of sandwich plates with a functionally graded porous core under the action of time-dependent loads. The plates had two isotropic faces at the top and bottom layers, and the middle layer was made of an open-cell material with functionally graded internal pores. By using the first-order shear deformation theory, the equations of motion used to describe the dynamic behavior of the plates were applied to generate accurate results with less computational effort. To solve the equations of motion, the Ritz method based on the Jacobi polynomials for the admissible displacements, cooperating with the time integration of Newmark, was used to find out the dynamic response of the plates. The results of the numerical experiments revealed that the plates carrying a larger number of internal pores at the middle zone of the core had a great improvement in flexural stiffness, providing less deflection under dynamic loads. The observed results of the plates’ dynamic behavior related to the effects of the porosity coefficient, plate’s geometrical ratio, dynamic loading types, porous distributions of the core, etc. are shown in the form of graphs and tables, which can be used as a benchmark for future research.

Slender structures are sensitive to wind loads, and aeroelastic effects during vortex-induced resonance have considerable influences on their survivability, serviceability, and habitability. However, the vortex-induced aeroelastic effects and the effects of turbulence intensity on unsteady aerodynamic forces of an aeroelastic prism remain far from been fully understood. In this study, a series of wind tunnel tests, including the pressure measurements of a rigid model and simultaneous measurements of the pressure and response of an aeroelastic model, were conducted in three different wind flows. The characteristics of unsteady aerodynamic forces and the effects of turbulence intensity on the unsteady aerodynamic forces were systematically investigated. The mechanism of aeroelastic effects and the variations of aerodynamic damping ratios were also discussed. Wind-induced responses were predicted by the unsteady aerodynamic forces and compared with the measured values. The experimental results show that vortex-induced aeroelastic effects on the wind-induced responses and the unsteady aerodynamic forces are significant. An increase in the turbulence intensity may result in a weak correlation of the unsteady aerodynamic forces and thus suppress the vortex-induced aeroelastic effects. Moreover, the amplitudes of the positive and negative peaks of the aerodynamic damping ratios decrease with the increase of the turbulence intensity. In addition, the wind-induced responses predicted by the unsteady aerodynamic forces measured from the aeroelastic model are the closest to the measured responses.

Flexible suspension bridges are susceptible to aerodynamic instability phenomena. In this paper, the torsional divergence is addressed in terms of underlying mechanism, 3D and turbulence effects. A 3D generalized analytical model is first established by reasonable simplification of the model. Comparisons among results from different models are performed. The mechanisms of symmetric and asymmetric torsional divergence are explored. Finally, the 3D and turbulence effects are investigated. The results show that the proposed 3D generalized model is feasible for estimating the critical wind speed of asymmetric torsional divergence, and its computational accuracy is higher than the method provided by the code. The effects of turbulence on torsional divergence are multifaceted: the buffeting response due to wind fluctuations can significantly reduce the aerostatic stability of the bridge, resulting in a much lower critical wind speed than that in a smooth flow; the threshold of divergence is ambiguous and the instability is intermittent; further, the left and right quarter span sections largely vibrate in opposite directions during asymmetric torsional divergence.

The most commonly used method for sampling damage parameters from the posterior distribution is the Markov chain Monte Carlo (MCMC) method. The population MCMC method as one of the MCMC methods has been utilized for damage identification by some researchers recently. Nevertheless, for the conventional population MCMC methods, these sampling methods often require significant computational resources and tuning of a large number of algorithm parameters. Aiming at the problem of difficulty in selecting the proposal distribution and low computational efficiency in the conventional MCMC method, this paper proposed a simple population Metropolis–Hastings (SP-MH) algorithm for the damage identification, which is realized by exchanging information among chains in a relatively small population and using tuning-free strategy. Then, a numerical cantilever beam and an experimental frame are utilized to verify the effectiveness and feasibility of the proposed algorithm, it can be seen that the convergence rate of the SP-MH algorithm is faster than that of the Differential Evolution Monte Carlo (DE-MC) algorithm, and in a small population state, the SP-MH algorithm can still maintain convergence, saving plenty of computing time for damage identification. The results show that the SP-MH algorithm is feasible and accurate in practice damage identification, and the SP-MH algorithm performs better than the DE-MC algorithm. Compared with the DE-MC algorithm, the SP-MH algorithm is simple and convenient for damage identification due to its tuning-free strategy and relatively small population.

Based on the consistent couple stress theory (CCST), we develop a Hermite-family $C^1$ finite layer method (FLM) for the three-dimensional (3D) free vibration analysis of a simply-supported, exponentially graded (EG) piezoelectric microplate under open- and closed-circuit surface conditions. In the formulation of the FLM, the microplate is artificially divided into a number of finite microlayers, and Fourier functions and Hermite polynomials are used to interpolate the in-plane and out-of-plane variations of a number of primary variables, respectively, including elastic displacement components and the electric potential variable for each individual layer. The Hermite-family $C^1$ FLM for analyzing EG piezoelectric microplates is reduced to the Hermite-family $C^1$ FLM for analyzing EG piezoelectric macroscale plates and functionally graded (FG) elastic microplates by assigning a value of zero to the material length scale parameter and by ignoring the piezoelectric and flexoelectric effects in the formulation, respectively. The accuracy and convergence rate of the FLM are assessed by comparing their solutions with the benchmark solutions of both the EG piezoelectric macroplates and the power-law-type FG elastic microplates that are available in the relevant literature. We examine and discuss some key effects on the free vibration characteristics of an EG piezoelectric microplate, including the impact of the material length scale parameter, the material-property gradient index, the length-to-thickness ratio, the piezoelectric effect, and the flexoelectric effect.

A size-dependent electromechanical Euler–Bernoulli micro/nanobeam is proposed to address the nonlinear vibration and instability regions on the basis of nonlocal strain gradient theory (NSGT) and von-Karman hypothesis. The micro/nanopiezoelectric sandwich beam is axially influenced by the parametric excitation. Moreover, the electric enthalpy energy density is employed to consider the effect of flexoelectricity. The nonlinear equations of motion are derived with the aim of Hamilton’s variational approach. In this study, the electrostatic and Casimir forces are considered. The multiple time scales method is employed to solve the equation. Based on the outcomes of this research, it can be claimed that the flexoelectric and piezoelectric parameters have a pivotal influence on the amplitude response and dynamic instability regions. Furthermore, the applied voltage enlarges the distance between the bifurcation points and has a softening effect on micro/nanobeam. This work tries to provide a comprehensive understanding of flexoelectric micro/nanosandwich beam and prepare valuable information for designing flexoelectricity-based micro/nanostructures such as actuators, sensors, switches and resonators.

The sloped bottom tank generates higher sloshing-induced base shear with less liquid mass compared to rectangular tanks. Due to the improved sloshing characteristics, sloped bottom TLD achieves better performance than its conventional flat-bottom counterpart. These improvements in sloshing characteristics are due to the modified tank configuration, which reduces the impulsive liquid mass and results in higher convective participation of liquid mass during sloshing. To further increase the convective characteristics, a sloped bottom tank with internal object is proposed. A velocity potential-oriented finite element model has been adopted for the numerical analysis where a combination of three-node triangular and four-node quadrilateral finite elements is used to discretize the liquid domain. Seismic characteristics of liquid sloshing inside a ground-supported sloped bottom tank with internal object are investigated under six different seismic motions categorized as low-, intermediate-, and high-frequency contents. Also, the influence of the internal object on slosh dynamics is investigated suitably for different heights of the object under all earthquakes considered. The dynamic impulsive and convective components of base shear force and hydrodynamic pressure are quantified successfully. The developed numerical model in this study can be utilized in tuning and designing structures coupled with sloped-bottom TLD.

This paper presents the results of a study aimed at assessing the effects of higher modes of vibration on the nonlinear dynamic response of tall framed-buildings subjected to narrow-banded motions. For this purpose, analytical models of a 20-story building were developed under the consideration of two types of hysteretic behavior and subjected to 20 seismic excitations having a dominant period of motion of 1s. While the fundamental period of vibration of the building equals 2.7s, its second period is close to 1s; as a result, the selected seismic excitations over-stimulate the participation of the second mode in the overall dynamic response of the building. The circumstances under which the contribution of higher modes gives place to an excessive response of the upper stories are identified, and quantitative measures are presented. From an engineering point of view, parameters that predict an excessive response of higher-level floors are proposed.