International Journal of Structural Stability and Dynamics

The design displacement, its corresponding acceleration performance, and the re-centering performance of bilinear hysteretic isolation systems are adopted as previously determined design objectives for equivalent linear analysis. To demonstrate the applicability and generalization of the analysis procedure, two sets of values for damping modification factors are employed in the analysis: those provided by ASCE/SEI 7-16, and those estimated for different ranges of the ratios of effective periods of seismic isolation systems to pulse periods of ground motions. To investigate a broad range of seismic responses of base-isolated structures, 15 pulse-like near-fault ground motions are used for numerical demonstration. The analysis procedure is numerically verified to be practically feasible. A numerical comparison also shows that the three design objectives previously determined in the analysis procedure are sufficiently conservative compared with analysis results from nonlinear dynamic response history, even when subjected to pulse-like near-fault ground motions. Regarding the approximation to maximum inelastic acceleration and displacement responses, it is particularly more conservative for the former when the design displacement is greater and when adopting values of the damping modification factors provided in ASCE/SEI 7-16. For the approximation to dynamic residual displacement responses, the influences of pulse-like near-fault ground motions and different design objectives on the re-centering performance of bilinear hysteretic isolation systems still need further study.

For a complete stability analysis of multi-dimensional controlled systems modeled in the framework of second-order linear differential equations with two time-delays, the determination of stability crossing curves (or stability switching curves) within the domain of the delays is significantly important. This paper presents a simple receptance-based approach to solve this problem for a single-input-multiple-output controlled system using its second-order model. The proposed approach is based on a reduced characteristic function of the controlled system. This characteristic function is directly related to the receptance of the uncontrolled system and has a peculiar form that is well-suited for an effective method of calculation of these curves. Moreover, this method can find the direction in which the characteristic roots cross the imaginary axis as the delays deviate from a stability crossing curve. An example case study with two independent and constant delays is given to demonstrate the effectiveness of the proposed approach.

To investigate the ground vibration caused by the internal blast loading of an explosion vessel while evaluating the damage caused by vibration propagation to surrounding buildings, a series of explosion vibration tests were carried out using an explosion vessel. The blasting vibration monitors recorded the vibration parameters, and the vibration velocity frequency distributions were analyzed by the Hilbert–Huang transform (HHT) method. The results show that the explosion vibration velocity is closely related to the explosive charge and propagation distance. The effect of an explosive charge and propagation distance on the vibration amplitude at frequencies of 20–60Hz is not apparent, but at frequencies of 5–10Hz, low-order frequencies are noticeable. Furthermore, the energy amplitude and vibration action duration increase with increasing explosive charge and decrease with increasing propagation distance. The results provide an essential reference for studying the propagation law and effects on ground vibration waves produced by blast loading in an explosion vessel.

Based on the finite Fourier series method and the principle of energy variation, a method for calculating the dynamic response of an orbit-girder system is proposed, which is suitable for general spring boundary and nonhomogeneous interlayer stiffness distribution. Two numerical examples are given to verify the effectiveness of the proposed method under different moving load speeds and different stiffness distribution patterns. Based on this method, the influence of boundary conditions, interlayer stiffness degradation mode and degradation amplitude as well as the motion load on the dynamic response of the orbit-girder system is analyzed. A formula for calculating the peak value of additional dynamic response caused by interlayer stiffness degradation is proposed based on the nonlinear fitting method, and the factors affecting the additional response are analyzed. Results show that the variation of boundary conditions does not affect the additional dynamic response of the orbit-girder system. The mode of interlayer stiffness degradation and the degree of nonhomogeneous distribution have a significant influence on the peak of additional dynamic response. The additional dynamic response peak value of the orbit-girder system increases significantly with an increasing degree of nonhomogeneous degradation of the interlayer stiffness. The orbit-girder system has multiple critical speeds under the action of moving load. The magnitude of moving load has an important effect on the additional response peaks of the orbit-girder system. The additional response peaks increase approximately linearly with the increase of the motion load.

This paper deals with seismic performance and damage assessment of concrete grain silos. An existing large silo is taken as a case study to conduct the numerical analyses. A global damage index based on target displacement is proposed to quantify numerically different damage states of the structure. To this aim, the classical N2 method is extended to adaptive multimodal to evaluate seismic performance of the structure for increasing pic ground acceleration levels with taking into account degradation of stiffness and modification of modal characteristics. The seismic capacity of the silo is evaluated, as an averaged curve, by conducting pushover and several incremental dynamic analyses using artificial and recorded accelerograms. The seismic demand is derived from the design spectrum of the Algerian seismic code (RPA 2003). The target displacement is determined by taking into account both the participation of the dominant modes, and the degradation of the structure’s modal characteristics. The nonlinear behavior of the structure’s walls is modeled by using nonlinear multilayered shell elements. The effect of the stored granular material is included through distributed equivalent masses. It is found that when the structure modal characteristics are updated as its stiffness is degraded, the target displacement is correctly computed. Whereas, it wrongly grows indefinitely, with increasing PGA, when constant modal characteristics of the intact structure are assumed, as usually done. The proposed global damage index is compared to three existing reliable indices. It better reflects the different damage states of studied silo.

Nonlinear buckling analysis for honeycomb auxetic-core sandwich toroidal shell segments with CNT-reinforced face sheets surrounded by elastic foundations under the radial pressure is presented in this study. The basic equation system of shells is established based on the von Kármán–Donnell nonlinear shell theory, combined with Stein and McElman approximation. Meanwhile, the foundation-shell elastic interaction is simulated by the foundation model based on the Pasternak assumption. The Galerkin procedure is utilized to achieve the pre-buckling and post-buckling responses for the shell, from which the radially critical buckling load is determined. Numerical analysis shows the various influences of auxetic-core layer, CNT-reinforced face sheets, and elastic foundation on the pre-buckling and postbuckling behavior of sandwich shells with CNT reinforced face sheets.

This paper presents the theory of multi-phase-lags thermoelasticity that was used to study the wave propagation on a fiber-reinforced thermoelastic medium with micro-temperatures. The medium was considered to be homogeneous, isotropic and thermal conductivity as a linear function of thermodynamic temperature. The Fourier transform and Laplace transform are employed to solve the governing equations and obtained the solution of the physical quantities. The graphical illustrations of the impact that initial stress, variable thermal conductivity, magnetic field, and the phase-lags have on the field functions are presented. The variable thermal conductivity, initial stress, and magnetic field have a good impact in all the physical quantities.

The macromodel, by which the beam and column are simulated by fiber beam elements, has been extensively used in the progressive collapse analysis of reinforced concrete (RC) frames due to its high computing efficiency as compared to the solid element model. However, there exist some problems that need to be solved to improve the accuracy of the macromodel. One typical issue is to develop an accurate beam-column joint model. In current practice, the beam-column joint is as part of the rectangular frame with rigid elements, neglecting the shear damage and bending moment distribution in the core region of the joint, although they are crucial to progressive collapse analysis. In this paper, a new macromodel that considers the shear damage and bending moment distribution in the core region of the beam-column joint is developed for the progressive collapse analysis of RC frame structures under blast loads. Nonlinear springs are used in the joint connection interfaces to consider the force transfers from the beams or columns to the joint. Also, nonlinear shear springs are used in the core region of the joint, whose characteristics are derived based on the actual force-deformation relationship of the sub-assemblage due to joint shear distortion, to model the shear damage of the joint under blast loading. The proposed beam-column joint macromodel is validated with the available test data in the literature. The results indicated that the proposed macromodel for beam-column joints is more accurate than the traditional beam-column joint macromodel, while the computing efficiency remains almost unchanged in progressive collapse analysis of RC structures, especially when the RC frame structures are seriously damaged or collapse under blast loadings.

The research work presented in this paper is focused on the investigation of dynamic characteristics and optimum design of rotating laminated composite multi-walled carbon nanotubes-reinforced magnetorheological elastomer (MWCNT-MRE) sandwich plate. Higher-order shear deformation theory (HSDT) and finite element (FE) formulations are employed to derive the governing equations of the composite MWCNT-MRE sandwich plate. The performance of the derived numerical model is validated by comparing it with the results available in the published literature. The free and forced vibrations of the composite MWCNT-MRE sandwich plate are examined at different magnetic fields and rotating speeds. Also, the optimal ply orientations of the MWCNT-MRE sandwich plate are identified using the developed numerical model coupled with a genetic algorithm (GA) to enhance the natural frequencies and loss factors.

In this paper, a novel equivalent parameter scheme based on the Riedel–Hiermaier–Thoma (RHT) model is proposed for blast response simulations of reinforced concrete (RC) frames. Considering the strengthening effect of longitudinal and stirrup reinforcements on concretes, constitutive parameters in the RHT model are modified to homogenize RC components based on reasonable simplifications and numerical tests. Numerical results of RC beams illustrate that this scheme significantly improves the computational efficiency and effectively predicts real explosion response behaviors with high accuracy. The scheme is then employed for the blast simulation of an RC frame with multiple components with results compared with those of real frame experiments to further demonstrate its reliability. Owing to its efficiency and accuracy, the present RHT-model-based equivalent parameter scheme can serve as a feasible tool to conduct blast response analysis of the RC frame and guide the corresponding anti-explosion designs.

In this paper, an evaluation of the influence of atmospheric humidity on the critical buckling load of reinforced concrete columns is performed. A particular case consisting of a real, extremely slender reinforced concrete pole was taken for the study. The chosen mathematical procedure for calculating the critical load is based on the Mechanics of Deformable Solids due to variations of structure vibration frequency over time. The rheological behavior of concrete related to creep and shrinkage, which illustrates the time-dependent aspect of the problem, was also considered in the analysis following normative recommendations from the Brazilian Association of Technical Standards (ABNT). In order to evaluate value changes of critical buckling loads, different time instants after loading the structure as well as different relative humidity from 0% to 100%, in 10% increments were considered. According to the selected criteria, it was possible to verify that a higher atmospheric humidity decreases the water transport from the interior out to the exterior surfaces of concrete, hence positively influencing structure stiffness. Therefore, the lowest reduction on critical buckling was 41.9% at 100% relative atmospheric humidity, versus the highest 60.7% at 0% relative humidity. A period of 7500 days after loading the structure was considered in the analysis.

Current practice in structural engineering requires dissipating some part of seismic energy by sacrificial elements rather than structural members and/or joints. As an easy-to-produce and plug-and-play damper with stable hysteretic loops and large displacement capacity, steel cushion (SC) is a significant device to improve the seismic performance of the structures. It was stated in the previous studies that SC is less effective in the transversal direction. Hence, the efficiency of the damper is improved by optimal sizing through intelligent optimization techniques in this study. The complex optimization problem could be converted to a relatively simple mathematical problem since closed-form equations of the damper are exist in the literature. The optimal sizing problem was solved using two distinct methods namely the $ϵ$-constraint method and the elitist non-dominated sorting genetic algorithm (NSGA-II). The employed optimization methods were verified by each other as almost similar geometric ratios were obtained. The efficiency of the optimization is evaluated through finite element analysis (FEA). It is shown that the optimally sized SC is superior in terms of energy dissipation.

This paper proposes a disturbance rejection method with extended state observer (ESO) and a tracking differentiator (TD) to realize vibration suppression of all-clamped plate structure in the presence of lumped disturbance, i.e. internal dynamic uncertainties, unknown external forces and accelerometer measurement noises. First, the structure is modeled as two degrees of freedom system based on vibration characteristics. Second, an ESO is employed to ensure the vibration suppression performance by estimating the lumped disturbances and compensating these disturbances via real-time feedforward mechanism. Meanwhile, a TD is introduced to eliminate the influence of the measurement noises. Moreover, the stability of the closed-loop system is discussed in detail. Finally, the proposed controller is verified on the hardware-in-loop plat-form based on NI PCIe-6343 data acquisition card. Theoretical analysis and experimental results show that the proposed method possesses good vibration suppression performance.

This work studies the nonlinear oscillations of an elastic rotating shaft with acceleration to pass through the critical speeds. A mathematical model incorporating the Von-Karman higher-order deformations in bending is developed to investigate the nonlinear dynamics of rotors. A flexible shaft on flexible bearings with springs and dampers is considered as rotor system for this work. The shaft is modeled as a beam and the Euler–Bernoulli beam theory is applied. The kinetic and strain energies of the rotor system are derived and Lagrange method is then applied to obtain the coupled nonlinear differential equations of motion for 6 degrees of freedom. In order to solve these equations numerically, the finite element method (FEM) is used. Furthermore, for different bearing properties, rotor responses are examined and curves of passing through critical speeds with angular acceleration due to applied torque are plotted. Then the optimal values of bearing stiffness and damping are calculated to achieve the minimum vibration amplitude, which causes to pass easier through critical speeds. It is concluded that the value of damping and stiffness of bearing change the rotor critical speeds and also significantly affect the dynamic behavior of the rotor system. These effects are also presented graphically and discussed.

The porous material is an emerging lightweight material, which is able to reduce structural weight and also keeps the superiority of the structure. Therefore, this work is devoted to the investigation of the functionally graded porous (FGP) annular and circular plates with general boundary conditions. The unified modeling method is proposed by combining the first-order shear deformation theory, the virtual spring technology, the multi-segment partition method, and the semi-analysis Rayleigh–Ritz approach. Afterwards, the convergency and correctness of the proposed method are verified, respectively. The frequency parameters, modal shapes, and forced vibration responses are uniformly calculated based on the proposed method. Finally, the dynamic analyses of the FGP annular and circular plates with different parameters, such as the porosity distribution types, porosity ratios, boundary condition types, geometry parameters, and load types, are conducted in detail. It is found that the reasonable porous design is able to keep the dynamic stability of the structure under different parameter variations.