International Journal of Structural Stability and Dynamics

Modeling, analysis, and design are conducted to reveal the nonlinear forced and free vibration behaviors of the functionally graded (FG) sandwich beams with auxetic porous copper core and metal-ceramic facesheets. The copper foams with negative Poisson’s ratio (NPR) are designed to be functionally distributed along the structural thickness direction and possess greater relative density in the adjacent sublayers to the facesheets. Meanwhile, the functionally graded material (FGM) facesheets are designed to be metal-rich in the inner surfaces. Through micromechanical modeling and following the Mori–Tanaka model, material properties of FGM facesheets are determined and further taken to be temperature-dependent with the consideration of thermal environments. Nonlinear finite element (FE) simulations are then conducted. From the results of numerical analysis, one can conclude that when compared with the counterpart having a non-auxetic core, the sandwich beam with an auxetic core has lower nonlinear-to-linear frequency ratios of free vibrations and smaller dynamic deflections under a sudden load.

This paper investigates the effect of the ambient temperature change on the dynamic interaction between pantograph and catenary (PAC). Thermal expansion/contraction of the components of the overhead contact system (OCS) is considered. Simulation results show that the thermal stress has a much greater influence on the longitudinal positioning of the contact wire than on the horizontal and vertical positioning. When ambient temperature reduces to $-60^{\circ }$ from design temperature of $20^{\circ }$C, the maximum longitudinal displacement of the positioner can reach as high as 301 mm, while the maximum horizontal and vertical displacement of the positioner is within 4mm. The change of ambient temperature results in the uneven tension distribution of the contact wire, especially near the central anchor. With the increase in temperature, the tension of contact wire decreases; vice versa, with the decrease in temperature, the tension of contact wire increases. For nine-span OCS, the tension change caused by ambient temperature change shall not exceed 2%. The variation of ambient temperature also leads to the deterioration of current collection quality. It is shown that a decreasing ambient temperature results in more significant changes in contact force, close to 5%. An increasing ambient temperature environment leads to a higher uplift of pantograph, close to 30%.

To investigate the influence of an energy-dissipation cladding panel system (EDCPS) on the dynamic responses of a precast concrete (PC) frame structure, a six-story, three-span planar frame structure with an EDCPS (called “damping structure”) and a counterpart planar bare frame structure (called “bare frame structure”) were designed. The middle span and bottom two stories of the frame were selected as the test substructures, whereas the rest were considered using the numerical substructure. Hybrid tests were conducted on the two structures under four earthquake levels. The test results indicated that the damage evolution characteristics of the PC frame were not affected by the introduction of EDCPS. The dampers in the EDCPS successfully yielded and dissipated seismic energy under the four earthquake levels. Moreover, the maximum inter-story drift ratio of the damping structure was reduced by 12.59%, 17.68%, and 10.34% under the design-basis earthquake, maximum considered earthquake, and very rare earthquake, respectively, exhibiting a satisfactory damage-control effect. The cladding panels remained intact under the four earthquake levels, indicating that this structure effectively prevents damage to the cladding panels. Finally, a numerical simulation method is recommended according to the damage characteristics of the damping structure and is validated against the test data.

Performance-based seismic design and assessment of precast concrete (PC) structures have been widely studied. Fragility models for PC components have rarely been developed; however, it is a critical foundation for the above-mentioned design and assessment. Hence, this study was focused on developing fragility models for PC shear walls (PCSWs) and columns (PCCs) connected using grouted sleeves. To this end, 46 full-scale PCSWs and 45 full-scale PCCs, connected using grouted sleeves, were collected, and their test results were analyzed. Six damage states (DSs) were recommended based on the typical damage characteristics and with reference to the associated reinforced concrete (RC) components. Subsequently, the fragility models of PCSW and PCC were established for each DS using the drift ratio as the engineering demand parameter. In addition, the influence of the design axial load ratio on the fragility models was revealed. Through the comparison of fragility models between the PC and RC components, differences in parameters and curves of fragility models were quantitatively compared. These study achievements can serve as valuable references for performance-based seismic design and assessment of PC structures connected using grouted sleeves.

Nonlinear energy sinks (NESs) and tuned mass damper (TMD) have achieved excellent control performance. However, their energy and frequency robustness, as well as a large desired slide mass, impede their wide application in practice. To address this limitation, this paper proposes an asymmetric NES that combines two types of inerter NES, the AsymI-1 NES and AsymI-2 NES, to improve the damping robustness of traditional control devices and reduce the damper mass. In addition, the distinction is achieved by adding an inerter between the sliding damper and the top or bottom story. Further, the mathematical formulation of the asymmetric inerter NES is deduced. The working principle of the proposed asymmetric inerter NES is presented, and motion equations of the asymmetric inerter NES-attached system are derived. The proposed asymmetric inerter NES is optimized using impulsive excitation to analyze its energy and frequency robustness. The control performance and wavelet spectrum analyses of the asymmetric inerter NES are conducted under the action of earthquakes. The analysis results show that combining the two asymmetric inerter NESs can help to absorb seismic energy rapidly, limit structural reaction, and ensure good energetic and frequency robustness. Furthermore, the proposed asymmetric inerter NES can significantly decrease the stroke requirement and damper mass.

According to the scientific research needs of deep multi-field coupling true triaxial compression testing machines, it is necessary to find a suitable boundary material to be placed between the rock and the transmission bar to achieve the effects of wave elimination and energy absorption. This enables the conditions of the test requirements to be met under the interaction of true triaxial and strong disturbance. Therefore, the improved split Hopkinson pressure bar (SHPB) device was used to carry out a series of experiments on the wave elimination and energy absorption characteristics of different boundary materials, and to study the energy evolution characteristics and stress wave propagation laws of different materials under static–dynamic coupling loading. The results show that under single impact loading, owing to the difference in wave impedance between the material and the rock rod, the porous material will not only reflect the tensile wave that has a greater impact on the rock rod, but also its weakening effect on the reflection stress is weaker than that of the wave-absorbing metal plate. In terms of overall energy conversion, the energy absorption rate of the porous material PM-1 is superior, and the conversion rate of the reflection and transmission energies is also greatly reduced. Under the impact of cyclic loading, the reflection stress of the wave-absorbing metal plate increased slightly with an increase in the number of impacts. However, with the increase of impact times, the reflection peak stress of porous material PM-1 decreases at first and then increases, and the reflected wave changes from tensile wave to compression wave, which is not as good as that of wave dissipation metal plate in terms of repeatability and fatigue resistance.

Establishing a concise and accurate analytical model is the key to developing a feasible progressive collapse design for engineering practice. However, existing models either focused on an individual force mechanism or required complicated computer programming. Among existing machine learning (ML) techniques, multi-gene genetic programming (MGGP) can be trained to obtain explicit formulas for engineering problems. In this study, a comprehensive database was established by data collection, Latin hypercube sampling and structural design, and was used to train the mathematical model for quantifying progressive collapse resistance of reinforced concrete (RC) beam-column substructures under middle column removal scenarios. Further, an energy-based error index was proposed to validate the accuracy of the MGGP model among others. The research outcomes can provide references for the development of simplified analytical models for calculating the progressive collapse progress of RC frame structures, and promote the development of the practical design method.

In this paper, we will present an approach to constructing of dynamical spatial Green’s function (elementary solutions, dominant function) for a thin infinite elastic plate of constant thickness. The plate material is anisotropic with a single plane of symmetry, geometrically coinciding with plate’s middle plane. The Timoshenko theory was used for describing the plate movement. Transient spatial Green’s functions for normal displacements and angles of orthogonal alteration to middle surface before deformation of material fiber are built in the Cartesian coordinate system.

To construct Green’s function, direct and inverse Laplace and Fourier integral transformations are applied. The originals of Laplace Green’s functions were analytically found with the theorem of residues. To construct Fourier originals, a specific method was used based on Fourier series transformation inversion integral connection with Fourier series on a variable interval.

Green’s function found for normal displacement made it possible to represent the normal transient function as three-fold convolution of Green function with distant load function. The functions of normal distant displacements were constructed in case of the impact of transient total loads concentrated and distributed across rectangular courts. The numerical method of rectangles was used to calculate the convolution integrals. The influence of the concentrated load speed on transient normal displacements of the anisotropic plate was analyzed.

As a verification of constructed transient spatial Green’s functions, the results of numerical solutions were compared with the results found using known transient Green’s functions for isotropic thin elastic rectangular simply supported Timoshenko’s plate which solutions are constructed using Laplace integral transformation in time and its decomposition into Fourier series on coordinates. Besides, its confidence was proved analyzing the nature of waves in anisotropic, orthotropic and isotropic plate, found in the process of numerical calculations. The results are represented as diagrams. Examples of calculations are given.

With the development of building materials, construction technology, and design concepts, suspended arched roofs (SARs) are becoming increasingly popular. The wind loads of arched roofs springing from ground level (ARSGL) and vaulted roofs on side walls (VRSW) have already been studied; however, the wind loads of SARs, which are very different from those of ARSGL or VRSW, have not received adequate attention. Based on the wind tunnel tests of a rigid model of an actual SAR design scheme, the mean value, root mean square (RMS) value, and most unfavorable value of the wind pressure coefficient and overall lift coefficient of this type of roof are analyzed. Furthermore, the influence of the buildings below or surrounding it is investigated and discussed. The test results indicate that the net wind pressure of the SAR is affected by the upper- and lower-surface wind pressures. Both the most unfavorable wind pressure (positive pressure) and suction (negative pressure) coefficients of the SAR are larger near the edge (arch foot) and smaller in the internal area. The maximum values of the most unfavorable pressure and suction coefficients of the tested SAR are 4.5 and 8.0, respectively, and these values are larger than those of ARSGL and VRSW. The buildings below cause airflow congestion under the SAR and eventually increase the net pressure coefficients near the windward edge of the SAR. The shielding effects of the surrounding buildings of the tested SAR reduce the wind pressure coefficient; however, the wind pressure in some areas of the tested SAR increases because of the narrow tube effects between surrounding buildings. The lift coefficient of the tested SAR significantly increases because of the presence of buildings below in some cases.

The quantitative analysis of seismic performance under small and moderate earthquakes is of great significance. However, only using the stiffness distribution index is no longer applicable to seismic performance evaluation, and the influence of mass distribution must be introduced. In this study, under the action of small and medium earthquakes, the equation of motion can be simplified into the equilibrium equation of the dynamic matrix by the quasi-static method. Furthermore, a condition number index of dynamic matrix is proposed to evaluate the seismic performance of truss structures, which can consider both stiffness distribution and mass distribution. Then, the correctness of the proposed index is verified by comparing with the displacement and strain indexes. In addition, the performance of truss structure is studied by the condition number of stiffness matrix, mass matrix and dynamic matrix. It is found that since the condition number of stiffness matrix and the condition number of mass matrix cannot consider both stiffness and mass, it is not comprehensive to use these two indexes to evaluate the seismic performance of truss structures. The evaluation result based on the condition number of dynamic matrix is more reasonable under small and medium earthquakes.

A family of structure-dependent methods is proposed based on discrete control theory. Although the displacement and velocity expression of this family method are similar to those of the previously published method developed by Mohammad Rezaiee-Pajand, the structure-dependent parameters of this family are different from the previously published method. The family of structure-dependent methods is named the MUSE algorithm method. Based on discrete control theory, a new family of integration algorithms is proposed by using the poles of the Newmark-$\beta$ method. Theoretical analysis indicated that the MUSE algorithm method possesses properties of zero amplitude decay and is self-starting. Also, its Period Elongation can be reduced by parameter ‘$s$’. Numerical examples show that parameter ‘$s$’ introduced in this paper can improve control Period Elongation and improve the accuracy of this method.

This study is focused on robust design optimization (RDO) of the tuned mass dampers (TMDs), which are widely used as a passive vibration controller in structural systems. The performance of the TMDs designed under the implicit assumption that all relevant system parameters (such as loading and structural characteristics) are deterministic is greatly affected by the inevitable inherent uncertainties in the system parameters. In this regard, a framework is proposed for the RDO of TMDs to determine its optimal solution which is less sensitive to system parameter variability. RDO is defined as a multi-objective optimization problem that aims to minimize the mean and variance of the performance function. In the case of multiple TMDs, the proposed framework uniquely avoids the presumption of their mass distribution, number, and placement location. In the proposed RDO framework, an augmented formulation is adopted wherein the design parameters are artificially introduced as uncertain variables with some prescribed probability density function (PDF) over the design space. The resulting optimization problem is solved using the stochastic subset optimization (SSO) and KN, a direct search optimization method. The effectiveness of the proposed framework is studied by analyzing four illustrative examples involving a single TMD attached to a single-degree-of-freedom (SDOF) structure, a single TMD attached to a multiple-degree-of-freedom (MDOF) structure, multiple TMDs attached to an MDOF structure, and an 80-story structure equipped with multiple TMDs.