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Civil engineering structures will exhibit hysteretic behavior due to damage caused by dynamic loads. Identifying the hysteretic behavior of structures is a practical and challenging problem that involves observing vibration data to determine strength and stiffness degradation. This paper proposes a modified square root central difference Kalman filter (MSRCD-KF) method to track this behavior. By combining the QR decomposition and strong tracking filtering technology, the proposed method makes the recursive calculation process unconditionally stable, while enabling the tracking of abrupt changes in structural parameters. A three degree-of-freedom (3-DOF) Duffing system is used in the simulation to verify the effectiveness of the proposed method. Numerical results show that the proposed method can converge to the true value quickly and accurately. Then, the proposed method is used to identify the structural parameters of a two-story concrete frame structure under different seismic loading sequences. In the first example, the structure is simplified as a 2-DOF linear system for which the equivalent stiffness and damping under different damage levels are identified. This information is then used to obtain the stiffness variation trend, damping ratio, and frequency. The second example uses the Bouc–Wen model to consider the stiffness and strength degradation of the structure. Finally, the experimental results demonstrate that the proposed method can accurately identify the structural parameters of nonlinear systems, and the identified hysteresis curves are in good agreement with the experimental ones.

Foundations can be subjected to dynamic or seismic loads depending on their applications and the site being constructed in. The researchers concentrated their works on investigating the reasons of the significant damage of piles during seismic excitation. Based on the findings of laboratory experiments and other numerical analyses, such failures were referred to as the kinematic impact of the earthquake on piles since they were associated with discontinuities in the subsoil because of sudden changes in soil stiffness. The current work investigates the seismic response of closed-end (CE) pipe pile using three-dimensional finite element analysis, including the impact of the scaling-up model, acceleration-time history of the ground motion, and ground conditions. The numerical model is developed using a variety of scaling rules and the outputs of the available laboratory tests. The current results showed that the saturated sand models have larger pile deformation factors than dry sand models. Pile frictional resistance was evaluated numerically, and the entire findings were evaluated against the earlier work. Mainly, the frictional resistance around the pile shaft was lower than that at the pile tip, and the frictional resistance factor on the soil surface of dry soil models was larger than that of saturated soil models. Owing to the acceleration amplifications, the pile and soil suffered cycles of compression and tension stresses. A hysteresis loop is broader and flatter on the x-axis as the shear strain increases serve to identify the shear stress–strain plane behavior. The main outputs of the scaled models were normalized to provide a deep insight of model to prototype scaling effects.

Soil liquefaction is considered as one of the most significant issues that leads to failure of shallow and deep foundations. However, the effect of liquefaction on the seismic response of piles still poorly understood. Therefore, this research examines the seismic response of a pile embedded in soil stratum of saturated fine-grained soils. Midas GTS/NX is used to carry out the number assessment. In addition, the modified UBCSAND soil constitutive model is used to depict the nonlinear features of saturated sand during earthquake waves. The developed three-dimensional model is first validated using the results of a shaking table test of a pile embedded in coarse-grained soil, where good agreement is obtained between the finite element model and the experimental results for the displacement, acceleration, and liquefaction ratio demonstrated good agreement. Furthermore, the orientations of the vectors produced by the numerical study, that matched a global circular flow characteristic, reflected the movement of the liquefied soil all around pile. The findings showed a considerable decrease in the pile frictional resistance during the seismic events as a consequence of increasing the pore water pressure and subsequent liquefaction. Regarding this, before the soil was entirely softened, resistance due to friction was observed near the ground, in correspondence with the loose sand layer. In addition, the pile showed excessive settling, which is due to the decrease of the soil stiffness caused by the increase of the pore water pressure. The results of this research provide an insight into the mechanism of the behavior of pile in saturated coarse-grained soils and thus, it helps to improve future research on the topic and also achieve better design of piles embedded in saturated coarse-grained soils.

In seismically active regions, more large scale wind turbines are installed. These turbines must consider loads induced by base shaking from an earthquake when calculating extreme loads. The objective of this paper is to study the dynamic characteristics of wind turbine considering wind and seismic loads while the turbine is operating. The 5 MW NREL utility scale reference turbine model is used. Different important scenarios are simulated with various loading conditions. The influence of turbulence intensity and the fatigue loads are analyzed and compared. The results indicate that the maximum of dynamic responses and fatigue loads will increase while the combination of earthquake and operational loads is considered, the mean of dynamic responses will decrease as the increase of turbulence intensity with the baseline control system working. It is concluded that it is significant to compressively analyze the dynamic property for wind turbines constructed in seismically active regions.

The past decade has witnessed the great development of super tall residential buildings in China. Optimal design is attracting interests due to the huge energy and material consumption. With the increase of height of modern super tall residential buildings, energy dissipation technologies are widely used to reduce the seismic responses of main structure. As an effective energy dissipation device, viscous damper (VD) can generate damping force by viscosity effects of the viscous liquid. Due to its velocity-dependent nature, viscous dampers can be applied to dissipate seismic energy under different earthquake levels, even frequent earthquake with small seismic responses. VD has been applied in super tall residential buildings, but the integrated optimization of primary structure due to the design redundancy caused by the installation of VD system is commonly not considered in current practices. In this paper, an integrated optimal design method is proposed to improve the stiffness performances through the application of VD system. The integrated optimization of primary structure is also considered in the proposed method. A 250-meter real super-tall residential building project is employed to illustrate the applicability and validity of the integrated optimal seismic performance design method.