Structural damages during an earthquake are typically controlled by seismic demands, which are represented by the combination of amplitude of ground motion and cyclic load effects. Since traditional methods normally assume the lognormal distributions of seismic demands and resistance parameters, uncertainties are inevitably induced in the seismic fragility analysis. In this paper, the Copula function and adaptive bandwidth kernel density estimation method (ABKDE) are used to establish a novel multidimensional seismic fragility analysis framework. Based on the results of incremental dynamic analysis for subway station structures, ABKDE is adopted to establish single-parameter seismic fragility curves for both the maximum inter-story drift ratio (MIDR) and cumulated dissipated hysteretic energy (CDHE), respectively. Subsequently, the Copula function is used to formulate a bivariate seismic fragility function considering the correlations among seismic demand measures and establish the corresponding fragility curves. Finally, comparative analyses are conducted to evaluate seismic fragility curves using Copula-based dual and single-parameter damage models as well as the traditional damage models. It is found that the seismic fragility analysis method using the Copula function has the ability to gain a comprehensive consideration of the MIDR and CDHE during the damage process of subway station structures. Moreover, this newly developed seismic fragility analysis framework can capture the influence of the correlation between deformation and energy under various peak ground accelerations on structural damage. Thus, this framework can provide a scientific basis for predicting structural damage in subway stations subjected to varying intensities of ground motion while considering multiple damage indicators.

为有效进行波浪荷载作用下海洋导管架平台动力响应实时预测,提出一种综合一维卷积与门控循环复合神经网络(1DCNN+GRU)的动力响应预测方法.基于SACS程序平台建立单层甲板的四桩腿导管架数值计算模型,通过非线性数值模型分析其在波浪作用下动力响应状态,从而得到结构动力响应时程样本数据,并经标准化处理后,输入到由Pytorch框架搭建的复合神经网络中进行训练与测试.计算分析结果表明:该1DCNN+GRU复合神经网络预测方法具有良好的求解精度和稳定性,各求解步时长远小于预测提前量,能够实现海洋导管架平台动力响应的实时预测,可为相关工程实践提供参考.

采用SACS软件建立海上风机导管架基础频域疲劳分析模型,选取不同波浪谱与谱参数生成波浪荷载,选用不同S-N曲线及SCF经验公式计算导管架基础及与塔筒连接部位疲劳寿命,分析关键参数对结构热点部位疲劳寿命计算结果的影响.分析表明,S-N曲线、SCF计算方法、波浪谱、腐蚀、桩土弱化作用等因素对导管架基础管节点疲劳寿命计算结果均具有较大影响.

The circular helicoid pile (CH pile) is a special-shaped pile with outstanding axial bearing properties developed in the last ten years, its pile-soil interaction problem has nonplanar strain and is non-axisymmetric. The coupled Eulerian-Lagrangian (CEL) method was applied to simulate the entire process of installation, axial compression and pullout loading of the CH pile in undrained clay to assess the interaction between the pile and soil, and the accuracy of the CEL model was verified by in-situ test results. The surfaces of the CH pile were divided into the bottom surface, outer and inner surfaces, with the inner surfaces including compressive and pullout surfaces. The variation in axial forces and moments on the CH pile and its various types of surfaces in the whole process of installation and bearing was clarified and the relative contribution of reacting forces and moments on various surfaces to the total resistance of the pile was evaluated. The stress distribution characteristics of the soil around the pile and the pile-soil interfaces after the installation of the CH pile and under the ultimate limit state were obtained, and then the force states of inner surfaces in the whole process of installation and bearing were analysed.

Using iron ore tailings (IOTs) as the main aggregate for concrete will not only save crushed stone mining but will also reduce the environmental impact of IOTs. A discrete element model of concrete with realistic IOTs shape was developed using particle flow coding 3D technique. The accuracy of the numerical model was verified with the laboratory uniaxial compressive test results, and the damage of concrete with IOTs of 40

Based on the theory of Biot’s two-phase medium and Novak’s thin layer, a coupled mechanical model of pipe pile and radially inhomogeneous saturated soil is established by comprehensively taking into account the saturated surrounding soil’s construction disturbance effect and the influence of the pipe pile’s saturated inner soil. First, the displacements and horizontal impedances of the surrounding and inner soil are derived using the potential function, Laplace transformation and variable separation methods. Second, the analytical solution for the horizontal impedance of pile head is obtained by combining the conditions of the displacement continuity and stress equilibrium on the soil-pile interface. Finally, the obtained solution for the pile head’s horizontal impedance is reduced to validate the rationality of the proposed solution by making comparisons with existing solutions. On this basis, a detailed parametric analysis is given to explore the influence of the pile parameters and construction disturbance effect on the horizontal vibration characteristics of pipe pile.

A rigorous analytical model for partially embedded large-diameter floating pile (PLFP) is devised based on a three-dimensional continuum pile and soil model. The analytical solutions to the dynamic response of PLFP are obtained using Fourier transformation and variable separation. Then, the accuracy of the obtained dynamic impedance and velocity is verified by comparing the derived values with existing solutions and the measured data of the experimental model. Finally, parameter analyses of dynamic impedance and velocity response are conducted. The results indicate the following. The use of a one-dimensional pile model to calculate the dynamic impedance of PLFP results in the overestimation of resonance amplitude and frequency. Defect detection is more difficult to implement in a partially embedded pile than in a fully embedded pile. In practice, the suitable position for a signal receiver installed on a pile head during low-strain pile integrity testing is 0.6r0.

To investigate the seismic response characteristics of piled wharf structures, a numerical model of the soil-structure interaction system is established. Extensive fiducial error and grey correlation analyses are also conducted to obtain the grey correlation degree sequence of the internal force of piled wharf structure and deformation, as well as the acceleration of surrounding soils. The results show that the peak acceleration at the typical point of the soil is more sensitive to the variations in friction angle and ground motion intensity, while the lateral extreme displacement is the most sensitive to the variations in the elastic modulus of the soil. The grey correlation sequences of the peak acceleration and lateral extreme displacement at the feature points of the soil around the pile greatly vary, indicating that the key factors of the different sequences control the target parameters corresponding to them. The sensitivity of the internal force of the pile foundation of the pier structure to the ground motion intensity and friction angle is more sensitive than the elastic modulus and cohesion. This presented parameter sensitivity analysis procedure for the seismic response of piled wharf structures can provide a reference for the seismic design of piled wharf structures, as well as for disaster prevention prediction.

为分析大直径浮承桩纵向振动特性,基于黏弹性连续介质理论同时考虑桩身和桩底土的三维波动效应,提出了一种三维虚土桩模型.首先,采用拉普拉斯变换和分离变量法求解得到桩身和桩底虚土桩的位移基本解;然后,结合桩-土及桩-虚土桩完全耦合条件,推导得出大直径桩桩顶动力阻抗解析解,并通过与已有解答对比分析验证了推导所得解析解的合理性和准确性;最后,利用数值算例分析了桩顶径向位置及三维虚土桩参数对大直径浮承桩桩顶动力阻抗的影响.计算结果表明:大直径桩顶动刚度和动阻尼呈现由桩中心向桩边缘减小的趋势,且桩长径比越小桩顶动力阻抗的这种径向不均匀性越明显;对于大直径桩忽略桩身径向波动效应会过高估计桩顶动力阻抗的振幅和频率,不利于桩基抗振防振设计;三维虚土桩模型不仅对于大直径浮承桩纵向振动问题具有更好的适用性,而且可以通过调整虚土桩参数将其应用于端承桩动力特性分析中.

The circular helicoid pile (CH pile) is a new type of special-shaped pile that has been developed in Japan and South Korea in the past decade and has been widely used in the fields of construction, transportation, natural energy and agriculture due to its excellent compressive and pullout bearing performances. Consequently, this new type of pile has good engineering application prospects. However, as an innovative engineering structure, the CH pile is not widely known by geotechnical engineers worldwide. The geometric structure of the CH pile is similar to a circular helicoid in differential geometry. Therefore, the pile-soil interaction problem cannot be reduced to a plane strain problem or an axisymmetric problem in theoretical research. In view of this, dry silica sand was used as the model foundation in this study, and a model test device and method that can effectively reflect the installation process and loading-bearing service state of CH piles were developed. Under different installation methods, pile structures and foundation soil conditions, 90 model tests were carried out to evaluate the engineering performances of CH piles during the whole process of installation and bearing, including the installation performances during the installation process, the compressive bearing performances under axial compressive loading and the pullout bearing performances under axial pullout loading. Compared with steel sheet piles and steel pipe piles, CH piles have better engineering performance and more economic benefits from the aspects of installation, construction, recycling, timeliness of engineering application, and the relative relationship between bearing capacity and pile mass.