Earthquake Engineering and Engineering Vibration最新文献

This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading. The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time, before the damping forces can dissipate a significant portion of the energy input into the system. The development of two sine series solutions, relating to different types of impulsive loadings, one involving a single concentrated force and the other a distributed line load, are presented. This study revealed that when a simply supported Euler-Bernoulli beam, resting on a Winkler soil model, is subject to an impact load, the resulting vertical displacements, bending moments and shear forces produced along the span of the beam are considerably affected. In particular, the quantification of this effect is best observed, relative to the corresponding static solution, via an amplification factor. The computed impact amplification factors, for the sub-grade moduli used in this study, were in magnitude greater than 2, thus confirming the multiple-degree-of-freedom nature of the problem.

With the rapid development of large megawatt wind turbines, the operation environment of wind turbine towers (WTTs) has become increasingly complex. In particular, seismic excitation can create a resonance response and cause excessive vibration of the WTT. To investigate the vibration attenuation performance of the WTT under seismic excitations, a novel passive vibration control device, called a prestressed tuned mass damper (PS-TMD), is presented in this study. First, a mathematical model is established based on structural dynamics under seismic excitation. Then, the mathematical analytical expression of the dynamic coefficient is deduced, and the parameter design method is obtained by system tuning optimization. Next, based on a theoretical analysis and parameter design, the numerical results showed that the PS-TMD was able to effectively mitigate the resonance under the harmonic basal acceleration. Finally, the time-history analysis method is used to verify the effectiveness of the traditional pendulum tuned mass damper (PTMD) and the novel PS-TMD device, and the results indicate that the vibration attenuation performance of the PS-TMD is better than the PTMD. In addition, the PS-TMD avoids the nonlinear effect due to the large oscillation angle, and has the potential to dissipate hysteretic energy under seismic excitation.

H-steel all-bolted connection steel frame structures with heat preservation and decoration composite wall boards were investigated and the seismic performances of three scaled specimens were studied. The failure modes, hysteresis curves, bearing capacity, ductility, energy dissipation capacity, stiffness degradation and strain distribution were discussed. The calculation method of structural theoretical internal force was presented. The results showed that the overall structural seismic performance was better, and the structural ductility met the demands of elastic-plastic inter-story drift angle for seismic design. The H-steel weak-axis connection structure obtained better energy dissipation capacity, and its bearing capacity and stiffness were slightly different from the strong-axis connection. The heat preservation and decoration performance of composite wallboard and the all-bolted connection of the steel frame realized prefabrication during the whole construction period. The plastic hinge of the steel beam can be moved outwards because of the L-angles, which effectively avoids stress concentration in joint areas and expands the plastic hinge range. The errors between the theoretical structural capacity calculated by the plastic analysis method and the test results were within 2.44%. In addition, structural failure mechanisms and bearing capacities were verified by the finite element (FE) analysis, and the effects of the main parameters on the structures were investigated. The FE verification results were the same as in the test. The research results provide theoretical support and technical guidance for the application of thermal insulation and decorative composite wall panels in H-shaped steel all-bolted steel frames.

A resilience-incorporated risk assessment framework is proposed and demonstrated in this study to manifest the advantageous seismic resilience of precast concrete frame (PCF) structures with “dry” connections in terms of their low damage and rapid recovery. The framework integrates various uncertainties in the seismic hazard, fragility, capacity, demand, loss functions, and post-earthquake recovery. In this study, the PCF structures are distinguished from ordinary reinforced concrete frame (RCF) structures by characterizing multiple limit states for the PCF based on its unique damage mechanisms. Accordingly, probabilistic story-wise pushover analyses are performed to yield story-wise capacities for the predefined limit states. In the seismic resilience analysis, a step-wise recovery model is proposed to idealize the functionality recovery process, with separate considerations of the repair and non-repair events. The recovery model leverages the economic loss and downtime to delineate the stochastic post-earthquake recovery curves for the resilience loss estimation. As such, contingencies in the probabilistic post-earthquake repairs are incorporated and the empirical judgments on the recovery parameters are largely circumvented. The proposed framework is demonstrated through a comparative study between two “dry” connected PCFs and one RCF designed as alternative structural systems for a prototype building. The results from the risk quantification indicate that the PCFs show reduced loss hazards and lower expected losses relative to the RCF. Particularly, the PCF equipped with energy dissipation devices at the “dry” connections largely reduces the expected economic loss, downtime, and resilience loss by 29%, 56%, and 60%, respectively, compared to the RCF.

This study presents a neural network-based model for predicting linear quadratic regulator (LQR) weighting matrices for achieving a target response reduction. Based on the expected weighting matrices, the LQR algorithm is used to determine the various responses of the structure. The responses are determined by numerically analyzing the governing equation of motion using the state-space approach. For training a neural network, four input parameters are considered: the time history of the ground motion, the percentage reduction in lateral displacement, lateral velocity, and lateral acceleration, Output parameters are LQR weighting matrices. To study the effectiveness of an LQR-based neural network (LQRNN), the actual percentage reduction in the responses obtained from using LQRNN is compared with the target percentage reductions. Furthermore, to investigate the efficacy of an active control system using LQRNN, the controlled responses of a system are compared to the corresponding uncontrolled responses. The trained neural network effectively predicts weighting parameters that can provide a percentage reduction in displacement, velocity, and acceleration close to the target percentage reduction. Based on the simulation study, it can be concluded that significant response reductions are observed in the active-controlled system using LQRNN. Moreover, the LQRNN algorithm can replace conventional LQR control with the use of an active control system.

Pile foundations are still the preferred foundation system for high-rise structures in earthquake-prone regions. Pile foundations have experienced failures in past earthquakes due to liquefaction. Research on pile foundations in liquefiable soils has primarily focused on the pile foundation behavior in two or three-layered soil profiles. However, in natural occurrence, it may occur in alternative layers of liquefiable and non-liquefiable soil. However, the experimental and/or numerical studies on the layered effect on pile foundations have not been widely addressed in the literature. Most of the design codes across the world do not explicitly mention the effect of sandwiched non-liquefiable soil layers on the pile response. In the present study, the behavior of an end-bearing pile in layered liquefiable and non-liquefiable soil deposit is studied numerically. This study found that the kinematic bending moment is higher and governs the design when the effect of the sandwiched non-liquefied layer is considered in the analysis as opposed to when its effect is ignored. Therefore, ignoring the effect of the sandwiched non-liquefied layer in a liquefiable soil deposit might be a nonconservative design approach.

Large numbers of basic transceiver stations, where the telecommunication room is one of the main components, comprise an important part of the telecommunication system. After earthquakes, considerable economic loss from telecommunication systems is often associated with seismic damage and functional loss of the telecommunication room. However, research related to this has been limited. In this study, shaking table tests were conducted for a full-scale typical telecommunication room, including a light-steel house and the necessary communication and power supply equipment. The tests not only focused on the seismic damage to all the structures but also considered the functions of the communication and power supply of the equipment. The interactions between these facilities and their effects on communication function were also investigated. Compared with the damage to structures, the interruption of the power supply due to earthquakes is a weak link. Finally, the damage indexes, together with their threshold values of different damage states for the communication and power supply equipment, were derived from the test results. The results of this research can contribute to the literature gaps regarding seismic performance studies of telecommunication rooms, and can serve as a valuable reference for future research on its seismic fragility and economic losses evaluation.

Earthquake-induced slope failures are common occurrences in engineering practice and pre-stressed anchor cables are an effective technique in maintaining slope stability, especially in areas that are prone to earthquakes. Furthermore, the soil at typical engineering sites also exhibit unsaturated features. Explicit considerations of these factors in slope stability estimations are crucial in producing accurate results. In this study, the seismic responses of expansive soil slopes stabilized by anchor cables is studied in the realm of kinematic limit analysis. A modified horizontal slice method is proposed to semi-analytically formulate the energy balance equation. An illustrative slope is studied to demonstrate the influences of suction, seismic excitations and anchor cables on the slope stability. The results indicate that the stabilizing effect of soil suction relates strongly to the seismic excitation and presents a sine shape as the seismic wave propagates. In higher and steeper slopes, the stabilizing effect of suction is more evident. The critical slip surface tends to be much more shallow as the seismic wave approaches the peak and vice versa.

Surface wave inversion is a key step in the application of surface waves to soil velocity profiling. Currently, a common practice for the process of inversion is that the number of soil layers is assumed to be known before using heuristic search algorithms to compute the shear wave velocity profile or the number of soil layers is considered as an optimization variable. However, an improper selection of the number of layers may lead to an incorrect shear wave velocity profile. In this study, a deep learning and genetic algorithm hybrid learning procedure is proposed to perform the surface wave inversion without the need to assume the number of soil layers. First, a deep neural network is adapted to learn from a large number of synthetic dispersion curves for inferring the layer number. Then, the shear-wave velocity profile is determined by a genetic algorithm with the known layer number. By applying this procedure to both simulated and real-world cases, the results indicate that the proposed method is reliable and efficient for surface wave inversion.

Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes, its application on polyethylene (PE) pipe remains relatively unexplored. The growth of internal cracks in PE pipe severely affects its pressure-holding capacity, hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies. This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe. Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration. Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency, leading to the selection of the T(0,1) mode at 50-kHz for the investigation. A transmission index based on the energy of the T(0,1) mode was developed to trace the extent of simulated crack growth. The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20% crack depth.