The availability of methods for the identification of nonlinear hysteretic systems is crucial for the assessment of the health and the repair of civil infrastructures during and after severe earthquakes. However, most methods used to identify hysteretic systems suffer from two problems: (1) the structural responses at all dynamic degrees of freedom(DOFs) must be measured, which is obviously impractical for real applications; and (2) the nonlinear model of a system is assumed to be known, and only the model parameters are to be identified, meaning that the nonlinear characteristics of the underlying structures may not be captured accurately. To overcome these two problems, this paper proposes a novel method that does not assume a nonlinear model and that does not require measurements at all DOFs. The new approach alternately uses the extended Kalman filter (EKF) and wavelet (W) multiresolution analysis. Within each time step, the identification can then be divided into two stages. In stage one, based on limited-state observations and the structural model at previous step, the structural responses at all DOFs are estimated using the EKF method. In stage two, based on the estimated full states, wavelet multiresolution analysis is used to identify the tangent stiffness matrix and the hysteresis-restoring force curves of the structure (i.e., the structural model is updated using the estimated full states). Two model structures with various nonlinearities at different locations, and with various state-observation schemes, are employed to conduct the numerical study. The numerical results verify the efficiency and accuracy of the proposed method. The best location for state observation is also discussed in the numerical study. DOI: 10.1061/(ASCE)EM.1943-7889.0000510. (C) 2013 American Society of Civil Engineers.
The screening effects of trenches on train-induced ground vibration are investigated by an analytical method. The embankment and soil banks beside the trench are modeled as elastic layers with appropriate widths. A fully saturated poroelastic half-space is first utilized in the investigation of the isolation of train-induced ground vibration. Biot's theory is applied to characterize the saturated poroelastic half-space, considering the coupling between the soil skeleton and the fluid. Based on Fourier transforms and Fourier series, the governing equations are solved. The various performances of the trenches on the single-phase elastic half-space and saturated poroelastic half-space as screening barriers to mitigate the ground vibration are specially investigated. It is found for the vibration generated by the axle train load with supercritical speed that the discrepancy between the screening efficiency of the trenches on the poroelastic half-space and elastic half-space is significant; the single-phase elastic half-space model may significantly underestimate the screening effect of the trench. In addition, an excellent screening effect can be achieved by an open trench to the ground vibrations generated by the dynamic wheel-rail load. DOI: 10.1061/(ASCE)EM.1943-7889.0000460. (C) 2013 American Society of Civil Engineers.
Reinforced concrete (RC) structures when subjected to sudden destruction of a column by blast pressure, experience dynamic effects in its response. Hence, reliability assessment of the damaged ductile frame against progressive collapse under dynamic loading conditions is conducted in this research. This paper aims at establishing three performance functions, two of which will consider structural collapse due to lack of strength and deformation capacity respectively while the third will incorporate the shear response of structural components for the weakest collapse mechanism. Since any of the performance functions may lead to structural collapse, a global performance function of the damaged structure is developed by considering the minimum of the functions. The results are then used in conjunction with Monte Carlo Simulation (MCS) to estimate the reliability of the damaged structure. A numerical example of a four storey RC frame is presented to address the applicability of the proposed approach and the effects of different structural parameters on its reliability against progressive collapse after the sudden column loss are investigated thereafter.
In the first part of this paper, an exact analytical solution in closed form for linear long-wave reflection by a submerged idealized breakwater or trench with various curvilinear slopes is given. The solution obtained finds almost all previous long-wave analytical solutions for wave reflection by idealized bathymetries to be its special cases, including the wave reflection by an infinite step, a continental shelf with a parabolic slope, a continental shelf with a linear slope, a rectangular obstacle, an obstacle of general trapezoidal shape with linear slopes, and a trench of general trapezoidal shape with linear slopes. In the second part, an exact analytical solution in the form of a Taylor series for linear long-wave reflection by a submerged quasi-idealized breakwater or trench is also constructed. It is shown by convergence analysis that the series solution converges in the entire physical domain. Based on the present analytical solutions, the reflection coefficients for long waves reflected by various breakwaters are calculated and the influence of the breakwater dimensions in the reflection effect is investigated. It is always found that the total reflection defined by the area under the reflection coefficient curve increaseswhen the front and back slopes become steep. It is also found that the phenomenon of zero reflection for a symmetrical rectangular breakwater still remains for a general breakwater with curvilinear slopes as long as the bathymetry is symmetrical about the breakwater. DOI: 10.1061/(ASCE)EM.1943-7889.0000483. (C) 2013 American Society of Civil Engineers.
AbstractHybrid simulation combines numerical simulation and experimental testing in a loop of action and reaction to capture the dynamic behavior of a structure. With an extended time scale, convergence of the desired displacements or forces can be assured in each actuator connected to the experimental component before advancing to the next time step. However, when the rate-dependent behavior of an experimental component is of interest, the hybrid simulation must be conducted in real time [i.e., real-time hybrid simulation (RTHS)]. In RTHS, the dynamic behavior of the loading system (i.e., actuators, controllers, and computers) is directly introduced into the RTHS loop. These dynamics consist of both time delays and frequency dependent time lags. At the same time, the phenomenon of control-structure interaction leads to a coupling of the dynamic behavior of the actuators and the structure. Traditional actuator control approaches for RTHS compensate for an apparent time delay or time lag rather than addres...
