Journal of Numerical Methods in Civil Engineering
Volume:3 Issue: 2, Dec 2018

This paper presents a new method for detecting beam and frame damage caused by an earthquake. Despite comprehensive investigations on structural damage detection, which mostly have focused on damage detection of elastic structures, the present study deals with nonlinear damage detection in structures. Furthermore, in the proposed method, only measurements of the damaged structures during an earthquake are required and the measurement of undamaged structure is redundant. The proposed method is based on the use of curvature of beams in order to detect plastic zones. To evaluate the efficiency of this method, the beams with different boundary conditions and mass distributions as well as a one-bay single-story moment frame were modeled in OpenSees software and exposed to the accelerations of Cape, Chichi, and El Centro earthquakes. The curvature vectors calculated using data from acceleration recording points were utilized to detect the place and severity of the damage. Furthermore, in an attempt to reduce costs of actual damage detection, the number of accelerometers were reduced using the cubic spline method of interpolation. Finally, an experimental study was operated to show the effectiveness of the proposed method to determine the length and depth of plastic zones with reasonable accuracy.

This paper presents the Real-Time Recursive Dynamics (RTRD) model that is developed for driving simulators. The model could be implemented in the Driving Simulator. The RTRD can also be used for off-line high-speed dynamics analysis, compared with commercial multibody dynamics codes, to speed up mechanical design process. An overview of RTRD is presented in the paper. Basic models for specific vehicle subsystems such as tire, steering, brake, power train, aerodynamics, etc., are interfaced with multibody dynamics to create a complete vehicle simulation model. Basic theories of each vehicle subsystem model are introduced and the interfaces with the multibody dynamic model are discussed. Required data for setting a vehicle model listed and an Army’s High Mobility Multipurpose Wheeled Vehicle (HMMWV) modeling example is illustrated. For operator-in-the-loop simulation, the interface between the RTRD model and the simulator subsystems, i.e., visual, motion, audio, and terrain database, is presented. Finally, the parallel processing algorithm of RTRD model is illustrated. Benchmarks for the baseline RTRD code are analyzed using two vehicle examples, a passenger car and a tractor-semitrailer.

While the design criteria for buckling-restrained braced frames are advancing, understanding the functional behavior of these types of frames during the occuring earthquakes can considerably contribute  in the evolution of the design criteria for these frames. In this regard, taking the modeling uncertainties into account  will help in carrying out a more rational seismic performance assessment and seismic design of these types of structures. The main goal of this manuscript  is to include the modeling uncertainties in the seismic loss mathematical curves of the buckling-restrained braced frames (BRBF). The variation of the modulus of elasticity and the yield strength constitute the sources of the uncertainties  for this study. The two-dimensional 4-, 8-, and 12-story frames ,selected from symmetrical three-dimensional structures, were studied. Finally, it was concluded that the uncertainties existed in the yield stress and the modulus of elasticity parameters were more effective on the probabilistic seismic demand curves for the lower intensity levels, than the higher strong ground motion intensities. Besides all these, the variations of seismic-induced loss curves are presented considering the effect of the uncertainties compared to those neglecting the uncertainties. The calculated loss curves confirm the  significance of taking the sources of uncertainties into account in the seismic loss analysis of the structures.

In this article, the buckling behavior of tapered Timoshenko nanobeams made of axially functionally graded (AFG) materials resting on Winkler type elastic foundation is perused. It is supposed that material properties of the AFG nanobeam vary continuously along the beam’s length according to the power-law distribution. The nonlocal elasticity theory of Eringen is employed to contemplate the small size effects. Based on the first-order shear deformation theory, the system of nonlocal equilibrium equations in terms of vertical and rotation displacements are derived using the principle of total potential energy. To acquire the nonlocal buckling loads, the differential quadrature method is used in the solution of the resulting coupled differential equations. Eventually, an exhaustive numerical example is carried out for simply supported end conditions to investigate the influences of significant parameters such as power-law index, tapering ratio, Winkler parameter, aspect ratio, and nonlocal parameter on the buckling capacity of AFG Timoshenko nanobeams with varying cross-section supported by uniform elastic foundation.

In super-tall buildings, the impacts of wind loads are of more importance than earthquakes, and inevitably, the wind tunnel testing provides reliable results of the wind loads due to their high level of sensitivity and accuracy, although it burdens a high cost. In this paper, we have applied the ‘numerical methods’ in order to obtain the 2D and 3D drag coefficients. The CFD simulation was performed by the “ANSYS FLUENT” software. The results shown by the k-ω Shear Stress Transport (SST) turbulence model within a fine mesh and by selection of the small time-step size and also increasing the number of iterations… , prove that the accuracy of the analysis is enhanced in which it is valid for the Large Eddy Simulation (LES) model as well. The Grid Convergence Index ( GCI ) is obtained using the uniform velocity and pressure coefficients within a reasonable range, which is maintained by an average mesh in order to minimize the spent time and the associated cost. Meanwhile, the pressure-correction gradient along the cell faces is more compatible with the results obtained by Kawamoto except one point. As the duration of winding increases, the negative (vacuum) pressure on the leeward side develops and the wake also moves farther. The results also show that the maximum wind pressure applied to the building using the SST method is larger than the one in the LES method, but the LES method has less variation in height. Moreover, the wind resisting behavior of super tall buildings is better represented by3D modeling and the results of the simulation are more accurate and realistic, according to the experimental results.

in this paper, the mechanical buckling behavior of circular plates with variable thicknesses made of bimorph functionally graded materials (FGMs) under uniform mechanical loading circumstances has been studied for the first time. The governing equations are derived based on the first-order shear deformation plate theory and von Karmanchr('39')s assumptions. The material characteristics are symmetric about the middle plane of the plate and these characteristics vary along the thickness direction according to the power law. The middle plane of the plate is made of pure metal, which changes to pure ceramic as it approaches the outer sides. In order to determine the pre-buckling force in the radial direction, the membrane equation is solved using the shooting method. Then, the stability equations are solved numerically with the help of pseudo-spectral method and choosing the Chebyshev polynomials as basis functions. The numerical results are presented for both clamped and simply supported boundary conditions by considering linear and parabolic patterns for the thickness variations. The influences of various parameters like volume fraction index, thickness profile and side ratio on the buckling behavior of these plates have been evaluated. The obtained numerical results show that there exists an optimal value for the thickness parameter, wherein the buckling load becomes maximum. The buckling load of circular FGM plates increases more than 100% when the volume fraction index increases from 0 to 5. The buckling load of the clamped circular FGM plates decreases about 15% as the side ratio increases from 0.01 to 0.2.