a. nikkhoo

One of the main damages of the nonstructural masonry walls during an earthquake is its instability and collapse on the combination of deformation at the in-plain direction caused by lateral inter-story drift of structures and out-of-plane inertial forces applied to the wall because of earthquake acceleration. In most of the researches, only one of these actions was investigated, or their interactions were not directly investigated.
In this research, a combination of in-plane and out-of-plane loadings was carried out, and the effect of reinforcing on the nonstructural walls by using fiber mesh reinforced mortar and bed joint rebar has been investigated.
For this purpose, three wall specimens with scale of 1 to 1 were made of Leca blocks. Walls were subjected to a combination of in-plane cyclic loading and out-of-plane loading. The results showed that nonstructural walls, without reinforcement, failed under out-of-plain force in low in-plain drift, and the test process was stopped. On the other hand, strengthening the nonstructural wall with fiber mesh reinforced concrete caused an increase of 15% and 54% in the drift ratio related to the reduction of the wall resistance and the maximum in-plane force compared to the nonstructural wall, which was strengthened with bed joint reinforcement.

One of the most common methods of identifying modal parameters in the field of operational modal testing is the method of identifying sub-random space and frequency domain analysis. Unfortunately, the scope of these methods' application is limited to static signals with a long pick-up time, and if the above conditions are violated, the results will be erroneous; This is in the context that the above two conditions are not met regarding the earthquake signal, and so far the reliability of these methods and their error rate in the face of this group of signals have not been studied. In this regard, in this study, the performance of these methods in earthquake conditions (both conditions are violated) is studied.
For this purpose, an numerical model of two two-dimensional frames with different heights (five and ten floors) is created and stimulated by using 20 earthquake records in the near and far fields. Using the obtained results and comparing them with the results of the numerical model, the error values for the modal parameters are obtained; Also, with the statistical study of the errors in the estimation of the frequency of the structure, the probability distribution function of the error and an estimate of the distance of the error are suggested .The results of the study showed that (a) the method of identifying random subspace has a better performance than the method of frequency domain analysis; (B) The random subspace detection method is not able to detect the first modes and is proposed to identify higher modes; (C) the efficiency of the frequency domain decomposition method decreases with increasing structural height; (D) By optimizing and locating the sensors, the performance of the frequency domain analysis method is dramatically improved. However, in the random subspace detection method, the detectability increases with the number of sensors.

In order to upsurge the maneuverability of micro aerial vehicles, a tubercle leading edge inspired by the whale flipper was applied as a passive stall control method. Although this method could be useful to control stall phenomena, the effect of geometrical properties on the flow physic should be investigated to reach the root of them. According to preceding research, the effect of some parameters on the tubercle leading edge wing is a hot topic among researchers. The aim of this research is to explore the effects of sectional wing geometries like amplitude, wavelength, thickness, maximum thickness location, and camber on the aerodynamic feature of full-span tubercle leading edge wing, particularly at 22 degree in post-stall circumstances. The results present that by reducing the amplitude about 2.5%c, the lift coefficient upsurges by about 3.5%; instead, the drag coefficient reduces about 6%. On the other hand, by decreasing the wavelength from 46.2%c to 11.7%c, the drag coefficient and the lift coefficient decrease by about 15% and 19%, respectively. Furthermore, as the thickness rises from 10.55%c to 18.14%c, the lift and drag coefficient goes down about 9.4% and 2.9%, respectively. Furthermore, by increasing the camber from 2.56%c to 3.34%c, the lift to drag ratio goes down by about 1.06%. Finally, by raising the last design variable (maximum thickness location) from 0.26c to 0.51c, the lift to drag ratio increases about 13.7%.

Dynamic analysis of cracked thin rectangular plates subjected to a moving mass first is investigated in this paper. To this end, the eigenfunction expansion method is utilized to solve the governing equation. For the first time, the intact plate orthogonal polynomials in combination with admissible crack functions as a composition, are employed in the eigenfunction expansion method formulation, required professional computer programming to solve the equation. The proposed approach guarantees upper bound of the true solution, which is the property of an appropriate numerical solution. Parametric investigation is performed to determine the effect of the moving mass weight, the moving mass velocity, the crack length, and the crack angular orientation as well as the plate’s aspect ratio, on the dynamic response of cracked plates. The results confirm, that the moving mass has a greater impact than the moving load on the dynamic responses of cracked plates. Furthermore, there is nonlinear relation among enhancing the dynamic responses of the cracked plates with various boundary conditions, and magnifying the moving mass weights, elevating the moving mass velocities, lengthening the crack length, raising the inclined crack angels as well as augmenting the plates aspect ratios.

In this paper, the dynamic responses of cracked beams under different moving forces, including moving load, moving mass, moving oscillator, and four-degrees-of-freedom moving system, are investigated. Structural elements such as beams are designed to withstand the predicted loads, but unfortunately, they are always exposed to unpredictable damage such as cracks. Several factors may cause these damages, and the important thing is that their presence can affect the dynamic behavior of the beam or even endanger its reliability and durability in some cases. Therefore, this study considers an Euler-Bernoulli single-span beam with simple supports and a crack. First, with the help of the function expansion method and by employing MATLAB software, the dynamic time history responses of the beam at its midpoint under the influence of each type of moving force are extracted. Then, the changes in maximum displacement responses due to various parameters such as velocity, load magnitude, crack depth, and crack location are plotted in different spectra and compared with each other. The results show that the beam will have close results under all types of moving force (moving load, moving oscillator, and moving system) except moving mass. Obviously, this difference is due to the effect of inertia on the moving mass.

This article identifies crack in beams under moving forces (a moving load, a moving mass, a moving oscillator and a four degree of freedom moving system) using the Hilbert Huang transform. Timely identification and repair of damage in structures (such as cracks in bridge decks), especially in those structures that are always under dynamic loads, is very important. In recent years, new methods have been proposed based on the recorded dynamic responses of the structure. most of these methods are based on developed model updating methods which are usually very costly computationally. To overcome this problem, this study presents a method based on the Hilbert-Huang transform. In this method, the bridge is modeled in the form of an Euler-Bernoulli beam and the vehicle is also modeled in different conditions as a moving load, a moving mass, a moving oscillator and a moving system. The results show that the proposed method is able to detect cracks in bridge decks with an acceptable accuracy in all cases.

In this paper, an enhanced method for extraction of modal parameters (frequencies and damping ratios) of a structure from stationary or non-stationary measurement dynamic responses recorded by a sensor is presented. Surely, one of the simplest methods in area of ambient modal identification (operational modal analysis) is autoregressive method. Major problem of autoregressive method is that for identification of m modes of a structure, at least m sensors are needed. Besides, this method like other similar methods in this area such as frequency domain decomposition and stochastic subspace identification is appropriate for extraction of modal parameters from stationary measured dynamic structural responses. To address these issues, in this study, the Hilbert vibration decomposition method, which is a simple method for time-varying vibration decomposition based on the Hilbert transform, is adopted to improve the performance of the autoregressive method for extraction of frequencies and damping ratios of a structure from stationary or non-stationary responses recorded by a sensor. The efficiency and performance of the newly enhanced method are investigated through two numerical examples and a verification example. The first numerical example deals with a single-degree-of-freedom system subjected to a non-stationary force and the second one presents a two-degree-of-freedom structure excited by a stationary force. Finally, by using the proposed method, the frequencies and damping ratios of a support tower of the segmental bridge via an experimental test are obtained. The results indicated that the proposed method adequately estimated the frequencies and damping ratios of a structure from stationary and non-stationary responses recorded by only one sensor. Moreover, it is found that this method outperforms other relevant methods when dealing with non-stationary responses. Consequently, the enhanced method is strongly recommended for extraction of the frequencies and damping ratios of the structures from stationary or non-stationary responses, especially when the dynamic response of the structure is non-stationary and measured using only one sensor.

This study is focused on the propagation of plane harmonic body waves in a transversely isotropic linear poroelastic fluid-saturated medium, where the material symmetry axes for both solid and fluid are coincide. Simplified formulation is considered as the framework. A set of two scalar potential functions is employed to decouple the coupled fluid continuity equation and equations of motion. The velocities and corresponding attenuation coefficients of both longitudinal and transverse waves are extracted from the presented acoustic equations for the body waves. To show the validity of the analytical solution given in this paper, degeneration to the case of a single phase transversely isotropic and consequently isotropic solid is presented to provide interesting comparisons with the solutions reported in the literatures. The incompressible solid and fluid are degenerated from the general slowness obtained in this study for some special cases. In addition, the effects of mechanical and hydraulic parameters of materials on the velocity of propagation and attenuation coefficient of the waves are investigated in more detail. To this end, various synthetic poroelastic transversely isotropic materials are defined and the dependency of wave motion to these parameters is illustrated by plotting the graphs.

Dynamics of beam structures subjected to various loads have been investigated for over a century. The importance of such a problem arises in the structural design of bridges in which the nature of loading could affect the design parameters substantially. It has been observed that as a bridge structure is subjected to moving masses and earthquake loading, the dynamic deflection and stresses can be significantly higher than those observed in the static case. Although only the horizontal component of earthquake excitation is taken into account in the modeling of bridges and parallel beams sustaining the bridge deck loads. there exist several pieces of evidences showing that some of the failure modes are in direct relation to the vertical one. Generally, in comparison with the horizontal component of earthquake, however, the vertical one has less power and most part of its influence occurs in a particular frequency domain that could be so destructive to the structures with natural frequency in these domains. In addition, there are clearly many problems of great physical significance in which the load inertia is not negligible and can significantly alter the dynamic behavior of the system; therefore, moving mass is the another important and affective dynamic loads in design of these routine bridges. In this article, the seismic effect of vertical earthquake on the bridges is studied aiming to explore the necessity of simultaneous acts of this force and the moving masses. By proving the intensifying effects of these loads combination via the obtained results, by employing a passive damper system, it is attempted to decrease the mentioned influences on the studied structure. Dampers are used in two ways. and the best one is chosen based on its performance in suppression of the beam deflection. Finally, through analyzing and comparing the results, a simple algorithm is introduced for reducing the section's dimensions of the bridge structures under this type of loading.

One of the major issues facing structural engineers is assessing the effects of dynamic loads on structural systems, including beams. The importance of this matter arises in moving vehicles such as cars and trains on bridge structures that are usually simulated by beam structures. Hence, in several studies, in order to explore the dynamic response of the beam structures under the excitation of dynamic loads, various analytical and numerical methods have been utilized. In this study, to examine the easier and faster procedures aimed at finding the dynamic response of Euler-Bernoulli, Timoshenko and Higher-Order beams, a simple semi-analytical method based on the characteristic orthogonal polynomials and trigonometric functions compatible with boundary conditions is presented. To this end, discrete equations of motion are derived for the three mentioned theories due to a moving mass according to the Hamilton’s principle. Then, the governing equations are transformed into ordinary differential equations in the time domain, and by applying an approximate method, displacement field of the beam is achieved. In order to consider the efficiency, convergence rate and accuracy of this method, two numerical examples are provided to compare the results of this paper with those presented by other researchers. In this regard, in the former one, free vibration frequencies of the beam with various theories for different boundary conditions were obtained, and it is shown that, the results for all three theories, give a good convergence rate and a high accuracy. Furthermore, in the latter example, the dynamic response of the beams subjected to a moving mass for different values of the base beam slenderness was achieved and compared with other studies. Analysis of the maximum dynamic response of the beam and the time history diagrams illustrated the obtained results are in a close agreement with those issued from the numerical method; despite using the lower number of the shape functions.