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This study aims to present a new three-dimensional moving macroelement for the numerical analysis of beam on the elastic foundation under moving loads as a railroad track vibration. Our research is based on a case study conducted in Iranian Railroad Projects. Due to involving a large number of elements, vibration analysis of beams as railroad tracks with standard three-dimensional elements is time-consuming. Two approaches are used and combined in this research to improve analysis of realistic models. The former is to use a macroelement with a number of degrees of freedom that can be used in lieu of standard three-dimensional elements. The latter is to use moving elements to ensure that the loads do not approach the boundaries of the model, thus leading to boundary errors. Accordingly, the moving element was formulated at different velocities to allow correct evaluation of the trains’ acceleration and deceleration effect. The analysis is based on a linear model. Examples with different number of elements and boundary conditions were included to evaluate the effects of the track parameters. One important aspect of the formulation is the asymmetric nature of stiffness and damping matrices due to the effects of velocity and the moving load. In the moving element method, with a sufficient number of elements, no end condition effect exists. However, because acceleration may be a more critical parameter than displacement, the number of elements must be determined for acceleration, as well. Our important achievements include formulating the interaction of lateral and torsional degrees of freedom, the possibility of calculating probable warping in the beam due to cross-sectional slenderness both directly and based on introducing a dependent degree of freedom, and also determining the model length based on vibrational acceleration at the end of the model. Besides, reduction of analysis time is a prominent feature of the present model.

Recently developed steel self-centring moment-resisting frames have been analytically and experimentally validated as having the potential to eliminate structural damage under a design basis earthquake and restore their original vertical position following a major earthquake. In this study, the repairability index of post-tensioned self-centring frame for near-field earthquake has been developed. According to the six models of the studied building, a building that can be repaired, the maximum rotation in its connection after the earthquake does not exceed the rotation of the immediate occupancy performance. Based on this, the output data of incremental dynamic analysis analyses were drawn according to the connection of relative rotation and spectral acceleration. According to the predicted performance levels for each acceleration level, the value of the connection opening is divided by the opening of the design-basis earthquake level. The resulting curve shows the repairability index according to spectral acceleration, which if less than one, the repairability target is achieved. To evaluate the damage, the angle failure probability of post-tensioned self-centring frame for near-field earthquake has been developed. This index equation is determined according to the fragility curve and the intensity of damage in each building.

Self-centering controlled rocking steel braced-frame (SC-CR-SBF) is proposed as an earthquake-resistant system with low damage. Pre-stressed vertical strands provide a self-centering mechanism in the system and energy absorbing fuses restrict maximum displacement. Presence of asymmetry in structures can highlight the advantages of employing this structural system. Moreover, these days designing and constructing asymmetric and irregular structures is inevitable and as a result of architectural attractiveness and requirements of different functions of buildings, they are of great importance. Consequently, in these types of structures in order to minimize seismic responses, particular measures should be taken into consideration. Proper distribution of strength and stiffness throughout the plan of structures with self-centering systems can play a considerable role in resolving problems associated with asymmetry in these structures. In this study, the asymmetric buildings with 10% and 20% mass eccentricities and having different arrangements of centers were simulated. The models were analyzed under a set of 22 bidirectional far-field ground-motion records and corresponding responses of maximum roof drift, acceleration and rotation of the roof diaphragms of the structures with different arrangements of the center of mass, stiffness and strength were computed and studied. Results show that proper distribution of stiffness and strength throughout the plan of the structures with SC-CR-SBF system reduces the maximum roof drift as well as the rotation of the roof diaphragm. With appropriate arrangement of the centers, maximum drift response of the asymmetric structure decreases as much as roughly 20% and the ratio of the maximum drift response of the asymmetric structure to the response of the similar symmetric structure with the same overall stiffness and strength was 1.1. In other words, maximum drift response of the asymmetric structure with SC-CR-SBF system is acceptably close to the one for the symmetric building.

Synthetic aperture radar (SAR) image registration is still a challenging task in remote sensing. The scale-invariant feature transform (SIFT) method and its extensions are most widely used feature detectors in SAR images. However, due to the presence of nonlinear speckle noise, some wrong features are chosen which directly influence the feature matching process. In this article, for the first time, the KAZE algorithm with a modified version of speeded-up robust features (SURF) descriptor is used for SAR image registration. It uses discrete stochastic second order nonlinear partial differential equations (PDEs) to model the SAR image's edge structure. KAZE uses nonlinear diffusion filtering to build up the scale levels of the SIFT descriptor. It preserves the edges while simultaneously decreasing the speckle noise in smoothing the image. Therefore, it captures the exact location of features in down-sampling and filtering stages of SIFT. Experimental results show that our proposed method has increased the localization accuracy and distinctiveness of feature extraction through the use of KAZE detector. Our method is also able to handle challenging cases in different image sources, different view angles, different image times, complex affine mapping, presence of blurring, and noise.

Vertical mass isolation approach is a new technique in which an individual structure is divided into two distinct subsystems and each possesses different characteristics. Such two subsystems–mass and stiff subsystems– are interconnected with passive dampers in vertical layers at the height of the frame. The primary task of such passive devices is to reduce the structure's seismic reactions by dissipating more of the seismic forces, as well as regulating the amount of structure displacement. In this paper, two models of stiff subsystem placement are introduced, the inner stiff subsystem(ISS) and the outer stiff subsystem(OSS). Structural models are introduced in two types of five and ten-story for both ISS and OSS systems. Metallic dampers were used as fuses to reconnect the isolated structures. For all models under seven distinct earthquake ground motions, nonlinear time history analyses were executed. The findings related to base shear forces, the shape of plastic hinges in structural components, the responses of roof acceleration, and the dampers’ hysteresis behavior are studied. Based on the numerical data, the ISS system has a minor advantage over the OSS system in improving the structure's seismic efficiency and reducing seismic reactions.

Assuming that damages to buildings in earthquake are repairable, retrofitting them is not always economically justified. As an alternative solution, buildings can be designed such that damages are limited to only easily repairable elements. One of the structural systems that provide this possibility is the post-tensioned self-centering moment resistant frame. In self-centering structures, after the event of an earthquake, due to an opening in the gap of beam to column connection and with the help of highly resistant strand tension, residual drift is eliminated. In this study, an attempt is made to develop an efficiency index of post-tensioned self-centering steel moment resistant connections through the analyses of dispersion indices. After a time-history and parametric analysis of three models of steel buildings with self-centering connections, a model will be selected for evaluating the efficiency index that has the lowest sensitivity resulting from dispersion analysis in the study population. Then, between the seven introduced indices, efficiency indices will be compared and optimized. Evaluations show that the Efficiency index of self-centering frame (EISCF), calculated based on coefficient of variance, will increase the accuracy and speed of analysis.

The present study is an attempt to investigate structures equipped with friction dampers under the influence of near-field earthquakes based on Stribeck friction behavior of velocity function. At present, the cyclic behavior of friction dampers in structural design engineering software is simple and based on the Coulomb friction force that is independent of velocity, which should be estimated and considered in terms of Stribeck velocity-dependent friction. Their sliding and vibration methods, including displacement, velocity, and acceleration, are calculated using numerical analysis and differential equation. For this purpose, the representative of the near-field records affects the structure with Stribeck frictional behavior of velocity function as a pulse of Ricker wavelet stimulation. The response of the structure is evaluated in the transition phase from impending motion with a friction coefficient of μs to kinetic motion with μk and vice versa, which makes the poor results of previous simplifications more accurate. Due to the nonlinear behavior of the damping force, programming has been used to perform nonlinear analytical dynamics. Also, behavioral models in OpenSees software are used to investigate the behavior of Stribeck friction for friction damper and to compare its results with the results obtained from accurate analysis.

A linked column frame (LCF) is a seismic-load-resisting system with ductile behaviour. In this system, the link beam, operating as a shear fuse, reduces or eliminates damage to other components of ...

Recently developed steel self-centering moment-resisting frames (SC-MRFs) have been validated analytically and experimentally as having the potential to eliminate structural damage under a ...

Effects of earthquakes on tunnels and underground structures can be investigated in two aspects: longitudinal tunnel behavior and Racking tunnel behavior. In this paper only the effects of the earthquake on tunnel section (racking behavior) is studied by modeling in plane-strain condition. Thus the obtained reduction factor is the tunnel racking reduction factor. In this paper, by performing a pushover analysis and using the proposed methods of Wang (Seismic design of tunnels: a state-of-the-art approach, Parsons Brinckerhoff Quade & Douglas, Inc., New York, 1993) and Hashash et al. (Tunn Undergr Space Technol 16:247–293, 2001) in determination of the tunnel racking deformation and proposing a trial and error pattern, the performance point of the tunnels in the earthquake is determined considering nonlinear behavior of the tunnel lining. In the next step, by using the pushover curve and applying the existing equations of calculating reduction factor in the structures and considering the soil-structure interaction, tunnel racking reduction factor (TRRF) are estimated. Finally, three nonlinear dynamic analyses consistent with the site are performed using finite element software. Comparison between the modified forces by using the reduction factor in the linear static analyses and the forces obtained by applying earthquake records in the nonlinear time history analyses, shows the good accuracy of the obtained reduction factors. The studies also show that implementing linear static analyses without tunnel racking reduction factor leads to very conservative results of lining force in tunnel. Since the TRRF values are sensitive to the soil type and overburden depth, the sensitivity analysis is performed for the overburden depths of 5 and 20 m and two soil types to achieve a more comprehensive result.

Stress reduction factor, λ, is a dimensionless coefficient in two-dimensional (2D) analysis based on convergence confinement method (CCM) of tunnel which represents stress relaxation in the tunnel walls at different excavation steps. The aim of this paper is to look into the influencing factors on parameter λ around the tunnel walls using finite difference code in order to improve the accuracy of the CCM. For this purpose, four different ground types with various tunnel radii, depths and cross section shapes are considered. Finally, the 2D analysis using uniform and variable stress reduction factors determined in this paper is compared with the 3D analysis of the tunnel. The results of this study enhance our understanding of the role of geometrical and soil material parameters of tunnel on stress relaxation around tunnel walls. The tunnel depth, soil type and tunnel shape have great influence on λ. Variable stress reduction factor enables the convergence–confinement method to predict the realistic behavior of third dimension of the tunnel and can also be used as the best alternative to 3D models.

Seyed Ali Tabatabaei1, Mohammad Soleimani2, Mahdi Alizadeh1, Morteza Movasat1, Mohammad Reza Mansoori1, Zakieh Alami1, Alireza Foroutan2, Mahmood Joshaghani2, Saeid Safari2, Arzhang Goldiz21Farabi Eye Research Centre, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran; 2Iran Eye Research Centre, Rassul Akram Hospital, Tehran, IranBackground: The purpose of this study was to determine the predictive value of flash visual-evoked potentials (VEP), relative afferent pupillary defect, and presence of orbital fractures in patients with traumatic optic neuropathy.Methods: A prospective study was conducted in 15 patients with indirect traumatic optic neuropathy. All patients underwent a thorough ophthalmic examination. Initial visual acuity, final visual acuity, and relative afferent pupillary defect were determined, and visual acuity was converted into logMAR units. We performed flash VEP and an orbital computed tomography scan in all patients.Results: There was a good correlation between relative afferent pupillary defect and final visual acuity (r = −0.83), and better initial visual acuity could predict better final visual acuity (r = 0.92). According to findings from flash VEP parameters, there was a relationship between final visual acuity and amplitude ratio of the wave (r = 0.59) and latency ratio of the wave (r = −0.61). Neither primary visual acuity nor final visual acuity was related to the presence of orbital fractures in the orbital CT scan.Conclusion: Patients with traumatic optic neuropathy often present with severe vision loss. Flash VEP, poor initial visual acuity, and higher grade of relative afferent pupillary defect could predict final visual acuity in these patients. Presence of orbital fracture was not a predictive factor for primary visual acuity or final visual acuity.Keywords: visual acuity, flash VEP, RAPD, orbital fracture, CT scan

Scour around pile groups is rather complicated and not yet fully understood due to the fact that it arises from the triple interaction of fluid–structure–seabed. In this study, two data mining approaches, i.e. Support Vector Machines (SVM) and Artificial Neural Networks (ANN), were applied to estimate the wave-induced scour depth around pile groups. To consider various arrangements of pile groups in the development of the models, datasets collected in the field and laboratory studies were used and arrangement parameters were considered in the models. Several non-dimensional controlling parameters, including the Keulegan–Carpenter number, pile Reynolds number, Shield's parameter, sediment number, gap to diameter ratio and number of piles were used as the inputs. Performances of the developed SVM and ANN models were compared with those of existing empirical methods. Results indicate that the data mining approaches used outperform empirical methods in terms of accuracy. They also indicate that SVM will provide a better estimation of scour depth than ANN (back-propagation/multi-layer perceptron). Sensitivity analysis was also carried out to investigate the relative importance of non-dimensional parameters. It was found that the Keulegan–Carpenter number and gap to diameter ratio have the greatest effect on the equilibrium scour depth around pile groups.

The main contribution of this study is investigating the possibility of controlling both displacements and accelerations of asymmetric buildings simultaneously by using linear viscous dampers. The structures are single-storey systems with moment-resisting steel frames and one-way stiffness, strength and damping eccentricities. Linear non-classical modal and nonlinear time history analyses with different ground motions are performed on the models considering different values of eccentricities. Suitable distributions found using the Weak Torsional Balance concept which uses mean square values of lateral displacement or acceleration are compared with distributions found when considering maximum values. The results show that the changes in structural modal properties and different responses by damper distribution are considerable in some cases. Also some distributions are suggested to control lateral displacement, diaphragm torsion and lateral acceleration of the diaphragm.

To investigate the effect of prophylactic subthreshold laser macular grid photocoagulation on drusen area and to evaluate the visual outcome and incidence of choroidal neovascularization in patients with soft drusen maculopathy.In a nonrandomized nonmasked clinical trial, 18 patients (36 eyes) with bilateral soft drusen maculopathy were studied. For each patient, one eye was treated with 48 subthreshold (invisible end-point) applications of 532-nm KTP-laser in a macular grid pattern and the fellow eye was observed. Soft drusen areas were calculated and compared between the two groups at baseline and follow-up visits at 3, 6, 12, and 30 months of therapy. Best corrected visual acuity was also compared in observed and laser-treated eyes. Reduction of drusen area, change in visual acuity, and rate of CNV were assessed in both groups.At baseline, there was no significant difference in the mean drusen surface area between the two groups (P = 0.90). The mean surface area of soft drusen in treated eyes was 6.51 mm(2) after 30 months and 7.58 mm(2) (P = 0.50) in the control eyes. There was a trend towards reduction in the mean soft drusen area after 30 months from baseline in laser-treated eyes (6.51 vs. 6.97 mm(2)). In treated eyes, there was no statistically significant difference between the mean best corrected visual acuity at the baseline (0.28 logMAR) and after 30 months (0.32 logMAR) (P = 0.40).Subthreshold macular grid photocoagulation with 532-nm KTP-laser did not seem to reduce drusen surface area significantly and did not improve best corrected visual acuity after 30 months. No exudative lesion developed in laser-treated eyes.