سال:1393 | دوره: | شماره: |تعداد مقالات:10

Bridges are key elements of transportation systems. Previous seismically induced damages to these structures revealed the necessity of seismic vulnerability assessment of them according to performance-based earthquake engineering philosophy. The purpose of this study is applying Incremental Dynamic Analysis for seismic assessment of a typical two span concrete bridge according to this philosophy. Incremental dynamic analysis consists of scaled time history analyses to gain structural performance under different levels of ground motion excitation. 2D model of the bridge structure was constructed in Open System for Earthquake Engineering Simulation. Peak Ground acceleration and column curvature ductility factor were chosen as intensity measure and seismic performance indicator, respectively. Eight time history records of past earthquakes were scaled and applied incrementally to the numerical model to evaluate seismic performance of the bridge. Damage states were defined as slight, moderate, extensive and collapse state. The resulted curves can be used to estimate mean annual frequency of exceeding each damage state.

Recently researchers and engineers have been in favour of optimized and efficient designs of all different types of structures, by directing their attention to non-destructive testing and most importantly computer simulations. Thus avoiding time consuming testing, and understanding the true behavior of materials within structures under different loading setups. One of the newly used computer aided analysis methods employed today is the discrete element method (DEM) embedded in PFC computer software. The main purpose of the DEM modeling conducted for this study was to supplement previous research conducted into the area of hot mix asphalt and rock fracture evaluation. The models created for this study demonstrated that PFC software is a powerful analysis tool that can be adapted to a variety of scientific and engineering applications, and has proved to be a very useful tool for modeling several HMA laboratory tests, and with proper modification it can also be adapted to modeling many other materials.

The purpose of this study is to design and construct an instrument for assessing three-dimensional hydraulic gradients based on the hydrogradient mathematical model in porous media. In order to properly investigate flow in porous media, three-dimensional details must be taken into consideration. Therefore, Mohr cyclides, which can be presented in three dimensions, are used and a beneficial instrument is designed and constructed based on the non-collinearity of the flow vector q and gradient vector J.The cyclide surface is a geometric locus for all possible states of flow movement in a porous media field; depending on the field’s hydraulic gradient components, in which one of these flow movements will occur. By specifying the values of the hydraulic gradient components, the flow direction will be assigned.

This paper presents the test results of three precast and one monolithic connection in moment-resisting concrete frame subjected to constant axial compression and lateral reversed cyclic loads. The precast specimens had cast-in-place concrete connections with different details, namely straight spliced (PC1), U-shaped (PC2), and U-shaped with steel plate (PC3).The results for Hysteresis loops, strength, damping, energy dissipation and ductility are presented. Comparisons of performance parameters revealed that the behavior of PC1 was more similar to monolithic Specimen and it can be used in high seismic zones. The other two precast connections are recommended to be used in moderate seismic regions.

In recent years, Pseudo-dynamic (PsD) technique is being adopted as an alternate to conventional shake-table technique to evaluate the seismic performance of structures. The shake-table technique has the merit of simulating all the three force parameters namely inertial, damping and elastic forces in the tested structure realistically; however the technique needs sophisticated shake-table driven by servo controlled actuators with appropriate control electronics. On contrary, PsD technique simulates the three force parameters by using a static actuator through application of an equivalent pseudo-dynamic force system with computation of inertial forces in the back-ground. Such a hybrid technique needs specialized algorithm based on an appropriate mathematical model for the off-line time integration and computation of inertial forces. Several time integrals have been proposed for application in PsD testing and majority of them are derived from Newmark-b family of algorithms. The traditional PsD testing uses constant acceleration version of Newmark time integral in explicit form for mathematical simplicity. This simplified explicit formulation results in numerical damping leading to considerable amplitude error in PsD testing, limiting its application to simple structures. However, for complicated structures improvement is needed in the time integral form leading to unconditional stability and zero numerical damping. This paper presents an improved form of Newmark implicit time integral for PsD testing. The improvement is based on the inclusion of an additional term in displacement predictor, which not only renders the algorithm more consistent, but also eliminates numerical damping and makes the algorithm unconditionally stable. The paper presents the analytical study carried out on the stability and energy dissipation properties of the improved time integral by evaluating its spectral characteristics for verifying its suitability in PsD testing.

Following a comparative study of a number of representative methods for the preparation of a concrete mix, the present paper presents the results one of such methods, namely that of Dreux-Gorisse. This method combines a graphical approach with an analytical one, alongside the use of established correction tables. This study therefore proposes to present the various stages necessary for preparation of a concrete mix using the Dreux-Gorisse method in an automatic way. The purpose of this automation is to enable the preparation of a variety of mixes, taking into account the presence of several parameters. This approach allows obtaining mixes in a comprehensive manner, which eventually can lead to a comparison with other methods for the preparation of concrete mixes.

A mixed particle swarm-ray optimization together with harmony search (HRPSO) is applied to detect damage in structures. In fact, PSO acts as the main engine of the algorithm, RO boost the movement vector of the particles, and HS is used to enhance the local search for better exploitation. The objective functions for damage detection are based on modal characteristics in both frame and truss. In addition, a hybrid double stage approach incorporates the advantages of both modal parameters and Modified Total Modal Assurance Criterion has been used. Numerical analysis is performed for skeletal structures under different damage scenarios with incomplete data. The results have shown the efficiency of the hybrid objective function in identifying damage by using HRPSO.

This paper deals with to determine the first natural frequency of tall buildings consists of framed tube, shear core, belt truss and outrigger system with multiple jumped discontinuities in the cross section of framed tube and shear core. In this paper, the continuous approach was accepted and by using energy method and Hamilton’s variational principle, the governing equation for free vibration of tall building can be obtained. The entire length of tall building is partitioned into uniform segments between any two successive discontinuity points and therefore partial differential equation of motion, by applying the separation of variables method on time and space, is reduced to an ordinary differential equation with constant coefficients for each segment. Tall building characteristics matrix can be derived based on the boundary conditions and the continuity conditions applied at the partitioned points. This matrix is particularly used to find combined system natural frequencies and mode shapes. A numerical example has been solved to demonstrate the reliability of this method. The results of the proposed mathematical model give a good understanding of the structure’s dynamic characteristics; it is easy to use, yet reasonably accurate and suitable for quick evaluations during the preliminary durations.

Selecting sufficient number of appropriate ground motions compatible with regional tectonic condition is a major step in Incremental Dynamic Analysis method (IDA). This article is intended to compare and assess the nonlinear structural response of the selected four frames (two steel moment-resisting frames and two RC Special Moment Frames) through performing IDA method by use of the traditional and Conditional Spectrum methods. First, the CMS and CS approaches are briefly explained and discussed. The selected frames are dynamically nonlinearly analyzed using the traditional IDA and CS methods at four hazard levels (50%, 10%, 2%, and 1%). The plots of results obtained from the two approaches, in the form of mean curves, are compared and assessed. It is concluded that the CS method ends up with more reasonable results except in case where the frame poses structural instability as the result of using CS method. The necessity of performing more research work in this area is highlighted.

This paper presents an improved magnetic charged system search (IMCSS) and open application programming interface (OAPI) for optimization of double layer barrel vaults. In IMCSS algorithm, magnetic charged system search (MCSS) and an improved scheme of harmony search (IHS) are utilized and some of the most important parameters in the convergence rate of HS scheme are improved to achieve a good convergence and good solutions especially in final iterations. The OAPI is also utilized for the process of structural analysis, to link the analysis software with the IMCSS algorithm through the programming language. The results demonstrate the efficiency of OAPI as a powerful interface tool for analysis of large-scale structures such as double layer barrel vaults and also the robustness of the IMCSS as an optimization algorithm in fast convergence and achieving the optimal results.