Impact Factor :
1.025
Q1(Year 2015)
ISSN : 1026-3098
e-ISSN : 2345-3605
Published Issues
PLACEMENT OF CONTROL DEVICES FOR PASSIVE, SEMI-ACTIVE, AND ‎ACTIVE VIBRATION CONTROL OF STRUCTURES
2013
Abstract :
An important subject in vibration control of large structures is the placement of control devices. The goal should be to achieve the best performance with minimum cost. A good number of papers have been published on distribution of control devices in recent years. The purpose of this article is to present a review of the papers published on placement of passive, semi-active, active, and hybrid devices for vibration control of structures subjected to various dynamic loading such as earthquakes and winds. Significant additional research is needed especially in the areas of semi-active and hybrid vibration control of large structures with hundreds or thousands of members to make the adaptive/smart structure technology cost effective.
Keywords :
Active control; actual placement; vibration control; semi-active control; smart structure
( 1190 Visit ) ( 215 Download )

PULVINO and Peripheral Joint Effects on Static and Seismic Safety of Concrete Arch Dams
2013
Abstract :
One of the methods in limiting tensile stresses in arch dams and removal stress concentrations at dam-foundation interface is setting the dam body on a concrete saddle called PULVINO. In the present study, effect of PULVINO and peripheral joint on the static behavior and seismic performance of arch dams are investigated. DEZ dam with 203m height was selected as case study and all contraction joints of the dam body were modeled using discrete crack approach based on as-built drawings. Also, surrounding rock was modeled as a mass-less medium tied to PULVINO. The dam-reservoir-foundation system was analyzed under static loads accounting for stage construction effects, hydrostatic and thermal loads and then the provided numerical model was excited using near- and far-field earthquake ground motions. It was found that modeling peripheral joint between saddle and the main dam body changes the direction of principal stresses and their distribution patterns and safety of the system is improved. In addition, over stressed surfaces on faces of the dam body decreased in comparison with the model without peripheral joint.


Keywords :
Contraction joints; Arch dam; Peripheral joint; PULVINO; Nonlinear seismic performance
( 1371 Visit ) ( 171 Download )

Geometrical and material nonlinear analysis of structures under static and dynamic loading based on quadratic path
2013
Abstract :
The Newton–Raphson method, which is based on the Taylor series expansion, and uses the tangent stiffness matrix, has been extensively used to solve nonlinear problems. This traditional method, especially for the large-scale, is time consuming. Consequently iterative algorithms cannot be effective for analyzing of the process. In the incremental-iterative analysis of elastic nonlinear structures, great saving in computation can be achieved if distinction is made between the predictor and corrector phases. This paper shows how a simple assumption can improve the computational efficiency of the nonlinear analysis of structures. It is shown that very high computational efficiency may be obtained by assuming the pursuit of each degree of freedom (DOF) by a quadratic curve. Through examples it is demonstrated how this efficiency significantly, decreases the computing time of analysis compared with time taken to deploy the Newton-Raphson, modified Newton-Raphson and conjugate gradient (CG) methods.


Keywords :
nonlinear analysis, large displacement, quadratic path, stiffness matrix
( 1421 Visit ) ( 179 Download )

Safe control of air cushion surge chambers in hydropower systems
2013
Abstract :
This paper presents an effective theory for safe controlof air cushion surge chambers (ACSCs) in hydropower systems. On the basis of the emergency pressures and heights of air in chambers, the acceptable limits of the monitoring parameters for three kinds of control modes are derived theoretically to control the air compressor. The prerequisites for each control mode are determined with considering the air leakage and solution. By analyzing these prerequisites, the selection criteria are established to determine the appropriate control mode for the practical hydropower system with the ACSC. According to the presented control scheme, the air compressor need not be actuated for any variation of the air temperature, and the operating conditions of the hydropower system need not be considered for safe control of ACSCs. Those are favorable for safety and economy of the hydropower plant. To detail and validate the derived limits and selection criteria for different control modes, the safe control theory is applied to the practical hydropower plant, and the graphic analysis is conducted on the basis of the perfect gas law and the relationship of the initial steady-state pressure and height of the enclosed air in chambers.
Keywords :
Air cushion surge chamber; Control mode; Hydropower system; Air compressor; Exhaust valve; Hydraulic transients
( 1068 Visit ) ( 63 Download )

A New Accelerated Firefly Algorithm for Size Optimization of Truss Structures
2013
Abstract :
An accelerated firefly algorithm (AFA) for fast size optimization of truss structures is proposed in this paper. Metaheuristic firefly algorithm has been recently developed and its effectiveness in solving practical problems such as sizing optimization of truss structures has not been thoroughly explored. The numerical experiments show that although the standard firefly algorithm (FA) is a powerful approach for truss optimization, it suffers from slow rate of convergence, and hence it should be modified to solve real-life problems. The proposed AFA imposes some improvements on the searching procedure by both reduction of randomness and scaling the random term in fireflies' motion. The effectiveness and robustness of the algorithm are investigated by solving some benchmark problems. The results revealed that the proposed AFA remarkably enhances the rate of convergence and stability of standard firefly algorithm.
Keywords :
Firefly algorithm, truss structures, size optimization, metaheuristics
( 1231 Visit ) ( 102 Download )

Mechanical Properties of Steel Fiber-Reinforced Concrete Slab Tracks on Non-ballasted Foundations
2013
Abstract :
Mechanical properties of slab tracks on a foundation with nonlinear stiffness are accounted for. At first, the cracking stages were inspected in FEM models, and it was gathered that slab tracks have one-way flexural behavior. Secondly, experimental full-scale models were made, and the accuracy of analyses was verified by comparing theFEM load-deflection curves with those of previous studies and validating the cracking and ultimate loads with those obtained from experiments. Finally, the effects of several parameters on the cracking and ultimate loads and the energy absorption of steel fiber-reinforced slab tracks were investigated by examining the real behavior of slab tracks on elastic foundations before and after cracking. Steel fibers increased the compressive and flexural strengths as well as ductility and energy absorption. The 2.5 m width was the optimal width and the fracture pattern changed at this width. Finally, based on the obtained fracture loads, design curves were plotted for AASHTO’s factored loads.
Keywords :
Slab track; Steel fiber-reinforced concrete; Spanning behavior; Load-deflection curve; (Concrete) Tensile strength
( 1184 Visit ) ( 203 Download )

Evaluation of the Effect of Anisotropic Consolidation and Principle Stress Rotation on Undrained Behavior of Silty Sands
2013
Abstract :
The dependence of undrained behavior of silty sand on initial state of stress and direction of principal stresses with respect to vertical (α) is assessed under generalized loading paths using hollow cylinder apparatus. During applying shear load, value of intermediate principal stress parameter (b) is held constant and α value is increased from zero to the aimed value and held constant. Specimens are consolidated both isotropically and anisotropically to evaluate the effect anisotropic consolidation on the behavior of these soils. Wet tamping method was selected to prepare specimen. Shear loading was carried out under strain-controlled condition to capture post-peak strain-softening response. The results of this study reveal that the principal stress direction and initial anisotropy in stress condition have considerable effects on the behavior of silty sands. By increasing α, susceptibility of silty sand to instability increases. In addition, increase in silt content, silty sand mixtures present higher tendency to flow compared to pure sand. For specimens with high silt content, it is observed that stress-strain response has a sudden reduction in shear strength after a peak. This study reveals that shear strength, steady state friction angle of the silty sands are affected by α and the amount of fines present in the sand.
Keywords :
Hollow Cylinder Test, Anisotropic Behavior, Silty Sand, Pore Water Pressure, Undrained Behavior
( 1476 Visit ) ( 173 Download )

Rheological master curves for modified asphalt binders
2013
Abstract :
Modified bitumen enhances the performance properties of asphalt mixtures. A number of studies in the last decade have evaluated the performance properties of modified binders at different service temperatures. It is however possible to evaluate some modified binder time-temperature characteristics and performance properties through their rheological master curves. In this research, styrene butadiene styrene, ethylene vinyl acetate, polyphosphoric acid and crumb rubber were used to modify a PG58-22 base binder. Rheological master curves for |G*| and phase angles of these binders were generated using data from the dynamic shear rheometerand bending beam rheometerat temperatures ranging from -30℃to about 88℃. The rheological interpretation of the results indicated improved high and low temperature properties and reduced temperature susceptibility for most of the modified binders. A comparison of the modified binders was done based on the visual inspection of master curves for different temperature ranges.
Keywords :
Modified binder, Complex modulus, Phase angle, Rheological master curve, Pavement performance
( 1434 Visit ) ( 221 Download )

Investigating pore network models as numerical tools to solve steady saturated groundwater flow
2013
Abstract :
In this paper, a novel procedure is introduced and employed to transform the partial differential steady saturated flow equation in porous media into a system of linear equations using Pore Network Models (PNMs). At first, a simple Square Pore Network Model (SPNM) is introduced and then this model is improved by increasing node connectivity (Square-Diagonal PNM; S-DPNM) and modification in handling impermeable boundaries by introducing imaginary nodes and pipes (S-DPNMi). Finally, a generalized formulation for unstructured discretization (Unstructured PNM; UPNM) of the domain is given and the effect of handling impermeable boundaries (UPNMi) on model accuracy is investigated. To explore the capabilities of these models as numerical tools, three examples are solved. Application of these models without modifications for impermeable boundaries (SPNM, S-DPNM, and UPNM) yields comparable results to those of traditional Finite Difference (FD) and Finite Element (FE) methods. Modification in handling impermeable boundary nodes not only yields results that are everywhere more accurate than FD and FE, but also benefits the simplicity of formulations.


Keywords :
groundwater, numerical methods, pore network model
( 1069 Visit ) ( 102 Download )

Nonlinear Dynamic Analysis of Concrete Gravity Dam Considering Elastoplastic Constitutive Model for Foundation
2013
Abstract :
Dam failure can result in a catastrophic break followed by a flood wave often with considerable loss of life or property. One of the main causes of dam failure is loss of shear strength and existence of discontinuity within foundation. Dynamic analysis of concrete dams usually considered concrete behavior to be nonlinear and foundation rock is assumed to be linear. In this study, seismic analysis of concrete gravity dam was conducted to investigate effect of foundation on the nonlinear response. A finite element model of dam-reservoir-foundation was considered to properly model the foundation as well as dam body nonlinear behaviors. An elasto-plastic formulation was used to model the foundation. Mohr-Coulomb model was utilized for the yield and potential functions of the foundation. The dam body modeled by using smeared crack model. After modeling the dam-reservoir foundation, horizontal recorded ground acceleration of Kobe 1995 earthquake was applied to the model and results were studied. It was found that cracks form at the crest and hill of the dam.Using elastoplastic model for the foundation is more realistic and under different boundary conditions a significant amount of energy will be dissipated in the foundation.


Keywords :
Foundation’s elastoplastic behavior, nonlinear dynamic analysis, Mohr-Coulomb model, smeared crack mode, seismic analysis, concrete gravity dam
( 1478 Visit ) ( 185 Download )

An analytical approach to reliability assessment of shear wave velocity relationship
2013
Abstract :
During earthquake seismic waves propagate vibrations that carry energy from the source of the shaking outwards. Seismic waves can be distinguished by the velocity and shape of propagation. The velocity of waves depends on the elastic properties and density of the soil layers through which the waves pass. Probabilistic analysis of earthquake waves can be used as an effective tool to evaluate inherent uncertainty in the soil properties and the resulting uncertainty in site classification. In this research the jointly distributed random variables method is used for probabilistic analysis and reliability assessment of shear wave velocityrelationship. The selected stochastic parameters are density, elastic modules and Poisson's ratio which are modeled using truncated normal probability distribution functions. The results are compared with the Monte Carlo simulation, point estimated method and first order second moment method. Comparison of the results indicates very good performance of the proposed approach for assessment of reliability. It is shown that this method can correctly predict the influence of stochastic input parameters and capture the expected probability distribution of shear wave velocity correctly. It is also shown that the modulus of elasticity is the most effective parameter in shear wave velocity.
Keywords :
Reliability, Jointly distributed random variables method, Monte Carlo simulation, Point estimated method, First order second moment method, Shear wave velocity
( 1207 Visit ) ( 118 Download )

Retrofitting I-Beam to Double-I Built-up Column Connections Using Through Plates and T-Stiffeners
2013
Abstract :
Double-I built-up sections were extensively used in Iran according to the previous versions of Iranian building codes. Despite the recent developments in steel moment connections, based on studies for I-beam to H-shaped column connections, there are not enough documents available for I-beam to double-I built-up column connections. Recent studies have revealed that connections with double-I built-up columns exhibit different behaviors comparing to the connections with H-shaped columns. Due to excessive out-of-plane deformations of the cover plate in the non-retrofitted moment connections, they have semi-rigid behavior. The objective of this study is to build on previous studies and to investigate strain distribution pattern and load transfer mechanism in the retrofitted I-beam to double-I built-up column connections using through plates and T-stiffeners. In this paper, both horizontal and vertical elements of the T-stiffeners were modified and studied. Analytical models were designed and analyzed under cyclic and monotonic loadings. Three different indices were computed in the connection region in order to assess the local failure potential; and the moment-rotation hysteretic curves were employed to evaluate the seismic performance of the connections. With the proposed configurations, strain is uniformly distributed within the critical elements. Moreover, excessive deformations of the column cover plate are eliminated.
Keywords :
T-Stiffener; Double-I Built-up Section; Through Plate; Retrofitting
( 1477 Visit ) ( 197 Download )

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Published Issues
2017
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
2016
2015
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology
2014
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology
2013
Transactions on Civil Engineering
Transactions on Mechanical Engineering
Transactions on Chemistry and Chemical Engineering
Transactions on Computer Science & Engineering and Electrical Engineering
Transactions on Industrial Engineering
Transactions on Nanotechnology

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