Impact Factor :
1.025
Q1(Year 2015)
ISSN : 1026-3098
e-ISSN : 2345-3605
Published Issues
Vertical vibration control of suspension bridges subjected to earthquake by Semi-active MR dampers
2017
Abstract :
In this paper, a semi-active control technique is presented to mitigate the seismic vertical response of suspension bridges using magneto-rheological (MR) dampers. MR dampers, as semi-active control devices, have received significant attention in recent years because of their adaptability of working as active control devices without requiring large power of sources. The most challenging problem in this study is that: how to install the dampers at the degrees along the bridge span far from the towers? In the present paper, to solve this problem, a "rigid truss" which is attached to the bottom of the bridge deck is proposed. The MR damper can be installed between the bridge deck and free-end of the truss. For numerical study, the Vincent-Thomas suspension bridge is chosen and different schemes, in point of number and location of the dampers view, have been proposed to get optimal performance of the dampers in reducing the bridge vertical responses. To reach this goal, all of the schemes are optimized, as well as the controlled and uncontrolled responses of the bridge are calculated under application of 15 major world-wide earthquake accelerogrames. The results indicate that the proposed models can effectively reduce the vertical responses of the example bridge.
Keywords :
Rigid truss, semi-active control, suspension bridge, MR damper, vertical vibration, Earthquake excitation
( 815 Visit ) ( 177 Download )

Simulating FRP Debonding From Concrete Surface in FRP Strengthened RC Beams: A Case Study
2017
Abstract :
Reinforced concrete (RC) beams strengthened with fiber reinforced polymer (FRP) sheets may fail due to debonding failure. In such cases, the FRP sheet detaches from the RC beam before real damages are inflicted on the beam. In this paper, a procedure is developed based on smeared cracks approach for simulating the debonding process in FRP strengthened RC beams within the framework of finite element. For this purpose, the challenges facing the simulation of debonding mechanism are initially studied and a method is proposed in a second stage for combating these problems using the cohesive elements available in the ABAQUS software. The validity of the proposed method is then tested by modeling four beams from those reported in the literature and by comparing the results with the experimental ones. Given the acceptable agreement observed between the experimental and numerical simulation results, the method is claimed to be valid and practicable. In a later section of the present paper, the proposed method will be used to investigate the effects of length and width of the strengthening sheet on beam’s behavior and its failure mechanism. The results of the present study have revealed that longer FRP sheets increase load carrying capacity and mid-span displacement of strengthened RC beams.
Keywords :
Flexural strengthening, Debonding, Fiber reinforcement Polymers, Finite element method
( 433 Visit ) ( 34 Download )

Stability analysis of arch dam abutments due to seismic loading
2017
Abstract :
Abutments of concrete arch dams are usually crossed by several joints which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams which should be investigated. For decades, the quasi-static method due to its simple approach is used by most of dam designers. In this study the dynamic method is presented and the obtained time history of sliding safety factors are compared to the quasi-static results. For this purpose, all three components of Kobe 1979 and Imperial Valley 1940 earthquakes are applied to the wedge, simultaneously and the magnitude and direction of wedge displacements are calculated based on Newmark method which is not possible in the quasi-static approach. A 3-D finite element model of Luzzone dam including dam-foundation-reservoir interactions is used to compute the thrust forces. The obtained results indicate that quasi static method is more conservative. The importance of uplift pressure effects on the abutment stability is investigated as well. It is shown that the uplift pressure can play a key role in the abutment stability analysis and it is necessary to control the uplift pressure and seepage in arch dam foundations.
Keywords :
Abutment stability analysis, Dynamic analysis, quasi static analysis,Safety factor of wedge, Uplift pressure, Londe method
( 357 Visit ) ( 88 Download )

Cost optimum design of doubly reinforced high strength concrete T-beams
2017
Abstract :
This paper presents a method for optimizing the design cost of a doubly reinforced High Strength Concrete (HSC) T-beam. The objective function used in the model includes the costs of HSC, steel and formwork. The constraint functions are set to satisfy design requirements of Eurocode 2 (EC-2). The cost optimization process is developed by the use of the Generalized Reduced Gradient algorithm.  An example problem is considered in order to illustrate the applicability of the proposed design model and solution methodology. It is concluded that the present approach is economically more effective when compared to conventional design methods and can be extended to deal other sections without major alterations.
Keywords :
Nonlinear programming, Cost optimum design, High strength concrete (HSC) T-beams, Doubly reinforcing, Generalized reduced gradient (GRG) algorithm,  Eurocode 2 (EC-2).
( 1679 Visit ) ( 69 Download )

Comparison of artificial neural network and coupled simulated annealing based least square support vector regression models for prediction of compressive strength of high-performance concrete
2017
Abstract :
High-performance concrete (HPC) is a complex composite material with highly nonlinear mechanical behaviors. Concrete compressive strength, as one of the most essential qualities of concrete, is also a highly nonlinear function of ingredients. In this paper, least square support vector regression (LSSVR) model based on coupled simulated annealing (CSA) has been successfully used to find the nonlinear relationship between the concrete compressive strength and eight input factors (the cement, the blast furnace slags, the fly ashes, the water, the superplasticizer, the coarse aggregates, the fine aggregates, Age of testing). To evaluate the performance of the CSA-LSSVR model, the results of the hybrid model were compared with those obtained by artificial neural network (ANN) model. A comparison study is made using the coefficient of determination R2 and Root Mean Squared Error (RMSE) as evaluation criteria. The accuracy, the computational time, the advantages and shortcomings of these modeling methods are also discussed. The training and testing results have shown that ANNs and CSA-LSSVR models have strong potential for predicting the compressive strength of HPC.
Keywords :
High performance concrete, compressive strength, Modeling, coupled simulated annealing, ANN, LSSVR
( 560 Visit ) ( 23 Download )

Data Envelopment Analysis (DEA) Approach for Making the Bid/No Bid Decision: A Case Study in a Turkish Construction Contracting Company
2017
Abstract :
Construction contracting companies face two critical decisions in competitive bidding environment, which include: the bid/no bid decision and the mark-up selection decision. Making the right bid/no bid decision is critical to the survival, sustainability, and success of the contractors in the industry. There are many factors that affect this decision. This makes the bidding decisions complex and complicated. Therefore, it is not an easy task for managers to consider all these factors’ combined impact on the bid/no bid decision within a limited time frame with limited capacity of information they have for every single bidding opportunity. This study proposes a data envelopment analysis (DEA) approach for making the bid/no bid decision. DEA is a robust non-parametric linear programming approach, which is mostly used for benchmarking, performance measurement, and decision making problems. The applicability of the proposed approach was demonstrated in a real case study conducted in a Turkish construction contracting company. In the case study, 49 bidding opportunities formerly faced by the studied company were evaluated via the developed DEA model. The accuracy rate of the proposed approach was 92%. Company management found the proposed approach satisfactory and implementable in future bid/no bid decision problems.
Keywords :
Bid/no bid decision, construction projects, data envelopment analysis, case study
( 563 Visit ) ( 18 Download )

Strain Rate Effect in the Mesoscopic Modeling of High-Strength Steel Fiber-Reinforced Concrete
2017
Abstract :
The research presented in this paper aims to investigate the behavior of a high-strength steel fiber-reinforced concrete (HSSFRC) mesoscopic finite element model, at compressive high strain rates. In order to produce a three-dimensional meso-scale finite element model, a computer code is developed to randomly produce mesoscopic models of SFRC specimen. The specimen is assumed to be reinforced by 0.6 percent volume fraction of hooked steel fibers (Dramix RC-65/35-BN) with random positions and orientations. Aggregates of the compound are assumed to have spherical shape and are produced according to Fuller grading curve.  Based on the initial mesoscopic model, a finite element model is produced and used in the explicit dynamic simulation. The contribution of inertial confinement in the dynamic strength enhancement of concrete at high strain rates was investigated and its effective role was observed. Accordingly defining a Dynamic Increase Factor (DIF) for mortar matrix led to overestimation; nevertheless, the inertial confinement by itself could not justify the increment of specimen strength under the dynamic loading. Obtained results also show that steel fibers have a negligible influence on the strength, strength enhancement ratio (DIF) and post peak behavior of the model at high strain rates.
Keywords :
Meso-scale, SFRC, SHPB, High strain rate, Impact
( 397 Visit ) ( 41 Download )

Polynomial Models Controlling Strength of Zeolite-Cement-Sand Mixtures
2017
Abstract :
The improvement of local soils with cement and zeolite can provide great benefits, including strengthening slopesin slope stability problems, stabilizing problematic soils and preventing soil liquefaction. Recently, dosage methodologies are being developed for improved soils based on a rational criterion as it exists in concrete technology.The present study aims to quantify the influence of the amount of cement, zeolite, the porosity and the curing time in the evaluation of unconfined compressive strength (UCS) of zeolite-cemented sand mixtures. A program of unconfined compression tests considering three distinct voids ratio, four cement contents (varying from 2 to 8%), six zeolite contents (varying from 0 to 90%) and three curing time (7,28 and 90 days) was performed in this paper. The results show that UCS values of samples substantially increased with increasing zeolite content to an optimum value of 30% after 28 days of curing time. The rate of improvement is approximately between 20 to 80% and 20% to 60% for 28 and 90 days curing times respectively. Moreover, the polynomial models are shown to be appropriate one to estimate UCS values of zeolite-cemented mixtures. Additionally, the sensitivity analysis reveals the influence of parameters and the contribution of each coefficients in the polynomial model. Cement and zeolite content relates more strongly among relative density and curing time. 
Keywords :
Zeolite, Cemented Sand, Unconfined Compressive Strength, Polynomial, Sensitivity analysis.
( 737 Visit ) ( 39 Download )

Stability of Supported Vertical Cuts in Granular Matters in Presence of the Seepage Flow by a Semi-Analytical Approach
2017
Abstract :
Vertical cuts are prone to several types of failure, such as piping, ground heaving and deep seated or base failure. The latter is the subject of this study and probably attracts less attention in comparison with other types of failure. Although it is commonly believed that such a failure is rare in normal conditions; in presence of the seepage flow, deep seated failure is much likely to initiate and advance prior to other types of failure. In this paper, the stability analysis of vertical cuts in granular soils in presence of the seepage flow is studied against the deep failure. To do so, the stability analysis is made by the use of the well-known method of stress characteristics with inclusion of the seepage flow force. This nonuniform flow field renders the stability analysis quite complex. A semi analytical approach, based on complex algebra, is presented to find the flow filed which is accurate and much faster for calculation of the seepage force at arbitrary points in the field. The solution of the flow field is a background solution for the stress field which is to be found to assess the stability.
Keywords :
Stability, Complex Analysis, Stress Characteristics, Seepage, Granular Matter
( 440 Visit ) ( 47 Download )

A new meta-heuristic algorithm: vibrating particles system
2017
Abstract :
In this paper, a new meta-heuristic algorithm based on free vibration of single degree of freedom systems with viscous damping is introduced and it is called vibrating particles system (VPS). The solution candidates are considered as particles that gradually approach to their equilibrium positions. Equilibrium positions are achieved from current population and historically best position in order to have a proper balance between diversification and intensification. To evaluate the performance of the proposed method, it is applied for sizing optimization of four skeletal structures including trusses and frames. Results show that the proposed algorithm is a robust and reliable method.
Keywords :
Vibrating particles system; meta-heuristic algorithm; global optimization; optimal design; truss structures; frame structures.
( 201 Visit ) ( 55 Download )

Application of Neural Network Models to Improve Prediction Accuracy of Wave Run-up on Antifer Covered Breakwater
2017
Abstract :
The primary goal of this study is to present a better way in terms of cost and experimenting duration, instead of using experimental ways for investigating the wave run-up (Ru) over rubble-mound breakwater and examining the effect of placement pattern of antifer units on the amount of wave run-up. To do so, artificial neural networks (ANNs) are suggested. For the sake of comparison, the proposed modeling is put into contrast by the ones obtained via other approaches in the literature. The Multi-Layer Perceptron (MLP) is selected as the artificial neural network exerted in this study. In the designed neural network, the numbers of inputs and outputs are selected as four and one, respectively. On the other hand, the number of neurons in the single hidden layer of the network should be determined by trial and error considering the Mean Square Error (MSE) of the training and validation samples, which has been chosen as seven in this paper. The regression equations and MSE for the results obtained by ANN have presented in this paper and are compared with other models in the literature. Moreover, the regular placement is preferred to other placement patterns due to its less MSE obtained by ANN.
Keywords :
Wave run-up, Breakwater, Artificial neural network, Multi-layer Perceptron (MLP), MSE.
( 359 Visit ) ( 22 Download )

Effect Of Curing Conditions On Strength And Durability Of High-Performance Concrete
2017
Abstract :
This paper describes the effects of variable curing temperatures on compressive strength and sulfate resistance of high-strength, high-performance concrete. Two different concrete mixtures were proportioned to attain the 56-day compressive strength of about 70 MPa upon moist-curing. One mixture contained more quantity of ASTM Class C fly ash than the other mixture. For each mixture, one set of specimens was cured in a standard moist-curing room at 23C and 100% relative humidity, and another set of specimens was sealed in plastic bags and cured in an elevated, variable-temperature curing environment (VTCE). The average temperature of the VTCE cycled between about 30C and 41C once per day. This study revealed that the VTCE-cured concrete did not exhibit significantly different compressive strength or ability to resist sulfates attack than the standard moist-cured specimens. Thus, based on the results of this research, it was concluded that additional effort to stabilize higher curing-temperatures would be necessary for field-cured concrete.
Keywords :
compressive strength, curing, fly ash, high-performance concrete, sulfate resistance, temperature.
( 464 Visit ) ( 38 Download )

Effects of shear deformation on Mechanical and thermo-mechanical nonlinear stability of FGM shallow spherical shells subjected to uniform external pressure
2017
Abstract :
In the present paper, the asymmetrical nonlinear response of a clamped functionally graded shallow spherical shell is subjected to uniform external pressure. It considers the effects of thermal stresses by both of the theories, Classical Laminate Theory, CLT and First-Order Shear Deformation Theory FSDT. Material properties are graded in the thickness direction according to the power-law distribution in terms of the volume fraction of the constituents. Mechanical and thermo-mechanical properties are assumed to be temperature-independent and linear elastic. All of the governing equations are derived by aid of first-order transverse shear deformation theory considering geometrical nonlinearity. The nonlinear differential equation system is solved employing Galerkin method. Buckling and post-buckling analysis have been done according to one-term deformation mode by the closed form relation of load-deflection that shows the equilibrium path. Parametric studies are conducted to bring out the effects of shear deformation on the equilibrium path in different geometries and boundary conditions. Numerical results are presented in graphical arrangement, showing that the geometrical nonlinear equilibrium paths. The effects of shear deformation on the equilibrium path are considered by comparing the results from FSDT and CLT and was verified by nonlinear finite-element method.
Keywords :
shallow spherical shells - functionally graded materials - nonlinear stability - transverse shear deformation - mechanical load - thermal load - snap through  
( 466 Visit ) ( 71 Download )

Download Papers All Files Of This Number
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

Scientia Iranica All Rights Reserved.
© 2014 - Journal Management System. Powered by ADAK Co