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Showing 35 results for Bridge

Saffar Zadeh M., Karbasi Zadeh B.,
Volume 2, Issue 1 (3-2004)
Abstract

In this paper, optimal bridge management system models have been presented. These optimization models are capable of allocating limited resources to the bridge preservation schemes in order to establish the optimal time of completing the activities. Bridge-based activities are divided into two main groups: repair projects, and maintenance activities and both models are presented in this paper. Particular attention has been made to optimize the management of the two system activities. The dynamic programming approach was utilized to formulate and analyze the two models. The developed models are found to be more accurate and faster than the previous ones.
M.kazem Sharbatdar,
Volume 6, Issue 1 (3-2008)
Abstract

FRPs (fiber reinforced polymer) possess many favorable characteristics suitable and applicable for construction industry when compared with steel reinforcement. There are new ideas to use FRPs as longitudinal or transverse reinforcement for new concrete elements particularly for bridge decks or beams. Although high tensile strength of FRP is main characteristic for applications at both areas, its weakness to bending and linear stress-strain behavior with virtually no ductility, makes it vulnerable to probably premature failures under reversal tension-compression loading during earthquake. A pilot research project has been conducted to explore the characteristics of large-scale cantilever concrete beams reinforced with FRP re-bars and grids and were tested under either simulated cyclic loading or monotonically increasing lateral loading. This paper presents the test parameters and results obtained during research. The analytical relationships are compared with those recorded experimentally, and test results showed the diagonal cracks and either rupturing of FRP bars in tension or stability failure in compression bars at long or short shear span beams. The comparison of nominal moment capacities between analytical and experimental values confirms that plane section analysis is applicable to FRP reinforced concrete members.
Farnad Nasirzadeh, Abbas Afshar, Mostafa Khanzadi,
Volume 6, Issue 2 (6-2008)
Abstract

Presence of risks and uncertainties inherent in project development and implementation plays

significant role in poor project performance. Thus, there is a considerable need to have an effective risk

analysis approach in order to assess the impact of different risks on the project objectives. A powerful risk

analysis approach may consider dynamic nature of risks throughout the life cycle of the project, as well as

accounting for feedback loops affecting the overall risk impacts. This paper presents a new approach to

construction risk analysis in which these major influences are considered and quantified explicitly. The

proposed methodology is a system dynamics based approach in which different risks may efficiently be

modeled, simulated and quantified in terms of time, cost and quality by the use of the implemented object

oriented simulation methodology. To evaluate the performance of the proposed methodology it has been

employed in a bridge construction project. Due to the space limitations, the modeling and quantification

process for one of the identified risks namely “pressure to crash project duration” is explained in detail.


T. Dahlberg,
Volume 8, Issue 1 (3-2010)
Abstract

The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be

very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness

is then, locally at that sleeper, very low. At insulated joints the bending stiffness of the rail has a discontinuity implying

a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from

an embankment to a bridge. At switches both mass and stiffness change rapidly. The variations of track stiffness will

induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue,

track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track

geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track

deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is

discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting

or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.


M. Saiidi, C. Cruz, D. Hillis,
Volume 8, Issue 1 (3-2010)
Abstract

Three unconventional details for plastic hinges of bridge columns subjected to seismic loads were developed,

designed, and implemented in a large-scale, four-span reinforced concrete bridge. Shape memory alloys (SMA),

special engineered cementitious composites (ECC), elastomeric pads embedded into columns, and post-tensioning

were used in three different piers. The bridge model was subjected to two-horizontal components of simulated

earthquake records of the 1994 Northridge earthquake in California. The multiple shake table system at the University

of Nevada, Reno was used for testing. Over 300 channels of data were collected. Test results showed the effectiveness

of post-tensioning and the innovative materials in reducing damage and permanent displacements. The damage was

minimal in plastic hinges with SMA/ECC and those with built in elastomeric pads. Conventional reinforced concrete

plastic hinges were severely damaged due to spalling of concrete and rupture of the longitudinal and transverse

reinforcement. Analytical studies showed close correlation between the results from the OpenSEES model and the

measured data for moderate and strong earthquakes.


S. A. Sadrnejad, S. A. Ghoreishian Amir,
Volume 8, Issue 2 (6-2010)
Abstract

A semi-micromechanical multilaminate model is introduced here to predict the mechanical behavior of soils.

This model is like a bridge between micro and macro scale upon the satisfaction of minimum potential energy level

during any applied stress/strain increments. The concept of this model is based on a certain number of sampling planes

which constitute the elastic-plastic behavior of the soil. The soil behavior presents as the summation of behavior on

these planes. A simple unconventional constitutive equations are used in each of the planes to describe the behavior

of these planes separately. An unconventional plasticity can predict the soil behavior as a smooth curve with

considering plastic deformation due to change of stress state inside the yield surface. The model is capable of

predicting softening behavior of the soil in a reasonable manner due to using unconventional plasticity. The influences

of induced anisotropy are included in a rational way without any additional hypotheses owing to in-nature properties

of the multilaminate framework. Results of this model are compared with test data and reasonable agreement is found.


Afshin Firouzi, Ali Reza Rahai,
Volume 9, Issue 3 (9-2011)
Abstract

Corrosion of reinforcement due to frequently applied deicing salts is the major source of deterioration of concrete bridge decks, e.g. severe cracking and spalling of the concrete cover. Since crack width is easily recordable in routine visual inspections there is a motivation to use it as an appropriate indicator of condition of RC bridge elements in decision making process of bridge management. While few existing research in literature dealing with spatial variation of corrosion-induced cracking of RC structures is based on empirical models, in this paper the extent and likelihood of severe cracking of a hypothetical bridge deck during its lifetime is calculated based on a recently proposed analytical model for corrosion-induced crack width. Random field theory has been utilized to account for spatial variations of surface chloride concentration, as environmental parameter, and concrete compressive strength and cover depth as design parameters. This analysis enables to track evolution of cracking process, spatially and temporally, and predict the time for the first repair of bridge deck based on acceptable extent of cracked area. Furthermore based on a sensitivity analysis it is concluded that increasing cover depth has a very promising effect in delaying corrosion phenomenon and extension of the service life of bridge decks.


M. Z. Kabir, A. Hojatkashani,
Volume 10, Issue 4 (12-2012)
Abstract

The aim of current study is to investigate the effect of Carbon Fiber Reinforced Polymer (CFRP) composites on the fatigue

response of reinforced concrete beams. 6 reinforced concrete (RC) beams from which 3 were retrofitted with CFRP sheets, were

prepared and subjected to fatigue load cycles. To predict and trace the failure occurrence and its growth, a small notch was

induced at the middle span in bottom surface of all RC specimens. At the certain points, strains in concrete and CFRP were

measured in each cycle. The upper limit of applied load was considered at the level of design service load of bridges. In addition,

strain measurements facilitated to the calculation of interfacial shear stresses between concrete substrate and the CFRP layer.

The variation of such stresses through load cycles has been presented and discussed. Also, a discussion on possibility of the local

debonding phenomenon resulted from such interfacial stresses was presented. Load–deflection curves, strain responses and

propagation of tensile cracks provided an insight on the performance of the CFRP strengthened beams subjected to different

cycles of fatigue loading. Variation of load-deflection curves through fatigue load cycles depicted stiffness degradation which

was discussed in the research.


A. Ghanbari, E. Hoomaan, M. Mojallal,
Volume 11, Issue 1 (5-2013)
Abstract

For calculating the natural frequency of structures such as buildings, chimneys, bridges and silos appropriate analytical

formulas exist. However, in the case of retaining walls undergoing the soil pressure at one side, calculating the natural frequency

is not a straightforward task and requires the effects of soil-structure interactions to be considered. By modeling the soil as series

of linear springs, a new formulation is presented in this article, to calculate the natural frequency of retaining walls. This formula

considers the vertical cross sectional width change, and hence, enables us to calculating the natural frequency of retaining walls

with different types of backfill. The geometrical properties of the retaining walls and its bending rigidity together with the soil’s

modulus of elasticity and its Poisson’s ratio are the most important parameters to calculate. A comparison of the results for

retaining walls with constant cross section obtained from the suggested method with those of the software analyses was carried

out and good agreement was detected. A second comparison of the results with those of other researchers revealed that the natural

frequency of flexible retaining wall is an upper bound for natural frequency of rigid walls. The Selected shape function is also

very close to the real shape mode.


M. Salamatian, A. R. Zarrati, S. A. Zokaei, M. Karimaee,
Volume 11, Issue 3 (9-2013)
Abstract

The efficiency of a collar in reducing the scour depth around circular and rectangular piers is studied at different flow intensities (ratio of upstream shear stress to sediment critical shear stress). Rectangular Piers aligned with the flow as well as skewed at 5º, 10º, 20º were examined. Previous studies had shown that with collar the equilibrium time of scouring increases considerably. To reduce the time of experiments low density sediment was used as the bed materials. Comparison between test results and available results with natural sediment showed that, though the relative equilibrium depths were approximately similar, the time to reach equilibrium condition diminished to less than 10 hours with low density sediment. Experimental results for circular and aligned rectangular pier showed that at u*/u*c=0.95 to 0.75 the collar could reduce the maximum scour hole from about 20% to 60% respectively. In rectangular pier, by increasing the skew angle and/or the flow intensity, the efficiency of collar decreased.
A. Tarighat,
Volume 11, Issue 3 (9-2013)
Abstract

Concrete bridge deck damage detection by measurement and monitoring variables related to vibration signatures is one of the main tasks of any Bridge Health Monitoring System (BHMS). Generally damage puts some detectable/discoverable signs in the parameters of bridge vibration behavior. However, differences between frequency and mode shape before and after damage are not remarkable as vibration signatures. Therefore most of the introduced methods of damage detection cannot be used practically. Among many methods it seems that models based on artificial intelligence which apply soft computing methods are more attractive for specific structures. In this paper an Adaptive Neuro-Fuzzy Inference System (ANFIS) is used to detect the damage location in a concrete bridge deck modeled by finite element method. Some damage scenarios are simulated in different locations of the deck and accelerations as representatives of response at some specific points are calculated. Excitement is done by applying an impact load at the center of the deck. In the proposed ANFIS damage detection model accelerations are inputs and location of the damage is output. Trained model by simulated data can show the location of the damage very well with a few training data and scenarios which are not used in training stage. This system is capable to be included in real-time damage detection systems as well.
A. R. Rahai, S. Fallah Nafari,
Volume 11, Issue 4 (12-2013)
Abstract

The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran, including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.
M. Khorami, J. Sobhani,
Volume 11, Issue 4 (12-2013)
Abstract

Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2 % and 4 % of waste agricultural fibers in combination with and without 5 % replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.
H. Rahami, A. Kaveh, M. Ardalan Asl, S. R. Mirghaderi,
Volume 11, Issue 4 (12-2013)
Abstract

In the process of structural analysis we often come to structures that can be analyzed with simpler methods than the standard approaches. For these structures, known as regular structures, the matrices involved are in canonical forms and their eigen-solution can be performed in a simple manner. However, by adding or removing some elements or nodes, such methods cannot be utilized. Here, an efficient method is developed for the analysis of irregular structures in the form a regular structure with additional or missing nodes or with additional or missing supports. In this method, the saving in computational time is considerable. The power of the method becomes more apparent when the analysis should be repeated very many times as it is the case in optimal design or non-linear analysis.
M. Abbasi, A. H. Davaei Markazi,
Volume 12, Issue 1 (3-2014)
Abstract

An important factor in the design and implementation of structural control strategies is the number and placement of actuators. By employing optimally-located actuators, the effectiveness of control system increases, while with an optimal number of actuators, an acceptable level of performance can be achieved with fewer actuators. The method proposed in this paper, simultaneously determines the number and location of actuators, installed in a building, in an optimal sense. In particular, a genetic algorithm which minimizes a suitably defined structural damage index is introduced and applied to a well-known nonlinear model of a 20-story benchmark building. It is shown in the paper that an equal damage protection, compared to the work of other researchers, can be achieved with fewer numbers of optimally placed actuators. This result can be important from economic point of view. However, the attempt to minimize one performance index has negative effect on the others. To cope with this problem to some extent, the proposed genetic methodology has been modified to be applied in a multi-objective optimization problem.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)
Abstract

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
P. Vahabkashi, A. R. Rahai, A. Amirshahkarami,
Volume 12, Issue 1 (3-2014)
Abstract

Piles or drilled shafts used in bridge foundation, waterfronts, and high rise buildings are generally subjected to lateral loads. In order to study the effect of concrete pile geometry on the structural behavior in layered soils, several models with different shapes and dimensions for piles and different properties for two soil layers with variable thickness were selected and analyzed using the finite difference method. The performance of piles situated in layered granular soil with different compaction and thicknesses were studied in two cycles of lateral loading and unloading. The applied finite difference procedure is also validated based on experimental and published results. The pile head displacement of different models due to their overall deformation and rotation were calculated under maximum loading. For a comparison of pile head displacement due to their overall deformation and rotation in different models, the "performance index” is defined as the ratio of “displacement due to deformation” to the “total displacement”.
A. Kaveh, A. Nasrolahi,
Volume 12, Issue 1 (3-2014)
Abstract

In this paper, a new enhanced version of the Particle Swarm Optimization (PSO) is presented. An important modification is made by adding probabilistic functions into PSO, and it is named Probabilistic Particle Swarm Optimization (PPSO). Since the variation of the velocity of particles in PSO constitutes its search engine, it should provide two phases of optimization process which are: exploration and exploitation. However, this aim is unachievable due to the lack of balanced particles’ velocity formula in the PSO. The main feature presented in the study is the introduction of a probabilistic scheme for updating the velocity of each particle. The Probabilistic Particle Swarm Optimization (PPSO) formulation thus developed allows us to find the best sequence of the exploration and exploitation phases entailed by the optimization search process. The validity of the present approach is demonstrated by solving three classical sizing optimization problems of spatial truss structures.
H. Shahnazari, M. A. Shahin, M. A. Tutunchian,
Volume 12, Issue 1 (1-2014)
Abstract

Due to the heterogeneous nature of granular soils and the involvement of many effective parameters in the geotechnical behavior of soil-foundation systems, the accurate prediction of shallow foundation settlements on cohesionless soils is a complex engineering problem. In this study, three new evolutionary-based techniques, including evolutionary polynomial regression (EPR), classical genetic programming (GP), and gene expression programming (GEP), are utilized to obtain more accurate predictive settlement models. The models are developed using a large databank of standard penetration test (SPT)-based case histories. The values obtained from the new models are compared with those of the most precise models that have been previously proposed by researchers. The results show that the new EPR and GP-based models are able to predict the foundation settlement on cohesionless soils under the described conditions with R2 values higher than 87%. The artificial neural networks (ANNs) and genetic programming (GP)-based models obtained from the literature, have R2 values of about 85% and 83%, respectively which are higher than 80% for the GEP-based model. A subsequent comprehensive parametric study is further carried out to evaluate the sensitivity of the foundation settlement to the effective input parameters. The comparison results prove that the new EPR and GP-based models are the most accurate models. In this study, the feasibility of the EPR, GP and GEP approaches in finding solutions for highly nonlinear problems such as settlement of shallow foundations on granular soils is also clearly illustrated. The developed models are quite simple and straightforward and can be used reliably for routine design practice.
U. H Issa, A. Ahmed,
Volume 12, Issue 2 (4-2014)
Abstract

Driven Precast Reinforced Concrete Piles (DPRCP) is extensively used as a foundation for bridges constructed over canals in Egypt in order to avoid the diversion of water canals. The objectives of this research include identifying the main activities of DPRCP execution in the bridge-construction industry in Egypt and the risk factors affecting them. In addition, assessment of the effects of these risk factors on the quality of activities of DPRCP. Four activities are identified in order to execute the process of construction of DPRCP. These activities include: preparing and casting piles, positioning piles and steering the driving machine, handling piles, and driving piles. Thirty one risk factors affecting the DPRCP activities execution are identified. A survey was executed in Egypt concerning probabilities of occurrence of these factors and their impacts on the quality of activities of DPRCP. In addition, a new membership function is introduced to represent the quality of activities and used in a fuzzy model for factors assessment. Results showed that the proposed membership function can be used effectively to assess the quality of activities associated with the construction of DPRCP. A list of risk factors is highlighted to show the most critical risk factors that help in preparing the quality management plan for the upcoming similar projects. The gentile distribution of data obtained for the different activities proved that the investigated risk factors for the DPRCP in this study are significant.

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