Journal of Ferdowsi Civil Engineering | Ferdowsi University of Mashhad (original) (raw)

Papers by Journal of Ferdowsi Civil Engineering

Research paper thumbnail of Seismic Behavior of Short Column in RC Structures with Different Floor Level

Journal of Ferdowsi Civil Engineering, 2011

Engineering structures as well as office or apartment buildings are affected by earthquakes. A co... more Engineering structures as well as office or apartment buildings are affected by earthquakes. A common cause of failure seems to be shear stresses. The earthquake tremor developed at different floor levels need to be brought down along the height to the ground by the shortest path. Short column phenomenon is one of the frquent causes of buildings failure in the past earthquakes. This destructive phenomenon is due to the column height difference in a story level that is predominantly owing to the location of building on sloppy ground. These buildings have unequal height columns along the slope, which causes poor effects like twisting and damage in shorter columns. In some buildings, few or no walls are provided at the first story (pilot). In the structures with difference in the story levels, major problems is due to the discontinuity of floors diaphragm that causes significant changes in natural period, stiffness and distribution of earthquake forces. In this study, at first, seismic behavior of short column phenomenon is determined, then, nonlinear behavior of RC short columns in the 4, 8 and 10 story buildings with story level difference is investigated. Short columns and mentioned structures are analyzed under the earthquake records of Elcentro and Tabas with different peak ground acceleration using IDARC software which is nonlinear dynamic analysis program. In this investigation, the results of maximum response, base shear, global damage index and displacement time history and effect of short column in structural failure are evaluated.

Research paper thumbnail of An Experimental Study on the Effect of T Shape Spur Dike on Down Sream Topography in a 90 Degree Bend

Journal of Ferdowsi Civil Engineering, 2011

One of the common methods of river training and bank protection is using spur dikes. Building spu... more One of the common methods of river training and bank protection is using spur dikes. Building spur dikes makes the flow path to be modified. Because of the concentration of flow in the middle part of the river it causes the river side not to be washed out. Setting spur dikes in the flow’s direction leads to a local scour in the spur dike site and the change in the bed’s topography of the bend down stream. this paper examines the effect bed’s topography around the T shaped spur dike located in a 90 degree bend by conducting several tests. These tests were carried out in an experimental channel with a bend of 90 degrees and under conditions with clear water. These experiments, in fact, measured the effects of such parameters like the length of the spur dike, the location of the spur dike in the bend, the flow Froud number on the down stream bed topography. The results of investigation show that two scour hole forms due to a T shaped spur dike. One at the nose of spur dike and the other one at the downstream of the spur dike. By increasing the length of the spur dike, the dimensions of first scour hole increase. But the dimensions of second scour hole decrease. By increasing the length of the spur dike the distance of location of second scour hole from the spur dike increases.Any change in the position of the spur dike toward the down stream of the bend, increases the dimensions of scour hole. Also, New equations for maximum scour depth and scour volumeat a T shaped spur dike are developed

Research paper thumbnail of The Effect of Circumferential Imperfections on Axial Load Carrying Capacity of Thin-Walled Cylindrical Shells

Journal of Ferdowsi Civil Engineering, 2011

The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells... more The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells exposed to axial loads are very sensitive to imperfections in the initial geometry. These imperfections are invariably caused by an assortment of manufacturing processes like displacing, installing or welding; one of the most important imperfections caused by welding that has been reported to have an essential detrimental effect on the buckling resistance of these shells under axial load is circumferential imperfections. Despite many determinations of the effect of imperfections on axial load carrying capacity of cylindrical thin-walled shells, the major part of these studies are concentrated on the existence of imperfections on the shell wall, and a comprehensive research on circumferential imperfections and their effects on axial load carrying capacity has not been performed. This is the main subject of this research. Also in this paper, the interaction of two imperfections on each other and on the load carrying capacity of cylindrical shells in various cases are analyzed and determined using a finite element program (ABAQUS).

Research paper thumbnail of Effect of Silica Fume, Metakaolin, Zeolite and Polypropylene Fiber on Chloride Diffusion in Concrete

Journal of Ferdowsi Civil Engineering, 2011

Rapid concrete deterioration in Persian Gulf region has become one of the major concerns since it... more Rapid concrete deterioration in Persian Gulf region has become one of the major concerns since it shortens the structure life span and increases the maintenance costs. The main cause of such concrete failure is claimed to be chloride permeation and subsequent corrosion. Pozzalns are widely being used in order to construct more durable concrete as a functional solution to this problem. The paper reports the performance of concrete incorporating silica fume (replacement level of 5%, 7.5% and 10%), metakaolin (replacement level of 5%, 10% and 15%), zeolite (replacement level of 10%, 20% and 30%) and Polypropylene Fiber in the binder to resist the chloride penetration in aggressive environments. The results showed that specimens containing pozzolans function better than control concretes.

Research paper thumbnail of Ductility Analysis of Lap-Spliced Reinforced Concrete Beams

Journal of Ferdowsi Civil Engineering, 2011

In this research, the ductility of lap-spliced concrete beams reinforced with steel and FRP bars ... more In this research, the ductility of lap-spliced concrete beams reinforced with steel and FRP bars is analyzed. A number of 16 beam specimens reinforced with steel bars and 7 with FRP bar were designed and manufactured in real sizes and dimensions for laboratory experiments. The parameters of concrete compressive strength, amount of transverse reinforcement over the splice length and the diameter of longitudinal bars, are selected as the main variables for the beam specimens. Mid-span displacements and the corresponding forces were obtained by means of a hydraulic jack, load cell, LVDT and a Data Logger set. The force versus mid-span displacement curves were obtained using the experimental data. A ductility index which has been defined by researchers, was used to evaluate the ductility of the specimens. Comparison of the ductility index of different specimens shows that the compressive strength of concrete and the amount and the bar diameter of the transverse reinforcement over the splice length, has a major effect on the ductility of lap-spliced reinforced concrete beams. The results show that by using an appropriate amount of transverse reinforcement, a satisfactory ductility response for different compressive strengths of concrete can be obtained.

Research paper thumbnail of A Comparative Study on Determination Soil Deformation Modulus, Using In-Situ and Laboratory Plate Load Tests

Journal of Ferdowsi Civil Engineering, 2011

Soil deformation modulus is one of the most complicated and important soil parameters, correlatin... more Soil deformation modulus is one of the most complicated and important soil parameters, correlating between stress and settlement. The magnitude of deformation modulus is not constant. Its value, which varies in a wide range, depends on many factors. The soil deformation modulus may be determined using in-situ and laboratory tests, including consolidation test, triaxial test, Standard Penetration Test (SPT), Cone Penetration Test (CPT), Plate Load Test (PLT) and many other tests. Although the in-situ test results are more accurate in comparison with laboratory tests, but in-situ tests are more expensive and time consuming and practically these tests are usually difficult and sometimes impossible to perform.In the present research the in-situ plate load test results are employed to determine the soil deformation modulus. This test is then modeled in the laboratory and results are compared. To achieve this, after soil sampling from the site, the samples were classified after which their moisture content and unit weight were determined. The plate load test, modeled in the laboratory, was then performed on the undisturbed samples, taken from the site. In order to compare and establish a mathematical correlation between the results of these two groups (the in-situ and laboratory plate load tests), the load-settlement curves of all two group tests were plotted, after which the initial tangent slope, secant slope and unloading slope for each sample was calculated and plotted and the results were then compared. Considering the complicated soil behavior, the results of this research seem to be appropriate and can be used in practical civil engineering purposes.

Research paper thumbnail of Graph Theoretical Methods for improving The conditioning of Flexibility Matrix of Structures

Journal of Ferdowsi Civil Engineering, 2011

In addition to reducing the size and time of analyses, reduction of analytical errors is one of t... more In addition to reducing the size and time of analyses, reduction of analytical errors is one of the most important considerations in ideal analysis of skeletal structures by computer. Appropriate matrixes with more zeros (sparse), well structure, and well condition are helpful for this aim. Therefore, an optimizing problem with multiple objectives will be considered.The objective of this research is reducing the analytical errors such as rounding errors in flexibility matrixes of skeletal structures by performing more constant and proper algorithm. These errors increase in special structures with unsuitable flexibility matrixes; the structures with different stiffnesses are one of the most prevalent examples for this case.Use of weak elements leads into high non-diagonal terms in flexibility matrix, which result in analytical errors. In numerical analysis, ill-condition of a matrix is soluble by movement or substitution of the rows; then specification and implementation of these changes before forming the flexibility matrix has been studied. By identifying cycle bases with specific qualities, simple typological and algebraic properties have been used basically in analyses for this purpose. In conclusion, stiffness matrixes with optimally condition number are obtainable and analytical errors reduce.

Research paper thumbnail of Seismic Behavior of Brick Walls

Journal of Ferdowsi Civil Engineering, 2011

In this paper, brick walls as seismic load carrying elements in masonry buildings have been studi... more In this paper, brick walls as seismic load carrying elements in masonry buildings have been studied. An experimented un-reinforced brick wall (UBW) has been chosen from ref.(1) to prove the ability of analytical modeling used in this paper by which a reinforced (RBW) and a confined brick wall (CBW), designed according to Iranian Earthquake Standards, have been modeled and nonlinearly analyzed. This analysis shows that UBW practically is not able to resist horizontal loads. According to the type and direction of cracks in UBW constructed by conventional methods, it is clear that these walls do not have sufficient shear strength, and the study of hysteresis curves of brick walls shows that the confinement in CBW and reinforcement in RBW increases the rigidity and capability to displacement of walls.

Research paper thumbnail of Optimization of Braced Frames Against Dynamic Spectral Loadings Using Migration Genetic Algorithm

Journal of Ferdowsi Civil Engineering, 2011

The purpose of optimization in civil engineering is design of a structure to achieve the minimum ... more The purpose of optimization in civil engineering is design of a structure to achieve the minimum weight and construction cost of the structure in addition to satisfaction of the technical aspects of the problem. Braced frame is a type of structure with large application in civil engineering. The arrangement of bracings in different panels and length of joint beam play an important role in performance of these structures. Therefore in this study a spectral dynamic analysis performed on such frames in order to optimize them against dead, live and earthquake loadings. In this procedure Migration Genetic Algorithm is used. The basis of this algorithm is inspiriting the nature of live creatures and the way inheritance transfers among different generations to calculate the optimum of mathematical functions. The model is applied on two and three dimensional braced frames. The results showed that defining the proper input data such as target function and restrictions leads to accurate optimum design as output.

Research paper thumbnail of Comparing Analysis of Elastic, Plastic and Elastoplastic of Single-layer Orthogonal Grids with Regards to both Large and Small Displacements with Nonlinearity Behavior of Material Modeling in both Real Behavior and using Plastic Hinges

Journal of Ferdowsi Civil Engineering, 2011

By the growing interest in space structure using , the need for precise analysis and design of th... more By the growing interest in space structure using , the need for precise analysis and design of these structures is more than ever sensed. plane single-layer orthogonal grids are types of space structures which used in the bridge decks, ships and covering of the ceilings with short opening. In the aspect of the presence the different methods to analyze these structures and in the spite of the determined and simple relations are obtained to analyze and design single layer grids by plastic method, it is necessary to aware of the effect of theories and also the role of each theory in the result of the analysis in order to acquire a precise and accurate analysis of the structure. First, in this paper, analysis and design of plane grids has been stated by the means of upper bound and lower bound methods, which led to find closed from relationships Then, nonlinear analysis (elastoplastic) is carried out by considering different kinds of material modeling methods and geometric nonlinear behavior.The analysis is also carried out without considering each nonlinear effects in single layer grids by SAP and ABAQUS softwares. The results are compared to the each other and the plastic analysis. the effects of the simplifying hypothesises in the analysis results are investigated and the allowable applications of each analysis method described.

Research paper thumbnail of Reliability-Based Optimization of a Prismatic Core Sandwich Panel

Journal of Ferdowsi Civil Engineering, 2011

Reliability-based design is applied as an important approach to achieve high safety with light we... more Reliability-based design is applied as an important approach to achieve high safety with light weight. In the engineering problems uncertainity should be considered in the design procedures so that the structural reliability is not smaller than a determined value. In this paper, the weight of a sandwich panel is optimized. First, the problem is solved by GA and then the weight is optimized by RIA, PMA and RDS methods based on the reliability indices. The results obtained from the aforementioned methods and GA method are compared. The comparision reveals that the panel with six wavelength core is more effective to obtain a high reliability.

Research paper thumbnail of Effect of Filler on Volumetric Properties and Film Thickness of Asphalt Mixtures

Journal of Ferdowsi Civil Engineering, 2011

Mineral filler is the finest fraction of aggregate used in concrete asphalt that can fill the voi... more Mineral filler is the finest fraction of aggregate used in concrete asphalt that can fill the void with effective interface in the mixture. It is essential for producing a mixture which is dense, cohesive, durable and resistance to the water penetration. Small change in the amount or the properties of the filler can cause the paving mixture to appear excessively dry or rich and film thickness can be a good parameter to predict concrete asphalt stability. It is generally believed that an asphalt paving mixture should have an adequate asphalt film thickness around the aggregate particles to ensure reasonable durability (resistance to aging) of the mixture. This study focuses on comparing volumetric properties and film thickness of the asphalt concrete using different fillers with a view to the geometry, physical and chemical properties. The fillers are limestone mineral and portland cement that used in two different specific surfacein the construction of Marshal test specimens. The range of the changes depends on the filler interaction with bitumen. Volumetric properties were investigated in the study are density, VFB, VTM, VMA. Other properties are Marshall stability, flow, optimum binder and film thickness. Results show that kind, content and filler properties have different effects on the volumetric properties and film thickness.

Research paper thumbnail of Dam Reservoir Interaction in Time Domain

Journal of Ferdowsi Civil Engineering, 2011

In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior inter... more In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior interaction is presented. The dam structure is flexible with infinite reservoir Exact consideration of the radiation boundary condition of the infinite reservoir and deformation of dam structure are included in the formulation which explicitly expresses the physical phenomena of fluid-structure system. The hydrodynamic pressure in the fluid domain of the structure-reservoir system is assumed to be governed by the pressure wave equation. The upstream face of the dam is considered vertical. The dam structure is modeled as a cantilever Euler-Bernoulli beam. The thickness of the dam is assumed to be variable. A new method for analysis of non-prismatic beams is presented. This new method is based on using new functions namely Basic Displacement Functions (BDFs).These functions are obtained by solving the governing equation of motion of a non-prismatic Euler-Bernoulli beam. Using this method dynamic shape functions are efficiently obtained for non-prismatic beams. Interactive behavior of the dam-reservoir system with different geometrical properties is demonstrated by numerical examples when the system is subjected to ramp acceleration and El Centro earthquake ground motions. The results are compared with those of literature and the competency of the method is shown in both economy and exactness.

Research paper thumbnail of Investigation of Effective Factors on the Performance of Grooving Method to Prevent Debonding of FRP Sheets from Concrete Surface

Journal of Ferdowsi Civil Engineering, 2011

A major challenges in flexural strengthening of reinforced concrete beams by FRP laminates is FRP... more A major challenges in flexural strengthening of reinforced concrete beams by FRP laminates is FRP sheet debonding from the concrete substrate, which leads to the premature failure of strengthened structural member. Surface preparation of concrete before FRP sheets installation is a suitable method to postpone debonding, however the effectiveness of the method is limited by the problems such as practical costs and environmental pollution. Grooving is an innovative technique to overcome debonding of FRP laminates from concrete surface, which has been recently used in Isfahan University of Technology (IUT). In this paper, the effect of some factors influencing the grooving capability aiming at reducing the debonding potential of FRP sheets from the concrete surface is addressed. These factors include the width and the depth of the grooves. In the experimental study, thirty-three prism specimens of dimensions 100×100×500 mm were subjected to 4-point flexural loading. The surfaces of the specimens have been grooved. After reinforcing the specimens by CFRP sheets, the four point flexural tests were carried out to measure the ultimate loading capacity. The results indicate that debonding can be completely prevented or highly limited by applying specified width and depth for the grooves.

Research paper thumbnail of Prediction and Control of Settlement of the Highway Constructed on Soft Soil using Reinforcement by Geotextile

Journal of Ferdowsi Civil Engineering, 2011

Construction the embankment on the soft soils leads to problems such as long term deformations an... more Construction the embankment on the soft soils leads to problems such as long term deformations and embankment stability due to high compressibility and low shear strength of the soil. Nowadays the use of geosynthetics is a practical procedure for improving soft soils characteristics. In this paper, a numerical modeling of the embankment constructed on the soft organic soil in the part of the Shahid Kalantari Highway was performed using the PLAXIS Code and Soft Soil Creep Model. The settlement of the highway after 9 years was reasonably predicted by numerical analysis. The effect of geotextile layer at the base of the embankment was then evaluated as a remedial action to control settlement. The results showed that the application of the geotextile layer, as a reinforcement layer, could significantly improve the performance of the embankment in this part of the highway.

Research paper thumbnail of Error Estimation and Stress Recovery in the Isogeometrical Analysis Method

Journal of Ferdowsi Civil Engineering, 2011

In the paper, a new approach is presented for improving the stress field and estimating the solut... more In the paper, a new approach is presented for improving the stress field and estimating the solution error based on the isogeometrical analysis method. In this approach, by using the superconvergent points for the components of the stress field in each area, an imaginary surface is generated. The surface is described by the same NURBS’ basis functions which are employed for approximating the displacement function in the isogeometrical analysis. The performance of the method is demonstrated by comparison of the exact and approximate energy error norms for a couple of examples that the exact solution is available. It seems that the proposed method can be used as a suitable approach for error estimation in the isogeometrical analysis method.

Research paper thumbnail of Reducing Frame Lateral Deflection by Active Control

Journal of Ferdowsi Civil Engineering, 2011

It is aimed to minimize the structure response against the earth vibration by the use of the open... more It is aimed to minimize the structure response against the earth vibration by the use of the open loop control system. In such a control, only one predicting neural network is utilized, which estimates only the earth vibration. The neural network is instructed by some recorded acceleration data, and it is able to predict the acceleration variation for the subsequent step. The control force is equal to the product of the mass of each story to its next step acceleration. This control system leads to the approximate minimum response. Moreover, to guarantee the system stability, a linear controller is added to the system. The resulted mixed control system can assure the system stability and also has better performance. Finally, the effect of the structural mass variation on the control system is investigated. The findings show that the effect of the structural mass variation on the mixed control system is smaller than the one by the predicting neural network.

Research paper thumbnail of Rutting Resistance Evaluation of Large Stone Asphalt Mixtures

Journal of Ferdowsi Civil Engineering, 2011

Rutting of hot mix asphalt pavements due to increased number of heavy vehicles, especially in tro... more Rutting of hot mix asphalt pavements due to increased number of heavy vehicles, especially in tropical regions, causes several performance problems. Large Stone Asphalt mixtures have more stiffness and shear resistance and so more rutting resistance compared to conventional mixtures. Hence, using these mixtures in thick layers of hot mix asphalt pavements at tropical regions could be an appropriate option for asphalt mix design. Large Stone Asphalt Mix (LSAM) is a mixture with the nominal maximum aggregate size between 25 and 63 mm. Modified Marshall mix design method according to ASTM-D5581 is used to design these mixtures. In this laboratory research, the rutting resistance of LSAM mixtures is evaluated and compared to conventional HMA mixtures. Large Stone Asphalt mixtures were designed with four different aggregate gradations as well as a conventional dense graded mixture. Rutting test specimens prepared at four different asphalt contents for Large Stone Asphalt mixtures and at optimum asphalt content for the conventional mixture. The rut depth of specimens at 60°C determined using Hamburg wheel tracking device after 12000 loading cycles. The data obtained from mix design and rutting tests analyzed using SPSS statistic software and the effects of various parameters such as asphalt content, air voids of compacted asphalt mixture and gradation on the rutting resistance of Large Stone Asphalt mixtures were evaluated. At the end, a mathematical model presented for predicting the rut depth of Large Stone Asphalt mixtures.

Research paper thumbnail of Evaluating the Combined Effects ofَ Friction Coefficient and Texture Depth of Asphalt Concrete Pavement on Freeway Accidents

Journal of Ferdowsi Civil Engineering, 2011

Many studies have been conducted focusing on the effects of friction coefficient or texture depth... more Many studies have been conducted focusing on the effects of friction coefficient or texture depth on the highway accident risk. However, combined effects of these parameters have not been still addressed. In this research the interaction between friction coefficient, texture depth and accident rate in 30 freeway sections were examined. The accident data were gathered and an apparatus was designed to measure friction coefficient. A nonlinear regression analysis was performed and a combined exponential model was obtained. The results indicated that despite cross correlation between friction coefficient and texture depth, thess parameters have some independent effects on accident rates which can be used to decrease freeway accidents significantly.

Research paper thumbnail of Assessing the Adhesion of Self-Compacting Concrete and Mortar Applied to Different Concrete surfaces, using twist-off and Friction-Transfer Methods, and its Estimation By Fuzzy Logic

Journal of Ferdowsi Civil Engineering, 2011

Invention of the self-compacting concrete has caused dramatic changes in the concrete industry wi... more Invention of the self-compacting concrete has caused dramatic changes in the concrete industry within the past twenty years. Compared with the ordinary concrete, self-compacting concrete does not need any compaction and by itself can produce concrete with sufficient compaction and smooth surfaces with no voids or honeycombing. Since the compaction has great influence on the adhesion of the concrete repair layers and due to the fact that the compaction of any repair layer is a very difficult task, it seems that SCC can be used with wide spread application as concrete repair materials. In this paper results of studies on the adhesion of self-compacting concrete applied to different concrete surfaces are presented. These studies are undertaken by the use of “twist-off” and “friction-transfer” methods and the prediction of the results by fuzzy logic, is also presented. The results tend to show that surface conditions of the substrate, aggregate to cement ratio of the repair layer, compressive strength of the repair layer, nature of the repair layer (concrete or mortar) and the degree of the moisture of the substrate concrete affect the adhesion along the repair/concrete interface. It is also realized that compared with statistical methods, fuzzy logic can be used for the prediction of the adhesion, with higher accuracy.

Research paper thumbnail of Seismic Behavior of Short Column in RC Structures with Different Floor Level

Journal of Ferdowsi Civil Engineering, 2011

Engineering structures as well as office or apartment buildings are affected by earthquakes. A co... more Engineering structures as well as office or apartment buildings are affected by earthquakes. A common cause of failure seems to be shear stresses. The earthquake tremor developed at different floor levels need to be brought down along the height to the ground by the shortest path. Short column phenomenon is one of the frquent causes of buildings failure in the past earthquakes. This destructive phenomenon is due to the column height difference in a story level that is predominantly owing to the location of building on sloppy ground. These buildings have unequal height columns along the slope, which causes poor effects like twisting and damage in shorter columns. In some buildings, few or no walls are provided at the first story (pilot). In the structures with difference in the story levels, major problems is due to the discontinuity of floors diaphragm that causes significant changes in natural period, stiffness and distribution of earthquake forces. In this study, at first, seismic behavior of short column phenomenon is determined, then, nonlinear behavior of RC short columns in the 4, 8 and 10 story buildings with story level difference is investigated. Short columns and mentioned structures are analyzed under the earthquake records of Elcentro and Tabas with different peak ground acceleration using IDARC software which is nonlinear dynamic analysis program. In this investigation, the results of maximum response, base shear, global damage index and displacement time history and effect of short column in structural failure are evaluated.

Research paper thumbnail of An Experimental Study on the Effect of T Shape Spur Dike on Down Sream Topography in a 90 Degree Bend

Journal of Ferdowsi Civil Engineering, 2011

One of the common methods of river training and bank protection is using spur dikes. Building spu... more One of the common methods of river training and bank protection is using spur dikes. Building spur dikes makes the flow path to be modified. Because of the concentration of flow in the middle part of the river it causes the river side not to be washed out. Setting spur dikes in the flow’s direction leads to a local scour in the spur dike site and the change in the bed’s topography of the bend down stream. this paper examines the effect bed’s topography around the T shaped spur dike located in a 90 degree bend by conducting several tests. These tests were carried out in an experimental channel with a bend of 90 degrees and under conditions with clear water. These experiments, in fact, measured the effects of such parameters like the length of the spur dike, the location of the spur dike in the bend, the flow Froud number on the down stream bed topography. The results of investigation show that two scour hole forms due to a T shaped spur dike. One at the nose of spur dike and the other one at the downstream of the spur dike. By increasing the length of the spur dike, the dimensions of first scour hole increase. But the dimensions of second scour hole decrease. By increasing the length of the spur dike the distance of location of second scour hole from the spur dike increases.Any change in the position of the spur dike toward the down stream of the bend, increases the dimensions of scour hole. Also, New equations for maximum scour depth and scour volumeat a T shaped spur dike are developed

Research paper thumbnail of The Effect of Circumferential Imperfections on Axial Load Carrying Capacity of Thin-Walled Cylindrical Shells

Journal of Ferdowsi Civil Engineering, 2011

The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells... more The load carrying capacity, buckling and post-buckling behavior of cylindrical thin-walled shells exposed to axial loads are very sensitive to imperfections in the initial geometry. These imperfections are invariably caused by an assortment of manufacturing processes like displacing, installing or welding; one of the most important imperfections caused by welding that has been reported to have an essential detrimental effect on the buckling resistance of these shells under axial load is circumferential imperfections. Despite many determinations of the effect of imperfections on axial load carrying capacity of cylindrical thin-walled shells, the major part of these studies are concentrated on the existence of imperfections on the shell wall, and a comprehensive research on circumferential imperfections and their effects on axial load carrying capacity has not been performed. This is the main subject of this research. Also in this paper, the interaction of two imperfections on each other and on the load carrying capacity of cylindrical shells in various cases are analyzed and determined using a finite element program (ABAQUS).

Research paper thumbnail of Effect of Silica Fume, Metakaolin, Zeolite and Polypropylene Fiber on Chloride Diffusion in Concrete

Journal of Ferdowsi Civil Engineering, 2011

Rapid concrete deterioration in Persian Gulf region has become one of the major concerns since it... more Rapid concrete deterioration in Persian Gulf region has become one of the major concerns since it shortens the structure life span and increases the maintenance costs. The main cause of such concrete failure is claimed to be chloride permeation and subsequent corrosion. Pozzalns are widely being used in order to construct more durable concrete as a functional solution to this problem. The paper reports the performance of concrete incorporating silica fume (replacement level of 5%, 7.5% and 10%), metakaolin (replacement level of 5%, 10% and 15%), zeolite (replacement level of 10%, 20% and 30%) and Polypropylene Fiber in the binder to resist the chloride penetration in aggressive environments. The results showed that specimens containing pozzolans function better than control concretes.

Research paper thumbnail of Ductility Analysis of Lap-Spliced Reinforced Concrete Beams

Journal of Ferdowsi Civil Engineering, 2011

In this research, the ductility of lap-spliced concrete beams reinforced with steel and FRP bars ... more In this research, the ductility of lap-spliced concrete beams reinforced with steel and FRP bars is analyzed. A number of 16 beam specimens reinforced with steel bars and 7 with FRP bar were designed and manufactured in real sizes and dimensions for laboratory experiments. The parameters of concrete compressive strength, amount of transverse reinforcement over the splice length and the diameter of longitudinal bars, are selected as the main variables for the beam specimens. Mid-span displacements and the corresponding forces were obtained by means of a hydraulic jack, load cell, LVDT and a Data Logger set. The force versus mid-span displacement curves were obtained using the experimental data. A ductility index which has been defined by researchers, was used to evaluate the ductility of the specimens. Comparison of the ductility index of different specimens shows that the compressive strength of concrete and the amount and the bar diameter of the transverse reinforcement over the splice length, has a major effect on the ductility of lap-spliced reinforced concrete beams. The results show that by using an appropriate amount of transverse reinforcement, a satisfactory ductility response for different compressive strengths of concrete can be obtained.

Research paper thumbnail of A Comparative Study on Determination Soil Deformation Modulus, Using In-Situ and Laboratory Plate Load Tests

Journal of Ferdowsi Civil Engineering, 2011

Soil deformation modulus is one of the most complicated and important soil parameters, correlatin... more Soil deformation modulus is one of the most complicated and important soil parameters, correlating between stress and settlement. The magnitude of deformation modulus is not constant. Its value, which varies in a wide range, depends on many factors. The soil deformation modulus may be determined using in-situ and laboratory tests, including consolidation test, triaxial test, Standard Penetration Test (SPT), Cone Penetration Test (CPT), Plate Load Test (PLT) and many other tests. Although the in-situ test results are more accurate in comparison with laboratory tests, but in-situ tests are more expensive and time consuming and practically these tests are usually difficult and sometimes impossible to perform.In the present research the in-situ plate load test results are employed to determine the soil deformation modulus. This test is then modeled in the laboratory and results are compared. To achieve this, after soil sampling from the site, the samples were classified after which their moisture content and unit weight were determined. The plate load test, modeled in the laboratory, was then performed on the undisturbed samples, taken from the site. In order to compare and establish a mathematical correlation between the results of these two groups (the in-situ and laboratory plate load tests), the load-settlement curves of all two group tests were plotted, after which the initial tangent slope, secant slope and unloading slope for each sample was calculated and plotted and the results were then compared. Considering the complicated soil behavior, the results of this research seem to be appropriate and can be used in practical civil engineering purposes.

Research paper thumbnail of Graph Theoretical Methods for improving The conditioning of Flexibility Matrix of Structures

Journal of Ferdowsi Civil Engineering, 2011

In addition to reducing the size and time of analyses, reduction of analytical errors is one of t... more In addition to reducing the size and time of analyses, reduction of analytical errors is one of the most important considerations in ideal analysis of skeletal structures by computer. Appropriate matrixes with more zeros (sparse), well structure, and well condition are helpful for this aim. Therefore, an optimizing problem with multiple objectives will be considered.The objective of this research is reducing the analytical errors such as rounding errors in flexibility matrixes of skeletal structures by performing more constant and proper algorithm. These errors increase in special structures with unsuitable flexibility matrixes; the structures with different stiffnesses are one of the most prevalent examples for this case.Use of weak elements leads into high non-diagonal terms in flexibility matrix, which result in analytical errors. In numerical analysis, ill-condition of a matrix is soluble by movement or substitution of the rows; then specification and implementation of these changes before forming the flexibility matrix has been studied. By identifying cycle bases with specific qualities, simple typological and algebraic properties have been used basically in analyses for this purpose. In conclusion, stiffness matrixes with optimally condition number are obtainable and analytical errors reduce.

Research paper thumbnail of Seismic Behavior of Brick Walls

Journal of Ferdowsi Civil Engineering, 2011

In this paper, brick walls as seismic load carrying elements in masonry buildings have been studi... more In this paper, brick walls as seismic load carrying elements in masonry buildings have been studied. An experimented un-reinforced brick wall (UBW) has been chosen from ref.(1) to prove the ability of analytical modeling used in this paper by which a reinforced (RBW) and a confined brick wall (CBW), designed according to Iranian Earthquake Standards, have been modeled and nonlinearly analyzed. This analysis shows that UBW practically is not able to resist horizontal loads. According to the type and direction of cracks in UBW constructed by conventional methods, it is clear that these walls do not have sufficient shear strength, and the study of hysteresis curves of brick walls shows that the confinement in CBW and reinforcement in RBW increases the rigidity and capability to displacement of walls.

Research paper thumbnail of Optimization of Braced Frames Against Dynamic Spectral Loadings Using Migration Genetic Algorithm

Journal of Ferdowsi Civil Engineering, 2011

The purpose of optimization in civil engineering is design of a structure to achieve the minimum ... more The purpose of optimization in civil engineering is design of a structure to achieve the minimum weight and construction cost of the structure in addition to satisfaction of the technical aspects of the problem. Braced frame is a type of structure with large application in civil engineering. The arrangement of bracings in different panels and length of joint beam play an important role in performance of these structures. Therefore in this study a spectral dynamic analysis performed on such frames in order to optimize them against dead, live and earthquake loadings. In this procedure Migration Genetic Algorithm is used. The basis of this algorithm is inspiriting the nature of live creatures and the way inheritance transfers among different generations to calculate the optimum of mathematical functions. The model is applied on two and three dimensional braced frames. The results showed that defining the proper input data such as target function and restrictions leads to accurate optimum design as output.

Research paper thumbnail of Comparing Analysis of Elastic, Plastic and Elastoplastic of Single-layer Orthogonal Grids with Regards to both Large and Small Displacements with Nonlinearity Behavior of Material Modeling in both Real Behavior and using Plastic Hinges

Journal of Ferdowsi Civil Engineering, 2011

By the growing interest in space structure using , the need for precise analysis and design of th... more By the growing interest in space structure using , the need for precise analysis and design of these structures is more than ever sensed. plane single-layer orthogonal grids are types of space structures which used in the bridge decks, ships and covering of the ceilings with short opening. In the aspect of the presence the different methods to analyze these structures and in the spite of the determined and simple relations are obtained to analyze and design single layer grids by plastic method, it is necessary to aware of the effect of theories and also the role of each theory in the result of the analysis in order to acquire a precise and accurate analysis of the structure. First, in this paper, analysis and design of plane grids has been stated by the means of upper bound and lower bound methods, which led to find closed from relationships Then, nonlinear analysis (elastoplastic) is carried out by considering different kinds of material modeling methods and geometric nonlinear behavior.The analysis is also carried out without considering each nonlinear effects in single layer grids by SAP and ABAQUS softwares. The results are compared to the each other and the plastic analysis. the effects of the simplifying hypothesises in the analysis results are investigated and the allowable applications of each analysis method described.

Research paper thumbnail of Reliability-Based Optimization of a Prismatic Core Sandwich Panel

Journal of Ferdowsi Civil Engineering, 2011

Reliability-based design is applied as an important approach to achieve high safety with light we... more Reliability-based design is applied as an important approach to achieve high safety with light weight. In the engineering problems uncertainity should be considered in the design procedures so that the structural reliability is not smaller than a determined value. In this paper, the weight of a sandwich panel is optimized. First, the problem is solved by GA and then the weight is optimized by RIA, PMA and RDS methods based on the reliability indices. The results obtained from the aforementioned methods and GA method are compared. The comparision reveals that the panel with six wavelength core is more effective to obtain a high reliability.

Research paper thumbnail of Effect of Filler on Volumetric Properties and Film Thickness of Asphalt Mixtures

Journal of Ferdowsi Civil Engineering, 2011

Mineral filler is the finest fraction of aggregate used in concrete asphalt that can fill the voi... more Mineral filler is the finest fraction of aggregate used in concrete asphalt that can fill the void with effective interface in the mixture. It is essential for producing a mixture which is dense, cohesive, durable and resistance to the water penetration. Small change in the amount or the properties of the filler can cause the paving mixture to appear excessively dry or rich and film thickness can be a good parameter to predict concrete asphalt stability. It is generally believed that an asphalt paving mixture should have an adequate asphalt film thickness around the aggregate particles to ensure reasonable durability (resistance to aging) of the mixture. This study focuses on comparing volumetric properties and film thickness of the asphalt concrete using different fillers with a view to the geometry, physical and chemical properties. The fillers are limestone mineral and portland cement that used in two different specific surfacein the construction of Marshal test specimens. The range of the changes depends on the filler interaction with bitumen. Volumetric properties were investigated in the study are density, VFB, VTM, VMA. Other properties are Marshall stability, flow, optimum binder and film thickness. Results show that kind, content and filler properties have different effects on the volumetric properties and film thickness.

Research paper thumbnail of Dam Reservoir Interaction in Time Domain

Journal of Ferdowsi Civil Engineering, 2011

In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior inter... more In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior interaction is presented. The dam structure is flexible with infinite reservoir Exact consideration of the radiation boundary condition of the infinite reservoir and deformation of dam structure are included in the formulation which explicitly expresses the physical phenomena of fluid-structure system. The hydrodynamic pressure in the fluid domain of the structure-reservoir system is assumed to be governed by the pressure wave equation. The upstream face of the dam is considered vertical. The dam structure is modeled as a cantilever Euler-Bernoulli beam. The thickness of the dam is assumed to be variable. A new method for analysis of non-prismatic beams is presented. This new method is based on using new functions namely Basic Displacement Functions (BDFs).These functions are obtained by solving the governing equation of motion of a non-prismatic Euler-Bernoulli beam. Using this method dynamic shape functions are efficiently obtained for non-prismatic beams. Interactive behavior of the dam-reservoir system with different geometrical properties is demonstrated by numerical examples when the system is subjected to ramp acceleration and El Centro earthquake ground motions. The results are compared with those of literature and the competency of the method is shown in both economy and exactness.

Research paper thumbnail of Investigation of Effective Factors on the Performance of Grooving Method to Prevent Debonding of FRP Sheets from Concrete Surface

Journal of Ferdowsi Civil Engineering, 2011

A major challenges in flexural strengthening of reinforced concrete beams by FRP laminates is FRP... more A major challenges in flexural strengthening of reinforced concrete beams by FRP laminates is FRP sheet debonding from the concrete substrate, which leads to the premature failure of strengthened structural member. Surface preparation of concrete before FRP sheets installation is a suitable method to postpone debonding, however the effectiveness of the method is limited by the problems such as practical costs and environmental pollution. Grooving is an innovative technique to overcome debonding of FRP laminates from concrete surface, which has been recently used in Isfahan University of Technology (IUT). In this paper, the effect of some factors influencing the grooving capability aiming at reducing the debonding potential of FRP sheets from the concrete surface is addressed. These factors include the width and the depth of the grooves. In the experimental study, thirty-three prism specimens of dimensions 100×100×500 mm were subjected to 4-point flexural loading. The surfaces of the specimens have been grooved. After reinforcing the specimens by CFRP sheets, the four point flexural tests were carried out to measure the ultimate loading capacity. The results indicate that debonding can be completely prevented or highly limited by applying specified width and depth for the grooves.

Research paper thumbnail of Prediction and Control of Settlement of the Highway Constructed on Soft Soil using Reinforcement by Geotextile

Journal of Ferdowsi Civil Engineering, 2011

Construction the embankment on the soft soils leads to problems such as long term deformations an... more Construction the embankment on the soft soils leads to problems such as long term deformations and embankment stability due to high compressibility and low shear strength of the soil. Nowadays the use of geosynthetics is a practical procedure for improving soft soils characteristics. In this paper, a numerical modeling of the embankment constructed on the soft organic soil in the part of the Shahid Kalantari Highway was performed using the PLAXIS Code and Soft Soil Creep Model. The settlement of the highway after 9 years was reasonably predicted by numerical analysis. The effect of geotextile layer at the base of the embankment was then evaluated as a remedial action to control settlement. The results showed that the application of the geotextile layer, as a reinforcement layer, could significantly improve the performance of the embankment in this part of the highway.

Research paper thumbnail of Error Estimation and Stress Recovery in the Isogeometrical Analysis Method

Journal of Ferdowsi Civil Engineering, 2011

In the paper, a new approach is presented for improving the stress field and estimating the solut... more In the paper, a new approach is presented for improving the stress field and estimating the solution error based on the isogeometrical analysis method. In this approach, by using the superconvergent points for the components of the stress field in each area, an imaginary surface is generated. The surface is described by the same NURBS’ basis functions which are employed for approximating the displacement function in the isogeometrical analysis. The performance of the method is demonstrated by comparison of the exact and approximate energy error norms for a couple of examples that the exact solution is available. It seems that the proposed method can be used as a suitable approach for error estimation in the isogeometrical analysis method.

Research paper thumbnail of Reducing Frame Lateral Deflection by Active Control

Journal of Ferdowsi Civil Engineering, 2011

It is aimed to minimize the structure response against the earth vibration by the use of the open... more It is aimed to minimize the structure response against the earth vibration by the use of the open loop control system. In such a control, only one predicting neural network is utilized, which estimates only the earth vibration. The neural network is instructed by some recorded acceleration data, and it is able to predict the acceleration variation for the subsequent step. The control force is equal to the product of the mass of each story to its next step acceleration. This control system leads to the approximate minimum response. Moreover, to guarantee the system stability, a linear controller is added to the system. The resulted mixed control system can assure the system stability and also has better performance. Finally, the effect of the structural mass variation on the control system is investigated. The findings show that the effect of the structural mass variation on the mixed control system is smaller than the one by the predicting neural network.

Research paper thumbnail of Rutting Resistance Evaluation of Large Stone Asphalt Mixtures

Journal of Ferdowsi Civil Engineering, 2011

Rutting of hot mix asphalt pavements due to increased number of heavy vehicles, especially in tro... more Rutting of hot mix asphalt pavements due to increased number of heavy vehicles, especially in tropical regions, causes several performance problems. Large Stone Asphalt mixtures have more stiffness and shear resistance and so more rutting resistance compared to conventional mixtures. Hence, using these mixtures in thick layers of hot mix asphalt pavements at tropical regions could be an appropriate option for asphalt mix design. Large Stone Asphalt Mix (LSAM) is a mixture with the nominal maximum aggregate size between 25 and 63 mm. Modified Marshall mix design method according to ASTM-D5581 is used to design these mixtures. In this laboratory research, the rutting resistance of LSAM mixtures is evaluated and compared to conventional HMA mixtures. Large Stone Asphalt mixtures were designed with four different aggregate gradations as well as a conventional dense graded mixture. Rutting test specimens prepared at four different asphalt contents for Large Stone Asphalt mixtures and at optimum asphalt content for the conventional mixture. The rut depth of specimens at 60°C determined using Hamburg wheel tracking device after 12000 loading cycles. The data obtained from mix design and rutting tests analyzed using SPSS statistic software and the effects of various parameters such as asphalt content, air voids of compacted asphalt mixture and gradation on the rutting resistance of Large Stone Asphalt mixtures were evaluated. At the end, a mathematical model presented for predicting the rut depth of Large Stone Asphalt mixtures.

Research paper thumbnail of Evaluating the Combined Effects ofَ Friction Coefficient and Texture Depth of Asphalt Concrete Pavement on Freeway Accidents

Journal of Ferdowsi Civil Engineering, 2011

Many studies have been conducted focusing on the effects of friction coefficient or texture depth... more Many studies have been conducted focusing on the effects of friction coefficient or texture depth on the highway accident risk. However, combined effects of these parameters have not been still addressed. In this research the interaction between friction coefficient, texture depth and accident rate in 30 freeway sections were examined. The accident data were gathered and an apparatus was designed to measure friction coefficient. A nonlinear regression analysis was performed and a combined exponential model was obtained. The results indicated that despite cross correlation between friction coefficient and texture depth, thess parameters have some independent effects on accident rates which can be used to decrease freeway accidents significantly.

Research paper thumbnail of Assessing the Adhesion of Self-Compacting Concrete and Mortar Applied to Different Concrete surfaces, using twist-off and Friction-Transfer Methods, and its Estimation By Fuzzy Logic

Journal of Ferdowsi Civil Engineering, 2011

Invention of the self-compacting concrete has caused dramatic changes in the concrete industry wi... more Invention of the self-compacting concrete has caused dramatic changes in the concrete industry within the past twenty years. Compared with the ordinary concrete, self-compacting concrete does not need any compaction and by itself can produce concrete with sufficient compaction and smooth surfaces with no voids or honeycombing. Since the compaction has great influence on the adhesion of the concrete repair layers and due to the fact that the compaction of any repair layer is a very difficult task, it seems that SCC can be used with wide spread application as concrete repair materials. In this paper results of studies on the adhesion of self-compacting concrete applied to different concrete surfaces are presented. These studies are undertaken by the use of “twist-off” and “friction-transfer” methods and the prediction of the results by fuzzy logic, is also presented. The results tend to show that surface conditions of the substrate, aggregate to cement ratio of the repair layer, compressive strength of the repair layer, nature of the repair layer (concrete or mortar) and the degree of the moisture of the substrate concrete affect the adhesion along the repair/concrete interface. It is also realized that compared with statistical methods, fuzzy logic can be used for the prediction of the adhesion, with higher accuracy.