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Showing 44 results for Crack

Khaloo R., Sharifian M.,
Volume 3, Issue 3 (9-2005)

Results of an experimental investigation performed to evaluate the effect of various concrete strength levels on behavior of lightweight concrete (LWC) under pure torsion are reported.The principle variable of the testing program was compressive strength of concrete (�'c) which ranged between 6.9 and 81.4 MPa. Ten mixture proportions were utilized for LWC of 1500 to 2050 kg/m3 unit weight. In total, sixty four (thirty two pairs) rectangular specimens with 100x 200 mm cross-section were tested. Ultimate torsion strength of LWC increases as uniaxial compressive strength increases however the increase rate reduces for high levels of concrete strengths. The test results are compared with predictions of elastic and plastic theories for torsion and the ACI Code. The Code underestimates the cracking torque of LWC under pure torsion. A regression equation incorporating test results is higher than the ACI equation prediction by a factor of 1.12.
B. Behnam, M.h. Sebt, H.m. Vosoughifar,
Volume 4, Issue 2 (6-2006)

By identifying the damage index of a structure, in addition to a correct understanding from real behavior of the structure, the required criterion for strengthening would be given. Researchers have given many relations for determination of damage index but such relations have been based upon laboratory methods which challenge their usage in a broad term. In this paper two new methods are given for calculation of damage index. Surveying the first crack limit and total structure failure is based upon the formation of plastic joints in the first column and basic floor columns. To give a qualitative simple and functional damage index, the functional method was given in the form of a qualitative method with statistical analysis and collection of different views. Using this method is very simple and meantime offers suitable accuracy. With a numerical study on three models it was made clear that the difference of new method with amended method of Papadopolos in approximate 3%. This shows that given qualitative method is suitable to be used in a broad terms.
M.h. Baziar, Sh. Salemi, T. Heidari,
Volume 4, Issue 3 (9-2006)

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been performed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax=0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.
S.a. Sadrnejad, M. Labibzadeh,
Volume 4, Issue 4 (12-2006)

Analysis and prediction of structural response to static or dynamic loading requires prediction of concrete response tovariable load histories. The constitutive equations for the mechanical behavior of concrete capable of seeing damage effects or crack growth procedure under loading/unloading/reloading was developed upon micro-plane framework. The proposed damage formulation has been built on the basis of five fundamental types of stress/strain combinations, which essentially may occur on any of micro-planes. Model verification under different loading/unloading/reloading stress/strain paths has been examined. The proposed model is capable of presenting pre-failure history of stress/strain progress on different predefined sampling planes through material. Many of mechanical behavior aspects happen during plasticity such as induced anisotropy, rotation of principal stress/strain axes, localization of stress/strain, and even failure mechanism are predicted upon a simple rational way and can be presented.
A.a. Khosroshahi, S.a. Sadrnejad,
Volume 5, Issue 1 (3-2007)

A framework for development of constitutive models including damage progress, based on semi-micromechanical aspects of plasticity is proposed for concrete. The model uses sub-loading surface with multilaminate framework to provide kinematics and isotropic hardening/softening in the ascending/descending branches of loading and can be able to keep stress/stain paths histories for each plane separately. State of stresses on planes is divided to four basic stress patterns i.e. pure compression, increasing compression-and shear, decreasing compression-shear and tension-shear and used in derivation of plasticity equations. Under this kind of categorized form the model is capable of predicting behavior of concrete under any stress/strain path such as uniaxial, biaxial and triaxial in the monotonic and cyclic loading, Also this model is capable of predicting the effects of principal stress/strain axes rotations and consequent plastic flow and has the potential to simulate the behavior of material with anisotropy, fabric pattern, slip/weak planes and crack opening/closing. The material parameters of model are calibrated by optimum fitting of the basic test data available in the literature. The model results under both monotonic and cyclic loading have been compared with experimental results to show capability of model.
P. Ghoddousi, A.m. Raiss Ghasemi, T. Parhizkar,
Volume 5, Issue 4 (12-2007)

Plastic shrinkage is one of the most important parameter which must be considered in hot weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especialy if silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity, temperature and wind velocity, sun rediation also is very important factor in evaporation rate. It is found that under solar radition condition, the evaporation was much larger than the estimated value in ACI 305 Nomogram. The rate of evaporaion under solar radiation was about two folds of evaporation rate under shade condition. The results showed that in terms of crack initiation time, crack width and total cracking area, concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water cement ratio in concrete with silica fume makes the concrete more sensitive in cracking. The results of this project also showed that the severity of the cracking is not related only to rate of bleeding but all environmental factors including like sun radiation or shading and also mix compositions have important roles.
M.kazem Sharbatdar,
Volume 6, Issue 1 (3-2008)

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.
S.h. Ebrahimi, S. Mohammadi, A. Asadpoure,
Volume 6, Issue 3 (9-2008)

A new approach is proposed to model a crack in orthotropic composite media using the extended finite element method (XFEM). The XFEM uses the concept of partition of unity in addition to meshless basic idea of approximating a field variable by its values at a set of surrounding nodes. As a result, higher order approximations can be designed with the same total number of degrees of freedom. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore mesh generating is performed without any consideration of crack conformations for elements and the method has the ability of extending the crack without any remeshing. Furthermore, the type of elements around the cracktip is the same as other parts of the finite element model and the number of nodes and consequently degrees of freedom are reduced considerably in comparison to the classical finite element method. Developed orthotropic enrichment functions are further modified to enable modeling isotropic problems.
Mahmood R. Abdi, Ali Parsapajouh, Mohammad A. Arjomand,
Volume 6, Issue 4 (12-2008)

Clay soils and their related abnormal behavior such as excessive shrinkage, swelling, consolidation settlement and cracking on drying has been the subject of many investigations. Previous studies mainly evaluated the effects of additives such as lime, cement and sand on these characteristics. Initial results indicated that the soil characteristics were improved. However, reportedly in many cases, these additives resulted in a decrease in plasticity and increase in hydraulic conductivity. As a result, there has been a growing interest in soil/fiber reinforcement. The present investigation has focused on the impact of short random fiber inclusion on consolidation settlement, swelling, hydraulic conductivity, shrinkage limit and the development of desiccation cracks in compacted clays. To examine the possible improvements in the soil characteristics, samples consisting of 75% kaolinite and 25% montmorillonite were reinforced with 1, 2, 4 and 8 percent fibers as dry weight of soil with 5, 10 and 15mm lengths. Results indicated that consolidation settlements and swelling of fiber reinforced samples reduced substantially whereas hydraulic conductivities increased slightly by increasing fiber content and length. Shrinkage limits also showed an increase with increasing fiber content and length. This meant that samples experienced much less volumetric changes due to desiccation, and the extent of crack formation was significantly reduced.
A. Khodaii, Sh. Fallah,
Volume 7, Issue 2 (6-2009)

An experimental program was conducted to determine the effects of geosynthetic reinforcement on mitigating reflection cracking in asphalt overlays. The objectives of this study were to asses the effects of geosynthetics inclusion and its placement location on the accumulation of permanent deformation. To simulate an asphalt pavement overlaid on top of a crack in a concrete or asphalt pavement, an asphalt mixture specimen was placed on top of two discontinuous concrete or asphalt concrete blocks with 100 mm height. Four types of specimens were prepared with respect to the location of geogrid: (I) Unreinforced samples, which served as control specimen, (II) Samples with geogrid embedded on the concrete or asphalt concrete block, (III) Samples with geogrid embeded one-thired depth of asphalt concrete from bottom, (IV) Samples with geogrid embedded in the middle of the asphalt beam. Each specimen was then placed on the rubber foundation in order to be tested. Simulated- repeated loading was applied to the asphalt mixture specimens using a hydraulic dynamic loading frame. Each experiment was recorded in its entirety by a video camera to allow the physical observation of reflection crack formation and propagation. This study revealed that geosynthetic reinforced specimens exhibited resistance to reflection cracking. Placing the geogrid at the one- third depth of overlay thickness had the maximum predicted service life. Results indicate a significant reduction in the rate of crack propagation and rutting in reinforced samples compared to unreinforced samples.
I. Rasoolan, S.a. Sadrnejad, A.r. Bagheri,
Volume 7, Issue 2 (6-2009)

Concrete is a heterogeneous material with a highly non linear behavior, which is mainly caused by the

initiation and propagation of micro cracks within the several components of the material. The damage behavior of

concrete is usually simulated on the macro scale using complex constitutive models. The direct determination of the

homogenized material parameters is often difficult and sometimes impossible. Furthermore these materials models do

not explicitly represent effects and bond behaviors of interfaces between the several components. So in order to predict

of concrete behaviors and characteristics, it should be modeled as a three phase composite material consisting of

aggregate, interfacial transition zone (ITZ) and cement paste. The size and distribution of aggregate affects concrete

characteristics. Because of the random distribution and size variation of aggregate in concrete, the modeling of

concrete behavior based on component in meso structure is difficult and so we must use simple assumption. In this

paper with mixing design and grading curve we developed a simple method to replace real aggregate with equivalent

sphere aggregate with effective diameter. So we can use simple methods instead of complex numeral and randomness

or x ray methods to find effective diameter and use it to determine two arrangements with maximum and minimum

aggregate volume as a repeatable basical element .As a result we can use this element to modeling the behavior of

sample concrete in meso scale and three phases.

A. Arabzadeh, A.r. Rahaie, A. Aghayari,
Volume 7, Issue 3 (9-2009)

In this paper a new method based on Strut-and-Tie Model (STM) is proposed to determine the shear capacity of simply supported RC deep beams and an efficiency factor for concrete with considering the effect of web reinforcements. It is assumed that, the total carried shear force by RC deep beam provided by two independent resistance, namely diagonal concrete strut due to strut-and-tie mechanism and the equivalent resisting force resulted by web reinforcements, web reinforcing reduces the concrete compression softening effect with preventing from the diagonal cracks opening or concrete splitting. The unknown function and parameters are determined from 324 experimental results obtained by other researchers. To validate the proposed method, the obtained results are compared with some of the existing methods and codes such as ACI 318-05 and CSA. The results indicate that the proposed method is capable to predict the shear strength of variety of deep beams with acceptable accuracy.
A.r. Khaloo, I. Eshghi, P. Piran Aghl,
Volume 8, Issue 3 (9-2010)

In this paper the response of cantilevered reinforced concrete (RC) beams with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is SuperelasticShape Memory Alloys (SE SMAs) which contains nickel and titanium elements. The SE SMA is a unique alloy that has the ability to undergo large deformations and return to their undeformed shape by removal of stresses. In this study, different quantities of steel and smart rebars have been used for reinforcement andthe behavior of these models under lateral loading, including their load-displacement curves, residual displacements, and stiffness, were discussed. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the beams and also residual deflections are created in the structure. It is found that by using SMA rebars in RC beams, these materials tend to return to the previous state (zero strain), so they reduce the permanent deformations and also in turn create forces known as recovery forces in the structure which lead into closing of concrete cracks in tensile zone. This ability makes special structures to maintain their serviceability even after a strong earthquake

M. Mazloom ,
Volume 8, Issue 3 (9-2010)

 According to the Iranian code of practice for seismic resistant design of buildings, soft storey phenomenon happens in a storey when the lateral stiffness of the storey is lower than 70% of the stiffness of the upper storey, or if it is lower than 80% of the average stiffness of the three upper stories. In the combined structural systems containing moment frames and shear walls, it is possible that the shear walls of the lower stories crack however, this cracking may not occur in the upper stories. The main objective of this research is to investigate the possibility of having soft storey phenomenon in the storey, which is bellow the uncracked walls. If the tension stresses of shear walls obtained from ultimate load combinations exceed the rupture modulus of concrete, the walls are assumed to be cracked. For calculating the tension stresses of shear walls in different conditions, 10 concrete structures containing 15 stories were studied. Each of the structures was investigated according to the obligations of Iranian, Canadian, and American concrete building codes. Five different compressive strengths of 30, 40, 50, 60, and 70 MPa were assumed for the concrete of the structures. In other words, 150 computerized analyses were conducted in this research. In each analysis, 5 load combinations were imposed to the models. It means, the tension stresses of the shear walls in each storey, were calculated 750 times. The average wall to total stiffness ratios of the buildings were from 0.49 to 0.95, which was quite a wide range. The final conclusion was that the soft storey phenomenon did not happen in any of the structures investigated in this research. 

Abolfazl Arabzadeh, Reza Aghayari, Ali Reza Rahai,
Volume 9, Issue 3 (9-2011)

An experimental-analytical investigation was conducted to study the behavior of high-strength RC deep beams a total of sixteen

reinforced concrete deep beams with compressive strength in range of 59 MPaOf'c O65 MPa were tested under two-point top

loading. The shear span-to-effective depth ratio a/d was 1.10 all the specimens were simply supported and reinforced by

vertical, horizontal and orthogonal steel bars in various arrangements. The test specimens were composed of five series based

on their arrangement of shear reinforcing. The general behavior of tested beams was investigated. Observations were made on

mid-span and loading point deflections, cracks form, failure modes and shear strengths. The test results indicated that both

vertical and horizontal web reinforcement are efficient in shear capacity of deep beams, also the orthogonal shear reinforcement

was the most efficient when placed perpendicular to major axis of diagonal crack. Concentrating of shear reinforcement within

middle region of shear span can improve the ultimate shear strength of deep beam. The test results were then compared with the

predicted ultimate strengths using the ACI 318-08 provisions ACI code tended to either unsafe or scattered results. The

performed investigations deduced that the ACI code provisions need to be revised.

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

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.

Saeed Reza Sabbaghyazdi1, Tayebeh Amiri Saadatabadi,
Volume 9, Issue 3 (9-2011)

In this research, a novel numerical algorithm is introduced for computation of temperature-induced before crack steady strainstress field in plane-stress problem. For this purpose, two dimensional heat transfer equation and force equilibrium equations are sequentially solved using Galerkin Finite Volume method on identical unstructured triangular meshes when proper convergence for each field is achieved. In this model, a proper thermal boundary condition that is suitable for unstructured triangular meshes is introduced for analysis. Two test cases are used to assess accuracy of thermal and structural modules of the developed solver and the computed results are compared with theirs analytical solution.First, thermal analysis is performed for a rectangular plate which is connected to a supporting body with constant temperature and expose to surrounding liquid at three edges.Second, structural analysis is performed for a plate under distributed loads in two directions. Having obtained acceptable results from thermal and structural modules, thermal stress analysis is performed for a plate with fixed-end condition at one of edges,due to a uniform temperature field and the computational principle stress contours are compared with the Finite Element method results which have been reported in the literatures.

A. A. Tasnimi, M. A. Rezazadeh,
Volume 10, Issue 3 (9-2012)

The torsional capacity of unreinforced masonry brick buildings is generally inadequate to provide a stable seismic behavior. The

torsional strength is believed to be the most important parameter in earthquake resistance of masonry buildings and the shear

stresses induced in the bed joints of such building’s walls is an important key for design purposes. Brick buildings strengthened

with wire-mesh reinforced concrete overlay are used extensively for building rehabilitation in Iran. Their quick and simple

applications as well as good appearance are the main reasons for the widespread use of such strengthening technique. However,

little attention has been paid to torsional strengthening in terms of both experimental and numerical approach. This paper reports

the response and behavior of two single-story brick masonry buildings having a rigid two-way RC floor diaphragm. Both

specimens were tested under monotonic torsional moment.Numerical work was carried out using non-linear finite element

modeling. Good agreement in terms of torque–twist behavior, and crack patterns was achieved. The unique failure modes of the

specimens were modeled correctly as well. The results demonstrate the effectiveness of reinforced concrete overlay in enhancing

the torsional response of strengthened building. Having evaluated the verification of modeling, an unreinforced brick building

with wall-to-wall vulnerable connections was modeled so that the effect of these connections on torsional performance of brick

building could be studied. Then this building was strengthened with reinforced concrete overlay and the effect of strengthening

on torsional performance of brick buildings with vulnerable connections was predicted numerically.

H. Famili, M. Khodadad Saryazdi, T. Parhizkar,
Volume 10, Issue 3 (9-2012)

Self-desiccation is the major source of autogenous shrinkage and crack formation in low water-binder ratio (w/b) concretes

which can be reduced by internal curing. In this paper performance of high strength self consolidating concrete (HS-SCC) with

w/b of 0.28 and 0.33 including autogenous shrinkage, drying shrinkage, compressive strength, and resistance to freezing-thawing

was investigated. Then, for the purpose of internal curing, 25% of normal weight coarse aggregate volume was replaced with

saturated lightweight aggregate (LWA) of the same size and its effects on the material properties was studied. Two modes of

external curing, moist and sealed, were applied to test specimens after demoulding. Autogenous shrinkage from 30 minutes to 24

hours after mixing was monitored continuously by a laser system. The initial and final setting time were manifested as a change

of the slope of the obtained deformation curves. Shrinkage after initial setting was 860 and 685 microstrain (&mu&epsilon) for 0.28 and 0.33

w/b mixtures, respectively. The saturated LWA reduced these values to 80 and 295 &mu&epsilon, respectively. By LWA Substitution the 28-

day compressive strength of 0.28 w/b mixture was reduced from 108 to 89 and 98 to 87 MPa for moist and sealed cured specimen,

respectively. The corresponding values for 0.33 w/b mixture was 84 to 80 and 82 to 70 MPa. Shrinkage of 0.28 w/b mixture

without LWA after moist and sealed cured specimen dried for 3 weeks was about 400 &mu&epsilon. Shrinkage of moist and sealed cured

specimen containing LWA was reduced 9% and 25%, respectively. On the contrary for 0.33 w/b mixture an increase was noticed.

Freezing-thawing resistance was improved by sealed curing, decreasing w/b and substituting LWA.

R. Ahmadii, P. Ghoddousi, M. Sharifi,
Volume 10, Issue 4 (12-2012)

The main objective of this study is to drive a simple solution for prediction of steel fiber reinforced concrete (SFRC) behavior

under four point bending test (FPBT). In this model all the force components at the beam section (before and after cracking)

are formulated by applying these assumptions: a bilinear elastic-perfectly plastic stress-strain response for concrete behavior

in compression, a linear response for the un-cracked tension region in a concrete constitutive model, and an exponential

relationship for stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical

cracked section is calculated by applying these assumptions and satisfying equilibrium lawat critical cracked section. After that,

parametric studies have been done on the behavior of SFRC to assess the sensitively of model. Finally the proposed model has

been validated with some existing experimental tests.The result shows that the proposed solution is able to estimate the behavior

of SFRC under FPBT with simplicity and proper accuracy.

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