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        Investigation of the model scale and particle size effects on the point load index and tensile strength of concrete using particle flow code

        Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Ahmadreza Hedayat,Mohammad Fatehi Marji 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.4

        In this paper the effects of particle size and model scale of concrete have been investigated on point load index, tensile strength, and the failure processes using a PFC2D numerical modeling study. Circular and semi-circular specimens of concrete were numerically modeled using the same particle size, 0.27 mm, but with different model diameters of 75 mm, 54 mm, 25 mm, and 12.5 mm. In addition, circular and semi-circular models with the diameter of 27 mm and particle sizes of 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, and 1.27 mm were simulated to determine whether they can match the experimental observations from point load and Brazilian tests. The numerical modeling results show that the failure patterns are influenced by the model scale and particle size, as expected. Both Is(50) and Brazilian tensile strength values increased as the model diameter and particle sizes increased. The ratio of Brazilian tensile strength to Is(50) showed a reduction as the particle size increased but did not change with the increase in the model scale.

      • KCI등재

        Using Risk-based Robustness Index for Seismic Improvement of Structures

        Hadi Faghihmaleki,Gholamreza Abdollahzadeh 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.3

        Nowadays, there are numerous indexes and parameters to review the seismic performance of improved structures. Response modification factor, fragility curves, ratio of different input energies to the structure affected by earthquake, maximum displacement and etcetera. are among these parameters, and most of these parameters are reviewed non-probabilistically. On one hand, since robustness index according to risk shapes probabilistically by reviewing uncertainty parameters of critical events and considering all existing parameters, it can be a beneficial index for reviewing the performance of improved structures. In this article, at first the robustness index is introduced according to risk analysis and one of its unique features is using percentage and amount of progressive collapse in it. After the considered robustness index, it has been used in reviewing the performance of a 4-story building of steel bending frame improved in two separate modes of concentrically brace frame and buckling restrained brace and a method has been suggested to obtain all effective parameters in intended robustness index. Ultimately, by reviewing this index for primary structureand improved structures, their behaviors have been compared and its results have been reported.

      • KCI등재

        Investigation of shear behavior of soil-concrete interface

        Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Mohammad Fatehi Marji,Alireza Masoumi 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.1

        The shear behavior of soil-concrete interface is mainly affected by the surface roughness of the two contact surfaces. The present research emphasizes on investigating the effect of roughness of soil-concrete interface on the interface shear behavior in two-layered laboratory testing samples. In these specially prepared samples, clay silt layer with density of 2027 kg/m3 was selected to be in contact a concrete layer for simplifying the laboratory testing. The particle size testing and direct shear tests are performed to determine the appropriate particles sizes and their shear strength properties such as cohesion and friction angle. Then, the surface undulations in form of teeth are provided on the surfaces of both concrete and soil layers in different testing carried out on these mixed specimens. The soil–concrete samples are prepared in form of cubes of 10*10*30 cm. in dimension. The undulations (inter-surface roughness) are provided in form of one tooth or two teeth having angles 15° and 30°, respectively. Several direct shear tests were carried out under four different normal loads of 80, 150, 300 and 500 KPa with a constant displacement rate of 0.02 mm/min. These testing results show that the shear failure mechanism is affected by the tooth number, the roughness angle and the applied normal stress on the sample. The teeth are sheared from the base under low normal load while the oblique cracks may lead to a failure under a higher normal load. As the number of teeth increase the shear strength of the sample also increases. When the tooth roughness angle increases a wider portion of the tooth base will be failed which means the shear strength of the sample is increased.

      • KCI등재

        Shear behavior of non-persistent joints in concrete and gypsum specimens using combined experimental and numerical approaches

        Hadi Haeri,V. Sarfarazi,Zheming Zhu,N. Nohekhan Hokmabadi,MR. Moshrefifar,A. Hedayat 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.2

        In this paper, shear behavior of non-persistent joint surrounded in concrete and gypsum layers has been investigated using experimental test and numerical simulation. Two types of mixture were prepared for this study. The first type consists of water and gypsum that were mixed with a ratio of water/gypsum of 0.6. The second type of mixture, water, sand and cement were mixed with a ratio of 27%, 33% and 40% by weight. Shear behavior of a non-persistent joint embedded in these specimens is studied. Physical models consisting of two edge concrete layers with dimensions of 160 mm by 130 mm by 60 mm and one internal gypsum layer with the dimension of 16 mm by 13 mm by 6 mm were made. Two horizontal edge joints were embedded in concrete beams and one angled joint was created in gypsum layer. Several analyses with joints with angles of 0°, 30°, and 60° degree were conducted. The central fault places in 3 different positions. Along the edge joints, 1.5 cm vertically far from the edge joint face and 3 cm vertically far from the edge joint face. All samples were tested in compression using a universal loading machine and the shear load was induced because of the specimen geometry. Concurrent with the experiments, the extended finite element method (XFEM) was employed to analyze the fracture processes occurring in a non-persistent joint embedded in concrete and gypsum layers using Abaqus, a finite element software platform. The failure pattern of non-persistent cracks (faults) was found to be affected mostly by the central crack and its configuration and the shear strength was found to be related to the failure pattern. Comparison between experimental and corresponding numerical results showed a great agreement. XFEM was found as a capable tool for investigating the fracturing mechanism of rock specimens with non-persistent joint.

      • KCI등재

        Effect of transversely bedding layer on the biaxial failure mechanism of brittle materials

        Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Ehsan Moosavi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.1

        The biaxial failure mechanism of transversally bedding concrete layers was numerically simulated using a sophisticated two-dimensional discrete element method (DEM) implemented in the particle flow code (PFC2D). This numerical modelling code was first calibrated by uniaxial compression and Brazilian testing results to ensure the conformity of the simulated numerical model’s response. Secondly, 21 rectangular models with dimension of 54 mm×108 mm were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was 0°, 15°, 30°, 45°, 60°, 75° and 90° while the angle of second layer, with high mechanical properties, related to loading direction was 90°, 105°, 120°, 135°, 150°, 160° and 180°. Is to be note that the angle between bedding layer was 90° in all bedding configurations. Also, three different pairs of the thickness were chosen in models, i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that in all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from 0° to 90° with increment of 15°. Numbers of shear cracks are constant by increasing the bedding thickness. It’s to be noted that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

      • KCI등재

        Simulating the influence of pore shape on the Brazilian tensile strength of concrete specimens using PFC2D

        Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Mohammad Fatehi Marji 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.5

        The Brazilian tensile strength of concrete samples is a key parameter in fracture mechanics since it may significantly change the quality of concrete materials and their mechanical behaviors. It is well known that porosity is one of the most often used physical indices to predict concrete mechanical properties. In the present work the influence of porosity shape on concrete tensile strength characteristics is studied, using a bonded particle model. Firstly numerical model was calibrated by Brazilian experimental results and uniaxial test out puts. Secondly, Brazilian models consisting various pore shapes were simulated and numerically tested at a constant speed of 0.016 mm/s. The results show that pore shape has important effects on the failure pattern. It is shown that the pore shape may play an important role in the cracks initiation and propagation during the loading process which in turn influence on the tensile strength of the concrete samples. It has also been shown that the pore size mainly affects the ratio of uniaxial compressive strength to that of the tensile one in the simulated material samples.

      • KCI등재

        On the proximal point method for an infinite family of equilibrium problems in Banach spaces

        Hadi Khatibzadeh 대한수학회 2019 대한수학회보 Vol.56 No.3

        In this paper, we study the convergence analysis of the sequences generated by the proximal point method for an infinite family of pseudo-monotone equilibrium problems in Banach spaces. We first prove the weak convergence of the generated sequence to a common solution of the infinite family of equilibrium problems with summable errors. Then, we show the strong convergence of the generated sequence to a common equilibrium point by some various additional assumptions. We also consider two variants for which we establish the strong convergence without any additional assumption. For both of them, each iteration consists of a proximal step followed by a computationally inexpensive step which ensures the strong convergence of the generated sequence. Also, for this two variants we are able to characterize the strong limit of the sequence: for the first variant it is the solution lying closest to an arbitrarily selected point, and for the second one it is the solution of the problem which lies closest to the initial iterate. Finally, we give a concrete example where the main results can be applied.

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