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Polymeric yarns for reinforcing cement composites have got great interest in all over the world. In this research the performance of bonding between Nylon tire cord grad yarns, and one kind of cement composite called fine grained concrete was studied. Two kinds of Nylon cord yarns, nylon 6 and 66, with different finesse were selected. The durability of yarns with time in alkaline media was investigated. Meanwhile the effect of usual tire cord coating on bonding performance and alkaline durability of yarns were studied by mechanical testing and SEM images. Then the bonding of these yarns to cement paste and the effects of finesse on bonding performance were investigated by pull out tests. The results show that coating could enhance alkaline durability. Results also show that yarns with higher finesse are more sensitive to alkaline media and their mechanical properties reduced more. SEM images show that in general, alkali damage of Nylon tire cord yarns was not deep and no significant changes were observed on the surface of filaments after exposed to alkali. The bonding of Nylon tire cord to cement composite was suitable and no slippage was observed. The pull out behavior of finer yarns is better than coarse yarns. Meanwhile tire cord coating could enhance bonding of yarns to cement paste.

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This paper aims to characterize the elastic modulus of structural modified normal density (MND) and lightweight aggregate concrete (LWAC) produced with different types of expanded clay lightweight aggregates (LWA). A comprehensive experimental study was carried out involving different concrete strengths ranging from 30 to 70 MPa and density classes D1.6 to D2.0. The influence of several factors on the LWAC elastic modulus, such as the cement content, initial wetting conditions, type and volume of coarse LWA and the partial replacement of normal weight coarse and fine aggregates by LWA are analyzed. The strength and deformability of LWAC seems to be little affected by the addition of high reactive nanosilica. Reasonable correlations are found between the elastic modulus and the compressive strength or concrete density. The obtained LWAC elastic moduli are compared with those reported in the literature and those estimated from the main normative documents. In general, codes underestimate the LWAC modulus of elasticity by less than 20%. However, the MND modulus of elasticity can be greatly underestimated. In addition, the prediction of LWAC elastic modulus by means of non-destructive ultrasonic tests is studied. Dynamic elasticity modulus and ultrasonic pulse velocity results are reported and high correlated relationships, over 0.95, with the static modulus are established.

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The main cause of structural damage in buildings subjected to seismic actions is lateral drift. In almost all reinforced concrete (RC) structures, whether designed with walls or frames, it is likely to be the code drift limits that control the design drift. The design drift limits and their contribution to damage may be represented indirectly through the material strain limits. The aim of this study is to investigate the seismic design indicators of RC columns using finite element analyses (FEA). The results of FEA have been compared with the results of experimental studies selected from literature. It is observed that the lateral load-deflection curves of analyzed columns are in agreement with the experimental results. Based on these lateral load-deflection curves, the drift limits and the material strain limits, given by the codes as performance indicator, are compared. It is observed that the material strain limits are non-conservative as performance indicator of RC columns, compared to the drift limits.

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

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An analytical nonlinear stress-strain model and a microscopic damage index for confined and unconfined concretes together with a macroscopic damage index for reinforced concrete (RC) structures under cyclic loading are proposed. In order to eliminate the problem of scale effect, an adjustable finite element computer program was generated to simulate RC structures subjected to cyclic loading. By comparing the simulated and experimental results of tests on the full-scale structural members and concrete cylindrical samples, the proposed stress-strain model for confined and unconfined concretes under cyclic loading was accordingly modified and then validated. The proposed model has a strong mathematical structure and can readily be adapted to achieve a higher degree of precision by modifying the relevant coefficients based on more precise tests. To apply the proposed damage indices at the microscopic and macroscopic levels, respectively, stress-strain data of finite elements (confined and unconfined concrete elements) and moment-curvature data of critical section are employed. The proposed microscopic damage index can easily be calculated by using the proposed simple analytic nonlinear stress-strain model for confined and unconfined concretes. The proposed macroscopic damage index is based on the evaluation of nonlinear local degradation of materials and taking into account the pseudo-plastic hinge produced in the critical section of the structural element. One of the advantages of the macroscopic damage index is that the moment-curvature data of the critical section is sufficient in itself and there is no need to obtain the force-displacement data of the structural member.

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An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.

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Experiments were carried out to observe the influence of loading type on concrete beam specimens. Beam specimens made of similar concrete mixture with the same geometry were tested under three point static loading and low velocity drop weight impact loading. Load – displacement behavior, absorbed energy dissipation capacity, stiffnesses, failure modes of beam specimens were obtained and discussed. A finite element (FE) model was prepared in ANSYS Explicit STR software and the results of FE analysis were compared with experimental results. The loading type and loading rate have significant influence on the maximum load, stiffness and energy dissipation capacity. Numerical results obtained from ANSYS Explicit STR FE models are consistent with the experimental results.

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This study focuses on non-linear seismic response of a concrete gravity dam subjected to translational and rotational correlated components of ground motions including dam-reservoir interaction. For this purpose rotational components of ground motion is generated using Hong Non Lee improved method based on corresponding available translational components. The 2D seismic behavior of the dam concrete is taken into account using nonlinear fracture mechanics based on the smeared- crack concepts and the dam-reservoir system are modeled using Lagrangian-Lagrangian approach in finite element method. Based on presented formulation, Pine Flat concrete gravity dam is analyzed for different cases and results show that the rotational component of ground motion can increase or decrease the maximum horizontal and vertical displacements of dam crest. These results are dependent on the frequency of dam-reservoir system and predominant frequencies of translational and rotational components of ground motion.

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Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers.

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This paper aims at finding the long term coupled effect of high temperature and constant high relative humidity on the corrosion rehabilitated patches of chloride contaminated steel reinforced concrete. This paper is an extension of previous research in which the authors experimentally corroborated re-corrosion in the repaired reinforced concrete (RC) patches in the form of macro-cells. In previous research, the coupled effect was investigated by laboratory controlled experimentation at varying temperature of 30, 40 and 50°C and a high ambient relative humidity of 85% in environmental control chambers for duration of one year. The specimens were prepared having total chloride concentration in mixing water 3% and 5 % by mass of binder. In this present research paper, the two year results of the same specimens are presented to get a deep insight of the long term phenomenon of macro-cell corrosion under the coupled effect of high temperature and humidity on repaired RC patches.

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In order to investigate the flexural behaviors of RC beams after freeze-thaw cycles, compressive strength test of concrete cubes after 0, 50, 100, 125 freeze-thaw cycles were made, and static flexural experiment of 48 RC beams after 0, 50, 100, 125 freeze-thaw cycles were made. The relationships of relative compressive strength, mass loss rate, relative dynamic elastic modulus and numbers of freeze-thaw cycles were analyzed. The influences of different numbers of freeze-thaw cycles on the flexural behaviors of RC beams with different concrete grades were studied. The results show that concrete cubes’ mass, relative dynamic elastic modulus and compressive strength decrease with the increasing of freeze-thaw cycles, and high-strength grade concrete could slow down the damage caused by freeze-thaw cycles. Experimental values of test beams stiffness under short-term load were smaller than theory value. Some under-reinforced RC beams occurs over-reinforced failure mode after freeze-thaw cycles. Boundary reinforcement ratio of RC beams after certain numbers of freeze-thaw cycles was derived and its correctness was verified by experiment. Current code for design of concrete structures about crack load and ultimate load are still suitable for RC beams after freeze-thaw cycles.

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This paper describes experimental and numerical investigations on two specimens of frames composed of steel reinforced concrete beam and angle-steel concrete column under horizontal low cyclic loading. Based on the test results, the relationship curves of the horizontal load-displacement and the failure modes are acquired. Meanwhile the hysteretic behaviors, skeleton curves, stiffness degradation, energy dissipation, residential deformation of the two specimens are studied. Nonlinear structural analysis program OpenSEES is employed to predict the experimental curves. Using the verified numerical model, the influences of slenderness ratio, axial compression ratio, steel ratio of column, cross-section moment resistance of I-shaped steel in beam, ratio of longitudinal rebars of beam and prestressing level on skeleton curves are investigated. The results indicated that the two specimens exhibited the favorable ductility and energy dissipation capacity, and the beam depth could be reduced to improve service function because of the application of the prestress. The ultimate horizontal load decreases with the increase of column slenderness ratio, and firstly increases then decreases with the increase of axial compression ratio. In the meantime, the descent segment of skeleton curve is smooth with the increase of column slenderness ratio, and becomes steeper with the increase of axial compression ratio.

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This paper presents theoretical and numerical state-of-the-art information in the field of hygro-thermo-mechanical deformation simulation in structural concrete. The aspects discussed include coupled hygro-thermo-mechanical performance of porous materials including concrete, multi-scale simulation of concrete properties especially the volumetric and structural deformation performance, and the multi-scale simulation of concrete under the coupling effect of multi-physics fields. The multi-scale simulation section includes the multi-scale simulation of composition and structure in concrete, the multi-scale simulation of concrete’s mechanical performance, and the multi-scale simulation of durability concerned performance of concrete. This paper presents an overview of the work, of which data from early 80 recent studies, carried out on the multiscale simulation of hygro-thermo-mechanical deformation performance of structural concrete. The relating previous studies and analysis showed that sufficient data have been obtained to give confidence in simulating hygro-thermo-mechanical performance of concrete based on the theory of heat and mass transfer in porous media, and the clear relationships have been obtained between moisture-heat transfer and hygro-thermal distribution at different scale. It is necessary to make further systematic multi-scale research on the relationship between micro-structure and property parameters of cement paste, threephase basic properties at meso level of concrete and the performance of concrete structures, which makes important practical significance to solve the crack of large-area and mass concrete structure and improve the durability of concrete structures

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A new model is proposed for two-dimensional simulation of the concrete fracture in compression. The model generated by using the Voronoi diagram method and with considering random shape and distribution of full graded aggregates at the mesoscopic level. The aggregates modeled by combining irregular polygons, which then is placed into the concrete with no intersection between them. By this new modeling approach, the simulation of high-strength concretes with possible aggregates fracture is also feasible. After generation of the geometrical model, a coupled explicit discrete element method and a modified rigid body spring model have been used for solution. In this method, all the neighboring elements are connected by springs. The mortar springs have Elasto-plastic behavior and considering normal concrete, the aggregate springs behave only elastically without any fracture. The proposed model can accurately predict the mechanical behavior of concrete under compression for small and large deformations both descriptively and quantitatively

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The current research intends to study the possibility of producing fiber recycled self-compacting concrete (FRSCC) using demolitions as a coarse aggregate (crushed red brick and crushed ceramic). Steel fibers were used in recycled self-compacting concrete (RSCC) to improve fresh and hardened properties of this type of concrete. Thirty nine concrete mixes were prepared to achieve the aim proposed in this paper. Steel fiber volume fraction varied from 0 to 2.0% by the volume of concrete with aspect ratio 65. The fresh properties of FRSCC were evaluated using slump flow, J-ring and V-funnel tests. Compressive strength, tensile strength, flexural strength and density tests were performed in order to investigate mechanical properties. The optimum volume fraction of steel fibers was 0.25% and 1.0% for the mixes contained crushed red brick and ceramic as a coarse aggregate respectively. At optimum content of steel fibers, the compressive strength for the RSCC mixes with steel fibers improved by 11.3% and 31.8% for the mixes with crushed ceramic and crushed red brick, respectively with respect to control mix. Also the tensile strength and the flexural strength for the mixes were improved

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This study simulates the temperature field and temperature stress of concrete face slabs, considering the cold waves that occur during construction as well as the contact friction between the face slabs and the cushion layer. The results show that when a cold wave occurs during construction, the surface and center temperature of the face slabs continually drop with the outside air temperature, with the surface temperature drop being the largest. In addition, the surface and center of face slabs are subjected to tensile stress, with the maximum principal stress on the surface being greater than that on the center. The maximum principal stress of the surface and center occurs at approximately half of the dam height. This study also examines the surface insulation of concrete face slabs. Surface insulation can significantly improve the temperature drop range and the maximum principal stress amplitude caused by the cold wave. A stronger heat preservation results in smaller tensile stress and an increase in the amplitude of face slabs.

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To study seismic performance of concrete-encased composite columns with T-shaped steel cross-section, twelve half-scale columns were tested under quasi-stastic cyclic loading. The result indicates that concrete-encased composite columns with T-shaped steel section possess good seismic performance. The failure modes include bending failure, shear-bond failure, shear compression failure and shear-composition failure. Unsymmetrical phenomenon of positive and negative hysteresis loop was shown evidently. Span ratio has a great influence on failure mode. The ductility performance decreases with increasing of axial compression level. As stirrup ratio increases, ductility and bearing capacity of columns are improved greatly, and energy dissipation capacity after yielding is enhanced. Cross tie can enhance ultimate bearing capacity, and lower strength attenuation and stiffness degradation on the later loading stage

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Steel-concrete hybrid systems are used in buildings, in which a steel structure has been placed on a concrete structure to make a lighter structure and have a faster construction. Dynamic analysis of hybrid structures is usually a complex procedure due to various dynamic characteristics of each part, i.e. stiffness, mass and especially damping. Dynamic response of hybrid structures has some complications. One of the reasons is the different stiffness of the two parts of structure and another reason is non-uniform distribution of materials and their different features such as damping in main modes of vibration. The available software is not able to calculate damping matrices and analyze these structures because the damping matrix of these irregular structures is non-classical. Also an equivalent damping should be devoted to the whole structure and using the available software. In the hybrid structures, one or more transitional stories are used for better transition of lateral and gravity forces. In this study, an equation has been proposed to determining the equivalent uniform damping ratio for hybrid steel-concrete buildings with transitional storey(s). In the proposed method, hybrid buildings are considered to have three structural systems, reinforced concrete, transitional storey and steel. Equivalent uniform damping ratio is derived by means of a semi-empirical error minimization procedure.

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The contribution of concrete to inelastic deformation capacity and shear strength of reinforced concrete (RC) columns failing in shear has been investigated extensively by various researchers. Although RC members are designed to have shear strengths much greater than their flexural strengths to ensure flexural failure according to the current codes, shear degradation of RC columns failing in flexure has not been studied widely. The aim of this study is to investigate the shear degradation of RC columns using finite element analyses (FEA). The results of FEA are compared with the results of experimental studies selected from literature, and it is observed that the lateral load-deflection curves of analysed columns are compatible with the experimental results. Twenty-six RC columns were analysed under monotonically increasing loads to determine the concrete contribution to shear strength. The results of analyses indicate that increasing the ratio of shear to flexural strength reduces the concrete contribution to shear strength of the columns.

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A fast converging and fairly accurate nonlinear simulation method to assess the behavior of reinforced concrete columns subjected to static oriented pushover force and axial loading (sections under biaxial bending moment and axial loading) is proposed. In the proposed method, the sections of column are discretized into “Variable Oblique Finite Elements” (VOFE). By applying the proposed oblique discretization method, the time of calculation is significantly decreased and since VOFE are always parallel to neutral axis, a uniform stress distribution along each oblique element is established. Consequently, the variations of stress distribution across an element are quite small which increases the accuracy of the calculations. In the discretization of section, the number of VOFE is significantly smaller than the number of “Fixed Rectangular Finite Elements” (FRFE). The advantages of using VOFE compared to FRFE are faster convergence and more accurate results. The nonlinear local degradation of materials and the pseudo-plastic hinge produced in the critical sections of the column are also considered in the proposed simulation method. A computer program is developed to calculate the local and global behavior of reinforced concrete columns under static oriented pushover and cyclic loading. The proposed simulation method is validated by the results of tests carried out on the full-scale reinforced concrete columns. The application of the “Components Effects Combination Method” (CECM) is compared with the proposed “Simultaneous Direct Method” (SDM). The obtained results show the necessity of applying SDM for nonlinear calculations. Especially during the post-elastic phase, which occurs frequently during earthquake loading.