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 Neither damage mechanics model nor elastoplastic constitutive law can solely describe the behavior of concrete satisfactorily. In fact, they both fail to represent proper unloading slopes during cyclic loading. To overcome the disadvantages of pure plastic models and pure damage approaches, the combined effects need to be considered. In this regard, various classes of plastic-damage models have been recently proposed. Here, the theoretical basics of the plastic-damage model originally proposed by Lubliner et al. and later on modified by Lee and Fenves is initially presented and its numerical aspects in three-dimensional space are subsequently emphasized. It should be mentioned that a part of the implementation in 3-D space needs to be reformulated due to employing a hyperbolic potential function to treat the singularity of the original linear form of plastic flow proposed by Lee and Fenves. The consistent algorithmic tangent stiffness, which is utilized to accelerate the convergence rate in solving the nonlinear global equations, is also derived. The validation and evaluation of the model to capture the desired behavior under monotonic and cyclic loadings are shown with several simple one-element tests. These basic simulations confirm the robustness, accuracy, and efficiency of the algorithm at the local and global levels. At the end, a four-point bending test is examined to demonstrate the capabilities of the model in real 3-D applications.

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 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. 

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Structural fire safety capacity of concrete is very complicated because concrete materials have considerable variations. In this paper, constitutive models and relationships for concrete subjected to fire are developed, which are intended to provide efficient modeling and to specific fire-performance criteria of the behavior of concrete structures exposed to fire. They are developed for unconfined concrete specimens that include residual compressive and tensile strengths, compressive elastic modulus, compressive and tensile stress-strain relationships at elevated temperatures. In this paper, the proposed relationships at elevated temperatures are compared with experimental result tests and pervious existing models. It affords to find several advantages and drawbacks of present stress-strain relationships and using these results to establish more accurate and general compressive and tensile stress-strain relationships. Additional experimental test results are needed in tension and the other main parameters at elevated temperatures to establish well-founded models and to improve the proposed relationships. The developed models and relationships are general, rational, and have good agreement with experimental data.

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 Puducherry is a coastal region in India where the growth of Ulva fasciata (Delile) is very abundant on all marine structures. Though the detrimental effect of this macro algae Ulva fasciata is a secondary one, its effect has to ascertain. To know its effect, the basic mechanism by which Ulva fasciata deteriorates concrete structures, M20 grade concrete cubes were casted and kept in the coastal area where there is abundant growth of Ulva fasciata and also laboratory simulation has been carried out. To ascertain the detrimental effect by the macro algae on concrete surface, samples were collected from the concrete cubes kept in the coastal area and also from the laboratory simulated one. The collected samples were analyzed by SEM, EDX and XRD to establish the degree of deterioration done by marine algae on concrete surface. The SEM and EDX results showed that there is a remarkable change in the base materials viz., Ca and Si content and XRD results revealed the absence of Calcium Hydroxide. Both the results confirmed the biodeterioration of concrete by the marine green algae.

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 Superior performances of Self-Compacting Concrete (SCC) in fresh state to achieve a more uniform distribution encourage the addition of fibers in concrete which is a motivation for structural application of fiberreinforced concrete. Fiber addition reduces the workability of Self-Compacting Fiber Reinforced Concrete (SCFRC). To provide required workability of the SCFRC, more paste is needed in the mixture. Therefore, the coarse aggregate content shall be adjusted to maintain its workability. The purpose of this study is to drive a model for estimating the aggregate contents for SCFRC. This model is based on constant covering mortar thickness theory. In this paper, all parameters which are participated in coarse aggregate content are discussed and presented in a relation. Then another relation is developed for predicting the void volume in the fibrous concrete. These relations are combined and a mathematical relation is deduced for predicting the coarse volume content in the function of the fiber factors. Proposed model is validated by conducting a rheological test. The result shows that the proposed model is simple, applicable and can be used as starting point in practical project.      Finally in order to complete the proposed model, another relation has been derived that can show the interaction of parameters involved in SCFRC rheology behavior. 

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 Concrete deformation due to temperature and moisture condition will always develop simultaneously and interactively. The environmentally (hygral and thermally) induced stress and deformation are essential to concrete durability. To simulate the deformation of concrete caused by the coupling effect of temperature and moisture, a numerical simulation approach is proposed comprising analytical process and finite element analysis is proposed based on the mechanism of heat and moisture transfer in porous medium. In analytical method, Laplace transformation and transfer function were used to simplify and solve the coupled partial differential equations of heat and moisture transfer. The hygro-thermal deformation of concrete is numerically simulated by finite element method (FEM) based on the obtained temperature and moisture stress transformed from the solved moisture distribution. This numerical simulation approach avoids the complex eigenvalues, coupling difficulty and low accuracy in other solving method, and also effectively calculates the moisture induced shrinkage which is almost impossible using familiar FEM software. Furthermore, a software named Combined Temperature and Moisture Simulation System for concrete (CTMSoft) was represented and developed by a mix programming of Visual Basic, Matlab and ANSYS. CTMSoft provided a simple and more intuitive interface between user and computer by providing a graphical user interface (GUI). The validity of the numerical simulation approach was verified by two cases analysis.

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Cost optimization of the reinforced concrete cantilever soil retaining wall of a given height satisfying some structural and geotechnical design constraints is performed utilizing harmony search and improved harmony search algorithms. The objective function considered is the cost of the structure, and design is based on ACI 318-05. This function is minimized subjected to design constraints. A numerical example of the cost optimization of a reinforced concrete cantilever retaining wall is presented to illustrate the performance of the presented algorithms and the necessary sensitivity analysis is performed.

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Self Compacting Concrete (SCC) specimens with limestone (L) and quartz (Q) powders were formulated. The influence of the type

of the powder on the properties of fresh and hardened concrete was evaluated. Dense packing theories were used for mix design

of samples. The equation of Fuller and Thompson for particle size distribution (PSD) of aggregates was modified with considering

fine particles and a proper PSD curve was obtained for SCC. Experimental results showed that this method needs use of less

powder content and results in higher strength/cement ratio compared to traditional mixing methods. No significant difference was

observed between the compressive strengths of specimens containing limestone (L-specimens) and quartz (Q-specimens) powders,

with similar proportions of materials. The residual compressive strength of specimens was examined at 500°C and contradictory

behaviors were observed. One Q-specimen suffered from explosive spalling, while no spalling was occurred for L-specimens. On

the other hand, the residual strength of remained Q-specimens showed considerable increase compared to L-specimens. The results

show the necessity for more detailed investigations considering different effective parameters.

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This article presents the application of two algorithms: heuristic big bang-big crunch (HBB-BC) and a heuristic particle swarm

ant colony optimization (HPSACO) to discrete optimization of reinforced concrete planar frames subject to combinations of

gravity and lateral loads based on ACI 318-08 code. The objective function is the total cost of the frame which includes the cost

of concrete, formwork and reinforcing steel for all members of the frame. The heuristic big bang-big crunch (HBB-BC) is based

on BB-BC and a harmony search (HS) scheme to deal with the variable constraints. The HPSACO algorithm is a combination of

particle swarm with passive congregation (PSOPC), ant colony optimization (ACO), and harmony search scheme (HS)

algorithms. In this paper, by using the capacity of BB-BC in ACO stage of HPSACO, its performance is improved. Some design

examples are tested using these methods and the results are compared.

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An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structure's force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.

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This paper describes a numerical model and its finite element implementation that used to compute the cavitation effects on

seismic behavior of concrete dam and reservoir systems. The system is composed of two sub-systems, namely, the reservoir and

the dam. The water is considered as bilinear compressible and inviscid and the equation of motion of fluid domain is expressed

in terms of the pressure variable alone. A bilinear state equation is used to model the pressure–density relationship of a cavitated

fluid. A standard displacement finite element formulation is used for the structure. The Structural damping of the dam material

and the radiation damping of the water and damping from foundation soil and banks have been incorporated in the analysis. The

solution of the coupled system is accomplished by solving the two sub-systems separately with the interaction effects at the damreservoir

interface enforced by a developed iterative scheme. The developed method is validated by testing it against problem for

which, there is existing solution and the effects of cavitation on dynamic response of Konya gravity dam and Morrow Point arch

dam subjected to the first 6 s of the May 1940 El-Centro, California earthquake, is considered. Obtained results show that impact

forces caused by cavitation have a small effect on the dynamic response of dam-reservoir system.

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One important application of fiber reinforced polymer (FRP) is to confine concrete as FRP jackets in seismic retrofit process

of reinforced concrete structures. Confinement can improve concrete properties such as compressive strength and ultimate axial

strain. For the safe and economic design of FRP jackets, the stress-strain behavior of FRP-confined concrete under monotonic

and cyclic compression needs to be properly understood and modeled. According to literature review, it has been realized that

although there are many studies on the monotonic compressive loading of FRP-confined concrete, only a few studies have been

conducted on the cyclic compressive loading. Therefore, this study is aimed at investigating the behavior of FRP-confined

concrete under cyclic compressive loading. A total of 18 cylindrical specimens of FRP-confined concretewere tested in uniaxial

compressive loading with different wrap thickness, and loading patterns. The results obtained from the tests are presented and

examined based on analysis of test results predictive equations for plastic strain and stress deterioration were derived. The

results are also compared with those from two current models,comparison revealed the lack of sufficient accuracy of the current

models to predict stress-strain behavior and accordingly some provisions should be incorporated.

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In this paper a discrete Big Bang-Big Crunch algorithm is applied to optimal design of reinforced concrete planar frames under

the gravity and lateral loads. Optimization is based on ACI 318-08 code. Columns are assumed to resist axial loads and bending

moments, while beams resist only bending moments. Second-order effects are also considered for the compression members, and

columns are checked for their slenderness and their end moments are magnified when necessary. The main aim of the BB-BC

process is to minimize the cost of material and construction of the reinforced concrete frames under the applied loads such that

the strength requirements of the ACI 318 code are fulfilled. In the process of optimization, the cost per unit length of the sections

is used for the formation of the subsequent generation. Three bending frames are optimized using BB-BC and the results are

compared to those of the genetic algorithm.

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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.

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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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A comparison between design codes i.e. ACI and AISC-LRFD in evaluation of flexural strength of concrete filled steel tubular

columns (CFTs) is examined. For this purpose an analytical study on the response of CFTs under axial-flexural loading is carried

using three-dimensional finite elements with elasto-plastic model for concrete with cracking and crushing capability and elastoplastic

kinematic hardening model for steel. The accuracy of the model is verified against previous test results. The nonlinear

modeling of CFT columns shows that the minimum thickness that recommended by ACI and AISC-LRFD to prevent local buckling

before the steel shell yielding for CFT columns could be decreased. The comparison of analytical results and codes indicates that

the accuracy of ACI method in estimation of axial-flexural strength of CFT columns is more appropriate than AISC-LRFD. The

ACI lateral strength of CFTs is located on upper bond of the AISC-LRFD’s provisions. AISC-LRFD estimates the lateral strength

conservatively but ACI in some ranges such as in short columns or under high axial load levels computes lateral strength in nonconservative

manner. Supplementary provisions for post local buckling strength of CFT columns should be incorporated in high

seismic region. This effect would be pronounced for column with high aspect ratio and short columns.

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Chloride ion ingress in concrete is the main reason of concrete corrosion. In real world both uncertainty and stochasticity are

main attributes of almost all measurements including testing and modeling of chloride content profile in concrete. Regarding

these facts new models should be able to represent at least some of the uncertainties in the predictions. In this paper after

inspiration from classical physics related to diffusion and random walk concepts a stochastic partial differential equation (SPDE)

of diffusion is introduced to show a more realistic modeling/calibration scheme for construction of stochastic chloride content

profile in concrete. Diffusion SPDE provides a consistent quantitative way of relating uncertainty in inputs to uncertainty in

outputs. Although it is possible to run sensitivity analysis to get some statistical results from deterministic models but the nature

of diffusion is inherently stochastic. Brownian motion process (Wiener process) is used in SPDE to simulate the random nature

of the diffusion in heterogeneous media or random fields like concrete. The proposed method can be used to calibrate/model the

chloride ion profile in concrete by only some limited data for a given depth. Then the stochastic chloride ion diffusion can be

simulated by langevin equation. Results of the method are compared with data from some references and all show good

agreements.

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This paper describes a methodology in designing high-performance concrete for simply supported beams, using a hybrid optimization strategy based on a variable neighborhood search threshold acceptance algorithm. Three strategies have been applied to discrete optimization of reinforced concrete beams: Variable Neighborhood Descent (VND), Reduced Neighborhood Search (RNS) and Basic Variable Neighborhood Search (BVNS). The problem includes 14 variables: two geometrical one material type one mix design and 10 variables for the reinforcement setups. The algorithms are applied to two objective functions: the economic cost and the embedded CO2 emissions. Firstly, this paper presents the application of these three different optimization strategies, which are evaluated by fitting the set of solutions obtained to a three-parameter Weibull distribution function. The Variable Neighborhood Descent with Threshold Accepting acceptance strategy algorithm (VND-TA) results as the most reliable method. Finally, the study presents a parametric study of the span length from 10 to 20 m in which it can be concluded that economic and ecological beams show a good parabolic correlation with the span length.

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The present study focuses on the performance of precast concrete beam-column dowel connections subjected to cyclic loading by conducting experiments. In this study, one-third scale model of two types of precast and a monolithic beam-column connection were cast and tested under reverse cyclic loading. The precast connections considered for this study is a beam-column connection where beam is connected to column with corbel using (i) dowel bar and (ii) dowel bar with cleat angle. The experimental results of the precast specimens have been compared with that of the reference monolithic connection. The sub-assemblage specimens have been subjected to reverse cyclic displacement-controlled lateral loading applied at the end of the beam. The performance of the precast connections in terms of the ultimate load carrying capacity, post- elastic strength enhancement factor, load-displacement hysteresis behaviour, moment-rotation hysteresis behaviour, energy dissipation capacity, equivalent viscous damping ratio and ductility factor were compared with that of the monolithic beam-column connection. The monolithic specimen was found to perform better when compared to the precast specimens in terms of strength and energy dissipation. In terms of ductility, the precast specimen using dowel bar and cleat angle showed better behaviour when compared to the reference monolithic specimen.

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Abstract: This paper presents the influence of adding steel fibers and incorporation of silica fume on the mechanical properties of high-strength concrete. The variables investigated were steel fiber volume fraction (0 to 1.5%), silica fume replacement (5, 10 and 15%) and water-to-binder ratio (0.25, 0.30, 0.35 and 0.40). The influence of fiber content in terms of fiber reinforcing index on the compressive and splitting tensile strengths of high-strength steel fiber reinforce concrete (HSFRC) is presented. The use of silica fume increased both the compressive and splitting tensile strengths of concrete at 28 days. On the other hand, the addition of crimped steel fiber into high-strength concrete improves splitting tensile strength significantly. Based on the test data, using regression analysis, empirical expression to predict 28-day tensile strength of HSFRC in terms of fiber reinforcing index was developed and the absolute variation and integral absolute error (IAE) obtained was 3.1% and 3.3, respectively. The relationship between splitting tensile and compressive strength of SFRC was reported with regression coefficient (r) = 0.9. The experimental values of previous researchers were compared with the values predicted by the model and found to predict the values quite accurately.