• Computers and Concrete
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• 제23권4호
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• pp.245-253
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• 2019

The studies on the applications of waste materials in concrete have been increased in Iraq since 2003. In this research, rubber wastes that resulting from scrapped tires was added to concrete mix with presence of superplasticizer. The mechanical properties of concrete and workability of concrete mixes were studied. The used rubber were ranging in size from (2-4) mm with addition percentages of (0.1% and 0.2%) by volume of concrete. The results of mechanical properties of concrete show that rubber enhance the ductility, and compressive and tensile strength compared to concrete without it. Also, the flexural behavior of hybrid strength concrete beams (due to using rubber at the bottom or top layer of section) was investigated. The rubber concrete located at bottom layer gives higher values of ultimate loads and deflections compared to the beam with top layer. A similar response to fiber concrete beam (all section contains 0.1% rubber) was recognized. Finite element modeling in three dimensions was carried for the tested beams using ABAQUS software. The ultimate loads and deflection obtained from experimental and finite elements are in good agreements with average difference of 8% in ultimate load and 20% in ultimate deflection.

• Structural Engineering and Mechanics
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• 제84권1호
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• pp.101-111
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• 2022

It is widely known that axially loaded fiber-reinforced polymer (FRP) confined concrete presents significant and enhanced mechanical properties with reference to the unconfined concrete. Therefore, to predict the mechanical behavior of FRP-confined concrete two quantities-peak strength and ultimate strain are required. Despite the significant advances, the determination of the ultimate strain of FRP-confined concrete is one of the most challenging problems to be resolved. This is often attributed to our persistence in desiring the conventional methods as the sole technique to examine this phenomenon and the complex nature of the ultimate strain of FRP-confined concrete. To bridge the research gap, this study adopted two machine learning (ML) techniques-artificial neural network (ANN) and Gaussian process regression (GPR)-to analyze observations obtained from 627 datasets of FRP-confined concrete circular and non-circular sections under axial loading test. Besides, the techniques are also used to predict the ultimate strain of FRP-confined concrete. Seven parameters namely width/diameter of the specimens, corner radius ratio, the strength of concrete, FRP elastic modulus, FRP thickness, FRP tensile rupture strain, and the axial strain of unconfined concrete-are the input parameters used to predict the ultimate strain of FRP-confined concrete. The results of the current study highlight the merit of using AI techniques in structural engineering applications given their extraordinary ability to comprehend multidimensional phenomena of FRP-confined concrete structures with ease, low computational cost, and high performance over the existing empirical models.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.361-373
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• 2022

This paper examines the flexural performance of concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars under fatigue loading. Experiments were carried out on concrete beams of size 1500×200×100 mm reinforced with 10 mm and 13 mm diameter GFRP bars under fatigue loading. Experimental investigations revealed that fatigue loading affects both strength and serviceability properties of GFRP reinforced concrete. Experimental results indicated that (i) the concrete beams experienced increase in deflection with increase in number of cycles and failed suddenly due to snapping of rebars and (ii) the fatigue life of concrete beams drastically decreased with increase in stress level. Analytical model presented a procedure for predicting the deflection of concrete beams reinforced with GFRP bars under cyclic loading. Deflection of concrete beams was computed by considering the aspects such as stiffness degradation, force equilibrium equations and effective moment of inertia. Nonlinear finite element (FE) analysis was performed on concrete beams reinforced with GFRP bars. Appropriate constitutive relationships for concrete and GFRP bars were considered in the numerical modelling. Concrete non linearity has been accounted through concrete damage plasticity model available in ABAQUS. Deflection versus number of cycles obtained experimentally for various beams was compared with the analytical and numerical predictions. It was observed that the predicted values are comparable (less than 20% difference) with the corresponding experimental observations.

• Computers and Concrete
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• 제13권1호
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• pp.71-82
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• 2014

Chloride ion ingress is one of the major problems that affect the durability of concrete structures such as bridge decks, concrete pavements, and other structures exposed to harsh saline environments. Therefore, durability based design of concrete structures in severe condition has gained great significance in recent decades and various mathematical models for estimating the service life of rein-forced concrete have been proposed. In spite of comprehensive researches on the corrosion of rein-forced concrete, there are still various controversial concepts in quantitation of durability parameters such as chloride diffusion coefficient and surface chloride content. Effect of environment conditions on the durability of concrete structures is one of the most important issues. Hence, regional investigations are necessary for durability based design and evaluation of the models. Persian Gulf is one of the most aggressive regions of the world because of elevated temperature and humidity as well as high content of chloride ions in seawater. The aim of this study is evaluation of some parameters of durability of RC structures in marine environment from viewpoint of corrosion initiation. For this purpose, some experiments were carried out on the real RC structures and in laboratory. The result showed that various uncertainties in parameters of durability were existed.

• Computers and Concrete
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• 제26권2호
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• Steel and Composite Structures
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• 제19권4호
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• pp.843-860
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• 2015

Recycled tire rubber-filled concrete (RRFC) is employed into the steel-concrete composite structures due to its good ductility and crack resistance. Push-out tests were conducted to investigate the static behavior of steel and rubber-filled concrete composite beam with different rubber mixed concrete and studs. The results of the experimental investigations show that large studs lead a higher ultimate strength but worse ductility in normal concrete. Rubber particles in RRFC were shown to have little effect on shear strength when the compressive strength was equal to that of normal concrete, but can have a better ductility for studs in rubber-filled concrete. This improvement is more obvious for the composite beam with large stud to make good use of the high strength. Besides that the uplift of concrete slabs can be increased and the quantity and width of cracks can be reduced by RRFC efficiently. Based on the test result, a modified empirical equation of ultimate slip was proposed to take not only the compressive strength, but also the ductility of the concrete into consideration.

• Structural Engineering and Mechanics
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• 제13권3호
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• pp.313-328
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• 2002

Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is proposed. To account for increasing ductility in high confinement of concrete, the ductility enhancement is considered using so called the strain enhancement factor. It is also developed a three-dimensional finite element model for reinforced concrete structural members based on the proposed constitutive law of concrete with the smeared crack approach. The concrete confinement effects due to the beam-column joint are investigated through numerical examples for simple beam and structural beam member. Concrete at compression fibers in the vicinity of beam-column joint behaves dominant not only by the uniaxial compressive state but also by the biaxial and triaxial compressive states. For the reason of the severe confinement of concrete in the beam-column joint, the flexural critical cross-section is observed at a small distance away from the beam-column joint. These observations should be utilized for the economic design when the concrete structural members are subjected to high confinement due to the influence of beam-column joint.

• Computers and Concrete
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• 제3권1호
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• pp.65-77
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• 2006

This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.

• Computers and Concrete
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• 제19권5호
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• pp.515-526
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• 2017

Recent trend is to use the lightweight concrete in the construction industry because it has several advantages over normal weight concrete. The Lightweight concrete can be produced from the industrial waste materials. In South East Asian region, researchers are very keen to use the waste materials such as oil palm shell (OPS) and palm oil clinker (POC) from the palm oil producing industries. Extensive research has been done on lightweight concrete using OPS or POC over the last three decades. In this paper the aggregate properties of OPS and POC are plotted in conjunction with mechanical and structural behavior of OPS concrete (OPSC) and POC concrete (POCC). Recent investigation on the use of crushed OPS shows that OPSC can be produced to medium and high strength concrete. The density of OPSC and POCC is around 20-25% lower than normal weight concrete. Generally, mechanical properties of OPSC and POCC are comparable with other types of lightweight aggregate concrete. It can be concluded from the previous study that OPSC and POCC have the noteworthy potential as a structural lightweight concrete.

• Computers and Concrete
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• 제21권1호
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• pp.87-94
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• 2018

This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms ($100{\times}100{\times}300mm$) and 150 concrete cubes ($100{\times}100{\times}100mm$) are cast and heated under five different temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$, $800^{\circ}C$) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress-strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.