• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.111-129
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• 2011

This paper presents a nonlinear analysis of reinforced concrete column with lap splice confined by FRP wrapping in the critical hinging zone. The steel stress-slip model derived from the tri-uniform bond stress model presented in the companion paper is included in the nonlinear frame analysis to simulate the response of reinforced concrete columns subjected to cyclic displacement reversals. The nonlinear modeling is based on a fiber discretization of an RC column section. Each fiber is modeled as either nonlinear concrete or steel spring, whose load-deformation characteristics are calculated from the section of fiber and material properties. The steel spring that models the reinforcing bars consists of three sub-springs, i.e., steel bar sub-spring, lap splice spring, and anchorage bond-slip spring connected in series from top to bottom. By combining the steel stress versus slip of the lap splice, the stress-deformation of steel bar and the steel stress-slip of bars anchored into the footing, the nonlinear steel spring model is derived. The analytical responses are found to be close to experimental ones. The analysis without lap splice springs included may result in an erroneous overestimation in the strength and ductility of columns.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.3
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• pp.188-193
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• 1998

An experimental study was performed on the pull-out behavior of 90-deg standard hooks from exterior beam-column connections. The effects of lateral confinement and fiber reinforcement of joint area were investigated. It was concluded ; (1) Substitution of the transverse column (confining) reinforcement with steel fibers at the joint region effectively reduces the extent of cracking in exterior joints caused by pull-out of hooked bars; and (2) The strength and ductility of hooked bars under pull-out forces are positively influenced by substituting the conventional confining reinforcement of exterior joints with steel fibers. Application of steel fibers to exterior joints seems to be an effective technique for improving the anchorage conditions of hooked bars, and also for reducing the congestion of reinforcement in exterior beam-column connections.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.189-192
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• 2005

Glass fiber reinforced polymer (GFRP) bars gain increasingly more attention as a reinforcing option for concrete because of their corrosion resistance and non-magnetism. GFRP reinforcement for concrete does not have the same shape as steel reinforcement. Therefore, the bond performance of FRP bars, unlike that of steel, is dependent on their design, manufacture and mechanical properties. This paper studied the effect of high strength concrete on the bond strength of GFRP bars. Twenty-nine specimens having different compressive strength of concrete were tested in order to examine the bond behavior of GFRP bars.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.254-257
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• 2006

Five bench scale specimens were used to evaluate corrosion performance of damaged epoxy-coated bars in chloride contaminated concrete. The test specimens were subjected 48 weekly cycles of ponding with sodium chloride solution and drying. Test results using linear polarization technique show that the current density of specimen with conventional steel becomes $0.715\;{\mu}A/cm^2$ indicating that the steel bars are in moderate or high corrosion condition. However, the corrosion rates of the specimens with damaged epoxy coated bars are much below $0.1\;{\mu}A/cm^2$ and the bars appears to be in passive condition. The corrosion protection performance provided by calcium nitrite is better than that of specimens with the other two inhibitors.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.114-117
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• 2006

Concrete beams reinforced with fiber reinforced polymer (FRP) bars exhibit large deflection and crack width as compared to concrete beams reinforced steel due to modulus of elasticity of FRP bars. Current design code for prediction and crack width developed in concrete structures reinforced with steel bars may not be used for concrete beams reinforced with FRP bars. Thus a number of researcher have attempted to propose modifications to the ACI 318 empirical equation for estimating the effective moment of inertia of reinforced concrete beams. Others used numerical method to calculate the deflection. The purpose of this paper is to evaluation of methods of ACI 440.1 R-01, ISIS Canada design manual, and others for predicting deflection for glass fiber reinforced polymer reinforced concrete beams.

• Structural Engineering and Mechanics
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• v.78 no.2
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• pp.199-207
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• 2021

In the present paper, an analytical model is proposed to determine the flexural and shear strength of normal and high-strength reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on evaluation of the resistance contribution due to beam and arch actions including interaction with stirrups. For the resistance contribution of the main bars in tension the residual bond adherence of steel bars, including the effect of stirrups and the crack spacing of R.C. beams, is considered. The compressive strength of the compressed arch is also verified by taking into account the biaxial state of stresses. The model was verified on the basis of experimental data available in the literature and it is able to include the following variables in the resistance provision: - geometrical percentage of steel bars; - depth-to-shear span ratio; - resistance of materials; - crack spacing; - tensile stress in main bars; - residual bond resistance including the presence of stirrups;- size effects. Finally, some of the more recent analytical expressions able to predict shear and flexural resistance of concrete beams are mentioned and a comparison is made with experimental data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.212-218
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• 2011

The effect of composite reinforcing bars on surface electrical resistivity of concrete was investigated through experimental program. The resistivity was measured by Wenner method using an equipment with 4 probe. Ordinary steel, GFRP, and CFRP reinforcing bars produced domestically were used and a specimen with no reinforcement was tested for the comparison. This investigation is motivated from the fact that measured value of resistivity of concrete is significantly affected by details of steel reinforcements, such as location, depth and direction of the internal steel reinforcement. These results could be valuable data for evaluation of corrosion degree of concrete structures reinforced or strengthened by the composite reinforcing bars.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.199-207
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• 2018

Experimental programs were performed to evaluate the flexural performance of fiber reinforced concrete(FRC) beams using a hybrid double-layer arrangement of steel bars and fiber reinforced polymer(FRP) bars or using FRP bars only. A total of seven beam specimens were produced with type of tensile reinforcing bar(CFRP bar, GFRP bar, steel bar) and the poly vinyl alcohol(PVA) fiber mixing ratio(0.5%, 0%) as variable. An analysis method for predicting the flexural behaviors of FRC beams with hybrid arrangement of heterogeneous reinforcing bars through finite element analysis was proposed and verified. In case of the specimens with the double-layer reinforcing bars, the test results showed that the first cracking load of specimen with a double-layer arrangement of steel bars was greater by 26-34% than specimens with a hybrid double-layer arrangement of steel and FRP bars. In maximum flexural strengths, the specimen that used CFRP bars as bottom tensile reinforcing bar showed the greatest strength among the specimens with the double-layer reinforcing bars. When the maximum moment value obtained through experiments was compared with that obtained through analysis, the ratio was 1.2 on average, the standard deviation was 0.085, and the maximum error rate was 22% or less. Based on these results, the finite element analysis model proposed in this study can effectively simulate the actual behavior of the beams with hybrid double-layer reinforcing bars.

• Computers and Concrete
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• v.21 no.2
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• pp.219-229
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• 2018

In this paper, a modified rigid body spring model (RBSM) is proposed and used to analyze the damage and failure process of reinforced concrete (RC) structures. In the proposed model, the concrete is represented by an assembly of rigid blocks connected with a uniform distribution of normal and tangential springs to simulate the macroscopic mechanical behavior of concrete. Steel bars are evenly dispersed into rigid blocks as a kind of homogeneous axial material, and an additional uniform distribution of axial and dowel springs is defined to consider the axial stiffness and dowel action of steel bars. Perfect bond between the concrete and steel bars is assumed, and tension stiffening effect of steel bars is modeled by adjusting the constitutive relationship for the tensile reinforcement. Adjacent blocks are allowed to separate at the contact interface, which makes it convenient and easy to simulate the cracking process of concrete. The failure of the springs is determined by the Mohr-Coulomb type criterion with the tension and compression caps. The effectiveness of the proposed method is confirmed by elastic analyses of a cantilever beam under different loading conditions and failure analyses of a RC beam under two-point loading.

• Earthquakes and Structures
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• v.14 no.3
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• pp.187-201
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• 2018

The paper describes a modified cyclic bar model including bond-slip phenomena between steel reinforcing bars and surrounding concrete. The model is focused on plain bar and is useful, for its simplicity, for the seismic analyses of RC structures with plain bars and insufficient constructive details, such as in the case of '60s -'70s Mediterranean buildings. The model is based on an imposed exponential displacements field along the bar including both steel deformation and slip; through the adoption of equilibrium and compatibility equations a stress-slip law can be deducted and simply applied, with opportune operations, to RC numerical models. This study aims to update and complete the original monotonic model published by the authors, solving some numerical inconsistencies and, mostly, introducing the cyclic formulation. The first aim is achieved replacing the imposed linear displacement field along the bar with an exponential too, while the cyclic behaviour is described through a formulation based on the results of parametric analyses concerning a large range of steel and concrete properties and geometric configurations. Validations of the proposed model with experimental results available in the current literature confirm its accuracy and the reduced computational burden, highlighting its suitability in performing nonlinear analyses of RC structures.