• KCI Concrete Journal
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• v.12 no.1
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• pp.113-120
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• 2000

This paper presents the behavior and strengthening effect of reinforced concrete rectangular beams strengthened using CFRP sheets with different strengthening level. In general, normally strengthened beams are failed by interfacial shear failure (delamination) within concrete, instead of by tensile failure of the CFRP sheets. The delamination occurred suddenly and the concrete cover cracked vertically by flexure was spalled off due to the release energy. The strengthened beams were stiffer than the control beam before and after reinforcement yielding. The ultimate load considerably increased with an increase of strengthening level, while the ultimate deflection significantly decreased. The tensile force of CFRP sheets and average shear stress of concrete at delamination failure were curvilinearly proportional to the strengthening level. Therefore, the increment of ultimate load obtained by strengthening was curvilinearly proportional to the strengthening level. The averaged horizontal shear stress of concrete at the interface ranges between (equation omitted) and (equation omitted) (in kg/$\textrm{cm}^2$) depending on strengthening level.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.5 s.51
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• pp.73-83
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• 2006

The purpose of this study is to investigate the seismic behavior of reinforced concrete pier walls under cyclic out-of-plane loading and to develop improved seismic design criteria. The accuracy and objectivity of the assessment process can be enhanced by using a sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. A 4-node flat shell element with drilling rotational stiffness is used for spatial discretization. The layered approach is used to discretize the behavior of concrete and reinforcement through the thickness. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The method is verified a useful tool to assess the seismic performance of reinforced concrete pier walls subjected to cyclic out-of-plane load through comparing with reliable experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.155-156
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• 2010

In current study, a nonlinear model for the shear behavior of Fiber-Reinforced Cementitious Composite (FRCC) panels has been introduced. The model is dealing with the multiple micro-cracking mechanism of FRCC materials which induce the high-ductile tensile characteristic, the compressive strain-softening, and the shear transfer mechanism in the cracked FRCC.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.173-183
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• 1995

A new vector algorithm is presented for computing the stiffness matrices of layered reinforced concrete shell elements. Each element stiffness matrix is represented in terms of three vector arrays of lengths 78, 96 and 36, respectively. One element stiffness matrix is calculated at a time without interruption in the vector calculations for the uncracked or cracked elements. It is shown that the present algorithm is 1.1 to 7.3 times more efficient then a previous algorithm developed by us on a Cray Y-MP supercomputer.

• International Journal of Concrete Structures and Materials
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• v.19 no.1E
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• pp.3-9
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• 2007

This paper presents a numerical procedure for analyzing the joints between precast post-tensioned segments. A computer program for the analysis of reinforced concrete structures was run for this problem. Models of material nonlinearity considered in this study include tensile, compressive and shear models for cracked concrete and a model for reinforcing steel with smeared crack. An unbonded tendon element based on the finite element method, that can describe the interaction between the tendon and concrete of prestressed concrete member, was experimentally investigated. A joint element is newly developed to predict the inelastic behavior of the joints between segmental members. The proposed numerical method for the joints between precast post-tensioned segments was verified by comparison of its results with reliable experimental results.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.1
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• pp.55-66
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• 1999

This paper presents an analytical prediction of the hysteresis behavior of reinforced concrete long column with rectangular section under the cyclic loading state. The mechanical characteristic of cracked concrete and reinforcing bar in concrete has been modeled, considering the bond effect between reinforcing bar and concrete, the effect of aggregate interlocking at crack surface and the stiffness degradation after the crack has taken place. The strength increase of concrete due to the lateral confining reinforcement has been also taken into account to model the confined concrete. The formulation of these models for concrete and reinforcing bar has been based on the smeared crack concept that the stress-strain relationship of reinforced concrete element would be defined using the average values. In addition to the material nonlinear properties, the algorithm for large displacement problem that may give an additional deformation has been formulated using total Lagrangian formulation. The analytically predicted behavior was compared with test result and they showed good agreement in overall behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.65-72
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• 1993

Steel fiber reinforced concrete(SFRC) which is made by short, randomly distributed steel fibers in concrete is superior in its tensile mechanical properties to plain concrete in enhancement of tensile strength and tensile ductility. These improvements are attributed to crack arresting mechanism and formation of longer crack paths due to fibers , which as a consequence lead to increase in energy absorption capacity of SFRC. In the post-peak region under tensile stresses, major macrocrack forms at critical section. The opening of this macrocrack is mainly resisted by both of the fiber pull-out bridging the cracked surfaces and the resistance by matrix softening. In this study, micromechaincal approach has been made in order to simulate tensile behavior of SFRC and based on which the theoretical model is presented. This model reflects the features of both the composite material concept and the spacing concept in predicting tensile strength of SFRC. The model also takes into account for the effects of matrix tensile softening and fiber bridging by pull-out on the resistance for the post-peak behavior of SFRC. It has been shown that the developed model satisfactory predicts the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.525-528
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• 1999

Structural walls have been favored for the design of reinforced concrete buildings in seismic zone areas because they provide an efficient bracing system and offer great potential for lateral load resistance and drift control. Loads on structures due to earthquakes are not unlikely to reach, if not exceed, the design load levels. Hence, structural damage to walls is inevitable, and it is necessary to repair this damaged walls. Yet, information on repair method and data related to the strength and deformation characteristics of repaired walls is limited. In this study, specimens which have their aspect ratios of about 1 to 3 will be repaired. For the repairing the damaged walls, new concrete and new reinforcing bar are replaced with cracked concrete and the buckled reinforcing bar, respectively. The objective of this study is to evaluate the performance of the repaired structural walls in the capacity of strength, stiffness, and maximum deformation comparing with the undamaged walls.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.1010-1021
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• 2002

The current ACI design code does not take into account the contribution of concrete for the torsional moment of reinforced concrete(RC) beams subjected to pure torsion. This code is not capable of evaluating the inter-effects between concrete and torsional reinforcement on the torsional resistance of the RC beams. Some test results indicated that the current ACI code was not successful in predicting the observed torsional moment of the RC beams with reasonable accuracy. The research reported in this paper provides an evaluation equation to predict the torsional moment of the RC beams subjected to pure torsion. The proposed equation is derived from the equilibrium as well as compatibility equations of the truss model for the cracked RC beams. Comparisons between the observed and calculated torsional moments of the 66 tested beams, showed reasonable agreement.

• Computers and Concrete
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• v.19 no.6
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• pp.631-639
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• 2017

This study experimentally investigated the flexural capacity of a concrete beam reinforced with a newly developed GFRP bar that overcomes the lower modulus of elasticity and bond strength compared to a steel bar. The GFRP bar was fabricated by thermosetting a braided pultrusion process to form the outer fiber ribs. The mechanical properties of the modulus of elasticity and bond strength were enhanced compared with those of commercial GFRP bars. In the four-point bending test results, all specimens failed according to the intended failure mode due to flexural design in compliance with ACI 440.1R-15. The effects of the reinforcement ratio and concrete compressive strength were investigated. Equations from the code were used to predict the deflection, and they overestimated the deflection compared with the experimental results. A modified model using two coefficients was developed to provide much better predictive ability, even when the effective moment of inertia was less than the theoretical $I_{cr}$. The deformability of the test beams satisfied the specified value of 4.0 in compliance with CSA S6-10. A modified effective moment of inertia with two correction factors was proposed and it could provide much better predictability in prediction even at the effective moment of inertia less than that of theoretical cracked moment of inertia.