• Earthquakes and Structures
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• v.16 no.3
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• pp.279-293
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• 2019

The overall seismic performance of existing pre 1960-70s reinforced concrete (RC) structures is significantly affected by the inadequate length of columns' lap-spliced reinforcement. Due to this crucial structural deficiency, the cyclic response is dominated by premature bond - slip failure, strength and stiffness degradation, poor energy dissipation capacity and low ductility. Recent earthquakes worldwide highlighted the importance of improving the load transfer mechanism between lap-spliced bars, while it was clearly demonstrated that the failure of lap splices may result in a devastating effect on structural integrity. Extensive experimental and analytical research was carried out herein, to evaluate the effectiveness and reliability of strengthening techniques applied to RC columns with lap-spliced reinforcement and also accurately predict the columns' response during an earthquake. Ten large scale cantilever column subassemblages, representative of columns found in existing pre 1970s RC structures, were constructed and strengthened by steel or RC jacketing. The enhanced specimens were imposed to earthquake-type loading and their lateral response was evaluated with respect to the hysteresis of two original and two control subassemblages. The main variables examined were the lap splice length, the steel jacket width and the amount of additional confinement offered by the jackets. Moreover, an analytical formulation proposed by Tsonos (2007a, 2019) was modified appropriately and applied to the lap splice region, to calculate shear stress developed in the concrete and predict if yielding of reinforcement is achieved. The accuracy of the analytical method was checked against experimental results from both the literature and the experimental work included herein.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.141-148
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• 1998

An analytical model which can simulate the post-cracking behavior of reinforced concrete structures subjected to in-plane shear and normal stresses is presented. Based on the force equilibriums, compatibility conditions, and bond stress-slip relationship between steel and concrete, a criterion to simulate consider the tension-stiffening effect is proposed. The material behavior of concrete is described by an orthotropic constitutive model, and focused on the tension-compression region with tension-stiffening and compression softening effects defining equivalent uniaxial relations in the axes of orthotropy. Correlation studies between analytical results and available experimental data are conducted with the objective to establish the validity of the proposed model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.499-503
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• 2001

Fatigue behavior of reinforced concrete (RC) elements has been experimentally and analytical investigated. Fatigue behavior influenced by longitudinal reinforcement ratio, strength of concrete and load ratio P／sub u／／P／sub o／. The purpose of these studies is to propose an empirical formula for fatigue behavior on basis of experimental results. Also an analytical method to predict the crack propagation of RC beams has been developed based on the relationships between bond stress and slip.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.47-53
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• 2009

12 concrete blocks, on which hybrid fibrous sheets (carbon fiber and glass fiber) had been bonded, were subjected to tensile load in order to estimate properties of the bonded interface. the sheet length was varied by 100mm, 200mm and 400mm. It was found that more than 150mm bond length is required to achieve the maximum bearing capacity of the interface. In this study, maximum bond stress $\tau_{F,max}$, ultimate slip $S_{FU}$ of the interface were estimated $\tau_{F,max}$=3.0MPa and $S_{FU}$= 0.175mm, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1161-1166
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• 2001

Fatigue behavior of reinforced concrete(RC) elements has been experimentally and analytical investigated. Fatigue behavior influenced by longitudinal reinforcement ratio, strength of concrete and load ratio $P_{u}$/ $P_{o}$. The purpose of these studies is to propose an empirical formula for fatigue behavior on basis of experimental results. Also an analytical method to predict the crack propagation of RC beams has been developed based on the relationships between bond stress and slip.

• Journal of the Korean Society for Railway
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• v.8 no.6 s.31
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• pp.495-499
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• 2005

Fatigue behavior of reinforced concrete(RC) elements has been experimentally and analytical investigated. Fatigue behavior is influenced by a longitudinal reinforcement ratio, strength of concrete and a load ratio Pu/Po. The purpose of this study to propose an empirical formula for the fatigue behavior on the basis of experimental results. Also an analytical method to predict the crack propagation of RC beams has been developed based on the relationships between bond stress and slip.

• Computers and Concrete
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• v.26 no.3
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• pp.257-273
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• 2020

Concrete bond strength with steel re-bars depends on multiple factors including concrete-steel interface and mechanical properties of concrete. However, the hydration development of cementitious paste, and in turn the mechanical properties of concrete, are negatively affected by cold weather. This study aimed at exploring the concrete-steel bonding behavior in concrete cast and cured under freezing temperatures. Three concrete mixtures were cast and cured at -10 and -20℃. The mixtures were protected using conventional insulation blankets and a hybrid system consisting of insulation blankets and phase change materials. The mixtures comprised General Use cement, fly ash (20%), nano-silica (6%) and calcium nitrate-nitrite as a cold weather admixture system. The mixtures were tested in terms of internal temperature, compressive, tensile strengths, and modulus of elasticity. In addition, the bond strength between concrete and steel re-bars were evaluated by a pull-out test, while the quality of the interface between concrete and steel was assessed by thermal and microscopy studies. In addition, the internal heat evolution and force-slip relationship were modeled based on energy conservation and stress-strain relationships, respectively using three-dimensional (3D) finite-element software. The results showed the reliability of the proposed models to accurately predict concrete heat evolution as well as bond strength relative to experimental data. The hybrid protection system and nano-modified concrete mixtures produced good quality concrete-steel interface with adequate bond strength, without need for heating operations before casting and during curing under freezing temperatures down to -20℃.

• Structural Engineering and Mechanics
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• v.5 no.4
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• pp.355-368
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• 1997

Fiber reinforced plastic (FRP) rods are used as reinforcement (prestressed or not) to concrete. FRP composites can also be combined with steel to form hybrid reinforcing rods that take advantage of the properties of both materials. In order to effectively utilize these rods, their bond behavior with concrete must be understood. The objective of this study is to characterize and model the bond behavior of hybrid FRP rods made with epoxy-impregnated aramid or poly-vinyl alcohol FRP skins directly braided onto a steel core. The model closely examines the split failure of the concrete by quantifying the relationship between slip of the rods resulting transverse stress field in concrete. The model is used to derive coefficients of friction for these rods and, from these, their development length requirements. More testing is needed to confirm this model, but in the interim, it may serve as a design aide, allowing intelligent decisions regarding concrete cover and development length. As such, this model has helped to explain and predict some experimental data from concentric pull-out tests of hybrid FRP rods.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.762-765
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• 2004

The main objective of this study is to provide a parametric evaluation of the pull-out response of steel fibers embedded in cementitious matrices. The various parameters controlling the behavior of the bond stress versus end slip relationship are analyzed; their effects on the entire pull-out load versus end slip response and the corresponding pull-out energy up to total pull-out are investigated. Also discussed are the effects of the fiber length, the water/binder ratio of the mixtures and embedded length.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.102-109
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• 2010

This paper investigates the bond behavior of reinforced concrete beams having high-strength transverse reinforcement. A total of four reinforced concrete beams were tested in this study to estimate the bond capacity of the proposed U-shape reinforcement. The proposed U-shape reinforcement not only has a simple structure to install, but also can increase the bond capacity of reinforced concrete beams by controling bond cracks. This study follow the test method proposed by Ichinose to obtain the bond stress and the bond slip of the specimens. The main test parameters were the yield strength, ratio, and reinforcing types of transverse reinforcements. It was found that the proposed U-shape reinforcement was able to effectively improve the bond performance of reinforced concrete beams with high-strength transverse reinforcement.