• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.104-107
• /
• 2004

The crack widths of reinforced concrete flexural members are influenced by repetitive fatigue loadings. The bond stress-slip relation is necessary to estimate these crack widths realistically. The purpose of the present study is, therefore, to propose a realistic model for bond stress-slip relation under repeated loading. To this end, several series of tests were conducted to explore the bond-slip behavior under repeated loadings. Three different bond stress levels with various number of load cycles were considered in the tests. The present tests indicate that the bond strength and the slip at peak bond stress are not influenced much by repeated loading if bond failure does not occur. However, the values of loaded slip and residual slip increase with the increase of load cycles. The bond stress after repeated loading approaches the ultimate bond stress under monotonic loading and the increase of bond stress after repeated loading becomes sharper as the number of repeated loads increases. The bond stress-slip relation after repeated loading was derived as a function of residual slip, bond stress level, and the number of load cycles. The models for slip and residual slip were also derived from the present test data. The number of cycles to bond slip failure was derived on the basis of safe fatigue criterion, i.e. maximum slip criterion at ultimate bond stress.

• Structural Engineering and Mechanics
• /
• v.81 no.2
• /
• pp.163-178
• /
• 2022

This paper aimed to study the local bond-slip behavior between ultra-high-performance concrete (UHPC) and a reinforcing bar after exposure to high temperatures. A series of pull-out tests were carried out on cubic specimens of size 150×150×150 mm with deformed steel bar embedded for a fixed length of three times the diameter of the tested deformed bar. The experimental results of the bond stress-slip relationship were compared with the Euro-International Concrete Committee (CEB-Comite Euro-International du Beton)-International Federation for Prestressing (FIP-Federation Internationale de la Precontrainte) Model Code and with prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress-slip relationship was proposed. The evaluation and comparison results showed that the modified CEB-FIP Model code 2010 proposed by Aslani and Samali for the local bond stress-slip relationship for UHPC after exposure to high temperatures was more conservative. In contrast, for both room temperature and after exposure to high temperatures, the modified CEB-FIP Model Code 2010 local bond stress-slip model for UHPC proposed in this study was able to predict the test results with reasonable accuracy.

• KCI Concrete Journal
• /
• v.13 no.2
• /
• pp.67-74
• /
• 2001

In this study, a numerical model for the simulation of reinforced concrete columns subject to cyclic loading is presented. The model consists of three separate models representing concrete, reinforcing steel bars and bond-slip between a reinforcing bar and ambient concrete. The concrete model is represented by the plane stress plastic-damage model and quadrilateral finite elements. The nonlinear steel bar model embedded in truss elements is used for longitudinal and transverse reinforcing bars. Bond-slip mechanism between a reinforcing bar and ambient concrete is discretized using connection elements in which the hysteretic bond-slip link model defines the bond stress and slip displacement relation. The three models are connected in finite element mesh to represent a reinforced concrete structure. From the numerical simulation, it is shown that the proposed model effectively and realistically represents the overall cyclic behavior of a reinforced concrete column. The present plastic-damage concrete model is observed to work appropriately with the steel bar and bond-slip link models in representing the complicated localization behavior.

• Magazine of the Korea Concrete Institute
• /
• v.6 no.4
• /
• pp.92-101
• /
• 1994

A new analytical model is proposed to better understand the transfer bond performance in a prestressed pretensioned concrete beam. The transfer length is divided into an elastic and a plas tic zones in this model. The bond stress is assumed t.o increase proportionally with the slip t.o the lirnit of maximum bond stress within the elastic zone and remains at a constant maximum value wthin the plastic zone. Four main stress patterns: bond stress, slip, steel stress, and concrete stress distributions within the transfer length are obtained precisely. The total transfer length al\ulcornerd free-end slip obtained here give a close comparison to the test results by Cousins et al.

• Steel and Composite Structures
• /
• v.10 no.4
• /
• pp.317-329
• /
• 2010

According to the results of 9 circular concrete filled steel tube (CFT) push-out tests, a new theoretical model for average bond stress versus free end slip curve is proposed. The relationship between verage bond stress and free end slip is obtained considering some varying influential parameters such as slenderness ratio and diameter-to-thickness ratio. Based on measured steel tube strain and relative slip at different longitudinal positions, the distribution of bond stress and relative slip along the length of steel tube is obtained. An equation for predicting the varying bond-slip relationship along longitudinal length and a position function reflecting the variation are proposed. The presented method can be used in the application of finite element method to analyze the behavior of CFT structures.

• KEPCO Journal on Electric Power and Energy
• /
• v.1 no.1
• /
• pp.127-134
• /
• 2015

Recently, the external bonding of carbon fiber reinforced polymer (CFRP) sheets has come to be regarded as a very effective method for strengthening of reinforced concrete structures. The behavior of CFRP-strengthened RC structure is mainly governed by the interfacial behavior, which represents the stress transfer and relative slip between concrete and the CFRP sheet. In this study, the effects of bonded length, width and concrete strength on the interfacial behavior are verified and a bond-slip model is proposed. The proposed bond-slip model has nonlinear ascending regions and exponential descending regions, facilitated by modifying the conventional bilinear bond-slip model. Finite element analysis results of interface element implemented with bond-slip model have shown good agreement with the experimental results performed in this study. It is found that the failure load and strain distribution predicted by finite element analysis with the proposed bond-slip are in good agreement with results of experiments.

• International Journal of Concrete Structures and Materials
• /
• v.1 no.1
• /
• pp.37-43
• /
• 2007

This paper discusses the failure mode of reinforced concrete beams strengthened with composite materials based on six experimental set-ups to determine the FRP-to-concrete bond strength. Interfacial bond behavior between concrete and CFRP plates was discussed. Shear test were performed with different concrete compressive strengths (21 MPa and 28 MPa) and different bonding length (100 mm, 150 mm, 200 mm, and 250 mm). Shear test results indicate that the effective bond length (the bond length beyond which the ultimate load does not increase) was estimated as $196{\sim}204\;mm$ through linear regression analysis. Failure mode of specimens occurred due to debonding between concrete and CFRP plates. Maximum bond stress is calculated as about $3.0{\sim}3.3\;MPa$ from the relationships between bond stress and slip. Finally, the interfacial bond-slip model between CFRP plates and concrete, which is governed debonding failure, has been estimated from shear tests. Average bond stress was about $1.86{\sim}2.04\;MPa$, the volume of slip between CFRP plate and concrete was about $1.45{\sim}1.72\;mm$, and the fracture energy was found to be about $1.35{\sim}1.71\;N/mm$.

• Computers and Concrete
• /
• v.16 no.3
• /
• pp.449-466
• /
• 2015

This paper aims to study the local bond stress-slip behavior of reinforcing bars embedded in lightweight aggregate concrete (LWAC). The experimental variables of the local bond stress-slip tests include concrete strength (20, 40 and 60 MPa), deformed steel bar size (#4, #6 and #8) and coarse aggregate (normal weight aggregate, reservoir sludge lightweight aggregate and waterworks sludge lightweight aggregate). The test results show that the ultimate bond strength increased with the increase of concrete compressive strength. Moreover, the larger the rib height to the diameter ratio ($h/d_b$) of the deformed steel bars is, the greater the ultimate bond stress is. In addition, the suggestion value of the CEB-FIP Model Code to the LWAC specimen's ultimate bond stress is more conservative than that of the normal weight concrete.

• Structural Engineering and Mechanics
• /
• v.32 no.2
• /
• pp.251-267
• /
• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

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