Local Bond Stress Slip Research Articles

Numerical Bond Analysis Using Experimentally Derived Local Bond Laws: A Powerful Method for Evaluating the Bond Strength of Steel Bars

The transfer of forces across the interface between steel bars and concrete through bond is one of the most important aspects that control the behavior of reinforced concrete members. This paper summarizes the results of a series of experimental and analytical studies undertaken by the writer at the American University of Beirut for evaluating the bond characteristics of developed or spliced bars in tension under different design and strength variables. Particular emphasis is placed on the evaluation of the average bond strength that develops in steel bars at bond failure by integrating experimentally based local bond law(s) into a numerical analysis technique of the bond problem. A general experimentally derived local bond stress–slip relationship corresponding to the splitting mode of bond failure is presented. With simple modification of the characteristic parameters, the relationship is applicable for plain normal-strength concrete, high-strength concrete, concrete confined with transverse steel ties,...

High-Bond Bars in NSC and HPC: Study on Size Effect and on the Local Bond Stress-Slip Law

Size effect is studied here with reference to the bonding of short, deformed bars, embedded in normal-strength concrete (NSC) and high-performance concrete (HPC). Tests on 48 cylindrical specimens reinforced with a single bar and subjected to a pull-out or push-in force show that bond exhibits a strong size effect, which is well described by Bazant’s general-type size-effect law. Four diameters are considered ( db =5 , 12, 18, and 26 mm ), with bonded length-to-bar diameter ratios equal to 3.5 (HPC) and 5 (NSC). All specimens are highly confined by means of a steel jacket to prevent or control cover splitting and to investigate bond behavior in highly confined conditions. Test results on short, anchored bars were instrumental in working out the local bond stress-slip law, taking into account size effect, which appears in the formulation of the maximum bond stress through the bar diameter. Short embedments also prevented bar yielding. The proposed local bond stress-slip law (1) is formulated as an extensio...

Realistic Models for Local Bond Stress-Slip of Reinforced Concrete under Repeated Loading

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.

Steel–concrete bond in lightweight fiber reinforced concrete under monotonic and cyclic actions

Experimental results of the local bond stress–slip relationship of reinforcing bars embedded in lightweight fiber reinforced concrete with expanded clay aggregates are presented. The effect of the following parameters were investigated: — dimension of specimens; — anchorage length; — percentages of hooked steel fibers; — geometrical ratio of transverse reinforcement; — confinement external transverse pressure. Prismatic specimens with deformed steel bars embedded for a fixed length equal to five and eight equivalent diameters were tested under both monotonic and cyclic reversal imposed displacements at the tip of the bars, in controlled displacement tests. The influence of the above mentioned parameters was investigated, and the effects in terms of strength and ductility of the confinement due to transverse steel, to the fibers or to the pressure applied externally are shown.

Evaluation of Bond Strength of Steel Reinforcing Bars in Plain and Fiber-Reinforced Concrete

This study aimed to analytically evaluate the development/splice strength of reinforcing bars in tension by incorporating a local bond-stress slip law more accurately derived by using beam specimens. The influence of several parameters, such as concrete compressive strength, on the development and bond properties of reinforcing bars embedded in conventional concrete, and the effect of fiber reinforcement on bond performance in comparison with plain unconfined concrete and concrete confined by transverse reinforcement, were investigated. Based on results of this analytical study and available experimental data, a design expression was proposed to evaluate the contribution of steel fiber reinforcement to the development/splice strength of reinforcing bars in tension.

Local Bond Stress-Slip Behavior of Reinforcing Bars Embedded in Plain and Fiber Concrete

This study summarizes the results of an experiment on the bond and slip characteristics of reinforcing bars embedded in fiber reinforced concrete (FRC). More than 100 concentric pullout specimens were tested and the effect of several parameters on the local bond stress-slip response of reinforcing bars was studied. Parameters included diameter of reinforcing bar; mode of bond failure; concrete splitting area surrounding the reinforcing bar; and type, volume fraction, and aspect ratio of fibers. The authors discuss the test results and present a simple analytical model describing the local bond stress-slip relationship for reinforcing bars embedded in plain and FRC and subjected to monotonically increasing load in tension. The model accounts for most of the important parameters that affect the local bond stress-slip response as observed in the experiment.

Interface Behavior in Reinforced Concrete

ABSTRACTThe mechanism of bond transfer between steel and concrete in a reinforced concrete member is studied in the present work. It is seen that the behavior of the interface zone can be represented by a simple generalized Mohr-Coulomb model. It is also seen that the complex relationships between the local bond stress and local slip suggested by other researchers (cubic or higher order polynomials) may be due to the geometry of the specimen and nature of stress distribution along the bar rather than intrinsic interface behavior. Behavior predicted by a generalized Mohr-Coulomb model is compared to predictions and observed behavior previously reported.

New Finite Element for Bond‐Slip Analysis

A new finite element for bond stress‐slip analysis is presented. A one dimensional model which is based on equilibrium and local bond stressslip law is developed. The relationship between axial force and slip at the elements nodes is expressed through a stiffness matrix. The global stiffness matrix is assembled and solution yields slip, strain and stress distributions along the steel bar. The nonlinear bond stress‐slip relationship leads to an iterative technique which is found to converge rapidly. The proposed method predictions are compared with experimental results of monotonic and push‐pull tests and very good correspondence is found.

Local bond-stress–slip relationships under repeated loading

Local bond-stress–slip relationships under repeated loading

Local bond-stress–slip relationships under repeated loading

Synopsis Pull-out specimens in which the reinforcing bar was embedded for 38 mm were tested under nine slow load cycles of constant amplitude in order to determine the effect of repeated loading upon the local bondstress–slip relationships for deformed bars. The local bond-stress–slip curves obtained under repeated loading form hysteresis loops and have residual slip at zero load. The results show that bond effectiveness is particularly sensitive to the magnitude of the peak stress reached in preceding cycles. Load cycling of constant amplitude produces only a gradual deterioration of bond. The curves can be used for modelling bond at the steel–concrete interface in finite-element analyses of reinforced concrete members.