شکافهای میله بتونی مسلح
Abstract
1. Introduction
2. Methodology
3. Brief description of experimental tests
4. Analytical study
5. Results and discussion
6. Summary and conclusions
Acknowledgements
References
Abstract
This paper presents an analytical model developed to predict the flexural load-deformation behavior of reinforced concrete members containing tension lap splices. The proposed model incorporates the effect of reinforcement slip of the lap splice and the effect of high strain rates on bond characteristics and material properties of concrete and steel. The main advantages of the proposed model are that bond-slip phenomena are captured through the use of pseudo-material stress-strain relationships, rather than giving consideration to the continuum of reinforcement and slippage over the entire structural element. Material properties and associated dynamic increase factors (DIF) are defined using accepted formulations. A suitable bond-slip law is presented and modified to account for the influence of strain rates on bond characteristics. Beam failure criteria are expressed in terms of a flexural failure of the member or a bond splitting failure of the splice. A comparison of the analytical predictions with experimental data demonstrated that the proposed analysis technique can reasonably predict the flexural response of beams with tension lap splices. The results also show that the model is equally applicable for use at low- and high- strain rate loading, such as those generated during blast and impact loading.
Introduction
The mechanism of force transfer between reinforcing steel and concrete, known as bond, is a fundamental characteristic of reinforced concrete behavior. This phenomenon is caused by the cumulative effect of surface friction, chemical adhesion and mechanical interlock of rebar lugs with concrete [1]. Considerable research over the past century has led to a thorough and exhaustive understanding of the factors affecting bond strength for the case of quasi-static loading [1]. However, little effort has been directed towards establishing the influence of high strain rates caused by short duration, dynamic loads on bond characteristics [2]. Strain rate ( ), defined as the rate of change of strain with respect to time, typically varies from 10−۵ s −۱ for static loading and up to 103 s −۱ for hard impact and blast events [3]. Bond strength, like the constitutive material properties of steel and concrete, experiences an apparent enhancement due to high strain rate effects [4–۶]. The degree of improvement is influenced by the quality of concrete [7,8], the size of reinforcement, and the presence of transverse reinforcement, in addition to being inversely proportional to an idealized crack splitting failure plane defined by the development length and the distance between the smallest concrete cover and the center of the developed bar [2]. In addition, confinement provided by transverse ties or increased cover depth, results in greater bond resistance but reduced strain rate sensitivity [8,9].