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International Concrete Abstracts Portal

Showing 1-5 of 12 Abstracts search results

Document: 

SP156-07

Date: 

September 1, 1995

Author(s):

C. Yan and S. Mindess

Publication:

Symposium Papers

Volume:

156

Abstract:

The bond between reinforcing bars and concrete under impact loading was studied both experimentally and by the finite element method. The experiments consisted of pullout tests and push-in tests, under three different types of loading: static, medium rate, and impact. Different concrete strengths (normal and high), types of fibers (polypropylene and steel), and fiber contents were considered. The study focused on the bond-slip relationships and the fracture energy in bond failure. The experimental results were compared with those obtained by the finite element method, in which a special "bond-link element" that was able to transmit both shear and normal forces was adopted to model the connection between the reinforcing bar and the concrete. It was found that higher loading rates, higher concrete compressive strengths, and the addition of steel fibers had significant effects on the bond resistance, the fracture energy, and the bond stress-slip relationship, especially for the push-in case. Reasonably good correspondence in the results between the two methods was also found, and a bond-stress-slip relationship under high rate loading could be established analytically.

DOI:

10.14359/942


Document: 

SP156-02

Date: 

September 1, 1995

Author(s):

Z. P. Bazant and R. Desmorat

Publication:

Symposium Papers

Volume:

156

Abstract:

The size effect caused by post-peak softening in the relation of interface shear stress and slip displacement between a fiber or reinforcing bar and the surrounding matrix was analyzed. The problem was simplified as one- dimensional. It was shown that the post-peak softening leads to localization of slip. The larger the bar or fiber size, the stronger the localization. The size effect in geometrically similar pullout tests of different sizes was found to represent a transition from the case of no size effect for small sizes to the case of a size effect of the same type as in linear elastic fracture mechanics, in which the difference of the pullout stress in the fiber and the residual pullout stress corresponding to the residual interface shear stress is proportional to the inverse square root of bar or fiber size. An analytical expression for the transitional size effect was obtained and was found to approximately agree with the generalized form of the size effect law proposed earlier by Bazant. Measurements of the size effect can be used for identifying the interface properties.

DOI:

10.14359/1019


Document: 

SP156-06

Date: 

September 1, 1995

Author(s):

A. Vervuurt and j. G. M. Van Mier

Publication:

Symposium Papers

Volume:

156

Abstract:

Crack propagation in composite materials is a very complex process. Of utmost importance seems the behavior of the interfaces between the constituting phases. In reinforced concrete, interfaces not only appear in the concrete itself, but also between the concrete and the steel reinforcement. Fracture of the steel-concrete interface can be seen as a combination of adhesion, mechanical interlock, and frictional stress transfer. In this paper, steel-concrete interface fracture is modelled at the meso level. At this level, a simple linear elastic fracture law seems to suffice to explain global fracture mechanisms of composite materials. Interfaces between aggregate and matrix and between matrix and reinforcing bars are simulated using a lattice model. In the model, the material is discretized as a lattice of brittle breaking beam elements. Disorder of the material is implemented by assigning different strength and stiffness properties to the beam elements. Cracking is simulated by removing in each load step the element with the highest stress over strength ratio. The model is applied to uniaxial tensile fracture of plain concrete specimens and to bond of steel to concrete. Comparison from the simulations presented in this paper with experimental data shows that crack mechanisms are simulated quite accurately. However, the bond-displacement behavior is still too brittle. This point can be improved when more detail is included in the material structure that is incorporated in the analysis. The macroscopic bond-slip behavior of a reinforcing bar depends strongly on the micro-cracking near the interfacial zone between concrete and reinforcing bar. The analyses clearly show the influence of adhesion between steel and concrete on the simulated crack patterns.

DOI:

10.14359/941


Document: 

SP156-08

Date: 

September 1, 1995

Author(s):

S. H. Li, S. P. Shah, Z. Li, and T. Mura

Publication:

Symposium Papers

Volume:

156

Abstract:

A new method to predict the debonding behavior of fiber-matrix interface has been proposed by applying the principles of the micromechanics of inclusion and fracture mechanics. The validity of the mathematical model is further verified by uniaxial tension tests carried out on steel fiber reinforced cementitious composite specimens by employing a digitally controlled closed-loop MTS testing machine. It was demonstrated that the debonding occurs before the bend over point; the debonded lengths are largely influenced by the sequence of the occurrence of transverse matrix cracks and the loading stage. A stable growth of debonding was observed in the investigation. The measured debonded lengths were compared with the theoretical prediction of the proposed model. A reasonable agreement was observed.

DOI:

10.14359/943


Document: 

SP156-05

Date: 

September 1, 1995

Author(s):

K. M. Lee, O. Buyukozturk, and Y. Kitsutaka

Publication:

Symposium Papers

Volume:

156

Abstract:

The global behavior of concrete is influenced by various scenarios of crack initiation and crack propagation. Recently, the study of the interface fracture and cracking in interfacial regions has emerged as an important research field, especially in the context of the development of high performance concrete composites. For a rigorous study, the use and further development of fracture mechanics based concepts are needed. The crack path criterion for elastically homogeneous materials is not valid when the crack advances at an interface because, in this case, the consideration of the relative magnitudes of the fracture toughnesses between the constituent materials and the interface is involved. In this paper, criteria based on energy release rate concepts are considered for the prediction of crack growth at the interfaces and an experimental/numerical study is presented on two-phase composite models of concrete to investigate the cracking scenarios in interfacial regions. From the testing and numerical analysis on physical models, the interface fracture and the crack propagation in concrete composites are studied, and the role of interface fracture toughness is discussed.

DOI:

10.14359/940


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