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International Concrete Abstracts Portal

Showing 1-5 of 23 Abstracts search results

Document: 

SP180-09

Date: 

October 1, 1998

Author(s):

A. J. Bigaj, J. A. den Uijl and J. C. Walraven

Publication:

Symposium Papers

Volume:

180

Abstract:

Bond properties are usually described by empirical relations that are based on pull-out tests of bars with short embedment lengths cast in low to medium strength concrete. The limited validity of these formulations is recognized and their applicability in structural analyses is reconsidered. Results of two test series with various confining conditions and concrete strengths provide the basis for the derivation of a new bond model for ribbed ibars. Pull-out bond failure in confined concrete and splitting bond failure in unconfined concrete have been studied. Steel yielding is found to have a iconsiderable influence on bond strength. Significant differences in bond of NSC and HSC are confirmed. An analytical bond model for ribbed bars is developed. It is based on the confining capacity of the concrete surrounding the bar. This is evaluated with a /thick-walled-cylinder model, from which the relation between the radial displacement and the radial compressive stress at the steel-to-concrete interface i s derived. The radial displacement at the interface is linked to the slip of the ribbed bar, distinguishing between the two modes of bond failure: pull-out and cover splitting. The model takes into account concrete toughness and bar contraction, also after yielding. Verification of the model against selected experimental results reflects the potential of the model to be used in a broad range of applications. In its present form the model is used for the analysis of isolated bond problems using a one-dimensional finite difference approach, but its application is also considered to count for three-dimensional deformations in FE codes that treat the bar as a one-dimesional element.

DOI:

10.14359/5878


Document: 

SP180-08

Date: 

October 1, 1998

Author(s):

E. Giuriani and G. A. Plizzari

Publication:

Symposium Papers

Volume:

180

Abstract:

In the present paper, the role of the confining forces both on bond capacity and on splitting crack opening under service loads is shown. In par-ticular, theoretical relationships between the transverse reinforcement area, the bond strength, the splitting crack opening and the stirrup stress are pre-sented. The theoretical predictions are contrasted with some experimental results and a discussion on the values provided by building codes is presented. The results show the strong influence of transverse reinforcement whose confining force is expressed by the stirrup index of confinement, which gov-erns bond behavior and is suitable for design. The comparison with several experimental results showed a good agreement between theory and tests. Adequate values of Q are also required to control splitting crack opening under service loads. For common amounts of transverse reinforcement, the splitting crack opening can be larger than one half of the flexural crack, which could be unacceptable for structural durability.

DOI:

10.14359/5877


Document: 

SP180-07

Date: 

October 1, 1998

Author(s):

J. A. den Uijl

Publication:

Symposium Papers

Volume:

180

Abstract:

From pull-out and push-in tests on specimens with short embedment length an empirical relation has been derived, which describes the local bond stress as a function of the local slip and steel stress change. With the help of this bond model the transfer length and the bi-linear relationship for the development length of a pretensioned strand (ACI Building Code 1989, CEB-FIP Model Code 1990) is simulated. It is also used to indicate the influence of strand yielding on the development length. For the estimation of the concrete cover and strand spacing required to prevent the occurrence of visible bond splitting cracks the response of the concrete to the radial displacement of the strand-to-concrete interface is analyzed by means of a so-called thick-walled-cylinder model. The radial interface displacement consists of transverse deformation of the strand coupled with steel stress change (Poisson effect) and wedging action caused by the shape of the strand (lack-of-fit effect) and surface roughness. Besides the section geometry, this model takes into account the softening behaviour of concrete loaded in tension. It is used to explain the influence of various parameters such as concrete cover, strand spacing, strand diameter and concrete strength on the bond properties of strand.

DOI:

10.14359/5876


Document: 

SP180-03

Date: 

October 1, 1998

Author(s):

R. Eligehausen, J. Ozbolt and U. Mayer

Publication:

Symposium Papers

Volume:

180

Abstract:

The bond between reinforcement and concrete should ensure high structural stiffness and small cracks in the serviceability limit state, generate small splitting forces and allow full utilization of the reinforcement ductility in the ultimate limit state. While bond behavior at service load and splitting behavior has been investigated intensively, bond behavior at large inelastic steel strains is not known very well. Therefore, in this paper the contribution of concrete between cracks at inelastic steel strains is investigated numerically based on a rational mechanical model and using realistic constitutive material laws. The model predictions agree rather well with a large number of test results. According to the results of the parametric study, after steel yielding the ratio of mean steel strain to the steel strain at the crack is mainly influenced by the reinforcement percentage and the shape of the steel stress-strain curve. It is much lower than at service load. Due to this lower ratio of mean steel strain to steel strain at the crack, the rotation capacity of plastic hinges and thus the structural ductility is reduced significantly and may be very low if reinforcement with low ductility is used. Therefore an optimization of bond seems to be necessary. Corresponding extensive numerical and experimental studies are under way in Germany.

DOI:

10.14359/5872


Document: 

SP180-11

Date: 

October 1, 1998

Author(s):

A. Azizinamini

Publication:

Symposium Papers

Volume:

180

Abstract:

Safety concerns and a lack of test data on bond capacity of deformed reinforcing bars embedded in high-strength concrete are among the reasons for the AC1 318 building code imposing an arbitrary limitation of 10,000 psi (69 MPa) when calculating tension development and splice lengths. This limitation was first introduced in the 1989 revision of the AC1 3 18 building code. In an attempt to evaluate the impact of this limitation and develop provisions for its removal, an investigation was carried out at the University of Nebraska-Lincoln, partial result of which will be presented in this paper. Results of the investigation are used to discuss the differences that exist between normal and high strength concrete, develop hypotheses to explain these observed differences, and suggest alternatives for removal of the current concrete compressive limitations existing in the ACI 3 18 building code for calculating tension development and splice lengths. In this paper high strength concrete is defined as concrete with compressive strength exceeding 10,000 psi (69 MPa).

DOI:

10.14359/5880


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