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International Concrete Abstracts Portal

Showing 1-5 of 10 Abstracts search results

Document: 

SP134-02

Date: 

September 1, 1992

Author(s):

W. H. Gerstle, P. Rahulkumar, P. P. Dey, and M. Xie

Publication:

Symposium Papers

Volume:

134

Abstract:

The fracture mechanics size effect in unreinforced concrete beams has been clearly demonstrated by Bazant. The effect of reinforcement on the fracture mechanics size effect has not been demonstrated quite as clearly. The bending failure of a singly reinforced concrete beam serves to illustrate the effect of reinforcement in the fracture mechanics size effect. The effect of prenotched and unprenotched beams is also considered. A simple analytical model has been developed for the behavior (up to peak load and beyond) of a singly reinforced concrete beam. This model takes into account the existence of an initial traction-free crack and assumes linear elastic behavior of concrete, elastic-plastic response of the steel, crushing of concrete, and simplified bond-slip between the steel and concrete. The model employs the fictitious crack model to determine the crack growth in small beams and linear elastic fracture mechanics to determine crack growth in large beams. The model demonstrates a size effect which starts with a high nominal strength for low values of á (small beams) and a low nominal strength for high values of á (large beams). Between these shelves, in the neighborhood of log(á) = 0, there is an S-shaped transition region, but not well-approximated by a line with a slope of negative one-half, as for unreinforced, prenotched concrete beams. Example problems show the importance of the size effect in design.

DOI:

10.14359/3055


Document: 

SP134

Date: 

September 1, 1992

Author(s):

Editors: Walter Gerstle and Zdenek P. Bazant / Sponsored by: Joint ACI-ASCE Committee 446

Publication:

Symposium Papers

Volume:

134

Abstract:

At the Fall meeting of the American Concrete Institute in Philadelphia in 1990, ACI Committee 446 sponsored a technical paper session entitled "Design Based on Fracture Mechanics." The purpose of the session was to present recent advances in our understanding or fracture in concrete in such a way that practitioners could understand and use it, and also to identify ways in which practitioners can make use of fracture mechanics in design of concrete structures. Currently, designers in the United States use the ACI 318 Building Code, which currently makes absolutely no use of fracture mechanics concepts. To enable designers to use fracture mechanics, a logical next step would be to incorporate these concepts into a revised building code. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP134

DOI:

10.14359/14166


Document: 

SP134-05

Date: 

September 1, 1992

Author(s):

Radomir Pukl, Rolf Eligehausen, and Vladimir Cervenka

Publication:

Symposium Papers

Volume:

134

Abstract:

Computer analyses of the pullout tests of anchors embedded in concrete were performed for the Round Robin Analysis of the RILEM Committee on Fracture Mechanics of Concrete. The test specimens were concrete plates with steel anchors in the plane stress state. The geometry of the specimen was varied in order to study the size effect and the shape effect. The investigation was performed by means of the computer simulation of the tests. Only limited comparison with the real laboratory experiments was used to verify the results. The computer simulation was made by means of the program SBETA, which was developed by the authors and is based on the smeared crack approach and the nonlinear elasticity. Two crack models were used to analyze each specimen: the rotated crack model and the fixed crack model. In total, 36 computer simulations were made. Each simulation provided the load-displacement diagram of the anchor and a sequence of crack patterns, deformed states, and stress states. A size effect law in the exponential form was derived from the computer experiments.

DOI:

10.14359/3091


Document: 

SP134-09

Date: 

September 1, 1992

Author(s):

Christian La Borderie, Jacky Mazars, and Gilles Pijaudier-Cabot

Publication:

Symposium Papers

Volume:

134

Abstract:

Progressive microcracking and crack closure effects are the most important phenomena which need to be described in finite element calculations of reinforced concrete structures subjected to cyclic or seismic loads. Microcracking produces a loss of stiffness which is usually modeled with continuous damage mechanics. Crack closure effects such as inelastic deformations and stiffness recovery remain features that must be incorporated in the constitutive relations describing the response of concrete under cyclic loadings. These effects are introduced into a novel damage model in a rigorous, consistent fashion. An attempt to derive the constitutive relations for fiber reinforced concrete using this model is also described. The implementation of these constitutive relations into a layered beam finite element code is discussed, and computations on medium-size bending beams and a beam-column joint subjected to cyclic loading are compared with experiments. Although the computational method remains simple and sufficiently fast for engineering applications, the good agreement obtained with test data shows that the constitutive relations capture very well the main characteristics of the behavior of concrete.

DOI:

10.14359/2710


Document: 

SP134-07

Date: 

September 1, 1992

Author(s):

C. Thomas Jan

Publication:

Symposium Papers

Volume:

134

Abstract:

The fracturing phenomenon in reinforced concrete structures has a profound effect on their flexural stiffness. Consequently, the effect of cracking in reinforced concrete has been the subject of intensive investigation for many years. Because of the complexities associated with the development of feasible methodologies, analytical procedures continue in many respects to investigate and verify with experimental results. Historically, a series of rational analytical procedures have evolved to incorporate various methodologies such as material nonlinear models, failure criteria, and layered finite elements to account for the effect of cracking. However, it is to complex and expensive to apply such approached in design practice. For practical purposes, the Direct Design Method and the Equivalent Frame Method are often adopted in accordance with ACI 318 to design two-way reinforced concrete slabs. But the effect of cracking in concrete is not included in those two methods. Hence, an incremental-iterative procedure is implemented as a tool to design reinforced concrete slabs. The proposed incremental-iterative proceduce follows Section 9.5.2.3 as defined in ACI 318 to treat the effect of cracking in reinforced concrete slabs. Although the use of ACI 318 Eq. (9-7) is primarily provided for flexural members, it is permitted for application for two-way slabs as well. In essence, cracks are smeared and assumed to propagate in in-plane directions determined by the maximum principal moment in a finite element. The effective slab stiffnesses are modified accordingly as progressive cracking is detected under increasing loads. Analytical results from design cases are presented to demonstrate its applicability. In addition, a modified procedure is presented to include the ACI 446.1R, based on fracture mechanics of concrete. Further investigations are also recommended for the future developments in the analysis and design of reinforced concrete slabs.

DOI:

10.14359/3109


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