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International Concrete Abstracts Portal

Showing 1-10 of 14 Abstracts search results

Document: 

SP118-13

Date: 

January 1, 1990

Author(s):

Arne Hillerborg

Publication:

Special Publication

Volume:

118

Abstract:

The stress-deformation relation now generally accepted for tensile fracture, i.e., with the descending branch described by means of a stress-displacement relation in a localized band, has been applied to the compressive stresses in a bent, reinforced beam. The displacement in this band is averaged over a length, which is proportional to the depth of the compression zone. The resulting average stress-strain relation, which is strongly size-dependent, is used for the analyses of the stresses in a rectangular beam section, and for the corresponding moment-curvature relationship. The results differ appreciably from those from conventional assumptions. The new approach shows a better agreement with test results than the conventional approach. Further test comparisons are, however, recommended. The new approach may form the basis of changed design assumptions, particularly for high-strength concrete.

10.14359/2983


Document: 

SP118-12

Date: 

January 1, 1990

Author(s):

T. Shioya, M. Iguro, Y. Nojiri, H. Akiyama, and T. Okada

Publication:

Special Publication

Volume:

118

Abstract:

Experimental and theoretical studies on shear strength of large reinforced concrete beams are presented. The shear strength of a reinforced concrete beam without shear reinforcement gradually decreases as an effective depth d of a beam increases, and is generally called the size effect. From the result of the experiment on large beams, the size effect of a beam exists even for a beam deeper than 100 cm which had been outside of the scope of past experiments, and the size effect at d ò 100 cm may be considered to be inversely proportional to the fourth root of the effective depth. According to the result of a nonlinear finite element analysis, the size effect on flexural tensile strength of concrete and shear transfer across crack surfaces must be considered in estimating the shear strength of a large reinforced concrete beam.

10.14359/2978


Document: 

SP118-11

Date: 

January 1, 1990

Author(s):

Y. S. Jenq and S. P. Shah

Publication:

Special Publication

Volume:

118

Abstract:

The shear resistance of reinforced concrete beams without shear stirrups has been shown to be dependent on the size of beams. It was reported that as the beam depth increases, the shear resistance of the reinforced concrete beams decreases. Furthermore, the final failure mode of the reinforced concrete beams were found to be dependent on the strength as well as beam size. All other factors (i.e., maximum aggregate size, steel ratio, and proportion of specimen dimensions) being equal, large beams and early age beams (which have relatively low strength) were observed to fail in diagonal shear while small beams and matured beams failed in flexure. To explain the size effect on the shear resistance and final failure mode of reinforced concrete beams, a fracture mechanics approach was used in the present study. It was concluded that the effect of size on the final failure mode and shear resistance of reinforced concrete beams can be reasonably explained using the fracture mechanics concept.

10.14359/2973


Document: 

SP118-10

Date: 

January 1, 1990

Author(s):

A. Carpinteri

Publication:

Special Publication

Volume:

118

Abstract:

Progressive cracking in structural elements of concrete is considered. Two simple models are applied, which, even though different, lead to similar predictions for the fracture behavior. Both virtual crack propagation model and cohesive limit analysis show a trend toward brittle behavior and catastrophical events for large structural sizes. Such a trend is fully confirmed by more refined finite element investigations and by experimental testing on plain and reinforced concrete members.

10.14359/2968


Document: 

SP118-09

Date: 

January 1, 1990

Author(s):

Jin-Ken Kim, Seok-Hong Eo, and Hong-Kee Park

Publication:

Special Publication

Volume:

118

Abstract:

In most of the structural members with initial cracks, the strength tends to decrease as the member size increases. This phenomenon is known as size effect. Among the structural materials of glass, metal, or concrete, etc., concrete represents the size effect even without initial crack. According to the previous size effect law, the concrete member of very large size can resist little stress. Actually, however, even the large-size member can resist some stress if there is no initial crack. In this study, the empirical models for uniaxial compressive strength that are derived based on nonlinear fracture mechanics are proposed by the regression analysis with the existing test data of large-size specimens.

10.14359/2962


Document: 

SP118-08

Date: 

January 1, 1990

Author(s):

Zdenek P. Bazant, Siddik Sener, and Pere C. Prat

Publication:

Special Publication

Volume:

118

Abstract:

This symposium contribution gives a preliminary report on tests of the size effect in torsional failure of plain and longitudinally reinforced beams of reduced scale, made of microconcrete. The results confirm that there is a significant size effect, such that the nominal stress at failure decreases as the beam size increases. This is found for both plain and longitudinally reinforced beams. The results are consistent with the recently proposed Bazants size effect law. However, the scatter of the results and the scope and range limitations prevent it from concluding that the applicability of this law has been proven in general.

10.14359/2955


Document: 

SP118-07

Date: 

January 1, 1990

Author(s):

Arne Hillerborg

Publication:

Special Publication

Volume:

118

Abstract:

A fracture mechanics approach is presented. In this approach, the complete material behavior during tensile fracture is described in a way suitable for the analysis of failure of structures. Two examples are given of practical applications, in which the results can be compared with code specifications. The first is the cracking strength of a beam. It is demonstrated that the formal flexural stress that causes cracking decreases as the depth of the beam increases. The second example is the shear strength of a beam without shear reinforcement. The theoretical results show a good agreement with test results. There seem to be reasons to revise the rules in the ACI Building Code regarding the influence of beam depth, of span-to-depth ratio, and of the amount of longitudinal reinforcement on the shear strength. The tensile toughness of concrete, expressed as fracture energy, proves to be an important material property, which ought to be taken into account.

10.14359/2947


Document: 

SP118-06

Date: 

January 1, 1990

Author(s):

L. Nobile

Publication:

Special Publication

Volume:

118

Abstract:

Focuses on the formulation of a self-consistent model for a compressed concrete containing randomly distributed flat microcracks. A general formulation of the constitutive law for such material is obtained, finding the overall mechanical response to be strongly nonlinear in the region near the maximum in the stress-strain curve.

10.14359/2942


Document: 

SP118-05

Date: 

January 1, 1990

Author(s):

Sawarng Ratanalert Ratanalert and MethiI Wecharatana

Publication:

Special Publication

Volume:

118

Abstract:

Many fracture mechanics models have been proposed in recent years to account for the nonlinear behavior of concrete around the crack tip region. These well-known models are the fictitious crack model (FCM) by Hillerborg, the crack band model (CBM) by Bazant, and the two-parameter fracture model (TPFM) by Jenq and Shah, etc. To model the fracture process zone or microcracked zone, these models often assumed the linear or bilinear stress-displacement relationship to simplify the analysis since actual relationships were not available due to difficulties in conducting direct tension tests. To avoid tedious numerical computation and the need of stress-displacement relationship, TPFM was proposed based on the simple LEFM concept. The model was quite accurate when applied to the notched beam test. All these models presented some degree of satisfaction when comparing with some experimental data. Since more direct tension tests with complete postpeak stress-displacement relationships have been successfully conducted in recent years, the need of assuming the stress-displacement relationship or using the indirect notched beam test is no longer necessary. An evaluation of the FCM using the observed stress-displacement relationships versus the assumed one seems to be an interesting task to verify the validity of the model. For TPFM, the proposed two unique fracture parameters should be verified for specimen size independence. A series of experiments were conducted on two types of test specimens (notched beam and compact tension) with different geometries. The results indicate that the parameters recommended in TPFM seem to be unique only for the notched beam specimen. The same two parameters were found to be tenfold larger for the compact tension specimen. For FCM, the predicted load-CMOD and load-deflection curves using the observed stress-displacement relationship are in better agreement with experimental data than those determined from the assumed linear relationship. Although theoretically both predicted load-CMOD and load-deflection curves should have the same order of accuracy, in this study, they were found to be substantially different.

10.14359/2934


Document: 

SP118-04

Date: 

January 1, 1990

Author(s):

J. C. Chern, C. H. Young, and K. C. Wu

Publication:

Special Publication

Volume:

118

Abstract:

Conventional concrete and mortar are both major construction materials because of their advantages in durability, economy, and comparably good mechanical properties. However, brittleness and low tensile strength are weak constitutions of these materials. Therefore, they provide less resistance to the propagation of cracks. Fibers can resist against the propagation of cracks due to the contribution of traction, resulting from the fibers-matrix bond mechanism, on the crack face. Some exact mathematical formulations to express thestress intensity factor and the crack opening displacement are proposed in this research to interpret the fracture behavior of fiber reinforced cementitious composites. Using these formulations, two fracture criteria can be performed to evaluate the tendency of crack propagation of this composite material. These two criteria are stress intensity factor and crack tip opening displacement. To achieve a more reasonable solution, the couple effect between the crack opening displacement and the fiber bridging traction is also considered. From the numerical results shown in this study, it is concluded that the fiber reinforced concrete provides higher resistance against the propagation of cracks than ordinary plain concrete, and one can clearly understand the resistance ability of fibers for the fracture behavior of concrete.

10.14359/2928


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