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International Concrete Abstracts Portal

Showing 1-5 of 15 Abstracts search results

Document: 

SP216-06

Date: 

October 1, 2003

Author(s):

D. Dupont and L. Vandewalle

Publication:

Symposium Papers

Volume:

216

Abstract:

During the last 4 years a large testing program has been carried out in order to investigate the shear capacity of concrete beams containing longitudinal reinforcement and steel fibers. The results of this research program are presented here and compared with calculated values. For the calculations two models were used: the model proposed by RILEM TC 162-TDF and the model of Imam which is originally derived from a formula proposed by Bazant and Sun. The results of this comparison indicate that the RILEM method is a conservative approach. Especially the contribution of the stirrups and the influence of the shear span to depth ratio are underestimated. In the formula of Imam the contribution of the stirrups is calculated in the same way as in the RILEM method and consequently underestimated. However, for SFRC beams containing longitudinal reinforcement but without stirrups the correlation between experimental results and values calculated with the formula of Imam is fairly good.

DOI:

10.14359/12893


Document: 

SP216-09

Date: 

October 1, 2003

Author(s):

T. S. Lok and G. Lu

Publication:

Symposium Papers

Volume:

216

Abstract:

This paper reports on a series of dynamic splitting tensile tests on 70 mm diameter cored concrete and steel fiber reinforced concrete (SFRC) specimens at moderate strain rates. A modified split Hopkinson pressure bar (SHPB) was specifically developed to test such large diameter heterogeneous specimens. Details of the modified SHPB and a novel striker bar are presented. Dynamic strength magnification of up to 4.5 times the static strength at moderate strain rate was obtained. For the SFRC specimens, hooked-end steel fibers were used with 0.3% fiber volume concentration. A high-speed camera with framing rate up to 106 frames per second was used to record the crack propagation mechanism and the progressive fracture of the specimens in tests. Numerical simulation of the test is briefly presented and discussed. Good approximation of the response is obtained.

DOI:

10.14359/12896


Document: 

SP216-12

Date: 

October 1, 2003

Author(s):

D. D. Theodorakopoulos and R. N. Swamy

Publication:

Symposium Papers

Volume:

216

Abstract:

A design method for determining the capacity of slab-column connections made with steel fibre concrete at ultimate load is presented. The proposed design equation is based on the authors' theoretical analysis, which considers the physical behaviour of the connections under load and is therefore applicable to both lightweight and normal weight concrete as well as to concrete without fibres. The design equation incorporates the effects of fibre reinforcement on resisting the upward movement of flexural cracking and of increasing the concrete tensile stress. Furthermore, it simplifies the calculation of the neutral axis depth still accounting for the steel strain hardening effect. The approach does not employ fitting factors to match the predictions to experimental data. However, a depth correction factor is used to account for the size effects. The proposed design equation is applied to predict the ultimate punching shear strength of sixty two slab-column connections tested by authors and other investigators, involving a wide range of fibre variables, concrete type and strength, tension steel ratio, size of slab and loaded area. The comparisons between computed values and the experimentally observed values are shown to validate the proposed design equation.

DOI:

10.14359/12899


Document: 

SP216-08

Date: 

October 1, 2003

Author(s):

S. Wen and D. D. L. Chung

Publication:

Symposium Papers

Volume:

216

Abstract:

Fiber-reinforced cement for piezoelectricity and pyroelectricity is introduced, as these phenomena are useful for the sensing of strain and temperature. The use of short steel fibers (8 µm diameter), together with polyvinyl alcohol, as admixtures greatly enhances these effects, thereby attaining longitudinal piezoelectric coupling coefficient 3 x 10-" mN (10kHz), and pyroelectric coefficient 6 x 10$ C/mz.K (10 kHz). The piezoelectric effect is comparable in magnitude to that of PZT. However, due to the high value (2,500) of the relative dielectric constant, the piezoelectric voltage coefficient and pyroelectric voltage are comparable to or even lower than those of plain cement paste or carbon fiber (15 µm diameter) cement paste. Carbon fiber cement paste and plain cement paste are comparable in the piezoelectric coupling coefficient, piezoelectric voltage coefficient and pyroelectric voltage, though the pyroelectric coefficient is higher for carbon fiber cement paste than plain cement paste.

DOI:

10.14359/12895


Document: 

SP216-11

Date: 

October 1, 2003

Author(s):

C. Sujivorakul and A. E. Naaman

Publication:

Symposium Papers

Volume:

216

Abstract:

The tensile stress-strain response of cement composites reinforced with newly developed twisted polygonal steel fibers (identified here as Torex fibers) is investigated in this study. The new fibers are produced from a prototype machine developed for this research. Parameters investigated are: 1) volume fraction of the fibers (Vf=1 % to 4%); 2) fiber equivalent aspect ratio (L/de = 60, 80 and 100); and 3) the compressive strength of the mortar matrix (20, 44, 68 and 84 MPa). It is observed that high performance fiber reinforced cement composites that exhibit strain hardening and multiple cracking behaviors can be obtained with a proper combination of these parameters. A comparison with hooked and straight steel fibers is also provided. The new Torex fibers leads to a significantly higher composite performance in terms of strength, ductility and cracking behavior.

DOI:

10.14359/12898


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