Assessment of Concrete Anisotropy in Relation to the Direction of Casting

Abstract

In numerical predictions of both static and dynamic response of concrete structures, the usual assumption of global isotropic behavior is usually accepted, constituting standard practice in structural analysis and design. It has been recognized, however, that in situ concrete compressive strength of drilled cores in the direction normal to the direction of casting is somewhat smaller than the strength in the vertical direction. Since the consideration of this factor may reduce model error in numerical schemes that assume isotropic behavior, experimental studies were conducted in order to quantify the degree of anisotropy that may be expected in concrete structures. These initial studies suggest that the effect may result in errors as high as 10% in the estimated carrying capacity, deserving in consequence additional research.

Assessment of concrete anisotropy by means of compression and indirect tensile tests

“…It may be seen that failure often occurs due to low tensile strength normal to a vertical plane in the central portion of the cylinder, thus reducing the influence of friction at the end plattens. The strength of sample S3 is roughly 20% smaller than the mean strength measured in conventional tests, result that suggests a strength reduction larger than that observed in cubic samples by Kosteski et al 7 , but still within the expected range.…”

“…These tests confirm that both the unconfined compressive strength as well as the indirect tensile strength determined on cylindrical samples are perceptibly influenced by the angle between the sample axis and the vertical orientation during casting. In connection with compression tests on cubic samples, the results of Kosteski et al 7 lead to evidence concerning the fact that the strength measured in the direction of casting, exceeds the strength measured in a direction orthogonal to the direction of casting, coincident with extensive results reported by Yi et al 8 . These authors, who continued earlier studies of Kim and Eo 9 , were concerned mainly with size and shape effects of samples used in different codes to assess fc', the compressive strength of concrete measured in standard cylindrical samples and somehow overlooked the fact that concrete always presents a perceptible degree of anisotropy, not only testing samples.…”

“…As previously noted, the available evidence on the meso-scale anisotropic behavior of concrete is based mainly on tests of concrete cores retired from built structures. The authors are not aware of laboratory investigations designed to examine this effect before the pilot study described by Kosteski et al 7 , in which two conventional concrete mixes, designated as materials C30 and C50, were employed in the preparation of the samples. The compositions of both concretes are indicated in Table 1 Assessment of concrete anisotropy by means of compression and indirect tensile tests maximum size of 19mm.…”

“…On the other hand, these horizontal cracks should cause a reduction of the influence of confining stresses on the vertical strength, in relation to the effect that might be expected in an isotropic material. Since the consideration of this factor may be important in some structural problems, the authors previously additional experimental studies in order to quantify, by means of compression tests of cubic laboratory samples, the degree of anisotropy that may be expected in concrete structures 7 . Those initial studies suggested that the effect may result in errors as high as 10% in the estimated carrying capacity of concrete elements and were expanded in the present contribution, in which results of compression tests, as well as indirect tensile tests using cylindrical samples, are reported.…”

Resistência à compressão axial do concreto com diferentes direções de carregamento e condições de contorno

“…Portanto, o presente estudo visa avaliar a anisotropia do concreto com base nas referências citadas, utilizando corpos de prova cúbicos, obtidos através de três traços de concreto, também avaliar a interferência das condições de contorno impostas no ensaio de compressão axial, visto que o atrito entre espécime e máquina de ensaio possui grande influência na resistência final do concreto. Em KOSTESKI et al [15] foram utilizados corpos de prova cúbicos para estudar o efeito da direção do lançamento do concreto na resistência a compressão axial, da mesma forma que vários outros trabalhos anteriores. Já em KOSTESKI, MARAN-GON e RIERA [27] foi estudado o mesmo efeito utilizando corpos de prova cilíndricos.…”