TY - JOUR
T1 - Microcracking and inelastic behavior of concrete
AU - Sturman, Gerald M.
AU - Shah, Surendra P.
AU - Winter, George
N1 - Funding Information:
This study is part of an investigation made possible by a research grant to Cornell University by the National Science Foundation. The project is actively directed by George Winter, head of the Department of Structural Engineering, and co-directed by Floyd 0. Slate, Associate Professor of Civil Engineering. The substantial contributions of Samuel Errera, manager of the Structural Laboratory; Ernest Pittman, laboratory technician, and Stanley Olsefski, instructor-technician are gratefully acknowledged. The help of Professor Slate in developing experimental techniques has been of great value in the course of the work.
Publisher Copyright:
© 1965 American Concrete Institute. All rights reserved.
PY - 1965/1/1
Y1 - 1965/1/1
N2 - Inelastic behavior of concrete was studied by direct observations of internal microcracking. Thin slices were made from strained specimens and internal cracks were examined by X-ray and microscope techniques. Bond cracks at the interface between coarse aggregates and mortar, exist in concrete even before any load is applied. Analytical and experimental studies showed that tensile stresses are present at the mortar-aggregate interface because of volume changes of mortar and may be partly responsible for bond cracks in virgin concrete. These bond cracks begin to propagate noticeably at applied compression stresses of one-quarter to one-third of the ultimate strength. At this level the stress-strain curve begins to deviate from a straight line. At about 70% to 90% of ultimate strength cracks through mortar begin to increase noticeably and bridge between bond cracks to form a continuous crack pattern. Upon further load increase this condition eventually leads to a descending stress-strain curve and failure. Other investigators have noted that in that same load range, the volume of concrete begins to increase rather than decrease. An hypothesis explaining this volume expansion and propagation of bond cracks in terms of shear bond strength of the interface and microcracking has been presented. In order to investigate the influence of flexural strain gradients, microcracking and the stress-strain relation of eccentrically loaded specimens were compared with those of concentrically loaded specimens. It was found that a flexural strain gradient definitely retards microcracking, especially mortar cracking as compared to cracking at the same strain in axial compression. The stress-strain curve for eccentric compression, which was computed by an experimental-statistical approach was found to differ materially from that for concentric compression. The peak of the flexural curve was located at a strain about 50% larger and at a stress about 20% larger than the peak of the curve for concentric compression. Structural implications of these findings are briefly examined.
AB - Inelastic behavior of concrete was studied by direct observations of internal microcracking. Thin slices were made from strained specimens and internal cracks were examined by X-ray and microscope techniques. Bond cracks at the interface between coarse aggregates and mortar, exist in concrete even before any load is applied. Analytical and experimental studies showed that tensile stresses are present at the mortar-aggregate interface because of volume changes of mortar and may be partly responsible for bond cracks in virgin concrete. These bond cracks begin to propagate noticeably at applied compression stresses of one-quarter to one-third of the ultimate strength. At this level the stress-strain curve begins to deviate from a straight line. At about 70% to 90% of ultimate strength cracks through mortar begin to increase noticeably and bridge between bond cracks to form a continuous crack pattern. Upon further load increase this condition eventually leads to a descending stress-strain curve and failure. Other investigators have noted that in that same load range, the volume of concrete begins to increase rather than decrease. An hypothesis explaining this volume expansion and propagation of bond cracks in terms of shear bond strength of the interface and microcracking has been presented. In order to investigate the influence of flexural strain gradients, microcracking and the stress-strain relation of eccentrically loaded specimens were compared with those of concentrically loaded specimens. It was found that a flexural strain gradient definitely retards microcracking, especially mortar cracking as compared to cracking at the same strain in axial compression. The stress-strain curve for eccentric compression, which was computed by an experimental-statistical approach was found to differ materially from that for concentric compression. The peak of the flexural curve was located at a strain about 50% larger and at a stress about 20% larger than the peak of the curve for concentric compression. Structural implications of these findings are briefly examined.
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M3 - Conference article
AN - SCOPUS:85111149048
VL - SP-012
SP - 473
EP - 499
JO - American Concrete Institute, ACI Special Publication
JF - American Concrete Institute, ACI Special Publication
SN - 0193-2527
T2 - 1964 International Symposium on Flexural Mechanics of Reinforced Concrete
Y2 - 10 November 1964 through 12 November 1964
ER -