Abstract
Throughout the several-hundred-year-long history of the concept of strength, inaccurate material strength as a result of the size effect and the inconsistency of strength theories have been two continuous and challenging issues, and have even been taken to be inherent attributes of material strength. Applying the structural stressing state theory and method, this study experimentally investigates the uniaxial load-bearing process of concrete specimens and reveals their stressing state mutation features at specific load levels. Exploration of this general feature resulted in the discovery of essential strength, which is basically without size effect. Then, biaxial and triaxial experiments with concrete specimens were conducted in order to obtain the results for various combinations of principal stresses on essential strength. Consequently, according to Yu’s unified strength theory, the formula for strength of concrete was determined by fitting the relation between the combined principal stresses and the essential strength, which was verified by experiments carried out using natural marble specimens. Essential strength could promote the accuracy of strength indices, and the formula for strength might replace the existing strength theories for brittle materials. The initial solution of these two classic issues could make a new contribution to Yu’s unified strength theory and its final goal, promoting related research on material strength and leading to a more rational use of material strength in practical engineering.
Highlights
Since the concept of strength was proposed by da Vinci in the 1500s and Galileo in 1638, scientists from around the world have developed up to one hundred theories addressing issues related to strength
Equation (6) is referred to as a formula for strength for two reasons: (1) the formula is directly derived by fitting experimental data, without the reliance on assumptions generally necessary for a strength theory; and (2) importantly, the essential strength and the formula for strength are derived from the consistent stressing state features of the specimens, which is the embodiment of the natural law stating that quantitative change in a system will lead to qualitative change in that system
Through the experimental investigation into the uniaxial stressing state of concrete specimens, the essential strength of concrete, which is essentially without the size effect, was revealed based on the failure loads of the specimens with respect to their general stressing state mutation features, which are an embodiment of the natural law that quantitative change in a system will lead to qualitative change in that system
Summary
Since the concept of strength was proposed by da Vinci in the 1500s and Galileo in 1638, scientists from around the world have developed up to one hundred theories addressing issues related to strength. Early in the 20th century, a number of famous scientists, including Voigt and Mohr, believed that it would be impossible to develop a single strength theory that would cover various materials [6,15], in other words, a single strength criterion did not exist for various materials Until now, it has commonly been taken for granted that there is no definite relation between material strength and combined principal stresses. The material strength defined by the unit body should be definite and independent of the sizes and shapes of specimens, like the specific gravity of a substance It could be seen from experimental observations of concrete specimens that specimens were severely broken at their ultimate load, and that most unit bodies were in complex (non-uniaxial) and non-identical stress states. The formula for strength was verified through biaxial and triaxial experiments using natural marble specimens
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