Experimental Study of the Influence of Multiple Cyclic Loading on the Static Modulus of Elasticity of Hardened Concrete

abstract

English

The study of concrete properties currently emphasises not only strength, e.g. compressive, but also elastic properties, such as the static modulus of elasticity [1, 2]. This property of hardened concrete affects primarily its deformation under load, the magnitude of deformation or shrinkage. Generally speaking, the higher the value of the modulus of elasticity, the lesser the degree to which a structure deforms. It could be said that concrete during its service life in a structure alternates between states of being loaded and unloaded. If a concrete structure is repeatedly acted upon by external mechanical loads during its service life, it can be considered as subjected to multiple cyclic loading. These cycles are not regular and may occur throughout the structure’s existence based on its purpose and manner of use. This paper deals with the dependence of the value of the static modulus of elasticity of concrete in compression on the number of loading cycles. It is assumed that the value of the static modulus of elasticity will decrease at a higher number of loading cycles. The main goal of the experiment was to describe the changes in the static modulus of elasticity in dependence on the number of loading cycles administered. The assumed number of cycles was 3000. The loading was performed in accordance with method B described in EN 12390-13 [3]. The testing procedure was configured in a way that allowed performing as many loading cycles as possible within several dozens of hours, while still performing a static loading test. The goal of the experiment was to observe the behaviour of concrete during loading in the elastic region of the stress-strain curve; for this reason, the upper loading stress was set to Sa = fc/3 MPa, where fc is compressive strength measured on reference specimens of the same shape and dimensions as the test specimens. According to [3], the basic loading force should be within 0.1 fc ≤ Sb ≤ 0.15 fc. This experiment used a lower loading stress of the highest possible value, i.e. Sb = 0.15 fc. The reason for this was to save time when transferring between the loading stresses. For the same reason, the highest allowed loading rate was chosen to be 0.80 MPa/s with a holding time of 2 s. The cyclic loading was performed using a mechanical testing press with a loading force range of 0–1000 kN. Deformation was measured by means of two electrical resistance strain gauges mounted on opposing faces of a specimen. Deformation readings were recorded at a frequency of 5 Hz. The static modulus of elasticity was evaluated according to [3] during each loading cycle. Thus, the testing of each specimen produced a set of 3000 values of the modulus of elasticity. The assumption that the modulus of elasticity would drop with an increasing number of loading cycles was not confirmed.

modulus of elasticity, multiple cycling, experiment, concrete

MISÁK, P.; KOCÁB, D.; DANĚK, P.; KUCHARCZYKOVÁ, B.; TOPOLÁŘ, L.

4. 9. 2017

Societa editrice esculapio

Bologna

978-889-385-041-4

Proceedings 20th International Conference on Composite Structures

179

179

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