FORMATION AND OPENING OF CRACKS IN SECTIONS, NORMAL TO THE LONGITUDINAL AXIS OF COMBINED REINFORCED STEEL-FIBER CONCRETE BEAMS

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Visnyk LNAU: Architecture and Farm Building 2019 №20: 33-37

FORMATION AND OPENING OF CRACKS IN SECTIONS, NORMAL TO THE LONGITUDINAL AXIS OF COMBINED REINFORCED STEEL-FIBER CONCRETE BEAMS

Bilozir V. Candidate of Engineering Science
Lviv National Agrarian University
Podhorecki A. Candidate of Engineering Science
University of Technology and Life Sciences in Bydgoszcz

https://doi.org/10.31734/architecture2019.20.033

Annotation

Steel fibre concrete has a set of advantages comparing to the ordinary reinforced concrete, particularly improved crack resistance, viscidity and resiliency, greater endurance as to oscillation and shock loading, better resistance to elimination and impact of high temperatures. Appearance of the new types of fibre armature of Ukrainian production requires additional researches of their bearing strength, inflexibility and crack resistance of the bending combined reinforced elements.

The experiment program expects producing and testing of the samples, reinforced with Bp-1 (1Ø5) armature, anchor fiber 50 mm long and 1 mm in diameter with a ratio of reinforcement in the volume 0; 0,7; 1,35 and 1,8, according to the scheme of one-turn beams, loaded with lumped forces in the third working run, which is equal to 900 mm. The distance from the extreme stretched fibers to the center of the rod weight accounts for 15mm. In the progress of the tests, the controlled parameters included deflection, deformation of the concrete at the section height, width of the normal cracks opening.

It was experimentally approved that all prototype models demonstrated almost linear growth of deflections until appearance of cracks. Afterwards, the deflections increased more intensively, especially in the models with no fiber reinforcement. After formation of normal cracks, the width of their opening increased and the height of the compressed concrete zone gradually decreased. An increase of in the models resulted in less intense decrease of the relative height of the compressed zone of concrete up to destruction. However, increase of the fiber share in the samples contributed to a decrease in the width of the normal cracks opening.

At the moment of crack formation, relative deformations of the extreme stretched fibres of concrete were equal to 17·10-5 on average. A gowth of loading caused that those deformations increased and their growth almost linearly depended on the growth of the bending moment relating to the degree of load, i.e it was equal to 85-90 % of the destructive one.

The work supplied proposals concerning computation of the moment cracks fromation and their opening width.

Key words

steel fiber concrete, beam, cracks formation, width of crack opening, calculation

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