Abstract
The paper describes changes of strength of steel anchors depending on the diameter of the drill hole, the crack width and presence of plastic and steel fibres. Tests were carried out on C20/25 concrete bases with two specific fibre admixtures. Two types of anchors were selected for the tests: stud and sleeve anchors with M12 diameter, for their frequent application in construction. Steelbet 50/0.8 fibres affect the strength of the connections which use stud anchors, reducing the pullout resistance by ca. 10% in non-cracked C20/25 concrete. For cracked concrete with crack width of 0.30 mm and connections using stud anchors, no effect of using steel fibres was found, a 30% increase in strength was found for connections using stud anchors and the minimum drill hole diameter and a 20% reduction in strength for the maximum drill hole diameter, as compared to the minimum diameter. For sleeve anchors, reductions and an increase of 10% in strength were observed. The obtained results indicate a need to develop assessment criteria for effects of external factors in the form of steel fibre admixtures.