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Abstract -The results of tests on cracking moment in steel fibre reinforced concrete beams based on waste sand are presented in this paper. The test defined cracking moment was compared with that calculated as proposed by Lok and Xiao, Tan, Paramasivam and Tan and by application of the methods contained in Eurocode 2 as well as in PN-84/B-03264. The best compatibility of the obtained test results with the calculated values was achieved for the Eurocode 2 method.
Keywords - beams, cracking moment, steel fibre, waste sand.
(ProQuest: ... denotes formula omitted.)
1. INTRODUCTION
The main objective for application of steel fibres in concrete elements is to limit cracking caused by external and internal loading. An important parameter describing the cracking phenomenon in steel fibre reinforced concrete "little beams" is the moment of appearance of the first crack [I]. This is determined, in most cases, on the basis of the load-strain relationship at the point in which the curve deviates from the straight line. Such interpretation is included in the majority of standards (ASTM C 1018, NBN B 15-238, JCI Standard SF-4) and recommendations (CUR, DBV, RILEM) [2], [3] regarding steel fibre reinforced concrete "little beam" testing irrespectively of their size. There is a big number of studies verifying the calculation methods included in the standards [4]-[8]. Unfortunately, those methods do not apply to calculations of full-size elements e.g. beams with longitudinal reinforcement and steel fibres because it is impossible to clearly define the cracking moment based on the load-deflection relationship [9], [10].
The fundamental parameter describing the cracking limit state is the cracking moment K. H. Tan, P. Paramasivam and K. C. Tan [11] have assumed that influence of fibres on the moment of inertia can be neglected and then the formula for the cracking moment would take the following form:
... (1)
where:
Ig - total moment of inertia,
yt - distance from the centre of gravity to stretched cross-section edge,
cpcf - strength for the first crack in steel fibre reinforced concrete little beams; it can be defined using an empirical formula proposed in 1974 by R. N. Swamy and P. S. Mangat [12] (recommended by ACI [13]), based on the so-called law of mixtures:
... (2)
where:
Vf- volume of steel...