This paper presents the development of simple semi-empirical formulae for the analysis of nominal flexural strength of high strength steel fiber reinforced concrete (HSFRC) beams. Such developed formulae were based on strain compatibility and equilibrium conditions for fully and partially HSFRC sections in joint with suitable idealized compression and tension stress blocks. The stress blocks were given by suitable empirical functions for the compressive and post-cracking strengths of HSFRC. The enhancement in compressive strength due to fibers inclusion is proposed as a function of concrete matrix strength and fiber reinforcing index. To account for the pullout resistance of fibers in tension, the post-cracking strength was evaluated as a function of fiber reinforcing index and bond strength. The fiber reinforcing index was considered as a function of volume content, aspect ratio, orientation and length efficiency factors of the fibers. In view of the degenerative nature of the pullout resistance of the fibers with the increase of crack width, a limit was placed on the useful tensile strain extent; depending on fiber length and crack spacing. It was found that there is a good agreement between the flexural strengths for HSFRC beams predicted by the proposed formulae and the experimental results reported in the literature, while the predicted flexural strengths as computed by ACI committee (544) were very conservative. The parametric studies indicate that the nominal moment section capacity increases with the increase of fiber content and fiber aspect ratio |
