calcestruzzo fibroso

A softened strut-and-tie macro model able to reproduce the flexural behavior of external beam-to- column joints with the presence of horizontal and vertical steel bars, including softening of compressed struts and yielding of main and secondary steel bars, is presented, to be used for the pushover analysis. The model proposed is able to calculate also the flexural response of fibrous reinforced concrete (FRC) beam-to-column sub-assemblages in term of a multilinear load-deflection curves. The model is able to take into account of the tensile behavior of main bars embedded in the surrounding concrete and of the softening of the compressed strut, the arrangement and percentage of the steel bars, the percentage and the geometry of steel fibers. First cracking, yielding of main steel and crushing of concrete were identified to determine the corresponding loads and displacement and to plot the simplified monotonic load-deflection curves of the sub-assemblages subjected in the column to constant vertical load and at the tip of the beam to monotonically increasing lateral force. Through these load-deflection curves the component (beam, joint and column) that first collapse can be recognized and the capacity design can be verified. The experimental results available in the literature are compared with the results obtained through the proposed model. Further, a validation of the proposed model is numerically made by using a non linear finite element program (ATENA-2D) able to analyze the flexural behavior of sub-assemblages.

For this paper is available an extended abstract after the text in Italian

In the present paper the experimental results referred to monotonic and cyclic tests on fibrous reinforced concrete (FRC) beams are presented and discussed. The influence of longitudinal and transverse steel bars, of type and percentages of fibers, of the shear to depth span ratios and of the cover thickness are estimated. Experimental results highlight that fibers are a very effective shear reinforcement in R.C. beams both under monotonic and cyclic actions, but under reversal cyclic actions, if shear failure is attained, the contribution due to the fibers reflects mainly in the bridging actions across the cracks and brittle failure can be partially avoided. In these cases and especially for seismic design ductile failure in flexure is more suitable and over strength in shear is required, the latter being obtained with a good combination of fibers and stirrups. Form theoretical point of view shear and flexural strength prevision was made by using a recent model developed by the authors able to take into account of the main parameters governing the flexural behavior of fibrous reinforced concrete beams. Finally, some design consideration for the use of FRC in seismic design of beams are given.

For this paper is available an extended abstract after the text in Italian

Flexural behaviour of external fibrous reinforced concrete beam-to-column joints

Fibrous reinforced concrete beams in seismic area: experiment and design