Steel Fiber Reinforced Polymer (SFRP) materials have recently emerged as a promising and cost-effective solution for external confinement of concrete members. The SFRP sheets consist of high carbon steel cords made by twisting steel wires instead of the mostly used carbon or glass fibers; they can be applied to the structural member according to a wet lay-up installation procedure. So far, only a few experimental and theoretical researches have been performed to investigate the compressive behaviour of concrete confined by SFRP wraps. This paper contributes to address these knowledge gaps by presenting the results of a wide experimental campaign performed on SFRP confined concrete cylinders (with 150 mm diameter and 300 mm height) tested in axial compression. Specimens were grouped within five series depending on the average value of the unconfined concrete strength, fc0,m. In particular: the first series (“S1”) included 40 specimens for which the fc0,m value was found to be 6.87 MPa; the second series (“S2”) gathered 94 cylinders with fc0,m = 14.51 MPa; the third series (“S3”) included 78 specimens by fc0,m = 31 MPa; the fourth (“S4”) and the fifth series (“S5”) were characterized by fc0,m = 42.15 MPa and 46.10 MPa, respectively, each including a set of 15 specimens. Within each series, most specimens were variably confined by using 1 to 3 SFRP layers characterized by equal or different steel fiber densities (low, medium and high); the remaining ones were not strengthened and used as reference (control) members. During tests, most SFRP confined specimens have experienced the rupture of the sheet involving the entire height or smaller portions of the cylinder; in a few cases, the rupture of the sheet was anticipated by severe damage of the fibers. Other samples, instead, mainly those wrapped with multiple layers, showed a combination of debonding and rupture. The debonding occurred by involving the outermost SFRP layer at the overlapping zone; then, the rupture of the inner layer/s followed by engaging half or the entire cylinder’s height. It has been observed that the sheet debonding frequently occurred in the case of medium-high concrete strengths and for confining systems employing high density sheets. Test results have shown that the SFRP confinement is an effective means for improving the performance of concrete. By focusing on the concrete series 2, it has been observed that the use of only one SFRP layer with low fiber density is sufficient by itself to almost double the unconfined concrete strength. However, by doubling the number of SFRP layers with same tape density, the resulting percent strength increase is not doubled, i.e., number of layers and strength gain are not linearly related; of course, the SFRP performance reduces with the increase of the unconfined concrete strength. Finally, early analytical studies have highlighted that the strength capacity of the SFRP confined concrete is well predicted by a relationship similar to that previously found for C/GFRP confining systems.
|Titolo:||Compressive behaviour of concrete confined by steel FRP wraps: experimental investigation|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||4.1.2 Proceedings con ISBN|