Prismatic RC columns externally confined with FRP sheets and pre-tensioned basalt fiber ropes under cyclic axial load

Abstract

This experimental investigation addresses the use of transversely placed composite ropes made of basalt as external standalone confining reinforcement in cases of reinforced concrete columns with square section or combined with already applied FRP sheets. Non bonded, non impregnated basalt fiber rope is wrapped around the columns by hand in 1 or 2 layers or is pre-tensioned with special mechanical devices. The efficiency of wrapped columns is compared with identical columns confined with polypropylene fiber ropes. Further, the columns are wrapped with externally bonded GFRP sheets and then with non bonded basalt fiber ropes in a hybrid scheme. The columns are subjected to multiple cycles of increasing compressive deformation to simulate seismic actions. The columns wrapped with two layers of basalt composite ropes (pre-tensioned or not) present an ever increasing stress-strain response for concrete axial strains higher than 5.6%, even for very high rope pretension level, without rope fracture. Both the polypropylene and basalt ropes reveal a high potential for strain redistribution around the variably damaged concrete core. In the cases of hybrid FRP – basalt rope confinement the strain redistribution potential of the rope is similarly remarkable, controlling the dilation of the column even after the multiple fracture of the GFRP sheet. The rope could increase the axial strain sustained by the concrete from 2.21% to beyond 5.1%, without rope fracture.