DEFORMABILITY AND DUCTILITY IN OVER-REINFORCED SCC BEAMS

Abstract

It is often to use a high percentage of steel reinforcement in a concrete flexural member in order to minimize structural depth and still provide adequate stiffness. This thesis shows that, by placing a steel helix in the compression zone of heavily over-reinforced Self-Compacting Concrete beam, considerable strength, stiffness and ductility may be achieved, even when steel percentage is as high as approximately 6 %. This is because the concrete in the compression becomes triaxially stressed and confined during loading, leading to a high uniax~al strain capacity in the concrete at an enhanced stress level. The testing programme described here consisted of seven tests on rectangular steel-reinforced Self-Compacting Concrete beams. Each helically reinforced specimen contained a single helix. The helix were formed from either 2 mm or 4 mm diameter mild steel wire, the three pitch values investigated for each helix wire diameter 20 mm, 40 mm and 60 mm. To show the full benefit of the presence of a circular helix, control specimen (no helix) were tested. Self-Compacting Concrete was used for concreting of the heavily reinforced beam sections. This research demonstrates that it is possible to heavily over-reinforced concrete structures and nonetheless expect a ductile response. This is potentially very useful to clients, consultants and contractors who wish to use shallower concrete members. Further, an ANSYS based analytical approach was development for predictive assessment. The analytical approach predicts behaviour reasonably accurately.