Optimisation of ductility of welded steel bars, ribbed coils and mesh fabric for reinforced concrete elements under severe seismic loads : final report

Some major open problems concerning steel reinforcement are addressed in the present research report. Ductility, intended both as ultimate to yield stress ratio and deformation at ultimate monotonic loading, is too low in several reinforcing products available in the European production. An optimised steel rebar, in terms of carbon content and equalisation temperature, has been formulated for a given yield stress of 450 MPa and optimising the ductility parameters. An optimised steel wire, in terms of carbon content and stretch amount, has been formulated for the same purposes. Energy dissipation during low-cycle fatigue tests is to be increased, in order to meet the requirements and expectations of reinforced concrete structure designers, especially in seismic areas. An extensive testing programme, involving different independent laboratories, has been completed for rebar, stretched wire and welded joints under cyclic loading conditions. The failure mechanism has been observed clearly and confirmed by all investigators. Special attention is to be paid to the welding procedures inside the 'plastic hinge', where currently welding is forbidden in seismic areas, but significant improvements are to be expected if proper and industrially controlled welding procedures are studied and then standardised. A set of experiments has been conceived, implemented and discussed an welded cruciform joints, demonstrating the technical capability to reach a joint which does not decrease the original mechanical properties of the parent materials, both in terms of strength and ductility. Reinforced concrete column prototypes are often adopted in the scientific and technical literature an reinforced concrete seismic structures as benchmarks to evaluate and compare ductility of the plastic hinge under cyclic loading. A set of reinforced concrete columns have been tested under horizontal cyclic loading; all of them were reinforced with the optimised material rebar and wire or mesh fabric. Results show clearly the extremely high energy dissipation in the plastic hinge for all columns which confirms the choice for the optimised steels.