Safety of construction
The ductility of reinforcing steel is its ability to achieve significant deformation without a significant increase in stress after exceeding the yield point. This term refers to the work of the structure in the phase of plastic deformation when the stresses have exceeded the maximum values, and the deformation increases nonlinearly with respect to the stresses - and therefore in the event of structural failure.
EPSTAL steel combines the most important for reinforcing steel features:
- high tensile strength (class A-IIIN),
- increased ductility (class C).
The ductility of the reinforcing steel has a great impact on the safety of the construction in the emergency state, i.e. after exceeding the permissible load values. When designing reinforced concrete structures, the maximum permissible load values are assumed with some safety reserves. It sometimes does not sufficiently protect the structure from the effects of unforeseen exceptional events such as impacts, explosions, improper use of structures, design or engineering errors, etc. Constructions that are particularly exposed to overloads are those built on mining or seismic areas and bridges that are constantly subject to dynamic loads and repeatedly changing loads. At the time of design of these structures, special consideration should be given to their behavior in an emergency.
Work of the construction in an emergency state
In elements reinforced with low ductility steel, exceeding the permissible loads causes brittle fracture of the reinforcement bars, which can lead to sudden and unexpected destruction of the structure. Experimental studies show that this damage can occur at very low deflection values of these components and with a slight scratch on the surface of the concrete - and therefore with no clear warning signs of catastrophe.
High-ductility steel, after exceeding the yield point, becomes plasticized, i.e. it acquires the properties which allow it to achieve very large deformations with even a slight increase in stress. Therefore, its breaking occurs after much larger elongation than breaking of the brittle steel in the same situation. This has a significant impact on the behavior of the structure - if it is reinforced with high-ductility steel, after exceeding the permissible load values, i.e. in an emergency, suffers large deflections and scratches. These signs, which are easily visible to the users, alert the approaching danger, thus enabling evacuation and corrective actions that can prevent a catastrophe.
Comparative study of beams
The following comparative study of single-span concrete beams reinforeced with steel of varying ductility perfectly reflects the nature of brittle and more plastic construction. At the time of destruction, the lowest deflections were observed in the case of low-ductility steel (class A according to EC2), the highest in the case of high-ductility steel (class C). The destructive force in each of the three cases was similar, because the reinforcing steel in each beam, with the same strength class, differed only in ductility. Large deflections and scratches occurring just before the moment of destruction are a warning signal and allow evacuation and corrective action.