1. Strength
The strength indicators for steel include the elastic limit (σe), the yield limit (σy), and the ultimate tensile strength (σu). In structural design, the yield strength is used as the primary reference; a higher yield strength allows for a reduction in the structure's self-weight, leading to steel savings and lower construction costs. The ultimate tensile strength (σu) represents the maximum stress the steel can withstand before failure. At this stage, the structure loses its functional utility due to significant plastic deformation; however, because it undergoes large deformations without collapsing, it meets the requirements for structural resistance against rare, extreme seismic events. The ratio σu/σy can be considered a parameter indicating the steel's strength reserve.
2. Ductility (Plasticity)
The ductility of steel generally refers to its ability to undergo significant plastic deformation without fracturing once the stress exceeds the yield point. The primary indicators for measuring the plastic deformation capacity of steel are elongation (δ) and the reduction of area (ψ).
3. Cold-Bending Performance
The cold-bending performance of steel measures its resistance to cracking when subjected to plastic deformation through bending at room temperature. This property is evaluated via a cold-bending test, which assesses the steel's ability to withstand a specified degree of bending deformation.
4. Impact Toughness
Impact toughness refers to the ability of steel to absorb mechanical kinetic energy during the fracture process when subjected to impact loads. It is a mechanical property that measures the steel's resistance to brittle fracture-which can be triggered by factors such as low temperatures or stress concentrations-under the influence of impact loads. Impact toughness values are typically determined through impact testing of standardized specimens.