During service, steel structures are subjected to various actions (such as loads, uneven foundation settlement, and temperature changes). Therefore, the steel must possess good mechanical properties (strength, ductility, and toughness) and processing characteristics (suitability for hot/cold working and welding) to ensure structural safety and reliability. While there are many types of steel, only a few meet the specific requirements for steel structures-examples include Q235 carbon steel, 16Mn low-alloy steel, and 20MnV steel (used for high-strength bolts).
Performance Indicators
1. Strength
Steel strength is characterized by the elastic limit (σe), yield limit (σy), and ultimate tensile strength (σu). Design calculations are based on the yield strength; high yield strength allows for reduced structural self-weight, material savings, and lower construction costs. Ultimate tensile strength (σu) represents the maximum stress the steel can withstand before failure. At this stage, the structure loses its serviceability due to significant plastic deformation; however, the fact that it deforms extensively without collapsing satisfies requirements for resisting rare, severe earthquakes. The ratio of σu to σy serves as an indicator of the steel's strength reserve.
2. Ductility (Plasticity)
Ductility generally refers to the steel's ability to undergo significant plastic deformation without fracturing after the stress exceeds the yield point. The primary indicators for measuring this capacity are elongation (δ) and reduction of area (ψ).
3. Cold-Bending Performance
Cold-bending performance measures the steel's resistance to cracking when subjected to plastic deformation during bending at ambient temperature. This property is evaluated through cold-bending tests, which assess the steel's ability to withstand a specified degree of bending deformation.
4. Impact Toughness
Impact toughness refers to the steel's ability to absorb mechanical kinetic energy during fracture under impact loading. It is a mechanical property that measures resistance to brittle fracture-which can be triggered by factors such as low temperatures or stress concentrations-when subjected to impact loads. Impact toughness values are typically determined through impact tests performed on standard specimens.
