Steel Construction Section

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Performance indicators of steel structure materials

1. Strength

The strength index of steel consists of elastic limit σe, yield limit σy, and tensile limit σu. The design is based on the yield strength of steel. High yield strength can reduce the weight of the structure, save steel and reduce the cost. The tensile strength σu is the maximum stress that the steel can withstand before failure. At this time, the structure loses its performance due to large plastic deformation, but the structure does not collapse due to large deformation, which meets the requirements of the structure to resist rare earthquakes.

2. Plasticity

The plasticity of steel generally refers to the property of having significant plastic deformation without fracture after the stress exceeds the yield point. The main indicators to measure the plastic deformation ability of steel are elongation δ and reduction of area ψ.

3. Cold bending performance

The cold bending performance of steel is a measure of the resistance of steel to cracks when it is plastically deformed during bending at room temperature. The cold bending performance of steel is to use the cold bending experiment tests the bending deformation performance of the steel to withstand the specified degree of bending.

4. Impact toughness

The impact toughness of steel refers to the ability of steel to absorb mechanical kinetic energy during the fracture process under the action of impact load. Generally, the impact toughness index of steel is obtained through the impact test of standard test pieces.

5. Welding performance

The welding performance of steel refers to obtaining welded joints with good performance under certain welding process conditions. Welding performance can be divided into two types: welding performance in the welding process and welding performance in use performance. Welding performance in the welding process refers to the sensitivity of the weld and the metal near the weld to not produce thermal cracks or cooling shrinkage cracks during the welding process. Good welding performance means that under certain welding process conditions, neither the weld metal nor the nearby base metal will produce cracks. Welding performance in terms of serviceability refers to the impact toughness at the weld and the ductility in the heat-affected zone. It is required that the mechanical properties of the weld and the steel in the heat-affected zone are not lower than those of the base metal. Our country adopts the welding performance test method in the welding process and also adopts the welding performance test method in terms of usability and use.

6. Durability

There are many factors that affect the durability of steel. First of all, the corrosion resistance of steel is poor, and protective measures must be taken to prevent steel from corroding and rusting. Protective measures include: regularly maintaining the steel paint, using galvanized steel, and using special protective measures in the presence of strong corrosive media such as acid, alkali, and salt. For example, the offshore platform structure adopts "anode protection measures to prevent jacket corrosion. Zinc ingots are fixed on the frame, and the seawater electrolyte will automatically corrode the zinc ingots first, thereby achieving the function of protecting the steel jacket. Secondly, under the action of high temperature and long-term load, the failure strength of steel is much lower than the short-term strength, so it is not suitable for long-term high temperatures. For the steel under the action, the durable strength should be measured. The steel will automatically harden and become brittle over time, that is, the "aging" phenomenon. The impact toughness of the steel under the low-temperature load should be tested.

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