Steel Structure Knowledge

1. The steel structure system has the comprehensive advantages of light weight, easy installation, short construction period, good seismic performance, fast return on investment, less environmental pollution, good plasticity and toughness, and good impact resistance.
2. The types of steel are: according to different thicknesses, thin plates (thickness of thin steel plates <4mm), medium plates (medium thickness 4-20mm) and thick plates (thickness 20-60mm) greater than 60 are extra-thick species. Of course, this division method is not strict, and the differentiation methods of different steel traders in different regions are also different.
3. What is the difference between ordinary bolts and high-strength bolts?
Ordinary bolts are generally made of ordinary carbon structural steel, without heat treatment, and high-strength bolts are generally made of high-quality carbon structural steel or alloy structural steel, which need to be quenched and tempered to improve the comprehensive mechanical properties. The high strength is divided into 8.8 grades, 10.9 grades, and 12.9 grades.
From the strength grade: high-strength bolts are commonly used in 8.8S and 10.9S two strength grades. Ordinary bolts generally have 4.4 grades, 4.8 grades, 5.6 grades, and 8.8 grades.
From the stress characteristics, the high-strength bolt applies pretension force and transmits the external force by friction, and the ordinary bolt transmits the shear force by the bolt rod shear force and the hole wall pressure.
According to the force characteristics, it can be divided into: friction type and pressure type. Friction type high-strength bolts are based on the friction between the connected parts to transmit the external force, when the shear force is equal to the friction force, the design limit load of the extremely friction type high-strength bolt connection. At this time, the rods of Lianzhong will not slip relatively, the bolt rod will not be sheared, and the bolt hole wall will not be pressurized. The pressure-bearing high-strength bolt is similar to the ordinary bolt, the shear force can exceed the friction force, and the relative slippage will occur between the connected components at this time, and the bolt rod is in contact with the hole wall, and the connection relies on the friction force and the shear and pressure of the bolt rod to transmit force together.
The deformation of pressure-bearing high-strength bolts is large, and it is not suitable for the connection of structures that directly bear dynamic loads.
5. There are several types of welding rods
There are more than a dozen types: carbon steel electrodes, low-alloy steel electrodes, molybdenum and chromium-molybdenum heat-resistant steel electrodes, low-temperature steel electrodes, stainless steel electrodes, hardfacing electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes, aluminum and aluminum alloy electrodes and special-purpose electrodes.
6. Non-destructive testing is a test method to check the surface and internal quality of the inspected parts without damaging the working state of the workpiece or raw materials.
Common non-destructive testing methods:
Ultrasonic flaw detection: a method of using ultrasonic energy to penetrate into the depths of metal materials, and when entering another section from one section to another, the characteristics of reflection at the edge of the interface are used to check the defects of parts, when the ultrasonic beam passes from the surface of the part to the inside of the metal, and the reflected waves occur respectively when the defect and the bottom surface of the part are encountered, and pulse waveforms are formed on the fluorescent screen, and the location and size of the defects are judged according to these pulse waveforms.
Radiographic flaw detection (X-ray, γ-ray): A flaw detection method that uses rays to penetrate an object to find internal defects in an object.
Magnetic particle testing: It is an inspection method used to detect surface and near-surface defects in ferromagnetic materials. When the workpiece is magnetized, if there is a defect on the surface of the workpiece, due to the increase of the magnetic resistance at the defect, magnetic flux leakage is generated, and a local magnetic field is formed, and the magnetic particle will show the shape and position of the defect here, so as to judge the existence of the defect.