What Is the Yield Point?

When the steel or specimen is stretched, when the stress exceeds the elastic limit, even if the stress no longer increases, the steel or specimen continues to undergo significant plastic deformation. This phenomenon is called yielding, and the minimum stress value when yielding occurs is For the yield point. With the development of building seismic technology and in-depth analysis of anti-seismic mechanism, energy dissipation earthquake resistance has become a development trend of building seismic technology. Low yield point steel, as the material for the main components in energy dissipation and seismic design, has attracted widespread attention since the 1990s, and has made significant progress in the research and development of steel grades and engineering applications.

Metal material with yield phenomenon, the sample is not strong during the tensile process

In addition to the high strength and good plasticity required for general structural seismic steels, the steel's strain aging sensitivity, brittle transition temperature, low cycle fatigue resistance, and welding properties must also be considered. Low yield point steel is mainly used to make energy dissipation dampers, and its seismic method determines the performance requirements of steel.

In an earthquake, the energy dissipation damper is required to withstand the seismic load before other structural parts, and it repeatedly deforms and absorbs seismic energy in the plastic area to achieve the purpose of earthquake resistance. Therefore, the low yield point steel must have a very low yield point and the yield range should be controlled within a narrow range. At the same time, it must have good processing and welding properties, and good plasticity, so it has good deformation ability.

In addition, seismic steel is subjected to repeated alternating loads during earthquakes. The duration of a strong earthquake is generally within 1 min, and the amplitude frequency is usually 1 to 3 Hz. It causes damage to the building within 100 to 200 cycles, which belongs to high strain and low cycle fatigue. Therefore, low yield point steel is required to have good low cycle fatigue resistance.

Energy dissipation dampers use soft steel's good hysteresis to dissipate the input seismic energy. During an earthquake, these dampers are subjected to seismic load before other structural components, and they yield first. The repeated energy hysteresis absorbs seismic energy and the seismic effect Better, the low yield point steel (or soft steel) used to make these energy dissipation dampers has become a new type of steel for seismic applications ^[2]

Low yield point steel is mainly used to make energy dissipation dampers for earthquake resistance, which is also known in the literature as energy dissipation dampers or seismic control devices, energy dissipation components or stiffening dampers (ADAS, added damping and stiffness). Etc., or energy dissipation is called energy dissipation.

Traditional seismic design relies on the deformation of building columns and beams to absorb seismic energy, and the deformation of its main structural parts is difficult to repair after the earthquake. The energy dissipation damper absorbs seismic energy by its repeated deformation, which effectively protects the safety of the main building. Moreover, these damper components are only a component of the lateral force resistance component, and its yield energy does not affect the load bearing capacity of the structure. Compared with other shock-absorbing materials, it has the advantages of simple structure, economy and durability, easy replacement after the earthquake, and strong reliability. It can be used for the earthquake resistance of new buildings and the improvement of earthquake resistance of old buildings. At present, unconstrained columns, steel shear walls, various types of shock absorbers and other seismic facilities made of low yield point steel have been widely promoted in many countries represented by Japan, and a large number of related seismic design technologies have been generated. .

Studies have shown that the core of an unconstrained column contains steel pipes and mortar to prevent deformation and to have stable recovery characteristics for tensile and compressive stresses. Full-size, large-capacity unconstrained column tests have confirmed its recovery characteristics and stress distribution, secondary bending moment effects, and the safety of steel pipes. Unconstrained columns made of ultra-high-strength steel and ultra-low-yield-point steel have been used to make new types of seismic structures. For example, elastoplastic hysteresis shear steel walls made of low yield point steel can fully maintain stability under large deformation conditions, and can be used as high toughness members for energy dissipation and earthquake resistance of buildings.

Chen et al. Studied the periodic behavior of low-yield steel shear walls. In the low-yield-point steel shear wall system, a low-yield-point steel plate is used as the steel guard plate, and traditional structural steel is used as the side frame. A series of experimental studies have been performed under alternating loads, and the low-yield-point steel shear force has been tested. The rigidity, strength, deformability and energy dissipation of the wall.

At the same time, the effects of the width-to-thickness ratio of the steel plate, the continuity of the shear wall, and the column-beam connection design of the side frames were analyzed. The results show that all the tested samples have good energy dissipating effects, and the rigid shear wall system and frame shear wall system have good deformation ability.

In addition, Susantha et al. Used the thickness and cross-section structure of the low yield point steel plate as the main variables to test, and studied the improvement of the ductility of steel bridge piers by low yield point steel. The results show that, compared with piers without low-yield-point steel, piers strengthened with low-yield-point steel plate with appropriate thickness have better ductility and energy dissipation.

In China, the seismic research on energy dissipation dampers made of low yield point steel has also become the focus of researchers. Through theoretical analysis and real-world seismic simulation, the seismic performance of X-shaped and triangular dampers and seismic columns of various structures are studied, and the design and test methods of these soft steel dampers are systematically summarized.

Ou Jinping and others carried out fatigue test research and theoretical analysis of the X-shaped steel plate yield damper, established the elastoplastic strain analysis method of the damper steel plate and the fatigue design criteria of the X-shaped and triangular steel plate damper. Guo Anxiu et al. Used low-cycle fatigue damage as the failure mode of soft steel dampers, established a method for probabilistic analysis of the amplitude of hysteretic deformation and the number of hysteretic cycles, and proposed the reliability of soft steel dampers under large earthquake Analytical methods. Zhou Yun introduced the test results, analysis model, design method and engineering application of the stiffening damper and the structure equipped with the stiffening damper.

According to the research and application of energy-consumption and vibration reduction technology at home and abroad, some directions for the future development of energy-consumption and vibration reduction technology and several issues to be further studied are proposed. China's "Code for Seismic Design of Building Structures" (GB50011-2001) also adds relevant content on seismic isolation and energy dissipation, which provides a reference for the application of energy dissipation technology.

In addition, Cai Kezhen and others studied the seismic behavior of low-yield-point steel made of anti-seismic column structures. The test results show that the three-stage design of seismic columns has good seismic performance. Li Yushun et al. Studied the seismic performance of steel frame structures with low yield point steel dampers. During the test, the frame column and the intermediate column were always in the elastic deformation range, and the soft steel damper produced a large plastic deformation, and the structural displacement was significantly reduced, indicating that it can effectively suppress the seismic response of the structure.

At present, every year, a large number of high-rise buildings abroad use low yield point steel dampers to improve the seismic resistance of buildings. China s seismic components made of low yield point steel have just started, and only a few new buildings use this. Anti-seismic technology.

China is a country prone to earthquakes. With the increase of high-rise buildings in our country and the improvement of the design level of high-rise steel structures, the future market prospect of low-yield point steel will be very broad ^[3]

(1) With the development and improvement of energy dissipation technology, the use of energy dissipation dampers has gradually become popular, and low yield point steels used to make energy dissipation dampers have gradually become one of the key products in seismic steels.

(2) From the current research, the measure to reduce the strength of the steel plate to less than 100 MPa is to reduce the C content in the steel, and eliminate the free C and N atoms in the steel by adding Ti and Nb to reduce its dislocation movement. Obstacle, the use of tempering on the basis of grain coarsening to further increase the grain size.

(3) The development of seismic technology for high-rise buildings has caused widespread research and development of low-yield point steels. With the increase of China's high-rise buildings and the promotion of steel structures, low-yield point steels will have a broad market prospect ^[1] .