With a design life of 120 years, what are the "special features" of the steel used in the Hong Kong-Zhuhai-Macao Bridge?
Nandu News The design life of 120 years, the Hong Kong-Zhuhai-Macao Bridge has broken the "100-year-old practice" of domestic bridges. What kind of steel can help the Hong Kong-Zhuhai-Macao Bridge to withstand typhoons, earthquakes, and seawater erosion for such a long time? Nandu reporter visited Baosteel Group Guangdong Shaoguan Iron and Steel Co., Ltd. (hereinafter referred to as "Shaogang"), one of the important steel suppliers of the Hong Kong-Zhuhai-Macao Bridge, to reveal the "special function" of the steel used to build the Hong Kong-Zhuhai-Macao Bridge from various aspects. It is understood that Shaogang supplies 70% of the Hong Kong-Zhuhai-Macao Bridge's rebar, disc screws, high-speed wires, epoxy-coated rebar base materials used for all steel box beams and piers, and some low-alloy high-strength structural steel plates and bridges. Plates for steel structures.
Special composition design enhances fatigue resistance of steel
What kind of steel can meet the needs of this "Big Mac" project? Song Jianqin, deputy director and senior engineer of Shaogang ’s Manufacturing Management Department (Technical Research Center) said that the Hong Kong-Zhuhai-Macao Bridge is a sea-crossing bridge. Therefore, it is necessary to consider the problem of long-term exposure of the pier to seawater. The bridge is also tested by the typhoon. In addition, the need for earthquake resistance must be considered. And every day, when cars come and go, steel also needs good anti-fatigue performance. "To sum up, the four aspects of mechanical properties, seismic performance, fatigue resistance and process connectivity must meet very high requirements," Song Jianqin told Nandu reporter. After receiving the order from Hong Kong-Zhuhai-Macao Bridge, Shaogang organized A dedicated research and development team conducts research and development of steel for the Hong Kong-Zhuhai-Macao Bridge.
How to make steel with excellent mechanical properties, seismic performance, fatigue resistance and process connection performance? Song Jianqin introduced that to achieve these properties, we must first design the material composition. "We have a special design for the composition of steel." He revealed that all steel used in the Hong Kong-Zhuhai-Macao Bridge has a narrow-band control of the composition. "Bills whose composition is not within the control range are not allowed to be used to produce steel bars for the project to prevent The effect of composition fluctuations on the strength properties of steel bars. "" To achieve high fatigue resistance,the molten steel must be high in purity, and efforts must be made to reduce harmful impurities. "It is understood that in order to achieve this goal, Shaogang provided steel for Hong Kong-Zhuhai-Macao Bridge All the molten steel is processed through refining, which makes the composition uniform, reduces inclusions, and improves the purity of the steel.During the rolling process of the steel bar, the rolling temperature will also affect the strength properties of the steel bar. Therefore, in accordance with the requirements of the Hong Kong-Zhuhai-Macao Bridge, Shaogang has specially designed the rolling process temperature. "We have carried out narrow-band control, which requires a rolling temperature of ± 15 ° C, a final rolling temperature of ± 25 ° C, and an upper cooling bed temperature of ± 10 ° C to prevent the influence of temperature fluctuations on the strength performance of the reinforcement." The cooling speed of the reinforcement must also be controlled Within a certain range. Song Jianqin introduced that too fast cooling will be more “brittle” and easily broken. "It needs both good strength and high toughness."The original production of 1,000 tons of rebar can only produce 300 tons As a sea-crossing bridge, the pier of the Hong Kong-Zhuhai-Macao Bridge will face seawater erosion. "Mainly because a large part of the bridge pier is underwater, it will be affected by the chlorination of seawater," said Song Jianqin. In order to resist the effect of chlorination, the steel bars used are epoxy-treated, that is, The electrostatic spraying method is used to spray epoxy powder on the surface of ordinary ribbed steel bars or ordinary light round steel bars to form a steel bar whose surface is a fusion bonded epoxy coating. It is understood that the surface of the epoxy-coated steel bar is smooth and has good corrosion resistance, and is suitable for industrial and civil buildings, roads, bridges, ports, docks and other reinforced concrete structures in humid environments or aggressive media. The epoxy coating on the surface of steel requires very high surface quality and appearance quality. Therefore, the Hong Kong-Zhuhai-Macao Bridge should not have sharp corners, burrs or other defects that affect the quality of the coating on the surface of the rebar, and must avoid pollution by oil, grease or paint. "Take rebar, for the beginning, we found that ordinary rebar is difficult to spray epoxy powder," Wang Cairen, assistant to the director of Shaogang Special Rolling Mill, told Nandu reporters that professional technicians were sent to this plant. Learn about spraying technology in Zhuhai, Lufeng and other places. "After returning, we modified the parameters of the finished hole, increased the helix angle and oblique angle of the transverse ribs, and finally achieved the requirements of the Hong Kong-Zhuhai-Macao Bridge through multiple modifications." Reduce the use quota of the finished hole type. Under normal circumstances, each hole can produce 1,000 tons of rebar, but when producing steel for the Hong Kong-Zhuhai-Macao Bridge, the hole must be replaced every 300 tons.
There must be no oil on the surface of the steel bar
The steel bars used in the Hong Kong-Zhuhai-Macao Bridge project not only have high requirements for performance, but also have high requirements for the surface quality of the steel bars: the surface must be smooth and clean, and free of oil and rust. However, from the production, hoisting, storage, delivery to the site of the construction site, there are multiple links, and accidental dripping of dirty oil will occur. Wang Cairen and Qiu Weifeng, the director of bar products of the manufacturing management department, still remember the first batch of steel bars shipped to the Hong Kong-Zhuhai-Macao Bridge. At that time, more than 2,000 tons of steel bars had been piled up at the Hong Kong-Zhuhai-Macao Bridge dock, but due to oil pollution on some surfaces, the project party did not agree to receive the goods. "At that time, one of our deputy directors personally took someone to remove all the oil on the surface of more than 2,000 tons of steel with degreasers in Curry and the port." Wang Cairen told reporters. Shaogang workers are cleaning the oil from the steel. At the same time, the general manager of the company personally led the deputy general manager in charge of production and quality and the leaders of the production department, quality department, sales department, storage department, production plant and other units to the production plant site to hold a cause analysis and solution meeting for the oil pollution problem on the steel bar surface We will track and find the cause of the oil pollution on the spot together. It was found that the main reason for the oil pollution on the surface of the steel bar was that during the lifting or stacking of the steel bar, the oil on the surface of the steel bar caused oil leakage due to the leakage of lubricant oil from the lifting equipment such as cranes, wire ropes and other equipment onto the steel bar. "For this reason, we immediately formulated a series of control measures," said Qiu Weifeng. Shaogang quickly checked and replaced the oil leakage equipment, installed the oil receiving device on the crane, replaced the wire rope, used oil-free spreaders, and steel bars. Stacked with stamped canvas, etc. "The steel wire ropes we used to tie the steel bars were all oily. With the use of lubricants, the life limit will be longer, but it will inevitably make the steel surface oily," Wang Cairen pointed to a pile of steel bars in the steel bar production workshop. Steel Wire Rope told reporters that since supplying products for the Hong Kong-Zhuhai-Macao Bridge, the factory has been replaced with oil-free steel wire rope. The cost will be higher, but it will not cause pollution to the surface of the steel bars."In fact, by providing products for such demanding projects as the Hong Kong-Zhuhai-Macao Bridge, it is also an improvement for us. Since then, we have higher requirements for many products." Song Jianqin said.
