Exchange of experience: wind-resistant countermeasures for long-span bridges (1)

The official completion and opening to traffic of Jiangyin Yangtze River Bridge indicates that China has the first suspension bridge exceeding 1,000 meters, and at the same time it has become the sixth country in the world to build a 1,000-meter bridge. Since China's reform and opening up in the early 1980s, more than 100 cable-stayed bridges have been built in China, making it the country with the largest number of cable-stayed bridges in the world. If we count the second Nanjing Yangtze River Bridge and Fuzhou Minjiang Bridge, which will be completed in 200 1, the cable-stayed bridges in China have occupied a very important position in the world over 500m .. 1996 China People's Communications Publishing House published the first Guide to Wind-resistant Design of Highway Bridges written by Tongji University and China Communications Highway Planning and Design Institute, which has been widely used in wind-resistant design of many large road bridges in recent years. On this basis, entrusted by the Ministry of Communications, Tongji University, China Communications Highway Planning and Design Institute, Central Institute of Meteorology and Xi 'an Highway Jiaotong University conducted special studies on several key issues, which laid the foundation for the final formation of the Code for Wind-resistant Design of Highway Bridges. This paper mainly introduces several main problems in the compilation of this code, including the determination of basic wind speed, the expression of wind load, the dynamic stability test of bridges and the requirements of wind tunnel test.

National basic wind speed and wind pressure

The basic wind speed is defined as the annual average wind speed above the ground 100 m height 100 once a year 10 minute under the open and flat terrain conditions in the bridge area.

In the compilation of this specification, the wind speed data recorded by 657 basic stations in China 196 1 995 are adopted, and the extreme value I distribution curve is used for fitting, and the reference height is changed from the original 20m height to 10m height, and the return period of 100 is considered. In view of the fact that there are quite a number of meteorological stations in China, due to the rapid development of urban construction in recent years, the station environment can not meet the requirements of open space and no shelter, which leads to the obvious small wind speed record caused by human factors. In this study, referring to the situation of surrounding stations, some calculation results are revised appropriately. At the same time, referring to other domestic codes, the lower limit of basic wind pressure is determined to be/kloc-0.35kn/m2 once every 0/00 years, 0.30kn/m2 once every 50 years and 0.20kn/m2 once every 0/00 years, and the corresponding lower limits of basic wind speed are 24m/s, 22m/s and18m/respectively. The national basic wind pressure map and wind speed map have the following characteristics:

1. The southeast coast is the wind pressure area of Chinese mainland. The wind pressure isoline is roughly parallel to the coast, and the wind pressure decreases rapidly from the coast to the inland. The wind speed at 50 km from the coast is about 75% of that at the seaside, and only about 50% at 100 km, which is related to the typhoon, the main weather system that causes strong winds in this area. There are roughly three extreme wind pressure areas in this area, namely, from the south of Zhanjiang to the coast of Hainan, the coast of Guangdong and the coast of Zhejiang to the central part of Fujian. The once-in-a-century wind pressure is above 0.90 kn/m2 (38m/s). Due to the typhoon barrier of Taiwan Province Island, the wind pressure in southern Fujian has weakened.

2. North-west and middle-northeast of North China are the wind pressure sub-regions of Chinese mainland. The gale in this area is mainly related to the strong cold air activity caused by the Siberian cold current, and the gradient of the isowind pressure line decreases from north to south.

3. Qinghai-Tibet Plateau is a region with high wind pressure. The gale in this area is mainly caused by high altitude. However, the air density in this area is relatively low, so although the wind speed is very high, the wind pressure formed is relatively small.

4. The wind pressure in Yunnan-Guizhou Plateau, the middle reaches of the Yangtze River and the southern hilly areas is relatively low, especially in central Sichuan, Guizhou, western Hunan and western Hubei. The wind pressure in most areas is below 0.4 kn/m2 (25m/s).

5. The wind pressure in Taiwan Province Province, Hainan Island and South China Sea Islands is sub-regional, and Taiwan Province Province is the wind pressure area in China. According to the analysis, the wind pressure along the eastern coast can reach more than 175kn/m2 (52m/s). The wind pressure on the western, northern and eastern coasts of Hainan Island is about 0.9 kn/m2 (40m/s). The Xisha Islands are affected by the typhoon in the South China Sea, and the once-in-a-century wind pressure reaches 1.80 kN/m2 (54m/s). The wind pressure of other islands in the South China Sea is slightly lower than that of Xisha.

Generally speaking, the new wind pressure distribution map has not changed the original general pattern of wind pressure distribution in the whole country, and it has decreased and increased, but it should be said that it is more reasonable. Moreover, the number of stations calculated this time greatly exceeds any previous analysis, and the data age is generally 30 ~ 35 years, which represents the current climate background value.

For important long-span bridges, temporary wind speed observation stations should be set up, and the observation period should not be less than 1 year. The annual extreme wind speed is deduced from the obtained short-term wind speed data, and the correlation with nearby weather stations is established accordingly.