China News Agency, Dongguan, May 6 Question: Humen Bridge's jitter has basically subsided and the opening time has not yet been determined
Author Cai Minjie
The abnormal shaking event of the Humen Bridge caused social concern. The famous bridge expert Wu Mingyuan said at the Q & A meeting of Humen Bridge vortex reporters on the evening of the 6th that the shaking of the Humen Bridge has basically subsided. According to the current test results, the vortex vibration has not affected the overall structure of the Humen Bridge.
Humen Bridge is a cross-sea bridge connecting Nansha District of Guangzhou City and Humen Town of Dongguan City in Guangdong Province, connecting both sides of the Pearl River and communicating with important cities such as Shenzhen and Zhuhai. The Humen Bridge started construction in 1992 and was opened to traffic in 1997.
Talking about the reason of jitter: the water horse changes the "aerodynamic shape" of the steel box beam
On the 5th, the Humen Bridge was abnormally shaken, the suspension bridge deck swayed relatively large, and the amplitude was relatively obvious, which caused discomfort to the traffic. In the early morning of the 6th, Guangdong Provincial Transportation Group said that according to the preliminary judgment of the expert group, the main reason for the vibration of the suspension bridge of Humen Bridge is that the continuous installation of water horses along the span of the bridge changes the aerodynamic shape of the steel box girder. Next, the bridge vortex phenomenon is generated.
The cause of vortex vibration is that after the wind flows through the cross section of an object, a periodic vortex shedding occurs behind the object, thereby generating a periodic forcing force on the structure.
Zhang Xinmin, deputy chief engineer of Humen Bridge, introduced that the water horse is equivalent to forming a wall in the longitudinal direction. The wind can not pass through, and the wind resistance becomes larger, so the impact on the bridge will be greater. "Erecting a water horse on the bridge deck is equivalent to changing the shape of the bridge. During the inspection work, real-time analysis will be carried out, and well-known experts from Mainland China will be invited to assess and analyze this piece. "
Wu Mingyuan said that after the noon on the 6th, the shaking of the Humen Bridge has basically subsided. According to the current test results, the vortex vibration has not affected the overall structure of the Humen Bridge.
Talk about continuous jitter: need enough time to calm down
From the surveillance video of the Humen Bridge Management Center, it can be seen that the water horses along the bridge's side fences began to be removed at 15:50 on the 5th, and they were removed at 17:42, but there were still jitters afterwards.
Zhang Xinmin, deputy chief engineer of Humen Bridge, said that due to the influence of wind and inertia, a structure will not stop immediately after vibration, but the energy consumption can eventually be eliminated. At present, vortex vibration has no effect on the structural safety of the bridge.
Wu Mingyuan said that the Humen Bridge is a large suspension bridge with a main span of 888 meters and weighs more than 15,000 tons. After vibration, it needs enough time to calm down. Twenty hours after the first occurrence of vortex vibration, that is, at 12:30 on the 6th, the vibration has subsided. In addition, the vortex vibration is generated under low wind speed. The average wind speed of the Humen Bridge deck is about 10 meters per second. It affects the comfort of vehicles. Unlike flutter, it affects the safety of the bridge. The main structure of the current bridge is safe.
Talking about vortex and flutter: the two are different in nature
Wu Mingyuan said that there will be two kinds of vibration in the suspension bridge, one will affect the comfort, called vortex vibration; the other will affect the safety of the bridge, called flutter, "This time it is mainly the vortex vibration that affects comfort, and the vortex vibration will not The bridge has a great impact. If eddy vibration occurs for a long time, fatigue problems will occur, but the bridge as a whole tends to be calm. "
"From our understanding, it is safe, and the Tacoma Strait Bridge belongs to flutter due to damage caused by design reasons. There is a big difference between the two bridges." Wu Mingyuan said.
Talking about the opening time: it is not sure yet
As for whether the Humen Bridge is overloaded, Wu Mingyuan said that it is safe to operate within the bridge load test standards. Recently, the Humen Bridge has imposed restrictions on vehicles such as large trucks, which is relatively safe.
Wu Mingyuan said that there is no problem with the safety of the bridge, and experts continue to conduct judgments on the evening of the 6th.
Zhang Xinmin said that the bridge is currently undergoing a comprehensive inspection. As for when it will be opened to traffic, it is still uncertain. (Finish)