Vortex vibration of Humen Bridge: There is no consensus on the cause of continuous vibration, it is recommended to improve the monitoring system
Due to obvious vibrations visible to the naked eye, the Humen Bridge connecting Nansha District of Guangzhou City and Humen Town of Dongguan City has been closed for more than 2 days since the afternoon of May 5. This is not unusual for the 23-year-old bridge across the sea and the citizens of Guangzhou and Dongguan living on both ends.
On the morning of May 6, Guangdong Transportation Group issued a report saying that the expert group judged that the vibration of the Humen Suspension Bridge was mainly due to the continuous installation of water horses along the bridge's side rails, which changed the aerodynamic shape of the steel box girder. Next, the bridge vortex vibration occurs.
On the afternoon of the incident, after the water horse was withdrawn, the vortex vibration was suspended at 18:00, however, at 2:00 that night, the vortex vibration occurred again on the Humen Bridge, and it continues to this day. On the evening of May 7, a spokesman for the Humen Bridge told the Beijing News reporter that the bridge is still slightly vibrating with the naked eye, and the inspection of the bridge is continuing. The bridge is still closed.
Several experts involved in the investigation said that the Humen Bridge's vortex vibration amplitude is within the safe range and will not affect the structural safety of the suspension bridge's subsequent use. However, an expert who did not wish to be named told the Beijing News that the experts failed to reach a consensus on the reasons for the continuous vibration of the bridge. Several experts suggested that Humen Bridge should improve its monitoring system.
"It's like a roller coaster"
At 7 pm on May 4th, Shenzhen citizen Yang Xu (pseudonym) carried his wife and drove back to Shenzhen from Guangzhou. As he walked to the middle of the Humen Bridge, Yang Xu suddenly felt the longitudinal vibration of the bridge deck, "like a roller coaster, one by one."
Yang Xu recalled that the amplitude of the bridge deck was relatively large at that time, "the vehicles in front were also going up and down suddenly." People feel weightless when throwing in the car, he and his wife sitting in the passenger seat feel dizzy and vomiting.
As the vibration continued, Yang Xu was a little nervous. He opened the window and accelerated away from the bridge in two or three minutes, and the sense of vibration disappeared.
The "moment of shock" experienced by Yang Xu was felt by many citizens who passed the Humen Bridge that day and the next day. A netizen said on social media that on the afternoon of May 5, when he passed the Humen Bridge from the direction of Humen-Nansha, the bumps on the bridge surface continued for tens of seconds. Not light ". He recalled that the driver initially thought it was a flat tire, but soon discovered that the vehicle in front was also "swinging like a wave" with the bridge deck.
Another video posted by a netizen who passed the Humen Bridge at 2 pm on May 5th showed that the weather was clear on that day, and the traffic on the bridge was not dense. On the right side of the screen, a vertical red water horse can be seen. The video continued for two. Seconds, at the end of the picture there is a clear sense of upswing. In the comment column, the netizen said that he thought it was caused by low blood sugar. Many netizens replied that they had the same experience, some thought that the road was uneven, and some thought that the vehicle they used had a flat tire.
According to public information, the main bridge of the Humen Bridge, where the vibration occurred, is the first large-span steel suspension bridge designed and constructed by China, with a total length of 888 meters. Since its completion in June 1997, the Humen Bridge has passed 23 years of wind and rain, and it is an important channel for crossing the river between Nansha in Guangzhou and Humen in Dongguan. Judging from public reports, no similar incidents have occurred in the Humen Bridge before.
At 15:32 on May 5, the Guangzhou Traffic Police Detachment announced that traffic control of the Humen Bridge was carried out. Subsequently, some media learned from the Traffic Management Bureau of the Public Security Bureau of Guangdong Province that the Humen Bridge was abnormally shaken, and the bridge management department had closed the bridge.
On the evening of May 7, a spokesman for the Humen Bridge told the Beijing News that the bridge will remain closed on the evening of the 7th.
The maximum amplitude of one side of the bridge deck reaches 31 cm
On the evening of May 5, the Guangdong Provincial Transportation Group issued a notice saying that at 15:20 on May 5, the suspension deck of the Humen Bridge was greatly affected by the wind speed of the main bridge, causing vortex vibration.
Cheng Shu (pseudonym), a road and bridge expert involved in the investigation, told the Beijing News that he learned from the Humen Bridge that the maximum amplitude of the unilateral side of the bridge deck reached 31 cm at the time of the incident.
Because the bridge was being repaired at the time of the incident, some netizens suspected that the generation of vortex vibration was related to the high load of the bridge. On the evening of May 6, at a media communication meeting held by relevant departments in Guangdong Province, Wu Mingyuan, a member of the on-site disposal expert group and the business director of CCCC Highway Planning and Design Institute, said that there are load standards in bridge design, as long as the load standards On the basis, the operation of the bridge is safe. "Especially Humen Bridge, due to various reasons and limited load regulations, so under the current conditions, it is safer than other large bridges."
The cause of the vortex vibration was quickly focused on the two rows of 1.2-meter-high red water horses (segmenting the road surface or forming obstructions of the plastic shells) arranged inline on the bridge deck.
On the evening of May 5, Zhang Xinmin, deputy chief engineer of the Humen Bridge Overhaul Office, said in an interview with CCTV that the experts discussed that the main reason for vortex vibration is that the water horses placed along the guardrail column block the ventilation hole of the guardrail column during bridge deck maintenance , Changing the wind-resistant shape of the bridge, which in turn produces vortex vibration. After the water horse was removed, and the wind speed decreased that night, the vortex vibration has been significantly reduced.
On the morning of May 6, Guangdong Transportation Group also issued a notice that the expert group judged that this vibration was mainly due to the continuous installation of water horses along the bridge's side rails, which changed the aerodynamic shape of the steel box girder. Under certain wind conditions, Bridge vortex vibration occurs.
"Vortex vibration occurs because the structure's natural vibration frequency and the frequency of vortex shedding are consistent, and resonance occurs." Cheng Shu explained to the Beijing News reporter. The so-called "vortex detachment" means that when the cross section of the bluff body is subjected to uniform flow, a vortex shedding is formed behind the cross section. The generation of vortex is not only related to wind direction and speed, but also affected by the shape of bridge cross-section and structural damping.
Zeng Xianwu, one of the designers of the Humen Bridge and a bridge expert, told the Beijing News that the Humen Bridge had undergone wind tunnel tests during the design and construction to test the wind resistance of the bridge. The section of the steel box girder of the Humen Bridge is streamlined. In order to minimize the influence of wind on the vibration of the bridge body, the designers have added deflectors at the positions of the air nozzles on both sides.
Cheng Shu said that according to the original design of the Humen Bridge, vortex vibration would not occur in theory, but adding a water horse to the bridge deck changed the aerodynamic shape of the bridge.
Ge Yaojun, a professor of the Department of Bridge Engineering at Tongji University, further explained that in addition to the change in the aerodynamic shape of the bridge in the afternoon of the 5th, the specific wind speed and wind direction are also one of the conditions. "The weather in Guangzhou has been very good in these two days, the wind speed is relatively uniform, and the angle of the wind will not change, so it is easier to cause vortex vibration."
However, Ge Yaojun also said that from the perspective of wind direction, there are 16 wind directions, and the probability of reaching a specific wind direction is one-sixteenth. At the same time, there are also requirements for wind speed. Therefore, the occurrence of eddy vibrations in the bridge is a "small probability event" ".
In response to reports from some citizens that they felt vibrations after crossing the bridge on the afternoon of May 4th, Liao Haili said, "The first time I said it happened on May 5th may be the most serious time, but before that, this vortex vibration Little by little, there is a process from small to large. "
Ge Yaojun also believes that the abnormal vibration may occur earlier than May 4. According to their understanding, as early as the end of April, water horses were placed on the bridge deck, but the number was not large, so the amplitude was not large.
There is no conclusion about the cause of the vibration
According to a report by the Beijing News, vortex vibration was suspended at 18:00 on the afternoon of the incident after the water horse was withdrawn. However, at 20 o'clock that day, vortex vibration occurred again on the Humen Bridge.
On the evening of May 7, a spokesman for the Humen Bridge told the Beijing News reporter that at present, the bridge is still slightly vibrating with the naked eye, and the detection of the bridge is continuing. There is no conclusion on the cause of the continuous vibration.
On the evening of May 6, in response to media questions, Wu Mingyuan, a member of the on-site disposal expert group, said that the Humen Bridge weighs more than 15,000 tons. Once vibration occurs, "it will take enough time to calm down."
Liao Haili, a professor at the School of Civil Engineering of Southwest Jiaotong University, also told the Beijing News reporter that from the current investigation, the water horse is the main cause of the vortex. The water horse is removed and the incentive is eliminated. "But the wind has some force on the bridge, but it is smaller than the water horse. When the energy is slowly dissipated, it should stay still."
On the afternoon of May 7, Guangdong organized another expert meeting. Cheng Shu told the Beijing News reporter that at the meeting, the experts made it clear that the subsequent vibration still belongs to vortex vibration, but there is no consensus on the reasons for the continued vortex vibration. Some people think that after closing, the bare box beam may also be one of the incentives for the continued vortex. Participants also had different views on whether the bridge can be restored to traffic.
Cheng Shu said that at the meeting, he and some experts suggested that Humen Bridge should improve the monitoring system.
A reporter from the Beijing News found that as early as 2002, scholars from the Department of Civil Engineering of Tsinghua University published a paper saying that in cooperation with Humen Bridge Co., Ltd., the GPS displacement monitoring system and strain monitoring system for the main span of the Humen Bridge were developed and put into operation. . The article introduces that the system is designed to monitor the strain response of the bridge box girder caused by vehicle load, wind load, earthquake load, etc. during the use of Humen Bridge, to achieve real-time monitoring, real-time analysis and alarming, and data network sharing.
However, Cheng Shu stated that during the investigation, the staff of the Humen Bridge provided the experts with wind speeds at four points of the bridge. Vibration related data, but did not see it in the afternoon meeting. He believes that although the Humen Bridge has a detection system, it does not seem to be complete. "We are asking them to improve."
On May 6th and 7th, a reporter from the Beijing News repeatedly contacted Zhang Xinmin, deputy chief engineer of the Humen Bridge Overhaul Office, to try to inquire about the reasons for the continued vortex vibration and the operation of the monitoring system.
Beijing News reporter Zhang Huilan intern Cao Yifan