The Humen Bridge suddenly shakes in a "wave-like" way, and it's time for the Internet

On the afternoon of May 5, at the peak of the return trip from the May Day holiday, the suspension bridge deck of the Humen Bridge suddenly experienced abnormal "wave-like" shaking, with a relatively obvious amplitude, causing discomfort to driving. After the incident occurred, many netizens reported, “I felt like a flat tire while driving on the Humen Bridge”, “I felt like the bridge was undulating, like riding on a boat, and I felt a bit seasick”, “The shaking of the Humen Bridge made people dizzy. ,horrible"……

Subsequently, the Humen Bridge Company issued a notice announcing that from 15:20 on May 5, 2020, the Humen Bridge will be fully closed to traffic control. At the same time, in order to ensure the safety of passing ships, the Guangdong Maritime Safety Administration and the Guangdong Provincial Department of Transportation have agreed to implement temporary water traffic control at 18:15 on May 5, and from 19:00, the navigable waters near the Humen Bridge will be closed to navigation.

1. Introduction to Humen Bridge

The Humen Bridge is China's first large-scale suspension bridge. Its main channel span is 888 meters and is known as "China's First Span". The bridge structure is similar to the Parrot Island Yangtze River Bridge. As a key thoroughfare in the Guangdong-Hong Kong-Macao Greater Bay Area, the Humen Bridge has played an important role in the interconnection and economic prosperity and development of cities in the Guangdong-Hong Kong-Macao Greater Bay Area since its opening to traffic 23 years ago. At the same time, the continuous growth of traffic volume has also caused the traffic artery to be overwhelmed. It is understood that the traffic volume of the Humen Bridge has increased from an average of 18,400 standard vehicle trips per day when it was completed in 1997 to a maximum daily average of 170,000 standard vehicle trips, far exceeding the design standard of 80,000 standard vehicle trips per day, with a saturation level of 2.1.

After the bridge vibration occurred, domestic experts in related fields rushed to the site to conduct investigations and gave the most credible statement so far. It was initially determined that the vibration of the Humen Bridge was mainly due to the continuous installation of water horses (retaining walls) along the bridge span guardrail. ), destroying the cross-section streamline of the bridge, and under the specific wind environment conditions, the vortex vibration phenomenon of the bridge is generated.

The bridge professionals of the Humen Bridge immediately responded that the main structure of the Humen Bridge has not been damaged at present. At the same time, experts said that it is normal for the bridge to sway when encountering special wind conditions. Generally, the bridge deck will sway significantly when encountering vortex winds.

2. Causes of bridge vortex vibration

Xinhua News Agency reported that domestic experts in bridge-related fields also rushed to the site for inspection as soon as possible. 12 well-known domestic bridge experts held a meeting overnight to make judgments and gave authoritative answers:

The main reason for the vibration of the suspension bridge of Humen Bridge is that water horses (retaining walls) are continuously installed along the guardrail of the bridge span, which changes the aerodynamic shape of the steel box girder and produces bridge vortex vibration under specific wind environment conditions.

Large-span suspension bridges have vortex vibrations at low wind speeds. The vibration amplitude is small and difficult to detect. Large amplitudes will only occur under special conditions. It will not affect the safety of the bridge structure, but will affect the driving experience and comfort. , easily lead to traffic safety accidents.

According to the existing data and observed phenomenon analysis of the Humen Bridge, the "jitter" of the Humen Bridge suspension bridge did not damage the main structure of the bridge, nor will it affect the structural safety and security of the subsequent use of the Humen Bridge suspension bridge. Durability.

However, although the "shaking of the Humen Bridge" was a false alarm, it also sounded the alarm for us. In recent years, bridge collapse incidents have emerged one after another, posing a huge threat to people's lives and property, and causing many tragedies of family fragmentation.

The most famous example of bridge collapse due to external force is the Tacoma Narrows Bridge in 1940, which was also a suspension bridge, but it was suddenly destroyed by a breeze 4 months after it was opened to traffic. Back in China, a similar phenomenon occurred on the Yingwuzhou Bridge on the Yangtze River not long ago. It is very important to study the influence of wind force on bridges, so it is necessary to understand why bridges sway under the action of wind force.

The plane of the bridge is in the same direction as the wind. When the wind speed is not high, there will be no vibration. The reason for the vibration is that the wind speed increases, and cyclones will be generated on the plane of the bridge. These cyclones are distributed on the left and right sides of the bridge, which will cause vibration. The frequency is not synchronized with the bridge, causing the bridge to vibrate. This is the phenomenon of bridge vortex vibration, and its principle is caused by Karman vortex street.

Teachers from Dongguan University of Technology have specially conducted this Karman vortex street experiment. The experimental process is to use a piece of paper under the hair dryer. When the wind speed is relatively small, the paper will not sway. When the wind speed of the hair dryer is increased, the tail of the paper strip will swing. Although there are errors in the experiment, it can well explain the reason why the bridge swings under the action of strong wind.

3. Application of Internet of Things in bridge monitoring

In recent years, a series of bridge damage and even collapse accidents have reminded us that we must attach great importance to the health inspection and safety assessment of bridges, as well as the damage detection and monitoring of dangerous bridges, and strive to eliminate hidden dangers. Therefore, it is of great significance to monitor and evaluate the health status of bridges and master their health status. Bridge structure monitoring has also become the main technical means for bridge structure safety maintenance and normal use.

Obviously, it is impossible to rely on manpower alone in the monitoring process, not to mention time-consuming, labor-intensive and expensive costs, and it is impossible to achieve real-time monitoring. Therefore, the Internet of Things technology has become an indispensable and important link in the remote bridge structural health monitoring.

In the mid-to-late 1980s, the United States began to deploy sensors on some bridges to detect various basic parameters of bridges such as environment, load, vibration, and local stress, trying to find some mechanical laws through data analysis.

A total of more than 500 sensors are installed on the Sunshine Skyway Bridge in the United States. These sensors are mainly used to collect displacement, strain and temperature changes in various stages of bridge construction and operation. Finally, people can use this information to find out the bridge structure and bridge body. Material, changes over time.

In China, Humen Bridge, Xupu Bridge, Jiangyin Yangtze River Bridge and other bridges are in the construction stage. Engineers have installed sensors on the bridge body. These sensors can monitor various indicators and parameters of the bridge body in real time.

The Tsing Ma Bridge, Kap Shui Mun Bridge and Ting Kau Bridge in Hong Kong also installed the largest real-time safety monitoring system in the world at that time. The system included 900 various sensors, 9 computer-controlled information collection systems, and 2 computer workstations responsible for information processing and analysis systems.

According to the paper, the monitoring system of Humen Bridge has added monitoring systems such as GPS displacement, real-time strain, long-term deformation, and over-limit and overloading. Through the functions of these systems, the force and working status of the bridge under various conditions, as well as wind resistance and Seismic and other structural parameters to realize the safety monitoring of bridges.

Judging from the performance of the Humen Bridge monitoring system, the future market of the infrastructure monitoring system integrated into the Internet of Things will accelerate expansion. According to data, China currently operates 129,000 kilometers of railways and 200,000 bridges; the total mileage of highways is 142,600 kilometers and 825,500 bridges; there are more than 20,000 hydropower stations, more than 200 airports and other large public infrastructure. In these large infrastructures, not all facilities have a complete safety monitoring system. At the same time, with the support of new infrastructure, the demand and market for related monitoring systems will only increase significantly.

4. Solution scenarios of IoT in bridge inspection

As mentioned in the above article, heavy and overloaded driving and special weather will have an impact on the bridge itself. In addition, unreasonable design and construction, natural disasters, diseases of the bridge itself, and other activities may cause the bridge to collapse. Tragedy occurs.

There is great potential for integrating the "power" of new infrastructure into old infrastructure and using the capabilities of the Internet of Things and other technologies to ensure the security of "old infrastructure". For example, the problems faced by traditional bridges such as labor costs, knowledge reserves, and real-time monitoring will be solved by adding a few ordinary sensors, deploying and utilizing NB-IoT and 4G networks for information transmission. It is also possible to put an end to the imagination that "the Nanfang'ao Bridge has not been independently monitored for 21 years".

Scenario 1: Dealing with overloading of trucks

Install road pressure sensors at both ends of the viaduct, identify vehicle load and type through the Internet of Things, and connect with cameras to obtain license plate information of illegal vehicles. While performing hierarchical real-time alarms, the overall road load can also be counted.

Case: At present, the intelligent management platform of transportation facilities has been put into trial operation in Shanghai. In the future, once an overloaded freight truck illegally drives onto a viaduct, the coil embedded on the bridge will automatically sense the slight change in force and simultaneously alert the intelligent management platform. According to relevant engineering and technical experts, in the past, most of the monitoring of heavy vehicles on viaducts was manual observation. In the future, sensors with signal transmitting functions can be implanted in the road to monitor the load and operating status of each facility in real time. Once a truck exceeding the load of the bridge appears, the sensor can sense it in time and automatically alarm the monitoring platform. The staff will report the information, and law enforcement will deal with the illegal truck in a timely manner. At present, this technology has been put into trial operation in Songjiang Chenta Bridge.

Scenario 2: Daily monitoring of bridge health

Several different types of sensing devices are implanted in the bridge, and a collection node/gateway and a real-time monitoring platform are set up. Technologies such as low-power wide area networks are used to wirelessly transmit monitoring data and send the data to the collection node, and then transmit the data to the platform layer. Carry out storage, processing and analysis, and take timely countermeasures based on the analysis results. For example, when the ultimate bearing capacity of the bridge is severely lost, consider dismantling it.

Case: In Wuhan, technicians from the China Railway Bridge Research Institute installed 1,929 sensors of 15 types on 42 bridges, and a total of 3,053 sets of hardware equipment of 25 categories. Technicians will use these sensors and hardware equipment to monitor the bridge's structural safety (i.e. strain, cracks, displacement, deflection, inclination, temperature and humidity), vehicle load (i.e. vehicle type, vehicle speed, vehicle weight, axle load, vehicle length), single column Key parameters such as pier ramp overturning and slippage (ie strain, displacement, inclination angle), settlement and bridge deck alignment (ie deflection, GPS) are monitored. Various monitoring data such as the bridge's structural condition, foundation settlement, vehicle monitoring and snapshots will be stored in the cloud computing data center server in real time through the Internet, thereby realizing "one bridge, one file" electronic household registration management.

Secondly, technicians will also go to the site to inspect the appearance of the bridge, and upload the inspection results through the mobile APP. Managers or technicians at all levels can log in and access through any computer browser or mobile APP to understand the health status of these 42 bridges in real time, which will help technicians handle emergencies in a timely manner, repair diseased bridges in a timely manner, and ensure Bridge operation safety.

In addition, the "smart bridge" system can also automatically generate maintenance recommendations, and provide a basis for subsequent tracing and claims by consulting surveillance videos and detection data in the system.

Scenario 3: Monitoring the structure

This is actually reflected in the inspection of the Humen Bridge, the first large-scale suspension bridge in China. According to data, at the beginning of the design of the Humen Bridge, GPS displacement, real-time strain, long-term deformation, overload and other detection systems were added to obtain real-time information on the bridge's stress capacity, status parameters, seismic performance and other information under various conditions. , to ensure the safety of the bridge.

Of course, IoT technology is not only applied to bridges. China is currently in the midst of a wave of large-scale infrastructure construction, and various structures such as tunnels, buildings, and tracks have begun to enter the long-term operation stage. The early design and construction cannot determine whether the structure is operating normally. A more real-time and faster method will be needed to conduct comprehensive and refined monitoring of the operating status, especially for old structures that have been in service for many years.

Haokun Technology, which focuses on the field of structural monitoring of the Internet of Things, once summarized the market status of structural monitoring:

The low-power wide-area network represented by LoRa has the characteristics of ultra-low power consumption, wider coverage, super-large connection, low cost, and high penetration, which can not only meet the requirements of large connections and high penetration of different structures in various complex environments We can provide sophisticated monitoring solutions to meet the monitoring needs of such companies, such as the following four advantages:

(1) High penetration, long distance, low power consumption

It can be seen from the above figure that LoRa's link budget of up to 157db makes its communication distance up to 15 kilometers, and its penetration is extremely strong. Its receiving current is only 10mA, and its sleep current is 200nA, which greatly improves the service life of the battery. The characteristics of high penetrability and long-distance transmission solve the problem of internal vibration monitoring signals in bridges, tunnels, etc. becoming weaker after penetrating multi-layer concrete structures or rock walls. The low power consumption feature not only improves the stability of the equipment's continuous and long-term safety monitoring, but also reduces the number of equipment maintenance and structural inspections, thereby improving safety efficiency and reducing labor costs.

(2) Intelligent gateways based on this technology support parallel processing of multiple channels and multiple data rates, and have large system capacity.

The gateway is the bridge between the node and the IP network. Each gateway can handle 5 million communications between nodes every day (assuming 10 Bytes are sent each time and the network occupancy is 10%). If the gateway is installed at the location of an existing mobile communication base station with a transmitting power of 20dBm (100mW), it can cover about 2 kilometers in a densely built urban environment, and in lower-density suburbs, the coverage can reach 10 kilometers. This wide range of coverage is particularly important for long-distance, multi-node monitoring such as tunnels and bridges.

(3) Systems based on terminals and gateways can support ranging and positioning

LoRa's distance measurement is based on the air transmission time of the signal rather than the traditional RSSI (Received Signal Sterngth Ind-ication), while positioning is based on the measurement of the air transmission time difference between multiple points (gateways) and one point (node). Its positioning accuracy can reach 5m (assuming a range of 10km). This ensures the accuracy of monitoring data.

(4) Low cost and easy to deploy

LoRa is a technology based on unlicensed spectrum, with low infrastructure and node (terminal) deployment costs, which can reduce a lot of costs for large-scale structural monitoring applications. LoRa network technology can meet the needs of industry customers to adjust the details of their agreements, and can quickly help customers build local area networks at low cost to achieve business operations. At the same time, it can not only adapt to the needs of decentralized applications, but also well meet the needs of industry applications.

The "shaking" of the suspension bridge of the Humen Bridge is not untimely. This year has been particularly eventful, and a series of events have made us gradually realize the importance of technology. This time the Humen Bridge's "tiger body shook" has once again sounded the alarm for us. Under the background of the new infrastructure construction in full swing, we hope that the integration of new and old infrastructure will bring us a safer, more convenient, economical and efficient life experience, and less Some people are afraid of such events.

5. The structural monitoring market emerged as the times require.

Not just bridges, as the wave of large-scale infrastructure construction in China gradually subsides, various structures such as tunnels, buildings, and tracks have begun to enter the long-term operation stage. However, under the loading of various natural uncertain external forces and the needs of economic development, overload fatigue operation phenomena of various structures are common.

China's structural monitoring market has just started. Combined with the development of the Internet of Things and smart cities, it will generate a market share of billions in the next five years. At the same time, as existing buildings gradually age, the market will become larger and larger. Since the life cycle of sensors is generally about 8 years, it is also an infinite cycle market. If new buildings adopt IoT structural monitoring solutions during the construction phase, the entire market will undoubtedly expand a lot.

According to statistics, as of 2015, there are more than 700,000 large and small bridges, more than 8,000 tunnels (total length of more than 4,000 kilometers), a total length of subways of more than 3,000 kilometers, thousands of large stadiums, old buildings, and high-rise buildings. Huge, there will be a demand for real-time online monitoring and early warning in the future.