Structural Health Monitoring System (SHMS) bridge construction monitoring systems have started to be applied and developed throughout the world in recent years. Most of the major bridge projects around the world are installed with different monitoring systems to continuously monitor and collect data (physical quantities) during the operation and exploitation of bridges. The US [1
], Japan [3
] China [6
], and Europe [10
] are places where monitoring systems are widely and effectively applied.
Monitoring systems are designed specifically for each bridge construction based on the structural characteristics of each project and the financial situation required by the investor. The bridge monitoring system must be highly durable with a high level of accuracy throughout the operation time. The cost of the entire monitoring system is not large compared with the total cost of bridge construction, accounting for 0.3% to 1.5% of the total value of the bridge construction investment, depending on the complexity of the system monitoring. The management and operation of the monitoring system is also not a large cost compared with the total cost of maintaining the works, but the monitoring system requires a high level of personnel as well as management experience.
The biggest advantage of the bridge construction monitoring system is the continuous monitoring of the structure’s activities and changes allowing the more effective and safe operation and exploitation of the works. Based on the analysis and evaluation of monitoring data [13
], we can make the right decisions for the maintenance of the bridge works. The monitoring results allow us to assess the correctness of the hypotheses given in the design and construction process. Regular monitoring of the work allows us to control the operation of the building under the influence of different load combinations, helping experts identify the aging processes of structures and ensuring the implementation of measures to prevent and improve the service life of bridges [14
The bridge construction monitoring system is a complex system that combines many components from construction structural monitoring, meteorological monitoring, and image monitoring to geographic monitoring. Monitoring plays an important role in the processes of construction, construction, and operation. It allows hypothetical conditions to be set during design and can affect the construction cost of the project. Therefore, the efficient and safe implementation and application of modern methods and advanced techniques to monitor bridge works for the construction, research, and management of works are essential and urgent.
The discovery of the spoilage of the bridge works before there are specific signs is one of the issues that is attracting the attention of many bridge researchers and engineers. Along with the development of science and technology, calculation software and simulations have been developed, but the received results of theoretical calculations are only relatively close to the actual behavior of the project. In the design process, setting up the hypotheses to simplify the calculation model leads to the issue that analysis and calculation cannot reflect the status of operation and behavior of the project under normal operating conditions, as well as in terms of exploitation. In addition, there is a big difference between simulation in design and reality. In order to determine this difference, one of the measures with significant potential to assess the process of the work and exploitation of bridge works is to install monitoring devices at reasonable locations related to the project’s demand to continuously measure the parameters affecting construction such as external forces (wind, earthquake, vehicle load) and behaviors of bridge construction (oscillation, displacement, stress) [17
]. The data collected will be the basis for checking the process of the analysis and calculation of works. Besides, the bridge monitoring system is also used for other purposes such as maintenance, construction, and traffic management on the bridge.
Because of their particularly important role and costly construction, large-span bridges often have to be checked regularly to ensure that they are safe [21
]. This testing process usually has high time and cost requirements, but sometimes it is still impossible to control all the risks of damage to the bridge. The construction and development of an automatic bridge monitoring system is something that developed countries such as the US [22
], Europe [23
], South Korea [24
], and China [13
] have been doing to reduce the costs of maintaining bridges as well as ensuring traffic safety for these works.
In the United States, in the mid-to-late 1980s, monitoring devices were installed on a number of large bridges. For example, more than 500 sensors were installed on the 440 m Sunshine Skyway bridge in the United States to monitor the state of the bridge [25
]. Monitoring research on the condition of bridges originated in the Europe and America in the mid-to-late 1960s–1980s [26
]. The United Kingdom also deployed sensors on the Foyle bridge, which is a three-span high-rise steel box girder bridge, with a total length of 522 m, to monitor the bridge in the operational stage. The monitored section responds to the vibration, deflection, and strain of the main beam under the action of the wind load, and the temperature of the environment and the temperature of the structure are also monitored. This system was one of the earliest installed and relatively complete monitoring systems, which achieved the purpose of real-time monitoring, real-time analysis, and data network sharing [27
Hong Kong’s Tsing Ma Bridge had an anemometer and an accelerometer installed on the bridge to establish a monitoring system regarding the wind and structure. The wind field characteristics and damping ratio when the typhoon actually attacked were matched with the parameters obtained by the wind tunnel test [28
]. The Chinese Tiger Gate Bridge and the Jiangyin Yangtze River Bridge are also equipped with corresponding monitoring systems. The Humen Bridge monitoring system is composed of strain gauges, acceleration sensors, temperature sensors, displacement sensors, GPS systems, etc. Based on the construction monitoring and the test system after the completion of the bridge body, the monitoring of the bridge after the bridge was opened to traffic has produced many positive effects to ensure the safe operation of the Humen Bridge.
In view of the lack of seismic capacity of bridges caused by the bare foundation of the bridge, structural reinforcement measures are applied for bridge foundation reinforcement protection, bridge demolition, and reconstruction. Alternatively, local reinforcement bridge foundation methods, such as concrete piers and supports, can also be applied. Amongst others, the bottom expansions are all based on the bridge structure and river characteristics, and each has its own applicability.
Wuxi Bridge is an important bridge connecting the Wufeng District of Taichung City with Caotun Town of Nantou County. It was rebuilt after the 921 (21 September) earthquake in the Republic of China. In recent years, the riverbed has been continuously washed away by floods, and the bridges between P9 and P13 have been cavitated.
The foundation is severely exposed; therefore, the vertical bearing capacity and lateral bearing capacity of the old foundation have been significantly reduced. Piles have been used to protect and reinforce the construction method several times, but the bridge is still affected by the continuous decline of the riverbed and the lateral erosion of the river channel. Owing to safety concerns, it is listed as a damaged bridge in the province. To improve the overall seismic capacity and flood resistance of the bridge, the superstructure of the project was rebuilt by the Republic of China in 1991, and the structure is still new and good. Therefore, under the conditions of using the existing superstructure and maintaining the original traffic conditions, the partial reconstruction of the bottom method was applied.
In recent years, bridges in Taiwan have been washed away. In the Republic of China in 1985, the typhoon He Bo caused severe collapses and sloping damages to the main bridges in the west. This included strong bridges that were as high as 6.3 to 9.3 m, and the southern Ligang Bridge was also damaged by the slope of the bridge. This resulted in traffic disruption [29
In 1990, the Xizhou Bridge on the first line was affected by typhoon Taozhi in the Republic of China. As a result, the depth of the riverbed at the bridge site of the Xizhou Bridge was reduced by more than 5 m, and the bridge foundation in the deep trough area was seriously exposed by up to 10 m, which was unsafe. To maintain bridge safety and to maintain unobstructed bridge traffic, the first bridge replacement method was carried out in Taiwan. Under the conditions of maintaining the structure and traffic of the bridge, the bridge load was temporarily transferred from the original pier to a temporary supporting steel frame, and the bareness was addressed. The damaged bridge foundation was replaced with the new bridge foundation, which met the requirements of flood resistance and seismic design. The difference between the bridge deck before and after construction was extremely small, and the shape and function of the original bridge could be maintained to effectively resolve the bridge erosion. Considering the problem of transportation disruptions and the advantages of saving engineering costs and construction period, and considering environmental protection and energy saving, environmental beauty, and ecological maintenance, this approach provides a good solution to the problem of bridge foundation exposure caused by domestic erosion through water damage [30
Jingzhou Xin et al. [31
] proposed the Kalman–ARIMA–GARCH model (autoregressive integrated moving average model (ARIMA), and generalized autoregressive conditional heteroskedasticity (GARCH)) to predict the deformation of bridge structure based on GNSS (Global Navigation Satellite System). Chiara Bedon [32
] explored the use of MEMS (Micro Electro-Mechanical Systems) Accelerometers for prototyping and validation for structure health monitoring in Italy. John Reilly et al. [33
] gave further evidence on how identifying temperature can affect structure health monitoring. Zengshun Chen et al. [30
] have combined three methods—the peak-picking method, the random decrement technique, and the frequency domain decomposition—for a smart structure health bridge monitoring system. Olga Thalla el al. [34
] performed an experiment in which they analyzed data to detect damage and combine the monitoring of wind data to explain the sequence of events.
The newest point of this study is that the research integrates the monitoring system (in real-time) using the computer software tool SAP200 to carry out a safety analysis of the bridge structure in the case study, namely that of Wuxi bridge.
2. Introduction to the Method
2.1. Method of Changing the Bottom of the Wuxi Bridge on Provincial Highway 3
In general, bridge reconstruction must be completed with full bridge closure, resulting in traffic disruption and inconvenience to passers-by. In this paper, the case study focused on the “Zhoudaotai 3 Line Wuxi Bridge”, which is an important contact bridge between the Caotun area and the Taichung area, where the traffic volume is very large. Therefore, the bridge replacement method was used to ensure the maintenance of the original traffic during the bridge reconstruction period.
2.2. Introduction of Wuxi Bridge’s Bottoming Method
During the reconstruction, six temporary support piles were erected around the foundation of the substructure (bridge foundation, bridge column, and cap beam), and a temporary cap beam structure (steel structure) was set up on the pile column as a pier (column). The temporary support system during the demolition and rebuilding period is shown in Figure 1
. This was added to the girders of the jacking jack, and a temporary support stiffening plate for the girders was added to increase the stiffness of the steel beams supported by the temporary cap beam steel frame. To ensure the safety of the bridge structure during jacking, a monitoring system was installed near the lifting device. The monitoring equipment includes an electronic tilt meter, electronic sinker, etc. to monitor the safety of the bridge.
The jack is shown in Figure 2
, and it was placed on the steel frame of the temporary cap beam. When the jacking was carried out, the section was lifted up, and after a cumulative increase of 50 tons (each jack load), the structure was stabilized after pausing for half an hour. At the same time, the measurements of each jack and the displacement of the beam were recorded. After that, the jacking was carried out, so that when there is an obvious separation of the old pier support, the lifting was stopped, and the steel spacers and anti-seismic steel structure were fixed. At this time, the weight of the bridge was transferred to the temporary supporting steel structure.
After the load was transposed, the old bridge pier and foundation could be removed. After the new foundation, pier, and cap beam were completed, the load was transferred to the new pier and the six temporary support piles could be removed. The temporary support of the steel frame was raised to complete the reconstruction work.
2.3. Structure Analysis (Computer Software Tools SAP2000)
The SAP2000 computer software (COMPUTERS & STRUCTURES, INC., Structural and Earthquake Engineering Software, Walnut Creek, CA, USA) is powerful full-window interface structure analysis software and is capable of the establishment of basic three-dimensional geometric shapes, the cross-sectional properties of rods and thin shell elements, the mechanical properties of reinforced concrete, steel structures, nonlinear elements, or the new definition of material properties. Even static analysis, dynamic analysis, response spectrum analysis, and diachronic analysis can be performed using SAP2000 computer software, and the analysis results can be displayed graphically or in a standardized text format for subsequent processing work.
This study used the finite element structure analysis in SAP2000 computer software to carry out the safety analysis of the Wuxi Bridge structure. The establishment of the FE (Finite Element) bridge model algorithm can be divided into the “whole bridge system” and the “single partial system”, which is the same as the vibration unit concept of the current bridge design code. The Finite Element “whole bridge system” model is suitable when the bridge type is geometrically irregular, such as for a cable bridge, which has a horizontal multi-channel expansion joint, and when the bridge is located in a soft soil. The “single partial system” is suitable for quantifying the strength and stiffness capacity of a single frame, such as piers, and involves vertical and horizontal analysis. The longitudinal axis should consider the adjacent-span effect and depends on the bridge length. The transverse axis also considers the adjacent-span effect. The upper structure can be regarded as a rigid member. The overall bridge analysis model must accurately describe the dimensions of all components, such as structural elements, thin-shell elements, springs, bearings and expansion joints, and other elements. The material properties comprise the behavior of the intact reaction structure. The section of the upper structure of the bridge is calculated to determine its section properties. According to the results of an on-site microseismic experiment of reinforced concrete bridges, the upper structure is pre-force concrete. The torsional stiffness parameter is calculated in 200% of the full section. The flexural rigidity of the horizontal axis parameter is calculated in 120% to 140% of the full section. The flexural rigidity of the vertical axis parameter is calculated in 100% to 120% of the full section. The cross-section of the rigid element is magnified 1000 times by the cross-section of the beam-column element. The design of the bridge reconstruction project after the 921 Jiji Earthquake and the completion map of the bridge reconstruction project were used to construct the Wuxi Bridge. The structural analysis model was used to perform microseismic tests on each span of the bridge (P9~P15) to modify the model constructed by the SAP2000 software, in order to make the model fit closer to the actual condition of the bridge.
2.4. Application of Monitoring System
Bridges are an indispensable transportation lifeline for all nations. However, given old bridge structures and the impacts of earthquakes and typhoon disasters over the years, the strength of bridge structures has decreased, and their life expectancy has been reduced. Thus, the safety of passers-by has also been jeopardized. There is still an unknown risk when a bridge is damaged. For example, on 28 August 1989, the Gaoping Bridge—an important transportation bridge in the southern part of the southern line—was broken and the bridge deck was slanted, causing 16 large and small vehicles to fall into the stream, resulting in 22 deaths and injuries. On 14 September 1997, the Hehou Bridge—an important transportation bridge on the 13th line of Central Taiwan Station—was also severely eroded due to the bridge foundation. The bridge pier was weak and the bridge was broken, causing six people to fall below.
Owing to the influence of weather and human factors, the lack of a monitoring system means that damages cannot be detected, thereby reducing the functionality of bridges. The level of bridge safety is unknown, which often causes serious damage to traffic and passers-by. Therefore, a monitoring system is required to monitor the condition of the structure and to evaluate the safety of the structure. Field verification of design theory has been widely used to facilitate the understanding of the structural characteristics of the bridge and for the improvement of the design technology.