Discussion on scientific decision-making on special inspection and disposal measures of cable-rod system
Background
Bridge cable-rod systems have been widely used in long-span bridges, including suspenders for suspension bridges, stay cables for cable-stayed bridges, and suspenders for mid- and bottom-bearing arch bridges.
The cable-rod system will reduce the serviceability and durability of the structure once it is damaged and may cause catastrophic sudden damage to the bridge structure (such as the recent Nannan'ao Bridge in Taiwan). The boom broke and collapsed), causing terrible social impact and heavy economic losses.
The performance of bridge cable rods will inevitably degrade, so frequent physical examinations are required, and measures such as cable replacement are taken when necessary to ensure the safe operation of the bridge.
However on the other hand, many bridges in China have carried out cable replacement projects, but it has also been found that in some bridges, based on anatomical inspection of the replaced bridge cable rods, it was found that most of the slings were not substantially damaged, causing huge losses. Waste.
So, how should the bridge cable rod system be tested scientifically, and how should scientific decisions be made about replacing it? Dr Lin combined his many years of experience in inspecting and maintaining bridge cable systems to put forward some opinions on scientific decision-making on special inspections and disposal measures, and he would like to discuss them with everyone.
Special inspection of bridge cable and pole systems
Special inspections of bridge cable rods generally include special inspection of the appearance of the PE sheath, non-destructive inspection and verification of internal broken wire corrosion, cable force testing of the entire bridge cable rods, and special inspection of anchor heads, cable guides and other structures.
0 1 Appearance inspection of PE sheath of cable rod
A cable-climbing robot can inspect the appearance of the PE sheath of the cable rod to accurately locate the PE sheath disease, grasp the disease status of the PE sheath of the stay cable, and determine the disease assessment scale.
Considering that construction can easily cause damage to the cable rod PE, it is necessary to carry out an appearance inspection of the cable rod PE sheath when the bridge is handed over to deal with some hidden dangers caused by the construction as soon as possible and form a detailed archive of the bridge after it is opened to traffic, which will be used for the future development of the bridge. Provide a basis for maintenance, repair, and safe operation.
0 2 Non-destructive testing and verification of corroded and broken wires inside cable rods
Magneto strictive guided wave non-destructive testing is used to accurately grasp the corrosion and broken wires of the steel wires inside the cable rods. This assessment of the internal defect scale of cable rods provides early warning and detection of corrosion and broken wires of bridge cable rods, providing a basis for safe use and later maintenance and repair of bridges.
The magneto strictive guided wave technology detection method is mainly used to detect long-distance cable structures rapidly and is especially suitable for detecting cable bodies and anchoring areas of stay cables and booms.
Its advantages are:
✔ Non-destructive and advanced: no need for full-cable climbing detection and no wear on PE; install excitation and receiving sensors on the cable body section near the bridge deck.
✔Accurate and high-precision: It can realize internal damage detection of the entire cable (including the cable body in the anchoring area) and can detect more than 5% of the cross-section metal loss; under ideal conditions, it can detect 2% of the cross-section metal loss.
✔Simple and efficient: There is no need for winches and other equipment; about 15 to 20 roots can be detected daily.
✔ Non-disturbing traffic: Guided wave non-destructive testing technology enables the detection of internal corrosion and broken wires in bridge cable rods without traffic closures, which can reduce economic losses caused by traffic closures.
Data processing mainly uses specific signal processing software for analysis and processing to obtain the detection waveform of each cable rod, find out the detection signal of the cable rod with abnormal echo, and determine the location of the internal rusted, broken wire based on the arrival time and amplitude of the abnormal echo. And size.
Therefore, once an abnormal detection signal is found and analyzed that it is not caused by structural interference (as shown in the picture above), it can be verified by opening a window with the owner's consent.
0 3Full bridge cable force detection
The cable force test is used to determine the cable's current stress status and analyze whether the internal force and linear shape of the structure deviate from the design state. At the same time, the cable force of the suspension rod provides a basis for subsequent evaluation of the cable carrying capacity.
The vibration frequency method is the most widely used and highly accurate cable force measurement method. It uses the random vibration of the environment as the vibration source of the structure to measure and analyze the vibration characteristics of the structure and then calculate the cable force; for unique cable bodies such as short cables, the pulling method and other methods should be used to measure the cable force more accurately.
0 4 Cable rod anchor head, cable guide and other structural inspection
Anchor heads, cable guides, etc., can be visually inspected for damage and evaluated.
The anchor head part can be done through visual inspection to see whether water has entered the anchor head part, whether the parts are rusty, damaged, peeled off or cracked, whether there is leakage or missing grease on the surface of the anchor, and whether there are cracks in the concrete next to the anchorage area. , exposed tendons and other phenomena.
In addition, you should check whether the anchor cover and fixing bolts are missing and deal with any problems promptly.
Scientific decision-making on whether to change cables or not
Assess the safety of rope poles as required.
Based on the inspection results of bridge cable rods, supplemented by historical operation and maintenance data of stay cables, the evaluation scale of the cable rod system is determined. Combined with the measured cable force, it is substituted into the finite element numerical model, and then, based on the iterative calculation results, the cable rods' load-bearing capacity is evaluated per the design and testing evaluation specifications. The load-bearing capacity evaluation needs to be carried out individually to ensure the accuracy of the entire bridge load-bearing capacity evaluation. Sex.
The assessment results of the load-bearing capacity of the bridge cable rods provide a scientific basis for the management and maintenance department to make decisions on maintenance, cable replacement, etc. When the decision is made to change the cable, a special cable rod replacement design is required.
Summary
The drawings propose the minimum service life of the bridge cable rods as a reference. A qualified bridge doctor should not arbitrarily believe the bridge is safe or blindly issue a critical illness notice to the bridge cable rods. Instead, he should carefully evaluate the bridge's cable rods. The cable-rod system undergoes detailed and in-depth testing and evaluation, and scientific diagnosis is made based on data and analysis.
