First, the common problems in bridge maintenance
For a long time, the maintenance of highway bridges has encountered many problems, among which the common ones can be summarized as the following eight main problems:
(1) The bridge deck is uneven and unclean.
Due to the lack of regular maintenance, the decks of many bridges are easily damaged under the constant action of vehicle tires, especially the decks of old bridges or asphalt materials that have been used for more than decades.
The influence of uneven bridge deck on driving varies from slight bumps to bumps, even at low speed. The joint filling material at the beam end joint of the simply supported beam and the cantilever fulcrum of the hanging beam fall off due to lack of maintenance, and suffer from the wear of the wheel, resulting in a large groove, which is the main reason for the trip.
When the vehicle passes through the car, it will cause serious vibration of the adjacent beam section, thus increasing the fatigue of the component. If this is not improved, the service life of the bridge will be shortened.
Because the bridge deck has not been cleaned for a long time, the bridge deck is not clean and the drainage holes are blocked. This problem is common in many small and medium-sized bridges.
The uncleanness of the bridge deck is often reflected in the accumulation of garbage under the wheel belt, and the dirt forms a triangular hard block, which leads to the blockage of the drainage hole. When it rains, water accumulates on the bridge deck, and mud splashes when vehicles cross the bridge, which affects the traffic of vehicles.
(2) The bridge deck railings are damaged incompletely.
Bridge deck railings were not repaired and restored in time after being damaged, which can be seen on many abandoned expressway lines. Most of the reasons for the local damage of bridge deck railings are caused by motor vehicle traffic accidents; Some bridges were accidentally damaged by heavy goods (such as cement poles). ) when driving on the bridge; The railings of a few bridges are caused by man-made damage or theft.
If the bridge railing is damaged, it will not only affect the landscape, but also make the traffic on the bridge feel insecure.
(3) Bump at the bridge head
Due to the uneven settlement of the high fill of the approach road at the bridgehead, the joints between the bridge deck and the approach road surface of many bridges are not smooth and comfortable, which leads to slight or serious bumps when vehicles pass the bridgehead.
Jumping at the bridge head not only affects the speed and reduces the driving quality, but also makes drivers and passengers disgusted. Long-term failure to eliminate vehicle bumps will also affect the service life of bridges; Serious tripping even leads to the fracture of automobile spring steel plate.
(4) The bridge members are not repaired due to minor defects.
Due to the defects such as cavities, cracks, subsidence and displacement of bridge components after construction or delivery, there is a lack of regular inspection and timely maintenance in daily maintenance, which leads to the corrosion of steel bars, the development of small cracks into large cracks, the loss of activity of movable bearings and the phenomenon of concrete falling off.
The lower pier, cone slope, revetment and the back of the upper object of the bridge are rarely inspected, so problems cannot be found in time. During the flood season, the flood control ability is extremely poor, and it is easy to be washed away by water, so some bridges are "seriously ill".
(5) The drainage of the bridge hole is not smooth, and the navigation clearance is insufficient.
Many small and medium-sized bridges have poor water flow in the bridge holes, and the riverbed near the bridge holes is silted up. Bridges located in the suburbs of cities and towns and near factories discharge a lot of domestic sewage and industrial wastewater, which makes the bridge hole blockage more serious.
After the bridge opening is blocked, the daily maintenance workload is small, and the river channel is not cleaned and dredged in time, so this kind of flood discharge preparation work is rarely done before the flood season. Therefore, in the flood season, the flood discharge capacity of bridge opening is poor, and bridges that should not be washed away by water will also be washed across by floods.
(six) the bearing capacity of the bridge is insufficient and the situation of the dangerous bridge is unknown.
Bridges on existing highways are built according to different technical standards in different periods, so the bearing capacity of * * * is obviously different. Especially for bridges built before the founding of the People's Republic of China, the standard is not suitable for the axle load of existing vehicles, which is too low. In addition, in recent years, due to the increasing number of overweight vehicles, the requirements for the bearing capacity of bridges are getting higher and higher. The lack of bridge bearing capacity is the main problem in the current bridge maintenance and reinforcement work.
For some bridges whose bearing capacity is really too low or seriously damaged, their bearing capacity is limited, and they can be designated as "dangerous bridges" to restrict the passage of vehicles. However, there is often a lack of necessary investigation and research on this part of the "dangerous bridge", and it is not clear to what extent the dangerous bridge is dangerous and how many vehicles can pass.
(7) Wide roads and narrow bridges form a "bottleneck", which affects traffic capacity.
Many bridges have narrow decks because of their long construction years and low standards. In the maintenance and reconstruction of highway routes, the pavement is often widened, but the bridge has not been widened accordingly, forming a "bottleneck", which not only affects the traffic capacity, but also increases the danger of driving.
(eight) the bridge load standard is unknown, resulting in errors and confusion.
Load signs must always be set at both ends of the bridge, especially on some trunk roads with heavy traffic and heavy transportation, and axle load limit signs should be set to remind drivers of vehicles crossing the bridge. However, due to the disrepair of some bridges, the data is lost, or although the data is complete, the signs are not paid attention to, so many bridges do not set load signs as required.
Due to the different construction years of bridges, their load standards are also different, and the design load standards of bridges change frequently. If we don't pay attention to the technical files of bridges, there will often be problems such as taking the wrong bridge load standard or setting unclear signs.
The above are the main problems that are easy to occur in bridge maintenance and reinforcement, and other possible special situations or problems must also be given necessary attention.
Second, the work content of bridge maintenance and reinforcement
Bridge maintenance and reinforcement includes maintenance and reinforcement.
(A) the maintenance of bridges
Bridge maintenance is the maintenance and management work in a specified period, including:
(1) minor repairs and maintenance of bridge structures, which include:
(1) Keep the surface of the structure clean and complete, prevent the surface from weathering, and repair the weathered part in time.
(2) Keep the drainage equipment in good condition, remove the blocked soil in the drainage pipe, prevent mortar leakage and repair the corroded part.
(3) Always check whether each part is faulty. When cracks, small holes, peeling, missing corners, exposed tendons and other local defects or surface damage are found on the masonry, they must be repaired in time.
(4) Ensure that the telescopic device can move freely, and remove obstacles that affect the bearing movement.
⑤ Anti-corrosion of wooden bridge and anti-rust paint for steel beam.
(2) Check the bridge structure regularly to verify its actual safe bearing capacity, so as to determine its damage degree. When the bridge structure is abnormal or damaged, it is necessary to analyze the reasons, judge the influence of the damage on the use of the structure, explain the necessity of maintenance and reinforcement, and compare the maintenance and reinforcement methods. If any abnormality is found, it must be repaired as soon as possible. If the damage is serious, after investigating the damage degree, historical situation, specific site conditions, characteristics, current and future traffic requirements for bridge width, design load and highway development planning, we need to make an economic comparison between the old bridge maintenance and reinforcement scheme and the partial or total reconstruction scheme, and make a decision and choose the best scheme through cost-benefit analysis.
(3) Overweight vehicles or tracked vehicles are not allowed to pass through existing bridges at will, and must be approved by the highway management department. Therefore, the management of overweight vehicles or tracked vehicles crossing the bridge is also an indispensable part of beam bridge maintenance.
(4) Manage the original technical data of the bridge, and establish and save the bridge files. The contents of technical data include: engineering geological and hydrological exploration data, bridge design drawings, design change notices and other relevant design data; Inspection records and concealed works records of bridge construction, quality accident treatment records, factory certificates of raw materials, semi-finished products and finished products, test and laboratory reports, settlement observation records, project completion drawings and other relevant construction documents; Settlement observation records, important inspection and setting records, construction drawings and overhaul and reinforcement construction records during bridge debugging.
(b) Bridge reinforcement and reconstruction
The main contents of bridge reinforcement and reconstruction work: thoroughly rectify, reinforce, improve and update the bridge and culvert equipment that has suffered serious diseases and cannot meet the transportation requirements. The purpose is to restore the overall efficiency of the original bridge building and extend its service life; Improve the load grade and passing capacity of the original bridge building.
The main contents of bridge reinforcement and reconstruction work are:
(1) Strengthening the superstructure of the old bridge;
(2) reinforce the lower components of the old bridge;
(3) Widening the carriageway or sidewalk of the bridge;
(4) Raise the height of the bridge superstructure;
(5) Replace the structure of bridge deck pavement or approach bridge pavement;
(6) Replace the damaged or worn bridge structure partially or completely.
The reinforcement and reconstruction of bridges should make full use of the original parts. Don't rebuild what can be reinforced. If it can be partially rebuilt, it should not be completely rebuilt.
Third, the steps of bridge maintenance and reinforcement
Generally speaking, the maintenance and reinforcement of old bridges can adopt the following steps:
(1) Check the condition and damage of the bridge;
(2) Investigate the historical and technical data of the bridge and the existing traffic conditions;
(3) Propose maintenance, reinforcement or reconstruction schemes, and make analysis and comparison;
(4) Determine the scheme and put it into practice, that is, carry out maintenance, reinforcement or transformation.
See Figure 9- 1-5 for the maintenance and reinforcement steps of the old bridge.
Figure 9- 1-5
(5) steel plate bonding method;
(6) adding longitudinal beam method;
(7) changing the reinforcement method of structural system;
(8) Prestressed reinforcement method;
(9) the method of replacing the main girder or all the main girders;
(10) joint filling method.
Pressure grouting method, shotcrete method and joint filling method are generally used to repair cracks and surface defects of concrete or masonry members, and the remaining reinforcement measures are used to improve the bearing capacity and passing capacity of existing bridges.
(B) the common maintenance and reinforcement methods of the substructure
The maintenance and reinforcement of the bridge substructure should adopt different methods according to the damage and existing problems of the old bridge.
Methods, commonly used maintenance and reinforcement methods are:
(1) Enlarged foundation reinforcement method;
(2) Pile-adding method (driving piles or pouring cement concrete piles in place);
(3) load reduction method;
(4) jack-up method;
(5) Supporting method or widening and thickening method (dealing with pier displacement);
(6) Reinforce the pier with reinforced concrete hoop (or sheath);
(7) riprap method;
(8) Other reinforcement methods; Such as jet grouting method and sand pile method.
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