I. Overview Speed is the lifeblood of modern transportation.
/kloc-the railway development history of more than 0/50 years is a history of speeding up. With the progress of science and technology and the acceleration of people's life rhythm, high-speed traffic has become the general trend of development. From the railway point of view, in the face of the competition and challenge between aviation and expressway, the train speed is also increasing. However, how to speed up the existing line, how to make full use of the existing equipment conditions, and how to improve the travel speed of passenger and freight trains through local transformation of the existing line, so as to increase the advantages of railway transportation, will become one of the main topics of railway transportation in the future.
There are many actual situations encountered in the reconstruction of existing lines, and the reconstruction and expansion projects are not the same. This paper only analyzes the bridge reconstruction, finds out the crux and puts forward the solution. In order to ensure the safety of driving and bridge operation after speeding up, it is necessary to carry out technical transformation and reinforcement on the projects where bridge equipment endangers driving safety and restricts operating conditions, so as to improve the bearing capacity and stability of the bridge to meet the requirements of high-speed operation.
Second, the questions raised.
According to the requirements of the Ministry of Railways "Planning for Building China Railway Express Passenger Transport Network" and Shenyang Railway Bureau's "Tenth Five-Year Plan", our institute is responsible for compiling the following speed-up schemes: Changchun-Jilin long-distance line will be140km/h in 2003; The long-distance line from Jilin to Tumen was120km/h in 2005; Meihekou-Tonghua line of Meiji line was 120km/h in 2005. Both Changtu Line and Meiji Line were built during the Japanese Puppet Period. It is a low-standard railway built by Japanese companies for the purpose of expanding their invasion of China after Japanese militarism occupied northeast China. It has a history of more than 60 years. Bridge equipment is old and aging, with many diseases. More than 70% of the existing bridge buildings were built in 1930s, and were used after emergency repair, while less than 20% were rebuilt in 1950s and 1980s. In the future, with the increase of railway transportation volume and speed, people are extremely concerned about whether these old bridges can continue to be used safely. Updating an old bridge requires a lot of investment. Obviously, it is of great significance to scientifically evaluate the safety status and residual life of existing aging bridges, give full play to their potential, and update and strengthen aging bridges in a planned and step-by-step manner to ensure the smooth progress of railway transportation and the smooth development of national economy.
III. Existing Bridge Equipment There are 229 bridges on Changtu Line and Meijia Line, the main types are deck steel plate beams, I-beams, reinforced concrete beams, plate beams and individual prestressed reinforced concrete beams. The span of the bridge is 2.6-20m, and a considerable part of it is non-standard beam.
During the war of liberation, it was damaged to varying degrees, interrupted in some areas, and then repaired and used. In the Great Leap Forward after the founding of the People's Republic of China and the early 1980s, some line reconstruction and station reconstruction projects were carried out respectively. So the situation of the bridge is more complicated. Some bridges are old and aging, and the unqualified rate reaches 30%. Most of these bridges were built by foreign colonists, with low standards and poor materials. In addition, they have been used for many years, aging and fatigue cracking of steel beams. Brick piers and abutments have low strength and severe weathering and peeling. Although most of them have been reinforced with hoops, most of them are separated from hoops and cannot be stressed together. Due to the drop of groundwater level, the pile foundation decays seriously in the air and its bearing capacity decreases. Although many bridges have been reinforced or rebuilt after liberation, there are still many diseases. Mainly manifested in: cracking of main components of steel beam, failure of bridge sleeper, failure of steel beam paint, insufficient bearing capacity of steel beam, insufficient bridge clearance, insufficient bridge aperture, cracking of masonry beam arch, leakage of masonry beam, loose pier corrosion, unstable pier and shallow pier.
Fourth, the main problems existing in the existing speed-increasing bridges
1. Diagnosis of existing bridge diseases?
2. Fatigue residual life assessment of existing bridges?
3. What is the dynamic impact of speed increase on bridge structure?
4. Under the action of time-varying load, can the strength, stiffness (vertical stiffness and lateral stiffness) and stability of bridge structure meet the requirements of existing codes and standards?
5. Do small and medium-span T-shaped parallel masonry beams need lateral reinforcement?
6. How to limit the rubber bearing of masonry beam?
7. What is the dynamic effect of rail joint on bridge? Is it necessary to weld or freeze?
8. Can the piers and foundations built during the Japanese Puppet Period meet the requirements of speed increase and heavy load after years of use?
9. What is the dynamic influence of plane curve and rail surface irregularity on bridge structure?
Theoretical analysis and practical experience of verb (abbreviation of verb)
When the train passes through the bridge at high speed, the deformation and internal force of the bridge structure are different from those under static and live loads, and the increased part is generally called dynamic action. From the point of view of vehicle dynamics, a railway locomotive or vehicle consists of a car body, a bogie, wheelsets and interconnected springs. When the train runs on the line, it is accompanied by certain vibration. The train enters the bridge in this initial vibration state, and the car body, wheel rail and bridge form an integrated power system on the bridge. From the reasons of dynamic action, when the train passes through the bridge, the main factors causing dynamic action are as follows:
1. Hammer action of unbalanced part of locomotive moving wheel.
2. The dynamic effect of vehicles crossing the bridge at a certain speed.
3. The influence of track surface irregularity.
4. The hunting movement between wheel and rail.
5. The frequency of bogie load causes the resonance of small-span bridges.
6. Local vibration of steel beam bridge members.
The dynamic effect of vehicles crossing the bridge at a certain speed is related to the car body mass, vehicle speed and bridge live load deflection. The power function increases with the increase of vehicle speed. In the early stage of railway construction, due to the limitation of mechanics and calculation technology at that time, it was impossible to carry out dynamic analysis according to the ideal vehicle-bridge system, so a simplified static analysis method was adopted. That is, the internal force and deformation of the bridge structure are solved according to the static equilibrium equation without considering the vehicle speed and the vibration of the sprung part of the vehicle, and then multiplied by the impact coefficient to express the dynamic influence. With the development of transportation, the speed and span are increasing, so it is necessary to know the dynamic response of bridge structure when vehicles pass at high speed.
When the train crosses the bridge, the bridge structure will vibrate vertically and laterally. The vertical stiffness of existing standard concrete beams in China can meet the requirements of quasi-high-speed train operation. When freight trains and passenger trains pass by, the general trend is that the amplitude increases with the increase of vehicle speed. When the frequency of the load is close to the transverse natural frequency of the beam, large transverse vibration may occur. It is necessary to judge whether the lateral stiffness of a bridge is sufficient from three aspects: dynamic strength, derailment safety and comfort. If the lateral stiffness of the bridge is not enough, it will cause great shaking and make passengers or drivers feel uncomfortable. Draw lessons from the experience of speed-up tests in Guangzhou-Shenzhen, Shanghai-Nanjing, Qin Jing and Shenshan: for non-diseased bridges, the strength, vertical stiffness and pier and abutment of existing small and medium-span steel beams and masonry beams can meet the requirements of "inspection" and speed-up and heavy load; Rubber bearings for small and medium-span masonry beams on existing lines can meet the requirements of speed increase and heavy load after lateral restraint; The transverse stiffness of the small and medium span deck steel plate beam on the existing line can not meet the requirements of "clearance inspection" and speed-up and heavy load. Another example is the second He Zi Bridge on the long line K562+595. The original 33.5-meter two-hole through steel beam is replaced by a 33.5-meter two-hole prestressed concrete post-tensioned T beam. On August 30th, 1998 Siping Works Section found that the bridge was severely shaken laterally, and cracks appeared in the diaphragm. Among them, there were 9 cracks in the first hole beam on Shenyang side, and cracks in the second hole on Changchun side 12, with the maximum length of 780 mm The verification results showed that the diaphragm was weak, which lost the function of structural space integrity, resulting in cracks in the roots. After the transverse prestress reinforcement of diaphragm, the transverse vibration of the bridge has been greatly suppressed, which meets the requirements of the Inspection Code and the overall working performance of the beam is good. Without erection of 33.5m prestressed concrete T-beam, the center distance of main girder is increased from1.8m to 2.0m, and the bridge decks are connected together at the site.
Theory and practice show that the problem of insufficient lateral stiffness of the bridge is obvious after the train speeds up. For this reason, the Works Bureau of the Ministry of Railways issued the "Temporary Technical Conditions for Railway Bridges and Tunnels on Existing Lines (Operating Speed 120- 160Km/h)" with Gongqiao (1996) No.24 document, which clearly put forward the reinforcement of juxtaposed beams, that is, T-shaped and I-shaped beams with spans greater than or equal to 12 meters. Track surface irregularity; The initial vibration of the train before it gets on the bridge; Assembly error of bridge structure (initial bending or initial eccentricity).
Six, the existing line speed bridge reconstruction countermeasures
(1) The principle of reconstruction is to combine capacity expansion with speed increase, and bridges with serious diseases should be reconstructed.
The condition evaluation of bridges and piers is one of the hot spots in the field of civil engineering. This work is a key link to ensure the safety of trains, reduce hidden dangers of accidents and evaluate whether existing lines can speed up passenger transport and overload freight transport. It can be completed by scientific research institutes or bridge inspection teams. The acceleration of passenger and freight trains on existing lines will inevitably increase the dynamic effect on bridges and shorten the deterioration period of equipment. It is suggested to organize forces to study and formulate inspection methods, technical standards, maintenance requirements and other provisions for the technical status of passenger and freight train line bridge equipment, so as to scientifically manage it in the future, improve the quality of line bridge and ensure traffic safety. In order to ensure that the railway can reduce the economic losses caused by replacing bridges as much as possible, it is necessary to find the diseases as soon as possible and make a feasible evaluation of the diseased beams to determine the causes, degrees and development trends of the diseases, and choose different countermeasures such as repair, reinforcement or replacement according to the evaluation results and economic comparison. In cooperation with Shenyang Railway Bureau, Dalian Railway Institute completed the evaluation of aging steel beam bridge on Harbin-Dalian railway line according to the requirements of Harbin-Dalian Electrochemical Company, strengthened or rebuilt it in a planned way, improved the bearing capacity of the bridge, and achieved remarkable social and economic benefits in safe transportation and production.
(2) transformation measures
1. Relevant bridges for changing the existing line from double-track section to double-track section are added, and new double-track bridges are considered in combination with the line plane alignment transformation.
2. Strengthen the bridge with insufficient bearing capacity to adapt to the increase of axle load of locomotives and vehicles.
3. Detect and reinforce the bridge with unknown foundation and shallow foundation, and reaming the bridge with insufficient aperture to improve the flood resistance of the bridge in flood season.
4. Reinforce or replace fatigue cracked steel beams, concrete beams and unstable pier foundations.
5. Pay attention to the regular maintenance of steel beam bridge to avoid the centralized failure of steel beam painting and bridge deck.
6. Track on the bridge: Improving the elasticity of the track at the joint between the track and the bridge to make it basically the same, and avoiding the train from getting on the bridge with initial vibration is an important condition to ensure the train to pass smoothly after speed increase, reduce the wheel-rail power and improve the comfort of the train; Seamless track is adopted on the bridge to eliminate joints and reduce the impact of train load on the beam; The plane curve of the bridge head of the deck steel plate girder bridge makes the initial state of the train worse when it gets on the bridge, and the transverse vibration amplitude increases obviously. In order to improve the vibration state of deck steel plate girder bridge and ensure the running safety and passenger comfort of speed-up passenger and freight trains, it is necessary to increase the curve radius and transition curve length. For steel beams and Liang Shi, the deviation between the center line of the line on the bridge and the center line of the beam span should not be greater than 50 mm. If it exceeds the specified limit, it should be inspected, and if it affects the bearing capacity or invades the clearance, it must be adjusted.
7. Steel beam: The open deck of steel beam is comprehensively treated with K-type separable fasteners and new hook bolts, and 5- 15 large-section wooden sleepers are laid at both ends of the open deck to enhance the stability of the line on the bridge; Small span old steel beam (span
8. Masonry beam: increase the track elasticity of the track on the masonry beam bridge, ensure the ballast thickness or adopt a new elastic cushion under the pillow to reduce the impact of train load and improve the stress state of the masonry beam; Replace the ballastless and ballastless masonry beam and adopt the ballasted bridge deck to make the transition from subgrade to bridge deck or bridge deck to subgrade continuous and stable in vertical and horizontal directions, which is beneficial to laying seamless lines; Reinforce the juxtaposed beams without transverse connection on the existing line, that is, add diaphragms at both ends and in the middle of the span to ensure their common stress; The reinforced concrete double-beam bridge with span greater than 12m and train running speed greater than 120Km/h is laterally strengthened to strengthen the lateral connection system between the two beams of these bridges and improve the integrity. For small and medium-span bridges with plate rubber bearings, the lateral limit of bearings is used to increase their lateral stability, and the lateral displacement of beams should not be greater than 2mm；. Vertical stiffness: the maximum deflection shall not be greater than L/1400; Transverse stiffness: transverse deflection
9. Pier foundation: At present, the piers and abutments of existing lines are mostly gravity type, which is less affected by the impact after the train speeds up. However, for the pier with unknown technical state, it is necessary to judge whether it needs reinforcement or not; The pier and abutment with cracks are reinforced by grouting or hoop. Brick piers and piers with serious diseases (instability, insufficient bearing capacity, shallow foundation, etc.). ) should be strengthened or reformed before speeding up.
10. The bridge platform should be widened to 3.5m away from the center line of the line, and its number should be increased by 1 times.
Seven. term
With the opening and operation of Changji Expressway, Tuwu Highway and 401-class Highway, the competition between public railways has intensified, and the phenomenon of passenger flow shifting to highways has become more serious, and the passenger volume of railways has shown a downward trend. In order to enhance railway competitiveness and improve railway transportation efficiency, it is imperative to speed up. The road surface in Northeast China is slippery in winter, so the safety factor of taking a train is greater than that of taking a car. Shortening the travel time will attract more passengers after the implementation of the speed-up project. Therefore, railway speed increase is the need of market economy. The fast, comfortable and safe operation of the train requires that the railway bridge must have sufficient rigidity and good integrity to prevent the bridge from generating large deflection and amplitude. Generally speaking, the design of high-speed railway bridges is mainly controlled by stiffness, and the strength basically does not control its design. When the existing line is speeding up, the bridge involves more problems and the situation is more complicated, so it should be treated differently. Do a good job in the inspection and evaluation of existing speed-increasing bridges, and combine new construction, reconstruction and reinforcement to meet the requirements of speed-increasing and heavy-duty railways.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd