First of all, the questions raised
With the passage of time, any highway bridge will become an old bridge, and there will be different degrees of defects and diseases for various reasons, which need to be maintained, strengthened and transformed. Most of the highway bridges in Jiangxi Province were built in 1960s and 1970s, and the design load standard is low, so they are still in use. By the end of 2000, there were 427 dangerous bridges in Jiangxi, 13849 linear meters. The task of rebuilding the old dangerous bridge is very heavy, which is neither realistic nor scientific, nor should it be.
Therefore, in the early 1980s, in the process of upgrading the technical level of highway reconstruction, our province began to study and practice the reinforcement and reconstruction technology of old highway bridges. According to different bridge types, different reinforcement technologies and methods have been adopted, and a number of scientific research projects for the reinforcement and reconstruction of old bridges have been completed, which have achieved remarkable economic and social benefits, two of which won the Jiangxi Science and Technology Progress Award. Because the old bridge detection, evaluation and reinforcement technology is a comprehensive and complex technology that is constantly developing and updating, it is also a hot issue that highway engineers and technicians pay attention to. Therefore, the following briefly introduces some research results and actual bridge situation of strengthening technology of old highway bridges in Jiangxi Province.
II. Introduction of Main Scientific Research Projects
1. 1983, our province has completed the "research on improving the bearing capacity of small beam slab bridges". In order to qualitatively measure the improvement degree of bridge stiffness and bearing capacity before and after reconstruction, two indexes, namely "stiffness improvement degree" and "bearing capacity improvement degree" and their calculation methods are put forward. Both of them reflect the condition of the whole bridge. The former refers to the increase of the stiffness of the whole bridge, and the latter refers to the increase of the bearing capacity of the whole bridge. This achievement has been repeatedly cited by other provinces.
2. The Study on Strengthening Hyperbolic Arch Bridge with Bolting and Shotcrete, which was completed in1988 ~1year, improved the original design load of a five-hole hyperbolic arch bridge with a span of 45 meters: steam-13, changed from drag -60 to steam -20, and hoisted -65438. This achievement has been confirmed by the retrieval and novelty retrieval of the Institute of Science and Technology Information of the Ministry of Communications. At that time, among the domestic bridges strengthened by bolting and shotcreting, the span was the largest and the bridge load grade was the highest.
3. 1994 successfully completed the research on strengthening the load-bearing beam bridge with external prestressed straight cables at the bottom of the first beam in China, and solved the technical problem of corrosion failure of external prestressed cables due to temperature change by bolting and shotcreting technology.
4. 1996 Project "Study on Strengthening of Ordinary Reinforced Concrete Double Cantilever Girder Bridges with Cantilevers" was completed, and the problems of concrete cracking and steel bar corrosion in the negative bending moment area of the bridge deck were successfully solved by using steel fiber concrete.
5. Successfully completed the cantilever widening research of bridge deck of beam bridge and arch bridge, and widened the bridge deck of net -7 to net -9+2×; 1.5m sidewalk, total width12.5m. ..
6. The research on strengthening the beam bridge with carbon fiber sheets has been successfully completed, and the certified static load test before and after strengthening has confirmed the strengthening effect of improving the bending capacity.
7. The superstructure of the bridge was successfully strengthened by pasting steel plates, pasting steel bars, wrapping concrete and arching. And various methods of strengthening the bridge substructure.
Three. Introduction of typical bridge reinforcement scheme
1, Dexing Xiangtun Bridge (anchor and shotcrete method, hyperbolic arch bridge)
1. 1 Introduction to Bridge Design Xiangtun Bridge is a bridge leading to Dexing Copper Mine, which was completed and opened to traffic in August 1969.
The design load of the bridge is steam-13 and drag -60, and the clear width of the bridge deck is-7+2×; 0.25m. The superstructure is a hyperbolic arch with 5 holes of 45m (rise-span ratio 1/6) and 6 ribs and 5 waves in the transverse direction. The substructure is gravity solid pier and U-shaped abutment with back seat. Except Dexing abutment is built on dense pebble bed, other abutments are built on phyllite bedrock.
1.2 Diseases of Xiangtun Bridge
(1) cracks in main arch ring
① Longitudinal cracks in waves of main arch ring. During the inspection, longitudinal cracks were found at the peak of each hole.
② There is a crack at the joint between rib and wave. Most of the joints between arch waves and arch ribs in each hole have cracks.
③ Cracks in arch ribs. There are transverse cracks in the arch ribs of each hole, mostly U-shaped cracks, which mostly occur in the range of about 10m before and after the vault.
(4) cracks in the beam. It's rare, but there are all holes except 1 and 4.
(2) The axis of the main arch ring drops. The main arch axis generally drops, the vault drops by 5 ~ 1~9cm, and the l/4 point drops by 0~9cm. The fluctuation values are very inconsistent.
(3) The deformation of the bridge deck and the longitudinal deformation of the damaged bridge deck have been wavy, but the height difference is not big. However, the damage of bridge deck is very serious, concentrated in holes 3, 4 and 5 and two back seats. The crack is particularly obvious at the expansion joint near the top of the pier, which leads to the fracture of the steel bar.
(4) Abdominal arch and vertical wall are both mortar rubble. Due to the poor quality of waterproof layer, there are traces of water seepage in many abdominal holes and vertical walls, which leads to the discovery of many stalagmites suspended by running water for many years. Cracks were also found in the abdominal arch ring and vertical wall.
(5) The abutment back seat is severely deformed, and the settlement joint at the joint between the abutment back seat retaining wall and abutment is all increased to 8 ~ 10 cm (designed as 2cm), and the cavity of internal filler can be seen from the outside. The retaining walls and back seats on both lateral sides are 5 ~ 8 cm away from the outer edge of abutment. The deck of the back seat has sunk many times. When repairing, it was found that the filler was about 2m of coal cinder in the upper layer. When the vehicle passes by, cinder leaks from the settlement joint, so the road surface above is unstable.
⑤ There are vertical cracks on each pier, which reflects some problems in concrete pouring and cement and aggregate quality during construction. However, most of the cracks are early cracks, and white crystal precipitates appear along the cracks due to the age.
Many vertical and inclined cracks have also been found on the stone bridge platform built with mortar, but they are all very subtle.
1.3 key points of reinforcement design of Xiangtun Bridge According to the inspection and analysis of the bridge, no disease was found in the pier foundation, and even the Dexing bank abutment placed on the non-rock foundation showed no signs of displacement, so the reinforcement of the bridge was mainly aimed at the superstructure and the back seat of the abutment.
1.3. 1 The main arch ring is a weak member because of its small size and poor lateral connection. In view of this disease, the original beam was changed from 1 16×; 15×; 18cm increase the section size to116x; 15×; 50cm, change the three beams of the vault to the diaphragm116×; 30×; 84cm, in order to strengthen the lateral integrity, make the whole arch width * * * stress. Except the end tie beams, other cross tie beams were originally constructed by bolting and shotcreting technology and then prefabricated and installed.
Because the main arch ring is stressed heavily and there are many cracks, the arch ribs and arch waves are wrapped with steel mesh, and the arch ring section is strengthened by spraying 25# 6cm thick concrete to improve the overall stiffness and bearing capacity of each hole. In order to reduce the stress at the arch foot, from each arch foot to the second abdominal hole, 30# reinforced concrete is cast on the top of the arch ring with a thickness of 10cm. The design is as follows:
1.3.2 The original bridge deck lacks a stable and solid foundation and its integrity is poor. It is necessary to completely dismantle the original bridge deck, remove a part of the gravel cushion (if it is not gravel filler, it must be removed, replaced with gravel filler, and compacted), and then lay a layer of cement stabilized macadam base with a thickness of 15cm, and pour a reinforced concrete bridge deck with a thickness of 20cm on it.
1.3.3 The reinforced bar at the back seat of abutment is removed from the pavement at the back seat of abutment, and it is replaced with 35cm thick 30# reinforced concrete one-way simply supported precast slab, which is supported on both sides of the wall. Connect the side wall with φ24mm anchor bars, lay a 30# concrete bridge deck with a thickness of 15cm on the side wall, and leave a gap between the reinforced concrete slab and the filler in the back seat, so that the live load pressure can directly act on the side wall, reduce the earth pressure of the live load on the side wall, and increase the shear capacity and base friction of the side wall.
1.4 bearing capacity evaluation after reinforcement
(1) Under the main combined load of steam-overload 20, the additional combined load of suspension cable-120 and the additional combined load of special suspension cable-150, it is predicted that the stress, deformation and crack width of each measuring point meet the allowable limits specified in the code, so this bridge can bear steam-overload 20 and suspension cable-.
(2) This bridge is reinforced by shotcrete, which improves the bearing capacity of the old bridge and achieves the expected effect.
(3) The interaction between the sprayed concrete reinforcement layer of this bridge and the old bridge is incomplete. Due to the existence of holes in sprayed concrete and the low bond strength, the interaction degree of * * * is only 65.6%. It is suggested that "wet shotcrete method" should be adopted in anchor shotcrete construction in the future, so as to improve the interaction between new and old concrete, make the shotcrete layer and the old bridge play an integral role and improve the reinforcement effect.
(4) As the shrinkage and creep of the old bridge have been basically completed, shotcrete does not bear the dead load of the original bridge and itself, but only the live load of the working stage, so the strength of shotcrete is out of control.
2.320 National Road Lingxi Bridge (externally prestressed straight cable plus shotcrete anchor method, beam bridge)
2. 1 Overview of Lingxi Bridge Lingxi Bridge is located on National Highway 320. It was originally an old-fashioned bridge with a long history. In June of 1970 and June of 10, the bridge was transformed from a seven-hole uneven-span splayed wooden beam bridge to a seven-hole unequal-span simply supported reinforced concrete beam bridge, with a total length of 1 19.99m and a four-beam T-beam as the superstructure. The substructure is gravity pier and splayed wall. The design loads are steam-13 and drag -60, and the bridge deck width is net-7+2×; 0.5m sidewalk. After the reconstruction of National Highway 320 into a second-class highway, the traffic volume of this bridge is relatively large, with heavy trucks of about 200-300 kN passing by, pedestrians, bicycles and scooters. Therefore, the bridge has become a necking section of the whole line, and traffic accidents occur from time to time. In order to ensure smooth traffic and traffic safety with pedestrians and vehicles, with the approval of the superior, the bridge reinforcement is widened to the load standard steam-20, suspension-100, and the bridge deck width is-9+2×; 1.5m sidewalk.
2.2 Lingxi Bridge Widening and Strengthening Scheme
2.2. 1 widening and strengthening the approach roads at both ends of Lingxi bridge have been converted into secondary roads, and the concrete pavement has been completed. It is impossible to change the position of the bridge and build a new one. Therefore, only two schemes of land transformation or widening and strengthening are compared.
(1) field reconstruction scheme. In order not to interrupt the traffic, it is necessary to take a temporary bridge for local reconstruction. Because the water depth under the bridge is about 3 ~ 4 m all the year round (due to dam construction downstream), the cost of taking temporary bridge is high; In addition, the original upper and lower structures need to be demolished, which requires a considerable cost. However, after the transformation, the structures with standard span of each bridge hole are "new" and feel more beautiful, durable and reliable psychologically.
(2) Broaden the reinforcement scheme. The scheme does not need to build a temporary bridge, but only needs to properly control the traffic and widen and strengthen it when it is opened to traffic. Because the original piers and abutments can be used, the widening and reinforcement are mainly carried out on the superstructure, so more investment can be saved. As long as the widening and reinforcement scheme is suitable, it can also meet the design load requirements. However, the size of bridge opening is different, and the grade of the original bridge concrete is low, so there are certain diseases. Although it has been widened and strengthened, it seems to be inferior to the new bridge.
Through research and discussion, it is considered that according to the current situation of tight funds for highway construction in Jiangxi Province, the construction cost that can be saved should be saved as much as possible for investing in other necessary construction projects, so the widening and reinforcement scheme is chosen.
2.2.2 The original bridge reinforcement scheme has many reinforcement methods, such as:
(1) Reinforce the steel bars in the tension area of T-beam and increase the cross section of the beam body by means of bolting and shotcreting or cast-in-place concrete;
(2) Bonding steel plates for reinforcement;
(3) external prestressing reinforcement, etc.
According to the calculation, the original main beam is reinforced to be able to withstand the automobile -20 grade, and the design load of trailer-100 needs to add more steel bars, so the cost is higher, so the method ① is not selected; (2) Because the steel plate is exposed, it needs frequent maintenance, and it is not easy to make it closely combined with the beam by pasting the steel plate, so it is not used. (3) This method uses less steel, prestress can reduce or close beam cracks, and the construction is simple. However, there are also problems of anticorrosion and regular maintenance of prestressed steel bars, which are directly affected by atmospheric temperature. After repeated research, it is decided to adopt the scheme of strengthening with external prestress first and then covering with shotcrete. This scheme not only solves the corrosion problem of prestressed reinforcement, but also avoids its direct influence by atmospheric temperature, and at the same time, the shear resistance of the beam body after shotcreting is improved.
(1) Use the space between the beam ends of the two holes on the pier top to set up the cast-in-place transverse cantilever cantilever cantilever beam, and install the prefabricated micro-bending plate on it.
(2) Erecting the prefabricated π-shaped sidewalk beam on the cantilever part of the cantilever beam. The sidewalk beams on both sides of the bridge hole are longer than the main beam, with one end supported on the side pier and the other end supported on the special pier on the embankment to avoid widening the abutment.
(3) 25 # concrete is poured between the inner side flange of the sidewalk beam and the old bridge deck, and the bridge deck pavement concrete is poured at the same time, forming a carriageway with a clear width of -9m. Steel wire mesh is set in the bridge deck pavement and bridge deck widening to enhance the overall performance.
(4) The bridge deck expansion joint is set in the center of the cantilever beam, and the roadway pavement is extended and erected on the cantilever beam. Two layers of linoleum are laid under the bridge deck pavement on the cantilever beam to make it shrink with temperature. The expansion joint is filled with polyurethane material.
2.3 Test conclusion after reinforcement
(1) deflection test results show that the deflection of sidewalk beam and T-beam is very small under test load. The calculated deflection of T-beam under steam -20 load (considering impact coefficient) is only 3.607mm, and its f/L =1/4574; The deflection of sidewalk beam is 4. 142mm, and its f/l= 1/4 104, all of which are far less than l/600, which fully meets the use requirements.
From the comparison table of measured deflection and calculated deflection in the second loading stage, it can be seen that the measured deflection is far less than the calculated deflection of the corresponding load, and its check coefficient is only 0.329 ~ 0.369, which shows that the actual stiffness of sidewalk beam and T-beam is much greater than that used in theoretical calculation. For example, the calculated cracking moment of inertia of T-beam is 0.0978m4, the calculated actual moment of inertia is 0. 14 135m4, and the calculated moment of inertia of beam is 0.0978m4..
(2) According to the test data, when the bending moment of mid-span load increases by 1.63 1 times before and after strengthening and widening, the measured deflection of the T-beam and the stress of the steel bar in the tension zone at the bottom of the beam only increase by 1.07 1 times and 1.063 times respectively, which indicates that the upper part of the bridge is strengthened and widened.
(3) The strain and stress values of the beam under steam -20 load, pedestrian load and dead load inferred from the test data are all less than the allowable values, so it can be seen that the reinforced and widened bridge structure completely meets the design requirements.
2.4 Bridge reinforcement effect evaluation
(1) It is effective to strengthen the T-beam with external prestress first and then bond the prestressed steel beam with shotcrete, achieving the expected purpose and effect. This method is the first time in China. It not only increases the bending strength, shear strength and stiffness of the beam, but also effectively prevents the prestressed steel beam from being corroded due to exposure to the atmosphere, and it is not directly affected by the atmospheric temperature, which can make the prestressed steel beam work safely and reliably and reduce the maintenance workload and expenses in the future. This method has the advantages of simple construction equipment, convenient operation, fast construction speed and basically uninterrupted traffic during construction. Especially by prestressing, the main girder will arch upwards, which is very beneficial to improve the deflection of the old bridge and reduce or close the cracks. The combination of external prestress and shotcrete is used to strengthen the old bridge, which fundamentally eliminates the stress concentration of the original structure caused by cracks and other reasons, restores the coordination of the deformation of the original structure, and enables it to resist greater external load. Sprayed concrete wrapping prestressed steel bars not only plays the role of prestress, but also gives full play to the advantages of sprayed concrete and solves the maintenance problem of external prestressed steel bars. The economic benefit is very remarkable, which provides a very effective and good method for the reinforcement and reconstruction of similar bridges.
(2) Lingxi Bridge adopts the method of erecting sidewalk beams on the cantilever beams poured on the piers to widen the deck, so that the sidewalk beams can not only bear the pedestrian load, but also share part of the traffic load, make full use of its bearing capacity and save the cost of building new deep-water piers, which can be used as a reference for similar beam bridges to widen the deck.
(3) The floating working platform is a very economical method to reinforce the beam bridge, which is simple to install and disassemble and stable and safe to use. It is worthy to be used in the reinforcement of beam bridges with water under the bridge all the year round and not very high.
(4) The bridge reinforcement and widening process is simple, the construction is convenient, the equipment is few, and the reinforcement cost is only 950,000 yuan. If you build a new bridge in situ, you need to build a deep-water temporary bridge, which costs a lot, with a total cost of 2.5 million yuan, and the cost of strengthening and widening is only about 40% of it. The economic benefit is remarkable.
(5) Except for some projects, the bridge reinforcement and widening construction is carried out in a half-open state. The rest are two-way traffic with obvious social benefits.
(6) The key point of this bridge design is to skillfully use the cantilever beam on the pier to widen the bridge deck and avoid widening the pier abutment, which not only saves money, but also greatly speeds up the progress, and the construction operation is simple.
(7) Different bridges have different characteristics, but bridges of the same type have the same characteristics, and their reinforcement methods can be used for reference. However, many difficulties can be solved through concrete analysis of specific problems and clever use of their characteristics. Such as the cantilever beam on the pier of Lingxi Bridge and the sidewalk beam with side holes.
(8) The bridge has been in operation since it was reinforced and widened, and it has been used well after tracking observation.
3. Ganzhou Xihe Bridge (steel fiber reinforced concrete reinforcement in negative moment area, double cantilever beam bridge)
3. 1 Overview of Xihe Bridge The Xihe Bridge in Ganzhou City is located in the urban area, spanning Zhangjiang, and serves as a river-crossing channel connecting the east and west urban areas and entering the urban area from 105 National Road. The bridge is 256.2m long and is a 9-hole double cantilever reinforced concrete beam bridge with an aperture of 12.6+7×. 33+12.6m, and the calculated span of cantilever beam is14m. The original design loads are steam- 10 and tow-60, and the bridge deck width is -7+2×. 1.5m sidewalk. The bridge was designed in 1955 according to the Soviet standard drawing and referring to the construction drawing of Luohe Bridge, and was completed and opened to traffic in 1956.
Due to the increasing traffic volume and truck load after completion, there are many cracks in the positive and negative bending moments of the main girder and bracket of the bridge, and the deck pavement and expansion joints are also broken and damaged. Due to the serious disease of the bridge, heavy vehicles are forbidden to pass. Since 1992, Ganzhou Highway Sub-bureau has organized three inspections and photographed the bridge. 1993 carried out a comprehensive and detailed inspection before the bridge reinforcement design.
3.2 Inspection of Bridge Diseases The diseases of Xihe Bridge are mainly manifested in:
(1) Cracks in the main girder and deformation cracks in the main girder mainly occur in the lower edge (positive bending moment area) of the middle girder of the anchor span and the upper edge (negative bending moment area) of the root of the cantilever beam, and the latter mostly runs through the whole wing plate of the roadway. The width of each crack is about 0.1~ 0.5 mm. This kind of crack is obviously caused by the passing of a large number of heavy vehicles, which is a normal phenomenon. However, due to the existence of cracks in the negative bending moment area, rainwater easily seeps into the beam from the cracks, resulting in corrosion of steel bars and reduction of concrete strength.
The permanent deformation of the main girder is serious, which can be clearly seen from the change of the bridge railing column. The height difference between the pier abutment and the bridge deck is about 6cm.
(2) Cracks in the bracket Most of the cracks in the bracket occur at the bracket of the main beam in the direction of the cantilever tunnel in Ganzhou. The maximum crack is 2 1mm, which is a vertical crack near the bearing. In the seventh hole, the bracket concrete in Nanchang direction fell off at the bearing, the bearing steel plate moved outward, the steel bar was exposed, and the beam hung on the bearing, which was seriously corroded. There are few corbel cracks on the cantilever beam, mostly oblique cracks or vertical cracks at the corner (embedded end).
Later, when the original concrete of corbel was chiseled, it was found that holes appeared due to dense steel bars and improper concrete pouring.
(3) The bridge deck and expansion joint bridge deck are wavy. Cracks and damages on bridge deck pavement are very serious, especially the expansion joints on pier tops and hangers, which lead to damage and falling off. The reason may be that there is a soft linoleum waterproof layer under the bridge deck pavement, which is easy to crack under the action of heavy vehicles and impact loads.
3.3 Xihe Bridge Reinforcement Scheme While carrying out the static load test before reinforcement, we also checked the structural strength of the main components of the bridge. The calculation shows that the bridge can only meet the requirements of steam- 10 load through simple repair, but can not meet the requirements of steam-20 load operation.
According to the allowable stress method, the maximum stress of concrete in the compression zone of the fulcrum section of cantilever hole reaches 13.5mpa, which exceeds the actual allowable compressive stress of concrete. According to the ultimate state of bearing capacity, the strength of the normal section of the mid-span section is insufficient, and the maximum bending moment that the beam can bear is 1 1839.87kn? M, the bending moment that cannot meet the requirements 135438+08438+0kn? M. According to the on-site inspection, test and calculation and analysis data, in order to make Xihe Bridge meet the requirements of carrying steam -20 and hanging-100 load levels through reinforcement, it is necessary to reinforce the main hanging beam bracket, main girder and its upper deck pavement, and transform the bracket support and expansion joint.
3.3. 1 Reinforcement of main girder and cantilever beam support of cantilever tunnel
(1) After calculation, the weakest section θ of the support is 28.86; Or θ = 41.19; For the inclined section (excluding H), the tensile stress is 2.0 MPa and 2.2mpa respectively according to the calculation of eccentric tension members. According to the calculation of whether the cross-section size of the corbel can meet the requirements of crack control, it is found that the cross-section size of the corbel is insufficient, and the coefficient β in the formula fvk≤β needs ≥ 1.39 to meet it, and the crack resistance value of the corbel under static load should be at least β=0.80. According to the above, it is reinforcement. In addition, the vertical load can actually increase a lot due to the bump and impact caused by the irregularity and unevenness of the expansion joints of the support. Therefore, the micro-cracks in the corbel concrete continue to develop, eventually causing serious cracking and damage.
(2) As the bracket is the key part of the cantilever beam bridge, whether it is firm and reliable is one of the decisive factors for the bridge to maintain safe traffic. The bracket is also the weak link of the cantilever beam, where the height of the beam suddenly decreases, the cross section has many concave corners, the concentrated force to be transmitted is very large, and it frequently bears the impact of vehicles, so it is a very complicated part. The existing checking methods are quite approximate and cannot fully reflect the stress situation. To this end, we put forward two schemes to strengthen the corbel:
Scheme 1: The original corbel low-grade concrete (old 170 concrete) is chiseled, and 30 steel fiber concrete is poured instead. When pouring steel fiber concrete, epoxy mortar is coated on the joint surface of new and old concrete to improve the bond between them.
Scheme 2: Put the hanging beam on the main beam from two fulcrums to the end beam with multiple fulcrums. This scheme can reduce the stress on the original support, but the concrete of the support is cracked due to rolling, so it is still necessary to cut hair and pour new concrete. Because the original width of the end beam is insufficient and the label is too low, it is also necessary to chisel hair and re-pour and widen it, which increases the engineering quantity. Another disadvantage of this scheme is that the transmission of force is not clear.
3.3.2 Reinforcement of negative bending moment of main girder
According to the inspection, test data and calculation results, under the general load, a large number of cracks are produced in the negative bending moment area of the main girder, and a large number of network cracks are also produced in the deck pavement on it. This kind of crack is not only unsightly, but also makes people feel insecure. In fact, it will also corrode the stressed steel bars due to rainwater infiltration into the main girder and flange plate, which will affect the service life of the bridge.
When considering the reinforcement scheme, longitudinal tensile reinforcement is added according to the calculated data and placed in the original pavement. The calculation results also show that the tensile stress of bridge deck concrete will reach 3.96mpa due to the negative bending moment of the load in the new design standard. When ordinary concrete with various labels listed in the current design code for bridges and culverts is used, the beam top will still crack due to the unsatisfactory tensile design strength. Only by using steel fiber reinforced concrete, its tensile design strength can be greater than this tensile stress, thus ensuring that there is no crack on the bridge deck. Therefore, in the reinforcement scheme, steel fiber concrete is used for the bridge deck pavement in the negative bending moment area, which is required to be truly and firmly combined with the beam end flange plate. Therefore, in addition to roughening the top of the beam top flange plate, it is also necessary to set anchor bars on it and brush adhesive on the top surface to make the new and old concrete closely combine. Before pouring steel fiber reinforced concrete pavement, polymer chemical materials should be pressed into the cracks at the top of the beam to bond the cracks.
Another scheme to strengthen the negative moment zone is to use unbonded prestressed steel bars within the scope of bridge deck pavement. This measure aims to further close the original cracks on the bridge deck, and at the same time, due to the reduction of the negative bending moment of the cantilever, reduce the deflection of the cantilever end and reduce the impact at the connection between the main beam and the cantilever beam. Because the construction period is short, the construction technology is relatively new, and certain equipment is needed, the general construction team may not have the conditions, so it is abandoned.
3.3.3 When calculating the reinforcement of the anchorage span of the main girder and the positive bending moment area of the hanging beam according to the limit state of bearing capacity, the section strength of the main girder is not satisfied under the load of steam -20 and hanging beam-100, so reinforcement is needed. The reinforcement measures are: after chiseling the original bridge deck pavement and linoleum, roughen the original bridge deck, add a layer of steel mesh to the original pavement thickness with anchor rods, and then pour 30 uea self-waterproof concrete to compensate shrinkage. The purpose of using uea shrinkage-compensating self-waterproof concrete is because uea shrinkage-compensating concrete is a kind of moderately expansive concrete. Under the constraint of steel bars and adjacent positions, the prestress of 0.2 ~ 0.7 MPa can be established in concrete, so that the structure can achieve the purpose of crack resistance and seepage prevention, that is, to solve the waterproof problem. Except that steel wire mesh is not added in the original pavement thickness, the reinforcement method of hanging beam is the same as that of main beam.
3.3.4 Bonding of main girder cracks
In order to improve the stress in the negative bending moment area of the main beam, increase the durability and rigidity of the beam slab, and at the same time, in order to ensure that the main beam and the hanging beam can safely bear the weight of the guiding beam equipment passing through the bridge when the holes of the guiding beam need to be moved in the reinforcement construction, the reinforcement design of the bridge adopts the method of pressure grouting the cracks of the main beam and the hanging beam with polymer chemical materials to bond the cracks.
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