5. 12 After the Wenchuan earthquake, roads and bridges in the disaster area were damaged to varying degrees, some were scrapped, and some were still usable after being repaired and reinforced. Through reinforcement and restoration, energy can be saved, project cost can be reduced, construction period can be shortened, garbage can be reduced and the environment can be protected. The reinforcement project of Longfei Bridge in Fujiang, Pingwu County, which was undertaken by our company, used new materials to strengthen the bridge, increased the section of the main arch ring of the bridge, successfully completed the construction task and was recognized by the relevant departments in the disaster area. In order to facilitate popularization, the construction method is formed through research and summary.
2. The characteristics of the construction method
2. 1 Reinforce the damaged or insufficient bearing capacity of the arch bridge.
2.2 Add a layer of reinforced concrete at the bottom of the main arch ring to restore the original design bearing capacity of the bridge.
2.3 The high-pressure joint filling treatment of structural cracks adopts cement-based permeable crystalline waterproof glue coagulation material, and the concrete construction adopts structural adhesive bar planting technology and building structure reinforcement materials.
2.4 This technology has the advantages of maintaining the original appearance of the bridge, ensuring the quality, reducing the project cost, saving energy and protecting the environment.
2.5 The transportation, installation and disassembly of movable Bailey truss are simple and convenient, with low labor intensity and fast construction speed.
3. Scope of application
This method is suitable for the integral reinforcement construction of arch bridges and buildings.
4. Process principle
This construction method is to reinforce the arch and cracks of the bridge without changing the mechanical characteristics of the original structure, mainly by reinforcing joint filling, chiseling the original concrete, boiling holes on the bridge deck, planting steel bars, binding the main reinforcement, supporting the bottom formwork and pouring self-leveling concrete to make it form a whole with the bridge, so as to realize the bearing capacity of the bridge with the original structure after formwork removal.
5.2 Key points of operation
5.2. 1 Erection and removal of scaffolding for reinforcement
1, the general idea of construction frame erection.
Scaffolding is only used for bridge reinforcement construction, not for formwork support. The erection height of scaffolding is about 18m, so it is not necessary to calculate the erection according to the conventional method. Its foundation is set on the pier and the beach at the bottom of the river. After the excavation and concrete pouring are completed, the Bailey frame is used as the erection platform of the construction frame, and scaffolding is erected on it.
2. Process flow
Leveling and excavating the floodplain → watering the Bailey frame foundation → assembling and erecting Bailey frame piers → erecting Bailey truss beams in the middle of the river → erecting the scaffolding of construction workers → erecting structural connection measures such as scissors → laying scaffolding for construction → hanging safety horizontal net and dense mesh safety net → inspection and acceptance.
3, the erection of the frame body
1) Erection requirements: the vertical and horizontal spacing of vertical poles is 1.5m, and the step distance is1.5m. When a full-house scaffold is erected, a 250mm×50mm long slab will be laid under the vertical poles.
2) Bar: during erection, the verticality of the vertical pole spacing should not be greater than 1/200 of the frame height, and the joints of two adjacent vertical poles should be staggered by 500mm, which is not in the same step. The cross-extending end of each steel bar should be greater than 100mm to prevent the steel bar from sliding. Inside and outside poles plus sweeping poles.
3) Scissors: The included angle between the scissors and the ground is 60, and five scissors are arranged every three steps. In addition to fastening the two ends of the scissors with the scaffold column with rotating fasteners, 2 ~ 4 fastening nodes are added in the middle, and the lap length is 1m, and three rotating fasteners are used to fasten the scaffold column.
4) Scaffolding: scaffolding is laid on all operating floors, and a scaffold is laid on the side as a scaffold board. For the scaffolding laid at the joint, there are two small bars under the joint.
Hanging net treatment: all exposed surfaces are covered with dense mesh safety net and tarpaulin, and the bottom of the operation layer is hung with large eye horizontal net.
4, outside the frame demolition
1) The order of dismantling the outer frame is to build it first and then dismantle it.
2) According to the actual situation of the project, if the scaffold is dismantled by sections and facets, connecting rods and braces should be set at both ends of the scaffold that will not be demolished.
3) Scaffolding demolition should pay attention to the protection of finished products, so as not to damage the finished wall and outer window glass.
4) All components must be classified and placed in time, and fasteners should be bagged and shipped out of the floor. Do not throw them. Steel pipes shall be transported to the ground manually and shall not be stacked on an outer frame.
5.2.2 Reinforcement planting construction
1. Construction process: positioning → drilling → hole cleaning → steel bar derusting → preparation of anchoring glue → steel bar planting → maintenance and protection → inspection and pull-out test.
2, the construction points:
1) positioning
Mark the drilling position and model according to the design requirements. If the hole position touches the existing steel bar on the base, the drilling position can be adjusted appropriately. However, it should be planted in the inner side of stirrups (for beams and columns) or distributed steel bars (for slabs and shear walls), and the holes should be as close as possible to the existing steel bars to be extended (better force transfer effect).
2) Drilling
The electric hammer drilled a hole. In case of reinforcement, adjust the hole position to avoid it.
B drilling diameter d+4~8mm (small diameter steel bar takes low value, large diameter steel bar takes high value, and d is the diameter of steel bar and bolt).
C when the strength grade of parent metal is not lower than C20, the anchorage force of single pull-out test is generally greater than the yield force of steel. For HRB335 (Grade Ⅱ), HRB400 and RRB400 (Grade Ⅲ) threaded steel bars, Q235 and Q345 bolts and 5.6 screws, the drilling depth is 15d. For unthreaded steel bars or screws, the drilling depth should be increased by more than 5d.
D The actual drilling depth can refer to the benchmark 15d. According to the actual anchorage force and structural length requirements, it is calculated and determined according to Code for Design of Reinforcement of Concrete Structures (GB50367-2006).
3) Borehole cleaning
A. After drilling, check the depth and diameter of the hole, then blow out the dust in the hole with compressed air, brush the hole wall with a brush and cotton cloth, and blow the hole with compressed air, and repeat this for 3~5 times until there is no dust debris in the hole. Finally, wipe the hole wall with cotton cloth dipped in acetone to temporarily close the hole. If there are waste holes, clean them up and fill them with steel glue.
Boreholes should be kept dry.
4) Rust removal of steel
Rust and oil stain within the anchorage length of steel bars shall be removed (blue scale of new steel bars and bolts shall also be removed) and polished to metallic luster. Angle grinder and wire wheel blade are used for faster speed.
5) Preparation of anchoring glue
aLYJGN？ The bar planting glue is a component A and a component B, and the glue should be mechanically stirred. The stirrer can be composed of an electric hammer and stirring teeth, and the stirring teeth can be made of cross φ 14 steel bars welded at the end of the electric hammer bit. A small amount (less than 0.5kg) can also be manually stirred with φ 6 and φ 8 fine steel bars. (Note: Only mixing with a greasy knife cannot guarantee uniform mixing).
B Take a clean container (plastic or metal basin, without oil, water and other impurities) and mix it with a scale according to the proportion, and stir it with a stirrer for about 10 minute until the components A and B are evenly mixed. It is best to stir in the same direction when stirring, and try to avoid mixing air to form bubbles.
C glue should be used now, and the amount of glue at a time should not be greater than 5kg.
6) Reinforcement planting
The structural steel bars planted in this project are also used as hanging formwork reinforcement (welding) bolts.
A vertical hole is planted with steel bars, and the glue can flow directly and be rammed into the hole.
B. Horizontal hole rebar planting can be rammed into the hole with φ 6 fine rebar combined with rubber pallet (clean plate), or the construction personnel wear leather gloves and put the prepared rubber lump into the hole.
C. For the inverted vertical hole, please choose high thixotropic rebar adhesive, which is not flowing, but can be inserted and rammed into the hole.
Steel bars and bolts can be driven into holes by rotating or hammering. When hammering, steel bars or bolts should be supported with one hand to ensure alignment and avoid rebound. If a small iron plate with a thickness of 6mm is welded at the end of the short electric hammer drill, and then the function of the electric hammer is set to the impact state, the continuous impact force of the electric hammer can be used to overcome the resistance of the rebar-planting adhesive, and the rebar can be quickly sent to the bottom of the hole without rebounding. This method is recommended for planting a large number of or large diameter steel bars.
E, the filling amount of anchoring glue should ensure that a small amount of glue overflows after inserting steel bars.
7) Curing and protection
A kind of rebar glue has a curing process. When the daily average temperature is above 25℃, the rebar shall not be disturbed within 12 hour, and the daily average gas is not allowed. When the temperature is lower than 25℃, the reinforcement shall not be disturbed within 24 hours, and replanting shall be carried out when the disturbance is large.
bLYJGN？ The rebar adhesive can be cured well at normal temperature and low temperature. If the curing temperature is about 25℃, it can bear the design load in 2 days. If the curing temperature is about 5℃, it can bear the load in 4 days, and the anchoring force will increase with time.
8) check
3~4 days after planting reinforcement, random sampling can be taken, and the system consisting of jack, anchorage and reaction frame can be used for pull-out test. Generally loaded to the design force value of steel, the test results are intuitive and reliable.
formwork
1, Introduction
Formwork is a temporary structure during construction. It controls the dimensional accuracy of the structure and directly affects the project quality, construction progress and project cost. Formwork must have sufficient strength, rigidity and stability, and can reliably bear all kinds of loads that may occur during construction. At the same time, the template should be simple to make, easy to disassemble and operate, and ensure safety.
2, construction technology and key points
Material selection → stress analysis → welding suspender → lofting processing template → template support → reinforcing template → supporting watering observation template.
1) Material selection: the formwork is made of glued wood boards. The size of each plywood is 2.44m×0.6m, and the square timber with the cross section of 100mm×50mm is used as the grid skeleton, and the plywood is fixed on the grid skeleton, and the square timber grid skeleton is used as the rib of the template. The formwork is divided into blocks along the arch span direction and transverse direction, and made into independent unit blocks, which are assembled into an integral arch formwork during installation. Template board face should be smooth, tight joints. Template gap should be filled with foam plastic and injected with 80 1 glue to ensure reliable sealing and no slurry leakage when pouring concrete.
2) Force analysis:
Force calculation of screws: number of screws:19×101=1919.
Template weight: (900m2× 0.03m+0.1m× 0.06m×1m× 50) × 900kg/m3 = 27270kg.
Weight of steel pipe:11m×100× 3.5kg/m = 3850kg.
Concrete weight: 90m3×2500kg/m3=225000kg.
Other additional load: 5000kg
Weight of each screw: (27270+3850+225000+5000) kg/19 =136.07kg.
The ability of each screw to bear tension is determined by experiments. The welded specimens of screw bar planting are sent to the laboratory for tensile test, and its tensile strength is 30KN, which meets the strength requirements of this scheme.
3) Weld steel screws on the arch ring rebar planting, and the screw spacing is 600 mm ..
4) Survey and lofting: According to the rise-span ratio of the original arch (1/5 in this project), lofting out the radian of the arch ring with enlarged section, and fixing the distance between the arc and the Xuan with nuts. So as to determine the thickness of self-leveling concrete (see 5.2.3- 1 for details of formwork construction).
Template structure detail 5.2.3- 1
5) The screw is used to fix the bottom template. A circular hole is opened on the square rib of the soffit template, steel pipes are distributed on both sides of the square rib, screws pass through the circular hole, butterfly buttons and nuts are added, and the steel pipes are connected to the screws to fix the soffit template.
For safety encryption, arch down screws with a spacing of 300mm (see 5.2.3-2 for details of screw planting).
Details of screw planting 5.2.3-2
6) Setting of observation hole and feed hole:
According to the actual situation of the vault, observation holes and feeding holes are set. Each row (vertical and horizontal) of observation holes is 300×300mm in size, with the spacing of 1m around and 2m in the middle, so that the concrete can be leveled automatically. Considering the overall compactness of concrete and the compactness of formwork, the observation hole and the blanking hole are set as the same hole.
5.2.4 Concrete pouring project
1, Introduction
Because the arch ring is thickened under the original soffit, it is difficult to pour and vibrate if ordinary concrete is used. Therefore, Huayu -45 building structure reinforcement material is used to strengthen arch ring concrete, which is a kind of material with good fluidity, no vibration and high strength, and is called self-leveling concrete.
2, process flow and construction requirements
Selection of pouring method → Determination of pouring line → Setting of concrete mixing and conveying → Division of labor and cooperation among teams → Key points of watering control → Maintenance → Form removal → Dismantling and treatment of suspenders.
1) After study, the method of window grouting under arch (slope on both sides of pier) and hole grouting above arch is adopted. The construction process is in an observable, controllable and continuous state.
Arch ring concrete pouring should follow the principle of symmetry and synchronization on both sides. Workers work in three shifts for 24 hours, and people do not stop to rest, and the method of continuous perfusion in one go.
2) Open a window on the formwork under the arch frame, pour the concrete of the inclined section near the arch frame, and pour the concrete of the vault at the top of the original main arch ring close to the horizontal section. The concrete pouring of reinforced arch ring is completed by combining pouring under the arch first and pouring on the arch afterwards. The position and number of windows on the soffit formwork should be considered from two aspects: reducing the concrete process and speeding up the progress. When pouring, the concrete hopper can be placed on the bridge deck, and the self-leveling concrete can be led to the pouring window through the hose to pour concrete.
3) Setting of mechanical equipment
There are four drum mixers on the bridge deck (two on the left and right sides of the bridge, with reservoirs or buckets beside the mixers), and special blanking passages, pedestrian passages and sufficient lighting facilities are set up.
4) Division of labor and cooperation among groups
The discharging end and the receiving end are provided with a receiving hopper and a construction operation platform. Operators are divided into three groups: material preparation group, feeding group and pouring group.
A material making team: make materials on the pavement of the bridge deck and transport them to the receiving hopper through the discharging hopper (the discharging hopper and the receiving hopper are connected by a special chute).
B, material delivery team: working on the construction platform, responsible for transporting from the receiving hopper to the pouring position.
C pouring group: operating on the construction platform, responsible for pouring self-leveling concrete and observing the compactness of concrete and whether the template leaks slurry at any time.
5) Irrigation control points
A mixing must be carried out according to the technical requirements provided by the manufacturer, and special attention should be paid to the control of water addition (12%- 14%) to ensure the fluidity and strength of concrete. Control of water addition According to the designed water addition amount and the amount of materials used in each tank, the water addition amount of each tank is weighed with a special container.
B, when pouring, send full-time observers to observe the compactness of self-leveling concrete through reserved observation holes. If you find that the flow resistance or density is not good, you can tap the template with a wooden hammer.
C. When pouring to the reserved hole on the bridge deck, the pouring shall be continued, and the pouring shall not be stopped until the reserved hole on the bridge deck takes a thick paddle. When pouring into the reserved hole or observation hole, the hole shall be sealed with a template prepared in advance (lower end is 300×300mm, upper end is 3 10×3 10mm). Before continuing pouring, check whether the seal is firm and whether there is slurry leakage.
D, in the process of concrete pouring, template engineering must have someone on duty, and ready to tools and maintenance template materials; During the formwork construction, carefully observe whether there is any deformation, shedding and slurry leakage, and take immediate measures to reinforce and repair the formwork when problems are found, so as to ensure the smooth concrete pouring construction.
6) After concrete pouring, the formwork shall be continuously wetted for more than 3 days, and then cured to the design strength.
7) Formwork removal: the formwork can only be demoulded after it is cured to 80% of the design strength. When removing the formwork, the formwork should be removed first, and then removed. Dismantled templates and materials shall be transported away in time, and shall not be stacked on scaffolding and construction platforms for a long time, and the stacking height shall not exceed1m.
8) Treatment of embedded screw: After the formwork is removed, the embedded screw used for formwork hanging construction shall be cut by hand grinding wheel. The cut screw head is screened with a fine screen of 5mm, and the remaining fine materials are mixed into mortar to block the screw head according to the mixture ratio of 12% water.
6. Materials and equipment
6. 1 material
6. 1. 1 Huayu -45 building structural steel bars are used as concrete, and self-sealing vibration-free concrete is adopted.
6. 1.2 steel bars must comply with the provisions of Steel for Reinforced Concrete (GB 1499—2007), and the specifications and models of steel bars must meet the design requirements, with the factory certificate, inspection report and mechanical performance re-inspection report of steel bars.
6. 1.3 The steel used shall have quality certificates and meet the requirements of design documents. In case of doubt about materials, sampling inspection shall be conducted, and the results shall conform to the provisions of national standards and the requirements of design documents before they can be adopted. Connecting materials (covered electrode, welding wire, flux, equal strength bolts, refined bolts, ordinary bolts and rivets, etc.). ) should be accompanied by a quality certificate, which should meet the requirements of design documents and the provisions of national standards. It is strictly prohibited to use covered electrode with peeling coating or rusty core, flux caked or charred by moisture, and high-strength bolts that are corroded, bruised or mixed.
6.2 mechanical equipment
6.2. 1 Earthwork excavation: excavators, loaders and dump trucks.
6.2.2 Concrete construction equipment: concrete vibrator, concrete mixer and concrete delivery pump.
6.2.3 Main machines and tools for reinforcement: electric hammer, pneumatic pick, air compressor, angle grinder, mixer and weighing instrument.
6.2.4 Monitoring system: level, theodolite, dynamometer, walkie-talkie and broadcasting equipment.
6.2.5 Other equipment: truck crane concrete cutter, hollow compressor, air hammer, electric welding machine, steel bar cutter, steel bar straightener, steel bar bender, universal bar and Bailey beam.
7. Quality management
7. 1 Relevant standards and specifications (see Table 7. 1).
7.2 Quality assurance measures
7.2. 1 Technical personnel should know the site situation carefully, be familiar with the design drawings, and make disclosure to the construction team seriously. Strictly inspect and supervise each working procedure, conscientiously implement the "three inspection system" of the project, and keep pace with the times to fill in and sign all kinds of engineering materials.
7.2.2 Do a good job of raw material inspection before use. In view of the common quality problems, practical corrective and preventive measures are formulated. As well as the construction and original inspection records, timely sorting, recording and archiving.
7.2.3 In the construction process, the quality assurance measures in the current steel bar construction technology standards, concrete construction technology standards and steel structure construction technology standards must be strictly implemented.
8. Safety assurance measures
8. 1 Abide by the operating rules of safety technology on the construction site and local regulations on production safety on the construction site.
8.2 Seriously implement the policy of "safety first, prevention first, comprehensive treatment" and relevant national laws and regulations, and organize the establishment of a safety production leading group composed of full-time safety officers, team leaders and electricity users, which is fully responsible by the project manager in combination with the specific characteristics of this project, implement the responsibility system for safety production, clarify the responsibilities of personnel at all levels, and pay special attention to the safety production of this project. Ensure the realization of the goal of safe production.
8.3 Seriously implement the post responsibility system, disclosure system and reward and punishment system for safe production. Before the construction of each working procedure, safety disclosure must be carried out step by step and fully implemented. Special type of work personnel must hold relevant certificates, and if an accident is caused by illegal operation, the direct responsibility of the parties concerned shall be investigated.
8.4 During concrete pouring construction, observe whether there is excessive deformation or looseness of formwork, hanging device and support, and handle the problems in time when found.
8.5 Temporary electricity utilization on the construction site shall be carried out in strict accordance with the relevant provisions of Technical Specification for Safety of Temporary Electricity Utilization on the Construction Site. The hand-held lighting used shall be 36V safe voltage. Temporary power consumption on site shall be connected according to the requirements of specifications, and illegal power consumption is not allowed. In order to ensure safety, sufficient lighting, warning signs and fence facilities should be set up on the construction site.
8.6 The construction of this project is carried out on the elevated platform across the river, and the stability and firmness of the scaffold should be carefully checked to ensure safety. Protective nets should be installed around and below the scaffold. Construction personnel must wear safety belts, safety helmets and protective gloves. Avoid falling and personal injury, falling objects from high altitude and personal injury, and avoid corrosion injury of reinforcement materials to opponents. Attention should be paid to safety when installing, dismantling and transporting bottom formwork.
8.7 Fire safety distance of various houses, warehouses, yards, etc. Should comply with the provisions of the public security department, indoor flammable items shall not be piled up; Strictly do not smoke in woodworking factories, warehouses and other places; Remove flammable debris from the site at any time; Don't pile up production materials in or near the fire.
8.8 Oxygen cylinders shall be stored separately from acetylene cylinders, and strictly ensure that oxygen cylinders are not polluted by grease. The acetylene generator has a safety device to prevent backfire.
8.9 Cable shall be connected in tn-s mode, and electrical equipment and lines must be well insulated. The hanging height and line spacing of power lines erected in the field should be set on special poles in addition to meeting the requirements of safety regulations. The metal shell of power distribution facilities should be connected with reliable protective wires, and the protective wires of mobile power tools and hand-held power tools must adopt copper core flexible wires and highly sensitive leakage protection devices.
8. 10 The construction site shall be arranged according to the safety regulations such as fire prevention, wind prevention, lightning protection and electric shock prevention, and various safety signs shall be improved.
9. Environmental protection measures
9. 1 Establish a construction environmental sanitation management organization, strictly abide by the relevant national and local laws, regulations and rules in the construction process, strengthen the control and treatment of construction fuel, engineering materials, equipment, wastewater, production and living garbage and waste residue, abide by the rules and regulations on fire prevention and waste disposal, do a good job in traffic guidance, fully meet the convenience requirements, and accept the supervision and inspection of relevant units at any time.
9.2 Restrict the construction site and operation within the scope of the project construction permit, reasonably arrange and standardize the scope, and ensure that the signs are clear and complete, all kinds of signs are eye-catching, and the construction site is clean and civilized.
9.3 Set up a special drainage ditch to discharge the construction sewage in an orderly and centralized way, and do a good job in harmless treatment, so as to fundamentally prevent the construction sewage from polluting the river.
9.4 Regularly remove construction waste, dregs and other engineering materials to prevent scattering and pollution along the way. Construction sewage shall be treated according to environmental sanitation indicators and discharged to designated places according to local environmental protection requirements. Abandoned slag and other engineering wastes should be piled up and treated reasonably according to the designated location and scheme of engineering construction.
9.5 Give priority to environmental protection machinery. Put an end to the spillage of concrete transport vehicles and reduce environmental pollution, and the concrete transport vehicles must be cleaned when entering and leaving the gate.
10. Benefit analysis
10. 1 With the post-disaster reconstruction and recovery of 12 Wenchuan earthquake, this construction method provides a new method for bridge repair, so as to avoid the demolition of the bridge and preserve its characteristics and historical features to the maximum extent.
10.2 This bridge reinforcement construction technology will minimize the bridge cost, shorten the construction period, and restore traffic as soon as possible, with little impact on the bridge structure itself and no impact on the adjacent bridge sections and surrounding environment. It paved the way for post-disaster reconstruction, accelerated the economic construction in the disaster area and provided convenient transportation for the lives of ordinary people.
10.3 Bridge reinforcement technology is energy-saving, low-cost, labor-saving and time-saving. According to statistics, the cost of bridge reinforcement is about 30% of the cost of demolition and reconstruction, and it also reduces the environmental pollution caused by demolition.
10.4 in the process of bridge reinforcement, this method combines Bailey frame with ordinary steel pipe scaffold system, which greatly shortens the construction period.
1 1. Application example
The reinforcement and reconstruction project of Longfei Bridge in Pingwu County, Sichuan Province, which was aided by our company, started on June 20, 2009, was completed on February 20, 2009, and was successfully opened to traffic on New Year's Day of 20 10. With an investment of nearly170,000 yuan, this project is one of the construction projects in Pingwu County, Sichuan Province, and it is also the most important bridge for the post-disaster reconstruction road network planning in Pingwu County.
Longfei Bridge in Pingwu County was built at 1986. It is a 26-hole deck masonry arch bridge with a total length of 487 meters. It is the only motor vehicle bridge in Pingwu County, and it is also an important traffic node for Pingwu County to enter Mianyang and Jiuzhaigou. In the 5. 12 Wenchuan earthquake, the bridge was seriously damaged and could not be used normally. It needs maintenance and reinforcement before it can be put into use.
After being used for more than half a year, no quality problems were found, which proved that the bearing capacity and stability after reinforcement were good and the project reinforcement was very successful.
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