1 arch ring description

The main arch ring of Xiaohe Bridge is a catenary hinged ribbed slab arch with equal cross section, with an equal height of 0.8 m, a rise-span ratio of 1/6 and an arch axis coefficient of 2.24. The abdominal arch ring is an arc rib arch with equal section, and the height of the section is 0.6 m; The design number of arch ring concrete is C40, and the main quantities are C40 concrete: 580 1.44 m3, and reinforcement:1.485t..

Arch ring is the main load-bearing structure of arch bridge and the key link of the whole arch bridge construction. According to the actual situation, this project plans to adopt the full-house support method for construction. Before arching, the site should be leveled and the basement should be treated. The arch is erected with bowl-shaped scaffolding, and the upper part is adjusted into an arch with a wooden arch. The bottom die, side die and groove die are made of bamboo veneer. On-site binding and welding of reinforcement. Arch ring concrete is made of commercial concrete, transported by concrete truck and pumped into the mould.

2. Specific plan

2. 1 foundation treatment

The key part of the cast-in-place structure support system is the foundation treatment under the bridge, and the bearing capacity of the foundation within the full length of the superstructure should meet the full load to ensure that the support is not deformed and the foundation is not settled. The concrete methods for the foundation treatment of this bridge are as follows: after the foundation pit of the bearing platform is backfilled, leveling and compacting, paving 40 cm thick building dregs and 20 cm thick macadam in layers, leveling and compacting, pouring C20 concrete with a thickness of 10 cm ~ 12 cm, and setting a 0.5% cross slope on the right side of the concrete surface to ensure the uniform distribution of water resistance, drainage and supporting pressure. The fourth span of the bridge is located in the center of the river. Based on the investigation of the water level and discharge of the river, in order to ensure the normal discharge of the river, a mortar rubble temporary bridge with a width of 8 m was built. Spread a piece of 20 cm×20 cm square timber on the temporary bridge, and then put a bracket on the square timber. When foundation treatment is carried out, special attention should be paid to the treatment of weak parts in the corner.

2.2 bracket installation

Bowl-buckle support is proposed for the support in this contract section, and the camber of the support is adjusted by wooden arch. First of all, according to the reinforced concrete load, formwork support weight, construction load (people, materials, machines, etc. ) and other possible loads (such as ensuring the load of facilities), check the strength, stiffness, stability and foundation bearing capacity of the bowl buckle bracket and wooden arch. The arrangement spacing of supports is 120 cm in the transverse direction, 120 cm in the longitudinal direction and120cm in the step distance; The transverse span of the wooden arch is 120 cm, and each longitudinal span is divided into 9 zones (1m+2m+3m+4m+10m+4m+3m+2m+1m). The engineering quantity can meet the simultaneous construction of 8 spans and half a bridge width.

Bowl buckle bracket steel pipe is φ48 mm×3.5 mm, and the vertical rod is equipped with adjustable jacking. A piece of 15 cm× 15 cm square timber shall be laid on the jacking, and a wooden arch shall be built on the square timber. Wooden arch adopts 10 cm× 10 cm square timber. The height of the adjustable jacking should meet the clear height requirements of bottom die adjustment and demoulding: the distance between the top of the pallet and the top of the steel pipe is about 16 cm. After the bottom die is adjusted in place, it is necessary to ensure that the jacking has at least 12 cm downward thread space. Before installing the adjustable jacking shaft, it should be cleaned with engine oil and the threads should be moved sufficiently to ensure the usability and flexibility after installation. During construction, technicians should determine the jacking elevation of the support according to the elevation values of the main arch bottom at each point, deducting the size of the bottom die and the wooden arch frame, and adding the pre-arch value of the support itself. In the process of installing the adjustable jacking, the length of the adjustable jacking protruding from the steel pipe should be controlled to be no more than 1/3 of the total length of the jacking. On the basis of concrete, two 10 cm× 10 cm×400 cm square timber are placed at the bottom of the support to cross the bridge, and the square timber is leveled to prevent the bottom of the steel pipe from being empty.

Because the height difference of the bracket varies greatly, in order to strengthen the stability of the bracket, diagonal braces are set in the longitudinal and transverse directions, the included angle between the diagonal braces and the horizontal plane should be between 45 and 60, and the horizontal projection width should be between 4m and 8m. The diagonal braces are all connected by rotating fasteners, and the fastener bolts should be tightened with special wrenches. The lap length of diagonal bars shall not be less than 0.4 m, and at least two rotating fasteners shall be used for lap joint. Tie rods, mandrels and diagonal braces are used to strengthen the transverse connection between wooden arches.

Steel pipes, fasteners and adjustable jacking should match and meet quality standards. Steel pipes shall be straight, crack-free, damage-free, with consistent specifications, and the initial bending shall not be greater than11000; The adjusting thread of jack shall be intact and shall not be damaged, and shall be protected with butter and shall not rust. Carry out bracket installation, operation and acceptance in strict accordance with operating procedures.

2.3 bottom die installation and preloading

Bottom module assembly

During construction, firstly, the surveyors accurately release the control elevation line of the bottom surface of the main arch ring, that is, the top elevation of the bottom die. Calculate the jacking elevation downwards and adjust the hanging line, install the square wood and the processed wooden arch on the jacking, and connect the square wood and the wooden arch with nails; Spread 16 cm square timber along the longitudinal direction on the wooden arch, and then spread the bottom formwork. The bottom die is made of 244cm×122cm×1.2cm bamboo plywood, and the square wood and bamboo plywood are fixed with nails. The long side of the bamboo veneer is arranged in the longitudinal direction of the bridge. The transverse joint is arranged in the middle of the belt wood, and the joint is filled with double-sided adhesive tape; The longitudinal joints shall be edged with wooden strips to prevent slurry leakage and deformation at the joints. The panel and the belt wood are fixed with nails, and the panel should be slightly bent along the belt wood to ensure the linear curve of the main arch.

In the range of the interval groove of the main arch ring, considering the operation space required for the welded joint of steel bars in the interval groove, the bottom formwork panel in this range is made into a separate detachable structure, and the bottom formwork panel is removed during the construction of the steel bar joint and restored before concrete pouring.

The formwork panel shall be made of bamboo glue board, which shall meet the following quality requirements: the surface shall be free from decay, mildew, foaming, degumming, warping, depression and pollution, the edge of the board shall be straight and free from defects, and the strength, moisture content and water absorption shall meet the requirements of the construction industry standard JG/T3026- 1995. Panel cutting should use electric dense tooth saw, and the deviation of template production and installation should meet the technological requirements. Template using the wood, the wood should be made of high quality dry pine.

The allowable deviation of formwork fabrication and installation shall meet the requirements of specification JTJ04 1-2000. Control: the deviation between the center line of arch ring plane and the design center line shall not be greater than 8 mm; Allowable thickness errors of bottom plate, side plate and top plate of arch ring:+10 mm and-0mm; The allowable error of arch ring bottom elevation is +20 mm and-10 mm.

2.3.2 Determination of lofting coordinates of bottom die

The setting-out coordinate value of the bottom die is determined by the setting-out coordinate value of the lower edge coordinate of the main arch provided by the design institute drawings after pre-camber, plus the pre-camber value that must be set due to the deformation of the whole bracket itself. The deformation pre-camber value of the whole support is determined by combining the observation and calculation of preloading test: ① the elastic deformation of the foundation and support in the direct preloading area is taken as the pre-camber value of the whole support itself (inelastic deformation has been basically eliminated in the weight); (2) According to the bottom die, deformation of steel pipe, settlement of filled foundation, total elastic and inelastic values of foundation support, the dead load of arch ring and the height of steel pipe support are comprehensively considered, and the area is not directly pre-pressed. Through the calculation and analysis of deformation, the pre-camber value of the whole support itself at each point is determined as the pre-camber value that must be set for the deformation of the support itself. For each span arch ring, according to the pre-camber value provided by the design institute drawings and the lower edge of the main arch, set the setting-out coordinate values after the pre-camber, form the setting-out coordinate values of the bottom die at specific points, and install the bottom die keel.

Method of simulating bottom die load: when the bottom die is installed with wood and the panel is not laid, choose a span for preloading; According to the observation results of preloading of this span, foundation height, steel pipe support and the differences of arch ring sections in different places, typical areas are selected for preloading of other spans. Stack sand bags on the paved belt wood, place steel bars on the sand bags, and preload the support and foundation. The weight load is determined according to 1.2 times of the weight of arch rings around. Three observation points and ***27 measuring points are respectively set on two arches of the main arch, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4 and 7/8. Observe carefully and make detailed records for the record.

Requirements for simulated load of bottom formwork: ① ballast can be recorded only when the foundation settlement no longer produces obvious settlement (observation is not less than 24h); (2) When weighing, sandbags and steel bars with corresponding weights should be stacked according to the regional load. The total load should be equal to 1.2 times the design load (the error should not exceed 1%) to reduce the error of the load. 2.4 Installation of side formwork and groove internal formwork

According to the length of each section of the main arch ring, the lateral formwork is longitudinally divided into 2 m ~ 3 m sections. The side formwork adopts a composite bamboo veneer panel with δ= 12 mm, which is reinforced by vertical tension belt, and the lower end of the side formwork is limited by wooden strips fixed on the bottom formwork. The top end is opposite to the top surface of the main arch ring concrete; The middle part is provided with a steel pull rod according to the situation, and the diaphragm beam is pulled against the internal mold through the steel pull rod. The tie bar is wrapped with plastic sleeve to restore the distance between the tie bar and the fixed formwork, and the formwork end of the tie bar side is connected with detachable H-nut to ensure the appearance quality of the arch ring side.

The slotted internal mold takes the composite bamboo veneer with δ= 12 mm as the panel and the stiffening band as the skeleton. The bottom plate of the internal formwork is not used, but only used as a side formwork to prevent the concrete from floating, extruding and deforming. Steel tie rods are used between the inner mold and the inner mold, and between the inner mold and the side mold, and plastic sleeves are sleeved outside the tie rods. On-site technicians can determine the specification, spacing and position of the pull rod according to the situation.

When installing internal formwork, attention should be paid to the fixation of internal formwork and the fixation between internal formwork, so as to prevent the buoyancy and impact force of concrete from affecting the internal formwork and causing the formwork to escape. For the position where the slope of the bottom and top of the main arch ring is large, the concrete surface of the bottom and top of the main arch ring should be covered with wooden boards to prevent concrete from overflowing.

Both the side formwork and the internal formwork can be processed off-site and assembled in blocks on site, and can be made into a small broken line shape according to the curve and linear shape of the main arch. It should be noted that the length of each broken line should not be greater than 1.0 m within the span range of arch foot area 1.3 and vault area1.5 m. When splicing, the gaps between templates should be filled with thin wooden strips to prevent slurry leakage.

2.5 arch ring reinforcement project

2.5. 1 Basic requirements of reinforcement

(1) The steel bars used in this project should meet the requirements of specifications before they can be considered for use on site. According to the requirements of the owner, all steel products of Changgang Group are adopted.

(2) The reinforcement shall be tested before entering the site and reported to the supervision engineer for approval before use.

(3) The procurement procedures of steel bars shall conform to the inspection procedures for materials entering the site of Xiaoheqiao Project Department.

(4) After the reinforcement comes into play, it must be accepted and piled up in batches according to the specifications, and shall not be mixed, and marked.

(5) The variety, specification and quantity of steel bars must be accurate, and the substitution of steel bars must be approved by the supervision engineer before operation.

preparation of reinforcement

(1) Reinforcement straightening and derusting

The surface of steel bar should be clean, free of surface oil stains, paint, etc. Should be removed before use. Steel bars shall be straight without local bending, and coiled steel bars and bent steel bars shall be straightened.

(2) The bending and end hook of steel bars shall comply with the design requirements and the provisions of JTJ04 1-2000.

(3) The longitudinal main reinforcement of the main arch shall be pre-processed according to the joint form of reinforcement, and conform to the requirements of the specification JTJ04 1-2000, and the length of the main reinforcement in each section of construction shall be calculated, and the reinforcement shall be welded into a whole at the site according to the calculated length.

2.5.3 On-site installation and connection of reinforcement

(1) The joints of longitudinal main reinforcement are all located in the construction interval groove of the main arch ring.

(2) The field connection of longitudinal main reinforcement mainly adopts welding. When welding, the overlapping ends of two steel bars should be folded to one side first, so that the axes of the two connected steel bars are consistent. The length of double-sided weld of joint shall not be less than 5 d, and the length of single-sided double-sided weld shall not be less than 10 d(d is the diameter of steel bar).

(3) When installing longitudinal main reinforcement, the welded joint shall meet the requirements in JTJ04 1-2000, that is, there shall be no two joints in the joint length section of the same reinforcement, and the cross-sectional area of the joint shall not exceed 50% of the total cross-sectional area of the tension zone. The length section of the welded joint refers to 35 d(d is the diameter of the reinforcement) and shall not be less than 50.

(4) Trial welding must be carried out before steel bar welding, and formal welding can be carried out only after it is qualified. The welder must have a work license, and the selection of covered electrode should comply with the provisions of the specification table JTJ04 1-2000. If required by the Engineer, lap joints can be sampled and tested on site. The welding of steel bar joints meets the requirements of specification JTJ04 1-2000.

(5) After the arch ring bottom die is laid, the center line, sideline and elevation shall be released, and the position of each subsection point and partition plate shall be marked as the basis for installing other templates and binding steel bars. Arch ring reinforcement is bent under the bridge and transported to the arch frame for welding and binding construction. The welding and binding sequence of reinforcement is as follows: from the arch foot to 1/4 arch span, stirrups are installed first, and then the main reinforcement is penetrated; From the arch span 1/4 to the vault section, the main reinforcement should be worn first and then the stirrup should be set, which is convenient for construction. Main reinforcement joints, stirrups and partition reinforcement connections are all welded; Except for the longitudinal reinforcement of the spacer groove, which is formed at one time when the sectional reinforcement is welded, the other transverse reinforcement and stirrup can be bound before pouring.

(6) When binding steel bars, check the spacing of steel mesh pieces to ensure that the protective layer of steel mesh pieces meets the requirements.

2.5.4 Reinforced protective layer

In order to ensure the appearance quality of concrete and reduce the contact area between the protective layer pad and the formwork, a plastic protective layer clip or pad is set between the steel bar and the formwork, and a semi-circular hole is set on the clip to insert the outer steel bar. Not less than 4 pieces /m2, arranged in a plum blossom shape.

Embedded steel bar

(1) If the embedded steel bar at the arch foot conflicts with the steel bar at the pier, the embedded steel bar at the main arch will not move, but the steel bar at the pier will move appropriately. Embedded steel bar position must be accurate and fixed firmly.

(2) The pre-embedded reinforcement of the upper abdomen arch ring of the main arch ring and the reserved reinforcement of the cushion stone shall not be omitted, and the reserved reinforcement of the abdomen arch ring shall meet the design and construction requirements of the abdomen arch ring.

2.6 main arch ring concrete works

This project plans to use commercial concrete, which will be transported to the site by concrete truck and poured into the mold by concrete pump.

2.6. 1C40 concrete materials and concrete quality

(1) The concrete mixture ratio shall be verified according to the relevant regulations, and its strength, workability, durability and other indicators meet the requirements of relevant specifications, and can only be used after being approved by the supervision engineer.

(2) The sand ratio and slump of concrete should meet the pumping requirements, with the sand ratio controlled at 40% ~ 50% and the slump controlled at 13cm ~ 15cm.

(3) The initial setting time of concrete shall not be less than 8 h ... Using high-efficiency and high-quality water reducing agent can prolong the initial setting time of concrete and improve the workability of concrete.

The maximum water-cement ratio and minimum cement content of concrete shall comply with the provisions of JTJ04 1-2000 specification.

The sand, gravel and cement of concrete are made in dosing machine, and the measurement system in dosing machine should be within the verification period.

The mixing time of concrete shall comply with the provisions in the table 10.4.2 in JTJ04 1-2000.

Concrete is transported by concrete truck. After the concrete is poured out of the mixer, it will be transported to the construction site by a concrete truck for no more than 30 minutes.

concrete pouring

(1) Arch ring concrete shall be poured symmetrically in sections along the arch span direction during construction, and the pouring speed at both ends shall be controlled accurately. The limit groove should be located at a quarter point and the arch foot, with a width of 1.6 m, and the joint surface of each section is perpendicular to the arch axis. According to the principle of symmetry, pouring starts from the arch foot to a quarter point, and then from the vault to a quarter point. Each section of concrete shall be poured continuously at one time. If it is interrupted for some reason, it should be poured into a construction joint perpendicular to the arch axis. If it has been poured into an inclined plane, it should be chiseled into a plane or stepped seam perpendicular to the arch axis. After the arch ring is poured in sections, the strength reaches 85% of the design strength, and the joint surface is well treated, the concrete of the spacer groove should be poured symmetrically from the arch foot to the vault. The concrete in the groove between the two arches should be poured last. The continuous pouring of concrete in each section shall not be interrupted, and the pouring shall be completed within the initial setting time of concrete.

(2) Concrete shall be vibrated with an internal vibrator, and the moving distance of the vibrator shall not exceed 1.5 times of its action radius; Keep a certain distance from the side formwork, and insert the lower concrete 5 cm ~ 10 cm. After each vibrating, the vibrator should be slowly lifted out while vibrating, so as to avoid the vibrator colliding with the formwork and reinforcement. When inserting the vibrator, it should be evenly distributed, and the slope angle and dead angle should be densely distributed, and no vibration leakage or excessive vibration is allowed. Principle of concrete vibrating: concrete no longer sinks and bubbles, and the surface begins to pan-slurry.

(3) The concrete pouring period of the main arch closure section (1/4) should be selected in the early morning when the temperature is relatively low and the temperature is about to rise, and the closure temperature is about 8℃.

This project is four spans and one connection. First, the first to the fourth cross the right. After the right picture of the first to fourth spans is poured, the right picture of the fifth to eighth spans will be poured in time. After the pouring of the right picture of the eighth span is completed and the design strength reaches 85%, it can be unloaded. When pouring, try to ensure that the four spans are poured synchronously and closed at the same time, and choose two pump trucks and a certain number of concrete transport vehicles that can meet the continuous pouring.

2.6.3 concrete curing and form removal

(1) After concrete pouring and initial setting, immediately spread geotextile and spray water for curing, and the curing time shall not be less than 7 d. The concrete shall not be eroded by water before initial setting.

(2) When the temperature is lower than 5℃ during curing, it shall be covered with heat preservation, and water shall not be sprayed on the concrete surface.

(3) After the concrete pouring of each segment is completed, the joint surface begins to whiten, and when the strength reaches about 2.5 MPa, the hair is cut. After treatment, the surface will not see white mud, and the rough concrete fresh surface will be visible. Thoroughly clean rough surfaces.

(4) The main arch ring can only be removed after the strength of the curing specimen reaches 70% of the design strength.

2.7 The main arch ring bracket falls off from the frame.

After the minimum concrete strength of the main arch ring reaches 85% of the design, unload the main arch ring. The principles of disassembly and assembly are small quantity, multiple times, uniformity and symmetry. Bearings must be uniformly unloaded at the same time in the transverse bridge direction, and the longitudinal bridge direction should be unloaded row by row from the vault to the arch foot, and the left and right sides should be synchronized and symmetrical. Unloading equipment should be placed at the beam and column of the support, the support should be unloaded from the middle of the span to both ends, and the formwork should be unloaded in stages. When a certain unloading amount is reached, the bracket can be separated from the beam. In the process of construction, close observation should be made to meet the requirements of optimal unloading.

3 technical parameters that must be achieved in the construction of each working procedure

3. 1 Allowable deviation of template fabrication and installation

The allowable deviation of formwork fabrication and installation shall not only meet the requirements in Table 8.6. 1-2000 and Table 8.6.2, but also meet the following requirements: the deviation between the center line of arch ring plane and the design center line shall not be greater than 30mm；; The allowable errors of the thickness of arch ring bottom plate, web plate and top plate are+10 mm and-5 mm; The allowable error of arch ring bottom elevation is +20 mm and-10 mm.

3.2 Allowable deviation of reinforcement processing

(1) The total length of steel bars processed along the length direction is +5 mm,-10 mm.

(2) The size of each part of the bending steel bar is 20 mm.

(3) The size of each part of the stirrup is 5 mm

3.3 Allowable deviation of steel bar installation

(1) the same row of reinforcement plus or minus 20 mm.

(2) The row spacing of more than two rows of steel bars is 5 mm

(3) reinforced bending starting point position plus or minus 20 mm.

(4) The spacing between stirrups and transversely distributed steel bars is 20 mm.

(5) The thickness of protective layer is 10 mm.

4 Other precautions

(1) The construction of the main arch shall be carried out in strict accordance with various construction safety operation procedures.

(2) Do a good job in protecting the riverbed support foundation to prevent the support and foundation from being washed away. At the same time, a dike should be set on the construction access road on the upstream side of the bridge site to prevent the bracket from being damaged by the unexpected high water level of the river.

(3) Strictly guarantee the quality of concrete during construction. After concrete pouring, it should be cured immediately. Concrete curing is very important for concrete quality assurance and should be carried out in strict accordance with relevant technologies.

(4) The embedded steel bars, drainage pipes and other embedded parts in the main arch construction shall not be omitted.

(5) The electric welding operation shall comply with the relevant safety regulations for electric welding to avoid burns and scalds. If welding is needed after formwork support, attention should be paid to protect the formwork from being burned.

(6) During the construction operation, attention should be paid to protecting the embedded monitoring equipment for the main arch ring construction.

(7) Matters not covered shall be handled in accordance with Technical Specification for Safety in Highway Engineering Construction (TJT076-95) and other relevant laws and regulations.

(8) Arch bridge is a structure with thrust. The quality of abutment has a great influence on the safety of the whole arch bridge. Before concrete pouring, rubble blocks behind the abutment must be completed. During construction, attention should also be paid to filling the soil behind the abutment in time and compacting it by layers.

(9) Pay attention to symmetrical and balanced construction in each stage of arch bridge construction to avoid abnormal deformation of arch axis and lead to safety and quality accidents.

(10) Conduct construction observation at each stage of construction to control the deformation of the main arch ring. In order to avoid the adverse effects caused by one-way thrust, the superstructure of adjacent holes should be erected as soon as possible during construction.

(1 1) Strictly control the internal quality and external quality of the main arch ring concrete. When pouring concrete, ensure the pouring progress and vibrating compaction, carefully chisel out and clean all working joints, ensure the bond strength of new and old concrete, and pay attention to concrete maintenance. The outer surfaces of all main arch rings are smooth and bright, and the concrete of the whole bridge has the same color.

(12) Strictly control the overall dimensions of the main arch ring, control the construction error within the scope permitted by the construction specifications, prevent the concrete of the main arch ring from cracking and bumping, and dismantle the formwork only after the concrete strength meets the relevant requirements.

Progress plan, crossing chart and construction plan

Look for it on the internet, for example, there are many Luwen construction service networks.