1. The precast yard of prestressed hollow slab beam of this project is planned to be located in a spacious open space.
There are 8 bearings arranged along the axial direction of the bridge. In order to ensure the construction quality of precast prestressed hollow slab beam and prevent the pedestal settlement caused by the self-weight of beam during tensioning, the pedestal foundation must be strengthened. Measure the position of 30m plate beam pedestal and its end, and adopt the method of enlarging the bearing area of foundation. The size of the foundation at the end of the plate beam is1.5m×1.5m. Dig a foundation pit with a depth of 1m, spread gravel on it and tamp it with a thickness of about 30cm, and then pour 70cm thick reinforced concrete. On the basis of expanding treatment, pedestal construction is carried out, and hard foam is set on both sides of the pedestal to prevent slurry leakage. The whole precast yard is plastered with concrete and equipped with vertical and horizontal drainage facilities. There are two longitudinal main drainage ditches in the prefabrication site, which are located outside the two gantry rails; There are seven horizontal drains, which are connected with the vertical drains, located at both ends and in the middle of the pedestal. The foundation adopts strip concrete foundation, and the bottom die adopts 8mm steel plate. The foundation size is determined according to the design drawing of 365JT.
2, plate girder prefabrication construction scheme:
① Construction preparation: The construction preparation of hollow slab beam mainly includes the construction of prefabricated site, the installation of gantry crane, the storage of materials and the processing of formwork. ② Construction process: ③ Precast yard construction: 365JT planning is carried out on the construction site by filling subgrade, the slab beam base needs to be treated, the surface is leveled with concrete, and the beam end base needs to be reinforced. The gantry crane for hoisting is assembled by Bailey pieces. (4) Formwork processing: The external formwork used in this bridge slab beam adopts assembled steel formwork processed by professional formwork factory, and the panel adopts 6mm steel plate, so as to minimize the weld seam of one formwork panel. The horizontal stiffening of the panel adopts channel steel. Intermittent welds are used between the stiffener and the panel, each weld is 5cm in length and not less than 6mm in thickness, and the panel is planed. The internal mould adopts movable wooden mould to nail iron sheet. Before using the template, check whether the dimensions of each part of the template meet the design requirements, and pay attention to the decontamination and rust removal of the template surface. ⑤ Disassembly and assembly of formwork: The external formwork is disassembled by simple small gantry crane electric hoist. Before template installation, first install the steel skeleton and end formwork, and then install the corrugated pipe and templates on both sides; After pouring the bottom concrete, install the internal mold. Disassembly and installation are in the same order. Template installation must be carried out in strict accordance with the lofting, to ensure accurate installation position and firm installation.
In order to ensure that the formwork joints are smooth and do not leak slurry, the following measures are taken: a. Smooth the formwork joints with a hard foam pad and a grinder. B, after each form removal, clean the surface of the template and coat it with engine oil to ensure that it will not rust next time. C, before each formwork erection, clean the surface of formwork, remove dirt, impurities or rust (if any), and apply a proper amount of release agent before formwork erection. ⑥ Fabrication and installation of steel bars: The steel bars used must have the factory certificate and pass the laboratory sampling inspection. The storage of steel bars must be classified in batches, and there are anti-erosion measures such as rain protection. The production of steel bars should be concentrated in the existing steel bar construction shed, and the manufactured semi-finished products and finished steel bars should be classified and piled up. During the fabrication and installation of steel bars, attention should be paid to avoid setting joints at the stressed parts of the structure, and the joints should be staggered. The joint spacing is greater than 50cm, and the spacing between the welding point and the elbow should be greater than 10d(d is the diameter of steel bar). Remove the welding slag left during welding, and the weld length meets the specification requirements (that is, double-sided welding for 5d and single-sided welding 10d). ⑦ Installation of steel strand (threading)
◆ When binding reinforcement, pay attention to the positioning of bellows on steel structure. The positioning of bellows must be carried out in accordance with the requirements of construction drawings. During construction, pay attention to the positioning of bellows. The reinforcement shall be firm and accurate, and the bellows joint shall be tightly sealed to avoid cement slurry leakage during concrete pouring. For example, when the corrugated pipe is tied, the position of the corrugated pipe conflicts with the steel bar, so move the position of the steel bar appropriately.
◆ The steel strand and anchorage fixture used shall have the factory certificate, and can only be used after passing the inspection (used in batches according to the specification requirements). Steel strand is cut by grinding wheel cutter, and the length of steel strand is cut strictly according to the drawing size, and it is combed straight one by one to avoid entanglement. Before threading the steel strand, check whether the channel is clear and free of water and other sundries, and pay attention to avoid scratching the bellows. After the steel strand is loaded into the pipeline, the opening at the end of the pipeline should be sealed. ⑧ Template assembly: After the bottom plate reinforcement is installed, the internal formwork must be installed first. The internal mold must be positioned accurately and installed firmly, and special attention should be paid to ensuring the thickness of the bottom plate. The side formwork installation can only be carried out after the steel bar binding installation has passed the re-inspection. When installing the formwork, attention should be paid to the tight, flat and no slurry leakage. At the same time, before each formwork erection, the surface of the formwork shall be cleaned to remove dirt and impurities, and an appropriate amount of release agent shall be applied. Pet-name ruby concrete pouring column:
◆ Before concrete pouring, check whether the template size and switch are correct, and whether the position of embedded parts and reserved pipes of prestressed tendons are correct. If there is a gap in the template, it should be blocked tightly with sponge or foam. Debris, water and dirt on the steel bars in the formwork should be cleaned up.
◆ The pouring concrete shall be cut in strict accordance with the mixture ratio provided by the laboratory, all materials shall pass the inspection, and the unqualified materials shall be resolutely put into use. In the process of pouring, full-time testers will conduct on-site monitoring, visually inspect the workability of concrete, and regularly detect the slump of concrete, and resolutely do not use unqualified concrete.
◆ Concrete shall be poured in layers according to a certain thickness, sequence and direction, and fed from one end of the beam to the other end in the opposite direction, and closed at intervals of 4-5m. Layered blanking and vibrating, the thickness of each layer shall not exceed 30cm. The upper concrete can only be poured after the lower concrete is vibrated and compacted.
◆ The vibrating method of concrete is mainly based on the attached vibrator assembled by side formwork vibrating frame, supplemented by plug-in vibrating. In the process of vibrating, the distance between the vibrator and the template should be kept at 5- 10cm, so as to avoid collision with the corrugated pipe, and vibration should not be directly or indirectly exerted by the steel bar. When vibrating the upper concrete, the vibrator should be inserted into the lower concrete by 5-10 cm; After each place is vibrated, the vibrator should be slowly pushed while vibrating to prevent large bubbles from appearing in the concrete. At the same time, in the process of pouring concrete, designated persons shall check and correct bellows, templates, etc.
◆ After pouring, cement slurry should be collected and brushed. After the whole hollow slab beam is poured, it should be cured by spraying water in time, and covering such as sacks should be laid at the top of the slab beam to keep the slab beam wet. After the template is removed, cover it with plastic film to keep it moist. Before the concrete strength reaches 2.5Mpa, it shall not bear all kinds of external loads. Attending tensioning and grouting: tensioning equipment should be calibrated before use. Only when the slab beam concrete member reaches 90% of the design strength can the prestressed steel strand be tensioned and anchored. The tensioning sequence shall be carried out according to the design regulations, and both ends shall be tensioned symmetrically at the same time, and both ends shall be synchronized. When tensioning, ensure that the line of action of jack tension is consistent with the axis of steel strand. 30m span prestressed tendons, tensile stress σk= 1395Mpa, and the tensioning sequence shall be in accordance with the numbering sequence of steel bars in the design drawings. The design of high-strength and low-relaxation steel strand adopts standard strength R= 1860Mpa, with symmetrical tension at both ends, and the tension control force per strand is 781.2kn..
16m span prestressed tendons have a controlled tensile stress of 1 125mpa, and the tensioning process of prestressed tendons is: 0→ initial stress (0. 1σk)→ 100%σk (lasting for 5 minutes). Double control of stress and strain should be adopted in the tensioning process, and 365JT technicians with rich construction experience should be selected to be responsible for the whole prestressed tensioning work, and tensioning operators should hold relevant certificates. Grouting should be carried out as soon as possible after the tensioning of prestressed tendons of the whole beam is completed. Before grouting, do a good job of cutting the redundant steel strand outside the anchor. The grouting sequence is from bottom to top, and the holes in one place should be pressed at one time. Piston grouting pump is used for grouting. The pressure should be small at first, and then gradually increase. Grouting shall reach the other end of the hole and be filled with cement slurry, and the cement slurry with the same consistency as specified shall be discharged. Pure cement slurry is used for hole grouting, and the water cement ratio is 0.4-0.45. Fill in the construction records carefully during grouting, and make cement slurry test blocks as required. The 30m plate beam pedestal can be set with an camber of about 1.7cm. ⑾ End sealing: Before end sealing, the end concrete of cement slurry shall be chiseled, and then the end steel mesh shall be welded and fixed to support the end formwork for anchor sealing. When pouring, be careful to vibrate to make the concrete at the anchorage dense.
3, plate beam transportation and beam storage:
① Movement and transportation of plate girder: Before the plate girder is moved and transported, special attention should be paid to the maintenance of hollow plate girder, and it can be hoisted and transported only after the concrete strength reaches 90%. When stacking, the hollow slab should be supported at two ends, and it is not allowed to be upside down. (2) The location of beam storage should be dense, and it should be cushioned according to the fulcrum.
4, hollow slab beam installation and continuous construction scheme
(1) Installation of hollow slab beam
1. Hoist with double dragon gate, lay track flat car and move. According to the layout of the prefabrication yard, the girder transport track is laid before the girder is loaded on Platform 6, and then the double-guide girder bridge-erecting machine is assembled on the girder transport track with Bailey pieces (about 108 pieces). The bridge-erecting machine passes through the hole, lifts the girder with a KQ-75 pier-crossing gantry, and transports the girder to the bridge-erecting machine with a girder transport flat car. The bridge-erecting machine first erects the prefabricated first hole1. Then the flat car is moved by the winch pulley system, and the plate beams on the bridge deck are transported to the double-guide-beam bridge erecting machine, and the plate beams are erected in turn by the double-guide-beam bridge erecting machine. Plate girder hoisting is not restricted by anchor bolt holes, and the hoisting point should be located near the center line of the bearing.
2. Re-survey of cushion stone and placement of rubber bearing: ◆ Re-survey the completed cushion stone elevation according to the design drawings and beam camber. Set out the center line of the capping beam and the center line of the bridge with the total station, and draw the bearing sideline, beam end and beam side sideline, and the bearing center position of the beam on the cushion stone to check the horizontal flatness of the bearing. ◆ There are two kinds of rubber bearings: ordinary rubber bearings and PTFE skateboard bearings. When installing the rubber bearing, it must be in close contact with the upper and lower structures without gaps.
3. Bridge-erecting machine and its supporting machines (1)JS30/ 100 double guide beam bridge-erecting machine is 1 set; (2) Two 60-type flat cars are used to transport the beam (1 car of 30KW mobile generator set is used as the power for transporting the beam flat car); (3) There are two hydraulic jacks QF60-20 (for moving the bridge erecting machine); (4) There are four 5T manual hoists.
4, bridge erecting machine via hole and beam transport
In order to ensure the safe operation of the cantilever bridge-erecting machine with double guide beams across the pier, after the bridge-erecting machine is installed, the simulated through-hole test must be carried out on the capping beams of piers 6 -5, and the through-hole should reach the front pier according to the actual counterweight requirements of the simulated through-hole. And do all the preparatory work before the plate girder installation. Hoist the beam to the beam carrier with a gantry, then transport it to the lower part of the bridge erecting machine by the beam carrier, then hoist the beam to the front cover beam with the bridge erecting machine, slowly lower it to about 30cm away from the support, preliminarily check the longitudinal position, and then traverse it in place.
5, bearing installation and girder hoisting in place
Rubber bearings can only be used after passing the test and being free from defects. Rubber bearing is installed at the corresponding position of the cushion stone, and the deviation is not more than 5 mm Put a wedge-shaped steel plate on the bearing to avoid the longitudinal deviation of the bearing caused by the longitudinal slope. Before the main girder is in place, clean the surface of the embedded steel plate of the bearing. On the installed bracket, hoist the main girder above the bracket with bridge erecting machine, then preliminarily locate whether the edge line of the main girder coincides with the edge line of the girder on the cushion stone with a triangular ruler, check whether the end line of the main girder coincides with the end line of the girder on the capping beam with a wire hammer, then lower the main girder in place, and check whether the center line of the main girder coincides with the center line of the bracket with a wire hammer. If it does not coincide or the verticality exceeds the specification, adjust the lateral verticality under the lower partition with a jack until the center line of the main girder coincides with the center line of the bearing, and the verticality is within the allowable range of the specification.
6. The main operation sequence of installing erection plate for double-guide girder bridge erecting machine is as follows: assembling double-guide girder bridge erecting machine → lifting beam by gantry crane, transporting beam (or transporting beam by rail flat car) → vertically moving bridge erecting machine, moving plate beam in place (and placing bracket) → horizontally connecting plate beam in place → longitudinally moving bridge erecting machine → longitudinally moving guide beam → vertically moving rail row forward → correspondingly completing erection of lower span beam.
(2) After continuous construction
1, partition or transverse reinforcement connection welding
After the two plate beams are in place, according to the weld length and width required by the design, immediately connect the diaphragm or transverse reinforcement with electric welding, so that the beams can be connected into a whole. Hanging blue is used for electric welding connection. Before welding, it should be cleaned and derusted. At the same time, the embedded steel plate should be welded with the certificate in a dry state. If the two clapboards are misaligned, a corrugated connecting plate shall be made according to the misaligned size, which shall be consistent with the embedded steel plate, welded and connected, and welding slag shall be removed. After the welded joints pass the inspection, they should be coated with antirust paint immediately, and then coated with ready mixed paint after drying.
2, wet joint concrete construction
After the welding of connecting steel plates is completed, the bridge erecting machine will be moved to the via hole for wet joint concrete construction after passing the inspection by the supervision engineer. Weld the wet joint reinforcement, send the formwork to the hole on the service road by crane, and support the formwork with nylon rope. The formwork is made of bamboo glue, and each wet joint will be divided into three formwork, which will be fixed on the dry support with screws. The screw is wrapped with plastic pipe, with a diameter of 2-3cm, and the length of each template is 200cm. Four wet joints can be poured at the same time. At the joint of formwork and partition, plug the joint with wooden strips, and then apply cement slurry on the surface to prevent slurry leakage. The mixture ratio of concrete is the same as the coarse aggregate of beam. The concrete is transported to the service road by the motor dump truck and poured into the rickshaw. The wet joints of the concrete are filled with cement slurry in the lifting basket. Concrete shall be vibrated by a flat vibrator, and wet sacks shall be covered in time after slurry collection (in summer). After the final set of concrete, direct water spraying curing. When the concrete strength reaches the formwork removal strength, the formwork can be removed. When the formwork is dismantled, it is bound with nylon rope and transported directly to the construction ship under the bridge. When the wet joint concrete is just adjacent to the beam transportation track, the beam transportation can only be carried out when the concrete strength reaches more than 80% of the design strength.
5. Construction scheme of expansion joints, sidewalk slabs and railings.
1. Bridge deck pavement: Before pouring concrete at the hinged joint between hollow slab and bridge deck pavement, the floating skin on the joint surface must be removed with a steel brush, and then concrete and cement mortar can be poured after being rinsed with water. Articulated joints between concrete and mortar must be vibrated and compacted.
① Construction technology: ② Cleaning of plate beam: After erection and installation, clean the plate beam in time, remove the floating skin on the joint surface and rinse it with water. (3) Joint construction: After the joint surface of plate and beam is cleaned, joint construction shall be carried out in time. During joint construction, attention should be paid to blocking the joint between the plate and the beam to prevent cement slurry from leaking, and the concrete at the joint should be vibrated and compacted. (4) Deck pavement: Laying bridge deck reinforcement according to the design requirements of drawings. Before concrete pouring, the top surface of plate beam should be brushed again, and the bridge deck should be cleaned again. The result of cleaning must be that there is no debris such as ash on the bridge deck. When pouring concrete on the mixed bridge deck, the ingredients should be made in strict accordance with the mixture ratio provided by the laboratory, and the workability and slump of the mixed concrete should meet the design requirements. When pouring concrete, we should pay attention to vibrating compaction, leveling the surface to collect slurry, and embossing at the same time.
2, expansion joint construction
The embedded parts of expansion joints shall be placed and installed in strict accordance with the manufacturer's requirements. The joint surface of the installed bridge deck expansion joint must be smooth without blockage, leakage, deformation and cracking. The anchoring reinforcement is welded evenly on the special-shaped steel plate along the bridge width direction (completed in the factory), and the reserved concrete tank is filled with epoxy resin concrete larger than c30.
3. Construction of sidewalk system
Sidewalk slabs and railings are prefabricated in strict accordance with the design size, and embedded parts must be accurately placed when prefabricated blocks are prefabricated. When paving the prefabricated components of the sidewalk system, the position must be accurate, the line type should be straight, and attention should be paid to the appearance decoration.