(1) Construction methods and processes.
1) Temporary consolidation measures for pier beams.
The temporary consolidation of pier girders is realized by setting up temporary supports and anchoring reinforcements. The temporary bearing is provided with a sulfur mortar interlayer with a resistance wire in a thickness of 15 20cm, and the temporary buttress can be lifted by melting the sulfur mortar by electrifying the resistance wire. A plastic film isolation layer is set at the top and bottom of the temporary pier, and the anchor steel bar consolidates the pier girder together.
2) Pier top cast-in-situ section (0 section) support method construction.
According to the site conditions, the construction of the string support method or the bracket method is adopted. When the main pier is located in the water or the main pier is high, the bracket method is adopted.
Bracket foundation. The lower end of the section support is supported within the cushion cap, and the upper end of the support is extended to the size required for the construction of section 0. The size of the beam cap is small, and it is indeed difficult to erect the support, and when the support needs to be supported outside the cushion cap, the ground is hardened with concrete, so as to ensure that the support does not produce uneven settlement.
Bracket design. The bracket design is carried out to check the stiffness and stability of the bracket, the allowable bearing capacity of the foundation, and the settlement of the foundation.
Bracket erection. The continuous box girder 0 section bracket is supported by steel.
The frame is assembled, and the height of less than 2m is adjusted by short steel pipes. The wing plate and the indoor support of the box adopt a door-type scaffold support, and the spacing can be pressed by 12m×1.2m arrangement, and at the same time connected with box girder support to ensure stability.
Stent preload. When erecting the bed mold, after the estimated reserved deformation is supported, the loading and preloading are carried out according to the design or specified requirements. The weight of the ballast is 1 of the design weight1 times more. Sand bags or steel ingots are used as loading, so that the load strength of the load is consistent with the load strength distribution of the beam. When the pressure test settlement is stable, the final settlement value of each measurement point is recorded, so as to calculate the elevation of each measurement point of the bottom mold, and then unload. According to the calculation results, the elevation of the bed mold is adjusted to make the reserved deformation more accurate, and it is also a test of the strength, stiffness and stability of the support.
3) pier top cast-in-situ section (section 0) bracket construction.
The bracket is processed into a triangular truss by channel steel, and is connected with the pier body by the embedded steel plate. Each node of the bracket is welded to reduce the inelastic deformation of the bracket. Preload after the bracket is erected.
When the longitudinal roof bundle pipeline is embedded, every 50cm with 8 positioning steel bars are welded on the beam reinforcement skeleton, so as to ensure that the pipeline positioning is accurate and firm. In order to prevent the cement slurry from seeping into the bellows and blocking the prestressed pipe, a rubber pipe slightly smaller than the diameter of the pipe is inserted into the longitudinal pipe before concrete pouring.
4) Templates. Beam bottom template: the cantilever part at both ends adopts a large steel template (hanging basket bottom mold), the adjustment of the longitudinal slope of the bottom of the beam at the end of the two cantilever ends, and the slope is adjusted by using the mold adjusting device, so that the bottom mold meets the slope requirements.
Outer formwork: Adopt a large steel formwork, use a mold adjusting device to adjust the width of the vertical mold in the widened part of the beam, and use a tension screw to pull it when the inner and outer side templates are assembled.
Partition wall formwork and web inner formwork: all adopt stereotyped composite steel formwork for on-site assembly, and the fastening of the inner formwork is mainly with a tension screw and connected with scaffolding. The chamfering formwork adopts a wooden mold.
Manhole formwork and support: the partition wall manhole adopts wooden formwork, wooden support, and the roof temporary manhole formwork adopts steel plate welding, and the support is welded with 12 steel bars and beam roof reinforcement mesh.
End mold: The end mold is made of self-processed steel formwork, which is firmly connected with the inner and outer mold and its skeleton, and the middle is left into the human hole to facilitate personnel access.
5) The installation of steel bars and prestressed channels, concrete pouring and curing, prestress application, channel grouting and other processes are described in detail below.
6) Construction of cantilever beam section.
Hanging baskets. a Hanging basket structure.
The construction hanging basket adopts a light diamond-shaped hanging basket, which is mainly composed of five parts: main truss, walking and anchoring system, sling system, bottom platform system and formwork system. The hanging basket has large bearing capacity and rigidity, high degree of mechanization, convenient and fast operation, safety and reliability.
b Hanging basket assembly.
After the hanging basket structural component arrives at the construction site, utilize the crane to lift to the top surface of the 0 beam section that has been poured and assemble, after the assembly is completed, the hanging basket applies the beam section load to preload, fully eliminates the inelastic deformation produced by the hanging basket, and in the suspension irrigation construction process, the elastic deformation of the hanging basket is included in the calculation of the precamber of the beam section construction.
c Hanging basket static load test.
During the load test, the load is loaded according to the load 1 of the beam section with the most unfavorable force of the hanging basket in the construction2 times loading, to determine the deflection generated by the hanging basket under the load of all levels and the internal force of the hanging basket control member under the maximum load. The loading method takes sandbag preloading.
d Hanging basket moved.
After the concrete pouring and prestress tensioning of each beam section are completed, the hanging basket is pulled by a guide chain along the walking track, and the hanging basket is moved to the position of the next beam section for construction, until the construction of the hanging beam section is completed.
e Hanging basket dismantled.
After the construction of the box girder cantilever beam section is completed, the hanging basket structure is dismantled. The dismantling sequence is: the inner mold system, the side mold system, the bottom mold system, the main truss, the sling system and the walking anchoring system are cross-operated in the process. The inner mold system takes out the dismantling, and the side mold, the bottom mold system adopts the winch to hoist as a whole, and the main couple takes the first retreat to the vicinity of the pier position and then uses the crane to dismantle the zero.
f Precautions for hanging basket assembly, disassembly and assembly.
The assembly and dismantling of the hanging basket are carried out at the same time to maintain the basic symmetry at both ends.
Cantilever pouring construction.
The continuous box girder block suspension pouring starts from 1 piece, and the length of each section of suspension pouring is carried out according to the design requirements, and each block is completed by pouring at one time. Before the construction of the cantilever hanging basket, the linear control point of the continuous beam and the control point of the center line of the bridge are established.
The formwork of each section should be closely integrated with the front section of the beam section, and the joints should be treated in strict accordance with the design requirements to prevent the misalignment and leakage of the joints.
Each section of beam section concrete is poured once before the initial setting, when pouring concrete, start from the end of the cantilever to the root sequentially poured, connect with the front section concrete at the root, adjust the deflection generated by the self-weight of the beam section on the hanging basket at any time during the pouring process to avoid cracks.
In the process of cantilever pouring, do a good job of monitoring and monitoring the suspension pouring of the box girder block.
A hanging basket moves forward: after the construction of the previous beam section is completed, lift and relax each hanging point, make the template detach from the beam body, release the rear anchor point on the beam, carry out anchoring conversion, the walking trolley support force is converted on the slideway, and the main truss is dragged by the inverted chain, and the whole hanging basket moves to the position of the next beam section in front.
B hanging basket adjustment and anchoring: after the hanging basket is in place, the anchor installation of the main truss and the bottom basket is carried out, and then the center line, elevation measurement and positioning are carried out by the measuring instrument, the elevation adjustment is carried out by the jack, and after the inspection is determined to be qualified, the final comprehensive anchoring is carried out.
c Template in place.
The allowable deviation of the size of the beam section formwork installation and the inspection method are in line with the relevant specifications.
7) side span cast-in-place section construction.
The straight section of the side span is constructed by the support method, and the whole is poured at one time. One end of the bracket is supported on the cushion cap, and the other end is placed on the steel pipe pile foundation. The foundation is supported by steel pipe piles. After the bracket assembly is completed, the pressure test should also be done, and after the pressure test is qualified, the concrete construction of the box girder of the straight section will be carried out.
Construction method. a Bracket erection.
Select a representative position to check the strength, stiffness and stability of the support, the allowable bearing capacity of the foundation, and the settlement of the foundation, and the support is erected after the design indicators meet the requirements of the specification.
b After the erection is completed, it will be inspected in detail to ensure that the bracket structure is stable before entering the next process. When laying the bed form, a round steel pipe is arranged as a sliding layer between the bed die and the distribution beam, so as to ensure the relative sliding between the beam body and the support when the temporary beam tension of the side span closure dragon is stretched, but before the side span closure is locked, temporary measures are taken to limit the longitudinal movement of the bed mold.
c Bracket preloading: see the bracket preloading in the "pier top cast-in-place section (0 section) support method construction".
D template: the bottom mold, the outer mold adopts a large block of steel template, and the inner and outer side templates are assembled with the tension screw rod of 18;The inner mold adopts a combined steel mold, the inner roof of the box girder adopts a steel pipe support formwork, the steel pipe support is supported on the bottom template, the concrete cushion block of the bottom cushion of the support and the concrete of the beam body is the same, and the adjustment and removal of the mold are completed by using a wooden wedge.
e Concrete pouring:
The concrete construction sequence spreads from the middle of the support to the fulcrum and the overhanging end to reduce the impact of the support settlement. The concrete is constructed by pumping method. After the concrete strength reaches the strength required by the design, the prestressed tensioning and hole grouting are carried out in batches according to the order of the design requirements.
8) Construction of Helong section and conversion of structural system.
The continuous box girder closure dragon first side span, then middle span. The temperature of the closure meets the design requirements, and the cantilever elevation and axis at both ends of the closure section are allowed to meet the design or specification requirements.
a hanger and formwork installation.
The closure beam section adopts the closure of the dragon hanger construction, and the closure of the dragon hanger and the formwork adopt the bottom basket and template system of the construction hanging basket.
b Set a counterweight.
The counterweight is set by adding water to the water tank at the cantilever end.
c Closure lock.
Before closing, the two cantilever ends of the closure section are temporarily rigidly connected, and the relative fixation is kept as much as possible to prevent the displacement change of the concrete in the closing section during the pouring and early hardening process. In addition to setting the balance weight at the cantilever end according to the balance requirements before closing, adjustment measures will be taken at the closure section if the construction control requires.
d Concrete for the closure section.
In the process of pouring concrete in the Helong section, the counterweight is removed according to the weight of the newly poured concrete (i.e., graded water discharge) to ensure balanced construction.
e Prestressed construction.
After the completion of the closure, the prestressed bundle is tensioned, and after the construction of the closure section is completed, the temporary prestressed bundle is removed and the pipeline is grouted.
f Dismantle the formwork and hanger.
9) Reinforcement works.
The steel bars are processed and produced by the steel bar processing plant, transported to the site to be lifted by a crane and tied and formed on site. When there is a contradiction between the position of the ordinary steel bar and the bellows, the position of the steel bar should be moved appropriately, the positioning steel mesh should be accurately installed, and the positioning steel mesh should be arranged according to the design requirements to ensure that the position of the pipeline is accurate.
Before the reinforcement binding, the surveyor remeasures the plane position and elevation of the formwork, wherein the elevation includes the precamber set according to the calculated deflection of the hanger, and the reinforcement is bound after the correctness. The connection method and connection length of the longitudinal ordinary steel bar at the joint of the two beam sections meet the design and specification requirements.
Reinforcement binding process of cantilever beam section and cast-in-situ section: first, the installation of the ordinary reinforcement of the bottom plate and the anchor end of the bottom of the vertical prestressed reinforcement beam (including the backing plate, anchor nut and anchor spiral bar) is carried out, and then the binding of the web reinforcement, the extension of the vertical bellows and the prestressed reinforcement, the installation of the longitudinal bellows in the web, and finally the binding of the ordinary reinforcement of the roof, the installation of the longitudinal bellows in the roof, and the installation of the transverse steel strand and the bellows.
10) Embedded parts.
Embedded parts are divided into structural embedded parts and construction embedded parts. When installing the embedded parts, the construction lofting is carried out first, and before each pouring concrete, the number of each embedded parts is carefully checked and its position is retested, and the concrete is poured after confirming that it is correct.
11) Concrete works.
The concrete is transported to the pier by mixer truck, pumped into the mold, and each piece is poured at one time. When the height of the concrete falls more than 2 m, it falls through a deceleration facility such as a string drum. Two symmetrical blocks and cross-section balanced perfusion for cantilever construction. Perfusion sequence: bottom plate first, then web, and finally top plate. In the process of concrete into the mold, protect the pipeline from being deflated and flattened at any time, and before the concrete is tamped, the operator must not walk around on the concrete surface, so as not to cause the pipeline to sag, resulting in the phenomenon of concrete "stranding" and "false reality".
At the chamfering place of the web and the bottom plate, pay attention to the vibration compact, after pouring the web concrete, the bottom plate concrete shall not be vibrated again, so as to prevent the concrete drum at the corner of the web stem, and the upper part is suspended and a cavity appears.
When pouring concrete, prevent the displacement and tilting of the anchor pad plate, and prevent the pipe from flattening and moving. After the concrete is poured, the bottom plate and roof of the beam body are slurred twice to remove the excess concrete to ensure the size of the beam body and seal the shrinkage cracks. When the temperature is low, the construction shall be handled in accordance with the relevant provisions of the construction in the middle and winter, and cold protection measures shall be taken.
After the concrete pouring is completed, the elevation measurement of the hanging basket is carried out, and the elevation data of the hanging basket before pouring is compared with the elevation data of the hanging basket before pouring, so as to provide reference for the subsequent construction to obtain empirical data. After the concrete is poured, the top surface is covered and sprinkled with water for curing, and the box is cured with spraying.
12) Prestressing engineering.
The three-way prestressed construction is carried out in the order of longitudinal first, then vertical, and then transverse.
Installation of prestressed tendons and their pipes.
a Longitudinal prestressing.
The longitudinal prestressed pipeline, set the positioning steel bar positioning, penetrate the rubber pipe into the pipeline to keep the pipeline straight, and rotate often in the concrete pouring process to prevent the prestressed bellows from leaking the slurry "condensation" hose, after the concrete pouring is finished after the initial setting, the longitudinal prestressed steel strand of the rubber pipe is pulled out with a bunching machine to wear a short bundle, and the whole bundle of the winch is pulled through the long bundle.
b Vertical prestressing.
In order to ensure the accuracy of the position of the vertical prestressed tendons, the positioning steel bar is used in the middle and the angle steel is used to locate the top surface. When there is a contradiction between the anchor end of the vertical prestressed tendon and the position of the pier reinforcement, the position of the anchor backing plate and the spiral reinforcement under the anchor should be guaranteed to be accurate and the position of the pier reinforcement should be adjusted. The vertical prestressed steel bar is cut with a cutting machine, and the prestressed steel bar should be pre-installed vertically.
c Transverse prestressing.
Transverse prestressed bellows are installed after the installation of vertical and longitudinal prestressed pipes. The transverse prestressed steel strand adopts the method of first wearing and then installing.
Prestressed tensioning and anchoring.
The prestressed tensioning equipment uses a jack and an oil pump matched with the anchor, which is calibrated before use, and calibrated regularly according to the requirements of the specification to ensure the tensioning quality. Symmetry and balance should be achieved when stretching, in accordance with the principle of first down and then up, first outside and then inside. Tensile program: 0 initial stress (02 con) con and hold the load for 5 minutes to anchor.
a Longitudinal prestressing.
The longitudinal prestressing adopts the through-center jack tensioning, and the tensioning sequence is the first web bundle, then the top plate bundle, and then the bottom plate bundle, and the left and right symmetrical synchronous tensioning.
b Transverse prestressing.
The transverse prestressed steel bundle is anchored by a flat anchor, and the working platform is erected by using the support of the cantilever plate, and the bundle is tensioned in both directions from the center of section 0 to both sides.
c Vertical prestressing.
The vertical prestressed steel bar is pre-tensioned on the platform according to the design tension force before installation, and the anchor end of the nut and the backing plate are fixed with epoxy resin to the lower end of the nut and the coarse steel bar before construction, and the unidirectional tension is symmetrical with the bridge axis from section 0 to both sides.
d The tensile tension of the prestressed tendon should be carried out after the concrete strength of the beam section reaches 100% of the design value and the elastic modulus reaches 100% of the design value, and the age of the concrete during tension must not be less than 5d. The tensioning of the prestressed tendon adopts the dual control of tensile force and elongation, mainly the tensile force, the difference between the actual elongation and the calculated elongation is controlled within 6%, and the tensioning step is carried out in strict accordance with the design or specification requirements. To find out the cause of insufficient elongation, take measures to make up the tension, and observe whether there is slippery and broken wire, and make a good tension record.
Grouting and anchor sealing.
a Arrangement of grouting pipes.
In addition to setting grouting holes and grouting holes at both ends of longitudinal prestressing, relay grouting holes need to be set in the middle according to the requirements of the specification. Horizontal and vertical prestressed pipelines, each section is provided with a grouting nozzle and an exhaust hole. The lower part of the adjacent two vertical prestressed pipes is connected by steel pipes, the upper part is the inlet, the other is the outlet, and the upper exhaust hole is treated by the method of pulling the seam and leaving the hole on the anchor plate.
b Grouting The prestressed pipeline grouting adopts cement slurry not lower than the design grade, and adds an expansion agent that meets the requirements according to the specified proportion. The vacuum grouting process is used in the construction to make the pipeline cement slurry more compact.
Precautions for grouting : Clean the prestressed pipe with clean water before grouting and then blow the water in the pipe with an air compressor. In strict accordance with the requirements of the specification of slurry and grouting, pay attention to observe whether there are string holes and leakage when grouting and make grouting records. If the hole is crossed, check the cause immediately and deal with it in time.
Vacuum-assisted grouting process: a vacuum pump is used to suck the air in the prestressed channel to make the hole pressure reach -0A vacuum of about 1MPa, and then at the other end of the hole with a grout press greater than 0The pressure of 7MPa presses the mixed cement slurry into the prestressed hole to improve the compactness of the hole grout and reduce the formation of bubbles.
c The anchor is sealed with the same concrete anchor as the design grade of the beam.
13) Linear control of large-span continuous box girder suspension irrigation construction.
In order to ensure the reliability and safety of the structure under construction and ensure that the alignment and stress state of the bridge meet the design requirements, the bridge cantilever construction is controlled.