CN117754722A - Two-stage symmetrical tensioning process for prefabricating middle bridge box girder of highway - Google Patents
Two-stage symmetrical tensioning process for prefabricating middle bridge box girder of highway Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 claims abstract description 90
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- 238000003860 storage Methods 0.000 claims abstract description 13
- 238000012423 maintenance Methods 0.000 claims abstract description 9
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- 230000002829 reductive effect Effects 0.000 claims description 6
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- 238000010438 heat treatment Methods 0.000 claims description 5
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Abstract
The invention discloses a two-stage symmetrical stretching process for prefabricating a middle bridge box girder of a highway, which comprises the following steps of: operating the steel bar and the template; pouring and removing the mould; steam curing operation; primary tensioning operation in the first stage; hanging off the pedestal and carrying out natural maintenance operation; final tensioning operation in the second stage; and (5) beam storage and exit. Symmetrical stretching of the prestressed steel bundles at two sides of the web plate effectively avoids side bending of the beam body; the primary tensioning operation in the first stage applies partial prestress to the beam body in the early stage, so that early cracking of concrete is effectively avoided, and the turnover of the template and the pedestal is quickened by hoisting away from the pedestal as soon as possible; the final tensioning of the second stage can ensure that the later-stage beam body has higher prestress level and good crack resistance, and the final effective prestress in each prestress steel beam is closer. The two-stage symmetrical tensioning process greatly improves beam manufacturing efficiency and beam manufacturing quality, is beneficial to the control of beam body linearity, ensures bearing capacity and durability, and has remarkable economic and social benefits.
Description
Technical Field
The invention relates to the technical field of bridge construction, in particular to a two-stage symmetrical tensioning process for prefabricating a middle bridge box girder of a highway.
Background
The middle bridge of the highway adopts a box girder section, and the body quantity is usually prefabricated in a concentrated way in a girder field, so that the production mode of the traditional girder field is to stretch the prestressed steel bundles to the design control stress one by one after the concrete box girder is poured on a fixed stretching pedestal and is cured until the strength and the elastic modulus reach 80% of the design values. The production time of each beam in the traditional one-time tensioning process reaches more than 10d, namely, the beam is manufactured by a single pedestal in a month mode, the turnover of the pedestal is slow, and the beam manufacturing efficiency is low. Meanwhile, the traditional one-time tensioning process is easy to cause excessive stress to cause concrete cracking, and excessive girder body arch and prestress loss are easy to be caused by excessive high-level prestressing, so that quality defects are formed in a girder manufacturing stage, and the girder body linearity, bearing capacity and durability are affected.
The method is limited by the traditional primary tensioning process of the middle bridge box girder of the highway, the existing girder manufacturing efficiency is difficult to improve, and the girder manufacturing quality is difficult to ensure, so that the requirement of introducing a new tensioning process is met.
Disclosure of Invention
The invention solves the technical problems that: the two-stage symmetrical stretching process for prefabricating the middle bridge box girder of the highway is provided, partial prestress is applied to the girder body in early stage, the turnover of the template and the pedestal is quickened, and the girder manufacturing efficiency is improved; the final effective prestress in each steel beam is closer by two-stage symmetrical tensioning, so that the overlarge arch of the beam body and early concrete cracking are avoided, the prestress loss is reduced, the beam body quality in the beam manufacturing stage is ensured, and the beam body in the later stage is ensured to have higher prestress level and good cracking resistance.
In order to solve the technical problems, the invention provides the following technical scheme: a two-stage symmetrical stretching process for prefabricating a middle bridge box girder of a highway comprises the following steps:
s1: operating the steel bar and the template;
s2: pouring and removing the mould;
s3: steam curing operation;
s4: primary tensioning operation in the first stage;
s5: hanging off the pedestal and carrying out natural maintenance operation;
s6: final tensioning operation in the second stage;
s7: and (5) beam storage and exit.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, in the step S1:
and (3) conveying and hanging the steel reinforcement framework and the templates to a pedestal by adopting a gantry crane for installation, sequentially installing a bottom die, a side die, a bottom web steel reinforcement framework, an inner die, a top plate steel reinforcement framework and an end die, and checking and accepting.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, the step S2 further includes:
obliquely segmenting the concrete during pouring, wherein the inclination is 30-45 degrees, the horizontal layering thickness is not more than 30cm, the interval time between two layers of concrete is not more than 1h, and the pouring time of each beam is not more than 4h;
and when the concrete reaches the specified form removal strength, sequentially removing the inner mold, the end mold and the side mold, and performing roughening treatment on the flange plate and the beam end after the form removal.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, in the step S3:
and adopting an intelligent temperature control steam curing system to carry out steam curing at four stages of static stop, temperature rise, constant temperature and temperature reduction on the beam body.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, in the step S4:
and (3) carrying out prestress steel beam penetrating after the strength and the elastic modulus of the concrete develop to reach 55-75% of the design values along with the time, and then carrying out symmetrical primary tensioning on the prestress steel beams on two sides of the web plates at the two ends of the beam body.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, the step S4 further includes:
the pre-tensioning of the pre-stress steel bundles is carried out in a mode that two ends are simultaneously and laterally symmetrical by taking a central axis which is symmetrical to the cross section of the component and balancing up and down and left and right as a principle, and the tensioning sequence of the pre-stress steel bundles is determined;
the prestress steel strand tensioning adopts double-index control of tensioning control stress and steel strand elongation, and the difference between an actual elongation value and a theoretical elongation value is not more than 6% when the tensioning control stress is taken as a main factor and the elongation is verified;
the prestress steel beam is loaded step by step during primary tensioning, and the overall tensioning procedure is as follows:
0 (synchronous loading), 15% sigma (measuring cylinder extension), 30% sigma (measuring prestress steel beam extension), sigma Initially, the method comprises (measuring the elongation of the prestressed steel bundles, holding the load for 5 min) to 0 (oil return anchoring);
wherein sigma represents the design tension control stress, sigma Initially, the method comprises Control stress, sigma, for first stage primary tensioning operation Initially, the method comprises And (3) taking 40-60% of sigma, wherein the concrete value is comprehensively determined according to the concrete strength and elastic modulus, the beam section size, the prestress steel beam configuration, the hoisting mode and the like.
As a preferable scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway, the invention comprises the following steps:
the primary stretching comprises three stages of loading, specifically:
first stage: synchronously and symmetrically stretching the two ends of the prestress steel strand by using intelligent stretching equipment, controlling the speed of an oil pump, enabling the two ends of the prestress steel strand to reach 15% sigma at the same time, enabling the prestress steel strand to reach a stress state from a relaxation state, and measuring the stretching-out amount of the oil cylinder;
second stage: after the stress of each steel strand in the prestress steel strand in the pipeline tends to be consistent, continuously and synchronously pressurizing the jacks at two sides to 30 percent sigma, and measuring the elongation of the steel strand loaded at the second stage;
third stage: continuing to stably boost, when the tensile stress reaches sigma Initially, the method comprises Measuring the elongation of the third-stage loaded steel strand, holding the load for 5min and completing automatic tensioning;
oil return anchoring: the tensioning system is controlled to enable the tensioning oil pressure to be slowly reduced to 0, and the piston return clamping piece automatically follows the anchoring.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, the step S5 further includes:
lifting the beam body to a final stretching area by adopting a bottom supporting lifting method for natural maintenance;
after the beam body of the final tension area is in place, the exposed steel stranded wires and the anchorage devices are subjected to rust prevention protection, and the special steel pipe sleeve is used for collapse prevention and deprotection.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, the step S6 further includes:
when the strength and the elastic modulus of the concrete develop to reach 100% of the design value along with time, and the concrete age is more than 7d, carrying out the final tensioning operation of the second stage, wherein the tensioning sequence of the final tensioning prestressed steel bundles is the same as that of the initial tensioning;
and (3) grouting the pore canal by using intelligent grouting equipment within 48 hours after final tensioning, then sealing and anchoring the beam end, and finally hanging the grouting material from the gantry crane to a beam storage area after the cement slurry strength and the sealing concrete strength in the pipeline reach the design requirements.
As a preferred scheme of the two-stage symmetrical stretching process for prefabricating the middle bridge girder of the highway according to the present invention, in the step S7:
and (3) placing the highway intermediate bridge box Liang Fang in a beam storage area for double-layer storage, transporting the highway intermediate bridge box Liang Fang from a beam field to a beam erecting field according to the engineering progress, and recording the two-stage symmetrical tensioning production quality information of the highway intermediate bridge box beam before exiting.
The invention has the beneficial effects that: symmetrical stretching of the prestressed steel bundles at two sides of the web plate effectively avoids side bending of the beam body; the primary tensioning operation in the first stage applies partial prestress to the beam body in the early stage, so that early cracking of concrete can be effectively avoided, the beam body has very low stress level in the hoisting stage, the pedestal can be hoisted away as soon as possible, turnover of the template and the pedestal is quickened, and beam manufacturing efficiency is improved; the final tensioning stage of the second stage can complement the pre-stress loss of the initial tensioning, ensure that the later-stage beam body has higher pre-stress level and good crack resistance, and enable the final effective pre-stress in each pre-stress steel beam to be closer. Compared with the traditional primary tensioning process of the middle bridge box girder of the highway, the two-stage symmetrical tensioning process is adopted to greatly improve the girder manufacturing efficiency, save the occupied area of a girder field, ensure the production quality, facilitate the control of the girder body alignment, ensure the bearing capacity and the durability, and have remarkable economic and social benefits.
Drawings
FIG. 1 is a schematic illustration of the basic flow of a two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to the present invention;
FIG. 2 is a graph showing the comparison of the prestress loss of the prestress steel bundles of different tensioning processes for a two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to one embodiment of the present invention;
FIG. 3 is a schematic drawing of a Liang Tizong cross-section prestressed steel strand for a two-stage symmetrical stretching process for prefabricating a highway mid-bridge girder according to one embodiment of the present invention;
FIG. 4 is a schematic view of a beam end A-A cross-section prestressed steel bundle arrangement for a two-stage symmetrical tensioning process for prefabricating a highway mid-bridge box girder according to one embodiment of the present invention;
fig. 5 is a schematic diagram of a midspan B-B section prestressed steel bundle arrangement for a two-stage symmetrical tensioning process for prefabricating a highway mid-bridge girder according to an embodiment of the present invention.
Detailed Description
So that the manner in which the above recited objects, features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments, some of which are illustrated in the appended drawings.
Examples
Referring to fig. 1-5, one embodiment of the present invention provides a two-stage symmetrical tensioning process for prefabrication of a bridge box girder in a highway, comprising the steps of:
s1: the operation of the steel bar and the template comprises the following steps:
and (3) conveying and hanging the steel reinforcement framework and the templates to a pedestal by adopting a gantry crane for installation, sequentially installing a bottom die, a side die, a bottom web steel reinforcement framework, an inner die, a top plate steel reinforcement framework and an end die, and checking and accepting.
S2: the pouring and demolding operation comprises the following steps:
obliquely segmenting the concrete during pouring, wherein the inclination is 30-45 degrees, the horizontal layering thickness is not more than 30cm, the interval time between two layers of concrete is not more than 1h, and the pouring time of each beam is not more than 4h;
the concrete vibration adopts an attached high-frequency vibrator as a main part and an inserted vibrator as an auxiliary part;
and when the concrete reaches the specified form removal strength, sequentially removing the inner mold, the end mold and the side mold, and performing roughening treatment on the flange plate and the beam end after the form removal.
S3: the steam curing operation comprises the following steps:
and adopting an intelligent temperature control steam curing system to carry out steam curing on the beam body in a static stop stage, a heating stage, a constant temperature stage and a cooling stage.
And (3) a static stop stage: standing for a period of time at room temperature before the concrete is poured and heated;
and (3) heating: the temperature of the steam curing shed is slowly increased, so that the steam curing temperature is increased to the temperature required by the constant temperature stage, and the box girder temperature is gradually increased. The rapid temperature rise can cause cracks on the surface of the concrete, so that the temperature rise rate needs to be controlled;
constant temperature stage: and continuously steaming the box girder at a constant temperature. In the constant temperature stage, the early strength of the concrete can be improved by proper constant temperature and constant temperature duration without adverse effect on the later strength;
and (3) a cooling stage: the temperature of the steam curing shed is slowly reduced, so that the temperature of the box girder is gradually reduced. Too fast cooling can cause huge temperature difference between the surface of the concrete and the core, resulting in cracking of the concrete, and therefore, the cooling rate needs to be strictly controlled.
Wherein the temperature in the steam curing shed at the constant temperature stage is 40-45 ℃, the constant temperature time is 12-16 h, and the relative humidity is maintained to be more than 95%; the temperature rise and the temperature reduction rate are not more than 5 ℃/h; the total time length of the heating, cooling and constant temperature is 28-32 h, the time length distribution of each stage of the steam curing is optimized by adopting a mode of pre-heating and pre-cooling, and the temperature of the concrete core part in the whole steam curing process is not more than 60 ℃; and opening the steam curing shed when the difference between the concrete core part of the beam body and the surface and the difference between the surface and the ambient temperature are smaller than 10 ℃, and ending the steam curing.
S4: the primary stretching operation of the first stage comprises the following steps:
when the strength and the elastic modulus of the concrete develop to reach 55-75% of the design value along with time, an automatic beam penetrating machine is used for penetrating the prestressed steel beams, and then 4 jacks of intelligent tensioning equipment are used for symmetrically initially tensioning the prestressed steel beams at two sides of the web plate at two ends of the beam body.
Taking prefabrication production of a middle bridge box girder of a certain highway as an example. As shown in figures 3-5, the beam is provided with 8 prestressed steel beams with nominal diameters of 15.2mm and nominal tensile strength of 1860MPa on the web plate and the bottom plate, and the numbers of the prestressed steel beams are N1, N2, N3 and N4 from top to bottom respectively. Except that the N3 prestress steel beam contains 6 prestress ribs, the rest prestress steel beams contain 5 prestress ribs. The pre-stress steel beam is initially tensioned by taking the central axis which is symmetrical to the cross section of the component and balancing up, down, left and right as a principle, and adopting a mode that two ends are symmetrical left and right at the same time. The tensioning sequence of the prestressed steel bundles is N1-N3-N2-N4. The prestress steel strand is tensioned by adopting double-index control of tension control stress and steel strand elongation, and the difference between an actual elongation value and a theoretical elongation value is not more than 6% when the elongation is verified by taking the tension control stress as a main part. The prestress steel beam is loaded step by step during primary tensioning, and the overall tensioning procedure is as follows: 0 (synchronous loading), 15% sigma (measuring cylinder extension), 30% sigma (measuring prestress steel beam extension), sigma Initially, the method comprises (measuring the elongation of the prestressed steel bundles, holding the load for 5 min) →0 (oil return anchoring). Wherein sigma represents the design tension control stress, sigma Initially, the method comprises Control stress, sigma, for first stage primary tensioning operation Initially, the method comprises 40 to 60 percent of sigma is taken, and the concrete value is based on concrete strength and elastic modulus, beam section size and prestressed steelThe beam configuration, the lifting mode and the like are comprehensively determined, and the precondition that the beam body can be lifted off after initial tensioning and no defects are generated is satisfied.
The primary stretching comprises three stages of loading, specifically:
first stage: synchronous symmetrical tensioning of two ends is carried out by using intelligent tensioning equipment, the speed of an oil pump is reasonably controlled, and meanwhile 15% sigma is reached, so that the prestressed steel strand is in a stressed state from a relaxed state, and the extension amount of an oil cylinder is measured;
second stage: after the stress of each steel strand in the prestress steel strand in the pipeline tends to be consistent, continuously and synchronously pressurizing the jacks at two sides to 30 percent sigma, and measuring the elongation of the steel strand loaded at the second stage;
third stage: continuing to stably boost, controlling the oil meter reading, and when the tensile stress reaches sigma Initially, the method comprises And measuring the elongation of the third-stage loaded steel strand, holding the load for 5min and completing automatic tensioning.
Oil return anchoring: the tensioning system is controlled to enable the tensioning oil pressure to be slowly reduced to 0, and the piston return clamping piece automatically follows the anchoring.
S5: the hanging-off pedestal and the natural maintenance operation comprise:
the beam body is lifted to a final stretching area for natural maintenance by adopting a bottom supporting lifting method, the lifting position is 1.2-1.5 m away from the beam end, the width of the supporting beam is 15-20 cm, and the requirements on lifting strength and rigidity are met;
the natural maintenance adopts an automatic spraying health preserving system for remote intelligent control, so that the outer surface and the inner cavity of the beam body are fully wetted;
after the beam body of the final tension area is in place, the exposed steel stranded wires and the anchorage devices are subjected to rust prevention protection, and the special steel pipe sleeve is used for collapse prevention and deprotection.
S6: the final tensioning operation of the second stage comprises:
and after the strength and the elastic modulus of the concrete are developed to reach 100% of the design values along with time and the concrete age is more than 7d, carrying out final tensioning operation in the second stage. The stretching sequence of the final stretching prestressed steel bundles is the same as that of the initial stretching, namely N1-N3-N2-N4;
the final stretching overall stretching procedure is as follows: 0 (synchronous loading) →σ Initially, the method comprises (measurement of prestressed Steel bundle elongation)Length) →σ Terminal (A) (measuring the elongation of the prestressed steel bundles and holding the load for 5 min) →0 (oil return anchoring), sigma Terminal (A) Taking 100% of the design tensioning control stress sigma for the control stress of the final tensioning operation in the second stage;
and (3) grouting the pore canal by using intelligent grouting equipment within 48 hours after final tensioning, then sealing and anchoring the beam end, and finally hanging the grouting material from the gantry crane to a beam storage area after the cement slurry strength and the sealing concrete strength in the pipeline reach the design requirements.
S7: the beam storage and departure comprises the following steps:
the highway middle bridge box Liang Fang is placed in a beam storage area for double-layer storage, and is transported to a beam erecting site from a beam field according to the engineering progress, and a 'two-stage symmetrical tensioning production quality record table of the middle bridge box beam' shown in the table 1 is filled in before the highway middle bridge box Liang Fang is discharged.
And a two-stage symmetrical stretching process is adopted, and stretching time and stretching stress of initial stretching and final stretching are respectively controlled so as to smoothly complete stretching operation of the prestressed steel bundles. Steam curing is adopted to lead the strength and the elastic modulus of the concrete to rapidly develop to 55 to 75 percent of the design value along with the time, and then the primary tensioning operation of the first stage is carried out, sigma Initially, the method comprises Taking 40-60% of sigma; the initial tensioning post-beam body is lifted off the tensioning pedestal and stored in a final tensioning area for natural maintenance, and the final tensioning operation in the second stage is carried out after the concrete strength and the elastic modulus develop to 100% of the design value along with the time and the concrete age is more than 7d, wherein sigma Terminal (A) Take 100% of sigma. The beam forming efficiency versus the different tensioning processes is shown in table 2. And the prestressed steel bundles are initially tensioned in 3d after the concrete pouring is finished, and then the box girders are lifted off the pedestal, so that the time of occupying the pedestal is shortened by 7d compared with that of the single-piece girders by the traditional one-time tensioning process, and the number of girders produced by the single pedestal per month can be increased by nearly 5 times, thereby greatly accelerating the turnover of templates and the pedestals and saving the girder field. The pairs of prestress of the steel bundles for different tensioning processes are shown in fig. 2. The final stretching can complement most of prestress loss caused by initial stretching, so that the prestress loss of the beam body under the two-stage symmetrical stretching process condition is about 10 percent less than that of the traditional one-time stretching process, the later-stage beam body is ensured to have higher prestress level and good crack resistance, and the final effective prestress in each prestress steel beam is realizedThe forces are closer together. The two-stage symmetrical tensioning process is adopted, so that the beam manufacturing efficiency and the beam manufacturing quality are improved, and the economic benefit and the social benefit are remarkable.
Table 1: and a production quality record table for two-stage symmetrical tensioning of the middle bridge box girder.
Table 2: and (5) comparing beam making efficiencies of different tensioning processes.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered in the scope of the claims of the present invention.
Claims (10)
1. The two-stage symmetrical stretching process for prefabricating the middle bridge box girder of the highway is characterized by comprising the following steps of:
s1: operating the steel bar and the template;
s2: pouring and removing the mould;
s3: steam curing operation;
s4: primary tensioning operation in the first stage;
s5: hanging off the pedestal and carrying out natural maintenance operation;
s6: final tensioning operation in the second stage;
s7: and (5) beam storage and exit.
2. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S1, a gantry crane is adopted to transport and hoist the steel reinforcement framework and the template to a pedestal for installation, a bottom die, a side die, a bottom web steel reinforcement framework, an inner die, a top plate steel reinforcement framework and an end die are sequentially installed, and inspection and acceptance are carried out.
3. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S2, further includes:
obliquely segmenting the concrete during pouring, wherein the inclination is 30-45 degrees, the horizontal layering thickness is not more than 30cm, the interval time between two layers of concrete is not more than 1h, and the pouring time of each beam is not more than 4h;
and when the concrete reaches the specified form removal strength, sequentially removing the inner mold, the end mold and the side mold, and performing roughening treatment on the flange plate and the beam end after the form removal.
4. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S3, an intelligent temperature control steam curing system is adopted to carry out steam curing at four stages of standing, heating, constant temperature and cooling on the beam body.
5. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S4, when the strength and the elastic modulus of the concrete are developed to reach 55-75% of the design value along with the time, the prestress steel bundles are penetrated, and then the prestress steel bundles on two sides of the web plates at two ends of the beam body are symmetrically and initially tensioned.
6. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 5, wherein:
in the step S4, further includes:
the pre-tensioning of the pre-stress steel bundles is carried out in a mode that two ends are simultaneously and laterally symmetrical by taking a central axis which is symmetrical to the cross section of the component and balancing up and down and left and right as a principle, and the tensioning sequence of the pre-stress steel bundles is determined;
the prestress steel strand tensioning adopts double-index control of tensioning control stress and steel strand elongation, and the difference between an actual elongation value and a theoretical elongation value is not more than 6% when the tensioning control stress is taken as a main factor and the elongation is verified;
the prestress steel beam is loaded step by step during primary tensioning, and the overall tensioning procedure is as follows:
0 (synchronous loading), 15% sigma (measuring cylinder extension), 30% sigma (measuring prestress steel beam extension), sigma Initially, the method comprises (measuring the elongation of the prestressed steel bundles, holding the load for 5 min) to 0 (oil return anchoring);
wherein sigma represents the design tension control stress, sigma Initially, the method comprises Control stress, sigma, for first stage primary tensioning operation Initially, the method comprises And (3) taking 40-60% of sigma, wherein the concrete value is comprehensively determined according to the concrete strength and elastic modulus, the beam section size, the prestress steel beam configuration, the hoisting mode and the like.
7. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 6, wherein:
the primary stretching comprises three stages of loading, specifically:
first stage: synchronously and symmetrically stretching the two ends of the prestress steel strand by using intelligent stretching equipment, controlling the speed of an oil pump, enabling the two ends of the prestress steel strand to reach 15% sigma at the same time, enabling the prestress steel strand to reach a stress state from a relaxation state, and measuring the stretching-out amount of the oil cylinder;
second stage: after the stress of each steel strand in the prestress steel strand in the pipeline tends to be consistent, continuously and synchronously pressurizing the jacks at two sides to 30 percent sigma, and measuring the elongation of the steel strand loaded at the second stage;
third stage: continuously and steadily boosting, when the tension stress isReaching sigma Initially, the method comprises Measuring the elongation of the third-stage loaded steel strand, holding the load for 5min and completing automatic tensioning;
oil return anchoring: the tensioning system is controlled to enable the tensioning oil pressure to be slowly reduced to 0, and the piston return clamping piece automatically follows the anchoring.
8. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S5, further includes:
lifting the beam body to a final stretching area by adopting a bottom supporting lifting method for natural maintenance;
after the beam body of the final tension area is in place, the exposed steel stranded wires and the anchorage devices are subjected to rust prevention protection, and the special steel pipe sleeve is used for collapse prevention and deprotection.
9. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S6, further includes:
when the strength and the elastic modulus of the concrete develop to reach 100% of the design value along with time, and the concrete age is more than 7d, carrying out the final tensioning operation of the second stage, wherein the tensioning sequence of the final tensioning prestress steel bundles is the same as that of the initial tensioning;
and (3) grouting the pore canal by using intelligent grouting equipment within 48 hours after final tensioning, then sealing and anchoring the beam end, and finally hanging the grouting material from the gantry crane to a beam storage area after the cement slurry strength and the sealing concrete strength in the pipeline reach the design requirements.
10. The two-stage symmetrical tensioning process for prefabrication of a highway mid-bridge box girder according to claim 1, wherein:
in the step S7, the highway intermediate bridge box Liang Fang is placed in a beam storage area for double-layer storage, transported from a beam yard to a beam erecting site according to the engineering progress, and the two-stage symmetrical tensioning production quality information of the highway intermediate bridge box beam is recorded before exiting.
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| CN115026944A (en) * | 2022-06-27 | 2022-09-09 | 中交(南京)建设有限公司 | Method for pre-stressed construction of highway municipal prestressed concrete precast box girder |
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