CN112323641A

CN112323641A - Construction method of pretensioned prestressing concrete hollow simply supported beam

Info

Publication number: CN112323641A
Application number: CN202011267448.1A
Authority: CN
Inventors: 宋博; 张明月; 李滨; 关宏生; 张荣福
Original assignee: Anshan Sanye Construction Engineering Co ltd
Current assignee: Anshan Sanye Construction Engineering Co ltd
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2021-02-05

Abstract

The invention belongs to the technical field of bridge engineering construction, and relates to a construction method of a pretensioning prestressed concrete hollow simply supported beam. Compared with the prior art, its beneficial effect is: the prestressed beam has the advantages of large span, light dead weight, low steel content, high flatness, high production speed, low production cost, strong practicability and the like, has low reinforcing steel bar consumption and high crack resistance of the hollow beam, has the advantages of high forming speed, high durability and the like of the pretensioned prestressed beam, can ensure the economical efficiency and safety of the construction of trestles with various lengths and widths, and is suitable for the construction of trestles and medium and small bridges.

Description

Construction method of pretensioned prestressing concrete hollow simply supported beam

Technical Field

The invention belongs to the technical field of bridge engineering construction, and particularly relates to a construction method of a pretensioned prestressing concrete hollow simply supported beam.

Background

The construction scheme of the precast beam applied in China at present mainly comprises the following two types: the first type is a post-tensioning construction scheme, namely, a beam prefabricating pedestal is constructed, reinforcing steel bars are installed on the pedestal, prestressed steel strands are installed in reserved channels in a beam body, an anchorage device and a base plate are installed at the beam end, then a template is installed and concrete pouring is carried out, tensioning operation is carried out when the concrete of the beam body reaches a certain strength, and the beam body is prefabricated after pipeline grouting and end sealing are carried out after prestress is applied to the beam body; although the post-tensioning method reduces the engineering quantity of a tensioning pedestal of a precast yard, hole forming, beam penetrating and grouting processes are inevitably added, and meanwhile, the defects and quality problems that the structure durability is affected, such as hole blocking, grouting incompactness and the like, easily occur in the construction process. The diseases are also found in the disassembly of a plurality of highways such as Shanhuning, Zhengluo and the like and some grand bridges in China, and the post-tensioned prestressed pipeline grouting is one of eight common diseases for the construction of highways in China because the department of transportation does not use post-tensioned prestressed pipeline grouting. And the second type is a construction scheme adopting a pre-tensioning method, wherein the construction scheme adopting a groove type, a frame type and a pier type pedestal is used for prefabricating a beam body, the prestressed tendons are tensioned before concrete of the beam body is poured, then concrete pouring operation is carried out, and the beam body is stressed by placing tension when the concrete strength of the beam body reaches a certain value. The pre-tensioned beam can avoid the problems of the post-tensioned beam, and has the advantages of simple process, less processes, high manufacturing speed, good beam durability, easy guarantee of construction quality, small maintenance workload and the like. However, the existing pretensioned beam mostly adopts linear reinforcement, the process is simple, but the stress requirement is difficult to meet in a large-span structure, the maximum span of the common pretensioned beam is limited below 20m, and the application range of the pretensioned beam is limited.

The pretensioned prestressed concrete hollow simply supported beam has the advantages of low reinforcing steel bar consumption and crack resistance of the hollow beam, concrete saving, high forming speed and high durability of the pretensioned prestressed concrete hollow simply supported beam, and no same construction technology is available for reference at home and abroad.

Disclosure of Invention

The invention aims to provide a construction method of a pretensioned prestressed concrete hollow simply supported beam, which overcomes the defects of the prior art, is used for manufacturing construction of a medium bridge with an urban B-level vehicle-mounted load and a pedestrian load of 3.5MPa, has the advantages of low reinforcing steel bar consumption and crack resistance of the hollow beam, high forming speed and good durability of the pretensioned prestressed beam, and can ensure the economy, safety and high efficiency of a trestle construction task with the length of 500-1000 meters and the width of 6-10 meters.

In order to achieve the purpose, the invention is realized by the following technical scheme:

a construction method of a pretensioning method prestressed concrete hollow simply supported beam is characterized by sequentially comprising the concrete operation steps of template manufacturing and installation, steel bar processing and installation, prestressed steel bar installation and tensioning, hollow beam lower layer concrete pouring, core mold installation, hollow beam upper layer concrete pouring, core mold dismantling, concrete steam curing, prestressed steel bar releasing and tensioning, mold dismantling and the like.

Compared with the prior art, the invention has the beneficial effects that:

1) the method is used for manufacturing the middle bridge construction with the vehicle-mounted load of the city grade B and the pedestrian load of 3.5MPa, so that the middle bridge construction has the advantages of low reinforcing steel bar consumption and crack resistance of the hollow beam, high forming speed and good durability of the pretensioned prestressed beam, and can ensure the economy, efficiency and safety of the trestle construction task.

2) By adopting the core mould technology and utilizing high-grade concrete, the section size can be reduced, the self weight of the beam is reduced, the spanning capacity of the bridge is also increased, the construction transportation and erection are facilitated, and the method is also suitable for manufacturing hollow bridges on other occasions.

3) By adopting the steam curing technology, the strength required by installation can be achieved within 2 days, and the construction progress is greatly accelerated.

4) The span of the prefabricated hollow beam slab can reach 10 meters, 13 meters, 16 meters, 20 meters and more, belongs to a hollow simply supported beam with super-long span, and can save the amount of reinforcing steel bars by about 20-40%.

5) Because the concrete is comprehensively compressed, the advantage of good compression resistance of the concrete is fully exerted, the rigidity of the beam is improved, and the anti-cracking performance and the durability of the beam can be greatly improved by the prestressed hollow beam slab.

6) The side mold adopts the large all-steel template, and galvanized iron sheets are laid on the concrete contact surface, so that the rigidity is high, the turnover frequency is high, the cost of template amortization is low, the flatness is high, and the quality is better.

Drawings

FIG. 1 is a schematic structural view of an embodiment of a pretensioned prestressing concrete hollow simply supported beam according to the present invention.

FIG. 2 is a schematic view of a reinforcing steel bar arrangement structure in an embodiment of the pretensioned prestressed concrete hollow simply supported girder of the present invention.

FIG. 3 is a schematic view of an application state of the pretensioned prestressing concrete hollow simply supported girder according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of the working state of the length compensator in the embodiment of the invention.

Fig. 5 is a schematic structural diagram of a length compensator according to an embodiment of the present invention.

Fig. 6 is a schematic view of the working state of the prestressed reinforcement handling apparatus in the embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The following embodiment is applied to the floor welding of the steel bridge of the expressway in some places.

Referring to fig. 1-6, which are schematic structural views of an embodiment of the pretensioned prestressing concrete hollow simply supported girder of the invention, the trestle is a prestressed concrete hollow slab simply supported girder bridge, the single span is 20m, the full width of the bridge is 8a, each span is composed of 6 prestressed concrete hollow slab girders, 4 middle slabs and 2 side slabs. The width of the middle plate is 125cm, the width of the side plate is 150cm, and the height of the beam is 95 cm. And adopting cast-in-situ seam connection.

The invention discloses a construction method of a pretensioned prestressed concrete hollow simply supported beam, which is characterized by sequentially comprising the following steps of template manufacturing and installation, steel bar processing and installation, prestressed bar installation and tensioning, hollow beam lower layer concrete pouring, core mould installation, hollow beam upper layer concrete pouring, core mould dismantling, concrete steam curing, prestressed steel bar releasing and mould dismantling, and the concrete operation steps are as follows:

step one) template manufacturing, which comprises the following steps:

101) the template bottom mould adopts a wood mould with the thickness of 35mm, the side mould adopts a steel template, phi 6 reinforcing steel bars with the length of 500mm are welded on the side mould according to the interval of 1m, and a rough surface with the roughness of 6mm is formed on the surface of the component. When the hollow slab is prefabricated, except for paying attention to the embedded steel bars and the pre-arranged parts according to design drawings, the bridge deck system, the expansion joints, the guardrails and other related auxiliary structures are constructed according to the related drawings, and the embedded steel bars of the guardrails are embedded in the prefabricated hollow slab.

102) The contact surface of the wood mould and the concrete is nailed with galvanized iron sheet to ensure that the surface of the member is flat and smooth and can be reused.

103) In the process of manufacturing the template, the shape and the size of each part of the hollow slab and the accuracy of the mutual positions of the parts must be ensured according to the sizes shown in the drawing.

104) When the bottom is paved, the battens are paved evenly and are strictly leveled, and particularly, the contact position of the beam end and the bearing platform seat is kept horizontal so as to ensure the position of the prestressed tendon.

105) When the isolating agent is coated on the inner side of the template, the steel bars and the embedded parts are strictly prohibited from being stained, and the coating is uniform.

106) The positions and the sizes of the exposed dowel bars and the reserved holes are required to be accurate and firm in installation, and walking displacement in the concrete pouring process is prevented.

107) Before the inflatable core mold is used, the inflatable core mold is checked to prevent air leakage, a specially-assigned person is required to check the steel wire head during installation, and the steel wire head is bent to the inner side. After each use, the product should be stored properly to prevent pollution, damage and aging.

108) The inflation pressure should remain stable from the beginning of concrete placement to the time the core is deflated.

109) When concrete is poured, effective measures are taken to fix the core mould in order to prevent the core mould from floating upwards and deviating, and the core mould is poured symmetrically and evenly.

110) The air release time of the core mould is determined by tests, and the strength of concrete is preferably enough to keep the member from deforming.

Step two), processing and installing the steel bars, and comprises the following steps:

201) the category and the diameter of the reinforcing steel bars are adopted according to the design specification. The size of the formed steel bar must meet the design requirements of drawings, the deviation is within an allowable range, and a mould can be manufactured if necessary to ensure the accuracy of the mutual position and the appearance size.

202) The position of the steel bar joint and the sectional area of the joint meet the requirements of JTJ 041-2000. And (5) timely inspecting the test piece for the butt-welded steel bars. The length of the designed steel bar is not reduced, and the actual construction blanking is controlled according to the requirements of relevant construction specifications.

203) The crossing point of the reinforcing steel bar is bound firmly by using iron wires, and if necessary, the steel bar can be tack-welded.

204) Because the prestressed concrete hollow slab is constructed by adopting a pretensioning method, the lower prestressed steel strand cannot be bound with the stirrup, the rigidity of the steel bar framework is small, and the hanging bracket is adopted during binding and hoisting to ensure that the framework is not deformed.

205) The spacing between the steel bars N9 is 40cm, the spacing between the steel bars N18 is 40cm, and the spacing between the steel bars N10 is 50 cm. The reinforcing steel bars N15, N19 correspond to the position of N14.

The tolerance of the spacing position of the reinforcing steel bars is in accordance with the requirements of the following table 1.

TABLE 1

Step three), manufacturing and installing prestressed tendons, comprising the following steps:

301) blanking of the prestressed tendons:

firstly, cutting the cut materials by using a grinder, and forbidding cutting by using electric welding and gas welding; the broken prestressed tendons are respectively stacked according to specification and size to show the application, and whether the length meets the requirements of drawing and tensioning is checked;

secondly, the prestressed tendons should be inspected one by one before being installed, so that damages such as breakage and bending cannot occur, and the severely corroded steel strand cannot be used accurately.

And thirdly, sleeving two ends of the failure prestressed reinforcement by using hard plastic sleeves, and tightly wrapping two ends of each sleeve to prevent concrete from immersing.

302) Manufacturing a bearing frame and an end beam:

and manufacturing the distance between the holes on the end beam, the drilling position and the size of the hole diameter according to the distance between the prestressed steel strands, the thickness of the concrete protective layer and the diameter of the steel strands on a drawing. When the rib is penetrated, whether the position of the drill hole is accurate or not needs to be checked, and the drill hole is inaccurate to be manufactured again.

The design bearing capacity is 400 tons.

303) Verification of prestress tension equipment

The prestress tension equipment comprises a 25-ton through jack, a high-pressure oil pump and a pressure gauge. And the YC600 type medium jack is applied to verify the YDCN250 type jack during the calibration. The oil pressure gauge has the advantages that the carrying scale is 60MPa, the precision grade is 1.5, the detection forces are respectively five data of 50KN, 100KN, 150KN, 194KN and 200KN, the detection is carried out for three times in each grade, the error is less than or equal to 0.2MPa, the pressurization is slow and accurate, and then the tension force and the corresponding elongation value of the prestressed reinforcement are calculated.

△L＝PL/EA＝166.7mm

In the formula: p is single root phi^s15.2 tensile resistance of the low-relaxation steel strand, 176400N; l: the length of the steel strand is 25800 mm; e: modulus of elasticity of steel strand, 1.95X 10⁵MPa; a, the section area of the steel strand is 140mm². Δ L: theoretical elongation values in mm.

304) Prestressed steel strand tensioning

The tensioning adopts a pre-tensioning construction process, namely, concrete is poured after the prestressed tendons are tensioned, and after the concrete is solidified to reach a certain strength, the concrete is rebounded by virtue of the adhesive force to generate the pre-compression stress.

Preparation work

A. Construction technicians who have pre-stress construction knowledge and correct operation are required in a construction site;

B. checking whether the anchorage device is installed correctly;

C. checking whether the action line of the tension force of the tension jack is coincident with the axis of the prestressed tendon or not;

D. checking whether the end beam, the bearing frame and various tensioning devices meet the requirements or not;

E. carrying out failure treatment on the steel strand according to design requirements, and fixing the position of the plastic pipe according to the designed failure length of the steel strand;

F. and making technical safety bottom crossing before construction.

Operation procedure

A. Adjusting the length of the prestressed tendons to ensure that each prestressed tendon bears uniform force; tensile design strength is 1260 Mpa.

B. Formal tensioning: one end is fixed and the other end is tensioned, and the tensioning sequence is symmetrically carried out from the middle to two sides;

C. holding the load: tensioning is controlled according to the tensioning force of 0 to initial stress to 1.03 times, and after the prestressed tendon is tensioned, the prestressed tendon is held for 3min according to the standard requirement so as to reduce the stress loss of steel wire anchoring;

if the length of the prestressed steel bar is insufficient, the length compensator can be used, the structure of the length compensator comprises a first pipe hoop 1, a second pipe hoop 2 and a connecting plate 3, the first pipe hoop 1 and the second pipe hoop 2 are arranged along the axis, the distance is 300 mm and 600mm, the upper part and the lower part of the first pipe hoop 1 and the second pipe hoop 2 are respectively provided with the connecting plate 3, the first pipe hoop 1, the second pipe hoop 2 and the connecting plate 3 are welded into a whole, when the pre-tensioning construction method is adopted, if the length of the prestressed steel strand 7 is insufficient, the length compensator 4 can be connected between the two prestressed steel strands 7, one end of the hollow simply supported beam 6 is connected, the other end of the hollow simply supported beam is connected with an end beam 5 of a prestressed force bearing system, and the prestressed steel strand is connected with the pipe hoop through a. The length compensator is a rigid structure, the actual working state of the steel strand is not influenced, and only the actual change of the elongation value of the steel strand needs to be considered.

And step three), when the broken strand needs to be replaced in the construction of the prestressed steel strand, using a prestressed steel bar loading and unloading device 8 to prop against the end beam 5 of the prestressed force-bearing system through a supporting seat 9, firstly stretching the prestressed steel strand 7 to enable the clamping piece anchorage device to be loosened, recovering the working state before anchoring, using the operating space generated by the supporting seat 9 to remove the clamping piece of the anchorage device from the hand hole on the supporting seat, and then releasing the stress, so that the broken strand steel strand can be replaced.

Step four), pouring the lower-layer concrete of the hollow beam, installing a template outside the steel bars, adopting a full-steel large template for the side mold, paving a galvanized iron sheet on the concrete contact surface, and after the steel bars and the template are installed, pouring the lower layer of the hollow beam by using C50 concrete, wherein the concrete is flush with the bottom surface of the core mold;

before pouring the hollow plate concrete, whether embedded parts of auxiliary facilities such as expansion joints, water drain pipes, guardrails, supports and the like are complete or not should be strictly checked, and pouring can be carried out after the situation that the embedded parts are correct is determined. During construction, accurate positions of prestressed reinforcements and common reinforcements are guaranteed, the maximum particle size of concrete aggregates is controlled not to be larger than 20mm, the concrete is fully vibrated and compacted during concrete pouring, and the quality of the concrete is strictly controlled.

Secondly, in order to prevent the prefabricated slab from arching too much and prevent the prefabricated slab and the cast-in-place layer of the bridge deck from generating too big shrinkage difference due to age difference,

the beam storage period is not more than 90d, and if the accumulated arch-up value exceeds the calculated value of 8mm, control measures are taken. After the steel beam tensioning of the prefabricated hollow slab is completed, the calculated value of the camber in the midspan of each beam storage period and the downwarp value generated by the second-stage dead load are shown in the following table 2:

TABLE 2

Note that positive values indicate upward displacement and negative values indicate downward displacement.

Step five), installing a core mold, namely placing an inflatable core mold in the middle of the reinforcing steel bar, coating a release agent on the surface of the inflatable core mold, and inflating until a cavity is fully occupied;

step six), pouring concrete on the upper layer of the hollow beam, wherein the concrete is poured in a horizontal layered oblique segmented continuous pouring mode, the concrete is sequentially pushed from one end of the simply-supported beam to the other end, the length of each segment is 6-10 m, the layered blanking thickness is not more than 30cm, the concrete on the upper layer needs to be covered before the initial setting of the concrete on the lower layer, and the concrete is timely leveled and collected after being poured to the top, the concrete is mainly vibrated by an inserted vibrator, and the vibration of an attached vibrator is assisted;

step seven), detaching the core mould, deflating the core mould after the concrete is initially set for 2-3 hours, and pulling out the core mould from one end of the hollow beam;

step eight), performing steam curing on the concrete, wherein during the steam curing, the component is sealed by using a buckle plate and a tarpaulin, and the steam curing is divided into 4 stages of standing still, heating, keeping constant temperature and cooling; the time of the static stop stage follows the principle of long time and short time, and is not less than 1.5 hours; controlling the temperature rising rate and the temperature reducing rate to be 15-25 ℃ per hour, and specifically determining according to seasons; in the constant temperature stage, the steam temperature is controlled at 80 ℃, the humidity is controlled at 85% -95%, and the constant temperature maintenance time is 12-16 hours.

Step nine), releasing tension and removing a mold of the prestressed reinforcement: when the strength of the concrete reaches more than 85% of the designed strength, the prestressed tendons are released; and (3) removing the mold, namely removing the side mold when the compressive strength of the concrete reaches 2.5Mpa, and pulling the mold plate open by using a crane and then lifting after the mold plate is separated from the beam body.

Wherein, the releasing and tensioning process of the prestressed tendon is as follows:

firstly, the tensioning pedestal should have enough strength and stability, and the prestressed reinforcement anchoring cross beam and the tensioning sand cylinder at two ends should have reliable fixing and other safety precautionary measures to prevent and control the occurrence of safety accidents such as upturning, slipping and the like.

Secondly, the pre-stressed reinforcing steel bars of the prefabricated hollow plate can be released after the strength of the concrete reaches 85% of the designed strength grade of the concrete, the age is properly increased when the condition is met, the elastic modulus of the concrete is improved, and the reverse camber is reduced.

And failure measures such as hard plastic sleeves or dense wrapping of hard plastic and the like adopted at two ends of part of prestressed reinforcements are stable and firm.

And fourthly, cutting the prestressed reinforcement from both ends of the long wire pedestal and then sequentially cutting towards the middle. Before cutting, the reinforcing steel bar must be cleaned and brushed with concrete slag, sludge and other impurities stuck thereon, and prestress release should be slowly carried out.

In the process of removing the formwork, the side formwork can be removed when the compressive strength of the concrete reaches 2.5Mpa, and after the formwork is separated from the beam body, the formwork is pulled open by a crane and then lifted.

Safety regulations in the operating process:

1. the operator should wear the prescribed labor protection articles during the work period and should carefully follow the safety operation regulations of the post, and the personnel entering the production site should wear the safety helmet.

2. Operators of all mechanical and electrical equipment should be familiar with the performance, maintenance and use methods of the equipment and do inspection work before use.

3. When the side walls of the mold are scattered and closed, the surrounding environment condition should be noticed, and the crowbar is prevented from hurting people.

4. When heavy objects such as the steel bar framework are transferred, a crane driver and field operators are closely matched to uniformly command, signals of the heavy objects are accurately transferred, and the heavy objects cannot be transferred on the tops of heads of ground operators.

5. During tensioning, people cannot stand at two ends of the component, and the oil pumps are placed at two sides of the end part of the component; people cannot stand behind the jack to prevent the prestressed steel strands or the anchorage devices from popping out to hurt people. After tensioning is finished, the tensioning equipment can be disassembled at the safe rear.

6. During tensioning, non-workers are prohibited from entering the field, and tensioning cannot be performed in rainy days.

Example materials selection

1. C50 concrete is adopted in the design of the prestressed concrete hollow slab, and C40 concrete is adopted in the end-capping concrete;

preparing a material for concrete: (1) the 525# ordinary portland cement is selected, and the cement must meet the current national standard and is attached with the cement quality test report of manufacturers. (2) The fine aggregate must be medium sand, and the fineness modulus is not less than 2.6. The grain size distribution of the sand meets the regulation in JTJ041-2000 technical Specification for highway and bridge construction. (3) The coarse aggregate should be hard, wherein the particle size is 5-20mm, and various inspection indexes of the coarse aggregate should meet technical regulations for highway, bridge and culvert construction (JTJ041-2000) (4) and the mixing water is selected as drinking water. (5) The dosage of the cementing material of the concrete per unit volume is as follows: the maximum water-gel ratio is 0.36, the minimum dosage is 360kg/m3, and the maximum dosage is 450kg/m 3.

2. Reinforcing steel bar, 1 prestressed steel bundle phi^s15.2 low-relaxation steel strand, which conforms to the national standard GB/T5224-2014, EP 1.95 × 105MPa, and the standard value of tensile strength 1860 MPa; when the steel strand enters the factory, the steel strand is inspected according to the following regulations except for the quality certificate, package, mark and specification of the steel strand which are self-inspected: (1) and (3) checking the appearance quality, wherein the surface of the finished steel strand is not required to be provided with a lubricant, grease and other substances for reducing the concrete-dividing adhesion of the steel strand, slight rust is allowed to exist, but the steel strand is not required to be rusted into macroscopic pits. (2) And (3) mechanical property inspection: and (3) cutting one sample from the normal position of the end part of each selected steel strand to perform surface quality, diameter deviation and mechanical property tests. If one test result is not qualified, the unqualified disc is rejected.

Ordinary reinforcing bar adopts HPB300 and HRB400 reinforcing bar, and the reinforcing bar should accord with "steel for reinforced concrete part 1: hot rolled plain steel (GB1499.1-2018) and "steel for reinforced concrete part 2: hot-rolled ribbed bars (GB 1499.2-2017). The steel bar should have a factory quality guarantee certificate or a test report, and samples are extracted according to the regulations for rechecking.

The clamp adopts a QM15-1 single-hole clamping piece clamp, and the clamp is checked and accepted in the factory: when the fixture enters the factory, the fixture is subjected to appearance inspection in addition to checking the anchoring sex, model, specification and quantity according to the factory qualification and quality certificate.

The method for installing the pretensioned prestressing concrete hollow simply supported beam into the bridge comprises the following steps:

the installation sequence is: filling hinge joints and sealing bottom joints, pouring hinge joints, pouring a bridge deck cast-in-place layer, pouring concrete pavement and accessory facilities, and forming a bridge after the strength of mortar reaches 50% of the design strength. Before the hinge joint is poured, heavy load on the bridge deck is completely removed, and after the strength of the hinge joint concrete cube reaches 90% of the designed concrete strength grade, construction of a bridge deck cast-in-place layer can be carried out.

Secondly, when transporting the prestressed concrete hollow slab, measures are taken to avoid the negative bending moment generated by the prestress from damaging, and a positive bending moment can be applied to the hollow slab by taking measures. The prefabricated hollow slab adopts a hoisting method of arranging hoisting holes to penetrate through the bottom of the beam-wrapping slab and adding carrying poles. If the bridge girder is hoisted by adopting a bridge girder erection machine, the bridge girder erection machine can be carried out by checking, and the weight of the bridge girder erection machine is required to fall on the upright post of the abutment.

And thirdly, cleaning and chiseling the floating slurry on the concrete joint surface at the end part of the precast slab before pouring the concrete at the seal end to pour new concrete. Before pouring hinge joints and pouring concrete on a cast-in-place layer of the bridge deck, floating slurry, oil stains and the like on the sides and tops of the prefabricated hollow slab plates are washed and removed completely to ensure that the new concrete and the old concrete are well combined.

And fourthly, roughening the top surface of the prefabricated hollow plate, roughening the joint surfaces of the new concrete and the old concrete, such as the anchoring end surface, the twisted seam surface and the like, to rough surfaces with the concave-convex diameter not less than 6mm, wherein not less than 1 point in 100 x 100mm area is beneficial to good combination of the new concrete and the old concrete.

When the plate type rubber support is installed, the elevation of the support is strictly controlled, the upper surface and the lower surface of the support are ensured to be smoothly and closely attached to the bottom surface of the plate and the top surface of the abutment supporting pad stone, force transmission is uniform, and the support is prevented from being empty.

Sixthly, the method is executed according to technical Specification for constructing bridges and culverts on roads, JTG/TF 50-2011.

And seventhly, anticorrosive coating of concrete: before silane is impregnated, the concrete is subjected to surface treatment, such as repairing honeycombs, exposed ribs, holes, cracks and the like by using epoxy mortar. Obvious defects of removing surface scraps and loose attachments, removing harmful substances and pollutants such as dust, oil stains and the like which are not beneficial to silane impregnation, wherein the surface of the concrete is dried before silane spraying, and the water content is not more than 6 percent. The silane paste is recommended to be used, the using amount is not less than 300g/m2, and if the silane paste needs to be sprayed for the second time, the construction can be carried out after the surface of the concrete is dried after the first spraying construction is carried out for 6-8 hours. The concrete is not drenched with rain within at least 24 hours after being sprayed with silane and is naturally dried.

When in construction, the construction should be stopped immediately when raining, so as to prevent the loss of the silane active ingredient before curing.

Anticorrosive coating of steel surface: the protective life of the coating system is 20 years. The details of the steel anti-adhesion coating fruit matching system are shown in the following table 3.

TABLE 3

The temperature and humidity should be strictly controlled during coating construction. When the temperature is lower than 5 ℃, construction cannot be carried out, the relative humidity is not more than 85% when the primer and the intermediate paint are constructed, and the relative humidity is not more than 75% when the finish paint is constructed.

The above embodiments are merely specific examples selected for illustrating the objects, technical solutions and advantages of the present invention in detail, and should not be construed as limiting the scope of the present invention, and various modifications, equivalent substitutions and improvements can be made without departing from the spirit and principle of the present invention.

Claims

1. A construction method of a pretensioned prestressing concrete hollow simply supported beam is characterized by sequentially comprising the following steps of template manufacturing and installation, steel bar processing and installation, prestressed steel bar installation and tensioning, hollow beam lower layer concrete pouring, core mold installation, hollow beam upper layer concrete pouring, core mold dismantling, concrete steam curing, prestressed steel bar releasing and mold stripping:

step one), template manufacturing and installation, which comprises the following steps:

101) the bottom formwork of the formwork is a wood formwork, the side formwork adopts a steel formwork, and reinforcing steel bars are welded on the inner wall of the side formwork at intervals of 1 meter;

102) nailing galvanized iron sheets on the contact surface of the wood pattern and the concrete;

103) in the process of manufacturing the template, the accuracy of the shape, the size and the mutual position of each part of the hollow slab must be strictly ensured;

104) when the bottom die is paved, the battens are paved uniformly and are strictly leveled, and the positions of prestressed tendons are ensured;

105) when the isolating agent is coated on the inner side of the template, the reinforcing steel bars and embedded parts are strictly prohibited from being stained, and the coating is uniform;

106) the positions and the sizes of the exposed dowel bars and the reserved holes need to be accurate and firm in installation;

107) before the inflatable core mold is used, the inflatable core mold needs to be checked, air leakage cannot occur, and the steel wire ends are all bent to the inner side during installation;

108) the inflation pressure needs to be kept stable from the beginning of concrete pouring to the time when the core mold is deflated;

109) when concrete is poured, effective measures are taken to fix the core mould, and a symmetrical balance mode is adopted for pouring;

110) the air release time of the core mould is determined by tests, and the concrete strength meets the requirement;

201) the size of the formed steel bars must meet the design requirements of drawings, and the accuracy of mutual positions and appearance sizes is ensured;

202) the position of the steel bar joint and the joint sectional area accord with the industry regulations, and the butt welded steel bar is sent to a test piece in time;

203) the crossing point of the steel bar is bound firmly by using an iron wire or is welded firmly by spot welding;

204) the lower prestressed steel strand cannot be bound together with the stirrup, and the steel bar framework is hoisted by adopting a hanger;

205) the distance between adjacent steel bars along the length direction is 40-50 cm, and the steel bars are distributed symmetrically left and right;

step three), mounting and tensioning the prestressed tendons, and comprises the following steps:

301) blanking of the prestressed tendons:

firstly, cutting materials by adopting a grinder, wherein the cut prestressed tendons meet the requirements of drawing and tensioning;

secondly, the prestressed tendons are inspected one by one before being installed, and damages such as fracture, bending and the like cannot occur;

thirdly, sleeving two ends of the failure prestressed reinforcement by using hard plastic sleeves, and tightly wrapping two ends of each sleeve;

302) manufacturing a bearing frame and an end beam:

determining the distance between the holes on the end beam, the drilling position and the size of the hole diameter according to the distance between the prestressed steel strands, the thickness of the concrete protective layer and the diameter of the steel strands, wherein the bearing capacity is not less than 400 tons;

303) and (3) verification of the prestress tension equipment:

the prestress tensioning equipment is a through jack with more than 20 tons, a high-pressure oil pump and a pressure gauge, the pressurization needs to be slow and accurate, and then the tensioning force and the corresponding elongation value delta L of the prestress steel strand are calculated;

△L=PL/EA

in the formula: p is the tensile resistance of a single steel strand, and the unit is N; l: the length of the steel strand is unit mm; e: the elastic modulus of the steel strand is in MPa; a is the cross-sectional area of the steel strand in mm²(ii) a Δ L: theoretical elongation in mm;

304) the prestressed steel strand tensioning adopts a pre-tensioning construction process, and the operation process is as follows:

preparation work

B. checking whether the anchorage device is installed correctly;

F. making technical safety bottom crossing before construction;

operation process-

A. Taking the prestressed steel strand as a main stress bar, and adjusting the length of the prestressed bar to ensure that each prestressed bar is stressed uniformly; the tensile design strength is not less than 1260 Mpa;

C. holding the load: tensioning is controlled according to 0-initial stress-1.03 times of tensioning, and after the prestressed tendon is tensioned, the prestressed tendon is held for 3min according to the standard requirement so as to reduce the stress loss of steel wire anchoring;

step eight), performing steam curing on the concrete, wherein during the steam curing, the hollow beam is sealed by a buckle plate and tarpaulin, and the constant-temperature curing time is 12-16 hours;

2. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 1, wherein: and step three), when the length of the prestressed reinforcement is insufficient, the length compensator can be used.

3. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 1, wherein: and in the fourth step) and the sixth step), when the pretensioned member is vibrated by using a vibrating spear during concrete pouring, the prestressed ribs and the internal mold are prevented from being contacted.

4. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 1, wherein: and nine) during prestress tension releasing, cutting the prestressed reinforcement from two ends of the long-line pedestal simultaneously during cutting, and then cutting towards the middle in sequence, wherein the prestress tension releasing is slowly performed.

5. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 1, wherein: the steam curing in the step eight) is divided into 4 stages of standing, temperature rising, constant temperature and temperature reduction; the time of the static stop stage follows the principle of long time and short time, and is not less than 1.5 hours; controlling the temperature rising rate and the temperature reducing rate to be 15-25 ℃ per hour, and specifically determining according to seasons; in the constant temperature stage, the steam temperature is controlled at 80 ℃, the humidity is controlled at 85% -95%, and the constant temperature maintenance time is 12-16 hours.

6. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 2, wherein: the length compensator structurally comprises a first pipe hoop, a second pipe hoop and a connecting plate, wherein the first pipe hoop and the second pipe hoop are arranged along the axis, the distance is 300-600mm, the upper part and the lower part of the first pipe hoop and the second pipe hoop are respectively provided with the connecting plate, the first pipe hoop, the second pipe hoop and the connecting plate are welded into a whole, when the pre-tensioning construction method is adopted, if the length of the prestressed steel strand is insufficient, the length compensator can be connected between two prestressed steel strands, and the prestressed steel strand is connected with the pipe hoop through a single clamping piece anchorage device to compensate the length shortage of the prestressed steel strand.

7. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 1, wherein: and step three), when the broken strand needs to be replaced in the construction of the prestressed steel strand, using the prestressed steel bar loading and unloading device to prop against the end beam of the prestressed force-bearing system through the supporting seat, firstly stretching the prestressed steel strand to enable the clamping piece anchorage device to be loosened, recovering the working state before anchoring, utilizing the operating space generated by the supporting seat, detaching the clamping piece of the anchorage device from the hand hole on the supporting seat, and then releasing the stress, so that the broken strand steel strand can be replaced.

8. The construction method of the pretensioned prestressing concrete hollow simply supported girder according to claim 7, wherein: the prestressed reinforcement loading and unloading device is a through front clamping type jack.