CN112031243B - Arc-shaped roof prestressed reinforcement laying system and construction method thereof - Google Patents
Arc-shaped roof prestressed reinforcement laying system and construction method thereof Download PDFInfo
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- CN112031243B CN112031243B CN202010910235.XA CN202010910235A CN112031243B CN 112031243 B CN112031243 B CN 112031243B CN 202010910235 A CN202010910235 A CN 202010910235A CN 112031243 B CN112031243 B CN 112031243B
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B7/00—Roofs; Roof construction with regard to insulation
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/08—Members specially adapted to be used in prestressed constructions
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/08—Members specially adapted to be used in prestressed constructions
- E04C5/12—Anchoring devices
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04G—SCAFFOLDING; FORMS; SHUTTERING; BUILDING IMPLEMENTS OR AIDS, OR THEIR USE; HANDLING BUILDING MATERIALS ON THE SITE; REPAIRING, BREAKING-UP OR OTHER WORK ON EXISTING BUILDINGS
- E04G21/00—Preparing, conveying, or working-up building materials or building elements in situ; Other devices or measures for constructional work
- E04G21/12—Mounting of reinforcing inserts; Prestressing
- E04G21/121—Construction of stressing jacks
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Abstract
The utility model provides an arc roofing prestressed reinforcement system of laying and construction method thereof, including upper and lower two-layer arc prestressed reinforcement layer, upper arc prestressed reinforcement layer is located upper non-prestressed reinforcement layer below, lower floor arc prestressed reinforcement layer is located lower non-prestressed reinforcement layer top, every layer arc prestressed reinforcement layer all includes that even interval sets up prestressed reinforcement, prestressed reinforcement includes slow bonding prestressed reinforcement, prestressed reinforcement all includes the stretching end, stiff end and the steel strand wires of connection at the stretching end, the stretching end is including the spiral muscle one that sets up in order, little bearing plate, clamping piece anchor and cave mould, the stiff end is including spiral muscle two, haplopore bearing plate and the extrusion anchor that sets up in order. The slow-bonding prestressed steel bars are independently arranged in the arc-shaped roof and effectively bonded with the full-length range of concrete, so that the prestressed steel strands can be flexibly cut off when holes need to be opened due to function change in the use stage, and the slow-bonding prestressed steel bars have obvious technical advantages compared with unbonded and bonded prestressed steel bars.
Description
Technical Field
The invention relates to the field of building construction, and particularly belongs to an arc-shaped roof prestressed reinforcement laying system and a construction method thereof.
Background
The prestressed reinforcement can bring better tensile resistance or compressive resistance when in use, and can effectively reduce temperature cracks caused by large span, thereby being popularized in the building industry. However, most of the existing prestressed reinforcements are unbonded prestressed steel strands, coating layers are made on the basis of the bonded steel strands, the bonded steel strands are not in direct contact with concrete, tensioning is convenient, the bond stress with the concrete is insufficient, loosening is easy to occur during use, the use performance is influenced, the bonded prestressed steel strands are in direct contact with the concrete, no plastic pipe is wrapped outside, the bond stress with the concrete is strong, tensioning is difficult, and the construction requirements are difficult to meet.
Disclosure of Invention
The invention aims to provide an arc-shaped roof prestressed reinforcement laying system and a construction method thereof, and aims to solve the technical problem that the prior art cannot meet construction requirements.
In order to achieve the purpose, the invention adopts the following technical scheme:
the utility model provides an arc roofing prestressing steel lays system which characterized in that: including upper and lower two-layer arc prestressing steel layer, upper arc prestressing steel layer is located upper non-prestressing steel layer below, and lower floor arc prestressing steel layer is located lower non-prestressing steel layer top, and every layer arc prestressing steel layer all sets up prestressing steel including even interval, prestressing steel includes slow bonding prestressing steel and unbonded prestressing steel, prestressing steel all includes stretch-draw end, stiff end and connects the steel strand wires at the stretch-draw end, stretch-draw end including spiral muscle one, little bearing plate, clamping piece anchor and the cave mould that sets up in order, the stiff end is including spiral muscle two, haplopore bearing plate and the extrusion anchor that sets up in order.
Further preferably, the retard-bonded prestressed reinforcement is bonded and fixed with the steel strand by a high-density polyethylene sheath through a polymer retard-bonding agent.
Further, the thickness of the sheath of the high-density polyethylene sheath is 0.8-1.4 mm, and the rib width of the sheathaThe length of the space between the ribs of the sheath is 0.4 to 0.7 times of the height of the ribs of the sheathh1.2mm or more, and the space between the ribs of the sheathl10 to 16 mm.
More preferably, tensioning end tip is equipped with the tensioning tool, the tensioning tool is including the clamping piece stopper, the clamping piece cushion, the punching jack and the work ground tackle that set up in order.
A construction method of an arc-shaped roof prestressed reinforcement laying system is characterized by comprising the following steps:
step one, prestressed reinforcement penetration: the prestressed reinforcement penetrates one by one after the steel bar support is basically fixed, if the penetration is difficult, a tractor can be installed, and concrete is poured after the penetration is finished;
step two: theoretical elongation value delta L of prestressed reinforcementtAnd (3) calculating:
in the formula (I), the compound is shown in the specification,F j -prestressing steel bar stretching end stretching force;A P -a pre-stressed reinforcement cross-sectional area;E P -a pre-stressed reinforcement modulus of elasticity;k -local deviation friction influence coefficient of pore canals of each meter;μ-the coefficient of friction between the prestressed reinforcement and the wall of the porthole;θ-total angle of intersection of the tangent to the curvilinear duct portion at the anchoring end from the tensile end;
step three, tensioning prestressed reinforcements: and when the strength of the prestressed concrete reaches over 75 percent under the same condition, tensioning the steel strand at the tensioning end by a tensioning tool, wherein the tensioning control stress is 0.75 time of the standard value fptk of the prestressed reinforcement strength, and the actually measured elongation value is controlled to be (1 +/-6%) times of the theoretical elongation value.
Further, the diameter of the steel strand of the slow bonding prestressed reinforcement in the second step is 15.2mm, k = 0.004-0.012, and μ = 0.004-0.12; the diameter of the steel strand of the unbonded prestressed reinforcement is 15.2mm, k =0.004, and mu = 0.09.
In addition, the step three of prestressed reinforcement tensioning specifically comprises the following steps:
More preferably, the standard value of the strength of the prestressed reinforcement in step three is fptk =1860 Mpa.
Compared with the prior art, the invention has the following characteristics and beneficial effects:
compared with the unbonded prestressed steel, the slow-bonding prestressed steel reduces two complex procedures of corrugated pipe embedding and grouting, greatly improves the construction convenience, has the same friction coefficient as the unbonded prestressed steel, has smaller prestress loss than the bonded prestressed steel, has the same earthquake resistance as the bonded prestressed steel, has the fatigue and the durability superior to the bonded prestressed steel, is more suitable for the fields of railways, highways and the like, is suitable for engineering with long design life, has the crack resistance superior to the unbonded prestressed steel and the bonded prestressed steel, can reduce the weakening of the section of a component, does not need to increase the field grouting procedure, does not need to maintain or stop in winter, and is particularly suitable for continuous construction operation in cold areas in winter;
the slow-bonding prestressed steel bars are independently arranged in the arc-shaped roof and effectively bonded with the full-length range of concrete, so that the prestressed steel strands can be flexibly cut off when holes need to be formed due to function change in the use stage, no obstacle and no danger exist for adjacent structures and construction operation, and the slow-bonding prestressed steel bars have obvious technical advantages compared with unbonded and bonded prestressed steel bars.
Drawings
FIG. 1 is a schematic view of the installation of prestressed reinforcement for arc-shaped roof according to the present invention;
fig. 2 is a schematic representation of the positional relationship of the prestressed reinforcement layers and the non-prestressed reinforcement layers to which the present invention relates in fig. 1;
FIG. 3 is a schematic structural view of a prestressed reinforcement tensioning end according to the present invention;
fig. 4 is a schematic structural view of a prestressed reinforcement fixing end according to the present invention;
FIG. 5 is a schematic view of a tensioning tool according to the present invention;
FIG. 6 is a longitudinal cross-sectional view of a retarded adhesive prestressed reinforcement according to the present invention;
fig. 7 is a cross sectional view of a retarded adhesive prestressed reinforcement according to the present invention.
Reference numerals: 1-an upper arc-shaped prestressed reinforcement layer; 2-lower arc prestressed reinforcement layer; 3-steel strand wires; 4-spiral rib I; 5-small bearing plate; 6-clip anchor; 7-hole molding; 8-spiral rib II; 9-a single-hole bearing plate; 10-extruding an anchor; 11-a clip retainer; 12-a clip pad block; 13-a feed-through jack; 14-a working anchor; 15-high density polyethylene sheath; 16-a polymer retarding adhesive; 17-an upper non-prestressed reinforcement layer; 18-lower non-prestressed reinforcement layer; a-sheath rib width;h-the sheath is high in rib height;l-sheath rib spacing; a-sheath rib width;h-the sheath is high in rib height;l-sheath rib spacing.
Detailed Description
In order to make the technical means, innovative features, objectives and functions realized by the present invention easy to understand, the present invention is further described below.
The examples described herein are specific embodiments of the present invention, are intended to be illustrative and exemplary in nature, and are not to be construed as limiting the scope of the invention. In addition to the embodiments described herein, those skilled in the art will be able to employ other technical solutions which are obvious based on the disclosure of the claims and the specification of the present application, and these technical solutions include technical solutions which make any obvious replacement or modification for the embodiments described herein.
The utility model provides an arc roofing prestressed reinforcement system of laying, as shown in fig. 1 and 2, including upper and lower two-layer arc prestressed reinforcement layer, upper arc prestressed reinforcement layer 1 is located upper non-prestressed reinforcement layer 17 below, lower floor's arc prestressed reinforcement layer 2 is located lower floor's non-prestressed reinforcement layer 18 top, every layer of arc prestressed reinforcement layer all sets up the prestressed reinforcement including even interval, the prestressed reinforcement includes slowly bonding prestressed reinforcement and unbonded prestressed reinforcement, the prestressed reinforcement all includes the stretch-draw end, stiff end and the steel strand wires 3 of connection at the stretch-draw end, as shown in fig. 3, the stretch-draw end is including the spiral muscle one 4 that sets up in order, little bearing plate 5, clip anchor 6 and cave mould 7, as shown in fig. 4, the stiff end is including the spiral muscle two 8 that set up in order, haplopore bearing plate 9 and extrusion anchor 10.
The retarded adhesive prestressed reinforcement is fixedly bonded with the steel strand 3 through a high-density polyethylene sheath 15 and a high-molecular retarding adhesive 16. The delayed bonding prestressed steel bars do not need to be provided with armpits and reserved for stretching and forming holes during construction, so that the cost of the delayed bonding prestressed steel bars is saved, two processes of corrugated pipe penetrating and grouting are reduced, the construction period is halved, the consumption of people, machines and materials is reduced, the cost is saved, the delayed bonding prestressed steel bars are dispersedly arranged, the stretching can be performed when the local pressure-bearing requirement is low and the concrete strength reaches over 75 percent, the construction period is saved, the cost is saved, the construction period is saved, the turnover rate of templates is improved, the cost is saved, the delayed bonding prestressed steel bars are independently arranged in the arc-shaped roof and effectively bonded with the full length range of concrete, when holes are required to be formed due to function change in the use stage, the prestressed steel strands can be flexibly cut, no obstacle and no danger are caused to adjacent structures and construction operation, and the delayed bonding prestressed steel bars have obvious technical advantages compared with unbonded prestressed steel bars and bonded prestressed steel bars.
As shown in figures 6 and 7, the sheath thickness of the high-density polyethylene sheath 15 of the slow bonding prestressed reinforcement is 0.8-1.4 mm, the sheath rib width a is (0.4-0.7) times of the sheath rib spacing length, the sheath rib height h is more than or equal to 1.2mm, and the sheath rib spacing l is 10-16 mm.
As shown in fig. 5, the tensioning tool includes a clip stopper 11, a clip cushion block 12, a feed-through jack 13 and a working anchor 14, which are sequentially arranged.
A construction method of an arc-shaped roof prestressed reinforcement laying system is characterized by comprising the following steps:
step one, prestressed reinforcement penetration: the prestressed reinforcement penetrates one by one after the steel bar support is basically fixed, if the penetration is difficult, a tractor can be installed, and concrete is poured after the penetration is finished;
step two: theoretical elongation value delta L of prestressed reinforcementtAnd (3) calculating:
in the formula (I), the compound is shown in the specification,F j -prestressing steel bar stretching end stretching force;A P -a pre-stressed reinforcement cross-sectional area;E P -a pre-stressed reinforcement modulus of elasticity;k -local deviation friction influence coefficient of pore canals of each meter;μ-the coefficient of friction between the prestressed reinforcement and the wall of the porthole;θ-total angle of intersection of the tangent to the curvilinear duct portion at the anchoring end from the tensile end;
the diameter of the steel strand of the slow-bonding prestressed reinforcement is 15.2mm, k = 0.004-0.012, mu = 0.004-0.12; the diameter of the steel strand of the unbonded prestressed reinforcement is 15.2mm, k =0.004, and mu = 0.09.
Step three, tensioning prestressed reinforcements: when the strength of the prestressed concrete reaches over 75 percent under the same condition, tensioning the steel strand 3 at the tensioning end by a tensioning tool, wherein the tensioning control stress is 0.75 time of the standard value fptk of the prestressed reinforcement strength, the standard value fptk of the prestressed reinforcement strength adopted by the invention is =1860 Mpa, namely the tensioning control stress is sigma con =0.75fptk =1395Mpa, the actually measured elongation is controlled to be (1 +/-6 percent) times of the theoretical elongation, and the tensioning of the prestressed reinforcement specifically comprises the following steps:
Prestressing force stretch-draw and attention points
1) Formwork installation and removal
The prestressed reinforcement side formworks and the non-prestressed reinforcement formworks are dismantled before prestressed reinforcement tensioning.
2) Prestressed reinforcement blanking
The blanking length of the prestressed reinforcement is the actual length of the pore channel plus the stretching working length.
Actual length of the channel: theoretical calculation is carried out in advance, a steel strand blanking statistical table of each layer is compiled, and the actual length of the pore passage is spot checked and checked on site.
Working length: the tensioning end should take the required length of the working anchor, the jack and the tool anchor into consideration and leave a proper margin.
And secondly, cutting the steel strand by using a grinding wheel cutting machine, and strictly forbidding fusing of electric arc welding.
Thirdly, the embedded fixed end adopts an extrusion anchor and operates conventionally.
4) Prestressed reinforcement penetration bundle
Firstly, the prestressed reinforcement is threaded one by one after the steel bar support is basically fixed, and if the prestressed reinforcement is difficult to thread, a tractor can be installed.
And secondly, checking the prestressed reinforcement after the penetration, and avoiding the penetration error.
And thirdly, the steel strands at the tensioning end are parallel and level and meet the working length required by tensioning.
5) Pouring concrete
Arranging a specially-assigned person to be on duty when pouring the concrete; the vibration force of the tensioning end position needs to be enhanced, and the compactness of concrete pouring of the tensioning end is ensured; during pouring, the vibrating rod needs to avoid the prestressed reinforcement, so that the prestressed vibrating deflection is avoided. The engineering concrete pouring adopts the sun water curing.
6) Requirement for tensioning
The strength grade of the engineering prestressed concrete is C35; the strength of the prestressed concrete reaches more than 90% of that of the test block under the same condition; when concrete is poured, a group of standard curing test blocks is reserved on each 100 sides, 3 groups of test blocks with the same conditions are reserved in each pouring unit, and tensioning can be carried out when the test blocks with the same conditions reach 90%; the tension control stress is σ con =0.75fptk =1395 MPa. The tension working life of the slow bonding prestressed reinforcement is 180 days, and the curing period is 540 days. The tensioning working life is 180 days under the condition that the room temperature is kept at 20-35 ℃. The construction stage of the project belongs to summer with proper temperature and little influence on the standard working life.
7) Preparation for stretching
Before tensioning, firstly cleaning tensioning, taking out the tensioning end cavity die, cleaning the tensioning groove, peeling the tensioning end steel strand, and then installing the anchorage device. The tensioning equipment adopts a 25t through jack. The anchorage device adopts a 15-1 single-hole anchorage device, the tensioning equipment needs to be calibrated before tensioning, the anchorage device is retested, and tensioning can be carried out after the retesting is qualified. Calculating the reading of the oil meter according to a regression equation calibrated by equipment; and calculating a theoretical elongation value according to the elastic modulus measured by the steel strand mechanical property experiment.
And (3) observing cracks of local pressure-bearing concrete at the tensioning end in tensioning, if the cracks of the concrete are more, stopping tensioning in time, withdrawing anchors and releasing tension, and completely removing the concrete at the pressure-bearing part and pouring again to reach the strength and then tensioning.
The method comprises the steps of measuring the length L1 of the prestressed steel bar between the tail end of the prestressed steel bar and the small bearing iron plate under a load-holding state, and measuring the length L2 of the prestressed steel bar between the tail end of the prestressed steel bar and the small bearing iron plate again after the jack returns oil; the difference between L1 and L2 is the retraction amount of the anchorage, the main influence factor of the retraction length is the notch depth of the limiting device, the retraction amount is usually not more than 5mm, and the displacement of the column top and the inverted arch value of the beam need to be measured before and after tensioning.
8) Tension control
The engineering tension control stress is 0.75fptk =1395 MPa; and (3) performing detailed bottom crossing on the tensioning team before tensioning, and performing bottom crossing on a tensioning method, tensioning control stress, tensioning oil meter reading, a tensioning theoretical elongation value and a tensioning elongation value measuring method. The tensioning time is divided into two conditions; the tension method for the prestressed steel bar with the elongation value less than 180mm is different from the tension method for the prestressed steel bar with the elongation value more than 180mm in that the length of the inner cylinder of the jack is not easy to be more than 185mm, so that the prestressed steel bar with the elongation value more than 180mm needs to be tensioned twice.
a. The first prestressed reinforcement with the elongation value less than 180mm adopts one-time tensioning, and the tensioning steps are as follows: controlling the tension force by 0 → 1.0 σ con → holding load 1min → relieving pressure → measuring the elongation → recording;
b. the second prestressed reinforcement with the elongation value larger than 180mm adopts a two-time tensioning method, and the tensioning steps are as follows: the tension force is controlled by 0 → the jack is stretched (less than 185 mm) and returns to the top; then, a second time of tension force control is performed as 0 → 1.0 σ con → hold load 1min → pressure relief → measurement of elongation → recording.
The relative allowable deviation between the measured elongation and the theoretical elongation is ± 6%. If the stretching is stopped immediately when the stretching is beyond the range, the stretching can be continued after the reason is found.
9) Cutting and sealing anchor
Observing the situation that the clamping piece does not retract after the steel strand is stretched for 12 hours, cutting off the steel strand subjected to stretching operation by using a handheld abrasive wheel cutting machine, wherein the exposed length of the cut steel strand is not less than 30 mm; and after the cutting is finished, performing anticorrosive treatment on the anchorage device and the exposed steel strand, and after the chiseling treatment is finished, sealing the anchorage by using micro-expansion fine aggregate concrete with the same label.
In the construction process of the prestressed reinforcement, in order to prevent slurry leakage, the two ends of the steel strand are bound by waterproof adhesive tapes, and the gaps of the clamping pieces are uniformly coated by anticorrosive paint after prestressed tensioning and cutting.
And after tensioning is finished, slowly bonding the prestressed reinforcement, entering a curing stage, forbidding construction and stacking in the curing period, and detaching the beam bottom support 48 hours after tensioning is finished.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (1)
1. A construction method of an arc-shaped roof prestressed reinforcement laying system is characterized in that,
arc roofing prestressing steel lays system: including upper and lower two-layer arc prestressed reinforcement layer, upper arc prestressed reinforcement layer (1) is located upper non-prestressed reinforcement layer (17) below, and lower floor arc prestressed reinforcement layer (2) are located lower non-prestressed reinforcement layer (18) top, and every layer arc prestressed reinforcement layer all sets up the prestressed reinforcement including even interval, the prestressed reinforcement includes slowly bonding prestressed reinforcement and unbonded prestressed reinforcement, the prestressed reinforcement all includes stretch-draw end, stiff end and connects at steel strand wires (3) of stretching the end, stretch-draw end including spiral muscle one (4) that set up in order, little bearing plate (5), clamping piece anchor (6) and cave mould (7), the stiff end is including spiral muscle two (8), haplopore bearing plate (9) and the crowded die that set up in order, the stiff end is including spiral muscle two (8), haplopore bearing plate (9) and crowded pressing die (7) that set up in orderThe slow-bonding prestressed reinforcement is fixedly bonded with the steel strand (3) through a high-molecular slow-bonding adhesive (16) by a high-density polyethylene sheath (15), the thickness of the sheath of the high-density polyethylene sheath (15) is 0.8-1.4 mm, and the rib width of the sheath is (1)a) A length of a space between the ribs of the sheath of 0.4 to 0.7 times and a height of the ribs of the sheath: (h) 1.2mm or more, and the distance between ribs of the sheath: (l) 10-16 mm; a tensioning tool is arranged at the end part of the tensioning end, and comprises a clamping piece limiter (11), a clamping piece cushion block (12), a feed-through jack (13) and a working anchor (14) which are sequentially arranged;
the construction method comprises the following steps:
step one, prestressed reinforcement penetration: the prestressed reinforcement penetrates one by one after the steel bar support is basically fixed, if the penetration is difficult, a tractor can be installed, and concrete is poured after the penetration is finished;
step two: theoretical elongation value delta L of prestressed reinforcementTAnd (3) calculating:
in the formula (I), the compound is shown in the specification,F j -prestressing steel bar stretching end stretching force;A P -a pre-stressed reinforcement cross-sectional area;E P -a pre-stressed reinforcement modulus of elasticity;k -local deviation friction influence coefficient of pore canals of each meter;μ-the coefficient of friction between the prestressed reinforcement and the wall of the porthole;θ-total angle of intersection of the tangent to the curvilinear duct portion at the anchoring end from the tensile end; in the second step, the diameter of the steel strand of the slow bonding prestressed reinforcement is 15.2mm, k = 0.004-0.012, and μ = 0.004-0.12; the diameter of the steel strand of the unbonded prestressed reinforcement is 15.2mm, k =0.004, mu = 0.09;
step three, tensioning prestressed reinforcements: the strength of the prestressed concrete reaches more than 90% of that of the test block under the same condition; when concrete is poured, a group of standard maintenance test blocks is reserved on every 100 sides, 3 groups of test blocks with the same conditions are reserved in each pouring unit, tensioning can be carried out when the test blocks with the same conditions reach 90%, a steel strand (3) at a tensioning end is tensioned through a tensioning tool, the tensioning control stress is 0.75 time of the standard value fptk of the strength of the prestressed reinforcement, and the actually measured elongation value is controlled to be (1 +/-6%) times of the theoretical elongation value; the standard value of the strength of the prestressed reinforcement fptk =1860 Mpa; the prestressed reinforcement tensioning method specifically comprises the following steps:
step 1, tensioning a piece of equipment: before tensioning, firstly cleaning a tensioning end, taking out a cavity die (7) of the tensioning end, cleaning a tensioning groove, peeling a steel strand at the tensioning end, then installing a tensioning tool, adopting a 25t penetrating jack for a penetrating jack (13), adopting a 15-1 single-hole anchor for a working anchor (14), retesting the anchor before tensioning, and tensioning after the retesting is qualified;
step 2, tensioning prestressed reinforcements: when the prestressed reinforcement with the actually measured elongation value smaller than 180mm is tensioned, one-time tensioning is adopted, the tensioning force is controlled from 0 to 1.0 sigma con, then the load is kept for 1min, and the elongation is measured and recorded after pressure relief; when the prestressed reinforcement which is actually larger than 180mm is tensioned, tensioning is divided into two times, the tensioning force is controlled from 0 to the jack extension smaller than 185mm, and then oil returns to the jack for jacking; and then, carrying out second tensioning tension control from 0 to 1.0 sigma con, then holding for 1min, and measuring and recording the elongation after pressure relief.
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