CN115199048A

CN115199048A - Large-span prestressed beam invagination type one-time tensioning process

Info

Publication number: CN115199048A
Application number: CN202210862874.2A
Authority: CN
Inventors: 陈冬泉; 江斌
Original assignee: Zhongyifeng Construction Group Co Ltd
Current assignee: Zhongyifeng Construction Group Co Ltd
Priority date: 2022-07-21
Filing date: 2022-07-21
Publication date: 2022-10-18

Abstract

The invention discloses a large-span prestressed beam invagination type one-time tensioning process, which belongs to the field of prestressed beams and comprises the steps of prestressed beam construction; pouring concrete in the prestressed girder; after the concrete is condensed, the beam side template is disassembled; tensioning the prestressed reinforcement; dismantling the prestressed beam template and cutting the exposed steel strand; grouting, and sealing the end part of the prestressed beam, so that good crack resistance and deformation resistance can be realized, the durability is high, the size of the section of the structure can be effectively reduced, the height of the structure is reduced, the using space is improved, the structural design is more economic, light and attractive, materials are saved, and the engineering cost is reduced.

Description

Large-span prestressed beam invagination type one-time tensioning process

Technical Field

The invention relates to the field of prestressed beams, in particular to an invagination type one-time tensioning process for a large-span prestressed beam.

Background

The large-span prestressed reinforced concrete frame structure can utilize the combined action of the high-strength steel strands and the high-strength concrete, reduce the section size of the structural member, lighten the self weight of the structure, increase the bearing capacity of the structure, effectively overcome and control the generation of cracks of the concrete member, and is widely applied to building structures. Although the prestressed concrete process is mature, the links such as prestressed tendon laying, grouting, concrete pouring, tensioning, anchorage plugging and the like must be considered in the design and construction of a prestressed structure because the using function of a building needs to be complex and changeable with the vertical surface of the building, and the process requirement is higher.

The traditional method is to bury corrugated pipes in a beam in advance, manufacture prestressed tendons and penetrate the prestressed tendons into a pore channel, then pour concrete and carry out maintenance, stretch the prestressed tendons after the concrete reaches the strength required by the design, anchor the prestressed tendons by using an anchorage device, and finally carry out pore channel grouting and anchor sealing.

Disclosure of Invention

1. Technical problem to be solved

Aiming at the problems in the prior art, the invention aims to provide an invagination type one-step tensioning process for a large-span prestressed beam, which adopts a construction process with a bonded prestressed structure, has good anti-cracking performance and anti-deformation capability and high durability, can effectively reduce the size of the section of the structure, reduce the height of the structure, improve the use space, enable the structure to be more economic, light and beautiful, save materials and reduce the engineering cost.

2. Technical scheme

In order to solve the above problems, the present invention adopts the following technical solutions.

The large-span prestressed beam invagination type one-step tension process comprises prestressed beam construction;

pouring concrete in the prestressed beam;

after the concrete is condensed, disassembling the beam side template;

tensioning the prestressed reinforcement;

dismantling the prestressed beam template and cutting the exposed steel strand;

grouting and sealing the end part of the prestressed beam.

Further, the prestressed beam construction includes:

laying a beam bottom template;

binding reinforcing steel bars in the beam bottom template, wherein the reinforcing steel bars comprise prestressed reinforcing steel bars and non-prestressed reinforcing steel bars;

marking the curve coordinates of the prestressed reinforcement;

welding the prestressed reinforcement bracket;

arranging corrugated pipes along the prestressed reinforcement support;

penetrating a steel strand in the corrugated pipe;

installing an anchor backing plate, welding and fixing the anchor backing plate and non-prestressed reinforcement, and arranging a spiral reinforcement behind the anchor backing plate;

and beam side templates are arranged on two sides of the beam bottom template to form a prestressed beam.

Further, the steel bar binding in the beam bottom template comprises:

marking the center elevation of the prestressed reinforcement according to the curve coordinate of the prestressed reinforcement;

the top surface of the beam bottom template is in contact with the ground of the corrugated pipe, so that the prestressed reinforcement cannot displace when concrete is poured.

Further, the discharging corrugated tube along the prestressed reinforced steel bracket comprises:

the corrugated pipes are connected in a screwing manner, the joints of the corrugated pipes are wrapped by sealing adhesive tapes, and the length of each corrugated pipe is not less than 200mm;

the tail end of the corrugated pipe is vertically arranged with the anchor backing plate.

Further, the steel strand penetrating in the corrugated pipe comprises:

the strand pulling device is adopted to pull the steel strand into the corrugated pipe, and when the steel strand is blocked, the steel strand is pulled forwards in a rotating mode to be pulled into the corrugated pipe continuously, and the corrugated pipe is guaranteed not to move;

and wrapping the steel strand positioned outside the corrugated pipe.

Further, the method also comprises the following steps:

arranging a grouting hole at the fixed end of the prestressed beam;

the grouting hole comprises a water seepage pipe, a hole is formed in the upper portion of the corrugated pipe, the water seepage pipe extends into the corrugated pipe through the hole, and a sealing adhesive tape is arranged at the joint of the corrugated pipe and the water seepage pipe.

Further, the pouring concrete in the prestressed girder includes:

the concrete is poured in a pouring and tamping mode, and the corrugated pipe is prevented from being directly impacted in the pouring process, so that the safety of the corrugated pipe is ensured;

curing the poured and mashed concrete to avoid cracks of the concrete;

and (5) keeping the construction test block, and curing in the same way as the concrete.

Further, the tensioning the prestressed reinforcement includes:

cleaning one end of a prestressed beam;

installing a tensioning device, connecting the tensioning device with one end of the prestressed beam, and enabling an action line of the tensioning device to coincide with a tangent line of the tail end of the prestressed tendon;

in the tensioning process, the deviation between the actual elongation value and the predicted elongation value of the prestressed reinforcement is within 6 percent, and the retraction amount of an anchorage device of the tensioning equipment is set to be less than or equal to 6-8 mm.

3. Advantageous effects

Compared with the prior art, the invention has the advantages that:

(1) According to the scheme, the position of the corrugated pipe is fixed by adopting a steel grid according to a tendon beam rise diagram; a reserved hole of the floor is used for tensioning; the elevation ratio of the boundary beam is adjusted to facilitate the effect of the outer vertical surface; the sizes of the haunches and the rise are adjusted to ensure that the prestressed tendons are more reasonably arranged; the sunken end is adopted for plugging and one-time tensioning construction, so that the effect of the outer vertical surface is better, and the construction progress is accelerated; the outer decoration structure on one side of the plugging end is constructed after tensioning is completed and plugging is finished, so that the construction process is optimized, and the construction difficulty is reduced; the grouting material is adopted to replace the traditional cement grouting liquid; setting a grout inlet valve and a grout outlet valve, circularly grouting by adopting a piston type grouting pump, and adopting a primary grouting process; because the construction process is improved, the treatment of key parts is enhanced, and the defects of the traditional process are effectively avoided.

(2) Reserving a hole channel in a large-span concrete structure in advance, manufacturing a prestressed tendon, penetrating the prestressed tendon into the hole channel, pouring concrete, curing, stretching the prestressed tendon after the concrete reaches the strength required by the design, anchoring by using an anchorage device, and finally grouting and sealing the hole channel. The tensile stress of the concrete caused by the load is reduced or offset by applying compressive stress in the structure in advance, so that the tensile stress of the structural member is controlled in a small range and even in a compressed state, the occurrence and the development of concrete cracks are delayed, and the crack resistance and the rigidity of the member are improved. The construction method meets the use requirements of people on the buildings with large-span spaces, and has the advantages of low construction cost, high construction speed and safe and reliable quality.

Drawings

FIG. 1 is a schematic view of a connection structure of a corrugated pipe according to the present invention;

fig. 2 is a schematic view of a connection structure of the bellows and the intake pipe 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 accompanying drawings in the embodiments of the present invention; it is to be understood that the embodiments described are merely exemplary embodiments, rather than exemplary embodiments, and that all other embodiments may be devised by those skilled in the art without departing from the scope of the present invention.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top/bottom", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplification of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "disposed," "sleeved/connected," "connected," and the like are to be construed broadly, e.g., "connected," which may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Referring to fig. 1-2, the process of once tensioning by sinking the large-span prestressed beam comprises the steps of constructing the prestressed beam;

pouring concrete in the prestressed beam;

after the concrete is condensed, disassembling the beam side template;

tensioning the prestressed reinforcement;

dismantling the prestressed beam template and cutting the exposed steel strand;

grouting and sealing the end part of the prestressed beam.

The drawing deepening design mainly comprises the steps of prestressed beam plane arrangement, prestressed tendon beam-shaped rise diagrams, stretching end plane arrangement diagrams, stretching hole reserved positions and haunches, boundary beam elevation, haunches and rise size adjustment, and construction after stretching and plugging of a structural decorative structure on one side of a stretching end.

(1) The elevation of the edge beam is changed from 4.600 to 4.750, the haunching height is changed to 600 and is flush with the beam bottom, and the installation of a window is not influenced;

(2) the elevation of the boundary beam is 4.750, the haunching height is modified to 750, and the boundary beam is level to the bottom of the beam, so that the installation of the window is not influenced. The rise is modified from 500 to 350;

(3) local haunching tensioning end structure needs to be made later, otherwise, the tensioning operation space is insufficient.

The prestressed tendon is blanked in a flat field, the prestressed tendon can be paid off by a pay-off reel frame, the prestressed tendon can also be paid off by a manual circle by circle, and measures are taken to prevent the prestressed tendon from popping out to hurt people during paying off.

The blanking length is divided into two parts: the length of the embedded concrete can be lofted or determined by calculation; the working length of the two ends is determined by the type of the jack and an anchoring system. The blanking is cut mechanically by a grinder, electric arc or gas cutting is not needed, and the notch is vertical to the steel strand. After blanking and cutting, labels are timely attached to the steel strands to mark the lengths, the numbers and the use positions of the steel strands. Then the materials are bundled and coiled into a plate, the diameter of the plate is not less than 2m, the plate is conveyed to a lower cushion upper cover on a construction site, and classification and stacking are proper.

Further, the prestressed beam construction comprises:

laying a beam bottom template;

marking the curve coordinates of the prestressed reinforcement; according to the elevation of the center of the prestressed tendon in the design drawing, the beam takes the bottom surface of the corrugated pipe as the standard, and a control point support tendon (phi 6-10) is welded on the stirrup, so that the shape of the prestressed tendon meets the design requirement and the prestressed tendon does not displace when concrete is poured.

Welding the prestressed reinforcement support;

arranging corrugated pipes along the prestressed reinforcement support;

the corrugated pipe is laid along the support rib. The corrugated pipe connection adopts the corrugated pipes with the same type and the same specification which are connected in a screwing way, the length is not less than 200mm, the joint is sealed by an adhesive tape to prevent slurry leakage (as shown in figure 1), and then the corrugated pipe and the support rib are bound together by lead wires to be firmly fixed.

Penetrating a steel strand in the corrugated pipe;

(1) The manual single-wire penetration method is adopted, a bullet-shaped penetration device is sleeved at the end part of the steel strand, and the steel strand can be penetrated and rotated while encountering a resistance without being drawn back and forth. After threading, whether the working length meets the requirements or not should be checked. The exposed steel strand is wrapped and protected by a plastic paper bag to prevent pollution.

(2) The various pipelines laid should not alter the position of the corrugated pipe.

(3) The exposed length of the prestressed tendon should be reserved with enough tension working length, and the end of the corrugated pipe should be perpendicular to the anchor backing plate.

(4) The steel strand does not allow electric welding, energization, lightning protection lap joint and the like.

Installing an anchor backing plate, fixedly welding the anchor backing plate with non-prestressed reinforcement, and arranging a spiral reinforcement behind the anchor backing plate;

when the anchor backing plate is installed, it is positioned according to the construction drawing size, and is fixed by short steel bar erection and non-prestressed reinforcement by electric welding, and after the spiral reinforcement is tightly attached to the anchor backing plate, it is fixed with backing plate and other non-prestressed reinforcements.

And beam side formworks are arranged on two sides of the beam bottom formwork to form the prestressed beam.

Further, the binding of reinforcing steel bars in the beam bottom formwork comprises:

Further, the discharging corrugated tube along the prestressed reinforcement bracket includes:

the corrugated pipes are connected in a screwing mode, sealing adhesive tapes wrap joints of the corrugated pipes, and the length of each corrugated pipe is not less than 200mm;

Further, the passing of the steel strand in the corrugated pipe comprises:

and wrapping the steel strand positioned outside the corrugated pipe.

Further, the method also comprises the following steps:

arranging a grouting hole at the fixed end of the prestressed beam;

the grouting hole comprises a water seepage pipe, a chisel hole is formed in the upper portion of the corrugated pipe, the water seepage pipe extends into the corrugated pipe through the chisel hole, and a sealing adhesive tape is arranged at the joint of the corrugated pipe and the water seepage pipe.

The single span beam is provided with grouting (bleeding) holes in the span and the support. A grouting (bleeding) hole is additionally arranged near the fixed end of the prestressed beam with one end stretched. When the drainage pipe is installed, a hole is punched at the upper part of the corrugated pipe and led out of the beam surface by using a plastic pipe, and the position where the plastic pipe is connected with the corrugated pipe is wrapped by using an adhesive tape.

Further, the pouring concrete in the prestressed girder comprises:

curing the concrete after the pouring and tamping are finished so as to avoid cracks of the concrete;

and (5) keeping the construction test block, and curing in the same manner as the concrete.

(1) Inspection before casting

The prestressed tendons should be checked before concrete pouring, and the key point of the check is whether the corrugated pipe is damaged or not; whether the line type position is correct; whether the tension end is properly installed or not; whether the exposed length of the tensioning end is enough. The quality of pipe laying and beam penetrating is the key of prestress construction, and the condition that slurry does not leak in a pore channel is the basis for meeting the designed prestress value is ensured. And recording for filing after inspection, and correcting before concrete pouring.

Because a plurality of subsequent processes are carried out after the laying, the positions of the anchor backing plates, the damage of the corrugated pipes and other conditions are checked before the concrete is poured, and if the conditions occur, the concrete can be poured after the adjustment and repair are carried out in time.

(2) Concrete pouring and tamping

When concrete is poured, a vibrator needs to prevent a vibrating rod from directly impacting the corrugated pipe so as to prevent the corrugated pipe from being damaged by vibration and causing slurry leakage, and in case of slurry leakage in the corrugated pipe, the tensioning and grouting of the prestressed tendons can be adversely affected. Concrete must be compacted by vibration, and especially attention should be paid to reinforcing steel bar dense areas and tensioning ends.

(3) Concrete curing

After concrete is pounded, the concrete should be maintained to be fully wet, so as to prevent the surface from generating cracks due to premature evaporation of water. Besides standard maintenance test blocks required in completion data, construction test blocks are also kept in the pouring process, and the construction test blocks and the members are maintained under the same conditions to determine the tensioning time.

Further, the tensioning the prestressed reinforcement includes:

cleaning one end of a prestressed beam;

in the tensioning process, the deviation between the actual elongation value and the predicted elongation value of the prestressed reinforcement is within 6%, and the retraction amount of an anchorage device of the tensioning equipment is set to be less than or equal to 6-8 mm.

(1) Tensioning equipment preparation

The stretching equipment comprises an oil pump, a jack, a matched limiter, an angle converter and the like.

Before tensioning, an oil meter and a jack are calibrated in a matched manner, the calibration validity period is half a year, the calibration state is consistent with the working state, the diameter of a pressure gauge is not less than 150mm, and the precision is not less than 1.5 grade; the precision of the tester or dynamometer for calibrating the tensioning device must not be lower than 2%.

(2) Stretch-draw end cleaning

After pouring concrete for a certain time, the concrete reaches the strength capable of detaching the end mould, the tensioning end part template is firstly detached, people are sent to clear the end part, and plastic sleeves outside the anchor backing plate are stripped off for the unbonded prestressed tendons.

Checking whether the tensioning end meets the requirements, whether concrete at the contact part of the anchor backing plate and the anchor ring is cleaned up, and the like one by one, checking the quality of the concrete after the anchor backing plate, and repairing before tensioning if a cavity phenomenon exists, and installing an anchorage device.

(3) Tensioning sequence

The prestressed beams in the same area must be tensioned from top to bottom according to the principle of symmetry, and for the prestressed bars tensioned at two ends, a method of tensioning one end and complementing the other end can be adopted.

(4) Tensioning procedure

0 → 0.2con (initial value) → 20MPa (if necessary, inverting the cylinder) → 1.0con (final value, hold load for 1 minute, anchor)

(5) The key points of the operation

(1) Before the anchorage device is installed before tensioning, the embedded part at the end part must be cleaned, the anchorage plate is installed firstly, and then the clamping pieces are installed hole by hole;

(2) when the tensioning equipment is installed, the action line of the tensioning force of the jack is coincided with the tangent line of the tail end of the prestressed tendon;

(3) during tensioning, the oil inlet speed is strictly controlled, and the oil return is stable;

(4) in the tensioning process, the elongation of the prestressed tendon should be carefully measured and well recorded;

(5) the difference between the actually measured elongation value and the calculated elongation value is in the range of-6% to +6%, otherwise, the tensioning is stopped, and the tensioning can be continued after the reason is checked and corresponding measures are taken;

(6) during tensioning, a limiting method is adopted to control the retraction amount of the anchorage device, and lambda is less than or equal to 6-8 mm;

(7) after tensioning is finished and before pore grouting, the anchorage device needs to be subjected to mortar plugging so as to facilitate grouting;

(6) Checking calculation in tension stage

The diameter of the 12-hole anchor used is 173mm, the thickness of the backing plate is 30mm, and after the 12-hole anchor is spread at 45 degrees, the diameter of the pressed area is increased to 173+2 multiplied by 30=233mm.

F _l ＝1.2A _p σ _con ＝1.2×140×1302×12＝2624832N

A _l ＝π×116.5 ² ＝42617mm ²

A _b ＝π×349.5 ² ＝383552mm ²

A _ln ＝42617-π×45 ² ＝36258.5mm ²

1.35β _c β _l f _c ′A _ln ＝1.35×1.0×3×19.1×36258.5＝2804775N>F _l ＝2624832N

(satisfy the requirements)

(7) Local compression bearing capacity checking calculation

HRB 400-grade spiral reinforcing steel bars are arranged under the anchor backing plate, and the diameter of each reinforcing steel bar is phi 16 and 6 circles (the circle distance is 60mm, and the circle diameter is 240 mm).

A _cor ＝π×120 ² ＝45216mm ²

F _lu ＝0.9(β _c β _l f _c '+2αρ _v β _cor f _y )A _ln

＝0.9×(1.0×3×19.1+2×1.0×0.05586×1.03×360)×36258.5

＝3221683N>F _l ＝2624832N

(satisfy the requirements)

(8) Calculation of tensile elongation values

The theoretical elongation value is calculated as follows:

in the formula σ _m -average tensile stress of the tendon;

E _p -the modulus of elasticity of the tendon;

l is the actual length of the prestressed tendon;

k is the friction coefficient considering the local deviation of the length per meter of the pore canal;

x is the length of the hole from the tensioning end to the calculated section;

mu-coefficient of friction between the tendon and the wall of the channel;

theta is the included angle from the tensioning end to the tangent of the part of the pore channel of the calculated section curve.

Grouting and plugging anchor device for 5.2.10 pore channels

And (3) grouting the pore channel as soon as possible after the bonded prestressed tendons are tensioned and anchored, cutting the prestressed tendons of the working length part, and plugging the anchorage device.

(1) Grouting cautions for pore passage

(1) Preparation of grouting work: determining the water-cement ratio, cleaning grouting holes and water draining holes thereof, ensuring that water and electricity are supplied to a grouting site, stirring cement slurry on the site, and absolutely stopping water and power supply during grouting.

(2) And (5) grouting as early as possible after the tensioning of the prestressed steel strand is confirmed to be correct.

(3) And grouting the prestressed duct with one end stretched from the fixed end to the stretching end until the other end is full and discharged.

(4) The pulping adopts 42.5 grade or above ordinary portland cement, and the mixing ratio of cement: water (weight ratio) =1:0.4. the strength of the grouting in 28 days can not be lower than 30MPa.

(5) The grouting is carried out by UB3 mortar pump, the pressure is 0.4-0.6 MPa.

(6) Grouting is required to be compact.

(7) If the pore channel is blocked and the pore channel which can not be filled is blocked, grouting from the other end or the middle vent hole. If the pore canal can not be filled at one time, manual slurry supplement can be adopted.

(2) Anchorage device plugging

Before grouting, the steel strand with the exposed tension end is cut by a mechanical method (a grinding wheel machine), and the distance between the cutting position and the clamping piece is not less than 30mm. The anchorage device and the exposed stranded wires can be plugged by C45 micro-expansion fine stone concrete, and when pouring, the tensioned anchorage device is protected, and the anchorage device cannot be directly vibrated.

The foregoing is only a preferred embodiment of the present invention; the scope of the invention is not limited thereto. Any person skilled in the art should also be able to cover the technical scope of the present invention by the equivalent or modified embodiments and the modified concepts of the present invention.

Claims

1. A large-span prestressed beam invagination type one-time tensioning process is characterized by comprising the following steps:

building a prestressed beam;

pouring concrete in the prestressed girder;

after the concrete is condensed, the beam side template is disassembled;

tensioning the prestressed reinforcement;

dismantling the prestressed beam template and cutting the exposed steel strand;

grouting and sealing the end part of the prestressed beam.

2. The large-span prestressed girder invagination type one-time tensioning process according to claim 1, wherein the prestressed girder construction comprises:

laying a beam bottom template;

marking the curve coordinates of the prestressed reinforcement;

welding the prestressed reinforcement bracket;

arranging corrugated pipes along the prestressed reinforcement support;

penetrating a steel strand in the corrugated pipe;

3. The process of claim 2, wherein the step of binding reinforcing steel bars in the beam bottom formwork comprises the following steps:

4. The large-span prestressed girder invagination type one-time tensioning process according to claim 2, characterized in that: the discharge corrugated tube along the prestressed reinforcement bracket includes:

5. The invaginated primary tensioning process for the large-span prestressed beam according to claim 2, wherein said passing of the steel strand in the corrugated pipe comprises:

and wrapping the steel strand positioned outside the corrugated pipe.

6. The invagination type one-time tensioning process for the large-span prestressed girder according to claim 1, characterized in that it further comprises:

arranging a grouting hole at the fixed end of the prestressed beam;

7. The invagination type one-time tensioning process for the large-span prestressed girder according to claim 2, wherein the concrete pouring in the prestressed girder comprises:

8. The invagination type one-time tensioning process for the large-span prestressed girder according to claim 2, wherein the tensioning of the prestressed reinforcement includes:

cleaning one end of a prestressed beam;