CN112049143A

CN112049143A - Method for building large-volume concrete bearing platform of large-scale low-temperature storage tank

Info

Publication number: CN112049143A
Application number: CN202010747501.1A
Authority: CN
Inventors: 章梓康; 郑国昌; 季家根; 谢士俊
Original assignee: China National Chemical Engineering No14 Construction Co ltd
Current assignee: CHINA NATIONAL CHEMICAL ENGINEERING CO LTD; China National Chemical Engineering No14 Construction Co ltd
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2020-12-08

Abstract

A large-volume concrete bearing platform construction method of a large-scale low-temperature storage tank is characterized in that the projection of the bearing platform on the horizontal plane is a circle 0; the construction steps are as follows: pouring concrete on a cushion layer → erecting a support system at the bottom of a cushion cap → installing a bottom template → measuring and paying-off → installing steel bars on a lower layer → installing steel bars on an upper layer → installing a tilt instrument conduit → installing embedded parts → erecting side templates and installing disassembly-free templates → pouring concrete → curing concrete → dismantling templates. The method divides the blocks according to a five-block partition method and adopts a construction process of 'jumping the cabin at intervals' from inside to outside. A template at the construction joint of the bearing platform adopts a disassembly-free metal mesh template; the leveling device for the upper surface of the concrete of the bearing platform is manufactured by utilizing on-site waste materials, and the flatness of the upper surface of the concrete with an ultra-large area is strictly controlled. The method improves the construction management level of similar projects, improves the construction efficiency, ensures the construction quality and reduces the construction cost.

Description

Method for building large-volume concrete bearing platform of large-scale low-temperature storage tank

Technical Field

The invention belongs to the technical field of engineering construction, and particularly relates to a method for building a large-size concrete bearing platform of a large-scale low-temperature storage tank.

Background

At present, most of domestic large-scale equipment infrastructure adopts a concrete structure, but the investment cost is higher due to the limitation of the traditional construction process. 16 ten thousand meters of a certain low-temperature tank project³The ethane low-temperature storage tank is taken as an example, and a bearing platform of the ethane low-temperature storage tank is of a reinforced concrete structure and belongs to large-volume concrete construction. The radius of the engineering bearing platform is 44.2m, the elevation of the bottom of the bearing platform is 5.7m, the thickness is 1.1 m-1.3 m, 437 pile foundations are arranged at the bottom, the bearing platform is divided into 5 areas for construction, and the consumption of concrete is about 7500m³. The bottom plate support system adopts a full-space support system, so the construction is not only large-volume concrete construction, but also ultra-dangerous engineering. The 16 km³The ethane low-temperature storage tank is the largest ethane low-temperature storage tank in the world at present, and the stability of the storage tank body is directly influenced by the quality of the construction of the bearing platform.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for constructing a large-volume concrete bearing platform suitable for the large-scale low-temperature storage tank, wherein the projection of the bearing platform on the horizontal plane is a circle 0; the construction steps are as follows: pouring concrete on a cushion layer → erecting a support system at the bottom of a cushion cap → installing a bottom template → measuring and paying-off → installing steel bars on a lower layer → installing steel bars on an upper layer → installing a tilt instrument conduit → installing embedded parts → erecting side templates and installing disassembly-free templates → pouring concrete → curing concrete → dismantling templates.

The concrete bearing platform building method comprises the following steps:

1) dividing construction areas and constructing sequence:

1.1) the construction subareas are divided into 5 construction areas, and on the projection of a horizontal plane:

the first area is square, and the center of the first area is superposed with the circle center of the circle 0; the second and third zones are mirror symmetric about the first zone; the fourth area and the fifth area are mirror symmetric with respect to the first area;

the circumference of the circle 0 is divided into four arc lines which respectively form the outer boundary lines of the second to fifth areas;

the connecting points of the four arc lines and the connecting lines of the four corners of the first area form side boundary lines of the second area to the fifth area; the four edges of the first area are the inner boundary lines of the second to fifth areas;

ensuring that the pouring square amount of concrete in each area is less than or equal to 1500m³；

1.2) the concrete pouring sequence is as follows: first region → second region → third region → fourth region → fifth region;

the pouring time of each construction area and the pouring construction interval of the concrete of the finally finished part in the previous area are more than or equal to 12d, and the distance between the construction joint and the pile edge is ensured to be at least 400 mm;

the first area adopts a water storage maintenance method;

2) the construction method of the non-dismantling formwork at the partition construction joint of each adjacent construction area comprises the following steps:

adopting non-dismantling metal template nets with the specification of 2200mm multiplied by 450mm to be mutually connected in a lap joint way along the partition construction joints;

temporarily binding and fixing the on-site waste reinforcing steel bars on the back of the template net with the upper layer reinforcing steel bars and the lower layer reinforcing steel bars of the bearing platform, and removing and recycling the reinforcing steel bars after the concrete is solidified;

3) the method for leveling the upper surface of the bearing platform comprises the following steps:

before concrete pouring, connecting a plurality of nuts on horizontal steel bars, wherein the nuts form a matrix; a vertical section screw rod is screwed on each nut, the top end of the screw rod is connected with a steel pipe bracket, and the height of each steel pipe bracket is adjustable;

the same steel pipes are erected on the steel pipe supports of each row respectively, the steel pipes are parallel and positioned on the same horizontal plane, and a scraping ruler is arranged on the tops of the adjacent steel pipes in a sliding mode;

(when in specific use, the nut is a hexagonal nut which is clamped and fixed by two parallel steel bar sections, and the steel bar sections and the horizontal steel bars are bound by binding wires.)

In the concrete pouring process, constructors erect the scraping ruler on steel pipes with the adjacent elevations consistent, and slide back and forth to judge whether concrete at the ultrahigh position is removed or concrete is added to the low-lying position;

4) the control of the construction quality point of the concrete comprises the following steps:

4.1) selection of concrete raw materials

The cement type is ordinary portland cement;

the fine aggregate is medium sand, the fineness modulus of the fine aggregate is 2.3-3.0, and the mud content is not more than 3%; the coarse aggregate is continuous gradation with the particle size of 5-25 mm, and the mud content is not more than 1%; (the coarse aggregate is broken stone with the grain diameter not larger than 25mm)

The PH value of the concrete stirring water is not less than 6 and not more than 8;

4.2) concrete layering

The concrete pouring of the bearing platform is divided into three layers by adopting an inclined plane layering method, the pouring thickness of each layer is controlled to be 400mm +/-5%, the upper layer concrete is poured before the initial setting of the lower layer concrete, and the time interval of the two layers of concrete pouring is not more than 30 min;

the layered structure is as follows:

A. the horizontal direction of the first area is divided into an upper layer and a lower layer, and the vertical direction of the first area is divided into n/2 rows; the column direction is inclined, and the inclined direction is taken as a construction starting end; dividing the construction into n blocks according to the construction sequence, wherein n is a natural number;

from the beginning, block 1 at the lower layer, then block 2 at the lower layer, then block 3 at the upper layer, … …; 1 block is finished in the lower layer before the upper layer;

B. the layered structures of the second to fifth areas are the same;

the horizontal direction is divided into an upper layer, a middle layer and a lower layer, and the vertical direction is divided into m/3 rows; the column direction is inclined, and the inclined direction is taken as a construction starting end; dividing the construction into m blocks according to the construction sequence, wherein m is a natural number;

from the beginning, … … for the 1 st block in the lower layer, followed by the 2 nd block in the lower layer, followed by the 3 rd block in the middle layer, followed by the 4 th block in the lower layer, followed by the 5 th block in the middle layer, followed by the 6 th block in the upper layer, followed by the 7 th block in the lower layer; in adjacent layers, the ratio of 1 block completed in the lower layer to the upper layer is taken as the standard;

4.3) concrete pouring

After the template is sprayed with water and wetted, concrete can be poured;

and (3) retention of the concrete test block: pouringThe building amount is 1000m³Every 100m³Sampling once, more than 1000m³Per 200m of³Sampling once, and reserving at least 2 groups of test blocks in each sampling; after the concrete test block is formed, the test block under the same conditions must be placed at a concrete pouring position, and is simultaneously cured with a poured concrete entity, the standard curing test block is placed in a curing chamber for curing after the concrete is formed, the curing temperature is 20 +/-2 ℃, and the humidity is more than 95%;

during pouring, the height of the blanking guide pipe from a concrete pouring surface is not more than 2 m; the concrete is vibrated by adopting an inserted vibrating rod, the quincunx inserting points are arranged, the vibrating rod vibrates from a low position to a high position when vibrating, so that the vertical insertion is realized, the fast insertion and the slow pulling are realized, and the vibration of the upper layer concrete is required to be carried out before the initial setting of the lower layer concrete; when vibrating, the vibrators are arranged in a line along the advancing direction of the pouring surface, and the vibrators are vibrated line by line and advance forwards; the vibration and the distribution are carried out in a layered mode, the depth of the vibrating rod for vibrating the upper concrete layer inserted into the lower concrete layer is not less than 50-100 mm, the distance between the inserting points is not more than 1.5 times of the vibration radius, and the vibration time is 5-15 s;

4.4) treatment of large-volume concrete bleeding

And the bleeding water is absorbed in time in the concrete construction process.

4.5) curing of concrete

After the concrete pouring is finished, cofferdam is made on the top surface of the bottom plate concrete, the cofferdam is covered, water storage and heat preservation maintenance are carried out on the cofferdam, and the temperature difference between the inside and the outside of the concrete is controlled within 25 ℃;

building a 10cm high mortar cofferdam at the edge area of the bottom plate; the concrete curing time is not less than 14 days.

Preferably, the requirement of the concrete admixture is that the water reduction rate of the admixture is more than or equal to 29 percent; the slump of the concrete is 150-180 mm; when concrete is cured, the water storage depth on the surface of the bearing platform is more than 5 cm; the temperature difference between the inside and the outside of the concrete is controlled to be less than 25 ℃.

Permanent disassembly-free metal formwork nets are adopted between adjacent construction areas as the partition formworks; the metal net template is fixed by phi 48 steel pipes, and the phi 48 steel pipes are removed after concrete pouring is finished.

The method comprises the following steps of (1) building a bearing platform bottom support system:

first, template and support system design

A supporting system of the bottom die of the bearing platform is built in a full way by adopting a common steel pipe with the diameter of 48 multiplied by 3.2 mm;

the distance between upright rods in the central area is 710 multiplied by 700mm, and the step distance of cross rods is 800mm/1000 mm; the vertical and horizontal spacing of the upright rods in the edge annular area is 700 mm;

the main keel adopts 2 steel pipes with the diameter of 48 mm multiplied by 3.2mm multiplied by 6000mm and is stressed together;

the secondary keel adopts 50mm multiplied by 100mm multiplied by 6000mm flitch; the distance between the secondary keels in the central area is 250mm, and the distance between the secondary keels in the outer ring area is 200 mm;

the bearing platform bottom die panel tiled on the secondary keel adopts a plywood with the thickness of 2440mm multiplied by 1220mm multiplied by 15 mm;

when the full supporting system is constructed:

the distance between the upright stanchion and the edge of the pile head is 250 mm; the main keel and the secondary keel are laid close to the pile head at the periphery of the pile head; if the distance between the longitudinal cross rods exceeds 700mm or the overhanging length of the main keel exceeds 250mm, the vertical rods are added around the pile head and prop against the secondary keel;

second, cushion layer construction

Before the cushion layer construction, the earthwork backfill material is tamped and leveled, and the smooth drainage around the storage tank is ensured;

pumping concrete, and pouring C25 concrete (the concrete C25 is a concrete test block, and the concrete test block is maintained for 28 days at 20 ℃ under laboratory conditions, and the compressive strength is not less than 25Mpa) with the thickness of 200 mm;

when the concrete is pumped for pouring, the height of a concrete outlet pipe opening is not more than 500 mm;

after final setting, the terrace concrete is subjected to watering maintenance, and the maintenance time is not less than 7 days;

thirdly, erecting a supporting system

Before the support system is erected, a measurer measures a center point of a bearing platform, a plate thickness gradient section of 1100mm-1300mm and an outer edge line of the bearing platform on a concrete cushion layer;

vertical rods are arranged on the concrete cushion, the longitudinal and transverse distances of the vertical rods in the central area are 710mm/700mm, and the longitudinal and transverse distances of the vertical rods in the outer ring area are 700 mm;

arranging a longitudinal floor sweeping rod 200mm away from the surface of the cushion layer, and vertically arranging the transverse floor sweeping rod close to the longitudinal floor sweeping rod; the step pitch of the supporting system is 800/1000 mm;

after the height of the jacking is adjusted to the designed elevation, a main keel consisting of 2 steel pipes with the diameter of 48 mm multiplied by 3.5mm is arranged on the jacking, and the main keel is bound together and fixed by iron wires; the main keels are provided with the secondary keels with the size of 100mm multiplied by 50mm, the spacing between the secondary keels in the central area is 250mm, and the spacing between the secondary keels in the outer ring area is 200 mm;

fourth, prepressing test

Before loading the template system, 2.8 multiplied by 2.8m, namely 4 spans are selected, loading with the same surface of 1.4 multiplied by 1.4m for 12 hours, and the next procedure can be carried out after the template system is qualified.

Further, in the lower layer and upper layer steel bar installation step:

1) the bottom layer of the bearing platform is provided with four layers of steel bar meshes;

the bottom radial steel bars with the radius within the range of 34.3-44.2 m are 1700 HRB400E steel bars with the diameter of 32 mm; the top radial steel bars with the radius of 34.3-44.2 m are 2100 HRB400E steel bars with the diameter of 32 mm;

the bottom and the top of the steel bar with the radius of 41.63-44.2 m are both HRB400E steel bars with the diameter of 25mm, and the distance between the steel bars is 150 mm;

the bottom and the top of the steel bar with the radius of 34.3-41.63 m are both HRB400E steel bars with the diameter of 28mm, and the distance between the steel bars is 150 mm;

the bottom and the top of the steel bar with the radius of 34.3m are HRB400E steel bars with the diameter of 25mm, and the distance between the steel bars is 150 mm;

and placing bottom layer transverse bars according to the preset positioning, placing stirrups after the binding is finished, and then placing top layer reinforcing steel bars. The specification of stirrup steel bars is HRB335 of phi 25, and the number of the stools is set according to the requirement that at least one steel bar is bound by two square meters; the thickness of the concrete cushion block is equal to that of the concrete protective layer.

2) Steel bar lap joint

2.1) the transverse clear space between two overlapped steel bars is not more than 4d or 50mm, otherwise, the overlapping length is increased;

2.2) the longitudinal distance between two adjacent groups of lap-jointed reinforcing steel bars is not less than 0.3 times of the lap-jointed length; for adjacent lap joints, the clear distance between lap joints of two groups of steel bars is not less than 2d or 20 mm;

if all the steel bars are distributed in one layer, the allowed overlap ratio of the tensioned steel bars is 100 percent; if the reinforcing steel bars are arranged in multiple layers, the lap joint rate is reduced to 50%;

and d is the lap joint length of the steel bars.

In the step of erecting the side templates and installing the disassembly-free templates:

the side mold adopts a factory-processed wood template, the panel is a 15mm plywood, the secondary keel is a 42mm multiplied by 92mm batten, the distance is 300mm, the main keel adopts two 80mm multiplied by 160mm battens as modeling woods, the minimum height of the center of the modeling woods is not less than 80mm, the main keel is provided with two channels, the distance is 800mm, and the distance from the bottom part and the upper part of the bottom plate is 200 mm;

when the side mould is installed, a drawknot rib of the HRB335 with the diameter of 16 of the fixed side mould is drawed with a main rib of the pile, and the connection part of the drawknot rib and the main rib of the pile is made into a 180-degree hook form;

the template is fixed by welding a phi 16 high-wall screw rod and a phi 16 threaded steel bar, bending a welded end of the steel bar into a ring shape, connecting the ring-shaped part with a pile foundation main bar, penetrating the template through the screw rod, and tightening and fixing the template through a triangular nut.

The construction method is beneficial to improving the construction management level of similar projects, improving the construction efficiency, ensuring the construction quality and reducing the construction cost.

Drawings

Fig. 1 is a sectional view of the concrete construction of the bearing platform, wherein: a first region 101, a second region 102, a third region 103, a fourth region 104, a fifth region 105;

fig. 2 is a schematic view of the present support system set-up arrangement, wherein: a longitudinal sweeping pole 201, a transverse sweeping pole 202, a concrete cushion 203 and a vertical upright pole 204.

FIG. 3 is a schematic view of a platform inclinometer duct mounting configuration, wherein: the steel bar 301 on the lower layer of the bearing platform, the steel bar 302 on the upper layer of the bearing platform, the limiting steel bar 303, the inclinometer guide pipe 304 and the U-shaped steel bar 305.

Fig. 4 is a schematic illustration of rebar lap joints, wherein: a main rib 401, an overlap length 402.

Fig. 5 is a schematic illustration of a sideform support in which: the steel bar composite floor comprises a counter-pulling cone 501, steel bars 502 which are connected with floor steel bars in a pulling mode, and a high-strength screw 503.

Fig. 6 is a schematic view of a construction joint process, wherein: the concrete-filled steel tube formwork comprises a batten 601 (fixed with a vertical supporting rod, and meanwhile, a metal formwork mesh is reinforced by a steel bar mesh piece, and is removed after concrete pouring is finished), a pile cap steel bar 602, steel tubes 603 of a supporting system (the distance between the steel tubes is not more than 200mm), a metal formwork 604, bottom reinforcing steel bars 605 (removed after concrete pouring is finished), and a phi 48 steel tube 606.

FIG. 7a is a schematic illustration of a first zone concrete placement sequence;

FIG. 7b is a schematic view of the concrete pouring sequence of the second to fifth regions;

FIG. 8a is a schematic illustration of concrete placement vibration;

FIG. 8b is a schematic top view of the structure of FIG. 8 a; wherein: concrete layering upper strata 801, concrete layering lower floor 802, vibrating rod 803, template 804.

FIG. 9a is a schematic view of the leveling system of the present example;

FIG. 9b is a partial top view of the leveling structure of the present example;

FIG. 9c is a schematic view of a slide rail of the present example;

FIG. 9d is a schematic view of the connection structure of the support body and the rail;

FIG. 9e is the left view of FIG. 9d (with the partial structure of the mesh containing reinforcing bars);

FIG. 9f is a schematic view of the connection between the steel bar nipple and the nut; in the figure: the steel bar net piece 901, the scraper 902, the slide rail 903, the track 904, the support 905, the track support block 906, the straight steel pipe 907, the screw 908, the nut 909 and the steel bar short joint 910.

Detailed Description

Under the combination of 16 ten thousand meters³The process is further illustrated by engineering examples of ethane cryogenic storage tanks:

1.1 construction process flow:

cushion concrete pouring → bearing platform bottom support system erection → bottom formwork installation → measurement line release → lower layer steel bar installation → upper layer steel bar installation → inclinometer conduit installation → embedded part installation → side formwork support and non-dismantling formwork installation → concrete pouring → concrete curing → formwork dismantling

1.2 bearing platform construction subareas

According to the requirements of construction design drawings, a bearing platform is divided into 5 construction areas, and the construction of the bearing platform is carried out by 'interval bin jumping' from the center to the outer ring, as shown in figure 1.

1.3 bearing platform bottom formwork engineering and supporting system

1.3.1 form and support System design

The supporting system of the bottom die of the bearing platform is built by adopting a common steel pipe with the diameter of 48 multiplied by 3.2 mm.

The project belongs to a concrete template project with the concentrated line load more than or equal to 20kN/m, and is a dangerous project.

The distance between the upright rods in the central area is 710 x 700mm, and the step distance between the cross rods is 800mm/1000 mm; the vertical and horizontal spacing of the upright rods in the edge annular area is 700 mm.

The main keel adopts 2 steel pipes with the diameter of 48 mm multiplied by 3.2mm multiplied by 6000mm and is stressed together.

The secondary keel adopts 50mm × 100mm × 6000mm flitch. The distance between the secondary keels in the central area is 250mm, and the distance between the secondary keels in the outer ring area is 200 mm.

The bearing platform bottom die panel tiled on the secondary keel adopts 2440mm 1220mm 15mm plywood. When meeting the pile head, the sawn panel is shaped to be tightly connected with the pile head.

When the full-scale supporting system is constructed, the distance between the vertical rod and the edge of the pile head is 250 mm. The main and secondary keels are laid near the pile head at the periphery of the pile head, and vertical rods are added around the pile head if the distance between the longitudinal and transverse rods exceeds 700mm or the overhanging length of the main keel exceeds 250mm, and the vertical rods are propped against the secondary keels.

1.3.2 bedding construction

Before the cushion layer construction, the earthwork backfill materials are tamped and leveled, sundries such as garbage and the like in a construction area are cleaned, and smooth drainage around the storage tank is ensured.

And pumping concrete by using an automobile pump, and pouring a C25 concrete floor with the thickness of 200 mm.

Before concrete pouring, a surveyor marks a control line of 1m at the upper part of the terrace top elevation on a pile in a pouring area.

When the concrete is pumped for pouring, the height of the concrete outlet opening is controlled within 500mm, and pouring is carried out according to the preset pouring direction.

And 3m of a scraper is used for leveling in the pouring process, and a 1m control line on the pile is used for controlling the leveling elevation at any time.

After the concrete is initially set, extracting the slurry by a slurry extracting machine and collecting the surface by a polishing machine.

And (4) carrying out watering maintenance after the terrace concrete is finally set, wherein the maintenance time is not less than 7 days.

1.3.3 support System erection

Before the support system is set up, a measurer measures a center point of a bearing platform, a thickness gradient section of 1100mm-1300mm and an outer boundary line of the bearing platform on a concrete cushion layer.

Vertical rods are arranged on the concrete cushion, the longitudinal and transverse distances of the vertical rods in the central area are 710mm/700mm, and the longitudinal and transverse distances of the vertical rods in the outer ring area are 700 mm.

Arranging a longitudinal floor sweeping rod 200mm away from the surface of the cushion layer, and vertically arranging the transverse floor sweeping rod close to the longitudinal floor sweeping rod; the support system step pitch is 800/1000 mm. The detailed arrangement is shown in figure 2.

The verticality of the step pitch, the longitudinal pitch, the transverse pitch and the vertical rod is checked and accepted in time in the process of erecting the supporting system, the requirement of the scheme is consistent with the field implementation, and the adjustable jacking is arranged on the vertical rod after the acceptance check is qualified.

After the height of the jacking is adjusted to the designed elevation, a main keel consisting of 2 steel pipes with the diameter of 48 mm multiplied by 3.5mm is arranged on the jacking, and the main keel is bound together and fixed by iron wires; when the main keels need to be extended, the lap joints of the two main keels are staggered. The main keel is provided with secondary keels with the size of 100mm multiplied by 50mm, the distance between the central areas is 250mm, and the distance between the outer ring areas is 200 mm.

When the supporting system is erected, if the vertical rods near the pile head have the longitudinal and transverse spacing of 250mm < L < 700mm due to the pile position, in order to prevent the panel deflection from being overlarge during concrete construction, the vertical rods are added around the pile column and connected with the surrounding vertical rods as much as possible by using horizontal pipe fittings to form a whole.

The frame body and the high pile are bound and connected, and the vertical rods around each construction section are horizontally connected and bound with the pile.

1.3.4 bottom form mounting

The bottom die is made of 15mm thick plywood, and before the construction of the template, technicians make safety technology for cross bottom to operators and lay the bottom die according to the partition requirements of drawings.

Before the bottom die is installed, measuring and placing a side line point of a bearing platform on the secondary keel, and setting an elevation control point on the poured concrete pile cap; so that workers can adjust the elevation of the template in time, and the elevation of the template can be ensured to meet the design requirements of drawings.

The panels are laid on the secondary keel according to the mark points, the joint positions of the panels are required to be arranged on the secondary keel, the templates are adjusted to ensure that the height difference between two adjacent templates does not exceed 2mm, and the flatness of the surfaces of the templates meets the standard requirement.

And after the template is adjusted, fixing the template and the secondary keel by using iron nails.

And cleaning up the garbage on the surface of the template, and sealing the joints of the template by using an adhesive tape to ensure that slurry does not leak during construction.

And (4) performing detail sealing treatment on the contact part of the bottom die and the pile head according to the size of the gap. Filling and leveling small gaps with putty, plugging large gaps with sponge strips, and adhering the surface layers with adhesive tapes.

1.3.5 Pre-compression test

Before loading the first area template system, selecting a 2.8X 2.8m (4 span) area, carrying out 1.4X 1.4m equal surface loading for 12 hours, checking that the deflection deformation of the primary and secondary keels meets the standard requirement, and the frame body is stable, and after forming a written acceptance record, carrying out next procedure construction.

1.4 measurement of pay-off

And (3) positioning a central point, an outer side line, an inner circle line, a 0 degree (180) line, a 90 degree (270) line, the position of the prestressed pipe, the position of the temporary drainage pipe, the position of the temporary opening and the position of the buttress column on the bottom die of the bearing platform by using a total station, snapping by using ink lines, and marking by using white paint or a white marker pen.

1.5 Embedded part installation

Installation of embedded part (settling point, lightning protection embedded part)

And positioning and paying off on the steel bars by using a total station before the embedded part is installed, determining the center position and controlling the elevation. A short reinforcing bar for fixation is added and reinforced with a wire or the like. And after the embedded part is positioned and installed, retesting and checking are carried out again to ensure the position of the embedded part.

When the embedded part is installed, a welding steel bar bracket is placed in advance, and the embedded plate/rod is placed in the bracket to be in place initially. And simultaneously, the positions of the bracket and the embedded plate/rod in the bracket are adjusted, so that the embedded part is accurately positioned under the measurement control. And the embedded part is firmly clamped in the bracket from the three-dimensional direction by adopting the positioning steel bar. And welding the positioning steel bars on the support steel bars after measurement and check are correct. The entire insert-holder-orientation system is spot-welded to the structural steel reinforcement after the measurement is checked again.

2.6 Embedded pipe installation

The pre-buried pipes are prestressed corrugated pipes, and the radian between the pre-buried pipes is 21 degrees. When the embedded pipe is installed, the embedded pipe is bound with the reinforcing ribs around the embedded pipe in a binding mode, and then the reinforcing ribs are bound with the stressed reinforcing steel bars of the bearing platform. After the installation of the embedded pipe is finished, the position of the embedded pipe is rechecked by professional measuring personnel, and the embedded pipe can be delivered to next construction after meeting the qualification.

1.6 bearing platform inclinometer guide tube installation

The specification of the inclinometer conduit embedded in the central axis position of the bearing platform is an ABS plastic pipe with the outer diameter phi of 70 mm. Installation of an inclinometer guide pipe: and (5) installing the inclinometer guide pipe after the upper layer reinforcing mesh of the bearing platform is bound. The inclinometer conduit is connected by a sleeve, the inclinometer conduit is inserted into the inclinometer conduit joint and pushed to the position, then the O-shaped ring is positioned, and then the whole joint is thermally shrunk by the heat shrinkable tube. The heat shrinkable tube extends out of two sides of the tube joint by not less than 15 cm. And placing U-shaped steel bars on the upper layer of the steel bar mesh, and binding the U-shaped steel bars on the upper layer of the steel bar mesh after error-free measurement. The U-shaped ribs are arranged at intervals of 1000mm-1500 mm. After the pipe penetrating is finished, the pipeline and the reinforcing steel bar support are bound together by using a binding wire, and an iron wire is used for tightening downwards to prevent the guide pipe from floating upwards in the pouring process, as shown in figure 3.

1.7 fabrication and binding of reinforcing steel bars

1.7.1 fabrication of reinforcing bars

Before compiling the reinforcing steel bar material list, a field engineer compares a template drawing, a construction sectional drawing and a reinforcement arrangement drawing, formulates the reinforcing steel bar material list according to a progress plan, and requires writing to require an owner to clarify if the reinforcing steel bar drawing has contradictions;

the method is characterized in that the project name, position, elevation, drawing number and color and shape of the used steel bar label are marked on the steel bar material sheet, particularly, when filling in the steel bar label, handwriting is neat and clear, and the specification of the steel bar with the steel bar number, the diameter of the steel bar, the number of the steel bars, the blanking length of the steel bar, a steel bar diagram and the total weight of the steel bars with various specifications are marked;

the rebar material is in six copies. One of them is kept by the builder, and the remaining five are delivered separately: one worker is grown on site, one person in charge of a steel bar processing yard is grown on site, two teams and groups are bound, and one material controller is grown on site;

before cutting and bending the reinforcing steel bars, various preparations are required to be made, each reinforcing steel bar is cut one before a large amount of reinforcing steel bars are cut, the size of each reinforcing steel bar is measured, mass cutting is started after error is checked, then the blanking amount is checked, and labels are hung on the cut reinforcing steel bars; checking whether the positioning baffle moves or not every 30 checks in the cutting process of the steel bars with the same quantity and larger quantity; for the reinforcing steel bars with complex shapes and high bending difficulty, firstly, a shorter reinforcing steel bar is used for trial bending, manufacturing parameters are adjusted according to conditions until a satisfactory result is obtained and taken as formal reinforcing steel bar bending parameters, and in order to ensure the consistency of the formed reinforcing steel bars, the bending angles and the sizes of the large reinforcing steel bars in a bending batch are rechecked every 30 reinforcing steel bars;

in a steel bar processing workshop, all steel bars are cut by a steel bar linkage line and a steel bar cutting machine, so that the flatness of the section of the steel bar is ensured, the U-shaped or bent steel bar cannot appear, and all the steel bars on a construction site are cut by the cutting machine.

After the reinforcing steel bars are bent and formed, the reinforcing steel bars are bound into bundles according to the requirements of specification, model, number of each bundle and the like, and reinforcing steel bar material plates are hung on the bundles. The content of the reinforcing steel bar material plate comprises: one surface is numbered and simplified by steel bars; and the other side is a building number and an engineering part, and the bundled steel bars are hoisted to a semi-finished product stacking area by a crane and are well cushioned by wood squares, and are hoisted to a construction site during binding construction.

1.7.2 binding of steel bars

Paying off on a bottom die before binding reinforcing steel bars, wherein a central area reinforcing steel bar initial position line and an annular area reinforcing steel bar initial position line are mainly arranged, and a cushion block is placed before binding the reinforcing steel bars at the bottom;

and binding the steel bar subsections according to the sequence of the drawing construction subsections. And binding from the outer ring to the inside during binding, arranging a bottom layer reinforcing mesh sheet, placing a split heads after the binding is finished, and then binding an upper layer mesh sheet. In order to make the joints of the steel bars of all the sections be identical, when the steel bars of the whole bearing platform are bound, a steel bar on a certain axis is defined as a reference. Aligning the position of the corresponding positioning steel bar of the upper layer steel bar mesh by using a plumb bob;

the bottom layer of the bearing platform is provided with four layers of steel bar meshes. The radius is within the range of 34.3-44.2 m, and the bottom radial steel bars are 1700 HRB400E steel bars with the diameter of 32 mm; the top radial steel bars are 2100 HRB400E steel bars with a diameter of 32 mm. The bottom and the top of the steel bar are HRB400E steel bars with the diameter of 25mm within the radius range of 41.63-44.2 m, and the distance between the steel bars is 150 mm; the bottom and the top of the steel bar are HRB400E steel bars with the diameter of 28mm within the radius range of 34.3-41.63 m, and the distance between the steel bars is 150 mm. HRB400E steel bars with a radius of 34.3m and a diameter of 25mm are arranged at a distance of 150 mm. And placing bottom layer transverse bars according to the preset positioning, placing stirrups after the binding is finished, and then placing top layer reinforcing steel bars. The specification of stirrup reinforcing bar is phi 25HRB335, and quantity, elevation and the position that need set up the split heads according to the requirement that two square meters are no less than one during steel bar ligature should accord with the drawing requirement. The thickness of the concrete cushion block is equal to that of the concrete protective layer.

Inserting the steel bar: before the insertion bars of the wall are bound, the steel bar mesh on the upper layer of the bearing platform needs to be paid off, a common steel bar is fixed on the steel bar mesh, and the quality requirement is as follows: guarantee superstructure's steel reinforcement protective layer, quantity, interval accord with the drawing design requirement and take place to shift in the dowel when avoiding concrete placement, must carry out the drawknot and consolidate. The concrete measure of the tie reinforcement is that after the inner ring dowel bars and the outer ring dowel bars are placed, the iron wires are firmly bound with the lap joint part of the bottom layer steel bars, and the tie bars are connected with the dowel bars. And phi 20 temporary horizontal reinforcing steel bars are arranged at the upper parts of the inner and outer ring steel bar inserting bottom plates every 1m along the circumferential direction, the tie bars are arranged in a staggered mode, and two inclined struts are arranged for fixing.

Mounting a prestressed bell mouth: before the beginning of binding the steel bars, the civil engineering construction unit and the prestress construction unit are well subjected to intermediate connection procedures and cross-fit construction, so that the accurate installation position of the prestress horn mouth is ensured. After the installation of the prestressed horn mouth is completed, the civil engineering team and team should prevent the prestressed fittings from being collided and displaced when binding the reinforcing steel bars, and the collision is damaged.

1.7.3 Steel Bar overlap

(1) The transverse clear space between two overlapping steel bars does not exceed 4d or 50mm, otherwise, the overlapping length should be increased. The increased length is the clear distance of the reinforcement at a distance exceeding 4d or 50 mm. d is the diameter of the rebar.

(2) The longitudinal distance a between two adjacent sets of overlapping bars is not less than 0.3 times the overlap length L0. For adjacent lap joints, the clear distance between two groups of steel bar lap joints is not less than 2d or 20mm

When the requirement is met, if all the steel bars are distributed in one layer, the allowed overlapping rate of the tensioned steel bars is 100 percent; if the reinforcing steel bars are arranged in multiple layers, the lap joint rate is reduced to 50%.

All the stressed steel bars and the distribution bars can be overlapped in one section. The overlapping arrangement of the reinforcing bars should meet the requirements of fig. 4.

1.8 processing and mounting of bearing platform side template

1.8.1 construction of side form

The side mould adopts factory processing wooden template, and the panel is 15mm plywood, and the secondary joist is 42mm 92mm flitch, and the interval is 300mm, and the main joist adopts two 80mm 160mm flitches to make the shaping wood, and the minimum height in shaping wood center is not less than 80mm, and the main joist sets up twice, and the interval is 800mm, and the distance from bottom plate bottom and upper portion is 200 mm. The side forms are constructed as shown in figure 5.

When the side form is installed, the template is reinforced, and the problems of expansion, die running and the like in the concrete pouring process are prevented. When the formwork is installed, the tie bars of the fixed side formwork are tied by steel bars of phi 16HRB335 and main bars of the pile, the connecting parts of the tie bars and the main bars of the pile are made into 180-degree hooks, and the length of the tie bars is processed according to the requirements of a construction site. And the outer sides of the side molds are provided with inclined struts which are connected with the main keels, the templates and the supports thereof are checked before concrete pouring, and pouring can be performed after the templates and the supports are qualified. In the pouring process, a specially-assigned person is arranged to check the stability of the template and the support, if the problems affecting the engineering quality and the use safety occur, the construction should be stopped immediately, and after the problems are treated, the construction can be continued after the experience folding lattice.

During the concrete pouring, if the formwork expansion occurs, the concrete pouring is stopped immediately, the concrete at the formwork expansion part is removed to reduce the side pressure, measures of increasing the number of main keels and internal pulling and external bracing are taken, and the concrete can be continuously poured after the reinforcement.

And drawing a template configuration diagram according to the construction drawing, arranging the template configuration diagram to be processed and assembled in a woodwork workshop according to the requirements of a schedule, and hoisting the formed template to a construction site after the template configuration diagram is qualified through self-inspection. Before the template is installed, workers should clean pollutants on the surface of the template in time to enable the surface of the template to be smooth and flat without quality defects such as holes, bulges, too wide seams and the like;

hoisting the template in place, aligning, fixing and connecting by a tower crane. When the template is erected, the template joint is smooth and tight, no obvious stubble staggering and gap phenomena exist, if the template has the quality defects, the gap can be sealed by a sponge strip, and a layer of paper-based adhesive tape is pasted on the gap;

form fixing by

High wall screw and

the deformed steel bars are welded, the other ends of the deformed steel bars are bent into a ring shape, the ring-shaped part is connected with the pile foundation main bar, the high-strength screw penetrates through the template, and the template is tightened and fixed by the triangular nut, so that the template is free from phenomena of slurry leakage, mold expansion, mold running and the like during concrete construction.

1.8.2 construction joint treatment

Adopt traditional wooden model construction and artifical chisel hair mode, slow, the efficiency is low, with high costs, and artifical chisel hair causes the damage to the concrete of chisel hair face moreover, and seam face quality is difficult to guarantee, combines to have adverse effect to the concrete, can not satisfy concrete quality and time limit for a project progress plan requirement. Therefore, the permanent disassembly-free metal formwork net is used as the partition formwork for concrete construction, a rough interface can be formed on the surface of concrete, concrete can be poured again without roughening and cleaning, and the construction joint is guaranteed to meet the requirement of concrete joint.

A non-dismantling metal mesh template is adopted at a construction joint between pouring sections and is fixed through a phi 48 steel pipe, the steel pipe must be dismantled after concrete pouring is completed, and a non-dismantling metal mesh needs to be used after a supervision party agrees before the non-dismantling metal mesh is used, as shown in figure 6.

And (3) treating the horizontal construction joint at the ring wall by using a steel wire brush before the initial setting of the concrete until the concrete aggregate is semi-exposed, and if the concrete aggregate cannot meet the requirement, chiseling by using an air pick or a pneumatic chiseling machine, wherein the chiseling effect meets the requirement of design and specification.

In the concrete pouring process, after the concrete pouring of the previous construction section is completed and the template is removed, sundries such as floating slurry and the like on the reinforcing steel bars of the adjacent construction sections should be cleaned in time, and the bonding force between the reinforcing steel bars and the concrete cannot be influenced. The surface of the template is washed clean by water, so that the impression quality of concrete cannot be influenced, and then reinforcing steel bars and concrete can be bound for the next construction section.

1.8.5 quality standard for construction of formwork

Item	Tolerance deviation (mm)	Inspection method
			Surface flatness of the plate	5	2m running rule and feeler gauge inspection
Height difference between two adjacent plates	2	Inspection of steel rule

1.9 concrete construction

The foundation bearing platform belongs to the bulk concrete, so the construction is required to be carried out according to the construction requirement of the bulk concrete during the construction, and the construction quality of the concrete is mainly controlled from the following aspects

1.9.1 selection of concrete raw material

a. According to the requirements of design documents of drawings, the type of cement is ordinary portland cement, and the quality of the cement must meet the regulations of 'general portland cement' GB 175-2007.

b. The fine aggregate is preferably medium sand, the fineness modulus of the fine aggregate is preferably 2.3-3.0, and the mud content is not more than 3%; the coarse aggregate is preferably selected from continuous gradation with the grain diameter of 5-25 mm, and the mud content is not more than 1%.

C. The coarse aggregate is broken stone with the grain diameter not larger than 25mm, and the coarse aggregate is subjected to routine reinspection according to batches when entering a field.

d. According to the requirements of design documents, the concrete mixing water is strictly executed according to the requirements of concrete water standard JGJ63-2006, and seawater cannot be used for preparing concrete. The pH of the concrete mixing water should not be less than 6 and not more than 8. The water used to mix and cure the concrete must not contain contaminants, especially those that can cause chloride or sulfate content in the concrete.

2.9.2 concrete layering

Before the concrete starts to be constructed, according to the thickness of a bearing platform (1100mm-1300mm), namely the requirement of a large-volume concrete construction process, the method of inclined surface layering is adopted to divide the bearing platform concrete pouring into three layers, the pouring thickness of each layer is controlled to be about 400mm so as to avoid reducing the generation of temperature cracks, the upper layer concrete must be poured before the initial setting of the lower layer concrete, the time interval of the two layers of concrete pouring is not more than 30min, and the layering is shown in figures 7a and b (the numbers in the figures indicate the pouring sequence):

1.9.3 concrete supply

The concrete is produced by a commercial mixing station and is transported to a pouring site through a mixing transport vehicle, the temperature of the concrete is required to meet the standard requirement, and all concrete wastes and the like are cleaned to a specified place by a loader.

1.9.4 concrete pouring

And checking the mix proportion of the concrete model, wherein no sundries or pollutants exist in the pouring area, and pouring the concrete after the template is sprayed with water and moistened.

Before concrete begins to pour, opening the quotation appraisal, organize construction unit technical responsible person by construction unit, the supervision engineer of supervision unit, construction unit project technical responsible person, concrete mixing unit's quality testing department represents and opens the quotation appraisal to the concrete mix proportion of using for the first time, construction unit should in time provide: the concrete test block comprises a concrete mix proportion design list, a cement delivery quality certificate, a cement 3d retest report, a sand test report, a stone test report, a concrete admixture qualification certificate, a concrete admixture delivery inspection report, an additive use and performance specification, an additive delivery qualification certificate and inspection report, an additive retest report, a trial concrete compression resistance report, a concrete test block 28d compression strength test report, and is matched with the opening identification of concrete in time, so that the quality of the concrete meets the design requirements.

And (3) retention of the concrete test block: the pouring square amount is 1000m³Every 100m³Sampling once, more than 1000m³Per 200m of³Sampling is carried out once, and at least 2 groups of test blocks are reserved in each sampling. After the concrete test block is formed, the test block with the same conditions must be placed at the concrete pouring position and cured with the poured concrete entity at the same time, and the standard curing test block should be placed in a curing chamber for curing after the concrete is formedAnd (4) maintaining, wherein the temperature (20 +/-2 ℃) and the humidity (more than 95%) of maintenance must meet the standard requirements.

In order to avoid segregation of concrete during pouring, the height of the blanking guide pipe from the concrete pouring surface is not more than 2 m. The concrete is vibrated by adopting an inserted vibrating rod, the quincunx inserting points are arranged, the vibrating rod vibrates from a low position to a high position when vibrating, the vertical insertion is realized, the fast insertion and the slow pulling are realized, and the vibration of the upper layer concrete needs to be carried out before the initial setting of the lower layer concrete. When vibrating, the vibrators are arranged in a line along the advancing direction of the pouring surface, and the vibrators are vibrated line by line and advance forwards; the same layering of vibration and cloth goes on, and the degree of depth that vibrates upper concrete vibrating rod and insert lower floor concrete is not less than 50mm ~ 100mm, and the insertion point interval is not more than 1.5 times of vibration radius, and the shock duration is in 5 ~ 15s to guarantee the closely knit degree of concrete but not segregation, vibrate according to actual need, use 4 people of vibrating of every cloth machine outfit as the standard. The distance between the vibrating rod and the template is 0.5 times of the vibration radius.

During concrete distribution, concrete is prevented from directly impacting a temperature measuring rod, a vertical dowel, a prestressed pipeline, an embedded part and the like, and collision damage or displacement is prevented. The corner parts are reinforced to vibrate, the compactness of concrete is ensured, and the vibrating rod is strictly prohibited from colliding with a prestressed pipeline, an embedded part and the like during vibration. The vibration of the concrete achieves the internal and external polishing.

Controlling the elevation of the concrete surface: before concrete pouring, elevation control points are arranged on the bearing platform joint bars and the side mould. After the concrete is vibrated and the leveling device is used, a 3m scraper is used for leveling, and in the concrete pouring process, a measurer discontinuously retests elevation control points on the insertion ribs to prevent settlement from generating deviation.

As in fig. 8a and 8 b.

1.9.5 large volume concrete bleeding treatment

Bleeding easily appears when carrying out bulky concrete construction, when bleeding is serious, can influence the construction quality of concrete, in order to eliminate and alleviate the influence of bleeding, the bleeding that upwells under the general condition and laitance can flow along the direction that the face is than lower, in time with dust catcher or sponge absorption processing at the in-process of concrete construction.

1.9.6 concrete curing

People, heaps and other construction work are strictly prohibited on the concrete surface before the concrete is poured and finally set (within 12 hours after pouring). After the concrete pouring is finished, cofferdams are arranged on the top surfaces of the bottom plate concrete, the cofferdams are covered, water storage and heat preservation maintenance are carried out on the cofferdams, and the temperature difference between the inside and the outside of the concrete is controlled within 25 ℃.

And a 10 cm-high mortar cofferdam is built at the edge area of the bottom plate, so that the moisture in a maintenance area is sufficient, the internal and external temperature difference of concrete is better controlled, and the generation of cracks is reduced. When the maximum temperature difference between the surface temperature of the concrete and the ambient temperature is less than 20 ℃, the temperature measurement can be stopped. The curing time of the mass concrete is not less than 14 days.

During the concrete curing, a specially-assigned person is responsible for taking care of the concrete, and if the water stored on the surface of the concrete is reduced or insufficient, the water should be supplemented in time, so that the surface of the concrete is always in a wet state.

The vertical surface of the side surface of the bottom plate is covered by cotton felt so as to keep the moisture of the concrete and avoid the too fast evaporation.

1.10 form removal

1.10.1 side die dismantling method

According to the standard requirements, the bearing platform side mold is dismantled 3 days after the concrete is poured, the time for dismantling the template can be determined by the strength of the on-site under the same condition maintenance test block when the supervision party agrees, and the integrity and the impression quality of the concrete are guaranteed when the wooden template is dismantled.

1.10.2 bottom die removal

After concrete pouring of the bearing platform is completed, heat preservation and moisture preservation maintenance should be carried out immediately, the bottom die can be disassembled after the strength grade of the bottom die reaches 100%, and the formwork disassembly sequence is carried out sequentially from the center to the edge according to the sequence of the bearing platform. When the template is dismantled, the template cannot be violently pried, so that the large template falls off, and the surface of the concrete is prevented from being damaged.

And after the strength of the concrete of the bearing platform reaches 75%, the template in the central area can be removed. When the bottom template is disassembled, the steps of first supporting and then disassembling, then disassembling first, and then disassembling the non-bearing template and the bearing template are adopted, and the bottom template is disassembled from the outside to the inside from top to bottom. The template can not be violently pried when being dismantled, and the large template can be prevented from falling off. The concrete surface can not be damaged, the detached templates and the support rods can not be thrown away, and the templates and the support rods can be stacked and placed in a specified place in order after being transported out and can be timely transported. And after the template is dismantled, the surface of the template is cleaned, and deformed and damaged parts are repaired.

2. Summary of the invention

(1) The concrete construction partition method of the outer tank bearing platform of the traditional low-temperature storage tank is changed, and the construction process of 'jumping from inside to outside at intervals' is adopted according to the 'five-block partition method' partition. The concrete pouring sequence of the bearing platform sequentially comprises the following steps: first region → second region → third region → fourth region → fifth region, the cap region is shown in detail in FIG. 1:

(2) a template at the construction joint of the bearing platform adopts a disassembly-free metal mesh template;

(3) the leveling device for the upper surface of the concrete of the bearing platform is manufactured by utilizing on-site waste materials, and the flatness of the upper surface of the concrete with an ultra-large area is strictly controlled.

3. Construction technology difficulty and solution

The construction processes of building a bearing platform bottom support system, installing reinforcing steel bars, installing a bottom die and a side die, pouring concrete and the like are the same as those of the traditional construction method, and are not described again. The following is mainly directed to the new processes of the concrete partition chamber jumping construction of the bearing platform, the installation of a non-dismantling metal template at a construction joint, the leveling of the upper surface of the bearing platform, the control of concrete cracks and the like.

3.1 reasonable zoning, construction from inside to outside of' interval chamber jumping

The number of the bearing platform partition blocks is reasonably set. Too many subareas are used, the materials and labor for construction measures are increased, the structural integrity is greatly weakened, and the construction period is prolonged. The number of subareas is too small, the single pouring concrete amount is large, the cement hydration heat is large, and the risk of harmful crack generation is increased. According to the five-block partition method, the pouring square amount of concrete in each area is ensured to be less than or equal to 1500m³And the pouring time of each stage and the pouring construction interval of the concrete of the finally finished part of the previous stage are more than or equal to 12d, and the distance between the construction joint and the pile side is ensured to be at least 400 mm. Thus not only reducing the expansion and shrinkage constraints of the concrete to a certain extent, but alsoThe large accumulation of hydration heat can be effectively prevented, the heat storage capacity of each area is reduced, and the temperature stress is released;

the warehouse is built at intervals from inside to outside, and a water storage maintenance method is adopted in the central area, so that the concrete stress in the edge area can be fully released, the number of cracks on the bearing platform is reduced, a working surface can be created for the construction of the outer tank wall in advance, and the purpose of optimizing the construction period is achieved.

3.2 construction of non-dismantling formwork at construction joint of bearing platform partition

The non-dismantling metal formwork net with the specification of 2200mm multiplied by 450mm is adopted to be mutually connected in a lap joint mode along the sub-area construction joints of the bearing platform, the back face of the formwork net can be temporarily bound and fixed with the upper layer steel bars and the lower layer steel bars of the bearing platform by using on-site steel bar waste materials, and after concrete is solidified, the reinforcing steel bars are dismantled and recycled. The template is a permanent template without disassembly, can be left in concrete, can form a rough surface on the concrete surface of a construction joint, can perform concrete pouring of adjacent areas without manual roughening and cleaning, can ensure that the construction joint meets the construction requirement of the concrete joint, can ensure that the liquidtightness of a bearing platform construction joint meets the requirement, and accelerates the construction progress.

3.3 leveling system for the upper surface of the bearing platform,

16 ten thousand meters³The upper surface area of the ethane low-temperature storage tank bearing platform reaches about 6000 square meters, so that the concrete quality is ensured, and the strict requirement on the flatness of the upper surface of the concrete with the structure is met. However, in actual field construction, due to the influence of various factors, the difficulty is very high in achieving the purpose that the flatness of the upper surface of the large-area concrete structure meets the strict design requirement. In the construction process, only measurement personnel are used for controlling instruments in the whole process, random factors are large, adverse conditions such as concrete pouring night construction and the like are met, and the construction quality cannot be guaranteed. Therefore, the leveling device has the advantages of being small in investment, high in precision, good in stability, easy to operate by constructors and capable of being recycled, and effectively solving the problem of high difficulty in controlling the flatness of the upper surface of concrete.

The method adopts a leveling system for concrete construction, which comprises a steel bar net sheet of a concrete structure, a scraping ruler and at least two slide rails; all the sliding rails are parallel to each other, and the top ends of the sliding rails are on the same plane; the distance between the adjacent slide rails is the same; the length of the scraping ruler is not less than the distance between the adjacent sliding rails, and the scraping ruler slides on the two adjacent sliding rails; the slide rail comprises a rail and a plurality of supporting bodies, wherein the supporting bodies are detachably and uniformly supported at the bottom of the rail along the length direction; the support body comprises a track supporting block and a height adjusting mechanism; the height adjusting mechanism is connected to the bottom of the rail supporting block; the height adjusting mechanism is connected to the reinforcing steel bar net piece. As in fig. 9a.

Referring to fig. 9b to 9e, in this example, in any one of the slide rails: the track is a straight steel pipe; the track supporting block is formed by pressing a steel plate, and the radial section of the track supporting block is in a semi-circular arc shape; the height adjusting mechanism comprises a screw and a nut which are connected in a rotating manner; the top of the screw rod is connected to the bottom surface of the track supporting block, and the axis of the screw rod penetrates through the middle point of the track supporting block; the nut is connected with a steel bar nipple, and the steel bar nipple is connected with the steel bar net piece through a steel bar binding wire.

As shown in fig. 9f, the short steel bars are provided with two pairs, and the two pairs are symmetrically connected to the left side and the right side of the nut about the center of the nut.

The steel bar short section and the nut can be welded, and the track supporting block and the screw can be welded.

in the order of 16 ten thousand meters³The concrete on the upper surface of the bearing platform of the ethane low-temperature storage tank is leveled for example, the leveling area reaches about 6000 square meters, the concrete quality is ensured, and the strict requirement of the design on the flatness of the concrete upper surface of the structure is met.

Before concrete pouring, the screw rods and the nut screws are connected together and fixed on the steel bar net pieces on the bearing platform along the through lines at intervals of 1.5m in the pouring area range. And uniformly measuring the elevation of the support body by using a level gauge, and placing the straight galvanized steel pipe on the arc-shaped rail supporting block to form a line. The same operation was carried out at a distance of 2.5m, with the support being arranged over the entire concrete casting area. And (4) slightly screwing the screw rod at the deviation position by means of a level gauge to enable the top elevation of the straight steel pipe to meet the design requirement.

In concrete placement, constructors erect 3m cursors on the straight steel pipes with the same adjacent elevations and slide back and forth to judge and remove concrete at the ultrahigh positions or add concrete to the low-lying positions, so that the integral control of the uniformity of the elevations of the top surface of the large-area reinforced concrete structure is realized. The problems of complex operation, high control difficulty, poor integral flatness and the like of constructors in concrete pouring of the structure are solved, and the purposes of meeting the site construction requirements, reducing the operation difficulty and improving the working efficiency are achieved.

After the bearing platform concrete is constructed by the leveling device, the flatness of the upper surface is controlled within the design allowable deviation range, and the bearing platform concrete is completely qualified, so that reliable guarantee is provided for subsequent outer tank wall structure and cold insulation construction.

In this system of making level, steel pipe, steel bar nipple joint, screw rod/nut and track tray all can utilize the current material of job site to make, for example the steel bar nipple joint can utilize the steel bar material in the concrete structure to cut off and make (or leftover bits), and the steel pipe of scaffold can be used to the steel pipe.

After the pouring is finished, the steel bar short section, the screw/nut and the track supporting block can be left in a construction plane.

The rail can be left in the construction plane or taken out after the leveling process and the gap left by the rail is filled with concrete according to the type of the project.

3.4 bearing platform concrete crack control

3.4.1 analysis of causes

(1) The concrete shrinks. Common types of cracks are those caused by shrinkage of the concrete, those caused by settlement of the concrete and those caused by heat of hydration.

(2) The temperature difference is too large, the raft plate concrete belongs to large-volume concrete, the inside and the outside have great temperature difference, the inside and the outside temperature difference can generate temperature stress in the concrete hardening process, and the stress can cause the concrete to crack before the concrete strength reaches a certain quantitative value.

3.4.2 technical measure

(1) The cement and cold water with lower hydration heat are used for mixing materials, the machine-out temperature of the concrete is reduced, sand aggregate is prevented from being exposed to the sun, the coarse aggregate is made of stone with less needle-shaped continuous gradation, the fine aggregate is made of natural medium sand, the dosage of the cement and water in the concrete is reduced by using lower sand rate, and the like, and an additive is added according to the standard requirement (the standard requirement is that the water reducing rate of the additive is more than or equal to 14%), the water reducing rate of the additive adopted by the project reaches 29% by detection, and the related requirements are met and the concrete cracks can be effectively controlled.

(2) After the concrete is vibrated, immediately leveling by using a scraping ruler and a wooden trowel, primarily calendaring by using a pulp lifting machine and a polishing machine, and then maintaining;

(3) slump test: and arranging a specially-assigned person to perform a concrete slump test before the mixer truck leaves a commercial mixing station and before on-site concrete pouring, wherein the concrete slump needs to be kept between 150mm and 180mm, and the concrete with unqualified slump needs to be processed for leaving the field. Slump is less than 150mm and can cause concrete bearing capacity not enough, and slump is greater than 180mm and can make the concrete produce harmful crack, and control concrete slump can effectively reduce the harmful crack of concrete.

(4) And (5) maintaining the concrete by adopting a water storage maintenance method on site. After concrete pouring and surface collection are finished, a layer of curing agent is immediately coated for curing, then a mortar cofferdam is built around the upper surface of the center area of the bearing platform for storing water, the depth of the stored water on the surface of the bearing platform is ensured to be more than 5cm, the advantage of large specific heat capacity of water is fully exerted, the cooling effect is achieved, the heat preservation effect on the surface of concrete is achieved, the rapid change of the temperature difference between the inside and the surface of the concrete is avoided, the temperature difference between the inside and the outside of the concrete is controlled within 25 ℃, and the risk of harmful cracks generated on the bearing platform concrete is reduced.

3.4.3 temperature control measures

(1) Temperature control index of mass concrete

The temperature control indexes of the mass concrete are suitable to meet the following regulations:

a. the temperature rise value of the concrete pouring body on the basis of the mold-entering temperature is not more than 50 ℃;

B. the temperature difference between the inner surface and the outer surface (equivalent temperature without concrete shrinkage) of the concrete pouring block is not more than 25 ℃;

c. the cooling rate of the concrete casting is not more than 2.0 ℃/d.

d. The temperature difference between the surface of the concrete casting and the atmosphere is not more than 20 ℃.

(2) General requirements for temperature control

The mold-entering temperature of the mass concrete should be strictly controlled, and the temperature of the concrete pouring body in the mold should not exceed 30 ℃. In the field construction process, the concrete transportation time is reduced as much as possible, and raw materials such as sand and stones are covered in case of high-temperature weather.

The temperature difference between the inner surface and the outer surface of a concrete pouring body is not more than 25 ℃, a specially-assigned person for concrete maintenance is arranged, and an experimenter is matched with the concrete temperature to monitor the concrete temperature at any time, if the temperature difference between the inner surface and the outer surface of the concrete exceeds the standard requirement, the concrete surface is required to be insulated in time, and cracks are prevented from being generated due to the overlarge temperature difference between the inner surface and the outer surface.

(3) Concrete temperature measurement measure

According to the technical specification of temperature measurement and control of mass concrete (GB/T51028-2015), the center of each area is required to be provided with one temperature measuring point, and the temperature measuring point is arranged 100mm away from the edge.

Each point is provided with 3 temperature measuring leads which are arranged at the position 100mm away from the upper surface of the bearing platform, the center of the bearing platform and the position 100mm away from the lower surface of the bearing platform.

During and after concrete pouring, the outdoor environment temperature, the concrete mold-entering temperature, the concrete surface temperature and the concrete internal temperature need to be measured so as to adjust the temperature difference. The temperature measurement requirements are as follows:

a. the concrete mold-entering temperature, the concrete surface temperature and the concrete internal temperature are measured by a JDC-2 portable electronic temperature measuring instrument.

b. And 1 thermometer (which can measure the range of-30-100 ℃) is hung on the bottom plate bracket on the west side and the north side respectively for measuring the outdoor environment temperature.

c. The temperature of the concrete is measured once every 2 hours within 72 hours from the final setting of the concrete at a measuring point, and once every 4 hours from the 4 th to the 7 th days, the temperature measurement lasts for 7 days until the temperature is stable, and the upper, middle and lower temperatures of the bottom plate and the ambient temperature and humidity should be recorded every time of temperature measurement.

(4) Concrete temperature measurement result and treatment

And (4) carrying out statistical calculation according to the highest temperature and the lowest temperature of the temperature measurement records, and immediately taking a heat preservation enhancing measure when the temperature difference between the inside and the outside of the concrete exceeds 25 ℃, so as to reduce the temperature difference between the inside and the outside and prevent cracks from appearing.

And determining the heat preservation and moisture preservation curing time of the concrete according to the field temperature measurement data, wherein the curing time of the mass concrete is not less than 14 days.

When the difference between the internal temperature of the concrete and the surface temperature of the concrete is less than 20, the temperature measurement can be finished.

And when the difference between the surface temperature of the concrete and the ambient temperature is more than 15 ℃, continuing the heat preservation and maintenance.

4. Positive technical effect brought by new process

4.1 project duration optimization aspect

Compared with the domestic built low-temperature storage tank, the bearing platform of the Yunyong port petrochemical low-temperature tank project has shorter completion time and high completion quality. The new processes of the bearing platform five-block partition method, the non-dismantling metal formwork and the like adopted by the project greatly accelerate the advance pace of the whole project, create a working surface for the construction of the outer tank 5 days in advance and lay a solid foundation for the advance completion of the civil engineering construction of the whole storage tank.

4.2 cost reduction aspect

The bearing platform has dense steel bars, narrow working surface and high operation difficulty at the construction joint of the bearing platform partition. The disassembly-free metal mesh is light in weight, easy to cut, easy to bend and easy to operate, and is convenient for the reinforcing steel bars to penetrate through the bearing platform. The construction joint template at the bearing platform partition line adopts the non-dismantling metal mesh template, so that the investment of construction measures is greatly reduced, the complex erecting and dismantling work brought by the traditional template construction method is reduced, and the construction joint roughening treatment time before concrete pouring of adjacent block areas is reduced. Compared with the economic effect of 'wooden template and chiseling', the disassembly-free metal template net saves 70.7 yuan per square meter by using the metal template net.

Claims

1. A large-volume concrete bearing platform construction method of a large-scale low-temperature storage tank is characterized in that the projection of the bearing platform on the horizontal plane is a circle 0; the construction steps are as follows: the method comprises the following steps of cushion concrete pouring → building of a support system at the bottom of a cushion cap → installation of a bottom template → measurement and paying-off → installation of lower-layer steel bars → installation of upper-layer steel bars → installation of inclinometer guide pipes → installation of embedded parts → support of side templates and installation of disassembly-free templates → concrete pouring → concrete curing → template disassembly, and is characterized in that in the concrete cushion cap building method:

1) dividing construction areas and constructing sequence:

the first area adopts a water storage maintenance method;

4.1) selection of concrete raw materials

The cement type is ordinary portland cement;

the fine aggregate is medium sand, the fineness modulus of the fine aggregate is 2.3-3.0, and the mud content is not more than 3%; the coarse aggregate is continuous gradation with the particle size of 5-25 mm, and the mud content is not more than 1%;

4.2) concrete layering

the layered structure is as follows:

B. the layered structures of the second to fifth areas are the same;

4.3) concrete pouring

After the template is sprayed with water and wetted, concrete can be poured;

and (3) retention of the concrete test block: the pouring square amount is 1000m³Every 100m³Sampling once, more than 1000m³Per 200m of³Sampling once, and reserving at least 2 groups of test blocks in each sampling; after the concrete test block is formed, the test block under the same conditions must be placed at a concrete pouring position, and is simultaneously cured with a poured concrete entity, the standard curing test block is placed in a curing chamber for curing after the concrete is formed, the curing temperature is 20 +/-2 ℃, and the humidity is more than 95%;

4.4) treatment of large-volume concrete bleeding

4.5) curing of concrete

2. The method for constructing a concrete cap according to claim 1, wherein the admixture for concrete is required to have a water-reducing rate of not less than 29%; the slump of the concrete is 150-180 mm; when concrete is cured, the water storage depth on the surface of the bearing platform is more than 5 cm; the temperature difference between the inside and the outside of the concrete is controlled to be less than 25 ℃.

3. The method for constructing a concrete cap according to claim 1, wherein a permanent non-dismantling metal formwork net is used as an inter-sectional formwork between adjacent construction areas; the metal net template is fixed by phi 48 steel pipes, and the phi 48 steel pipes are removed after concrete pouring is finished.

4. A method of constructing a concrete cap according to claim 1, wherein said cap base support system building step comprises:

first, template and support system design

when the full supporting system is constructed:

second, cushion layer construction

thirdly, erecting a supporting system

fourth, prepressing test

5. A method for constructing a concrete cap according to claim 1, wherein said lower and upper reinforcing bars are installed by:

2) Steel bar lap joint

and d is the lap joint length of the steel bars.

6. The method for constructing a concrete cap according to claim 1, wherein said sideform erecting and formwork-dismantling-free installing step comprises: