AU2021106549A4 - A construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank - Google Patents
A construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank Download PDFInfo
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- AU2021106549A4 AU2021106549A4 AU2021106549A AU2021106549A AU2021106549A4 AU 2021106549 A4 AU2021106549 A4 AU 2021106549A4 AU 2021106549 A AU2021106549 A AU 2021106549A AU 2021106549 A AU2021106549 A AU 2021106549A AU 2021106549 A4 AU2021106549 A4 AU 2021106549A4
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Abstract
The present invention discloses a construction method for an unbonded prestressed
large-diameter reinforced-concrete thin-walled circular tank, comprising the following steps:
carrying out surveying and setting-out at the construction site on the basis of tank design
conditions; carrying out earth excavation on the basis of the results of surveying and
setting-out; constructing the foundation cushion of the tank; binding the bars of the tank floor
and erect the formwork; placing tank floor concrete; erecting the wall formwork and binding
the wall bars; placing and binding the wall unbonded prestressing bars; placing and curing
wall concrete; prestressed tensioning the wall unbonded prestressing bars; blocking anchor
ends of the wall unbonded prestressing bars; performing watertightness sealing for tank floor
cup; and performing overflowing water test on the tank. The construction method effectively
reduces wall thickness at the same time of ensuring designed functions of a circular tank
during the construction of a circular tank, thereby lowering the construction cost and reducing
the difficulty in construction of the tank.
2/4
Upper large formwork
200 mm high formwork inside the
cup
Find sand inside the cup
Tank floor
Fig. 2
Description
2/4
Upper large formwork
200 mm high formwork inside the cup
Find sand inside the cup
Tank floor
Fig. 2
Technical Field
1. The present invention relates to the field of concrete construction technology, specifically to a construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank.
Background
o Large-scale wastewater treatment plants usually require large-sized bio-treatment tanks,
secondary sedimentation tanks and primary sedimentation tanks. These tanks preferably have circular sections; for some tanks, the diameter can be as great as 60 m with a height of more than 7 m. Traditionally, when a circular tank is designed, the force-bearing conditions are usually met by using ordinary reinforced concrete in vertical design; however, for horizontal design, the large diameter, diurnal and seasonal temperature variations can cause large circumferential tensile stresses, and ordinary reinforced concrete can hardly simultaneously meet the strength and anti-cracking conditions. To satisfy these conditions at the same time, the wall thickness must be increased and the bars must be placed densely. This practice often increases the construction cost of such a large-sized tank, results in waste of resources, and o increases the difficulties in construction.
Summary
The present invention aims to solve the following technical problem: at least solve some of the above technical problems by providing a construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank.
To achieve the objectives above, the technical solution of the present invention is as follows:
a construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank, comprising the following steps:
step 1. carrying out surveying and setting-out at the construction site on the basis of tank design conditions;
step 2. carrying out earth excavation on the basis of the results of surveying and setting-out; step 3. constructing the foundation cushion of the tank; step 4. binding the bars of the tank floor and erect the formwork; step 5. placing the tank floor concrete; step 6. erecting the wall formwork and binding the wall bars; step 7. placing and binding the wall unbonded prestressing bars; step 8. placing and curing the wall concrete; step 9. prestressed tensioning the wall unbonded prestressing bars; step 10. blocking the anchor ends of the wall unbonded prestressing bars; step 11. performing watertightness sealing for the tank floor cup; and step 12. performing overflowing water test on the tank.
Further, in step 5, the floor concrete is pumped for pouring from the tank center and radially outwards; the concrete is properly vibrated during placing to prevent the formation of cold joints; an elevation control bar is welded onto the surface of the reinforcing mesh sheet to control concrete elevation at the tank floor; during placing, a 5 mmx5 mm wire mesh is placed at the intersection between a reinforcing belt and the concrete-placed part of any other members to ensure compliant dimensions of concrete placing of the reinforcing belt; and the concrete meeting the standard for the reinforcing belt is placed when the placing process proceeds to a reinforcing belt, and the concrete intersection between a reinforcing belt and a non-reinforcing belt needs to be further vibrated for better concrete bonding; curing is performed immediately after concrete placing.
Further, in step 7, when the wall unbonded prestressing bars are placed and bound, the specification, dimensions and packing plastic tubes need to be inspected for quality, and leveling and setting-out are performed based on the design positions of the unbonded prestressing bars; when ordinary bars and pipes are installed, the unbonded prestressing bars must pass through smoothly as a priority in construction; in placing, neighboring unbonded prestressing bars are placed in parallel to prevent twisting and tangling; the unbonded prestressing bars are placed with the ends aligned precisely; the pressurized sheet of the tensioned end of an unbonded prestressing bar is perpendicular to the unbonded prestressing bars, with the vertical deviation restricted to 5 mm; the length of exposure of an unbonded prestressing bar is determined on the basis of the length required for the operation of the tensioning machine used; the horizontal curvature of the unbonded prestressing bar is consistent with the curvature of the wall; and after placing and installation, the unbonded prestressing bars need to be inspected and accepted before concrete placing.
Further, in step 6, when the wall formwork is erected, the formwork is erected using the bamboo plywoods coated with film; the dimensions of the wall formwork are 1.22 mx2.44 m; the wall formwork pieces are spliced using 50x100 batten back nails; the wall formwork is generally supported on a double-pole scaffold erected with D48 steel pipes; the double-pole scaffold is supported on a D22 steel hoop buried in the tank floor using a steel pipe diagonal bracing; the horizontal steel pipes of the double-pole scaffold and the steel pipes used to o reinforce the wall formwork are pre-curved according to the curvature of the wall to ensure that the wall formwork has a smooth curvature on surface; the wall formwork is installed horizontally along the length, with the rigidity along the length relatively small to control surface curvature of the formwork; with the wall formwork on one side installed, it is needed to verify formwork curvature and verticality before binding the wall bars and proceeding with the wall formwork on the other side; due to a relatively small working face of the cup connecting the wall and the tank floor, the part of wall inside the cup is supported using a 200 mm high wall formwork; a whole piece of wall formwork is used outside the cup to facilitate removal of the wall formwork and any damage to the formwork; fine sand is filled up inside the cup and outside the wall formwork to prevent grout leakage at the bottom of the wall o formwork placing concrete is placed; after concrete is placed, the fine sand is removed the wall formwork in this position is released; M12 waterstop split bolts are used for splitting between the inner and outer wall formwork, with a 50x50 waterstop strip welded between the split bolts and a ©40x20 plastic gasket fit at the ends, and after concrete shaping, the plastic gaskets are scraped off; and the exposed bolts are cut off and then the surfaces are leveled with waterproofing mortar.
Further, in step 8, when the wall concrete is placed, the pumpcrete is continuously supplied, and stones with small grain size are used to prevent the separation between cement slurry and stones due to the bars densely placed in the wall; at the boundary between placed layers, a vibrating rod is inserted 500 mm into the lower concrete layer to vibrate and better bond concrete; further vibration is needed where the bars are densely placed; and the vibrating rod needs to be inserted into the center of the wall, and any contact with the wall bars, unbonded prestressing bars, tank formwork and screws by the vibrating rod during concrete vibration is not allowed.
Further, in step 9, for prestressed tensioning the unbonded prestressing bars in walls, the post-tensioning method is adopted; a combined mechanism consisting of wire harness heading anchorage and steel strand anchorage is used for anchoring; for the unbonded prestressing bars, high-strength and low-relaxation unbonded steel strands with <pj of 15.24 mm2 are used, of which the standard tensioning strength is fptk=1,860 MPa; YMI5-2 anchorage is used for the tensioning end; before tensioning, the holes are subject to resistivity determination and the tensioning equipment is inspected and tested; tensioning operations are performed after the designed concrete strength is reached; after the unbonded prestressing bars are tensioned as required, the excessive exposed length of the unbonded prestressing bars o is cut away using an abrasive wheel cutting machine; after cutting, the length of the unbonded prestressing bars protruding out of the anchorage clamping piece is no less than 30mm; the surface of wall anchorage rib is roughened and cleaned; the anchorage and the surface of the prestressed sheet are applied with waterproofing coating, with C40 micro-expansive concrete used to seal the tensioning anchorage; curing is carried out immediately; and the sealing concrete at the head of the anchorage zone does not contain oxides.
Further, before performing tensioning, each strand of each section of the unbonded prestressing bars is led through the anchor ring hole; a work anchor is fit into the positioning ring of the backing plate, with a clamping piece inserted close to the anchor backing plate and secured by hammering; a limiting board is fit; the unbonded prestressing bars pass through the o limiting board into a jack; the axis of the jack is superimposed with the unbonded prestressing bars; as the last step, the work anchor is installed; before tensioning, the inner and outer wall formwork is removed to reduce the constraint in tensioning; during tensioning, the wall is divided into eight sections to be tensioned respectively; the opposite ends are tensioned at the same time, and the sections tensioned at the same time are under the same stress; when one section of wall is tensioned, the unbonded prestressing bars at wall top, the unbonded prestressing bars at wall bottom, the unbonded prestressing bars at wall sub-top, the unbonded prestressing bars at wall sub-bottom... are tensioned sequentially; there are no unbonded prestressing bars at the wall center, and the unbonded prestressing bars are tensioned from zero stress to 1.03 times the control stress for tensioning and then anchored.
Further, during prestressed tensioning of the wall unbonded prestressing bars, the stress control method is adopted and the elongation of the unbonded prestressing bars is checked; if the actual elongation is 10% greater or 5% smaller than the calculated elongation, tensioning needs to be stopped to find out the cause and take measures; tensioning is continued with proper adjustment; during tensioning, the tensioning force and rate are strictly controlled, and the prestressed elongation is monitored to prevent breakage of the unbonded prestressing bars; for tensioning, preliminary tensioning is performed at first, i.e. tensioning with 10-30% of the tensioning force; after preliminary tensioning, oil returns to the oil pump, and the elongation is scribed and marked as LO; tensioning is continued till the control tensioning force is reached; loading is performed simultaneously at wall ends in a step-up and alternative way, with 20% of the tensioning force applied for each step; with the tensioning force gradually reaching the designed tensioning tonnage, elongation Li is measured, under which condition the oil pump continues operation at constant pressure and is then stopped for 5 minutes; top o pressure is applied simultaneously at the ends, and then the two ends are simultaneously jacked; after jacking, the oil pump is returned to zero; the retraction amount is measured, and the exposed amount of the clamping piece after unloading the top pressure is measured.
Further, in step 11, after the tensioning of the unbonded prestressing bars is completed, the watertightness treatment for the cup of tank floor is carried out, with a blower and a broom used for cleaning the inside of the cup of the tank floor; polysulfide sealant is adopted for filling and treating the cup of the tank floor for sealing and water-proofing, and a filling and sealing water-proofing treatment height control line is marked on the wall; when the polysulfide sealant is poured, the polysulfide sealant is poured from one point to two sides in a radiation ring direction, and the pouring is finished at one time; For pouring the interface o between the cup of the tank floor and the wall and in the comers between the two, a small-diameter bar tool is used for vibrating to ensure that the pouring is compact, and after the polysulfide sealant is dried, the upper concrete sealing construction is carried out.
Further, in step 12, the overflowing test on the tank is carried out after the cup is subject to watertightness treatment; before the overflowing test on the tank, preformed holes, buried pipe openings and water inlet & outlet need to be temporarily blocked; the water filling and discharging gates are checked against seepage; a water level observation scale is installed on the wall; a calibrated water level point gauge is selected for proper observation position; for the overflowing test, water filling is carried out three times, respectively at 1/3 wall depth, 2/3 wall depth and the designed overflowing position; observation scales are installed 20 cm above and below the water filling positions; in water filling, the rising speed of water level does not exceed 2 m/d; the time interval between water filling is no shorter than 24 hours; the reduction in water level is measured 24 hours after each water filling; water seepage is calculated by taking into account the natural evaporation amount, and when the evaporation amount is determined, a galvanized stainless steel cylindrical bucket filled with half water is hung up aside the tank subject to overflowing test for measuring the unit reduction in 24 hours, which is the evaporation amount.
Compared with the prior art, the present invention has the following beneficial effects:
in the process of constructing a concrete circular tank described in the present invention, when the wall or barrel bars for the structure is bound, the prestressing bars are fixed into the formwork ring by ring based on design requirement, with a support system consisting of large-sized bamboo plywoods and steel pipes used to ensure appearance quality of the wall concrete before concrete is placed. At the same time, the ring-shaped concrete reinforcing o belts are formed on the floor; a large-area floor featured in high waterproof performance is thus constructed with the shrinkage of peripheral concrete compensated by the expansion of concrete of the reinforcing belts. The wall and the floor are constructed as separated structures, with the wall inserted into the floor cup, in which polysulfide sealant is filled for watertightness sealing, with the purpose of reducing the deformation constraint between the wall and the floor and achieve the desired waterproof effect. After the designed concrete strength is reached, unbonded prestressing bars, which are not bonded to concrete and sliding, are tensioned at both ends. Work anchors are used to lock and fix steel strands to the end anchorage board, with the anchor end sealed by concrete to prestress the circular structure. This method improves the content of technology in construction and the efficiency in on-site o construction, reduces the labor intensity for construction personnel, accelerates the construction progress and enhances housekeeping at the site. Meanwhile, the use of large-sized bamboo plywoods realizes higher appearance quality of tank concrete. In comparison with traditional construction methods, the method in the present Invention saves approximately 15% of the cost solely in material, which is highly worthy of promotion.
Brief Description of the Drawings
Fig. 1 is a schematic diagram of forming reinforcing belts in floor concrete placing according to the present invention.
Fig. 2 is a schematic diagram of fabricating a formwork inside a cup during fabrication and installation of a wall formwork according to the present invention.
Fig. 3 is a schematic plan of a tensioning process in prestressed tensioning work according to the present invention.
Fig. 4 is a sectional layout of tensioning the prestressing bars in the prestressed tensioning work according to the present invention.
Fig. 5 is a schematic diagram of blocking the prestressing bar ends in prestressed tensioning work according to the present invention.
Fig. 6 is a schematic diagram of connecting wall and floor in cup watertightness sealing work according to the present invention.
Description of the Preferred Embodiments
In order to make the purpose, technical scheme and advantages of the present invention more clear, the figures shall be referred to further describe the present invention. Apparently, the embodiments as described are simply parts of the embodiments of the present invention, o rather than all of the embodiments. According to the embodiments of the present invention, other embodiments obtained by an ordinary person skilled in the art without creative work also fall into the protection scope of the present invention.
In the description of the present invention, it should be noted that the direction or position relations indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are the direction or position relations based on the drawings, only to facilitate description of the present invention and simplified description, but not to indicate or imply that the indicated device or element must have a special direction, be made or operated in a special direction, thus it cannot be understood as the restriction to the present invention. In addition, the terms "first", "second" and "third" are only used for o describing the purpose, but cannot be understood to indicate or imply relative importance.
In the description of the present invention, it should be noted, unless otherwise explicitly specified and defined, the terms "installation" and "connection" are to be understood in a broad sense, for example, a fixed connection, a removable connection, or an integral connection. Of course, it may also be a mechanical connection or electric connection. In addition, it may also be a direct connection or indirect connection through an intermediate, or internal connection between two elements. For an ordinary person skilled in the art, the specific implications of the above terms in the present invention can be comprehended according to specific conditions.
As shown in Figs. 1-6, the construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank described in the present invention, comprising the following steps: step 1. carrying out surveying and setting-out at the construction site on the basis of tank design conditions.
step 2. carrying out earth excavation on the basis of the results of surveying and setting-out.
step 3. constructing the foundation cushion of the tank.
step 4. binding the bars of the tank floor and erect the formwork.
step 5. placing tank floor concrete. The floor concrete is pumped for pouring from the tank center and radially outwards; concrete is properly vibrated during placing to prevent the formation of cold joints; an elevation control bar is welded onto the surface of the reinforcing mesh sheet to control concrete elevation at the tank floor; during placing, a 5 mmx5 mm wire o mesh is placed at the intersection between a reinforcing belt and the concrete-placed part of any other members to ensure compliant dimensions of concrete placing of the reinforcing belt; and the concrete meeting the standard for the reinforcing belt is placed when the placing process proceeds to a reinforcing belt, and the concrete intersection between a reinforcing belt and a non-reinforcing belt needs to be further vibrated for better concrete bonding; curing is performed immediately after concrete placing.
step 6. erecting the wall formwork and binding the wall bars. When wall formwork is erected, the formwork is erected using bamboo plywoods coated with film; the dimensions of the wall formwork are 1.22 mx2.44 m; the wall formwork pieces are spliced using 50x100 batten back nails; the wall formwork is generally supported on a double-pole scaffold erected with <D48 o steel pipes; the double-pole scaffold is supported on a (D22 steel hoop buried in the tank floor using a steel pipe diagonal bracing; the horizontal steel pipes of the double-pole scaffold and the steel pipes used to reinforce the wall formwork are pre-curved according to the curvature of the wall to ensure that the wall formwork has a smooth curvature on surface; the wall formwork is installed horizontally along the length, with the rigidity along the length relatively small to control surface curvature of the formwork; with the wall formwork on one side installed, it is needed to verify formwork curvature and verticality before binding the wall bars and proceeding with the wall formwork on the other side; due to a relatively small working face of the cup connecting the wall and the tank floor, the part of wall inside the cup is supported using a 200 mm high wall formwork; a whole piece of wall formwork is used outside the cup to facilitate removal of the wall formwork and any damage to the formwork; fine sand is filled up inside the cup and outside the wall formwork to prevent grout leakage at the bottom of the wall formwork placing concrete is placed; after concrete is placed, the fine sand is removed the wall formwork in this position is released; M12 waterstop split bolts are used for splitting between the inner and outer wall formwork, with a 50x50 waterstop strip welded between the split bolts and a <D40x2O plastic gasket fit at the ends, and after concrete shaping, the plastic gaskets are scraped off; and the exposed bolts are cut off and then the surfaces are leveled with waterproofing mortar.
step 7. placing and binding the wall unbonded prestressing bars. When the wall unbonded prestressing bars are placed and bound, the specification, dimensions and packing plastic tubes need to be inspected for quality, and leveling and setting-out are performed based on the design positions of the unbonded prestressing bars; when ordinary bars and pipes are installed, o the unbonded prestressing bars must pass through smoothly as a priority in construction; in placing, neighboring unbonded prestressing bars are placed in parallel to prevent twisting and tangling; the unbonded prestressing bars are placed with the ends aligned precisely; the pressurized sheet of the tensioned end of an unbonded prestressing bar is perpendicular to the unbonded prestressing bars, with the vertical deviation restricted to 5 mm; the length of exposure of an unbonded prestressing bar is determined on the basis of the length required for the operation of the tensioning machine used; the horizontal curvature of the unbonded prestressing bar is consistent with the curvature of the wall; and after placing and installation, the unbonded prestressing bars need to be inspected and accepted before concrete placing.
step 8. placing and curing wall concrete. When the wall concrete is placed, the pumpcrete is o continuously supplied, and the stones with small grain size are used to prevent the separation between cement slurry and stones due to the bars densely placed in the wall; at the boundary between placed layers, a vibrating rod is inserted 500 mm into the lower concrete layer to vibrate and better bond concrete; further vibration is needed where the bars are densely placed; and the vibrating rod needs to be inserted into the center of the wall, and any contact with the wall bars, unbonded prestressing bars, tank formwork and screws by the vibrating rod during concrete vibration is not allowed.
step 9. prestressed tensioning the wall unbonded prestressing bars. For prestressed tensioning the unbonded prestressing bars in walls, the post-tensioning method is adopted; a combined mechanism consisting of wire harness heading anchorage and steel strand anchorage is used for anchoring; for the unbonded prestressing bars, high-strength and low-relaxation unbonded steel strands with pj of 15.24 mm2 are used, of which the standard tensioning strength is fptk=1,860 MPa; YMI5-2 anchorage is used for the tensioning end; before tensioning, the holes are subject to resistivity determination and the tensioning equipment is inspected and tested; tensioning operations are performed after the designed concrete strength is reached; after the unbonded prestressing bars are tensioned as required, the excessive exposed length of the unbonded prestressing bars is cut away using an abrasive wheel cutting machine; after cutting, the length of the unbonded prestressing bars protruding out of the anchorage clamping piece is no less than 30mm; the surface of wall anchorage rib is roughened and cleaned; the anchorage and the surface of the prestressed sheet are applied with waterproofing coating, with C40 micro-expansive concrete used to seal the tensioning anchorage; curing is carried out immediately; and the sealing concrete at the head of the anchorage zone does not contain oxides.
o Before performing tensioning, each strand of each section of the unbonded prestressing bars is led through the anchor ring hole; a work anchor is fit into the positioning ring of the backing plate, with a clamping piece inserted close to the anchor backing plate and secured by hammering; a limiting board is fit; the unbonded prestressing bars pass through the limiting board into a jack; the axis of the jack is superimposed with the unbonded prestressing bars; as the last step, the work anchor is installed; before tensioning, the inner and outer wall formwork is removed to reduce the constraint in tensioning; during tensioning, the wall is divided into eight sections to be tensioned respectively; the opposite ends are tensioned at the same time, and the sections tensioned at the same time are under the same stress; when one section of wall is tensioned, the unbonded prestressing bars at wall top, the unbonded o prestressing bars at wall bottom, the unbonded prestressing bars at wall sub-top, the unbonded prestressing bars at wall sub-bottom... are tensioned sequentially; there are no unbonded prestressing bars at the wall center, and the unbonded prestressing bars are tensioned from zero stress to 1.03 times the control stress for tensioning and then anchored.
During prestressed tensioning of the wall unbonded prestressing bars, the stress control method is adopted and the elongation of the unbonded prestressing bars is checked; if the actual elongation is 10% greater or 5% smaller than the calculated elongation, tensioning needs to be stopped to find out the cause and take measures; tensioning is continued with proper adjustment; during tensioning, the tensioning force and rate are strictly controlled, and the prestressed elongation is monitored to prevent breakage of the unbonded prestressing bars; for tensioning, preliminary tensioning is performed at first, i.e. tensioning with 10-30% of the tensioning force; after preliminary tensioning, oil returns to the oil pump, and the elongation is scribed and marked as LO; tensioning is continued till the control tensioning force is reached; loading is performed simultaneously at wall ends in a step-up and alternative way, with 20% of the tensioning force applied for each step; with the tensioning force gradually reaching the designed tensioning tonnage, elongation Li is measured, under which condition the oil pump continues operation at constant pressure and is then stopped for 5 minutes; top pressure is applied simultaneously at the ends, and then the two ends are simultaneously jacked; after jacking, the oil pump is returned to zero; the retraction amount is measured, and the exposed amount of the clamping piece after unloading the top pressure is measured.
step 10. blocking the anchor ends of the wall unbonded prestressing bars.
step 11. performing watertightness sealing for tank floor cup. After the tensioning of the unbonded prestressing bars is completed, the watertightness treatment for the cup of the tank o floor is carried out, with a blower and a broom used for cleaning the inside of the cup of the tank floor; polysulfide sealant is adopted for filling and treating the cup of the tank floor for sealing and water-proofing, and a filling and sealing water-proofing treatment height control line is marked on the wall; when the polysulfide sealant is poured, the polysulfide sealant is poured from one point to two sides in a radiation ring direction, and the pouring is finished at one time; For pouring the interface between the cup of the tank floor and the wall and in the corners between the two, a small-diameter bar tool is used for vibrating to ensure that the pouring is compact, and after the polysulfide sealant is dried, the upper concrete sealing construction is carried out.
step 12. performing overflowing water test on the tank. The overflowing test on the tank is o carried out after the cup is subject to watertightness treatment; before the overflowing test on the tank, preformed holes, buried pipe openings and water inlet & outlet need to be temporarily blocked; the water filling and discharging gates are checked against seepage; a water level observation scale is installed on the wall; a calibrated water level point gauge is selected for proper observation position; for the overflowing test, water filling is carried out three times, respectively at 1/3 wall depth, 2/3 wall depth and the designed overflowing position; observation scales are installed 20 cm above and below the water filling positions; in water filling, the rising speed of water level does not exceed 2 m/d; the time interval between water filling is no shorter than 24 hours; the reduction in water level is measured 24 hours after each water filling; water seepage is calculated by taking into account the natural evaporation amount, and when the evaporation amount is determined, a galvanized stainless steel cylindrical bucket filled with half water is hung up aside the tank subject to overflowing test for measuring the unit reduction in 24 hours, which is the evaporation amount.
With the construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank described in the present invention, the wall thickness of a 60 m diameter and 7.8 m high tank can be 300 mm. The unbonded prestressing steel strands need to be applied with lubricating and anticorrosive coatings including asphalt, etc. along the full length of the prestressing bars, which are protected by casings. The main principle is that there is no cohesive force generated between the prestressing bars and the concrete, and the advantages including no grouting, simple construction flows, relatively small tensioning frictional resistance are realized in comparison with bonded prestressing bars. With unbonded prestressing reinforced concrete placed with the post-tensioning method, the tank resists o concrete shrinkage and expansion effectively; with fewer microfractures formed, the tank has a higher anti-seepage capability to meet the designed functions.
In the present invention, the construction technology with unbonded prestressing steel strands is adopted to keep the overall tank structure undisturbed and optimize the tank strength and anti-seepage performance; the construction equipment for unbonded prestressing steel strands is simply structured and easy to operate; with no deformation joints or post-cast strips made in an ultra-long circular concrete tank wall and a large-area concrete floor, there will be no cracks formed in concrete and thus the waterproof capability is improved; with the formwork fabricated from bamboo plywoods coated with film, it is easier to control appearance quality of wall concrete, accelerate the construction progress and increase material turnarounds; o 50x50 water stops are provided for formwork split screws to effectively ensure high anti-seepage performance of the tank; separated wall and floor structures reduce the deformation constraint between the wall and the floor; construction materials are saved; the non-bonded prestressing construction technology reduces the consumption of concrete by 20%-40% and the consumption of the non-prestressing bars by 20%.
In the process of constructing a concrete circular tank described in the present invention, when binding the wall or barrel bars for the structure, the prestressing bars are fixed into the formwork ring by ring based on design requirement, with a support system consisting of large-sized bamboo plywoods and steel pipes used to ensure appearance quality of the wall concrete before concrete is placed. At the same time, ring-shaped concrete reinforcing belts are formed on the floor; a large-area floor featured in high waterproof performance is thus constructed with the shrinkage of peripheral concrete compensated by the expansion of concrete of the reinforcing belts. The wall and the floor are constructed as separated structures, with the wall inserted into the floor cup, in which polysulfide sealant is filled for watertightness sealing, with the purpose of reducing the deformation constraint between the wall and the floor and achieve the desired waterproof effect. After the designed concrete strength is reached, unbonded prestressing bars, which are not bonded to concrete and sliding, are tensioned at both ends. Work anchors are used to lock and fix steel strands to the end anchorage board, with the anchor end sealed by concrete to prestress the circular structure.
When floor concrete is placed in the present invention, the floor concrete is pumped for pouring from the tank center and radially outwards; concrete is properly vibrated during placing to prevent the formation of cold joints. An elevation control bar is welded onto the surface of the reinforcing mesh sheet to control concrete elevation at tank floor; during o placing, a 5 mmx5 mm wire mesh is placed at the intersection between a reinforcing belt and the concrete-placed part of any other members to ensure compliant dimensions of concrete placing of the reinforcing belt, as shown in Fig. 1. concrete with different mix proportions meeting the standard for the reinforcing belt is placed when the placing process proceeds to a reinforcing belt, with C30 expansive concrete used, and the concrete intersection between a reinforcing belt and a non-reinforcing belt needs to be further vibrated for better concrete bonding; curing is performed immediately after concrete placing.
In process of laying unbonded prestressing steel strands in the present invention, before laying unbonded prestressing bars, the specification, dimensions and packing plastic tubes need to be inspected for quality, and leveling and setting-out are performed based on the design positions o of unbonded prestressing bars. When ordinary bars and pipes are installed, the unbonded prestressing bars must pass through smoothly as a priority in construction. Each unbonded prestressing bar shall be placed in parallel to prevent twisting and tangling. prestressing bars are placed with the ends aligned precisely. The bearing boards at the tensioning ends are perpendicular to the prestressing bars, with the vertical deviation restricted to 5 mm. The length of exposure of an unbonded prestressing bar is determined on the basis of the length required for the operation of the tensioning machine used. prestressing bars are installed in designed positions; the horizontal curvature of a bar is consistent with the curvature of the wall. After placing and installation, unbonded prestressing bars need to be inspected and accepted before concrete placing.
When wall formwork is fabricated and installed in the present invention, the formwork is erected using bamboo plywoods coated with film; the dimensions of the formwork are 1.22 mx2.44 m; the wall formwork pieces are spliced using 50x100 batten back nails; the wall formwork is generally supported on a double-pole scaffold erected with <D48 steel pipes. The double-pole scaffold is supported on a D22 steel hoop buried in the tank floor using a steel pipe diagonal bracing; the horizontal steel pipes of the steel pipe scaffold and the steel pipes used to reinforce the formwork are pre-curved to ensure that the formwork has a smooth curvature on surface. The formwork is installed horizontally along the length, with the rigidity along the length relatively small to control surface curvature of the formwork; with the wall formwork on one side installed, it is needed to verify formwork curvature and verticality before binding the wall bars and proceeding with the wall formwork on the other side.Due to a relatively small working face of the cup connecting the wall and the floor, the part of wall inside the cup is supported using a 200 mm high wall formwork; a whole piece of wall o formwork is used outside the cup to facilitate removal of the formwork and to avoid any damage to the large formwork, as shown in Fig. 2. To prevent grout leakage at the bottom of the formwork, fine sand is filled up inside the cup and outside the formwork; after concrete is placed, the fine sand is removed the wall formwork in this position is released. M12 waterstop split bolts are used for splitting between the inner and outer wall formwork with a spacing of 450x500. A 50x50 waterstop strip is welded between the split bolts and a <D40x20 plastic gasket fit at the ends, and after concrete shaping, the plastic gaskets are scraped off, the exposed bolts are cut off and then the surfaces are leveled with waterproofing mortar. If no exterior decoration is designed for the tank, leveling needs to be carried out in a way to ensure aesthetics of tank wall.
o In the present invention, placing wall concrete can be difficult due to the high and thin tank wall, in which the bars are densely placed after the formwork is erected, thus the following precautions need to be followed in the process of placing: (1) pumpcrete is recommended for pacing the tank wal; concrete needs to be supplied continuously. Considering bar binding in the tank wall, stones of small grain size are used in concrete to prevent the separation of cement slurry and stones.
(2) At the boundary between placed layers, a vibrating rod is inserted 500mm into the lower concrete layer to vibrate and better bond concrete; further vibration is needed where the bars are densely placed.
(3) The vibrating rod needs to be inserted into the center of the wall, and any contact with the bars, the unbonded prestressing steel strands, the formwork and the screws by the vibrating rod during concrete vibration is not allowed.
In the prestressed tensioning work described in the present invention, the post-tensioning method is adopted on the basis of characteristics of hydraulic structures; a combined mechanism consisting of wire harness heading anchorage and steel strand anchorage is used for anchoring; for prestressing bars, high-strength and low-relaxation unbonded steel strands with pj of 15.24 mm2 are used, of which the standard tensioning strength is fptk=1,860 MPa; YMI5-2 anchorage is used for the tensioning end. Before tensioning, the holes are subject to resistivity determination. The tensioning equipment is inspected and tested. Tensioning operations: each strand of each section of the steel strands is led through the anchor ring hole; a work anchor is fit into the positioning ring of the backing plate, with a clamping piece inserted close to the anchor backing plate and secured by hammering; a limiting board is fit; o the steel strands pass through the limiting board into a jack; before installing the jack, the axis of the jack is superimposed with the axis of the steel strand; a work anchor is installed.
In the present invention, the prestressing bars are tensioned after the designed concrete strength is reached. Before tensioning, the inner and outer formwork of the wall is released to reduce the tensioning constraint. prestressing bars are tensioned in 8 sections for each ring, as shown in Fig. 3. The ends of each section are tensioned symmetrically at the same time, that is, sections 1 and 5, sections 2 and 6, sections 3 and 7 and sections 4 and 8 are tensioned at the same time, with the end stress controlled to be uniform. prestressing bars are tensioned from zero stress to 1.03 times the control stress for tensioning, and then anchored in the order shown in Fig. 4: HJ1, HJ12, HJ2, HJ11, ... HJ6, HJ7.
o Initial tensioning in the present invention: 10-30%; oil returns, and the elongation is scribed and marked as LO; Tensioning is continued till the control tensioning force is reached; loading is performed simultaneously at wall ends in a step-up and alternative way, with 20% of the tensioning force applied for each step; with the tensioning force gradually reaching the designed tensioning tonnage, elongation LI is measured, under which condition the oil pump continues operation at constant pressure and is then stopped for 5 minutes; top pressure is applied simultaneously at the ends, and then the two ends are simultaneously jacked; after jacking, the oil pump is returned to zero; the retraction amount is measured, and the exposed amount of the clamping piece after unloading the top pressure is measured.
In the present invention, the stress control method is adopted for tensioning, with the elongation of prestressing bars verified. If the actual elongation is 10% greater or 5% smaller than the calculated elongation, tensioning needs to be stopped to find out the cause and take measures; tensioning is continued with proper adjustment. During tensioning in the present invention, the tensioning force and rate are strictly controlled, and the prestressed elongation is monitored to prevent breakage of unbonded prestressing bars. In the present invention, after the unbonded prestressing bars are tensioned as required, the excessive exposed length of the unbonded prestressing bars is cut away using an abrasive wheel cutting machine; after cutting, the length of the unbonded prestressing bars protruding out of the anchorage clamping piece is no less than 30mm; the surface of wall anchorage rib is roughened and cleaned; the anchorage and the surface of the prestressed board are applied with waterproofing coating, with C40 micro-expansive concrete used for secure blocking; curing is carried out immediately, and the sealing concrete at the head of the anchorage zone does not contain oxides. Anchor end blocking in the present invention: after tensioning and anchoring, the o excessive length of prestressing bars is cut off. The length of the prestressing bars protruding out of the anchorage clamping piece is no less than 30 mm. Then the tensioning anchorage is blocked using C40 fine aggregate concrete. The blocking of tensioning ends is as shown in Fig. 5.
In the present invention, for cup watertightness sealing, the wall and the floor are connected as shown in Fig. 6. Cup watertightness sealing is carried out after the tensioning of prestressing bars. Before grouting, a blower and a broom are used to clean the inside of the cup, with a filling height control line marked on the wall. The polysulfide sealant is poured from one point to two sides in a radiation ring direction, and the pouring is finished at one time. Small-diameter bars or other proper tools are used to vibrate concrete at filling the o openings, edges, corners, etc. to ensure dense filling. Upper concrete sealing is carried out after the polysulfide-sealed surface is dried.
In the present invention, the overflowing test is performed after the work on cup watertightness sealing is completed. Before the overflowing test on the tank, preformed holes, buried pipe openings and water inlet & outlet need to be temporarily blocked; the water filling and discharging gates are checked against seepage. The tank is usually filled in 3 times. A water level observation scale is installed on the wall; a calibrated water level point gauge is selected for proper observation position, respectively at 1/3 wall depth, 2/3 wall depth and the designed overflowing position. Observation scales are installed approximately 20 cm above and below the three positions The natural evaporation amount is taken into account for the test. When the evaporation amount is determined, a cylindrical bucket filled with half water is used. The container is preferably steel or galvanized material, which is hung up aside the tested tank for the measurement of the 24-hour water loss per unit, i.e. the evaporation amount, and the result is recorded. In water filling, the rising speed of water level does not exceed 2 m/d; the time interval between water filling is no shorter than 24 hours. The reduction in water level is measured 24 hours after each water filling, and water seepage is calculated.
) The following materials and equipment are used in the present invention. Main materials: C15 concrete, C30 concrete, C40 concrete, bamboo plywoods coated with film, M12 waterstop 5 split bolts, steel strands, steel wires, heat-treated steel bars for prestressing, ordinary bars of various sizes, polysulfide sealant and other auxiliary materials.
Table 1 Main Equipment and Tools
S/N Equipment name Unit Quantity Remarks 1 Electric saw Set 4 2 Electric planer Set 4
3 Manual saw Set 8 Adjusted on the basis of site conditions
4 Electrically Set 2 powered drill 5 Cutting-off machine Set 2 6 Bending machine Set 2
7 Butt welding Set 4 machine
8 Electric welding Set 4 machine
9 Abrasive wheel Set 2 cutting machine 11 Jack Set 12 12 Oil pump Set 12 13 Small jack Set 2 Standby 14 Pressure gauge Set 12 0.4-levelpxcision 15 Small blower Set 1 For cup cleaning 16 Crane Set 2 Liftingfornwoketc.
For quality control during construction in the present invention,
Table 2 Quality Control for Main Tensioning Processes
S/N Process description Technical standard Inspection method
3 Error in elongation of +6% Tape measurement steel strand
No more than one piece broken in a strand Obseation and Strand slipping and 4 breakage No more than 1% total wires in the same Observation and section record Slipping in each strand no more than 2% Tape measurement elongation of the strand and calculation
5 Anchorage of steel 5cm reserved beyond work anchor Tape measurement strand 4 Stress inspection and test Measured value not 5% higher and 3% Test records lower than design value
Before the construction process in the present invention, materials, mechanical equipment and tensioning processes need to be inspected. Mobilized steel strands must be provided with quality certificates and meet the designed condition of 186 Mpa and the provisions in the current standard (Unbonded PrestressingSteel Strands, JG/T 161-2016) . After mobilization,
steel strands are accepted in batches, which are checked for damage, rust and oil; slight floating rust is permitted, but there shall be no pockmark visible to the naked eye. Steel strands are subject to tests on mechanical properties roll by roll, and the properties shall conform to the standards. Steel strands must be cut by an abrasive wheel cutting machine. The cut ends are bound with 20# galvanized steel wires to prevent loosening after cutting. Before stranding, steel strands shall be straightened out. Then, steel strands are bound, with tags attached and numbers designated according to the design drawing. In the process of steel strand construction, welding sparks are strictly prohibited to touch the steel strand. Check the equipment inspection report and ensure that the pressure gauge and the jack as well as the oil meter and the pressure gauge are well matched. After the tensioning process is completed, tensioned bars shall be inspected, focusing on the following positions: positions bearing heavy loads, anchor heads and positions where abnormal conditions occur during construction. Quality management system documents are prepared and management is carried out in the
production process in strict accordance with the procedures in the Quality Management System Document (IS09000).
Housekeeping is a requirement for construction in the present invention. Machinery and equipment operators shall work with permits; personnel engaged in different jobs on site shall strictly comply with the technical procedures for safe operation, who shall focus on the work, work carefully, do not leave the site without permission, and never operate the machinery drunk; faulty mechanical equipment must be immediately maintained and repaired. Equipment shall never be operated with a fault or in violation of codes to eliminate accidents in construction; personnel at the site shall keep records of the jobs accurately and timely and implement safety systems strictly. Work areas and hours are arranged properly to ensure normal working of construction personnel; wafety warning signs need to be set up in working areas; equipment and tools are arranged neatly and orderly; construction scaffolds must be stable and safe, and construction workers working at height must wear safety ropes. The safe operating procedures for prestressed tensioning shall be followed.
During the construction process in the present invention, environmental protection measures must be taken, with an environmental protection system and a water protection system led by the Project Manager established under the Project Department. Environmental and water protection groups are set up under the Project Department to strictly implement laws and regulations on environmental protection. The regulations, guidelines, policies and ordinances promulgated by the state and local governments on environmental protection and soil and water conservation are strictly implemented, in combination with the design documents and project requirements; relevant environmental protection designs are submitted in a timely o manner and construction activities are implemented according to approved documents. Environmental protection measures are the responsibilities of specially appointed personnel, who shall carry out inspections on a regular basis. Enhanced education on environmental protection awareness is provided for construction teams to further implement relevant policies.
The technology described in the present invention brings along the following economic and social benefits: as a scientific and technological progress promotion program, the application of the construction technology of unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank effectively improves the content of technology in construction and the efficiency in on-site construction, reduces the labor intensity for construction personnel, o accelerates the construction progress and enhances housekeeping at the site. Meanwhile, the use of large-sized bamboo plywoods realizes higher appearance quality of tank concrete. The adoption of the unbonded prestressing technology saves approximately 15% of the cost solely in material, which is highly worthy of promotion.
Finally, it is noted that the above embodiments are only the superior embodiments of the present invention used to explain the technical solution of the present invention and shall not be construed as a limitation, surely not restricting the scope of patent of the present invention; Although the present invention is described in detail with reference to the embodiments, ordinary technical personnel in the art should understand that they can still modify the technical proposal recorded in the embodiments or equivalently replace some or all of technical features. These modifications or replacements do not make the essence of the corresponding technical proposal break away from the range of technical proposal of the embodiments in the present invention; that is, all modifications or polishing without any substantive meaning based on the main design idea and spirit of the present invention should fall into the protection scope of the present invention if they still solve the technical problem which is consistent with the one of the present invention; besides, the application of the technical solution in the present invention, either director or indirectly, to other relevant technical fields, is similarly included in the scope of patent protection of the present invention.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.
It will be understood that the terms "comprise" and "include" and any of their derivatives (e.g. o comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.
In some cases, a single embodiment may, for succinctness and/or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. o Further a phrase referring to "at least one of' a list of items refers to any combination of those items, including single members. As an example, "at least one of: a, b, or c" is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
Claims (10)
1. A construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank, characterized by comprising the following steps:
step 1. carrying out surveying and setting-out at the construction site on the basis of tank design conditions;
step 2. carrying out earth excavation on the basis of the results of surveying and setting-out;
step 3. constructing the foundation cushion of the tank;
step 4. binding the bars of the tank floor and erect the formwork;
step 5. placing the tank floor concrete;
step 6. erecting the wall formwork and binding the wall bars;
step 7. placing and binding the wall unbonded prestressing bars;
step 8. placing and curing the wall concrete;
step 9. prestressed tensioning the wall unbonded prestressing bars;
step 10. blocking the anchor ends of the wall unbonded prestressing bars;
step 11. performing watertightness sealing for the tank floor cup; and
step 12. performing overflowing water test on the tank.
2. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 5, the floor concrete is pumped for pouring from the tank center and radially outwards; the concrete is properly vibrated during placing to prevent the formation of cold joints; an elevation control bar is welded onto the surface of the reinforcing mesh sheet to control concrete elevation at the tank floor; during placing, a 5 mmx5 mm wire mesh is placed at the intersection between a reinforcing belt and the concrete-placed part of any other members to ensure compliant dimensions of concrete placing of the reinforcing belt; and the concrete meeting the standard for the reinforcing belt is placed when the placing process proceeds to a reinforcing belt, and the concrete intersection between a reinforcing belt and a non-reinforcing belt needs to be further vibrated for better concrete bonding; curing is performed immediately after concrete placing.
3. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 7, when the wall unbonded prestressing bars are placed and bound, the specification, dimensions and packing plastic tubes need to be inspected for quality, and leveling and setting-out are performed based on the design positions of the unbonded prestressing bars; when ordinary bars and pipes are installed, the unbonded prestressing bars must pass through smoothly as a priority in construction; in placing, neighboring unbonded prestressing bars are placed in parallel to prevent twisting and tangling; the unbonded prestressing bars are placed with the ends aligned precisely; the pressurized sheet of the tensioned end of an unbonded prestressing bar is perpendicular to the unbonded prestressing bars, with the vertical deviation restricted to 5 mm; the length of exposure of an unbonded prestressing bar is determined on the basis of the length required for the operation of the tensioning machine used; the horizontal curvature of the unbonded prestressing bar is consistent with the curvature of the wall; and after placing and installation, the unbonded prestressing bars need to be inspected and accepted before concrete placing.
4. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 6, when the wall formwork is erected, the formwork is erected using the bamboo plywoods coated with film; the dimensions of the wall formwork are 1.22 mx2.44 m; the wall formwork pieces are spliced using 50x100 batten back nails; the wall formwork is generally supported on a double-pole scaffold erected with <D48 steel pipes; the double-pole scaffold is supported on a (D22 steel hoop buried in the tank floor using a steel pipe diagonal bracing; the horizontal steel pipes of the double-pole scaffold and the steel pipes used to reinforce the wall formwork are pre-curved according to the curvature of the wall to ensure that the wall formwork has a smooth curvature on surface; the wall formwork is installed horizontally along the length, with the rigidity along the length relatively small to control surface curvature of the formwork; with the wall formwork on one side installed, it is needed to verify formwork curvature and verticality before binding the wall bars and proceeding with the wall formwork on the other side; due to a relatively small working face of the cup connecting the wall and the tank floor, the part of wall inside the cup is supported using a 200 mm high wall formwork; a whole piece of wall formwork is used outside the cup to facilitate removal of the wall formwork and any damage to the formwork; fine sand is filled up inside the cup and outside the wall formwork to prevent grout leakage at the bottom of the wall formwork placing concrete is placed; after concrete is placed, the fine sand is removed the wall formwork in this position is released; M12 waterstop split bolts are used for splitting between the inner and outer wall formwork, with a 50x50 waterstop strip welded between the split bolts and a <D40x2 plastic gasket fit at the ends, and after concrete shaping, the plastic gaskets are scraped off; and the exposed bolts are cut off and then the surfaces are leveled with waterproofing mortar.
5. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 8, when the wall concrete is placed, the pumpcrete is continuously supplied, and stones with small grain size are used to prevent the separation between cement slurry and stones due to the bars densely placed in the wall; at the boundary between placed layers, a vibrating rod is inserted 500 mm into the lower concrete layer to vibrate and better bond concrete; further vibration is needed where the bars are densely placed; and the vibrating rod needs to be inserted into the center of the wall, and any contact with the wall bars, unbonded prestressing bars, tank formwork and screws by the vibrating rod during concrete vibration is not allowed.
6. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 9, for prestressed tensioning the unbonded prestressing bars in walls, the post-tensioning method is adopted; a combined mechanism consisting of wire harness heading anchorage and steel strand anchorage is used for anchoring; for the unbonded prestressing bars, high-strength and low-relaxation unbonded steel strands with pj of 15.24 mm2 are used, of which the standard tensioning strength is fptk=1,860 MPa; YMI5-2 anchorage is used for the tensioning end; before tensioning, the holes are subject to resistivity determination and the tensioning equipment is inspected and tested; tensioning operations are performed after the designed concrete strength is reached; after the unbonded prestressing bars are tensioned as required, the excessive exposed length of the unbonded prestressing bars is cut away using an abrasive wheel cutting machine; after cutting, the length of the unbonded prestressing bars protruding out of the anchorage clamping piece is no less than 30mm; the surface of wall anchorage rib is roughened and cleaned; the anchorage and the surface of the prestressed sheet are applied with waterproofing coating, with C40 micro-expansive concrete used to seal the tensioning anchorage; curing is carried out immediately; and the sealing concrete at the head of the anchorage zone does not contain oxides.
7. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 6, characterized in that, before performing tensioning, each strand of each section of the unbonded prestressing bars is led through the anchor ring hole; a work anchor is fit into the positioning ring of the backing plate, with a clamping piece inserted close to the anchor backing plate and secured by hammering; a limiting board is fit; the unbonded prestressing bars pass through the limiting board into a jack; the axis of the jack is superimposed with the unbonded prestressing bars; as the last step, the work anchor is installed; before tensioning, the inner and outer wall formwork is removed to reduce the constraint in tensioning; during tensioning, the wall is divided into eight sections to be tensioned respectively; the opposite ends are tensioned at the same time, and the sections tensioned at the same time are under the same stress; when one section of wall is tensioned, the unbonded prestressing bars at wall top, the unbonded prestressing bars at wall bottom, the unbonded prestressing bars at wall sub-top, the unbonded prestressing bars at wall sub-bottom... are tensioned sequentially; there are no unbonded prestressing bars at the wall center, and the unbonded prestressing bars are tensioned from zero stress to 1.03 times the control stress for tensioning and then anchored.
8. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 6, characterized in that, during prestressed tensioning of the wall unbonded prestressing bars, the stress control method is adopted and the elongation of the unbonded prestressing bars is checked; if the actual elongation is 10% greater or 5% smaller than the calculated elongation, tensioning needs to be stopped to find out the cause and take measures; tensioning is continued with proper adjustment; during tensioning, the tensioning force and rate are strictly controlled, and the prestressed elongation is monitored to prevent breakage of the unbonded prestressing bars; for tensioning, preliminary tensioning is performed at first, i.e. tensioning with 10 -3 0 % of the tensioning force; after preliminary tensioning, oil returns to the oil pump, and the elongation is scribed and marked as LO; tensioning is continued till the control tensioning force is reached; loading is performed simultaneously at wall ends in a step-up and alternative way, with 20% of the tensioning force applied for each step; with the tensioning force gradually reaching the designed tensioning tonnage, elongation Li is measured, under which condition the oil pump continues operation at constant pressure and is then stopped for 5 minutes; top pressure is applied simultaneously at the ends, and then the two ends are simultaneously jacked; after jacking, the oil pump is returned to zero; the retraction amount is measured, and the exposed amount of the clamping piece after unloading the top pressure is measured.
9. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 11, after the tensioning of the unbonded prestressing bars is completed, the watertightness treatment for the cup of tank floor is carried out, with a blower and a broom used for cleaning the inside of the cup of the tank floor; polysulfide sealant is adopted for filling and treating the cup of the tank floor for sealing and water-proofing, and afilling and sealing water-proofing treatment height control line is marked on the wall; when the polysulfide sealant is poured, the polysulfide sealant is poured from one point to two sides in a radiation ring direction, and the pouring is finished at one time; For pouring the interface between the cup of the tank floor and the wall and in the comers between the two, a small-diameter bar tool is used for vibrating to ensure that the pouring is compact, and after the polysulfide sealant is dried, the upper concrete sealing construction is carried out.
10. The construction method for an unbonded prestressed large-diameter reinforced-concrete thin-walled circular tank according to claim 1, characterized in that, in step 12, the overflowing test on the tank is carried out after the cup is subject to watertightness treatment; before the overflowing test on the tank, preformed holes, buried pipe openings and water inlet & outlet need to be temporarily blocked; the water filling and discharging gates are checked against seepage; a water level observation scale is installed on the wall; a calibrated water level point gauge is selected for proper observation position; for the overflowing test, water filling is carried out three times, respectively at 1/3 wall depth, 2/3 wall depth and the designed overflowing position; observation scales are installed 20 cm above and below the water filling positions; in water filling, the rising speed of water level does not exceed 2 m/d; the time interval between water filling is no shorter than 24 hours; the reduction in water level is measured 24 hours after each water filling; water seepage is calculated by taking into account the natural evaporation amount, and when the evaporation amount is determined, a galvanized stainless steel cylindrical bucket filled with half water is hung up aside the tank subject to overflowing test for measuring the unit reduction in 24 hours, which is the evaporation amount.
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| CN114908970B (en) * | 2022-06-15 | 2024-03-26 | 中交一公局第六工程有限公司 | Construction technology of ultra-high super-thick tank wall of sewage treatment plant |
| CN115162731A (en) * | 2022-06-16 | 2022-10-11 | 北京市政路桥股份有限公司 | Pool construction method based on prestress engineering |
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| CN202954585U (en) * | 2012-12-24 | 2013-05-29 | 中国市政工程华北设计研究总院 | Externally bound type unbonded prestressed circular water basin |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115142722A (en) * | 2022-06-10 | 2022-10-04 | 河南沃克曼建设工程有限公司 | Accurate positioning and rapid construction method for circular pool template of large sewage treatment plant |
| CN115142722B (en) * | 2022-06-10 | 2024-04-05 | 河南沃克曼建设工程有限公司 | Precise positioning and rapid construction method for circular pool template of large sewage treatment plant |
Also Published As
| Publication number | Publication date |
|---|---|
| CN112663774A (en) | 2021-04-16 |
| AU2021106549B4 (en) | 2023-06-15 |
| CN112663774B (en) | 2022-06-28 |
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