CN114892887A - Prestressed precast beam and superposed beam formed by same - Google Patents

Abstract

The invention discloses a prestressed precast beam and a superposed beam formed by the prestressed precast beam, wherein the prestressed precast beam integrally adopts a U-shaped section, the self weight can be reduced by 30-55 percent, the on-site hoisting is convenient, and the cost of a hoisting machine is reduced; the connecting ribs are arranged along the length direction of the U-shaped prestressed precast beam at intervals, so that the lateral rigidity of the U-shaped prestressed precast beam is increased, and the lateral deflection deformation of the prestressed precast beam after the prestressing force is released and tensioned is reduced; and post-cast concrete is cast on a construction site to form the integral superposed beam, and the inner wall of the U-shaped section of the prestressed precast beam is provided with a key slot or shear steel bars to enhance the common working performance of the precast part and the post-cast part of the superposed beam. The invention does not need to control the self weight of the precast beam by reducing the section height of the precast beam or a method for forming a large composite beam by splicing small precast beams, can really realize the construction of the precast beam without supporting a formwork and a floor slab without supporting on a construction site, has less high-altitude operation on the site and less construction safety risk, and simultaneously the stress performance of the formed composite beam is basically consistent with that of the integral cast-in-place beam.

Description

Prestressed precast beam and superposed beam composed of same

Technical Field

The invention belongs to the technical field of buildings, relates to an assembled concrete building, and particularly relates to a prestressed precast beam and a composite beam formed by the prestressed precast beam.

Background

For multi-storey warehouses and industrial plants, the floor load and the beam span are large, and the prestressed concrete beam is adopted to replace a common reinforced concrete beam or steel beam, so that the steel consumption can be greatly reduced, the beam section height can be reduced, and the indoor clear height can be increased, and the method is a cost-reducing way frequently adopted in actual engineering. Meanwhile, the heights of the multi-story warehouse and the industrial factory building are more than 6m, high formwork construction needs to be carried out when cast-in-place concrete beams and cast-in-place concrete floors are adopted, the high formwork construction cost is higher, the construction safety risk is large, the construction speed is low, high formwork construction can be avoided by adopting precast concrete beams and formwork-free floor support plates or precast concrete floors, the cost is saved, meanwhile, large-scale mechanical equipment can be adopted for industrial construction on site, the on-site manual work amount is greatly reduced, and the construction efficiency is improved. The prefabricated concrete beam top surface stretches out the stirrup, and the roof surface longitudinal bar is worn to establish at the job site, and post-cast concrete forms whole superposed beam, and the precast of superposed beam, post-cast part wholeness are strong, and the atress performance is close with whole cast-in-place roof beam. The precast concrete beam can be manufactured by adopting a long-line platform pretensioning method prestress process, a reserved hole channel is not needed to penetrate through a prestress steel strand for post-tensioning method prestress construction after the hole channel is on site, the prestress steel strand of the precast concrete beam extends into post-cast concrete of a connected component to be anchored, the cost of the pre-tensioning method prestress is lower than that of the post-tensioning method, and the pre-tensioning method prestress precast beam becomes an optimal technical path for assembling construction of heavy-load structures such as multi-story warehouses, industrial plants and the like.

The cross section size of a frame beam of a heavy-load structure such as a multi-story warehouse, an industrial factory building and the like is mostly 300 multiplied by 900-800 multiplied by 1500mm (cross section width multiplied by height), the dead weight of the frame beam is mostly 10-30 tons, the cost for hoisting a prestressed precast beam by a heavy tower crane on a construction site is higher, the prestressed precast beam is mostly hoisted upstairs by a truck crane, the dead weight of the truck crane is larger, the influence of construction load on the floor is considered, the dead weight of the upstairs truck crane is strictly controlled, the dead weight of the truck crane is in direct proportion to the hoisting capacity of the truck crane, and the dead weight of the prestressed precast beam is generally controlled within 12 tons.

The pretensioned prestressed precast beams disclosed by patents ZL201010297701.8, ZL201010297695.6, ZL201210291532.6 and ZL201210291481.7 are all solid rectangular cross sections, the self weight is large, when the cross section height of the beam is high in actual engineering, the cross section height of the precast beam is often required to be reduced to control the self weight of the precast beam, after the precast beam is hoisted in place on a construction site, a high post-beam casting area exists between the top surface of the precast beam and the bottom surface of a floor slab, two side molds on two sides need to be erected in the post-beam casting area at high altitude on site, the mold erecting is difficult and high in risk, slurry is easy to leak in the post-beam casting area, prefabricated and post-cast concrete connecting stubbles exist on the side surfaces of the formed composite beam, and the apparent quality is poor; and the formwork-free floor bearing plate or the precast concrete floor slab can not be directly supported on the top surface of the precast beam, the support-free construction of the floor slab can not be really realized, and the on-site construction measure cost is high. The pretensioning method prestressed precast beam disclosed by patent ZL201210291452.0 and ZL201210291044.5 adopts an inverted T-shaped cross section to reduce the dead weight of the precast beam, but the dead weight of the precast beam with the inverted T-shaped cross section can be reduced by only 20% compared with that of a solid precast beam with a rectangular cross section, and the post-cast concrete areas on two sides of the precast beam with the inverted T-shaped cross section on a construction site still need to be provided with side molds in a high altitude manner, so that the mold supporting is difficult, the risk is large, the post-cast areas of the beam are easy to leak slurry, and the apparent mass of the concrete is poor; when the precast beam with the inverted T-shaped cross section is produced, the side mold and the stirrups extending upwards from the bottom edge are mutually interfered, the side mold is difficult to support the mold, the stirrups extending upwards from the bottom edge need to be processed into a U shape firstly, and are manually bent into closed stirrups after the mold is removed, one precast beam stirrup is hundreds of stirrups, the workload of manually bent stirrups is large, and the bending quality is difficult to control.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a prestressed precast beam and a composite beam composed of the prestressed precast beam, wherein the prestressed precast beam adopts a U-shaped cross section to reduce the self weight by 30% -55%, the top surface of the precast beam is contacted with the bottom surface of a floor slab after the precast beam is hoisted under the premise of controlling the self weight, the formwork-free and support-free construction of the precast beam on a construction site is really realized, meanwhile, the connecting ribs are arranged at certain intervals along the length direction of the prestressed precast beam, the lateral bending deformation of the thin U-shaped side wall after the U-shaped side wall is released is controlled, the post-cast concrete on the construction site forms the integral composite beam, the prefabricated and post-cast parts of the composite beam have strong integrity and good stress performance.

In order to achieve the purpose, the invention adopts the technical scheme that:

a prestressed precast beam is prefabricated and processed by adopting a prestressed long-line pedestal and a pretensioning process, and is applied to buildings such as multi-storey warehouses, industrial plants and the like with large span and large floor load.

Bottom prestressed steel strands are distributed in the U-shaped bottom edge, the bottom prestressed steel strands are distributed in the length direction of the prestressed precast beams, extend out of two ends of the prestressed precast beams and are anchored in the connected columns or walls, the bottom prestressed steel strands ensure bending bearing capacity in a laminated beam span formed by the prestressed precast beams and bending bearing capacity under the action of positive bending moment at the end parts through tension, and the number and the area of the bottom prestressed steel strands are determined by calculation according to the bending bearing capacity in the laminated beam span and at the end parts; the height of the U-shaped bottom edge is not less than 150mm, so that the bottom prestressed steel strands can be conveniently arranged, and the phenomenon that the compressive stress of concrete with the U-shaped bottom edge is too large after the prestress is released and tensioned is avoided.

The U-shaped side walls are positioned on two side edges of the prestressed precast beam, and the height of the U-shaped side walls is required to ensure that the top surface of the U-shaped side walls is flush with the bottom surface of a floor in the structure after the prestressed precast beam is hoisted in place in a construction site. In order to avoid the situation that the concrete at the top of the U-shaped side wall is cracked under tension due to the fact that the prestressed precast beam is reversely arched after the prestressing force is released, upper anti-cracking prestressed tendons are distributed on the upper portion and the middle portion of the U-shaped side wall, the upper anti-cracking prestressed tendons are prestressed steel wires or steel strands, and the number and the area of the upper anti-cracking prestressed tendons are determined according to anti-cracking calculation. The thickness of the U-shaped side wall is not less than 100mm, so that concrete can be poured when the prestressed precast beam is manufactured, a certain rigidity of the prestressed precast beam is ensured, and the reverse arch and lateral deflection deformation of the prestressed precast beam after the prestressed is placed and tensioned are controlled.

After the U-shaped section is adopted to replace the traditional solid rectangular section, the self weight of the prestressed precast beam can be reduced by 30-55% compared with that of a solid rectangular section precast beam, the hoisting cost of the prestressed precast beam on a construction site is greatly reduced, and the construction measure cost increment caused by hoisting a large-tonnage truck crane upstairs is avoided.

A plurality of opening stirrups are arranged on the outer sides of the bottom prestressed steel strand and the upper anti-cracking prestressed reinforcement along the U-shaped cross section, the opening stirrups extend out of the top surfaces of the U-shaped side walls on the two sides, the extending ends are provided with 180-degree hooks to ensure that the hooks do not extend out of the inner sides of the U-shaped side walls, the problem that the hooks of the opening stirrups interfere with the installation and the removal of a core mold during the manufacturing of the prestressed precast beam is avoided, the plane where the opening stirrups are located is perpendicular to the length direction of the prestressed precast beam, and the diameters and the intervals of the opening stirrups meet the requirements of the existing design Specification concrete Structure design Specification 'building anti-seismic design Specification'.

Particularly, a plurality of contact ribs are arranged along the length direction of the prestressed precast beam, the contact ribs are made of reinforced concrete and are simultaneously poured along with the prestressed precast beam in the concrete pouring process, the bottoms of the contact ribs are connected with the U-shaped bottom edge, the side edges of the contact ribs are connected with the U-shaped side walls on the two sides, the contact ribs and the U-shaped side walls on the two sides play a role of jointly bearing force under the action of external force, the lateral rigidity of the U-shaped side walls can be greatly improved, and the contact ribs are beneficial to controlling the lateral deflection deformation of the U-shaped side walls after the prestress is released. The cross section of the prestressed precast beam at the connecting ribs is a solid rectangular cross section, the thickness of the connecting ribs along the length direction of the prestressed precast beam is not less than 150mm, and the distance between every two adjacent connecting ribs is 2.0-4.0 m.

And pre-buried sleeves in the contact ribs close to the two ends of the prestressed precast beam form hoisting holes, after the prestressed precast beam is manufactured, a hoisting tool is arranged in the hoisting holes in a penetrating mode for hoisting the prestressed precast beam, the diameter of each hoisting hole is not less than 40mm, and the hoisting holes are arranged in a penetrating mode along the horizontal direction of the cross section of the contact rib.

The prestressed precast beam is manufactured by adopting a prestressed long-line pedestal and a pretensioning process, the concrete manufacturing process comprises the steps of distributing bottom prestressed steel strands, upper anti-cracking prestressed tendons and stirrups in an outer long-line bench mold, occupying a core mold at the position of a U-shaped cross section, pouring concrete between the outer long-line bench mold and the core mold to form the prestressed precast beam after the bottom prestressed steel strands and the upper anti-cracking prestressed tendons are tensioned, and removing the core mold to form the U-shaped cross section after the concrete reaches the strength required by mold removal.

The core mould is disconnected at the connection ribs, namely the core mould between the connection ribs is a plurality of independent moulds, the net distance between the adjacent connection ribs is ensured to be standardized and modular length by adjusting the thickness of the connection ribs and the distance between the connection ribs at the two ends of the prestressed precast beam and the end part when the prestressed precast beam is designed, the standardization and the modular length of the core mould are realized, and then the prestressed precast beams with different lengths can be manufactured by combining a plurality of core moulds with the standard lengths, so that the repeated practicability of the core mould is realized, and the cost for spreading and selling of the core mould is reduced.

The core mold adopts different forms according to the cross section width of the prestressed precast beam, and specifically comprises the following steps:

when the width of the cross section of the prestressed precast beam is not more than 400mm, the clear distance between the U-shaped side walls at two sides is not more than 200mm, the core mold adopts an integral mold, the cross section of the integral mold is a trapezoid with a wide upper bottom and a narrow lower bottom so as to be convenient for mold removal, the U-shaped bottom side and concrete in the U-shaped side walls at two sides are integrally cast and formed at one time, and the cross section of the cavity part of the U-shaped cross section of the prestressed precast beam after the core mold is removed is a trapezoid with a wide upper bottom and a narrow lower bottom. The top surface of the bottom edge of the U-shape has no stirrup extending into the cavity part of the U-shape section limited by the integral mould.

Or when the width of the cross section of the prestressed precast beam is larger than 400mm, the core mold adopts paired independent steel molds as inner side molds of the U-shaped side wall, and the core mold and the long-line table outer mold form a side mold of the U-shaped side wall together; the upper surface of the U-shaped bottom edge is not provided with a mold for sealing, a stirrup or a lacing wire can be arranged in the middle of the U-shaped bottom edge at the moment, the stirrup or the lacing wire extends into the cavity part of the U-shaped section from the upper surface of the U-shaped bottom edge, and the requirement of the existing design specification concrete structure design specification for building earthquake resistance design specification for beam stirrup limb distance is met by additionally arranging the stirrup or the lacing wire in the middle of the cross section of the prestressed precast beam; in the manufacturing process of the prestressed precast beam, concrete is poured to the upper surface of the U-shaped bottom edge at first, concrete in the U-shaped side walls on two sides is poured before the concrete in the U-shaped bottom edge is initially set, and the upper width and the lower width of the U-shaped side walls are consistent.

Further, when the prestressed precast beam supports the secondary beam in the non-parallel direction in the integral structure, a placing notch is arranged at the position, corresponding to the supporting position, of the prestressed precast beam to support the secondary beam, and the size of the placing notch meets the placing requirement of the secondary beam; in the manufacturing process of the prestressed precast beam, the gap occupying die is adopted to occupy space, no concrete is ensured in the range of the placing gap, the upper anti-cracking prestressed tendon in the range of the placing gap is cut off after the prestressed precast beam concrete reaches the design strength, the prestressed precast beam stirrup is not arranged in the range of the placing gap, and no concrete or steel bar is arranged in the range of the placing gap. At the moment, the connection rib of the prestressed precast beam is arranged at the position of the placing gap so as to improve the local pressure-bearing capacity of the placing gap, and particularly, when the distance between every two adjacent placing gaps is larger than 4.0m, the connection rib is additionally arranged between every two adjacent placing gaps.

After the prestressed precast beam is hoisted in place in a construction site, two ends of the prestressed precast beam are placed on the connected columns or walls, and floor load in the construction process is transmitted to the connected columns or walls through the prestressed precast beam, so that support-free construction of the beam and the floor is realized. When the floor load in the construction process is large, the solid rectangular cross section is adopted in a certain length range at two ends of the prestressed precast beam, so that the phenomenon that the beam end is deformed greatly or concrete is crushed due to insufficient local bearing capacity is avoided, the solid rectangular cross section range is also used as an end connection rib of the prestressed precast beam, and the certain length is not more than the length of a beam end stirrup encryption area required by the existing design specification. Specifically, the stirrup with the solid rectangular cross section at the beam end can adopt a common closed stirrup to replace an open stirrup, so that the concrete compression performance and the shear transfer performance of a plastic hinge area at the beam end are improved.

After the prestressed precast beam is hoisted in place at a construction site, the top surface of the U-shaped side wall is flush with the bottom surface of a floor in the structure, a formwork-free floor bearing plate or a precast concrete floor can be directly supported on the top surface of the U-shaped side wall, so that the support-free floor in the construction site is realized, and the formwork-free laminated beam is continuously realized by the floor and the U-shaped side wall of the prestressed precast beam. Binding the superposed layer longitudinal rib and the superposed layer lacing wire at the top of the prestressed precast beam, wherein the two ends of the superposed layer lacing wire are 135-degree hooks and jointly form an integrally closed stirrup with an opening stirrup extending out of the U-shaped side wall of the prestressed precast beam, pouring concrete in a post-beam pouring area, and jointly forming the integrally superposed beam to participate in structural stress of the prestressed precast beam and the post-beam pouring area. Particularly, the post-cast concrete of the superposed beam between adjacent contact ribs is mutually occluded with the contact rib concrete, so that the shearing resistance of the interface between the precast concrete of the superposed beam and the post-cast concrete is improved, and the integrity of the superposed beam can be improved.

Further, preferably, when the U-shaped bottom edge of the prestressed precast beam is not provided with a hoop or a tie bar extends into the post-cast area of the composite beam, a shear steel bar can be pre-embedded in the U-shaped bottom edge in the manufacturing process of the prestressed precast beam, the shear steel bar is arranged perpendicular to the U-shaped bottom edge, after the concrete in the post-cast area of the beam is poured, the shear steel bar forms a pin bolt function near the upper surface of the U-shaped bottom edge to participate in shearing, and the shearing resistance of the interface between the precast concrete of the composite beam and the post-cast concrete is improved. In order to realize the pin bolt effect, the diameter of the shear steel bar is not less than 16mm, the distance between adjacent shear steel bars is 400-1000 mm, and the length of the shear steel bar extending out of the upper surface of the U-shaped bottom is not less than 10 times of the diameter of the shear steel bar.

Specifically, when the core mold adopts an integral mold, holes reserved for inserting the shear steel bars are formed in the integral mold according to a certain distance, and the shear steel bars are inserted into the holes of the integral mold after the integral mold is installed in place in the manufacturing process of the prestressed precast beam; when the core mold adopts paired independent steel molds, shear steel bars are arranged in gaps between the independent steel molds.

Further, as preferred, a series of steel occupation strips are adhered and welded on the surface of the core mould facing to the U-shaped side wall and the bottom edge of the U-shaped side wall, the length direction of the occupation strips is perpendicular to the length direction of the prestressed precast beam, the cross section of each occupation strip is trapezoidal, the size of the bottom edge attached to the core mould is larger than that of the bottom edge far away from the core mould, a series of convex-concave key grooves are formed in the inner wall of the prestressed precast beam after the core mould is removed, and the size of the key grooves meets the structural requirements of the conventional design specification 'assembly type concrete structure technical rules' on the shearing resistant key grooves of the new and old concrete interfaces. After the concrete in the post-cast area of the beam is cast in the construction site, the concrete of the prestressed precast beam and the post-cast concrete in the post-cast area of the beam are mutually occluded and shear-resistant at the key groove position, and the shear resistance of the interface between the precast concrete and the post-cast concrete of the composite beam is further improved.

After the prestress is released, the concrete around the prestressed steel strand at the bottom resists the pretension force in the prestressed steel strand at the bottom by bearing the compressive stress, in addition, the concrete in the U-shaped bottom edge of the prestressed precast beam bears the additional compressive stress under the action of the negative bending moment at the beam end of the superposed beam, and the superposition of the two effects can cause the concrete in the U-shaped bottom edge of the end part of the prestressed precast beam in the structure to bear larger compressive stress. When the section width of the prestressed precast beam is large, and the prestressed precast beam is influenced by a core mould and is inconvenient to arrange a stirrup or a tie bar in the middle of the U-shaped bottom edge in the manufacturing process, the U-shaped transverse rib or the additional stirrup is arranged in the middle area of the U-shaped bottom edge of the prestressed precast beam, the phenomenon that the stirrup limb distance in the range of the U-shaped bottom edge of the prestressed precast beam is too large is avoided, the constraint effect of concrete in the range of the U-shaped bottom edge of the prestressed precast beam is improved, the compression performance of the concrete in the range of the U-shaped bottom edge is improved, and the ductility of the superposed beam under the action of negative bending moment is improved. The U-shaped dowel bars are inserted into the inner wall of the U-shaped section of the prestressed precast beam in a construction site, and form combined stirrup with the U-shaped transverse bars or the additional stirrups in the prestressed precast beam in the middle of the section of the superposed beam, so that the phenomenon that the limbs of the stirrup in the superposed beam are too large is avoided, the constraint effect of post-cast concrete in the middle of the cross section of the superposed beam is improved, and the buckling degree of the longitudinal bars of the superposed layer in the middle of the cross section of the superposed beam is reduced when the longitudinal bars are pressed.

Further, preferably, when two ends of the prestressed precast beam are U-shaped cross sections, energy-consuming steel bars are laid on the upper surfaces of the U-shaped bottom edges of the two ends of the prestressed precast beam on a construction site, the energy-consuming steel bars are arranged along the length direction of the prestressed precast beam, one end of each energy-consuming steel bar extends into a connecting column or a wall at the end part of the prestressed precast beam to be anchored, and a 90-degree hook is arranged at one end of each energy-consuming steel bar and extends into the prestressed precast beam to be anchored in post-cast concrete of the superposed beam; and (3) coating an isolation sleeve on the surface of the energy-consuming steel bar extending to the length range of 100-500 mm from the junction position of the prestressed precast beam and the connected column or wall, and isolating the energy-consuming steel bar and the post-cast concrete of the superposed beam in the range of the isolation sleeve to form an unbonded section. The preferred low strength reinforcing bar of power consumption reinforcing bar, the clear distance of power consumption reinforcing bar and U-shaped bottom edge surface is 20 ~ 50mm, and the preferred internal diameter of isolation sleeve is managed with the PVC that power consumption reinforcing bar diameter is close. Under the action of the positive bending moment of the beam end of the composite beam, the energy-consuming reinforcing steel bars can be subjected to plastic deformation and energy consumption without bonding sections after being subjected to tensile yield, the energy consumption capacity of the beam end of the composite beam under the action of the positive bending moment is enhanced, and the defect that the energy consumption capacity of a pre-tensioning method prestressed precast beam is poor is overcome.

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

(1) the prestressed precast beam is integrally provided with the U-shaped cross section, the self weight of the prestressed precast beam can be reduced by 30% -55% compared with that of a solid rectangular cross section precast beam, the self weight of the prestressed precast beam is obviously lower than that of the existing rectangular cross section or inverted T-shaped cross section precast beam, the self weight of the precast beam with the common cross section and span in a multilayer heavy-load structure can be controlled within 12 tons, the hoisting cost of a construction site is greatly reduced, a large-tonnage truck crane is not needed to go upstairs, and the influence of additional construction load on the structural design and the cost increment are avoided.

(2) According to the invention, on the premise of realizing self-weight control, after the prestressed precast beam is hoisted in place at a construction site, the top surface of the U-shaped side wall of the prestressed precast beam is flush with the bottom surface of a floor in the structure, a formwork-free floor bearing plate or a precast concrete floor can be directly supported on the top surface of the U-shaped side wall, so that the support-free floor at the construction site is realized, the formwork-free laminated beam is continuously realized by the floor and the U-shaped side wall of the prestressed precast beam, and the defects that the formwork-free laminated beam and the support-free floor cannot be really realized by reducing the self-weight of the existing prestressed precast beam through reducing the height of the section of the precast beam or adopting an inverted T-shaped section are avoided.

(3) For a large-span beam with the cross section width larger than 600mm, the invention can integrally prefabricate the beam along the cross section width direction on the premise of controlling the dead weight, the integrity of the superposed beam formed by post-pouring concrete in the on-site post-pouring U-shaped cross section is good, the torsional rigidity and the torsional bearing capacity are consistent with those of the integrally cast-in-place beam, and the problems of poor integrity, weakened torsional rigidity, inconsistent calculation assumption and actual stress and the like caused by adopting two rectangular solid prefabricated beams with smaller cross section width to be spliced into the superposed beam with larger cross section width on site are avoided.

(4) The connecting ribs are arranged between the U-shaped side walls at the two sides at certain intervals, so that the lateral rigidity of the prestressed precast beam is improved, the lateral deflection deformation of the U-shaped side walls after the prestressing force is released and tensioned is greatly reduced, the deformation of the U-shaped side walls under the condition of bearing construction load transmitted by the secondary beam can be limited, and meanwhile, the connecting ribs can be mutually meshed with post-cast concrete of the superposed beam to provide the integrity of the superposed beam.

(5) When the prestressed precast beam is manufactured, the U-shaped inner walls are convenient to be provided with key slots or shear-resistant reinforcing steel bars to improve the shear resistance of the new and old concrete interfaces of the composite beam, and meanwhile, energy-consuming reinforcing steel bars can be arranged in the U-shaped inner walls at the two ends of the construction site to improve the energy-consuming capability of the prestressed precast beam.

Drawings

Fig. 1 is a three-dimensional schematic view of a prestressed precast beam according to the present invention, in which the width of the beam section is not more than 400 mm.

Fig. 2 is a schematic sectional view taken along line a-a in fig. 1.

Fig. 3 is a schematic view of a mold assembly in a process of manufacturing the prestressed precast beam of fig. 1.

Fig. 4 is a three-dimensional schematic view of a composite girder composed of the prestressed precast girders in fig. 1 at a construction site.

Fig. 5 is a schematic cross-sectional view of B-B in fig. 4.

Fig. 6 is a schematic cross-sectional view of a laminated beam composed of the existing prestressed precast beams, which is a comparative example of the laminated beam shown in fig. 5.

Fig. 7 is a modification of the composite girder of fig. 4, in which the prestressed precast girders extend with shear bars at the U-shaped bottom edges thereof.

Fig. 8 is a schematic cross-sectional view of C-C in fig. 7.

Fig. 9 is a modified form of the space occupying core used in the fabrication of the prestressed precast beam of fig. 3.

Fig. 10 is a second modification of the composite beam of fig. 4, in which energy-consuming reinforcing bars are arranged above the U-shaped bottom edges of the end portions of the prestressed precast beams.

Fig. 11 is a third modification of the composite beam of fig. 4, wherein lateral restraint of the lower, top load-bearing rebars is enhanced.

Fig. 12 is a three-dimensional schematic view of the prestressed precast beam according to the present invention, in which the width of the beam section is greater than 400mm, and the middle of the prestressed precast beam supports a plurality of sub-beams in non-parallel directions.

Fig. 13 is a schematic cross-sectional view taken along line D-D of fig. 12.

Fig. 14 is a schematic cross-sectional view E-E of fig. 12.

Fig. 15 is a schematic view illustrating a mold assembly in a process of manufacturing the prestressed precast beam of fig. 12.

Fig. 16 is a three-dimensional schematic view of a composite girder composed of the prestressed precast girders in fig. 12 at a construction site.

Fig. 17 is a schematic sectional view taken along line F-F in fig. 16.

Fig. 18 is a schematic cross-sectional view of a composite girder according to a comparative example of the composite girder shown in fig. 17, i.e., a composite girder in which existing prestressed precast girders are doubly spliced.

Fig. 19 is a modified version of the composite beam of fig. 16, wherein the cross-sectional central integral stirrup is modified to two separate reinforcing bars.

Fig. 20 is a modified form of the composite girder of fig. 19, in which the U-shaped bottom edge of the prestressed precast girder is extended with shear reinforcement.

In the figure: 1-prestressed precast beam; 11-U-shaped bottom edge; 12-U-shaped side walls; 13-bottom prestressed steel strands; 14-upper anti-crack prestressed tendons; 15-opening stirrup; 16-closed stirrups; 17-shear reinforcement; 18-U-shaped transverse ribs; 19-additional stirrups; 2-a beam end stirrup encryption area; 3-linking ribs; 4-hoisting holes; 51-long line table external mold; 52-beam end divider plate; 53-core mold; 54-gap occupying mode; 55-placeholder bars; 6-post-beam casting area; 61-stacking layer lacing wire; 62-overlapping the longitudinal ribs; 63-energy consumption steel bars; 64-U-shaped dowel bars; 7-a floor slab; 8-resting notch.

Detailed Description

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, and it is apparent that the described examples are some, but not all, of the embodiments of the present invention.

Fig. 1 to 5 provide a first preferred embodiment of the prestressed precast beam and the composite beam composed of the prestressed precast beam according to the present invention, which is used in the case that the width a of the beam section is not greater than 400 mm.

Referring to the prestressed precast beam shown in fig. 1 and 2, the cross section of the prestressed precast beam 1 is U-shaped, and the U-shaped cross section includes a U-shaped bottom edge 11 at the bottom and U-shaped side walls 12 extending from the U-shaped bottom edge at two sides. Bottom prestressed steel strands 13 are distributed in the U-shaped bottom edge 11, the bottom prestressed steel strands 13 are distributed in the length direction of the prestressed precast beam 1, extend out of two ends of the prestressed precast beam 1 and are anchored in the connected columns or walls, the bottom prestressed steel strands 13 ensure bending bearing capacity in a laminated beam span formed by the prestressed precast beam 1 and bending bearing capacity under the action of positive bending moment at the end part through tension, and the number and the area of the bottom prestressed steel strands are calculated and determined according to the bending bearing capacity in the laminated beam span and at the end part; the height c of the U-shaped bottom edge 11 is not less than 150mm, so that the arrangement of the bottom prestressed steel strands 13 is facilitated, and the crushing caused by overlarge compressive stress after the prestress is released and tensioned in the concrete in the U-shaped bottom edge 11 is avoided.

The U-shaped side walls 12 are positioned at two side edges of the prestressed precast beam 1, and the height d of the U-shaped side walls 12 is required to ensure that the top surfaces of the U-shaped side walls 12 are flush with the bottom surface of the floor slab 7 in the structure after the prestressed precast beam 1 is hoisted in place in a construction site. In order to avoid the situation that the concrete at the top of the U-shaped side wall 12 is cracked under tension due to the fact that the prestressed precast beam 1 is reversely arched after prestressing force is released, upper anti-cracking prestressed tendons 14 are distributed on the upper portion and the middle portion of the U-shaped side wall 12, the upper anti-cracking prestressed tendons 14 are prestressed steel wires or steel strands, and the number and the area of the upper anti-cracking prestressed tendons 14 are determined through calculation according to anti-cracking checking calculation. The upper anti-crack prestressed tendons 14 in the middle of the U-shaped side wall 12 extend out of two ends of the prestressed precast beam 1, and the upper anti-crack prestressed tendons 14 at the top are cut off at the end face of the beam end of the prestressed precast beam 1 after being released. In order to facilitate the pouring of concrete from the top of the U-shaped side wall 12 during the manufacturing of the prestressed precast beam 1 and ensure that the prestressed precast beam 1 has enough rigidity to control the reverse arch deformation and the lateral deflection deformation of the prestressed precast beam 1 after the prestressing is released and tensioned, the thickness b of the U-shaped side wall 12 is not less than 100 mm.

The U-shaped cross section shown in the figures 1 and 2 is adopted to replace the traditional solid rectangular cross section, the thickness b of the U-shaped side wall 12 and the height c of the U-shaped bottom edge 11 are controlled, the self weight of the prestressed precast beam 1 can be reduced by 30-55% compared with that of a solid rectangular cross section precast beam, the hoisting cost of the prestressed precast beam 1 on a construction site is greatly reduced, and the construction measure cost caused by hoisting a large-tonnage truck crane upstairs is avoided.

A plurality of opening stirrups 15 are arranged on the outer sides of the bottom prestressed steel strand 13 and the upper anti-cracking prestressed reinforcement 14 along the U-shaped cross section, the opening stirrups 15 are integrally U-shaped, two opposite sides of the U-shaped opening stirrups 15 extend out from the top surfaces of the U-shaped side walls 12 on the two sides, 180-degree hooks are arranged at the extending ends, it is guaranteed that the hooks of the opening stirrups 15 do not extend out of the inner side edge of the U-shaped side walls 12, the opening stirrups 15 are prevented from interfering with installation and dismantling of a core mold 53 when the prestressed precast beam 1 is manufactured by the hooks of the opening stirrups 15, the plane where the opening stirrups 15 are located is perpendicular to the length direction of the prestressed precast beam 1, and the diameter and the distance of the opening stirrups 15 meet the relevant requirements of concrete structure design Specifications for building design.

Referring to fig. 1, a plurality of contact ribs 3 are arranged along the length direction of a prestressed precast beam 1, the contact ribs 3 are made of reinforced concrete, and are simultaneously poured along with the prestressed precast beam 1 in the concrete pouring process, the bottoms of the contact ribs 3 are connected with a U-shaped bottom edge 11, and the side edges of the contact ribs are connected with two side U-shaped side walls 12, so that the effect of jointly bearing force under the action of external force by cooperating with the two side U-shaped side walls 12 is achieved, the lateral rigidity of the U-shaped side walls 12 can be greatly improved, and the lateral bending deformation of the U-shaped side walls 12 after the prestress is released is reduced. The cross section of the prestressed precast beam 1 at the connection rib 3 is a solid rectangular cross section, the thickness of the connection rib 3 along the length direction of the prestressed precast beam 1 is not less than 150mm, and the distance between adjacent connection ribs 3 is 2.0-4.0 m.

After the prestressed precast beam 1 is manufactured, the hoisting hole 4 is used for penetrating through a hoisting tool to hoist, in order to avoid damage to concrete around the hoisting hole 4 in the hoisting process, as shown in fig. 1, the hoisting hole 4 is arranged in the contact ribs 3 close to two ends of the prestressed precast beam 1, the diameter of the hoisting hole 4 is not smaller than 40mm, the horizontal direction of the cross section of the contact rib 3 is arranged in a through mode, and the hoisting hole 4 is formed by pre-buried sleeves when the prestressed precast beam 1 is manufactured.

Referring to fig. 3, in the first preferred embodiment, the prestressed precast beam 1 is manufactured by adopting a prestressed long-line pedestal and a pretensioning process, and the specific manufacturing process is as follows:

A. arranging bottom prestressed steel strands 13, upper anti-cracking prestressed tendons 14 and opening stirrups 15 in the long-line table external mold 51, and simultaneously installing beam-end partition plates 52;

B. installing a core die 53 on the inner side of the open stirrup 15 to occupy space to form a U-shaped section, wherein the width a of the section of the prestressed precast beam 1 is not more than 400mm, the clear distance between the U-shaped side walls 12 at two sides is not more than 200mm, the core die 53 adopts an integral die, and the cross section of the integral die adopts a trapezoid with a wide upper bottom and a narrow lower bottom so as to be convenient for removing the die;

C. pouring concrete in the U-shaped bottom edge 11 and the U-shaped side walls 12 on the two sides through the top of the mold simultaneously to finish the concrete pouring of the prestressed precast beam 1;

D. and (3) removing the core mold 53 after the concrete is initially set, performing prestress releasing construction after the concrete strength reaches the releasing and stretching required strength, cutting off continuous prestressed tendons among a plurality of prestressed precast beams 1 on the same long line platform, removing the long line platform outer mold 51 and the beam end separation plate 52, and finishing the manufacture of the prestressed precast beams 1, wherein the cross section of the cavity part of the U-shaped section of each prestressed precast beam 1 is a trapezoid with a wide upper bottom and a narrow lower bottom as shown in fig. 2.

The central portion of the cross section of the prestressed precast beam 1 in fig. 2 and 3 cannot be provided with a stirrup or a tie bar extending from the U-shaped bottom edge 11, which is blocked by the integral die used for the core die 53.

Particularly, the core mold 53 in fig. 3 is broken at the connection rib 3, that is, the core mold 53 is a plurality of independent integral molds, and the thickness of the connection rib 3 and the distance between the connection rib 3 at the two ends of the prestressed precast beam 1 and the end part are adjusted during the design of the prestressed precast beam 1, so that the clear distance between the adjacent connection ribs 3 is the standardized and modular length, thereby realizing the standardization and the modular length of the core mold 53, and further manufacturing the prestressed precast beams 1 with different lengths by combining a plurality of core molds 53 with the standard length, realizing the repeated practicability of the core mold 53 and reducing the cost of the core mold 53 for amortization.

Fig. 4 and 5 show a composite beam consisting of prestressed precast beams in a preferred embodiment of a construction site, wherein other components in the structure are not shown, both ends of the prestressed precast beam 1 rest on the connecting columns or walls, and no support is arranged at the lower part of the prestressed precast beam 1, so that support-free construction is realized. After the prestressed precast beam 1 is hoisted in place in a construction site, the top surface of the U-shaped side wall 12 is flush with the bottom surface of a floor slab 7 in the structure, namely the height d of the concrete part of the prestressed precast beam 1 is the height f of the cross section of the superposed beam minus the thickness e of the floor slab 7, a formwork-free floor bearing plate or a precast concrete floor slab can be directly supported on the top surface of the U-shaped side wall 12, the support-free floor slab in the construction site is realized, the floor slab 7 is continuous with the U-shaped side wall 12 of the prestressed precast beam, and a post-beam pouring area 6 does not need formwork support. Binding a superposed layer longitudinal rib 62 and a superposed layer tie bar 61 at the top of the prestressed precast beam 1, forming an integral closed tie bar together with an opening tie bar 15 extending out of the prestressed precast beam 1 by using 135-degree hooks at two ends of the superposed layer tie bar 61, pouring concrete in the post-cast beam area 6, and forming an integral superposed beam together with the post-cast beam area 6 to participate in structural stress. Particularly, post-cast concrete in the beam post-cast area 6 between the adjacent contact ribs 3 is mutually occluded with concrete of the contact ribs 3, so that the shearing resistance of the interface between the prefabricated and post-cast concrete of the composite beam is improved, and the integrity of the composite beam can be improved.

Fig. 6 is a schematic cross-sectional view of a laminated beam composed of existing prestressed precast beams, which is a comparative example of a preferred embodiment of the present invention, in which a prestressed precast beam 1 has a solid rectangular cross-section, and the self weight of the prestressed precast beam 1 is controlled by reducing the height d of a concrete portion of the prestressed precast beam 1. The top surface of the concrete part of the prestressed precast beam 1 in the comparative example of the first preferred embodiment is not in contact with the bottom surface of the floor slab 7 in the structure, the prestressed precast beam 1 cannot support a template system of the floor slab 7, a post-cast area with the height of h between the prestressed precast beam 1 and the floor slab 7 needs to be manually provided with a side mold at high altitude, the support-free floor slab and the support-free superposed beam on a construction site cannot be realized, the construction efficiency is low, the construction measure cost is high, prefabricated and post-cast concrete connection is arranged on the side surface of the superposed beam, the apparent quality is poor, and the benefits of the first preferred embodiment of the invention in the aspects of construction efficiency, construction quality, construction safety and the like cannot be achieved.

Fig. 7 and 8 show an improved first preferred embodiment, which is specifically improved in that a row of shear-resistant steel bars 17 are embedded in the middle of a U-shaped bottom edge 11 in the manufacturing process of a prestressed precast beam 1 along the length direction of the prestressed precast beam 1, the shear-resistant steel bars 17 are arranged perpendicular to the U-shaped bottom edge 11, the concrete post-shear-resistant steel bars 17 in a post-cast beam region 6 form a steel bar bolt function near the upper surface of the U-shaped bottom edge 11 to participate in shearing, so as to improve the shearing resistance of an interface between precast concrete and post-cast concrete of a composite beam, while the interface between precast concrete and post-cast concrete of the composite beam in the preferred embodiment only transmits shearing force through bonding, the shearing resistance is poor and is easily affected by post-cast concrete shrinkage, and the overall working performance of the composite beam can be weakened after shear slip occurs on the interface between precast concrete and post-cast concrete of the composite beam.

In order to realize the steel bar bolt function, the diameter of the shear steel bars 17 in the first improved type is not less than 16mm, the distance between the adjacent shear steel bars 17 is 400-1000 mm, and the length of the shear steel bars 17 extending out of the upper surface of the U-shaped bottom edge 11 is not less than 10 times of the diameter of the shear steel bars 17. Specifically, in the manufacturing process of the prestressed precast beam 1, holes for inserting the shear steel bars 17 are reserved on the core mold 53 shown in fig. 3 at certain intervals, after the core mold 53 is installed in place, the shear steel bars 17 are inserted into the whole mold holes, the concrete of the prestressed precast beam 1 is poured to pre-embed the shear steel bars 17, and the diameter of the whole mold holes is slightly larger than that of the shear steel bars 17 so as to prevent the shear steel bars 17 from influencing the removal of the core mold 53.

Fig. 9 shows an improved occupying core mold 53 used in the manufacturing process of a prestressed precast beam according to a preferred embodiment, which is specifically improved in that a series of steel occupying strips 55 are adhered and welded on the surface of the core mold 53 facing the U-shaped side wall 12 and the U-shaped bottom edge 11, the length direction of the occupying strips 55 is perpendicular to the length direction of the prestressed precast beam 1, the cross section of the occupying strips 55 is trapezoidal, the size of the bottom edge adhered to the core mold 53 is larger than the size of the bottom edge far away from the core mold 53, a series of convex-concave key grooves are formed in the inner wall of the prestressed precast beam 1 after the core mold 53 is removed, the size of the key grooves is consistent with the size of the cross section of the occupying strips 55, and the requirements of the existing design specification, namely the assembly concrete structure technical rules, on the shear resistant construction of the new and old concrete interface are met. After the concrete in the post-cast area 6 of the beam is cast in the construction site, the concrete of the prestressed precast beam 1 and the post-cast concrete in the post-cast area 6 of the beam are mutually occluded and shear-resistant at the key groove position, and the shear-resistant performance of the interface between the precast concrete of the composite beam and the post-cast concrete is improved.

Fig. 10 shows an improved version two of the first preferred embodiment, which is specifically improved in that energy-consuming steel bars 63 are laid on the upper surfaces of U-shaped bottom edges 11 at two ends of a prestressed precast beam 1 in a construction site, the energy-consuming steel bars 63 are arranged along the length direction of the prestressed precast beam 1, one end of each energy-consuming steel bar extends into a connecting column or a wall at the end of the prestressed precast beam 1 for anchoring, one end of each energy-consuming steel bar is provided with a 90-degree hook and extends into the prestressed precast beam 1 and anchors the concrete in a post-cast area 6 of the beam, in particular, an isolation sleeve is sleeved on the surface of each energy-consuming steel bar 63 extending 100-500 mm in length from the junction position of the prestressed precast beam 1 and the connecting column or the wall into the prestressed precast beam 1, and the energy-consuming steel bars 63 and the concrete in the post-cast area 6 of the beam are isolated from each other within the range of the isolation sleeve to form an unbonded section. The energy-consuming steel bars 63 are preferably low-strength steel bars, the clear distance between the energy-consuming steel bars 63 and the upper surface of the U-shaped bottom edge 11 is 20-50 mm, and the isolation sleeve is preferably a PVC pipe with the inner diameter close to the diameter of the energy-consuming steel bars. Under the action of the positive bending moment of the beam end of the composite beam, after the energy-consuming steel bars 63 are tensioned and yield, the unbonded sections can generate plastic deformation energy consumption, and the energy consumption capacity of the beam end of the composite beam under the action of the positive bending moment is enhanced. Compared with the second improved embodiment, in the first preferred embodiment, only the bottom prestressed steel strand 13 of the prestressed precast beam 1 extends into the connecting column or the wall for anchoring, the tensile strength of the bottom prestressed steel strand 13 is high, no obvious yield platform exists when the prestressed steel strand is pulled, the beam end of the composite beam consumes no energy of the steel bars and only cracks in concrete under the action of positive bending moment, the energy consumption capability is poor, the earthquake resisting effect is not facilitated, and the energy consumption of the beam end is increased by the improved two-way energy consumption steel bars 63.

Fig. 11 shows a third modification of the first preferred embodiment. After the prestress of the prestressed precast beam 1 is released, the concrete around the prestressed steel strand 13 at the bottom resists the prestress in the prestressed steel strand 13 at the bottom by bearing the compressive stress, and in addition, the concrete in the U-shaped bottom edge 11 of the prestressed precast beam 1 bears the additional compressive stress under the action of the negative bending moment at the beam end of the superposed beam, and the superposition of the two effects can cause the concrete in the U-shaped bottom edge 11 of the prestressed precast beam 1 in the structure to bear larger compressive stress. When the section width a of the prestressed precast beam 1 is large in the first preferred embodiment, the manufacturing process is stopped by the integral die adopted by the core die 53, the stirrup or the tie bar in the middle of the cross section of the composite beam cannot be arranged in the middle of the U-shaped bottom edge 11, the stirrup leg distance of the composite beam can exceed the requirement of the existing design specification concrete structure design specification (building earthquake resistance design specification), and the concrete constraint effect and the compression performance near the middle of the U-shaped bottom edge 11 cannot be ensured. The improved third mode is that a U-shaped transverse bar 18 is arranged in the middle area of the U-shaped bottom edge 11 of the prestressed precast beam 1, the U-shaped transverse bar 18 extends into the U-shaped side wall 12 by bypassing the bottom prestressed steel strand 13 in the middle of the cross section, so that the phenomenon that the stirrup limb distance is too large in the range of the U-shaped bottom edge 11 of the prestressed precast beam 1 can be avoided, the constraint effect of concrete in the range of the U-shaped bottom edge 11 of the prestressed precast beam 1 is improved, the compression performance of the concrete in the range of the U-shaped bottom edge 11 is improved, and the ductility of the superposed beam under the action of negative bending moment is improved; the U-shaped dowel bars 64 are inserted into the inner wall range of the U-shaped section of the prestressed precast beam 1 in a construction site, the U-shaped dowel bars 64 and the U-shaped transverse ribs 18 in the prestressed precast beam 1 form combined stirrups in the middle of the section of the superposed beam, the phenomenon that the limb distance of the stirrups in the superposed beam is too large is avoided, the requirement of the existing design specification on the limb distance of the stirrups can be still met by the limb distance of the stirrups in the superposed beam when the U-shaped bottom edge 11 cannot extend out of the stirrups is guaranteed, the constraint effect of post-cast concrete in the middle of the cross section of the superposed beam is improved, and the buckling degree of the longitudinal ribs 62 in the middle of the cross section of the superposed beam when being pressed is reduced.

Fig. 12 to 17 provide a second preferred embodiment of the prestressed precast beam and the composite beam composed of the prestressed precast beam according to the present invention, which is used in the case that the width a of the beam section is greater than 400 mm. The requirements of the U-shaped cross section of the prestressed precast beam 1, the specific requirements of the prestressed reinforcement and the arrangement of the connecting ribs of the prestressed precast beam 1 of the second preferred embodiment are the same as those of the first preferred embodiment. In the second preferred embodiment, the prestressed precast beam 1 needs to support the secondary beam in the non-parallel direction in the overall structure, referring to fig. 12, a placing notch 8 is arranged at a position, corresponding to the support position, of the prestressed precast beam 1 to support the secondary beam in the non-parallel direction, the size of the placing notch 8 meets the placing requirement of the secondary beam, and no concrete or steel bar exists in the range of the placing notch 8; the contact ribs 3 of the prestressed precast beam 1 are arranged at the position of the laying gap 8, so that the local pressure bearing capacity of the position of the laying gap 8 is improved, the local concrete crushing phenomenon of the prestressed precast beam 1 when supporting the secondary beam is avoided, the top surfaces of the contact ribs 3 are flush with the bottom surfaces of the laying gaps 8, and particularly, if the distance between every two adjacent laying gaps 8 is larger than 4.0m, one contact rib 3 needs to be additionally arranged between every two adjacent laying gaps 8.

In the second preferred embodiment, the prestressed precast beam 1 needs to bear the floor construction load transmitted by the secondary beam, and transmits the floor construction load to the connecting column or wall at the beam end, so as to avoid the large deformation or concrete crushing caused by the insufficient local bearing capacity of the beam end, referring to fig. 12 and 14, the two ends of the prestressed precast beam 1 adopt solid rectangular sections within a certain length range, the solid rectangular section range is also used as an end contact rib 3 of the prestressed precast beam 1, and the certain length is not more than the length of the beam end stirrup encryption area 2 required by the existing design Specification for concrete Structure design Specification for building earthquake resistance design Specification; at the moment, the stirrups with the solid rectangular cross sections at the beam ends can adopt common closed stirrups 16 to replace the open stirrups 15 in the U-shaped cross section in the figure 13, so that the concrete compression performance and the shear force transfer performance of the beam end stirrup encryption area 2, namely the potential plastic hinge area under the earthquake action, are improved.

Referring to fig. 15, in the second preferred embodiment, the prestressed precast beam 1 is manufactured by adopting a prestressed long-line pedestal and a pretensioning process, and the specific manufacturing process is as follows:

A. arranging bottom prestressed steel strands 13, upper anti-cracking prestressed tendons 14 and stirrups in the long-line table external mold 51, and meanwhile, installing beam-end partition plates 52;

B. installing a core die 53 on the inner side of the open stirrup 15 to occupy space to form a U-shaped section, wherein the width a of the section of the prestressed precast beam 1 in the second preferred embodiment is greater than 400mm, the core die 53 adopts paired independent steel dies as an inner die of the U-shaped side wall 12, and forms a side die of the U-shaped side wall together with the long-line platform outer die 51, and the upper surface of the bottom edge of the U-shaped side wall is not provided with a die for closing;

C. installing a gap occupying die 54;

D. pouring concrete from the gap between the pair of core molds 53 to the upper surface of the U-shaped bottom edge 11;

E. before the concrete in the U-shaped bottom edge 11 is initially set, pouring concrete in the U-shaped side walls 12 on two sides through the top of the mold to finish the concrete pouring of the prestressed precast beam 1;

F. and (3) removing the core mold 53 and the gap occupying mold 54 after the concrete of the U-shaped side wall 12 is initially set, performing prestress releasing construction after the strength of the concrete reaches the releasing requirement strength, cutting off continuous prestressed tendons among a plurality of prestressed precast beams 1 on the same long-line platform, removing the external mold 51 and the beam end partition plate 52 of the long-line platform, and cutting off the upper anti-crack prestressed tendons 14 in the gap 8 to finish the manufacture of the prestressed precast beams 1.

Considering that the core mold 53 in the second preferred embodiment is a pair of independent steel molds with a gap in the middle, referring to fig. 12 and 13, the closed stirrup 16 can be arranged in the middle of the bottom edge of the U-shape, the closed stirrup 16 extends into the cavity part of the U-shape section from the upper surface of the bottom edge 11 of the U-shape, the height of the closed stirrup 16 is the same as that of the open stirrup 15, and the distance from the outer skin of the closed stirrup 16 to the inner wall of the side wall 12 of the U-shape should meet the installation requirement of the core mold 53. The closed stirrups 16 are arranged in the middle of the U-shaped bottom edge, so that the stirrup leg distance of the composite beam in the second preferred embodiment can meet the requirements of the existing design specification concrete structure design specification building earthquake resistance design specification.

In particular, the core mold 53 of the second preferred embodiment is a pair of independent steel molds, which is convenient for mold removal, and referring to fig. 13, the width b of the U-shaped sidewall 12 can be kept uniform up and down without being designed into the shape of the first preferred embodiment.

Fig. 16 and 17 show a composite beam composed of prestressed precast beams in a second preferred embodiment of a construction site, wherein other members in the structure are not shown, both ends of the prestressed precast beam 1 are placed on the connecting columns or walls, the top surfaces of the U-shaped side walls 12 are flush with the bottom surface of a floor slab 7 in the structure, and the second preferred embodiment can also realize the support-free floor slab 3 and the formwork-free post-cast area 6 of the beam in the construction site. In particular, the corresponding position of the prestressed precast beam 1 opening stirrup 15 needs to be bound with the superposed layer lacing wire 61 to form an integral closed stirrup.

Fig. 18 is a schematic cross-sectional view of a composite beam composed of existing prestressed precast beams, that is, a comparative example of a second preferred embodiment of the present invention, in which a prestressed precast beam 1 has a solid rectangular cross section, and in a construction site, the two prestressed precast beams 1 having a larger cross-sectional width are assembled in two pieces to form a composite beam having a cross-sectional width a half of the cross-sectional width of the composite beam, the two prestressed precast beams 1 are installed side by side and connected only by post-cast concrete in a post-cast beam region 6, and the precast sections are not connected and have a certain gap. According to the comparative example of the second preferred embodiment, the dead weight of the prestressed precast beam 1 is controlled by splicing the small-sized precast beams and reducing the height d of the concrete part of the prestressed precast beam 1, so that the assembly type construction of the composite beam with a large section width in the structure is realized, but the top surface of the concrete part of the prestressed precast beam 1 in fig. 18 is not in contact with the bottom surface of the floor slab 7 in the structure, the prestressed precast beam 1 cannot support a template system of the floor slab 7, a post-cast area with the height h between the prestressed precast beam 1 and the floor slab 7 needs to be manually supported at high altitude by a side mold, so that no slurry leakage is caused during concrete casting in the post-cast area 6 of the beam, the support-free floor slab and the support-free composite beam in the construction site cannot be realized, the construction efficiency is low, the construction measure cost is high, and the side surface of the composite beam has prefabricated and post-cast concrete connecting stubbles, and the apparent quality is poor; in addition, the double-spliced prestressed precast beam 1 is not connected, the torsional rigidity and torsional bearing capacity of the formed superposed beam are lower than those of the integral cast-in-place beam, the structural design needs to be considered independently, the influence of the disconnection of the prefabricated part cannot be accurately considered by the existing design software, and post-cast concrete in the post-cast area 6 of the beam is easy to crack when the stress on the two sides of the superposed beam is uneven. The prestressed precast beam 1 of the second preferred embodiment adopts a U-shaped section to realize self-weight control, the beam can be integrally precast along the width a direction of the section, a superposed beam with larger actual structural width is formed without double splicing of two prestressed precast beams 1, the torsional rigidity and torsional bearing capacity of the formed superposed beam are consistent with those of an integrally cast-in-place beam and higher than those of a comparative example, structural modeling calculation is carried out according to the integral beam without special consideration in structural design, and the calculation assumption is consistent with the actual stress of the superposed beam, so that the defects that the comparative example cannot realize the support-free floor slab and the formwork-free superposed beam in a construction site are avoided.

Fig. 19 shows an improvement of the second preferred embodiment, and the specific improvement is that on the premise that the cross-section shearing calculation requirement of the composite beam can be met only by considering the peripheral stirrup of the cross section, the closed stirrup 16 in the middle of the cross section of the composite beam in the second preferred embodiment is eliminated, no stirrup extends from the top of the U-shaped bottom edge 11 during the manufacturing of the prestressed precast beam 1, and the installation and the removal of the core mold 53 are more convenient. In order to strengthen the restraint effect of the middle part of the cross section of the composite beam, the improved type is that the additional stirrup 19 is arranged in the middle area of the U-shaped bottom edge 11 of the prestressed precast beam 1, the additional stirrup 19 does not extend out of the top surface of the U-shaped bottom edge 11, the phenomenon that the stirrup limb distance is too large in the range of the U-shaped bottom edge 11 of the prestressed precast beam 1 can be avoided, the restraint effect of concrete in the range of the U-shaped bottom edge 11 of the prestressed precast beam 1 is improved, the compression performance of the concrete in the range of the U-shaped bottom edge 11 is improved, and the ductility of the composite beam under the action of negative bending moment is improved; the U-shaped dowel bars 64 are inserted into the inner wall range of the U-shaped section of the prestressed precast beam 1 in a construction site, the phenomenon that the limb distance of the stirrup in the composite beam is too large is avoided, the restraint effect of post-cast concrete in the middle of the cross section of the composite beam is improved, and the buckling degree of the longitudinal ribs 62 of the composite layer in the middle of the cross section of the composite beam when being pressed is reduced.

Fig. 20 provides an improved version of the composite beam shown in fig. 19, which is specifically improved in that shear-resistant steel bars 17 are embedded in the U-shaped bottom side 11 in the manufacturing process of the prestressed precast beam 1, the shear-resistant steel bars 17 are arranged perpendicular to the U-shaped bottom side 11, the post-cast concrete in the post-cast beam region 6 forms a steel bar cotter effect near the upper surface of the U-shaped bottom side 11 to participate in shearing, so that the shearing resistance of the interface between the precast concrete and the post-cast concrete of the composite beam is improved, meanwhile, the shear-resistant steel bars 17 can be respectively connected with the additional stirrups 19 and the U-shaped stirrups 64 in an overlapping manner, so that the overlapping force transmission between the additional stirrups 19 and the U-shaped stirrups 64 is realized, and stirrups capable of transmitting tensile force are formed in the middle of the cross section of the composite beam to participate in the shearing work of the oblique section, so as to improve the shear bearing force of the oblique section.

When the existing beam with a large cross section is a prestressed precast beam, the dead weight of the precast beam is reduced by reducing the height of the cross section of the precast beam or adopting an inverted T-shaped cross section, the construction of the precast beam without formwork and supporting of a floor slab on a construction site can not be really realized, the cost of site construction measures is high, and the potential safety hazard of construction exists. The invention discloses a prestressed precast beam and a composite beam composed of the prestressed precast beam, wherein the prestressed precast beam integrally adopts a U-shaped section, the self weight can be reduced by 30-55%, the top surface of the precast beam is directly contacted with the bottom surface of a floor slab after the precast beam is hoisted under the premise of controlling the self weight, the construction of the composite beam without formwork support and the construction of the floor slab without support in the construction site can be realized, a beam with larger section width can also adopt a prestressed precast beam integrally prefabricated to form the composite beam without adopting a precast beam double-splicing scheme with poorer stress performance, the out-of-plane bending deformation after the beam is released is controlled by arranging a contact rib between U-shaped side walls, and meanwhile, the core mould of the U-shaped section is standardized and has high generalization degree and low mould spreading cost.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes and substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. A prestressed precast beam is prefabricated and processed by adopting a long-line platform and a pretensioning method, and is applied to a structure with larger span and large floor load, and is characterized in that the cross section of the prestressed precast beam (1) is U-shaped, the height of a U-shaped bottom edge (11) is not less than 150mm, and the thickness of U-shaped side walls (12) at two sides is not less than 100 mm;

bottom prestressed steel strands (13) are distributed in the U-shaped bottom edge (11), upper anti-cracking prestressed tendons (14) are distributed at the middle upper parts of the U-shaped side walls (12) on the two sides, the bottom prestressed steel strands (13) and the upper anti-cracking prestressed tendons (14) are distributed in the full length direction of the prestressed precast beam (1), the number and the area of the bottom prestressed steel strands (13) and the upper anti-cracking prestressed tendons (14) are determined according to design calculation, and the upper anti-cracking prestressed tendons (14) are prestressed steel wires or steel strands;

the periphery of the U-shaped cross section is provided with a plurality of opening stirrups (15), the opening stirrups (15) extend out from the top surfaces of the U-shaped side walls (12) on the two sides, the extending end is provided with a 180-degree hook, the plane where the opening stirrups (15) are located is perpendicular to the length direction of the prestressed precast beam (1), and the diameters and the intervals of the opening stirrups (15) meet the requirements of the current design specifications.

2. The prestressed precast beam according to claim 1, wherein a plurality of connection ribs (3) connecting the U-shaped side walls (12) at two sides are arranged along the length direction of the prestressed precast beam (1), the connection ribs (3) are made of reinforced concrete, the upper surfaces of the connection ribs are flush with the top surfaces of the U-shaped side walls (12), the connection ribs (3) are simultaneously formed by pouring in the concrete pouring process of the prestressed precast beam (1), the cross section of the prestressed precast beam (1) at the connection ribs (3) is a solid rectangular cross section, the thickness of the connection ribs (3) along the length direction of the prestressed precast beam (1) is not less than 150mm, and the distance between the adjacent connection ribs (3) is 2.0-4.0 m;

and hoisting holes (4) are formed by pre-buried sleeves in the contact ribs (3) close to the two ends of the prestressed precast beam (1), the diameters of the hoisting holes (4) are not less than 40mm, and the hoisting holes are arranged in a penetrating manner along the horizontal direction of the cross section of the contact ribs (3).

3. The prestressed precast beam according to claim 1 or 2, characterized in that during the manufacturing process of the prestressed precast beam (1), the bottom prestressed steel strand (13), the upper anti-cracking prestressed tendon (14) and the stirrup are arranged in the long-line-table outer mold (51), the position of the U-shaped cross section is occupied by the core mold (53), after the bottom prestressed steel strand (13) and the upper anti-cracking prestressed tendon (14) are tensioned, concrete is poured between the long-line-table outer mold (51) and the core mold (53) to form the prestressed precast beam (1), and the core mold (53) is removed to form the U-shaped cross section;

the cross section width of the prestressed precast beam (1) is not more than 400mm, the core mould (53) adopts an integral mould, the cross section of the core mould (53) is in a trapezoid shape with a wide upper bottom and a narrow lower bottom, the U-shaped bottom edge (11) and concrete in the U-shaped side walls (12) at two sides are integrally cast and formed at one time, the cross section of a cavity part of the U-shaped cross section of the prestressed precast beam (1) is in a trapezoid shape with a wide upper bottom and a narrow lower bottom after the core mould (53) is removed, and no stirrup extends out of the upper surface of the U-shaped bottom edge (11);

or the width of the cross section of the prestressed precast beam (1) is larger than 400mm, the core die (53) adopts paired independent steel dies and forms a side die of the U-shaped side wall (12) together with the long-line platform outer die (51), the upper surface of the U-shaped bottom edge (11) is not provided with the die, a stirrup or a tie bar arranged in the middle of the cross section of the prestressed precast beam (1) is designed to extend out of the upper surface of the U-shaped bottom edge (11), concrete is poured to the upper surface of the U-shaped bottom edge (11) firstly in the manufacturing process of the prestressed precast beam (1), concrete in the U-shaped side wall (12) on two sides is poured before the concrete in the U-shaped bottom edge (11) is initially solidified, and the upper width and the lower width of the U-shaped side wall (12) are consistent.

4. The prestressed precast beam according to any one of claims 1 to 3, wherein when the prestressed precast beam (1) supports the secondary beam in a non-parallel direction, a placing notch (8) is arranged at a corresponding supporting position of the prestressed precast beam (1), the size of the placing notch (8) meets the placing requirement of the secondary beam, a notch occupying die (54) is adopted in the manufacturing process of the prestressed precast beam (1) to occupy space and ensure that no concrete exists in the range of the placing notch (8), and the upper anti-cracking prestressed ribs (14) in the range of the placing notch (8) are cut off after the concrete of the prestressed precast beam (1) reaches the design strength;

the connecting ribs (3) of the prestressed precast beam (1) are arranged at the positions of the placing notches (8), and when the distance between every two adjacent placing notches (8) is larger than 4.0m, one connecting rib (3) is additionally arranged between every two adjacent placing notches (8).

5. The prestressed precast beam according to claim 1 or 2, characterized in that after the prestressed precast beam (1) is hoisted in place at a construction site, both ends of the prestressed precast beam (1) are placed on the connected columns or walls, floor load in the construction process is transmitted to the connected columns or walls through the prestressed precast beam (1), when the floor load in the construction process is large, both ends of the prestressed precast beam (1) adopt solid rectangular cross sections within a certain length range, the solid rectangular cross section range is also used as the end connection ribs (3) of the prestressed precast beam (1), and the certain length is not more than the length of the beam end stirrup encryption area (2) required by the current design specifications.

6. The composite beam composed of the prestressed precast beams according to claim 1, characterized in that after the U-shaped prestressed precast beams (1) are hoisted in place at a construction site, the top of the prestressed precast beams (1) is bound with the composite layer longitudinal bars (62) and the composite layer tie bars (61), both ends of the composite layer tie bars (61) are 135-degree hooks and form an integral closed hoop with the open hoop (15), the post-cast beam area (6) is poured with concrete, and the prestressed precast beams (1) and the post-cast beam area (6) form an integral composite beam.

7. The composite beam as claimed in claim 6, wherein when the U-shaped bottom edge (11) of the prestressed precast beam (1) has no stirrup or tie bar extending into the post-cast beam region (6), shear steel bars (17) are pre-embedded in the U-shaped bottom edge (11) in the manufacturing process of the prestressed precast beam (1), the shear steel bars (17) are arranged perpendicular to the U-shaped bottom edge (11), and the shear steel bars (17) form a pin bolt function near the upper surface of the U-shaped bottom edge (11) to participate in shearing after the post-cast beam region (6) is cast with concrete;

the diameter of the shear steel bar (17) is not less than 16mm, the distance between adjacent shear steel bars (17) is 400-1000 mm, the length of the shear steel bar (17) extending out of the upper surface of the U-shaped bottom edge (11) is not less than 10 times of the diameter of the shear steel bar (17), and a hole for inserting the shear steel bar (17) is reserved in an integral die adopted by a core die (53).

8. The composite beam as claimed in claim 6, wherein a series of steel occupying strips (55) are welded on the surfaces of the core mould (53) facing the U-shaped side wall (12) and the U-shaped bottom edge (11), the length direction of the occupying strips (55) is perpendicular to the length direction of the prestressed precast beam (1), the cross section of the occupying strips (55) is trapezoidal, the size of the bottom edge tightly attached to the core mould (53) is larger than that of the bottom edge far away from the core mould (53), a series of key slots are formed on the inner wall of the prestressed precast beam (1) after the core mould (53) is removed, and the size of the key slots meets the construction requirements of the existing design specifications on the shear key slots of the new and old concrete interfaces; after the concrete in the post-cast area (6) of the beam is poured, the concrete of the prestressed precast beam (1) and the concrete in the post-cast area (6) of the beam are mutually occluded and shear-resistant at the position of the key groove.

9. The composite beam as claimed in claim 6, wherein when the prestressed precast beam (1) is inconvenient to extend a stirrup or tie bar from the U-shaped bottom edge (11) in the manufacturing process, the U-shaped transverse rib (18) or the additional stirrup (19) is arranged in the middle of the U-shaped bottom edge (11), the U-shaped dowel (64) is inserted in the range of the inner wall of the U-shaped section to restrain the longitudinal rib (62) of the composite layer in the construction site, and the U-shaped transverse rib (18) or the additional stirrup (19) in the prestressed precast beam (1) and the U-shaped dowel (64) in the post-cast beam area (6) form the composite stirrup in the middle of the cross section of the composite beam.

10. The composite beam according to claim 6, wherein when the two ends of the prestressed precast beam (1) are U-shaped sections, energy-consuming steel bars (63) are laid on the upper surfaces of the U-shaped bottom edges (11) at the two ends of the prestressed precast beam (1) in a construction site, the energy-consuming steel bars (63) are arranged along the length direction of the prestressed precast beam (1), one end of each energy-consuming steel bar extends into a connecting column or a wall at the end of the prestressed precast beam (1), one end of each energy-consuming steel bar is provided with a 90-degree hook and extends into a post-beam casting area (6), and the clear distance between each energy-consuming steel bar (63) and the upper surface of the U-shaped bottom edge (11) is 20-50 mm;

the energy dissipation steel bars (63) are sleeved with isolation sleeves on the surfaces, within the length range of 100-500 mm, extending into the prestressed precast beam (1) from the junction position of the prestressed precast beam (1) and the connected columns or walls, and the energy dissipation steel bars (63) in the isolation sleeves form an unbonded section after the beam post-pouring area (6) is poured with concrete.

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