Prestressed assembly type prefabricated concrete corbel beam

Abstract

This invention relates to a prestressed precast concrete cap beam, comprising a precast concrete cap beam shell, a transverse prestressed tensioning and anchoring system, a pile-beam composite anchoring assembly, and post-cast concrete. The transverse prestressed tensioning and anchoring system includes a reinforced bearing pad located outside the retaining structure. The precast concrete cap beam shell includes side plates and a bottom plate. Multiple embedded pipes are arranged side-by-side along the length of the side plates, with steel strands inserted into them. The ends of the steel strands pass through inclined holes in the retaining piles and extend into the pressure bearing pad. Anchors are provided at the ends of the steel strands. Post-cast concrete is poured within the space of the side plates, bottom plate, and retaining structure. Functionally, this invention can simultaneously replace existing cap beams, steel supports, tensioned beams, and other structures within the foundation pit. The precast concrete cap beam components are prefabricated off-site and quickly hoisted and assembled upon arrival on-site, significantly shortening the on-site construction cycle and allowing for earlier initiation of the foundation pit excavation process.

Description

Technical Field

[0001] This invention relates to a prestressed precast concrete cap beam for foundation pit support, belonging to the field of building construction technology. Background Technology

[0002] As a key top connecting component of the foundation pit pile support system, the capping beam can effectively connect the discrete retaining piles, enabling the single pile support structure to form an overall coordinated force-bearing system. It bears and transmits the lateral pressure of water and soil in the foundation pit and the anchoring reaction force of the internal support, playing an important role in restraining the horizontal displacement of the pile top and ensuring the overall stability of the foundation pit support.

[0003] Currently, foundation pit support engineering commonly adopts a combination of cast-in-place reinforced concrete capping beams and concrete or steel supports. This type of support system mainly relies on the passive bearing capacity of the support structure to resist the lateral loads of the soil. However, traditional concrete supports and ordinary steel supports are difficult to apply effective preload, and cannot apply active preload constraints to the retaining piles before foundation pit excavation. The support structure can only passively bear force after soil deformation, lacking the ability to actively control foundation pit deformation. Under complex conditions such as soft soil and ultra-deep foundation pits, problems such as excessive support deformation and insufficient safety reserve are very likely to occur.

[0004] Meanwhile, the traditional cast-in-place cap beam construction process is complex, requiring multiple steps such as removing laitance from pile heads, binding reinforcing cages on-site, erecting formwork and support systems, pouring concrete on-site, and long-term moisture curing. The limited working space on-site leads to low construction efficiency and a long curing period, severely hindering the progress of subsequent earthwork excavation. Furthermore, open-air cast-in-place construction is significantly affected by environmental temperature and humidity, rainfall, and the skill level of the workers, making the finished product prone to quality defects such as honeycomb texture, shrinkage cracks, and deviations in the reinforcing steel protective layer. Uneven roughening of the pile-beam interface can easily create a weak bond between the old and new concrete layers, reducing the overall load-bearing capacity of the pile and beam.

[0005] Furthermore, cast-in-place construction involves a large amount of wet work on-site, requires significant investment in reusable materials such as formwork and scaffolding, generates substantial amounts of construction waste and dust, and has poor green construction characteristics. Therefore, existing traditional cast-in-place cap beam support methods suffer from drawbacks such as low construction efficiency, poor controllability of finished product quality, and the support system's passive ability to bear loads without actively controlling foundation pit deformation. These shortcomings make it difficult to simultaneously meet the demands of modern foundation pit engineering construction that prioritizes efficient construction, structural quality, and high-precision deformation control. Summary of the Invention

[0006] The purpose of this invention is to overcome the various shortcomings of existing cast-in-place cap beams in terms of construction cycle, forming quality, stress control, and anchoring durability. It provides a prestressed precast concrete cap beam, which adopts a composite stress-bearing structure consisting of a factory-prefabricated L-shaped hollow shell and a post-cast inner cavity concrete. It is equipped with a transverse prestressed tensioning anchoring system penetrating the retaining piles and a pile-beam composite anchoring structure. Relying on an industrialized prefabrication combined with on-site assembly construction, it significantly reduces the amount of wet work on-site. By using prestressed tensioning technology to apply inward-converging prestress to all retaining piles before excavation, it achieves proactive control of pile top deformation from the stress source, improving the overall connection reliability between the piles and the cap beam.

[0007] The present invention adopts the following technical solution:

[0008] A prestressed precast concrete cap beam includes a precast concrete cap beam shell, a transverse prestressed tensioning and anchoring system, post-cast concrete, and a beam composite anchoring assembly. The transverse prestressed tensioning and anchoring system includes a reinforced bearing pad located outside the retaining structure. The precast concrete cap beam shell includes side plates and a bottom plate; the side plates are arched, and the bottom plate is perpendicular to the bottom of the side plates and integrally formed with them. Multiple embedded pipes are arranged side-by-side along the length of the side plates, and steel strands are inserted into the embedded pipes. The end of the steel strand passes through the inclined hole opened on the retaining pile and extends into the reinforced bearing pad block, and the end of the steel strand is provided with an anchor; post-cast concrete is poured in the space of the side plate, bottom plate and retaining structure; the side plate has two inclined sides on both sides and one straight side in the middle; the pile-beam composite anchoring assembly includes multiple pre-embedded sleeves vertically embedded at the position of the straight side of the side plate, and inserting reinforcing bars into the pre-embedded sleeves; multiple anchoring bars are vertically implanted in the retaining structure opposite to the side plate through on-site drilling, and the anchoring bars are opposite to or parallel to the inserting bars.

[0009] Furthermore, the retaining structure consists of multiple retaining piles arranged side by side.

[0010] Furthermore, multiple trapezoidal concrete shear keys are spaced apart on the inner side of the side plate, and the embedded sleeves and reinforcing bars are positioned between adjacent concrete shear keys.

[0011] Preferably, the inner walls of the side plates and bottom plates are coated with an interface release agent for recycling after the precast concrete cap beam shell is disassembled, and the concrete cap beam shell can be reused.

[0012] Preferably, a tensioning operation groove is excavated in the soil outside the retaining structure, and the reinforcing pressure pad is set in the tensioning operation groove.

[0013] Furthermore, the reinforced pressure-bearing pad is a cast-in-place structure with a sleeve embedded inside for the steel strands to pass through.

[0014] Preferably, the embedded pipe is made of steel, and multiple pipes are arranged side by side and parallel to each other.

[0015] Preferably, the anchorage is provided with a prestressing device.

[0016] The beneficial effects of this invention are as follows:

[0017] 1) High degree of functional integration: Functionally, it can simultaneously replace existing structures in the foundation pit, such as capping beams, steel supports, and tensioned beams. Existing capping beams use a lot of material and require support underneath. This invention significantly reduces material usage and lowers costs, while also possessing the functions of steel supports and tensioned beams. It can also apply prestress to the sidewalls of the foundation pit, making it particularly suitable for shallow foundation pits.

[0018] 2) In terms of construction period and economic benefits: Precast components are processed off-site in advance and quickly hoisted and assembled on site, which greatly shortens the on-site construction cycle and allows the foundation pit excavation process to start earlier; the precast concrete cap beam shell can be reused as a temporary formwork or used as a permanent formwork, saving the investment in turnover materials such as formwork and scaffolding; the amount of post-cast core concrete used is much lower than that of a fully cast-in-place cap beam, effectively saving raw material costs and reducing the overall project cost.

[0019] 2) Structural safety and deformation control: Prestressed concrete can effectively tighten the retaining piles, significantly reduce the lateral deformation of the pile top under soft soil and deep foundation pit conditions, and reduce the cost of additional internal support and anchor cables in the later stage; the composite anchoring structure improves the shear bearing capacity of the pile-beam interface, and the joint stress performance of the pile body and the cap beam is better than that of conventional cast-in-place structures.

[0020] 3) In terms of green construction and quality control: Most construction procedures are transferred to the prefabrication plant, and the amount of dust, construction waste and construction wastewater discharged at the construction site is greatly reduced, meeting the requirements of green and low-carbon construction; prefabricated components are cured and formed in the factory according to the standard mold, avoiding common problems such as honeycomb surface, protective layer deviation and inadequate vibration in cast-in-place construction, and the quality stability of finished products is significantly improved.

[0021] 4) Engineering applicability: This invention can be adapted to various retaining piles such as cast-in-place piles and interlocking piles. It can flexibly adjust the prestressing tension according to the depth of the foundation pit and the mechanical parameters of the soil layer. It can be used for small and medium foundation pits in conventional strata, and can also be promoted and applied in foundation pits in coastal soft soil and complex strata with high pressure water. It has a wide range of applicable scenarios. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structural layout of the prestressed precast concrete cap beam of the present invention.

[0023] Figure 2 This is a schematic diagram of a prestressed tensioning anchorage structure.

[0024] Figure 3 Details of the precast concrete cap beam construction Figure 1 .

[0025] Figure 4 Details of the precast concrete cap beam construction Figure 2 .

[0026] Figure 5 This is a schematic diagram of the cross-sectional structure of a precast concrete cap beam.

[0027] In the figure, 1. Precast concrete cap beam shell, 2. Transverse prestressed tensioning and anchoring system, 3. Pile-beam composite anchoring assembly, 4. Post-cast concrete, 5. Tensioning operation slot, 6. Reinforced bearing pad, 7. Through-hole jack, 8. Anchorage, 9. Steel strand, 10. Retaining pile;

[0028] 101. Side plate; 102. Bottom plate;

[0029] 101a. Embedded pipe, 101b. Inserted rebar, 101c. Concrete shear key, 101d. External locking nut, 101f. Internal limiting nut, 101g. Embedded sleeve;

[0030] 10a. Rebar installation;

[0031] 11. Interface isolator. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] See Figure 1-2 A prestressed precast concrete cap beam includes a precast concrete cap beam shell 1, a transverse prestressed tensioning and anchoring system 2, and post-cast concrete 4.

[0034] Combination Figure 1-2 The transverse prestressed tensioning anchoring system 2 includes a reinforced pressure-bearing pad 6 located on the outside of the retaining structure;

[0035] Combination Figure 3-5 The precast concrete cap beam shell 1 includes a side plate 101 and a bottom plate 102. The side plate 101 is arched, and the bottom plate 102 is perpendicular to the bottom of the side plate 101 and is integral with the side plate 101. Multiple embedded pipes 101a are arranged side by side along the length direction inside the side plate 101. Steel strands 9 are inserted into the embedded pipes 101a. The two ends of the steel strands 9 pass through the inclined holes opened on the retaining piles 10 and extend into the reinforcing pressure pad 6. Anchors 8 are provided at the ends of the steel strands 9. Post-cast concrete 4 is poured in the space of the side plate 101, the bottom plate 102 and the retaining structure.

[0036] In this embodiment, see Figure 1The side plate 101 has two inclined sides on both sides and a straight side in the middle.

[0037] See also Figure 1 The retaining structure consists of multiple retaining piles 10 arranged side by side.

[0038] Combination Figure 3 , Figure 4 and Figure 5 The prestressed precast concrete cap beam also includes a pile-beam composite anchoring component 3, which includes multiple pre-embedded sleeves 101g vertically embedded at the position of the straight edge of the side plate 101, with reinforcing bars 101b inserted into the pre-embedded sleeves 101g; and multiple anchor bars 10a vertically implanted through on-site drilling on the retaining structure opposite to the side plate 101, with the anchor bars 10a being directly opposite or parallel to the reinforcing bars 101b.

[0039] It should be noted that the anchor bar 10a and the insert bar 101b are not used to directly and continuously transmit the tensile force of the main reinforcement, but to bear the shrinkage stress, secondary structural stress, and interface shear force mainly from the direction of gravity.

[0040] See Figure 5 Multiple trapezoidal concrete shear keys 101c are provided at intervals on the inner side of the side plate 101, and the pre-embedded sleeve 101g and the dowel bar 101b are located between adjacent concrete shear keys 101c.

[0041] See also Figure 5 The inner walls of the side plate 101 and the bottom plate 102 are coated with an interface release agent 11 for recycling after disassembly of the precast concrete cap beam shell 1, and the precast concrete cap beam shell 1 can be reused.

[0042] See Figure 1 The soil outside the retaining structure is excavated with a tensioning operation groove 5, and the reinforcing pressure pad 6 is set in the tensioning operation groove 5.

[0043] In this embodiment, see Figure 2 The reinforced pressure-bearing pad 6 is a cast-in-place structure, with a sleeve embedded inside for the steel strand 9 to pass through.

[0044] In this embodiment, see Figure 5 The pre-embedded pipe 101a is made of steel, and multiple pipes are arranged side by side and in parallel.

[0045] In this embodiment, see Figure 2 The anchorage 8 is equipped with a prestressing device.

[0046] The details of this embodiment are further explained below:

[0047] See Figure 1The overall structure of the precast concrete cap beam mainly consists of the precast concrete cap beam shell 1, the post-cast concrete 4, the transverse prestressed tensioning anchoring system 2, and the pile-beam composite anchoring component 3. Figure 1 The four sections of the post-cast concrete are only partially shown; in reality, they fill the entire precast concrete cap beam shell 1.

[0048] The precast concrete cap beam shell 1 is standardized and cast in the prefabrication plant using a mold. The finished product is an L-shaped hollow trough structure. It is prefabricated in sections according to the spacing of the retaining piles on site. After being transported to the construction site, it is hoisted and placed sequentially at the design elevation of the top of the retaining piles 10 using crane equipment. The ends of adjacent shells are spliced ​​together to form a continuous and closed outer frame structure. The core is cast after the shell cavity is formed by pouring concrete on site. The precast concrete cap beam shell 1 and the cast concrete 4 are interlocked and bonded to form a complete composite cap beam.

[0049] The pile-beam composite anchorage component 3 includes a through-embedded pipe 101a pre-embedded in the side wall of the shell, a finely threaded reinforcing bar 101b with an inner limiting nut 101f and an outer locking nut 101d, and a pre-embedded reinforcing bar 10a for the retaining pile. The precast concrete cap beam shell 1 has an integrally cast concrete shear key 101c. During construction, the finely threaded reinforcing bar 101b is inserted into the pre-embedded sleeve from the outside of the precast concrete cap beam shell 1. The precast concrete cap beam shell 1 is fixed by bidirectional clamping with the inner limiting nut 101f and the outer locking nut 101d. The reinforcing bar 10a is inserted into the retaining pile 10, extending into the cavity of the precast concrete cap beam shell 1. Then, concrete 4 is poured to completely enclose the reinforcing bar 10a and the reinforcing bar 101b, forming a multi-force transmission structure of mechanical interlocking and bonded anchorage with the concrete shear key 101c of the precast concrete cap beam shell 1. A layer of interface release agent 11 is applied to the surface of the concrete shear key 101c and the bottom plate 102 of the precast concrete cap beam shell 1 to facilitate demolding after the project is completed. The L-shaped hollow trough structure can be recycled and reused.

[0050] See Figure 1 Tensioning operation trenches 5 are formed by partially excavating soil at both ends of the longitudinal direction of the cap beam. (See [reference]) Figure 2 The bottom of the trench is formed by casting C60 concrete reinforced bearing pad 6. Multiple strands of steel strands pass through the embedded pipe 101a of the precast concrete cap beam shell 1. One end of the steel strand 9 is anchored to the reinforced bearing pad 6 on one side by a clip-type anchor 8, and the other end extends to the tensioning groove on the opposite side. After the precast shell is assembled, the anchoring components are laid out, and the concrete is poured and cured in the shell, the steel strand 9 is tensioned to the design prestress using a through-type tensioning machine (through-type jack 7) according to the graded loading process. The anchor is locked to achieve the overall pre-tightening of the retaining pile.

[0051] The construction process of this invention is coherent and concise. First, the batch casting, standard curing, and storage and transportation of the L-shaped precast concrete cap beam shell 1 are completed simultaneously in the prefabrication plant. This process can be carried out in parallel with the construction of the retaining piles on the construction site. After all the retaining piles on site have reached the curing standard, the pile body is trimmed and the rebar is installed. At the same time, tensioning operation grooves 5 are excavated at both ends of the precast concrete cap beam shell 1 and the end reinforcing pressure pads 6 are poured. Then, the precast concrete cap beam shell 1 is positioned in sections using hoisting equipment, the insert bars 101b are inserted and the nuts on both sides are tightened. Post-cast concrete is pumped from the top surface of the precast concrete cap beam shell 1 to fill the shell cavity. After the concrete is cured to the design strength, the through steel strands 9 are laid out and prestress is applied in stages to complete the forming of the entire prestressed prefabricated cap beam.

[0052] The main innovations of this invention are described below:

[0053] 1. Innovative Cross-Sectional Structure: The design employs an L-shaped hollow precast shell combined with locally cast-in-place concrete in the inner cavity, abandoning the traditional fully cast-in-place method. The precast concrete cap beam shell 1 (hereinafter referred to as the "shell") directly serves as the formwork for the cast-in-place concrete. The inner wall of the shell utilizes concrete shear keys 101c and reinforcing bars 101b. The shear keys achieve mechanical bonding and force transfer between the old and new concrete, while the reinforcing bars 101b increase the horizontal connection between the old and new concrete, effectively preventing the delamination and separation of the composite cap beam. The L-shaped structure also reduces the self-weight of the precast components, optimizing component transportation and on-site hoisting conditions. An interface release agent 11 isolates the surfaces of the old and new concrete, preventing adhesion and facilitating demolding and recycling after project completion.

[0054] 2. Innovative stress system: The structure of transverse steel strand 9 running through the entire row of retaining piles changes the traditional passive stress mode of the cap beam relying solely on its own rigidity and internal support. Before the foundation pit is excavated, the steel strand 9 is used to apply inward prestress to the retaining piles, which in advance offsets the outward expansion deformation of the pile top caused by the lateral pressure of water and soil, and realizes active control of support deformation. The prestress is anchored by the cast-in-place reinforced bearing pads 6 at both ends of the foundation pit, eliminating the need for a large number of pre-embedded anchoring components in the pile body, and is suitable for various pile types and diameters.

[0055] 3. Innovative Anchoring Structure: A composite anchoring system is constructed, consisting of rebar anchoring in the pile body and double-nut locking of precision-rolled insert bars. This differs from the traditional method of single rebar anchoring. The anchored rebar bears the vertical shear force and pull-out force, while the insert bars bear the interface shear force and horizontal pull-out force. The double nuts can quickly lock and position the precast shell, and the insert bars serve the dual functions of assembly limitation and structural stress bearing, significantly improving the anti-slip performance of the pile-beam interface.

[0056] 4. Construction technology innovation: The construction adopts a low-wet-operation mode of factory prefabrication and on-site assembly. The industrial prefabrication of the cap beam shell can be carried out simultaneously with the on-site pile foundation construction. The construction site reduces a large number of processes such as on-site binding of steel cages, large-area formwork erection and dismantling, and scaffolding erection. Only assembly, anchoring, a small amount of binding, local post-pouring construction, tensioning and other contents are retained, which effectively reduces the amount of on-site wet work and fits the industrialized construction concept of prefabricated buildings.

[0057] The prestressed precast concrete cap beam of this invention is particularly suitable for large-scale, large-area excavation foundation pit projects. It is equipped with precast concrete cap beam shell components prefabricated in sections at the factory, which can be directly erected onto the top of the retaining piles, forming a complete external load-bearing system in conjunction with the retaining piles. It is suitable for key projects with strict schedule control and tight completion deadlines; the system requires no internal support within the foundation pit, eliminating the need to wait for steel or concrete supports to be erected during earthwork excavation, allowing excavation processes to be carried out in advance, significantly reducing the overall construction period of the foundation pit support stage. It can be used in various reinforcement engineering scenarios: reinforcement of existing foundation pit support defects, emergency reinforcement of soft soil / miscellaneous fill slopes, protective support reinforcement of surrounding buildings (structures), and is also suitable for emergency construction projects such as public works projects and pipeline repairs.

[0058] The above are preferred embodiments of the present invention. Those skilled in the art can make various modifications or improvements based on these embodiments. Without departing from the overall concept of the present invention, such modifications or improvements should fall within the scope of protection claimed by the present invention.

Claims

1. A prestressed precast concrete cap beam, characterized in that: It includes a precast concrete cap beam shell (1), a transverse prestressed tensioning anchoring system (2), post-cast concrete (4), and a pile-beam composite anchoring assembly (3). The transverse prestressed tensioning anchoring system (2) includes a reinforced pressure-bearing pad (6) located on the outside of the enclosure structure. The precast concrete cap beam shell (1) includes a side plate (101) and a bottom plate (102). The side plate (101) is arched, and the bottom plate (102) is perpendicular to the bottom of the side plate (101) and is integral with the side plate (101). Multiple embedded pipes (101a) are arranged side by side along the length direction inside the side plate (101). Steel strands (9) are inserted into the embedded pipes (101a). The two ends of the steel strands (9) pass through the inclined holes opened on the retaining piles (10) and extend into the reinforcing pressure pad (6). Anchors (8) are provided at the ends of the steel strands (9). Post-cast concrete (4) is poured within the space of the side plate (101), bottom plate (102), and enclosure structure. The side plate (101) has two inclined sides on both sides and a straight side in the middle; The pile-beam composite anchoring assembly (3) includes multiple pre-embedded sleeves (101g) vertically embedded at the position of the straight edge of the side plate (101), and inserting reinforcing bars (101b) inserted into the pre-embedded sleeves; multiple anchoring bars (10a) are vertically implanted through on-site drilling on the retaining structure opposite to the side plate (101), and the anchoring bars (10a) are opposite to or parallel to the inserting bars (101b).

2. The prestressed precast concrete cap beam as described in claim 1, characterized in that: The retaining structure consists of multiple retaining piles (10) arranged side by side.

3. The prestressed precast concrete cap beam as described in claim 1, characterized in that: Multiple trapezoidal concrete shear keys (101c) are provided at intervals on the inner side of the side plate (101), and the pre-embedded sleeve (101g) and the dowel bar (101b) are located between adjacent concrete shear keys (101c).

4. The prestressed precast concrete cap beam as described in claim 1, characterized in that: The inner walls of the side plate (101) and the bottom plate (102) are coated with an interface release agent (11) for recycling the precast concrete cap beam shell (1) after disassembly. The precast concrete cap beam shell (1) can be reused.

5. The prestressed precast concrete cap beam as described in claim 1, characterized in that: The soil outside the retaining structure is excavated with a tensioning operation groove (5), and the reinforcing pressure pad (6) is set in the tensioning operation groove (5).

6. The prestressed precast concrete cap beam as described in claim 5, characterized in that: The reinforced pressure-bearing pad (6) is a cast-in-place structure, with a sleeve embedded inside for the steel strand (9) to pass through.

7. The prestressed precast concrete cap beam as described in claim 1, characterized in that: The pre-embedded pipe (101a) is made of steel, and multiple pipes are arranged side by side and in parallel.

8. The prestressed precast concrete cap beam as described in claim 1, characterized in that: The anchor (8) is equipped with a prestressing device.

Images