Design method of multi-lateral asymmetric pile cap

Abstract

The present application relates to the technical field of building engineering, and more particularly to a design method of a multi-edge asymmetric pile cap, comprising: collecting information data of a multi-edge asymmetric pile cap engineering site, and establishing a three-dimensional finite element model of the multi-edge asymmetric pile cap according to the collected information data; using the three-dimensional finite element model for numerical simulation to obtain a stress-strain distribution nephogram of the multi-edge asymmetric pile cap, and identifying key areas in the stress-strain distribution nephogram under different working conditions; judging a main failure mode of the multi-edge asymmetric pile cap according to stress and strain distribution characteristics of the identified key areas, and selecting a corresponding design model according to the main failure mode; and recalculating the number and arrangement of the required reinforcement of the multi-edge asymmetric pile cap according to the selected design model; the method not only improves the bearing capacity and safety of such a pile cap, but also effectively controls the material cost.

Description

Technical Field

[0001] This invention relates to the field of building engineering technology, and in particular to a design method for a polygonal asymmetric pile foundation cap. Background Technology

[0002] In modern construction engineering, pile caps are widely used in various engineering fields. As a structural component that connects the superstructure and the foundation, the pile cap transfers the load from the superstructure to the piles, and then from the piles to the foundation; therefore, it must have sufficient bearing capacity. Generally, the planar dimensions and shape of a pile cap are determined by the number and arrangement of the piles, and are usually rectangular or circular. However, in actual engineering projects, irregularly shaped pile caps, such as polygonal asymmetric pile caps, may appear due to topography, geology, or design changes. Currently, there is considerable research on regular pile caps in existing technologies, but relatively little research on the calculation models, force transmission mechanisms, failure modes, and calculation methods for irregular pile caps. Therefore, how to solve the difficulties in designing and calculating irregular pile caps in existing technologies has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0003] To address the aforementioned problems, this invention discloses a design method for polygonal asymmetric pile foundation caps, thereby solving the difficulties in designing and calculating polygonal asymmetric pile foundation caps in the prior art.

[0004] A design method for a polygonal asymmetric pile cap foundation includes the following steps:

[0005] Step S1: Collect information data from the site of the polygonal asymmetric pile foundation project, and establish a three-dimensional finite element model of the polygonal asymmetric pile foundation based on the collected information data.

[0006] Step S2: Numerical simulation is performed using the three-dimensional finite element model to obtain the stress-strain distribution cloud map of the polygonal asymmetric pile cap, and key areas in the stress-strain distribution cloud map under different working conditions are identified.

[0007] Step S3: Based on the stress and strain distribution characteristics of the identified key areas, determine the main failure modes of the polygonal asymmetric pile cap, and select the corresponding design model according to the main failure modes;

[0008] Step S4: Recalculate the required amount and arrangement of reinforcement for the polygonal asymmetric pile cap based on the selected design model.

[0009] In some of these embodiments, the information data includes geological and seismic conditions, superstructure load conditions, and existing pile location layout.

[0010] In some embodiments, step S1 is characterized in that a three-dimensional finite element model of the polygonal asymmetric pile cap is established using engineering calculation software based on the collected information data.

[0011] In some of these embodiments, the plastic behavior of concrete and the elastic-plastic deformation of steel reinforcement are considered in the process of building the three-dimensional finite element model of the polygonal asymmetric pile cap.

[0012] In some embodiments, in step S2, the critical region includes the region of maximum bending moment and the region of shear stress concentration.

[0013] In some embodiments, in step S3, if the main failure mode is determined to be bending failure, a beam system design model is selected; if the main failure mode is determined to be punching shear failure, a tension / compression bar design model is selected.

[0014] In some embodiments, the design method further includes:

[0015] Step S5: Use the three-dimensional finite element model to simulate and verify the required amount and arrangement of reinforcement for the recalculated polygonal asymmetric pile cap.

[0016] Compared with the prior art, the above invention has at least one of the following advantages or beneficial effects:

[0017] This invention provides a design method for multi-sided asymmetric pile foundation caps, which overcomes the limitations of traditional design methods in dealing with multi-sided asymmetric pile foundation caps. It not only improves the bearing capacity and safety of such caps, but also effectively controls material costs and achieves structural optimization. Attached Figure Description

[0018] The invention, its features, shape, and advantages will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference numerals denote like parts throughout the drawings. The drawings are not drawn to scale; their focus is on illustrating the gist of the invention.

[0019] Figure 1 This is a flowchart illustrating the design method of a polygonal asymmetric pile cap in an embodiment of the present invention.

[0020] Figure 2 This is a basic plan layout diagram of the building project in an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention;

[0022] Figure 4aThis is a diagram showing the bottom reinforcement in the X direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention.

[0023] Figure 4b This is a bottom reinforcement cloud diagram in the X direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention;

[0024] Figure 5a This is a diagram showing the bottom reinforcement in the Y direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention.

[0025] Figure 5b This is a cloud diagram of the bottom reinforcement in the Y direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention;

[0026] Figure 6a This is a diagram showing the top reinforcement of the polygonal asymmetric pile cap CT4a in the X direction in an embodiment of the present invention.

[0027] Figure 6b This is a cloud diagram of the top reinforcement in the X direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention;

[0028] Figure 7a This is a diagram showing the top reinforcement of the polygonal asymmetric pile cap CT4a in the Y direction in an embodiment of the present invention.

[0029] Figure 7b This is a cloud diagram of the top reinforcement in the Y direction of the multi-sided asymmetric pile cap CT4a in an embodiment of the present invention;

[0030] Figure 8 This is a schematic diagram of the bottom reinforcement structure of the polygonal asymmetric pile cap CT4a in an embodiment of the present invention;

[0031] Figure 9 for Figure 8 Sectional view at point 4a-4a;

[0032] Among them, 1 is the foundation; 2 is the pile; and 3 is the column. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but these are not intended to limit the scope of the invention.

[0034] like Figure 1 As shown in the figure, this embodiment discloses a design method for a polygonal asymmetric pile cap, including the following steps:

[0035] Step S1 involves collecting on-site information data for the polygonal asymmetric pile foundation project and using engineering calculation software to establish a three-dimensional finite element model of the polygonal asymmetric pile foundation based on the collected data. The plastic behavior of concrete and the elastic-plastic deformation of reinforcing steel are considered during the model establishment process. This information data includes geological and seismic conditions, superstructure load conditions, and existing pile location layout.

[0036] Step S2: Numerical simulation is performed using a three-dimensional finite element model to obtain stress-strain distribution cloud maps of the polygonal asymmetric pile cap. Key regions in the stress-strain distribution cloud maps under different working conditions are identified through these stress-strain distribution cloud maps. These key regions mainly include the maximum bending moment region and the shear stress concentration region.

[0037] Step S3: Based on the stress and strain distribution characteristics of the identified key areas, determine the main failure mode of the polygonal asymmetric pile cap, and select the corresponding design model according to the main failure mode. Specifically, by analyzing the stress and strain distribution trends and reaction flow direction in the key areas, determine whether the main failure mode of the pile cap is bending failure or punching shear failure; when the bearing capacity of the pile cap is controlled by bending, it is bending failure; when it is controlled by compression, it is punching shear failure.

[0038] Specifically, if the main failure mode is determined to be bending failure, a beam system design model is selected; if the main failure mode is determined to be punching shear failure, a tension / compression bar design model is selected. Both the beam system design model and the tension / compression bar design model are well known in the art and will not be described in detail here.

[0039] Step S4: Recalculate the required amount and arrangement of reinforcement for the multi-sided asymmetric pile cap according to the selected design model. For asymmetric layouts, pay special attention to ensuring that the reinforcement in each direction meets the actual stress requirements.

[0040] Step S5 involves using a three-dimensional finite element model to simulate and verify the required amount and arrangement of reinforcement for the recalculated polygonal asymmetric pile cap. Specifically, further finite element simulations are performed on the final design scheme to confirm its safety and rationality, and details are adjusted until all performance requirements are met.

[0041] The invention will be further illustrated below with specific examples from architectural engineering projects:

[0042] In this example, addressing the irrationality of the commonly used engineering software PKPM in calculating polygonal asymmetric pile caps, a finite element analysis was performed on a polygonal asymmetric pile cap from this example to define it as subject to bending failure. Based on this definition, a beam-type system design model was selected to calculate the polygonal asymmetric pile cap, determining the amount and configuration of longitudinal reinforcement. The two reinforcement directions were arranged symmetrically along the line connecting the two piles.

[0043] Specifically, the construction project is located within a factory area, with a site topography of alluvial deposits at the foot of a mountain. It has 5 floors above ground, and the structural system is a cast-in-place reinforced concrete frame structure. The indoor and outdoor height difference is 300mm, and the building height is 31.940m. The foundation adopts pile caps, and the foundation design grade is Class B. The building pile foundation is a bored cast-in-place pile, and the design grade is Class B.

[0044] Figure 2 This is the foundation plan of the building project. Due to an error in the initial site plan regarding the building's location, the entire building was shifted 600mm to the right from its original position. However, seven piles had already been completed on site. In order to make full use of the existing piles and avoid waste, the original four-pile platform was transformed into a polygonal asymmetric pile cap, hereinafter referred to as a polygonal asymmetric pile cap; such as: CT3, CT4, CT4a, CT5, and CT5a.

[0045] This paper analyzes the irrationality of PKPM, a commonly used engineering software, in calculating multi-sided asymmetric foundations:

[0046] Taking CT4a as an example, such as Figure 3 As shown, the CT4a includes an irregularly shaped pier body 1, piles 2 disposed below the pier body 1, and columns 3 disposed on the pier body 1.

[0047] The PKPM calculation results are as follows:

[0048]

[0049] Calculation of flexural reinforcement for pile caps (the following are calculation results extracted from the PKPM program):

[0050] DMX1=7667.68kN*m; DMX2=7667.68kN*m; ASXI= 4964.16mm*mm / m; AXmin=1875.00mm*mm / m; DMY1=3389.43kN*m; DMY2= 3389.43kN*m; AYmin= 1875.00mm*mm / m;

[0051] X-direction bending reinforcement ASX = 4964 mm*mm / m;

[0052] Y-direction bending reinforcement ASY = 1875 mm * mm / m;

[0053] Maximum vertical axial force: 8879 kN;

[0054] Therefore, it can be determined that PKPM is calculated based on the most unfavorable cross section!

[0055] X-axis: DMX1 = 7667.68 kN*m;

[0056] The reinforcement area A = (7667.68 x 1000) / 0.9 x 360 x 1.2 = 19721 mm*mm;

[0057] Cross-sectional width b = A / ASX = 19721 / 4964 = 3.97m;

[0058] Y direction: DMY1 = 3889.43 kN*m;

[0059] The reinforcement area A = (3889.43 x 1000) / 0.9 x 360 x 1.2 = 10003.68 mm*mm;

[0060] The cross-sectional width b = A / ASX = 10004 / 1875 = 5.34m.

[0061] The PKPM design only considers the stress on a specific section of the foundation, which is obviously unsuitable for irregular foundations. They are asymmetrical polygons, not rectangles, and some of the reinforcing steel bars need to be cut off. If the horizontal and vertical reinforcements are calculated separately according to the program results, the actual reinforcement will be seriously insufficient. Obviously, this design is unreasonable.

[0062] Select as Figure 3 A three-dimensional finite element model of the pile cap CT4a is established, and then numerical simulation is performed using the three-dimensional finite element model to obtain stress-strain distribution contour maps of this polygonal asymmetric pile cap under different working conditions. The reinforcement diagrams and reinforcement contour maps for the top and bottom in the X and Y directions are shown below. Figure 4a , Figure 4b , Figure 5a , Figure 5b , Figure 6a , Figure 6b , Figure 7a , Figure 7b As shown.

[0063] From the reinforcement diagrams and reinforcement contour maps of the bottom surface of the foundation in the X and Y directions, it can be seen that the stress distribution of the steel reinforcement under the column foundation is characterized by a large stress at mid-span and a decreasing stress closer to the support after the steel reinforcement yields. The steel reinforcement under the column at the bottom surface of the foundation yields, forming plastic strands. From the reinforcement diagrams and reinforcement contour maps of the top surface of the foundation in the X and Y directions, it can be seen that the stress in the steel reinforcement under the column foundation is uniformly distributed, indicating structural reinforcement. Therefore, it can be determined that the main failure mode of the foundation is bending failure. The bending curvature is greatest in both directions at the lower part of the foundation near the column edge. After the load exceeds the yield zone of the steel reinforcement, the stress in the steel reinforcement at the mid-span section reaches yield. Based on this main failure mode, a beam-type system design model is selected.

[0064] In order to scientifically and reasonably calculate the reinforcement of a polygonal asymmetric pile cap, a specific analysis and calculation must be performed on the specific pile cap, and the two reinforcement directions should be arranged according to the symmetrical connection line of the two piles.

[0065] (1). Calculate the reinforcement area in the X direction.

[0066] Taking the largest net pile reaction force of the two piles (2870.66 kN), the following can be calculated using the formula for reinforcement area:

[0067] ;

[0068] Please refer to Article 8.2.12 of the Foundation Code for the formula of the reinforcement area.

[0069] 34.156 25 Considering the live load reduction (0.95), take 33. 25;

[0070] (2). Calculate the reinforcement area in the Y direction.

[0071] Take the largest net reaction force of the two piles (2957.52kN).

[0072] ;

[0073] 11.2 25 (take 13) 25);

[0074] The basic anchorage length of tensile reinforcement is determined according to the National Building Standard Design Atlas 2201-1 (No. 58). =32d (determined by the type of steel reinforcement, concrete strength grade, and seismic resistance grade) is the diameter of the steel reinforcement.

[0075] Furthermore, according to Article 9.2.3 of the Code for Design of Concrete Structures (GB50010-2010): Longitudinal reinforcing bars subjected to negative bending moment at the support section of reinforced concrete beams should not be cut off in the tension zone. However, if cutting off is necessary, the following provisions shall be met, wherein the first provision is that when V is not greater than... When this is not the case, the reinforcement should be extended to a point at least 20d beyond the section where the flexural capacity calculation does not require it, and the length extending from that point beyond the section where the reinforcement's strength is fully utilized should not be less than 1.2. ,

[0076]

[0077] The distance between the section where the reinforcement is not needed in the calculation of the flexural capacity of the cross section is [missing information]. Then, the distance from the cross-section of the stressed reinforcing bar to the section where the reinforcing bar strength is fully utilized is taken as:

[0078] Based on the above calculation results, the reinforcement of the polygonal asymmetric pile cap CT4a is specified. Figure 8 and Figure 9 .

[0079] In summary, this invention discloses a design method for polygonal asymmetric pile foundation caps. By analyzing the force transmission mechanism of polygonal asymmetric pile foundation caps, it provides a reliable theoretical basis for their design; it solves the stress problem of polygonal asymmetric pile foundation caps in engineering, and improves the bearing capacity and safety of the caps; it provides a new method and idea for the design of irregular pile foundation caps, and has broad application prospects.

[0080] Those skilled in the art should understand that variations can be implemented by combining existing technology with the above embodiments, which will not be elaborated here. Such variations do not affect the essence of the present invention, and will not be elaborated here either.

[0081] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and the devices and structures not described in detail should be understood as being implemented in a conventional manner in the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention's technical solutions still fall within the protection scope of the present invention.

Claims

1. A design method for a polygonal asymmetric pile cap, characterized in that, Includes the following steps: Step S1: Collect information data from the site of the polygonal asymmetric pile foundation project, and establish a three-dimensional finite element model of the polygonal asymmetric pile foundation based on the collected information data; the information data includes geological and seismic conditions, superstructure load conditions and existing pile location layout; and consider the plastic behavior of concrete and the elastic-plastic deformation of steel bars in the process of establishing the three-dimensional finite element model of the polygonal asymmetric pile foundation. Step S2: Numerical simulation is performed using the three-dimensional finite element model to obtain the stress-strain distribution cloud map of the polygonal asymmetric pile cap, and key regions in the stress-strain distribution cloud map under different working conditions are identified. The key regions include the maximum bending moment region and the shear stress concentration region. Step S3: Based on the stress and strain distribution characteristics of the identified key areas, determine the main failure modes of the polygonal asymmetric pile cap, and select the corresponding design model according to the main failure modes; Step S4: Recalculate the required amount and arrangement of reinforcement for the polygonal asymmetric pile cap based on the selected design model; Step S5: Use the three-dimensional finite element model to simulate and verify the required amount and arrangement of reinforcement for the recalculated polygonal asymmetric pile cap.

2. The design method for polygonal asymmetric pile caps as described in claim 1, characterized in that, In step S1, the characteristic is that an engineering calculation software is used to establish a three-dimensional finite element model of the polygonal asymmetric pile cap based on the collected information data.

3. The design method for polygonal asymmetric pile caps as described in claim 1, characterized in that, In step S3, if the main failure mode is determined to be bending failure, a beam system design model is selected; if the main failure mode is determined to be punching shear failure, a tension / compression bar design model is selected.

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