Design method of multilateral asymmetric pile foundation bearing platform

Abstract

The invention relates to the technical field of constructional engineering, in particular to a design method of a multilateral asymmetric pile foundation bearing platform, which comprises the following steps: collecting information data of a multilateral asymmetric pile foundation bearing platform engineering site, and establishing a three-dimensional finite element model of the multilateral asymmetric pile foundation bearing platform according to the collected information data; performing numerical simulation by utilizing the three-dimensional finite element model to obtain a stress-strain distribution cloud picture of the polygonal asymmetric pile foundation bearing platform, and identifying key areas in the stress-strain distribution cloud picture under different working conditions; judging a main failure mode of the multilateral asymmetric pile foundation bearing platform according to the identified stress and strain distribution characteristics of the key area, and selecting a corresponding design model according to the main failure mode; according to the selected design model, recalculating the number and the arrangement mode of the reinforcing bars required by the multilateral asymmetric pile foundation bearing platform; according to the method, the bearing capacity and safety of the bearing platform are improved, and the material cost is effectively controlled.

Description

Technical Field

[0001] The invention relates to the technical field of construction engineering, and in particular to a design method for a polygonal asymmetric pile foundation cap. Background Art

[0002] In modern construction projects, pile foundation caps are widely used in various engineering fields. As a structural component that connects the upper and lower parts, the cap transfers the load from the upper structure to the piles, and then from the piles to the foundation, so it must have sufficient bearing capacity. Generally speaking, the plane size and shape of the pile foundation cap are determined by the number and arrangement of the piles, usually rectangular and circular. However, in actual engineering, irregular-shaped caps may appear due to terrain, geology or design changes, such as multilateral asymmetric caps. At present, there are many studies on regular pile foundation caps in the prior art, but there are relatively few studies on the calculation model, force transmission mechanism, failure mode and calculation method of irregular caps; therefore, how to solve the problems of design and calculation difficulties of irregular caps in the prior art has become a technical problem that needs to be solved urgently by technicians in this field. Summary of the invention

[0003] In view of the above-mentioned problems, the present invention discloses a design method for a polygonal asymmetric pile foundation cap, so as to solve the problems such as the difficulty in designing and calculating the polygonal asymmetric pile foundation cap in the prior art.

[0004] A design method for a multi-sided asymmetric pile foundation cap comprises the following steps:

[0005] Step S1, collecting information data of the multilateral asymmetric pile foundation cap project site, and establishing a three-dimensional finite element model of the multilateral asymmetric pile foundation cap according to the collected information data;

[0006] Step S2, performing numerical simulation using the three-dimensional finite element model to obtain a stress-strain distribution cloud map of the polygonal asymmetric pile foundation cap, and identifying key areas in the stress-strain distribution cloud map under different working conditions;

[0007] Step S3, determining the main failure mode of the multi-sided asymmetric pile foundation cap according to the stress and strain distribution characteristics of the identified key areas, and selecting a corresponding design model according to the main failure mode;

[0008] Step S4, recalculating the quantity and arrangement of reinforcement required for the polygonal asymmetric pile foundation cap according to the selected design model.

[0009] In some of the embodiments, the information data includes geological and seismic conditions, upper load conditions and existing pile position arrangements.

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

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

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

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

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

[0015] Step S5, using the three-dimensional finite element model to simulate and verify the recalculated number of reinforcements and their arrangement required for the polygonal asymmetric pile foundation cap.

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

[0017] The present invention provides a design method for a multilateral asymmetric pile foundation pedestal, which overcomes the limitations of traditional design methods in dealing with multilateral asymmetric pile foundation pedestals, not only improves the bearing capacity and safety of such pedestals, but also effectively controls material costs and achieves structural optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention and its features, appearance and advantages will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings. The same reference numerals indicate the same parts in all the drawings. The drawings are not drawn to scale, and emphasis is placed on illustrating the subject matter of the present invention.

[0019] Figure 1 Flow chart of a design method for a multi-sided asymmetric pile foundation cap according to an embodiment of the present invention;

[0020] Figure 2 A basic plan layout diagram of a construction project in an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the structure of a multi-sided asymmetric pile foundation cap CT4a in an embodiment of the present invention;

[0022] Figure 4aIt is the X-direction bottom reinforcement diagram of the multi-sided asymmetric pile foundation cap CT4a in the embodiment of the present invention;

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

[0024] Figure 5a It is a Y-direction bottom reinforcement diagram of the multi-sided asymmetric pile foundation cap CT4a in the embodiment of the present invention;

[0025] Figure 5b It is a Y-direction bottom reinforcement cloud diagram of the multilateral asymmetric pile foundation cap CT4a in the embodiment of the present invention;

[0026] Figure 6a It is the X-direction top reinforcement diagram of the multi-sided asymmetric pile foundation cap CT4a in the embodiment of the present invention;

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

[0028] Figure 7a It is a Y-direction top reinforcement diagram of the multi-sided asymmetric pile foundation cap CT4a in the embodiment of the present invention;

[0029] Figure 7b It is a Y-direction top reinforcement cloud diagram of the multilateral asymmetric pile foundation cap CT4a in the embodiment of the present invention;

[0030] Figure 8 Schematic diagram of the bottom reinforcement structure of the multi-sided asymmetric pile foundation cap CT4a in an embodiment of the present invention;

[0031] Fig. 9 for Figure 8 A cross-sectional view at 4a-4a;

[0032] Among them, 1 is the foundation, 2 is the pile, and 3 is the column. DETAILED DESCRIPTION

[0033] The present invention is further described below with reference to the accompanying drawings and specific embodiments, but is not intended to be a limitation of the present invention.

[0034] like Figure 1 As shown, this embodiment discloses a design method for a multi-sided asymmetric pile foundation cap, comprising the following steps:

[0035] Step S1, collect information data of the multilateral asymmetric pile foundation cap engineering site, and use engineering calculation software to establish a three-dimensional finite element model of the multilateral asymmetric pile foundation cap according to the collected information data, and in the process of establishing the three-dimensional finite element model of the multilateral asymmetric pile foundation cap, the plastic behavior of concrete and the elastic-plastic deformation of steel bars are considered. The information data includes geological and seismic conditions, upper load conditions, and existing pile position layout.

[0036] Step S2, using a three-dimensional finite element model to perform numerical simulation to obtain the stress-strain distribution cloud map of the polygonal asymmetric pile foundation cap, and identifying the key areas in the stress-strain distribution cloud map under different working conditions through these stress-strain distribution cloud maps; the key areas mainly include the maximum bending moment area and the shear stress concentration area.

[0037] Step S3, judging the main failure mode of the multi-sided asymmetric pile foundation cap according to the stress and strain distribution characteristics of the identified key areas, and selecting the corresponding design model according to the main failure mode. Specifically, by analyzing the stress and strain distribution trend and reaction flow direction of the key areas, judging whether the main failure mode of the pile foundation cap is bending failure or shear failure; when the bearing capacity of the cap is controlled by bending, it is bending failure; when it is controlled by the compression rod, it is shear failure.

[0038] Specifically, if the main failure mode is judged to be bending failure, the beam system design model is selected; if the main failure mode is judged to be shear failure, the tension-compression rod design model is selected; the beam system design model and the tension-compression rod design model are both well known in the art and will not be described in detail here.

[0039] Step S4, recalculate the number of reinforcements and their arrangement required for the multilateral asymmetric pile foundation cap according to the selected design model. For the asymmetric layout, special attention is paid to ensuring that the reinforcement in each direction can meet the actual force requirements.

[0040] Step S5, using a three-dimensional finite element model to simulate and verify the number of reinforcements and their arrangement of the recalculated multi-sided asymmetric pile foundation cap. Specifically, further finite element simulation is performed on the final design to confirm its safety and rationality, and the details are adjusted until all performance requirements are met.

[0041] The present invention will be further described below with reference to a specific construction engineering example:

[0042] In this example, in view of the irrationality of the calculation of the multi-sided asymmetric cap by the commonly used engineering software PKPM, the multi-sided asymmetric cap in the example was selected for finite element analysis, and this type of cap was defined as being damaged by bending. According to the definition results, the beam system design model was selected to calculate the multi-sided asymmetric cap and determine the reinforcement amount and configuration of the longitudinal reinforcement. The two reinforcement directions were arranged according to the symmetrical connection line of the two piles.

[0043] Specifically, the construction project is located in a factory area. The site topography is a piedmont alluvial landform, with 5 floors above ground. The structural system is a cast-in-place reinforced concrete frame structure. The height difference between indoor and outdoor is 300mm, and the building height is 31.940m. The foundation adopts pedestal piles, and the foundation design grade is Class B. The building pile foundation is bored cast-in-place piles, and the design grade is Class B.

[0044] Figure 2 This is the basic plan layout of the construction project. Due to the error in the building positioning in the general plan in the early stage, the entire building was shifted 600mm to the right according to the original positioning. However, 7 piles had been completed on site. In order to make full use of the existing piles and avoid waste, the original four-pile platform was made into a multilateral asymmetric pile foundation pedestal, hereinafter referred to as the multilateral asymmetric pedestal; such as: CT3, CT4, CT4a, CT5, CT5a.

[0045] The irrationality of the calculation of multi-sided asymmetric caps by the commonly used engineering software PKPM is analyzed:

[0046] Take the platform CT4a as an example. Figure 3 As shown, the CT4a includes an irregularly shaped foundation body 1, piles 2 arranged below the foundation body 1, and columns 3 arranged on the foundation body 1.

[0047] The PKPM calculation results are as follows:

[0048]

[0049] Calculation of bending reinforcement of the cap (the following is the calculation result of the program intercepted by PKPM):

[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; ASYI= 1248.95mm*mm / 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: 8879KN;

[0054] From this, we can judge that PKPM is calculated based on the most unfavorable cross-section!

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

[0056] Reinforcement area A = (7667.68x1000) / 0.9x360x1.2 = 19721 mm*mm;

[0057] Section width b = A / ASX = 19721 / 4964 = 3.97m;

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

[0059] Reinforcement area A = (3889.43x1000) / 0.9x360x1.2 = 10003.68 mm*mm;

[0060] Section width b = A / ASX =10004 / 1875 =5.34m.

[0061] PKPM only considers the stress on a certain special section of the foundation during design. This is obviously not suitable for irregular foundations. It is an asymmetric polygon, not a rectangle. Part of the stress-bearing steel bars need to be cut off. If the horizontal and vertical reinforcement are carried out separately according to the results calculated by the program, the actual reinforcement will be seriously insufficient. Obviously, this design is unreasonable.

[0062] Select as Figure 3 A three-dimensional finite element model is established for the cap CT4a shown in the figure. Then, the three-dimensional finite element model is used for numerical simulation to obtain the stress-strain distribution cloud diagram of the multi-sided asymmetric pile foundation cap under different working conditions. Among them, the reinforcement diagram and reinforcement cloud diagram of the top and bottom of the X-direction and Y-direction are shown in FIG. Figure 4a , Figure 4b , Figure 5a , Figure 5b , Figure 6a , Figure 6b , Figure 7a , Figure 7b shown.

[0063] From the reinforcement diagram and reinforcement cloud diagram of the bottom surface of the pedestal in the X and Y directions, it can be seen that the stress distribution of the steel bars of the pedestal under the column is large in the middle of the span and smaller as it is closer to the support. The steel bars under the column on the bottom surface of the pedestal yield to form plastic strands. From the reinforcement diagram and reinforcement cloud diagram of the top surface of the pedestal in the X and Y directions, it can be seen that the stress of the steel bars of the pedestal under the column is evenly distributed, and all are structural reinforcement. From this, it can be judged that the main failure mode of the pedestal is bending failure. The bending curvature of the lower part of the pedestal column side in both directions is the largest. After the load exceeds the steel bar yield area, the steel bar stress on the mid-span section reaches yield. The beam system design model is selected based on this main failure mode.

[0064] In order to scientifically and reasonably calculate the reinforcement of a multilateral asymmetric pedestal, specific analysis and calculation of the pedestal must be carried out, and the two reinforcement directions should be arranged according to the symmetrical connection line of the two piles.

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

[0066] Take the largest net reaction force of the two piles (2870.66 kN); according to the formula of reinforcement area, we can get:

[0067] ;

[0068] For the formula of this reinforcement area, please refer to Section 8.2.12 of the Foundation Code.

[0069] 34.156 25 Considering the reduction of live load (0.95) Take 33 25;

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

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

[0072] ;

[0073] 11.2 25 (take 13 25);

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

[0075] According to Article 9.2.3 of the Code for Design of Concrete Structures (GB50010-2010): The longitudinal force-bearing steel bars of the negative moment of the support section of reinforced concrete beams should not be cut off in the tension zone. However, if they need to be cut off, they should comply with the following provisions: When the steel bar is extended to a point not less than 20d beyond the cross section where the steel bar is not needed according to the cross section bending bearing capacity calculation, and the length extending from the point where the steel bar strength is fully utilized shall not be less than 1.2 ,

[0076]

[0077] The strength of the steel bar is fully utilized. The cross-sectional distance from the cross-sectional bending bearing capacity calculation to the positive cross-sectional bending bearing capacity calculation does not require the cross-sectional distance of the steel bar. , then the distance between the cross section of the stressed steel bar and the cross section where the strength of the steel bar is fully utilized is:

[0078] According to the above calculation results, the reinforcement of the multi-sided asymmetric cap CT4a is carried out. Figure 8 and Fig. 9 .

[0079] In summary, the present invention discloses a design method for a multilateral asymmetric pile foundation pedestal. By analyzing the force transmission mechanism of the multilateral asymmetric pile foundation pedestal, a reliable theoretical basis for its design is provided; the force problem of the multilateral asymmetric pedestal in engineering is solved, and the bearing capacity and safety of the pedestal are improved; a new method and idea is provided for the design of irregular pedestals, which has broad application prospects.

[0080] Those skilled in the art should understand that those skilled in the art can implement variations by combining the prior art and the above embodiments, which will not be described in detail here. Such variations do not affect the essential content of the present invention, and will not be described in detail here.

[0081] The above describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and the devices and structures that are not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can use the above-disclosed methods and technical contents to make many possible changes and modifications to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention, or modify them into equivalent embodiments of equivalent changes, which 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 technical solutions of the present invention are still within the scope of protection of the technical solutions of the present invention.

Claims

1. A design method for a multi-sided asymmetric pile foundation cap, characterized in that: The steps include: Step S1, collecting information data of the multilateral asymmetric pile foundation cap project site, and establishing a three-dimensional finite element model of the multilateral asymmetric pile foundation cap according to the collected information data; Step S2, performing numerical simulation using the three-dimensional finite element model to obtain a stress-strain distribution cloud map of the polygonal asymmetric pile foundation cap, and identifying key areas in the stress-strain distribution cloud map under different working conditions; Step S3, determining the main failure mode of the multi-sided asymmetric pile foundation cap according to the stress and strain distribution characteristics of the identified key areas, and selecting a corresponding design model according to the main failure mode; Step S4, recalculating the quantity and arrangement of reinforcement required for the polygonal asymmetric pile foundation cap according to the selected design model.

2. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: The information data includes geological and seismic conditions, upper load conditions and existing pile position arrangements.

3. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: In the step S1, it is characterized in that a three-dimensional finite element model of the polygonal asymmetric pile foundation cap is established according to the collected information data using engineering calculation software.

4. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: The plastic behavior of concrete and the elastic-plastic deformation of steel bars are taken into consideration in the process of establishing the three-dimensional finite element model of the polygonal asymmetric pile foundation cap.

5. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: In the step S2, the key area includes a maximum bending moment area and a shear stress concentration area.

6. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: In step S3, if it is determined that the main failure mode is bending failure, the beam system design model is selected; if it is determined that the main failure mode is shear failure, the tension-compression rod design model is selected.

7. The design method of a multi-sided asymmetric pile foundation cap according to claim 1, characterized in that: The design method further comprises: Step S5, using the three-dimensional finite element model to simulate and verify the recalculated number of reinforcements and their arrangement required for the polygonal asymmetric pile foundation cap.

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