A method for reinforcing existing shallow foundation with negative bending moment compensation

Abstract

The application relates to the technical field of building foundation reinforcement, in particular to a negative bending moment compensation type existing shallow foundation reinforcement method, which sequentially comprises the following steps: determining an existing foundation to be reinforced; calculating bearing moments M R and shears V R of each existing foundation; selecting new pile parameters and guiding loads on the upper structure of the existing foundation; determining the size of a joint pile cap and determining the number and positions of piles, so that the top of the new piles on the periphery of the joint pile cap generates a negative bending moment; calculating the design values M1 of the bending moments and V1 of the shears of each existing foundation; comparing M R and M1, V R and V1 until M R >M1 and V R >V1. The application has the effect of effectively improving the bearing capacity of the existing foundation under the condition of limited clearance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building foundation reinforcement, in particular to a negative bending moment compensation type existing shallow foundation reinforcement method. BACKGROUND

[0002] In the process of reconstruction and reinforcement of existing shallow foundation buildings, when the original foundation needs to be supplemented and supported for reinforcement due to the large difference in bearing capacity of the original foundation caused by the increase of the upper structure load or the change of the force transmission mode, the original foundation type changes from shallow foundation to deep foundation, and the bearing stratum changes from the original base soil to the pile end soil, and the foundation bearing capacity is greatly improved.

[0003] After the existing shallow foundation becomes a multi-pile combined pile cap, the new pile cap needs to be reinforced due to the increased stress, and since the bottom of the existing foundation cannot be added with steel bars, the common reinforcement method is to increase the reinforced concrete superimposed layer on the top surface of the existing shallow foundation to improve its bearing capacity, and the core idea is to increase the bearing capacity of the existing foundation by increasing the cross-sectional height of the foundation.

[0004] However, in actual engineering applications, the above technical means still has the following defects: 1. When the existing shallow foundation has a shallow depth or even the top surface of the foundation is exposed, in order not to affect the clearance of the bottom building, the existing technology does not have enough implementation space; 2. When the steel bars at the bottom of the existing shallow foundation are arranged according to the structural reinforcement, increasing the cross-sectional height of the foundation will inevitably reduce the reinforcement ratio, resulting in that it cannot meet the requirement of the minimum reinforcement ratio specified in the specification. SUMMARY

[0005] In order to overcome the defects of the existing technical means, the present application provides a negative bending moment compensation type existing shallow foundation reinforcement method.

[0006] The negative bending moment compensation type existing shallow foundation reinforcement method provided by the present application adopts the following technical scheme:

[0007] A negative bending moment compensation type existing shallow foundation reinforcement method, comprising the following steps in sequence:

[0008] Determine the existing foundation to be reinforced;

[0009] Calculate the bearing moment M R and shear force V R of each existing foundation;

[0010] Select the new pile parameters and guide the load of the upper structure of the existing foundation;

[0011] Determine the size of the combined pile cap and determine the number and position of the piles, so that the top of the new piles around the combined pile cap generates a negative bending moment;

[0012] Calculate the bending moment design value M1 and the shear force design value V1 of each existing foundation;

[0013] Compare MR and M1, V R and V1 up to M R > M1, V R > V1.

[0014] In one specific embodiment, the jointed pile cap comprises a plurality of pile cap beams arranged in sequence, the existing foundation is connected through the pile cap beams, the pile is supplemented and reinforced within the range of the pile cap beams, and the newly added pile located outside the jointed pile cap is moved to the inside of the jointed pile cap, so that the overall bending moment of the jointed pile cap is moved to the negative direction.

[0015] In one specific embodiment, the jointed pile cap comprises a raft, and the existing foundation is connected through the raft, and the pile is supplemented and reinforced within the range of the raft.

[0016] In one specific embodiment, the bending moment of the raft is analyzed by using finite element calculation.

[0017] In one specific embodiment, the existing foundation is chiseled, so that the stress reinforcement at the bottom of the existing foundation is exposed, and shear reinforcement is implanted according to the side surface of the existing foundation.

[0018] In one specific embodiment, the jointed pile cap foundation bottom reinforcement is welded and connected with the stress reinforcement of the existing foundation.

[0019] In one specific embodiment, anchor reinforcement is reserved at the top of the newly added pile.

[0020] In one specific embodiment, jointed pile cap negative bending moment reinforcement is arranged, the jointed pile cap is anchored through the negative bending moment reinforcement and the anchor reinforcement at the top of each newly added pile, and finally the overall jointed pile cap is formed by pouring.

[0021] In one specific embodiment, before the jointed pile cap is added, if the thickness of the top surface of the existing foundation is increased by less than 10 cm, the concrete on the top surface of the existing foundation is chiseled down by 3-5 cm;

[0022] If the thickness of the top surface of the existing foundation is increased by not less than 10 cm, the concrete on the top surface of the existing foundation does not need to be chiseled.

[0023] In summary, the present application includes at least one of the following beneficial technical effects:

[0024] 1. Under the condition of limited clearance, the technical problem that the bearing capacity of the existing foundation is difficult to be greatly improved is effectively solved;

[0025] 2. Under the condition of using structural reinforcement for the existing foundation, the technical problem that the sectional reinforcement ratio does not meet the minimum reinforcement ratio of the specification caused by increasing the section for reinforcement is effectively solved;

[0026] 3. The reinforcement construction difficulty is low, the reinforcement period is reasonable, and the construction quality is reliable. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a design flow chart for embodying a negative bending moment compensation type existing shallow foundation reinforcement method in Embodiment 1 of the present application.

[0028] Figure 2 is a structural schematic diagram for embodying a conventional reinforcement system pile supplement in Embodiment 1 of the present application.

[0029] Figure 3 is a schematic diagram for embodying a stress model of a conventional reinforcement system in Embodiment 1 of the present application.

[0030] Figure 4 is a schematic diagram for embodying a bending moment distribution of a conventional reinforcement system in Embodiment 1 of the present application.

[0031] Figure 5 is a structural schematic diagram for embodying a negative bending moment compensation type pile supplement reinforcement existing independent foundation in Embodiment 1 of the present application.

[0032] Figure 6 is a schematic diagram for embodying a stress model of a negative bending moment compensation type reinforcement system in Embodiment 1 of the present application.

[0033] Figure 7 is a schematic diagram for embodying a negative bending moment distribution of a negative bending moment compensation type reinforcement system in Embodiment 1 of the present application.

[0034] Figure 8 is a structural schematic diagram for embodying a conventional pile supplement reinforcement existing independent foundation in Embodiment 2 of the present application.

[0035] Figure 9 is a structural schematic diagram for embodying a negative bending moment compensation type pile supplement reinforcement existing independent foundation in Embodiment 2 of the present application.

[0036] Figure 10 is a schematic diagram for embodying a raft X direction bending moment calculation result of a conventional pile supplement reinforcement in Embodiment 2 of the present application.

[0037] Figure 11 is a schematic diagram for embodying a raft Y direction bending moment calculation result of a conventional pile supplement reinforcement in Embodiment 2 of the present application.

[0038] Figure 12 is a schematic diagram for embodying a raft X direction bending moment calculation result of a negative bending moment compensation type in Embodiment 2 of the present application.

[0039] Figure 13 is a schematic diagram for embodying a raft Y direction bending moment calculation result of a negative bending moment compensation type in Embodiment 2 of the present application.

[0040] The reference signs are explained as follows: 1, existing foundation; 11, outer existing foundation; 12, inner existing foundation; 2, new pile; 21, outer new pile; 22, inner new pile; 3, joint pile cap; 31, pile cap beam; 32, raft. DETAILED DESCRIPTION

[0041] The application is described in detail below with reference to the accompanying drawings. Figures 1-13 The application is described in detail below with reference to the accompanying drawings.

[0042] The application discloses a negative bending moment compensation type existing shallow foundation reinforcement method.

[0043] Embodiment 1

[0044] With reference to Figures 1 to 7 A negative bending moment compensation type existing shallow foundation reinforcement method comprises the following steps in sequence:

[0045] Determine the existing foundation 1 to be reinforced;

[0046] Calculate the bearing bending moment M R and shear force V R of each existing foundation 1;

[0047] Select the parameters of the new pile 2 and guide the load of the upper structure of the existing foundation 1, and in this embodiment, a conventional reinforced concrete pile is used;

[0048] Determine the size of the joint pile cap 3 and determine the number and position of the piles, and in this embodiment, the joint pile cap 3 comprises a plurality of pile cap beams 31 arranged in sequence, each existing foundation 1 is connected through the pile cap beam 31, and the piles are reinforced within the range of the plurality of pile cap beams 31;

[0049] Calculate the bending moment design value M1 and the shear force design value V1 of each existing foundation 1, and compare M R and M1, V R and V1 until M R >M1 and V R >V1.

[0050] With reference to Figures 2 to 4 In this embodiment, the conventional reinforcement system pile is used as a comparison, the existing foundation 1 relatively forms the outer existing foundation 11 and the inner existing foundation 12 in space, and correspondingly, the new pile 2 is also divided into the outer new pile 21 and the inner new pile 22, and the span between adjacent piles is set as L. The outer existing foundation 11 and the inner existing foundation 12 are simplified as load F P , the outer new pile 21 and the inner new pile 22 are simplified as a single-direction hinge support, and the bending moment M at each new pile cap beam 31 is calculated, and it can be known from Figure 4 that at the inner existing foundation 12 position, the bottom positive bending moment M1>M R , and the reinforcement system should be adjusted.

[0051] Specifically, referring to Figures 5 to 7 , the number of new piles 2 is adjusted, and the position of the outer new pile 21 is adjusted inwardly so that the overhanging length is a, so that the bending moment of the new pile cap moves negatively as a whole, thereby reducing the positive bending moment M1 at the bottom and making it satisfy M1 R . According to the calculation of the conventional reinforcement system, the maximum bending moment at the bottom of the foundation is M MAX = 0.116F P L; according to the method of the embodiment of the application, the maximum bending moment at the bottom of the foundation is M = 0.156F P L-F P a. According to the comparative calculation, when the inward distance a is greater than or equal to 0.04L, the bending moment at the bottom of the foundation calculated by the negative bending moment compensation type reinforcement method is less than that of the conventional reinforcement system. At the same time, when a is greater than or equal to 0.156L, the bending moment calculated by the embodiment of the application is less than 0, which has a significant effect.

[0052] Specific construction: excavate the existing foundation 1 within the range of the joint pile cap 3;

[0053] New pile 2 construction, anchor bar is reserved at the top of the new pile 2;

[0054] Chamfer the existing foundation 1 to expose the bottom stress reinforcement of the existing foundation 1, and embed shear reinforcement on the side of the existing foundation 1; before adding the joint pile cap 3, if the thickness of the top surface of the existing foundation 1 is increased by less than 10 cm, the concrete on the top surface of the existing foundation 1 is removed downward by 3 to 5 cm, and if the thickness of the top surface of the existing foundation 1 is increased by not less than 10 cm, the concrete on the top surface of the existing foundation 1 does not need to be removed;

[0055] The joint pile cap 3 foundation bottom reinforcement is welded and connected with the stress reinforcement of the existing foundation 1;

[0056] Set the negative bending moment reinforcement of the joint pile cap 3, and the joint pile cap 3 is anchored by the negative bending moment reinforcement and the anchor bar at the top of each new pile 2; pour to form an integral joint pile cap 3;

[0057] Backfill to the original design ground level to restore the ground level.

[0058] The implementation principle of example 1 is: to reinforce the existing foundation 1 with continuous pile cap beams 31 and new piles 2, on the one hand, to satisfy the shear bearing capacity requirement of the existing foundation 1 by widening the existing foundation 1, that is, by adjusting the size of the joint pile cap 3 composed of the pile cap beams 31, and on the other hand, to make the positive bending moment design value of the control section directly satisfy the original bending bearing capacity of the existing foundation 1 by changing the design bending moment envelope of the joint pile cap 3, that is, M1 RBy stress analysis of the joint bearing platform 3, it is found that a positive bending moment is generated at the part of the existing foundation 1, by adjusting the pile position, a certain negative bending moment is generated at the top of the newly added pile 21 on the outside, thereby causing the bending moment envelope line value to move towards the negative direction, thereby reducing the positive bending moment at the part of the existing foundation 1. Through repeated trial calculation, the bending moment at the part of the existing foundation 1 is finally less than its original bending resistance capacity.

[0059] Example 2

[0060] With reference to Figures 8 to 13 , the difference between this embodiment and example 1 is that the joint bearing platform 3 is provided as a raft 32, the existing foundation 1 is connected through the raft 32, the pile is supplemented and reinforced within the range of the raft 32, and the bending moment of the raft 32 is calculated by finite element method.

[0061] With reference to Figure 8 , Figure 10 and Figure 11 , in this embodiment, the conventional reinforcement system pile supplement is taken as a comparison, the pile supplement and reinforcement plane layout is as shown in Figure 8 , the X-direction bending moment of the raft 32 calculated by finite element method is as shown in Figure 10 , and the Y-direction bending moment of the raft 32 calculated by finite element method is as shown in Figure 11 .

[0062] With reference to Figure 9 , Figure 12 and Figure 13 , the negative bending moment compensation type pile supplement and reinforcement plane layout is as shown in Figure 9 , the X-direction bending moment of the raft 32 calculated by finite element method is as shown in Figure 12 , and the Y-direction bending moment of the raft 32 calculated by finite element method is as shown in Figure 13 .

[0063] The corresponding data is shown in the following table:

[0064] Table 1 raft bending moment calculation results

[0065] Maximum positive bending moment in X direction Maximum negative bending moment in X direction Maximum positive bending moment in Y direction Maximum negative bending moment in Y direction Traditional patching 287.07 -132.32 202.34 -84.79 Negative bending moment compensation type 58.35 -419.44 145.12 -242.62

[0066] By comparison, this method effectively reduces the maximum positive bending moment at the bottom of the existing foundation 1 by increasing the negative bending moment at the top of the pile. Taking the construction data of this embodiment as an example, the X-direction maximum positive bending moment is about 20.3% of the conventional method, and the Y-direction maximum positive bending moment is about 71.7% of the conventional method.

[0067] The implementation principle of the embodiment 2 is to reinforce the existing foundation 1 by the raft 32 and the new pile 2. On one hand, the shear bearing capacity requirement of the existing foundation 1 is met by widening the existing foundation 1, that is, the size of the raft 32 is adjusted, and on the other hand, the positive bending moment design value of the control section is directly met by changing the design bending moment envelope of the raft 32. The stress analysis of the raft 32 shows that the downward positive bending moment is generated at the position of the existing foundation 1. By adjusting the pile position of the new pile 2, a certain negative bending moment is generated at the top of the outer new pile 21, thereby causing the bending moment envelope value to move negatively, thereby reducing the positive bending moment at the position of the existing foundation 1, and finally making the bending moment at the position of the existing foundation 1 less than the original bending bearing capacity of the existing foundation 1.

[0068] The embodiments of the specific implementation are the preferred embodiments of the present application, and do not limit the protection scope of the present application. Therefore, any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for reinforcing existing shallow foundations with negative bending moment compensation, characterized in that... In order, they include: Identify the existing foundation to be reinforced (1); Calculate the bearing moment M of each existing foundation (1) R and shear force V R ; Select the parameters for the new pile (2) and apply the load to the superstructure of the existing foundation (1); Determine the dimensions of the combined pile cap (3) and the number and location of piles, so that the top of the newly added piles (2) on the periphery of the combined pile cap (3) generates a negative bending moment; Calculate the design value of bending moment M1 and design value of shear force V1 for each existing foundation (1); Comparison M R and M1, V R and V1 up to M R >M1, V R >V 1； The combined foundation (3) includes several foundation beams (31) arranged in sequence. The existing foundation (1) is connected through the foundation beams (31). The foundation is reinforced by additional piles within the range of the foundation beams (31). The newly added piles (2) located outside the combined foundation (3) move to the inside of the combined foundation (3), so that the bending moment of the combined foundation (3) moves in the negative direction as a whole.

2. The method for reinforcing existing shallow foundations with negative bending moment compensation according to claim 1, characterized in that... The existing foundation (1) is roughened to expose the bottom reinforcing steel bars of the existing foundation (1), and shear reinforcing steel bars are inserted into the side of the existing foundation (1).

3. The method for reinforcing existing shallow foundations with negative bending moment compensation according to claim 2, characterized in that... The foundation bottom reinforcement of the combined foundation (3) is welded to the existing foundation (1) reinforcing steel.

4. The method for reinforcing existing shallow foundations with negative bending moment compensation according to claim 1, characterized in that... Anchor bars are reserved at the top of the newly added pile (2).

5. A method for reinforcing existing shallow foundations with negative bending moment compensation according to claim 4, characterized in that... The negative moment reinforcement of the joint pile cap (3) is set, and the joint pile cap (3) is anchored to the pile top anchor bar of each newly added pile (2) through the negative moment reinforcement. Finally, the overall joint pile cap (3) is formed by pouring.

6. The method for reinforcing existing shallow foundations with negative bending moment compensation according to claim 1, characterized in that... Before adding the joint foundation (3), if the thickness of the top surface of the existing foundation (1) is less than 10 cm, the concrete on the top surface of the existing foundation (1) will be chiseled down 3 to 5 cm. If the thickness of the top surface of the existing foundation (1) is increased by not less than 10 cm, then it is not necessary to remove the concrete on the top surface of the existing foundation (1).

Images