A prefabricated beam pedestal foundation structure and design method

Abstract

The present invention relates to the technical field of beam-making pedestal foundation, and in particular to a beam-making pedestal foundation structure and design method for a precast beam, wherein the beam-making pedestal foundation structure for the precast beam includes a pedestal enlargement foundation and a pedestal foundation, the pedestal foundation is arranged at the center of the top of the pedestal enlargement foundation, and the precast beam template is arranged on the top of the pedestal foundation to transfer the weight of the precast beam template and the weight of the precast beam to the pedestal foundation. The beam-making pedestal foundation structure for the precast beam overcomes the problems of large amount of original soil replacement of the foundation and long construction period and high cost caused by large-area concrete foundation laying on the foundation during the construction of the existing precast beam site by adopting the coordinated design of the pedestal foundation and the pedestal enlargement foundation, and reduces the laying area and amount of concrete by optimizing the size and layout of the pedestal foundation and the pedestal enlargement foundation, thereby reducing the construction cost and shortening the construction period.

Description

Technical Field

[0001] The invention relates to a beam-making pedestal foundation structure, and in particular to a beam-making pedestal foundation structure for prefabricated beams and a design method thereof. Background Art

[0002] The existing precast beam site foundation structure usually adopts a large area of ​​concrete base to support the precast beams and precast beam formwork. This foundation structure can provide sufficient support and stability through large-scale concrete pouring and is widely used in the construction of precast beam sites under various geological conditions.

[0003] However, this foundation structure has significant problems. First, the amount of original soil replacement in the foundation is large, especially on soft foundations and special soil foundations, which requires a lot of soil treatment, increasing the difficulty and cost of construction. Second, the laying area of ​​the concrete base is large, resulting in material waste, low construction efficiency, long construction period and high overall cost. These problems have led to extended construction period and increased economic burden during the construction of prefabricated beam sites, which urgently need optimization and improvement. Summary of the invention

[0004] The purpose of the present invention is to reduce the concrete laying area and laying amount by adopting a coordinated design of a pedestal foundation and a pedestal expansion foundation, so as to solve the problems of long construction period and high cost caused by a large amount of original soil replacement of the foundation and large-area laying of concrete base on the foundation during the construction of the existing prefabricated beam site, thereby reducing construction costs, shortening construction period, and improving construction efficiency. In addition, the design can also improve the bearing capacity and anti-subsidence capacity of the foundation, ensuring stability and reliability when building on soft foundations and special soil foundations.

[0005] The technical solution adopted by the present invention to solve the above problem is: a prefabricated beam making pedestal foundation structure, comprising:

[0006] The pedestal expands the foundation.

[0007] A pedestal foundation is arranged at the center of the top of the pedestal enlarged foundation, and a precast beam template is arranged on the top of the pedestal foundation to transfer the weight of the precast beam template and the weight of the precast beam to the pedestal foundation.

[0008] Among them, the bottom of the pedestal expansion foundation is directly in contact with the foundation to transfer the weight of the precast beam, the weight of the precast beam template, the weight of the pedestal foundation and the weight of the pedestal expansion foundation to the foundation, and the effective area of ​​the bottom of the pedestal expansion foundation in contact with the foundation is configured to limit the stress diffusion angle of the pedestal expansion foundation to between forty-five degrees and sixty degrees.

[0009] Preferably, the shapes of the pedestal enlarged base and the pedestal base are both configured as rectangular parallelepiped, and the long side of the pedestal base is smaller than the long side of the pedestal enlarged base, and the short side of the pedestal base is smaller than the short side of the pedestal enlarged base.

[0010] In particular, a design method for a precast beam pedestal foundation structure includes:

[0011] The effective area of ​​the pedestal foundation is obtained based on the designed size and weight of the precast beam and the weight of the precast beam template, and the thickness of the pedestal foundation is obtained based on the compressive strength of concrete, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template.

[0012] According to the stress diffusion angle range of the pedestal expansion foundation between forty-five degrees and sixty degrees, the selection range of the effective area of ​​the pedestal expansion foundation is obtained.

[0013] According to the selection range of the effective area of ​​the pedestal enlarged foundation and the detection parameters of the treated foundation, the selection range of the thickness of the pedestal enlarged foundation is obtained.

[0014] Preferably, the effective area of ​​the pedestal foundation is obtained according to the design size and weight of the precast beam and the weight of the precast beam template, and the thickness of the pedestal foundation is obtained according to the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template. This step includes:

[0015] The size of the precast beam template is obtained through the design size of the precast beam, and the weight of the precast beam template is obtained based on the size of the precast beam template.

[0016] The effective area of ​​the pedestal foundation is obtained based on the size and weight of the precast beam formwork.

[0017] The thickness of the pedestal foundation is determined based on the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template.

[0018] Preferably, the effective area of ​​the pedestal foundation is obtained according to the size of the precast beam template and the weight of the precast beam template. In this step, the effective area of ​​the pedestal foundation can be obtained by:

[0019] Length of precast beam formwork L template :

[0020] .

[0021] Width B of precast beam formwork template :

[0022] .

[0023] Height of precast beam formwork H template :

[0024] .

[0025] in, For precast beam formwork at length L template The increased boundary length in the direction, For precast beam formwork in width B template The border width increases in the direction, For precast beam formwork at height L template The height of the border that increases in the direction.

[0026] .

[0027] .

[0028] Here, α is an empirical coefficient, usually taking a value between 0.05 and 0.10.

[0029] Length of the base L base :

[0030] .

[0031] Width B of the pedestal base base :

[0032] .

[0033] Effective area A of the pedestal foundation base :

[0034] .

[0035] Preferably, the thickness of the pedestal foundation is obtained according to the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template. The thickness of the pedestal foundation in this step can be obtained by the following formula:

[0036] .

[0037] .

[0038] .

[0039] Among them, t base Indicates the thickness of the pedestal foundation, f c Indicates the compressive strength of concrete, W beam Indicates the weight of precast beam, W template Indicates the weight of precast beam formwork, W total represents the total weight of the precast beam and precast beam formwork, f c,effIt represents the effective compressive strength, which is the concrete compressive strength f after considering the first safety factor FS c FS usually takes a value between 1.5 and 3, and K represents the empirical coefficient, which usually takes a value between 0.1 and 0.2.

[0040] Preferably, the selection range of the effective area of ​​the pedestal expansion foundation is obtained according to the stress diffusion angle range of the pedestal expansion foundation being between 45 degrees and 60 degrees. In this step, the effective area of ​​the pedestal expansion foundation can be obtained by the following formula:

[0041] .

[0042] Where K' represents the calculation constant:

[0043] .

[0044] in:

[0045] θ0 is the reference diffusion angle, usually 45°.

[0046] E1 is the elastic modulus of the expanded foundation of the pedestal, and E2 is the elastic modulus of the treated foundation.

[0047] ν1 is the Poisson's ratio of the expanded foundation of the pedestal, and ν2 is the Poisson's ratio of the treated foundation.

[0048] is the internal friction angle of the treated foundation.

[0049] e is the void ratio of the treated foundation.

[0050] ρ s is the particle density of the treated foundation and ρ0 is the reference density of the treated foundation.

[0051] σ is normal stress.

[0052] τ0 is the reference shear strength.

[0053] α1, α2, α3, β1, β2, β3 and γ are empirical coefficients of the correction function.

[0054] Preferably, the thickness selection range of the pedestal enlarged foundation is obtained according to the effective area of ​​the pedestal enlarged foundation and the detection parameters of the treated foundation. In this step, the thickness selection range of the pedestal enlarged foundation can be obtained by the following formula:

[0055] .

[0056] in:

[0057] t exp It is the thickness of the base expansion.

[0058] W total ' is the total weight of the pedestal foundation, precast beam formwork and precast beams.

[0059] It is the net bearing capacity of the treated foundation.

[0060] It is the effective area of ​​the pedestal to expand the foundation.

[0061] Preferably, the net bearing capacity of the foundation It can be obtained by the following formula:

[0062] .

[0063] Among them, q u Indicates the ultimate bearing capacity of the foundation.

[0064] .

[0065] Where c represents the cohesion of the soil, σ' represents the effective stress at the bottom of the pedestal expansion foundation, γ' represents the unit weight of the foundation soil, N c 、N q and N γ are bearing capacity coefficients, depending on the internal friction angle of the soil FS' is the second safety factor, which is usually any value between 1.5 and 2.

[0066] Preferably, after the thickness range of the pedestal expansion foundation is initially selected, in order to ensure that the bearing capacity of the pedestal expansion foundation can meet the bearing requirements of the bearing pedestal foundation, the precast beam template and the precast beam, the thickness range of the pedestal expansion foundation needs to be further selected. The further selection range of the thickness of the pedestal expansion foundation can be obtained by the following formula:

[0067] .

[0068] in:

[0069] W base It is the weight of the pedestal foundation.

[0070] Beneficial effects of an embodiment of the present invention:

[0071] The foundation structure of the beam pedestal of the precast beam overcomes the problems of long construction period and high cost caused by large amount of original soil replacement of the foundation and large area of ​​concrete paving on the foundation during construction of the existing precast beam site by adopting the coordinated design of the pedestal foundation and the pedestal expansion foundation. By optimizing the size and layout of the pedestal foundation and the pedestal expansion foundation, the laying area and amount of concrete are reduced, thereby reducing the construction cost and shortening the construction period. In addition, the design of the pedestal expansion foundation ensures that the stress diffusion angle is between 45 degrees and 60 degrees, improves the bearing capacity and anti-settlement ability of the foundation, and ensures the stability and reliability of the structure.

[0072] The design method of the foundation structure of the beam pedestal of the precast beam determines the design size and weight of the precast beam and the weight of the precast beam template, calculates the effective area and thickness of the pedestal foundation, overcomes the problems of large foundation treatment volume and complex construction in traditional methods, and further calculates the effective area selection range of the pedestal expansion foundation according to the reasonable range of the stress diffusion angle, and determines the thickness selection range of the pedestal expansion foundation in combination with the detection parameters of the treated foundation. Through this design method, the use of concrete and the laying area are effectively reduced, the construction cost is significantly reduced, the construction period is shortened, and the bearing capacity and anti-subsidence capacity of the foundation structure are ensured, so as to achieve the effect of optimizing the construction process and improving the project quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0074] Figure 2 It is a front cross-sectional view of an embodiment of the present invention.

[0075] Figure 3 It is a flow chart of a design method of a beam-making pedestal foundation structure of a precast beam in an embodiment of the present invention.

[0076] Figure 4 The present invention Figure 3 The flowchart of "deriving the selection range of the effective area of ​​the pedestal expansion foundation based on the stress diffusion angle range of the pedestal expansion foundation between forty-five degrees and sixty degrees" is provided.

[0077] Among them: 100, pedestal foundation; 200, pedestal expansion foundation; 300, prefabricated beam formwork. DETAILED DESCRIPTION

[0078] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0079] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description created by the present application, unless otherwise specified, "multiple" means two or more.

[0080] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0081] See also Figure 1-2. The present embodiment provides a beam-making pedestal foundation structure for precast beams, including a pedestal foundation 100 and a pedestal enlarged foundation 200. The pedestal foundation 100 is fixedly connected at the center of the top of the pedestal enlarged foundation 200, and the shapes of the pedestal foundation 100 and the pedestal enlarged foundation 200 are both constructed as a rectangular parallelepiped, the length of the long side of the pedestal foundation 100 is less than the length of the long side of the pedestal enlarged foundation 200, and the long side of the pedestal foundation 100 is arranged parallel to the long side of the pedestal enlarged foundation 200, the length of the short side of the pedestal foundation 100 is less than the length of the short side of the pedestal enlarged foundation 200, and the short side of the pedestal foundation 100 is arranged parallel to the short side of the pedestal enlarged foundation 200. The precast beam template 300 is fixedly installed at the center of the top of the pedestal foundation 100 before the beam is made, so as to transfer the weight of the precast beam template 300 and the weight of the precast beam to the pedestal foundation 100 and the pedestal enlarged foundation 200. Afterwards, because the bottom of the pedestal enlarged foundation 200 is in direct contact with the treated foundation, the pedestal enlarged foundation 200 will transfer the weight of the precast beam, the weight of the precast beam template 300, the weight of the pedestal foundation 100 and the weight of the pedestal enlarged foundation 200 to the foundation. The effective area of ​​the bottom of the pedestal enlarged foundation 200 of the precast beam in contact with the foundation is configured to prevent uneven settlement of the pedestal enlarged foundation 200. In summary, the beam-making pedestal foundation structure of this type of precast beam adopts a coordinated design of the pedestal foundation 100 and the pedestal expansion foundation 200, and designs the stress diffusion angle of the pedestal expansion foundation 200 to be between 45 degrees and 60 degrees, thereby effectively exerting the performance of load stress dispersion, avoiding uneven settlement of the pedestal expansion foundation 200, and avoiding the waste of concrete caused by the excessive volume of the beam-making pedestal foundation structure, thereby reducing the investment in earthwork.

[0082] Specifically, the pedestal foundation 100 and the pedestal enlarged foundation 200 are both rectangular concrete structures cast by concrete. When casting the beam-making pedestal foundation structure for making precast beams, the construction personnel can directly build a casting template for the pedestal enlarged foundation 200 and the pedestal foundation 100 that are cast in one go by selecting and cooperating with the template support, so that the pedestal enlarged foundation 200 and the pedestal foundation 100 of the concrete structure are integrally formed. It is understandable that the original foundation soil of the site where the beam-making pedestal foundation structure of the precast beam is constructed mostly needs to be processed before the beam-making pedestal foundation structure is constructed thereon. Therefore, this treated foundation has a higher foundation bearing capacity and a stronger ability to resist uneven settlement of the beam-making pedestal foundation structure of the precast beam.

[0083] In some embodiments, for the soil of the foundation, the foundation can be treated by replacing the slag with the filling to improve the bearing capacity of the foundation. The specific slag replacement can be selected in combination with the design size of the prefabricated beam and the bearing capacity of the original foundation soil of the construction site. The conventional slag replacement is between 1m and 2m.

[0084] In some embodiments, for certain soft soil foundations, the soft soil foundation site can be gridded and quickly processed to improve the bearing capacity of the original foundation, and the ultimate bearing capacity of the pipe piles can be improved, and the synergy between the pipe piles and the soil between the piles can be enhanced to improve the body of the foundation and enhance its resistance to horizontal displacement and vertical bearing capacity. It should be noted that the "method for gridding and quickly processing soft soil foundation sites" can be specifically referred to as "a method for rapid gridding foundation treatment construction under soft plastic geological conditions".

[0085] See also Figure 3 The design parameters of the pedestal foundation 100 and the pedestal enlarged foundation 200 used to carry the precast beams and the precast beam templates 300 mentioned above need to meet the following conditions at the same time: first, the pedestal foundation 100 and the pedestal enlarged foundation 200 can carry the precast beams and the precast beam templates 300; second, they also need to prevent the pedestal enlarged foundation 200 from uneven settlement; and finally, the volume of the beam-making pedestal foundation structure needs to be moderate to reduce the construction cost. Therefore, in order to make the pedestal foundation 100 and the pedestal enlarged foundation 200 meet the above requirements at the same time, the design parameters of the beam-making pedestal foundation structure can be obtained through the following steps:

[0086] The effective area of ​​the pedestal foundation 100 is obtained based on the designed size and weight of the precast beam and the weight of the precast beam template 300, and the thickness of the pedestal foundation 100 is obtained based on the compressive strength of concrete, the effective area of ​​the pedestal foundation 100, the weight of the precast beam and the weight of the precast beam template 300.

[0087] The effective area of ​​the pedestal enlarged base 200 is obtained based on that the stress diffusion angle range of the pedestal enlarged base 200 should be limited to between 45 degrees and 90 degrees.

[0088] The thickness selection range of the pedestal enlarged foundation 200 is obtained according to the effective area of ​​the pedestal enlarged foundation 200 and the detection parameters of the treated foundation.

[0089] See also Figure 4 The effective area of ​​the pedestal foundation 100 is obtained according to the design size and weight of the precast beam and the weight of the precast beam template 300, and the thickness of the pedestal foundation 100 is obtained according to the compressive strength of the pedestal foundation 100, the effective area of ​​the pedestal foundation 100, the weight of the precast beam and the weight of the precast beam template 300. This step includes:

[0090] The size of the precast beam template 300 is obtained by the design size of the precast beam, and the weight of the precast beam template 300 is obtained according to the size of the precast beam template 300.

[0091] The effective area of ​​the pedestal foundation 100 is obtained according to the size of the precast beam template 300 and the weight of the precast beam template 300 .

[0092] The thickness of the pedestal foundation 100 is obtained according to the compressive strength of the pedestal foundation 100 , the effective area of ​​the pedestal foundation 100 , the weight of the precast beam and the weight of the precast beam template 300 .

[0093] The size of the precast beam template 300 is obtained by the design size of the precast beam, which can be obtained by the following method:

[0094] The size of the precast beam template 300 is usually directly derived from the design size of the precast beam, and the design size of the precast beam is designed according to the shape and mechanical performance requirements of the engineering building. Therefore, the shape and material of the precast beam have been determined in the engineering design stage, and will not be repeated here. At this time, the design size of the precast beam has been determined, and the length of the precast beam is L, the width of the precast beam is B, and the height of the precast beam is H.

[0095] The size of the precast beam template 300 should be slightly larger than the size of the precast beam to facilitate casting and demoulding. The size of the precast beam template 300 can be determined by the following formula:

[0096] Length L of precast beam formwork 300 template :

[0097] .

[0098] Width B of precast beam formwork 300 template :

[0099] .

[0100] Height H of precast beam formwork 300 template :

[0101] .

[0102] in, , and It is the margin added for pouring and demoulding, specifically For precast beam formwork 300 in length L template The increased boundary length in the direction, For precast beam formwork 300 in width B template The border width increases in the direction, For precast beam formwork 300 at height L template The value of the boundary height increased in the direction should be determined according to the specific design parameters of the precast beam. The larger the design parameters of the precast beam, , and The size of the precast beam template 300 is also increased accordingly to ensure the overall strength and stability of the precast beam template 300 after pouring concrete. , and The specific value of depends on construction specifications and experience, and can usually be obtained by multiplying it by the empirical coefficient α, which usually takes a value between 0.05 and 0.10.

[0103] Determination of the weight of precast beam formwork 300:

[0104] The weight of the prefabricated beam template 300 depends on the material, thickness and size of the template. First, determine the material of the prefabricated beam template 300. The material of the prefabricated beam template 300 is usually steel template and wooden template. The thickness of the prefabricated beam template 300 is roughly uniform and the same. When calculating the volume of the prefabricated beam template 300, the prefabricated beam template 300 can be divided into a plurality of regular-shaped flat plates to calculate the area A on one side of each flat plate perpendicular to its own thickness direction. template , and then calculate the area A on the side of each plate perpendicular to its thickness direction template Multiply by the thickness t of the precast beam template 300, and then calculate the volume V of the precast beam template 300 template Finally, the volume of the prefabricated beam template 300 is multiplied by the density of the material of the prefabricated beam template 300. , we can get the weight W of the prefabricated beam template 300 template .

[0105] The effective area of ​​the pedestal foundation 100 is obtained according to the size of the precast beam template 300 and the weight of the precast beam template 300, which can be obtained by the following steps:

[0106] In order to determine the effective area of ​​the pedestal foundation 100, and considering that the length and width of the pedestal foundation 100 are slightly larger than the size of the precast beam template 300 placed on top of it. According to experience, the length and width of the pedestal foundation 100 should be increased by a boundary length compared to the length and width of the precast beam template 300, which is usually to ensure that the edge of the pedestal foundation 100 has sufficient strength and stability. Each edge of the pedestal foundation 100 should be increased by 5% to 10% compared to the size of the precast beam template 300. This is to provide sufficient safety margins to prevent edge damage and settlement. It should be noted that the effective area of ​​the pedestal foundation 100 refers to the area of ​​the pedestal foundation 100 where the pedestal foundation 100 is directly in contact with the precast beam template 300 and bears the weight of the precast beam and the precast beam template 300. This area determines the stress that the pedestal foundation 100 can disperse when supporting the precast beam and the precast beam template 300, which can affect the stability and bearing capacity of the pedestal foundation 100. The specific calculation method of the effective area of ​​the pedestal foundation 100 is as follows:

[0107] The length L of the pedestal base 100 base :

[0108] .

[0109] Width B of pedestal base 100 base :

[0110] .

[0111] The effective area A of the pedestal foundation 100 base It can be obtained by the following formula:

[0112] .

[0113] According to the compressive strength f of the pedestal foundation 100 c 、Effective area A of the pedestal foundation 100 base , Precast beam weight W beam and the weight W of the precast beam formwork 300 template The thickness t of the pedestal base 100 is obtained base , this step can be achieved through the following steps:

[0114] Total load calculation:

[0115] .

[0116] Wherein, Wtotal represents the total weight of the precast beam and the precast beam template 300 .

[0117] Calculate the average stress acting on the pedestal foundation 100:

[0118] .

[0119] f c,eff It represents the effective compressive strength, which is the concrete compressive strength f after considering the first safety factor FS c , and the safety factor , usually taking any value between 1.5 and 3.

[0120] .

[0121] When designing the thickness of the pedestal foundation 100, the first safety factor is very important, because there are many uncertain factors in actual construction, such as material unevenness, fluctuations in construction quality, environmental impact, etc. By introducing the first safety factor , the compressive strength of concrete Adjusted to effective compressive strength f c,eff to ensure that the structure has sufficient safety margin when bearing the load.

[0122] The thickness of the pedestal foundation 100 is calculated based on the concrete compressive strength and average stress. The thickness of the pedestal foundation 100 should meet the bearing capacity requirements of the structure, which can be obtained by the following formula:

[0123] .

[0124] The thickness calculation formula of the pedestal foundation 100 takes into account that the thickness of the pedestal foundation 100 needs to ensure that it has sufficient rigidity and strength to resist the load transmitted by the upper prefabricated beam and the prefabricated beam template 300. Therefore, the rigidity of the pedestal foundation 100 is proportional to its thickness. The greater the thickness, the greater the rigidity. When the thickness of the pedestal foundation 100 is large enough, it can effectively ensure that the upper load can be evenly distributed on the pedestal foundation 100, avoiding local stress concentration and causing damage to the pedestal foundation 100. In the specific structural design, the thickness of the pedestal foundation 100 needs to be determined according to the load distribution, and is usually adjusted through empirical formulas and specifications.

[0125] In the formula It is partly derived from the relationship between load distribution and material strength. In structural mechanics, the stiffness of a plate is proportional to its thickness. Therefore, this cubic root relationship can more reasonably describe the effect of thickness on the bearing capacity of a structure.

[0126] The empirical coefficient K is summarized based on a large amount of actual engineering data. It combines specific construction conditions, material properties and safety requirements. It usually takes a value between 0.1 and 0.2. This coefficient range makes the formula applicable to most actual engineering situations.

[0127] According to the theory of structural mechanics and foundation bearing capacity, the stiffness of the pedestal foundation 100 should be proportional to its thickness, and the load distribution should be inversely proportional to the area of ​​the pedestal foundation 100. Therefore, the selection These two factors can be better balanced.

[0128] In actual projects, actual engineering data can be used for verification. The accuracy and rationality of the formula calculation results can be verified through experiments and field test results. By comparing the actual and calculated values ​​of the foundation thickness in different projects, the value ranges of the empirical coefficients K and n can be adjusted to ensure that the calculation results meet the requirements of engineering practice.

[0129] According to the fact that the stress diffusion angle range of the pedestal enlarged foundation 200 should be limited to between 45 degrees and 60 degrees, the effective area of ​​the pedestal enlarged foundation 200 can be obtained by the following method:

[0130] First, the stress diffusion angle of the pedestal expansion base 200 is limited to between 45 and 60 degrees, which can effectively ensure that the pedestal expansion base 200 can reasonably disperse the stress when subjected to force to avoid excessive concentration. This design principle is based on the following theoretical and practical engineering considerations:

[0131] Stress diffusion principle: When the pedestal expansion foundation 200 is under load, the stress will be transferred from the superstructure to the pedestal expansion foundation 200, and then from the pedestal expansion foundation 200 to the foundation. The stress diffusion angle is an angle that describes the diffusion of stress from the pedestal expansion foundation 200 to the foundation. A reasonable stress diffusion angle ensures that the treated foundation can effectively disperse the load to a larger area of ​​the foundation to reduce local stress concentration and prevent foundation failure.

[0132] The reason why the stress diffusion angle is between forty-five and sixty degrees is that if the stress diffusion angle is less than forty-five degrees, it means that the stress diffusion path is short, and the stress will be concentrated on the edge of the pedestal expansion foundation 200, increasing the local stress of the pedestal expansion foundation 200 and the foundation, which may lead to shear failure of the edge of the pedestal expansion foundation 200 or local settlement of the foundation. The stress diffusion angle of forty-five degrees meets the Moore-Coulomb failure criterion, ensuring that the stress at the bottom of the pedestal expansion foundation 200 can be effectively transferred to the foundation, utilizing the bearing capacity of the foundation, and the forty-five-degree diffusion angle can provide a more uniform stress distribution, effectively reduce local stress concentration, and ensure the overall stability of the pedestal expansion foundation 200. The stress diffusion angle of less than sixty degrees is a parameter obtained based on actual construction experience. When the stress diffusion angle is between forty-five and sixty degrees, the area of ​​the foundation dispersing the upper load is just moderate. At this time, the load transfer between the pedestal expansion foundation 200 and the foundation meets a reasonable diffusion path, ensuring that the stress distribution at the bottom of the pedestal expansion foundation 200 is uniform and avoiding excessive local stress concentration. In actual engineering design, using a stress diffusion angle of forty-five to sixty degrees can ensure reasonable stress diffusion.

[0133] According to the condition that "the stress diffusion angle range of the pedestal expansion base 200 should be limited to between 45 degrees and 60 degrees", the value range of the effective area of ​​the pedestal expansion base 200 can be obtained by the following steps:

[0134] Stress diffusion angle formula:

[0135] .

[0136] Where θ0 is the reference diffusion angle, usually 45°.

[0137] E1 is the elastic modulus of the pedestal enlarged foundation 200, and E2 is the elastic modulus of the treated foundation.

[0138] ν1 is the Poisson's ratio of the pedestal enlarged foundation 200, and ν2 is the Poisson's ratio of the treated foundation.

[0139] is the internal friction angle of the treated foundation.

[0140] e is the void ratio of the treated foundation.

[0141] ρ s is the particle density of the treated foundation and ρ0 is the reference density of the treated foundation.

[0142] σ is normal stress.

[0143] τ0 is the reference shear strength.

[0144] α1, α2, α3, β1, β2, β3 and γ are empirical coefficients of the correction function.

[0145] Reference area A ref It is a reference area used for standardization and comparison. Usually 1 square meter can be selected as the reference area, or an appropriate value can be selected based on specific engineering conditions.

[0146] It should be noted that in the stress diffusion angle formula, the reference diffusion angle θ0, reference density ρ0, reference shear strength τ0 and reference area A are introduced. ref The purpose is to standardize and simplify the calculations and ensure the reliability and consistency of the results. The following are specific instructions:

[0147] The reference diffusion angle θ0 is usually taken as 45°. It is a benchmark value used to standardize the calculation of the stress diffusion angle. As a calculation constant, θ0 helps normalize the influence of other parameters, making the calculated diffusion angle more universal and comparable. Through standardization, it is easier to compare the stress diffusion angles in different situations.

[0148] The reference density ρ0 is a benchmark density value of the foundation soil. In the formula, the density of the actual foundation soil ρ s The ratio to the reference density ρ0 is used to correct the stress diffusion angle to reflect the effect of different soil densities on the diffusion angle. The introduction of reference density can help standardize the effect of density on the results.

[0149] The reference shear strength τ0 is a benchmark value used to standardize the shear strength of soil. In the formula, the ratio of the actual stress σ to the reference shear strength τ0 is used to correct the stress diffusion angle to reflect the influence of different shear strengths on the diffusion angle. By introducing the reference shear strength, the influence of shear behavior on stress diffusion under different soil conditions can be more accurately evaluated.

[0150] Reference area A ref It is a base area used for standardization and comparison, usually 1 square meter or other appropriate value. exp With reference area A refThe ratio of is used to correct the stress diffusion angle, reflecting the influence of different foundation areas on the diffusion angle. The introduction of reference area helps to standardize the area effect, making foundations of different sizes comparable in calculation.

[0151] In summary, by introducing the above reference values, the formula can better adapt to the calculation requirements under different engineering conditions, while ensuring the comparability and consistency of the calculation results. This can make the design more standardized and ensure that reasonable results can be obtained in different situations, thereby improving the reliability and safety of the design.

[0152] Elastic modulus E1 and E2, Poisson's ratio ν1 and ν2, internal friction angle of the treated foundation , the void ratio e of the treated foundation, the soil particle density ρ of the treated foundation s The reference density ρ0, normal stress σ, reference shear strength τ0 of the treated foundation and the empirical coefficients of correction functions such as adjustment coefficients α1, α2, α3, β1, β2, β3 and γ are all known values.

[0153] Calculate the constant part:

[0154] .

[0155] Set the stress diffusion angle range:

[0156] .

[0157] Solve the inequality to find the effective area:

[0158] .

[0159] .

[0160] .

[0161] Get the index:

[0162] .

[0163] Need to explain, The formula for the influence of the stress diffusion angle comprehensively considers the influence of the foundation detection parameters and the effective area of ​​the pedestal expansion foundation 200 on the stress diffusion angle, among which the logarithmic function form is used. It can more reasonably reflect the influence of effective area on stress diffusion angle. The specific establishment process is as follows:

[0164] Basic Assumptions

[0165] It is assumed that the building and foundation materials are homogeneous and isotropic media.

[0166] It is assumed that the stress diffuses at a certain angle in the medium and forms a cone or fan-shaped diffusion area.

[0167] Determine basic parameters

[0168] Elastic modulus E1, E2: Indicates the stiffness of the material when it is deformed by force.

[0169] Poisson's ratio ν1, ν 12 : Describes the degree of lateral deformation that occurs when a material is compressed in one direction.

[0170] Internal friction angle : Reflects the friction characteristics between soil particles.

[0171] Porosity ratio e: It refers to the ratio of the pore volume in the soil to the volume of soil particles.

[0172] Density ρ s , ρ0: represents the ratio of the mass to volume of the material.

[0173] Shear strength τ0: describes the shear resistance of soil under shear force.

[0174] Establishment of correction function

[0175] Stress diffusion angle formula:

[0176] .

[0177] The correction functions are defined as follows:

[0178] Influence of material elastic modulus ratio:

[0179] .

[0180] The elastic modulus ratio of the material affects the stress distribution and deformation characteristics. A higher elastic modulus means that the material has greater stiffness and smaller deformation. The elastic modulus reflects the stiffness and ability to resist deformation of the material. A higher elastic modulus ratio means that the material is more difficult to deform when subjected to force, thereby affecting the stress distribution. The elastic modulus ratio of the pedestal expansion foundation 200 and the foundation material directly affects the stress transfer path and deformation behavior, thereby affecting the stress diffusion angle.

[0181] Effect of compression modulus ratio:

[0182] .

[0183] The compression modulus ratio affects the volume deformation characteristics of the material when it is stressed. Considering the influence of Poisson's ratio, the deformation behavior of the material under three-dimensional stress state can be described more accurately. The compression modulus represents the volume deformation characteristics of the material when it is compressed. Considering Poisson's ratio can more comprehensively reflect the deformation behavior of the material under three-dimensional stress state. The compression modulus ratio of the pedestal expansion foundation 200 and the foundation material affects the volume deformation and stress transfer, and thus affects the stress diffusion angle.

[0184] Effect of internal friction angle:

[0185] .

[0186] The internal friction angle reflects the friction characteristics between soil particles and affects the shear strength and stability of the soil. The internal friction angle reflects the friction characteristics between foundation soil particles and affects the shear strength and stability of the foundation soil. The larger the internal friction angle, the stronger the shear resistance of the foundation soil, and the stress diffusion angle will also increase accordingly.

[0187] Effect of shear modulus ratio:

[0188] .

[0189] The shear modulus ratio affects the deformation characteristics of the material under shear stress. Taking into account the Poisson's ratio, the deformation behavior of the material under shear stress can be described more accurately. The shear modulus represents the deformation characteristics of the material under shear stress. Taking into account the Poisson's ratio, the deformation behavior of the material under shear stress can be described more accurately. The shear modulus ratio of the pedestal expansion foundation 200 and the foundation affects the shear deformation and stress transfer, and thus affects the stress diffusion angle.

[0190] Effect of void ratio and density:

[0191] .

[0192] The void ratio reflects the size of pores in the soil, affecting the compressibility and permeability of the soil. Density affects the mass characteristics and mechanical behavior of the soil. The void ratio reflects the size of pores in the foundation soil, affecting the compressibility and permeability of the foundation soil. Density affects the mass characteristics and mechanical behavior of the foundation soil. The void ratio and density affect the overall mechanical properties of the foundation soil, thereby affecting the stress diffusion angle.

[0193] Influence of shear strength:

[0194] .

[0195] Shear strength reflects the shear resistance of soil under shear stress. Considering the influence of normal stress and internal friction angle, the shear resistance of soil can be more accurately described. Shear strength reflects the shear resistance of soil under shear stress. Considering the influence of normal stress and internal friction angle, the shear resistance of soil can be more accurately described. The higher the shear strength of foundation soil, the larger the stress diffusion angle, and the better the foundation soil can resist shear stress.

[0196] Influence of effective area:

[0197] .

[0198] The larger the effective area, the wider the range of stress diffusion and the larger the angle. The effective area reflects the actual area of ​​contact between the foundation and the ground. The logarithmic function form can more reasonably reflect the impact of area change on the stress diffusion angle, especially when the area change is large. In addition, the larger the effective area, the larger the stress diffusion angle, because a larger area can disperse more stress.

[0199] By comprehensively considering the above correction functions, a more accurate and practical stress diffusion angle formula can be established, which can reflect the changes in stress diffusion angle under different materials and structural conditions, provide a scientific basis for basic design, and ensure the safety and reliability of structural design.

[0200] Furthermore, the parameters in the stress diffusion angle formula can be obtained by the following method:

[0201] The elastic modulus E1 and E2 are determined by standard compression test, tensile test or triaxial compression test. Applicable materials include concrete, steel bar, soil, etc.

[0202] The Poisson's ratios ν1 and ν2 are obtained simultaneously with the elastic modulus test and are usually calculated from the stress-strain curve.

[0203] The applicable materials are concrete, steel bars, soil, etc.

[0204] Internal friction angle It is determined by direct shear test, triaxial compression test or direct shear test. The applicable material is soil.

[0205] The void ratio e can be calculated from the dry density and saturated density of the soil.

[0206] Density of soil particles ρ s Measured by the pycnometer test (density bottle test) and determined by standard test methods.

[0207] The normal stress σ is measured on site, calculated based on the load conditions in the actual project, or directly measured by instruments such as earth pressure gauges and strain gauges.

[0208] Reference shear strength Reference values ​​given based on experience and standard specifications.

[0209] The empirical coefficients α1, α2, α3, β1, β2, β3 and γ are fitted by regression analysis and experimental data. Specifically, these coefficients can be obtained by regression analysis and fitting through a large amount of experimental data. They also need to be calibrated and adjusted according to specific circumstances and actual engineering cases.

[0210] Specific steps

[0211] Standard mechanical tests (such as compression test, tensile test, triaxial compression test) are carried out on the material to determine the elastic modulus E1, E2 and Poisson's ratio ν1, ν2.

[0212] Conduct shear tests (such as direct shear test, triaxial test) to determine the internal friction angle and reference shear strength . Use soil pressure gauges, strain gauges and other instruments to directly measure the normal stress σ at the construction site. Determine the porosity e and the density ρ of soil particles according to the actual situation of the soil s .

[0213] Data fitting and regression analysis:

[0214] A large amount of experimental data was collected, and the empirical coefficients of the correction function, α1, α2, α3, β1, β2, β3 and γ, were obtained through regression analysis and fitting. The parameters in the model were calibrated by using actual engineering cases to make the model prediction results consistent with the actual measurement results.

[0215] Through the above laboratory tests, field measurements and data analysis, the various parameters in the revised stress diffusion angle formula can be obtained. The accurate acquisition of these parameters is the key to ensuring the effectiveness of the formula application and engineering safety. In this way, the stress diffusion angle under different material and structural conditions can be effectively predicted, providing a scientific basis for basic design.

[0216] According to the effective area of ​​the pedestal enlarged foundation 200 and the detection parameters of the treated foundation, the thickness selection range of the pedestal enlarged foundation 200 is obtained, which can be obtained by the following method:

[0217] In order to calculate the thickness of the pedestal expansion base 200, the bearing capacity formula in foundation mechanics can be used. It is mainly determined based on the effective area of ​​the pedestal expansion foundation 200 and the bearing capacity of the foundation. The calculation formula is as follows:

[0218] ;

[0219] in:

[0220] t exp The thickness of the pedestal is 200mm.

[0221] W total’ is the total weight of the pedestal foundation 100, the precast beam formwork 300 and the precast beam;

[0222] q net is the net bearing capacity of the treated foundation;

[0223] A exp It is the effective area of ​​the pedestal expansion base 200.

[0224] The above formula is based on the theory of foundation mechanics and foundation bearing capacity. The thickness of the pedestal foundation expanded by 200 needs to ensure that under the maximum load, the foundation will not suffer shear failure and excessive settlement.

[0225] Bearing capacity: According to the foundation bearing capacity theory, the foundation bearing capacity q net It is the maximum load that the foundation can withstand under the ultimate condition. The square root relationship in the thickness formula reflects the nonlinear relationship between thickness and load, ensuring that the foundation has sufficient stability when bearing weight.

[0226] The net bearing capacity of the foundation is calculated as follows:

[0227] The ultimate bearing capacity of the foundation q u :

[0228] .

[0229] in:

[0230] c represents the cohesion of the treated foundation soil.

[0231] σ' represents the effective stress at the bottom surface of the pedestal enlarged foundation 200 .

[0232] γ' represents the unit weight of foundation soil.

[0233] N c 、N q and N γ are bearing capacity coefficients, depending on the internal friction angle of the soil .

[0234] Calculate the bearing capacity parameters of the foundation:

[0235] According to the shear strength parameters and bearing capacity coefficient of the treated foundation soil, the ultimate bearing capacity qu of the foundation soil is calculated.

[0236] The bearing capacity coefficients Nc, Nq and Nγ can be found from the relevant tables (according to the internal friction angle ).

[0237] A safety factor FS' is used, usually between 1.5 and 2, to ensure the safety of the foundation.

[0238] Net bearing capacity of foundation:

[0239] .

[0240] Wherein, FS' is the second safety factor, which is usually any value between 1.5 and 2.

[0241] It should be further explained that the effective stress σ' at the bottom surface of the pedestal enlarged foundation 200 can be obtained by the following steps:

[0242] The effective stress σ' at the bottom of the pedestal enlarged foundation 200 refers to the effective stress of the soil layer at the bottom of the pedestal enlarged foundation 200 under the vertical load. In foundation design, the effective stress is very important for determining the foundation bearing capacity and settlement calculation.

[0243] Determine the total stress σ'' at the bottom of the pedestal expansion foundation 200. The total stress is the vertical load on the soil layer at the bottom of the foundation, including the self-weight of the pedestal expansion foundation 200 and the upper structure load. Calculate the pore water pressure u. The pore water pressure is the pressure generated by the water in the pores of the soil, which is usually related to the groundwater level. Calculate the effective stress σ'. The effective stress is the total stress σ'' minus the pore water pressure u. The basic formula for effective stress is:

[0244] .

[0245] Total stress σ'' at the bottom of the pedestal expansion foundation 200:

[0246] .

[0247] in:

[0248] It is the load on the upper part of the foundation.

[0249] It is the buried depth of the pedestal expansion foundation 200. This is an estimated value. The specific data needs to be determined based on the actual size of the pedestal expansion foundation 200.

[0250] Calculate the pore water pressure u:

[0251] .

[0252] in:

[0253] γ w is the unit weight of water (usually 9.81 kN / m³).

[0254] hw is the depth of the groundwater level.

[0255] After the thickness range of the pedestal expansion foundation 200 is initially selected, in order to ensure that the bearing capacity of the pedestal expansion foundation 200 can meet the bearing requirements of the pedestal foundation 100, the precast beam template 300 and the precast beam, the thickness range of the pedestal expansion foundation 200 needs to be further selected. The further selection range of the thickness of the pedestal expansion foundation 200 can be obtained by the following formula:

[0256] .

[0257] in:

[0258] W base It is the weight of the pedestal base 100.

[0259] The above formula ensures that the pedestal expansion foundation 200 has sufficient thickness when bearing all the loads of the superstructure to avoid failure of the pedestal expansion foundation 200. The various parameters in the formula are determined based on the actual structural load and foundation bearing capacity to ensure structural safety.

Claims

1. A design method for a precast beam pedestal foundation structure, characterized in that: The beam-making pedestal foundation structure comprises: The pedestal expands the foundation; A pedestal foundation, the pedestal foundation is arranged at the center of the top of the pedestal enlarged foundation, and a precast beam template is arranged on the top of the pedestal foundation to transfer the weight of the precast beam template and the weight of the precast beam to the pedestal foundation; The shape of the pedestal enlarged base and the shape of the pedestal base are both constructed as a rectangular parallelepiped, and the long side of the pedestal base is smaller than the long side of the pedestal enlarged base, and the short side of the pedestal base is smaller than the short side of the pedestal enlarged base; wherein the bottom of the pedestal enlarged foundation is in direct contact with the foundation to transfer the weight of the precast beam, the weight of the precast beam formwork, the weight of the pedestal foundation and the weight of the pedestal enlarged foundation to the foundation, and the effective area of ​​the bottom of the pedestal enlarged foundation in contact with the foundation is configured to limit the stress diffusion angle of the pedestal enlarged foundation to between forty-five degrees and sixty degrees; The design method is as follows: The effective area of ​​the pedestal foundation is obtained according to the design size and weight of the precast beam and the weight of the precast beam template, and the thickness of the pedestal foundation is obtained according to the compressive strength of the pedestal, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template; According to the stress diffusion angle range of the pedestal expansion foundation, which is between 45 degrees and 60 degrees, the selection range of the effective area of ​​the pedestal expansion foundation is obtained; According to the selection range of the effective area of ​​the pedestal enlarged foundation and the detection parameters of the treated foundation, the selection range of the thickness of the pedestal enlarged foundation is obtained; The step of obtaining the effective area of ​​the pedestal foundation according to the design size and weight of the precast beam and the weight of the precast beam template, and obtaining the thickness of the pedestal foundation according to the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template includes: The size of the precast beam template is obtained through the design size of the precast beam, and the weight of the precast beam template is obtained according to the size of the precast beam template; The effective area of ​​the pedestal foundation is obtained according to the size of the precast beam template and the weight of the precast beam template; The thickness of the pedestal foundation is obtained according to the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template; The stress diffusion angle range of the pedestal expansion foundation is between 45 degrees and 60 degrees, and the selection range of the effective area of ​​the pedestal expansion foundation is obtained. In this step, the effective area of ​​the pedestal expansion foundation is obtained by the following formula: Where K' represents the calculation constant: in: θ0 is the reference diffusion angle, which is 45°; E1 is the elastic modulus of the expanded foundation of the pedestal, and E2 is the elastic modulus of the treated foundation; ν1 is the Poisson’s ratio of the expanded foundation of the pedestal, and ν2 is the Poisson’s ratio of the treated foundation; Φ is the internal friction angle of the treated foundation; e is the void ratio of the treated foundation; ρ s is the particle density of the treated foundation; ρ0 is the reference density of the treated foundation; σ is normal stress; τ0 is the reference shear strength; α1, α2, α3, β1, β2, β3 and γ are the empirical coefficients of the correction function; A ref is the reference area, which is a base area used for standardization and comparison; The thickness selection range of the pedestal enlarged foundation is obtained according to the selection range of the effective area of ​​the pedestal enlarged foundation and the detection parameters of the treated foundation. In this step, the thickness selection range of the pedestal enlarged foundation is obtained by the following formula: in: t exp It is the thickness of the pedestal’s enlarged base; W total’ is the total weight of the pedestal foundation, precast beam formwork and precast beams; q net is the net bearing capacity of the treated foundation; A exp It is the effective area of ​​the pedestal to expand the foundation.

2. The design method of a precast beam pedestal foundation structure according to claim 1 is characterized in that: The effective area of ​​the pedestal foundation is obtained according to the size of the precast beam template and the weight of the precast beam template. In this step, the effective area of ​​the pedestal foundation is obtained by: Length of precast beam formwork L template : L template =L+ΔL; Width B of precast beam formwork template : B template =B+ΔB; Height of precast beam formwork H template : H template =H+ΔH; Where ΔL is the length of the precast beam template. template The increased boundary length in the direction, ΔB is the precast beam template in width B template The width of the boundary increased in the direction, ΔH is the width of the precast beam template at the height L template The height of the border increases in the direction; ΔL=L template ×α; ΔB=B template ×α; ΔH=H template ×α; Among them, α is an empirical coefficient, which can take any value from 0.05 to 0.10; Length of the base L base ; L base =L template +2·ΔL; Width B of the pedestal base base ; B base =B template +2·ΔB; The effective area of ​​the pedestal foundation A base ; A base =L base ×B base 。 3. The design method of a precast beam pedestal foundation structure according to claim 2 is characterized in that: The thickness of the pedestal foundation is obtained according to the compressive strength of the pedestal foundation, the effective area of ​​the pedestal foundation, the weight of the precast beam and the weight of the precast beam template. The thickness of the pedestal foundation in this step is obtained by the following formula: IN total =In beam +W template ; Among them, t base Indicates the thickness of the pedestal foundation, f c Indicates the compressive strength of concrete, W beam Indicates the weight of precast beam, W template Indicates the weight of precast beam formwork, W total represents the total weight of the precast beam and precast beam formwork, f c,eff It represents the effective compressive strength, which is the concrete compressive strength f after considering the first safety factor FS c , FS takes any value between 1.5 and 3, K represents the empirical coefficient, and takes any value between 0.1 and 0.

2.

4. A method for designing a foundation structure of a precast beam pedestal according to any one of claims 1 to 3, characterized in that: Net bearing capacity of foundation q net Obtained by the following formula: Among them, q u Indicates the ultimate bearing capacity of the foundation; q u =cN c +σ′N q +0.5γ'A exp N γ ; Where c represents the cohesion of the treated foundation soil, σ' represents the effective stress at the bottom of the expanded foundation, γ' represents the unit weight of the foundation soil, N c 、N q and N γ Both are bearing capacity coefficients, which depend on the internal friction angle Φ of the soil. FS' is the second safety factor and can take any value between 1.5 and 2.

5. The design method of a precast beam pedestal foundation structure according to claim 4 is characterized in that: After the thickness range of the pedestal expansion foundation is initially selected, in order to ensure that the bearing capacity of the pedestal expansion foundation can meet the bearing requirements of the bearing pedestal foundation, precast beam template and precast beam, it is necessary to further select the thickness range of the pedestal expansion foundation. The further selection range of the pedestal expansion foundation thickness is obtained by the following formula: in: W base It is the weight of the pedestal foundation.

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