Steel bar connecting method for detecting uplift bearing capacity of foundation pile

Abstract

The invention provides a steel bar connecting method for detecting uplift bearing capacity of a foundation pile. The steel bar connecting method comprises the following steps: selecting a connecting unit according to the diameter and tensile strength of a longitudinal bar of a concrete pile; prefabricating upper reinforcing steel bars according to the height of the counter-force platform; connecting units are installed at the tops of the concrete pile longitudinal bars and the bottoms of the upper steel bars correspondingly, and foundation pile bearing capacity detection is conducted; and after the bearing capacity of the foundation pile is detected, the counter-force platform, the connecting unit of the upper reinforcing steel bars, the upper reinforcing steel bars and the connecting unit of the concrete pile longitudinal bars are removed. The connecting unit is light in weight and convenient and fast to connect with concrete pile longitudinal bars and upper steel bars, a power source, special equipment and professional technicians are not needed, the environmental adaptability is high, and the steel bar connecting time is far shorter than that of a welding connecting method, a mechanical connecting method and a sleeve grouting material connecting method; the connecting unit can be recycled, provides pre-tensile stress, ensures that the reinforcing steel bars of the concrete piles are stressed uniformly and reliably, is suitable for connection of a plurality of longitudinal bars of the concrete piles, and is low in total cost.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation pile construction, and in particular is a steel bar connection method for detecting the pull-out bearing capacity of foundation piles. Background Art

[0002] The main steel bar connection methods include binding lap joint technology, mechanical connection technology, sleeve grouting material connection technology, and steel bar welding connection technology. The main engineering features of the steel bar connection method in pile bearing capacity testing are as follows:

[0003] 1. The steel bar connection mainly bears the vertical tension, so the binding and lap connection method cannot be used;

[0004] 2. In the bearing capacity test of each pile under inspection, one or four longitudinal reinforcements of concrete piles need to be connected. The reinforcement connection engineering is relatively small. The connected reinforcements are embedded in the concrete piles. It is difficult to thread the reinforcement joints. Therefore, mechanical connection methods are not suitable.

[0005] 3. The steel bar connection part is exposed to the environment and affected by the temperature, especially under negative temperature, so it is not suitable to use the sleeve grouting steel bar connection method;

[0006] 4. The service life of the steel bar connection is synchronized with the load duration, generally 24 to 36 hours, which is much shorter than the steel bar connections in other structures.

[0007] Based on the above engineering characteristics, in the pile bearing capacity test, the steel bar connection generally adopts the welding connection method which is less affected by the external environment and has reliable force. However, the engineering problems encountered by the welding connection method also restrict the progress of the pile bearing capacity test. The main influencing factors are as follows:

[0008] 1. The pile bearing capacity test is generally carried out in the early stages of construction projects. The conditions for introducing power into the foundation pit are insufficient, and there is a lack of technical personnel specialized in welding work.

[0009] 2. The steel bar connection needs to be welded on both sides. The steel bar overlap length is relatively large. After the pile bearing capacity test is completed, the steel bar needs to be cut off when the loading equipment is dismantled, resulting in waste of steel bar connection materials.

[0010] 3. Before loading the foundation piles, the welding connection failed to provide effective pre-tension stress, and the steel bar connection was unevenly stressed during the foundation pile bearing capacity test loading process.

[0011] For example, a vertical pull-out static load test fixture for pile foundations disclosed in a Chinese invention patent with application publication number CN109797785A comprises a support frame arranged above the pile foundation, a driving member is provided on the support frame, a weight is provided above the driving member, a connecting steel bar is passed through the weight along the vertical direction, a middle fixed sleeve of the connecting steel bar is provided with an abutment sleeve, a pair of hoops are detachably connected on both sides of the pile foundation, a horizontally arranged connecting plate is fixed on the hoops, support plates are fixed on both sides of the connecting plates, the support plates are vertically arranged and fixedly connected to the hoops, a connecting plate is passed through the bottom end of the connecting steel bar, the abutment sleeve abuts on the connecting steel bar, and is connected to the upper connecting steel bar through a hoops arranged around the pile foundation.

[0012] The above-mentioned prior art has the following problems:

[0013] 1. The versatility of this connection method is relatively poor. The size of the hoop needs to be customized according to the cross-sectional size of the foundation pile. Foundation piles with different cross-sectional sizes require different sizes.

[0014] 2. Except for precast piles, the cross-sectional shape of the foundation piles is not completely regular. Therefore, even if there are plugs on the inner wall of the hoop, the hoop may still slip vertically, resulting in failure of the inspection work;

[0015] 3. If the clamp is installed too close to the pile top, it is easy to cause the pile head to crack under the pull-out load;

[0016] 4. The insert generates local pressure on the pile body, which may cause the pile body to crack, and generates circumferential tension on the clamp, which may cause the clamp to break.

[0017] Therefore, how to effectively solve the poor versatility and reliability of the connection between the longitudinal reinforcement of the foundation piles and the upper reinforcement, low detection efficiency and quality, high detection cost, and high labor intensity are technical problems that need to be solved urgently. Summary of the invention

[0018] In view of the deficiencies in the above-mentioned background technology, the present invention proposes a steel bar connection method for detecting the pull-out bearing capacity of pile foundations, which solves the problems of poor versatility and reliability of the connection between the longitudinal reinforcement of the pile foundations and the upper reinforcement, low detection efficiency and quality, high detection cost, and high labor intensity.

[0019] The technical solution of this application is:

[0020] A steel bar connection method for detecting the pull-out bearing capacity of a pile foundation comprises the following steps:

[0021] S1: Select the connection unit according to the diameter and tensile strength of the longitudinal reinforcement of the concrete pile;

[0022] S2: Prefabricate the upper reinforcement according to the height of the reaction platform;

[0023] S3: Install connection units at the top of the concrete pile longitudinal reinforcement and the bottom of the upper reinforcement and perform pile bearing capacity testing;

[0024] S4: After the pile bearing capacity test is completed, the reaction platform, the connection unit of the upper steel bars, and the connection unit of the upper steel bars and the longitudinal bars of the concrete piles are removed.

[0025] Furthermore, the connecting unit includes an upper connecting member and a lower connecting member with the same structure, the upper connecting member and the lower connecting member are connected by a positioning member, the upper connecting member and the lower connecting member both include connected baffles and anchors, bolt holes are provided at both ends of the baffles, the positioning member includes bolts, the bolts pass through the bolt holes of adjacent baffles in turn and cooperate with the nut threads.

[0026] Furthermore, the anchor is arranged at the center of the baffle.

[0027] Furthermore, the anchor of the upper connecting member fits with the anchor of the lower connecting member.

[0028] Furthermore, the concrete pile longitudinal reinforcement and the upper reinforcement are arranged on the same straight line.

[0029] Furthermore, the design value of the tensile bearing capacity of the upper steel bars is greater than the design value of the tensile bearing capacity of the longitudinal bars of the concrete pile.

[0030] Furthermore, the total tensile bearing capacity design value of the two bolts is not less than the tensile bearing capacity design value of the connected steel bars.

[0031] Furthermore, the length of the baffle is:

[0032] L = 2(d1+d2+d3+d A / 2),

[0033] Where d1 is the distance from the edge of the bolt hole to the outer edge of the baffle;

[0034] d2 is the diameter of the bolt hole;

[0035] d3 is the distance from the edge of the bolt hole to the outer edge of the anchor;

[0036] d A is the diameter of the anchor.

[0037] Furthermore, the width of the baffle is greater than d A .

[0038] Furthermore, the shear strength of the baffle is greater than the maximum shear stress of the bolts acting on it:

[0039]

[0040] Where, fv is the design value of the baffle shear strength;

[0041] h is the baffle thickness;

[0042] d n is the net width of the baffle, d n =d A -d2.

[0043] The specific beneficial effects of the present invention include:

[0044] 1. The connection unit is light in weight, and the connection with the longitudinal reinforcement of the concrete pile and the upper reinforcement is convenient and quick. It does not require power supply, special equipment and professional technicians, has strong environmental adaptability, and the reinforcement connection time is much less than the welding connection method, mechanical connection method and sleeve grouting material connection method;

[0045] 2. The connection unit can be recycled and provide pre-tension stress to ensure that the reinforcement of the concrete pile is evenly and reliably stressed. It is suitable for connecting the longitudinal reinforcement of multiple concrete piles, and the overall cost is low;

[0046] 3. The bearing capacity calculation and design method of the connection unit is detailed and clear, which can ensure that no damage occurs during the bearing capacity test of the pile foundation;

[0047] 4. The specification of the connection unit is only related to the diameter of the steel bar, and is not affected by the pile diameter and the grade of the longitudinal reinforcement, so it has strong versatility;

[0048] 5. The bolts, baffles and anchors used in the connection unit are easy to obtain on the market and do not require special customization and processing. In addition, the manufacturing accuracy requirements of the connection unit are not high. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0050] Figure 1 It is a schematic diagram of the use state of the present invention;

[0051] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0052] Figure 3 It is a schematic diagram of the connection unit in the present invention;

[0053] Figure 4 is a schematic diagram of a baffle and an anchor in the present invention;

[0054] Figure 5It is a side view of the connection unit in the present invention.

[0055] Description of Figure Numbers:

[0056] 1. The pile to be tested; 3. The connection unit;

[0057] 5. Buttress; 6. Steel beam;

[0058] 7. Jack; 8. Top plate;

[0059] 31. Concrete pile longitudinal reinforcement; 32. Upper reinforcement;

[0060] 301, baffle; 302, anchor;

[0061] 33. Bolt; 34. Nut. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] The binding overlap technology in the steel bar connection method has the advantages of convenient construction and low cost. However, with the improvement of steel bar strength and the development of mechanical connection technology, its application scope is more strictly restricted. For axially tensile and slightly eccentrically tensile concrete components, binding overlap is no longer used as a connection method for stressed steel bars.

[0064] Mechanical connection technology has the advantages of stable connection quality, simple operation, energy saving and power saving, and the quality of the joint is less affected by human factors. It has a wide range of applications. Mechanical connection technology requires threading or special mechanical tools in engineering applications and is suitable for projects with large steel bar engineering quantities.

[0065] The bearing capacity of the sleeve grouting connection depends on the mutual bonding strength among the steel bars, grouting materials and sleeves, and is also affected by the ambient temperature. The higher the curing temperature, the faster the early strength development of the grouting material. In a negative temperature environment, the sleeve specimen does not have the strength, and leakage occurs during the grouting construction, resulting in the connection quality of the longitudinal stress-bearing steel bars cannot be guaranteed.

[0066] Rebar welding connection technologies include arc welding, gas pressure welding, electroslag pressure welding and flash butt welding. The strength, rigidity and ductility of the steel bars are more reliably guaranteed, and the quality of the steel bar connection is less affected by the ambient temperature. However, the power consumption is high, the welding quality is greatly affected by the welder's technical level, and the labor cost is relatively high.

[0067] It can be seen that each steel bar connection technology has its own advantages and disadvantages and is suitable for different conditions and environments. In engineering applications, factors such as structural type, force characteristics, ambient temperature, on-site construction conditions and construction costs should be considered to make a reasonable choice.

[0068] The static load test is currently recognized as the most intuitive and reliable method for testing reinforced concrete piles. According to the different static loads applied to the top of the pile, the static load test of reinforced concrete piles can be divided into three types: single pile vertical compressive static load test, single pile vertical tensile static load test and single pile horizontal static load test. The first two are the most common in the bearing capacity test of reinforced concrete piles. For the single pile vertical compressive static load test, the common reaction force devices are the weighted platform method, the anchor pile method and the weighted platform-anchor pile combined method. The load-bearing platform of the weighted platform method is simple to build and is suitable for static load tests of reinforced concrete piles with different loads. The reaction force is provided by the gravity of the heavy objects on the load-bearing platform. The heavy objects are large in size, occupy a large space in the warehouse, are expensive in transportation, and are prone to collapse accidents during use. For this reason, the "Code for Design of Building Foundations" (GB50007-2011) recommends the use of the anchor pile method as a priority. Whether it is the anchor pile method, weighted platform-anchor pile method, or single pile vertical tensile static load test in a single pile, the key technology is the connection between the longitudinal force-bearing reinforcement of the inspected pile and the reaction device. Therefore, choosing a reasonable reinforcement connection method is an objective requirement for the bearing capacity test of reinforced concrete piles. Exploring reinforcement connection technology with low cost, reliable connection and strong engineering adaptability is an inevitable choice for modern engineering testing.

[0069] To explore the steel bar connection method suitable for reinforced concrete pile bearing capacity testing, it is necessary to first analyze its engineering characteristics. The main engineering characteristics are as follows:

[0070] (1) The steel bar connection mainly provides vertical tensile stress, so the binding lap connection method cannot be used.

[0071] (2) In the bearing capacity test of each pile under test, it is necessary to connect the longitudinal steel bars of one or four reinforced concrete piles, and the steel bar connection work is relatively small. The connected steel bars are embedded in the pile under test, and it is difficult to thread the steel bar joints. Therefore, it is not suitable to use the threading mechanical connection method.

[0072] (3) During the static load test of reinforced concrete piles, the steel bar connection parts are exposed to the environment and affected by temperature, especially under negative temperatures. It is not appropriate to use the sleeve grouting steel bar connection method.

[0073] (4) The service life of the steel connection is synchronized with the load duration in the reinforced concrete pile bearing capacity test, generally 24 to 36 hours, which is much shorter than the steel connection in other structures.

[0074] Based on the above engineering characteristics, in the bearing capacity test of reinforced concrete piles, the steel bar connection generally adopts the welding connection method which is less affected by the external environment and has reliable force. However, the engineering problems encountered by the welding connection method also restrict the progress of the bearing capacity test of reinforced concrete piles. The main influencing factors are as follows:

[0075] (1) The bearing capacity test of reinforced concrete piles is usually carried out in the early stages of construction preparation. The conditions for introducing power into the foundation pit are insufficient, and there is a lack of technical personnel specialized in welding work.

[0076] (2) The steel bar connection needs to be welded on both sides. The steel bar overlap length is relatively large. After the test, when the loading equipment is dismantled, the steel bar needs to be cut off, resulting in material waste.

[0077] (3) Before the static load test of reinforced concrete piles, the connection between the longitudinal reinforcement of the tested pile and the upper reinforcement failed to provide effective pre-tension stress. During the loading process of the reinforced concrete pile bearing capacity test, the reinforcement connection was subjected to uneven stress, which is also the main reason for the failure of the pull-out pile or anchor pile method.

[0078] In order to overcome the limitations of welding connection application, according to the engineering characteristics of steel bar connection in pile bearing capacity detection, a steel bar connection method for pile pull-out bearing capacity detection is proposed, including the following steps:

[0079] S1: Select the connection unit 3 according to the diameter and tensile strength of the concrete pile longitudinal reinforcement 31;

[0080] S2: Prefabricate the upper reinforcement 32 according to the height of the reaction platform, and the upper reinforcement 32 is preferably made of precision-rolled threaded reinforcement;

[0081] S3: installing the connection unit 3 at the top of the concrete pile longitudinal reinforcement 31 and the bottom of the upper reinforcement 32 respectively and performing pile bearing capacity testing;

[0082] S4: After the pile bearing capacity test is completed, the reaction platform, the connection unit 3 of the upper reinforcement 32, the upper reinforcement 32, and the connection unit 3 of the concrete pile longitudinal reinforcement 31 are removed. The connection unit 3 at the end of the concrete pile longitudinal reinforcement 31 can be removed by hammering for recycling.

[0083] Based on the above implementation, as a preferred implementation, Figure 2-Figure 5 As shown, the connecting unit 3 includes an upper connecting member and a lower connecting member with the same structure, and the upper connecting member and the lower connecting member are connected by a positioning member. The upper connecting member and the lower connecting member both include a connected baffle 301 and an anchor 302, and bolt holes are symmetrically arranged on the baffle 301. The positioning member includes bolts 33, and the bolts 33 pass through the bolt holes of adjacent baffles 301 in sequence and are threadedly matched with nuts 34.

[0084] Specifically, a bolt hole is provided at each end of the baffle 301, and the bolt hole is as close to the anchor 302 as possible. The anchor 302 and the baffle 301 are welded or integrally manufactured, and the baffle 301 and the bolt 33 are fixed with nuts 34, the purpose of which is to ensure that the anchor 302 and the baffle 301, and the baffle 301 and the bolt 33 are rigidly connected, and the bolt 33 generates pre-tension stress by tightening the nut 34, and the pre-tension stress is transmitted to the longitudinal reinforcement 31 of the concrete pile, such as Figure 3 shown.

[0085] On the basis of the above-mentioned embodiment, as a preferred embodiment, the positioning member can also be configured as a screw rod, and the screw rods respectively pass through the bolt holes of adjacent baffles 301 and are threadedly matched with the nuts 34 .

[0086] Specifically, the nut 34 may also be configured as a double nut, and each set of double nuts is disposed on the upper and lower sides of the baffle 301 to enhance the stability of the connecting unit 3 .

[0087] On the basis of the above-mentioned implementation manner, as a preferred implementation manner, the anchor 302 is arranged at the center of the baffle 301 to maintain balanced force.

[0088] On the basis of the above-mentioned embodiment, as a preferred embodiment, the anchor 302 of the upper connecting member 31 is fitted with the anchor 302 of the lower connecting member 32, the upper connecting member 31 and the lower connecting member 32 are arranged in a mirror image, the anchor 302 of the upper connecting member 31 is pressed on the anchor 302 of the lower connecting member 32, the concrete pile longitudinal reinforcement 31 and the upper steel bar 32 are inserted into the anchor 302 for connection, and under the action of the mechanical bite force provided by the anchor 302, the tensile stress of the upper steel bar 32 is transmitted to the concrete pile longitudinal reinforcement 31, and the connection is convenient and the force is reliable.

[0089] On the basis of the above implementation, the anchor 302 of the upper connecting member is coaxial with the anchor 302 of the lower connecting member, the concrete pile longitudinal reinforcement 31 and the upper steel bar 32 are arranged on the same straight line, and the tensile stress of the upper steel bar 32 is transmitted to the concrete pile longitudinal reinforcement 31.

[0090] On the basis of the above implementation, as a preferred implementation, the design value of the tensile bearing capacity of the upper steel bar 32 is greater than the design value of the tensile bearing capacity of the concrete pile longitudinal bar 31, that is, the design value of the tensile bearing capacity of the connecting steel bar is greater than the design value of the tensile bearing capacity of the connected steel bar.

[0091] On the basis of the above embodiment, as a preferred embodiment, a bolt hole is provided at each end of the baffle 301, and two bolts 33 are provided on the connecting unit 3, and the total tensile bearing capacity design value of the two bolts 33 is not less than the tensile bearing capacity design value of the connected steel bars:

[0092] N ≥ F / 2 (1)

[0093] In formula (1), N is the design value of the tensile bearing capacity of a single bolt, in kN;

[0094] F is the design value of the tensile bearing capacity of the connected steel bars.

[0095] Specifically, in the pull-out test of pile bearing capacity, the maximum tensile force provided by the steel bar is required to be 1.2 times the ultimate bearing capacity of the pile. The design value adopted in formula (1) has a large safety reserve and takes into account the situation that the two bolts are subjected to uneven force in the tensile test of the connector.

[0096] Based on the above implementation, as a preferred implementation, Figure 4 As shown, the length of the baffle 301 is:

[0097] L = 2(d1+d2+d3+d A / 2),

[0098] Wherein, d1 is the distance from the edge of the bolt hole to the outer edge of the baffle 301;

[0099] d2 is the diameter of the bolt hole;

[0100] d3 is the distance from the edge of the bolt hole to the outer edge of the anchor 302;

[0101] d A is the diameter of the anchor 302.

[0102] Based on the above implementation, as a preferred implementation, the width of the baffle 301 is greater than d A .

[0103] On the basis of the above-mentioned embodiment, as a preferred embodiment, the connection unit 3 cannot be damaged before the upper steel bar 32 or the concrete pile longitudinal bar 31, and the baffle 301 mainly undergoes shear failure, and the shear strength of the baffle (301) is greater than the maximum shear stress of the bolt 33 acting on it:

[0104]

[0105] In the formula, f v is the design value of shear strength of baffle 301;

[0106] h is the thickness of the baffle 301;

[0107] d n is the net width of the baffle 301, d n =d A -d2.

[0108] Specifically, the diameter and grade of the connected steel bars are known, so the grade and diameter of the upper steel bars 32 and bolts 33 can be determined, and the corresponding anchors 302 can be selected. The width of the baffle 301 is determined by the outer diameter of the anchor 302 and should not be less than the diameter of the anchor 302; the length, thickness and steel grade of the baffle 301 are determined by the design value of the bearing capacity of the connection unit 3.

[0109] The technical and economic comparison of the present invention is shown in Table 1:

[0110] Table 1 Technical and economic comparison

[0111]

[0112] Note: ① Connection time refers to the connection time of a single steel bar; ② For the anchor-bolt connection method, the connection cost refers to the cost of the connecting parts used for a single steel bar, including the material cost and cost of the baffle, anchor and bolt. For the welding connection method, the connection cost mainly includes the welding rod material cost, electricity cost and labor cost, etc.

[0113] Specifically, Figure 1 As shown, a connection unit consisting of bolts 33, nuts 34, baffles 301, and anchors 302 is prefabricated; before the pile inspection, a plurality of vertical concrete pile longitudinal bars 2 are exposed on the top of the inspected pile 1, piers 5 are symmetrically arranged on both sides of the inspected pile 1, a steel beam 6 is erected on the top of the two piers 5, a jack 7 is arranged in the middle of the steel beam 6, and the jack 7 is supported under the top plate 8, and the concrete pile longitudinal bars 31 and the upper steel bars 32 are connected by the connection unit.

[0114] The details not described in detail in the present invention are all conventional technical means known to those skilled in the art.

[0115] The above content shows and describes the basic principles, main features and beneficial effects of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A steel bar connection method for pile pull-out bearing capacity detection, characterized in that: The following steps are involved: S1: Selecting a connection unit (3) according to the diameter and tensile strength of the concrete pile longitudinal reinforcement (31); S2: prefabricate upper reinforcement (32) according to the height of the reaction platform; S3: installing the connection unit (3) at the top of the concrete pile longitudinal reinforcement (31) and at the bottom of the upper reinforcement (32) and performing a pile bearing capacity test; S4: After the pile bearing capacity test is completed, the reaction platform, the connection unit (3) of the upper reinforcement (32), the upper reinforcement (32), and the connection unit (3) of the concrete pile longitudinal reinforcement (31) are removed.

2. The steel bar connection method for pile pull-out bearing capacity detection according to claim 1, characterized in that: The connection unit (3) comprises an upper connection member and a lower connection member of the same structure, the upper connection member and the lower connection member are connected via a positioning member, the upper connection member and the lower connection member both comprise a connected baffle (301) and an anchor (302), both ends of the baffle (301) are provided with bolt holes, the positioning member comprises bolts (33), the bolts (33) sequentially pass through the bolt holes of adjacent baffles (301) and are threadedly engaged with nuts (34).

3. The steel bar connection method for pile pull-out bearing capacity detection according to claim 2, characterized in that: The anchor (302) is arranged at the center of the baffle (301).

4. The steel bar connection method for pile pull-out bearing capacity detection according to claim 3 is characterized in that: The anchor (302) of the upper connecting member fits the anchor (302) of the lower connecting member (32).

5. The method for connecting steel bars for detecting the pull-out bearing capacity of pile foundations according to any one of claims 1 to 4, characterized in that: The concrete pile longitudinal reinforcement (31) and the upper reinforcement (32) are arranged on the same straight line.

6. The method for connecting steel bars for testing the pull-out bearing capacity of pile foundations according to any one of claims 1 to 4, characterized in that: The design value of the tensile bearing capacity of the upper steel bars (32) is greater than the design value of the tensile bearing capacity of the concrete pile longitudinal bars (31).

7. The method for connecting steel bars for testing the pull-out bearing capacity of pile foundations according to any one of claims 2 to 4, characterized in that: The total tensile bearing capacity design value of the bolts (33) is not less than the tensile bearing capacity design value of the connected steel bars.

8. The method for connecting steel bars for testing the pull-out bearing capacity of pile foundations according to any one of claims 2 to 4, characterized in that: The length of the baffle (301) is: <h2 style=";text-align:left;direction:ltr">L = 2(d1+d2+d3+d<h2 style=";text-align:left;direction:ltr"> A <h2 style=";text-align:left;direction:ltr"> / 2) Wherein, d1 is the distance from the edge of the bolt hole to the outer edge of the baffle (301); d2 is the diameter of the bolt hole; d3 is the distance from the edge of the bolt hole to the outer edge of the anchor (302); d A is the diameter of the anchor (302).

9. The method for connecting steel bars for testing the pull-out bearing capacity of pile foundations according to any one of claims 2 to 4, characterized in that: The width of the baffle (301) is greater than d A .

10. The method for connecting steel bars for testing the pull-out bearing capacity of pile foundations according to any one of claims 2 to 4, characterized in that: The shear strength of the baffle (301) is greater than the maximum shear stress exerted on it by the bolt (33): In the formula, f v is the design value of the shear strength of the baffle (301); h is the thickness of the baffle (301); d n is the net width of the baffle (301), d n =d A -d2.

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