Construction method of foundation pit engineering steel pipe inner support serving as support changing component

Abstract

The invention relates to the technical field of foundation pits, and discloses a foundation pit engineering steel pipe inner support construction method serving as a support changing component, which comprises the following construction steps: 1) arranging a steel enclosing purlin and a steel pipe support; 2) excavating to the bottom of the foundation pit; 3) forming a main body bottom plate; (4) a main body side wall is formed, a supporting interval is formed between the main body side wall and the inner side wall of the foundation pit, and a front support replacing plate strip is arranged in the supporting interval; (5) steel replacement supports are arranged between the main body side walls; (6) the steel pipe supports are dismantled; (7) the steel enclosing purlins are dismantled, and a rear support replacement plate strip is formed through construction in the support interval; (8) a main body top plate is formed through construction, and after the main body top plate is maintained for set time, the front support replacement plate strip and the steel support replacement plate strip are dismantled; the foundation pit engineering steel pipe inner support construction method has the following advantages: 1) the problem that the main body side wall is easy to leak is solved; compared with a conventional process adopting a concrete support, the construction speed can be increased, and the construction period is shortened; building solid waste is avoided, and the construction cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of foundation pits, and more specifically, to a construction method for a steel pipe internal support in a foundation pit project that also serves as a replacement bracing member. Background Art

[0002] With the increasing urban population, in recent years, to relieve the huge pressure brought by ground traffic, more and more cities have started to vigorously construct rail transit in the urban underground space to meet people's daily travel needs. To further enrich the functions of rail transit and avoid duplicate construction, it has become increasingly common for multiple different rail transits to converge at the same station, enabling it to have the function of multi-rail transit transfer. For such underground projects, during construction, the foundation pits need to be excavated to a greater depth, and each floor of the subsequent main structure also has the characteristic of high clear height.

[0003] To ensure the safety and stability of the foundation pit during construction, before the earth excavation of the foundation pit, a vertical retaining structure needs to be constructed along the outside of the excavation area, and then, according to the progress of the earth excavation of the foundation pit, a horizontal bracing structure with both ends connected to the vertical retaining structure is set up.

[0004] For the vast majority of foundation pits, the vertical enclosing structure and the horizontal bracing structure only serve as temporary structures to ensure the safety of the foundation pit during construction. When the main structures such as the basement start to be constructed, this temporary structure of the horizontal bracing structure will also be demolished as the construction progresses.

[0005] With the demolition of the temporary structure, the function of maintaining the safety and stability of the foundation pit that it originally played is lost. Therefore, to ensure the safety and stability during the construction stage of the main structure, a replacement bracing structure is constructed in the foundation pit. After the strength of the replacement bracing structure reaches the requirements, the horizontal bracing structure is then demolished.

[0006] In the prior art, although the safety of the foundation pit after the demolition of the horizontal bracing structure can be ensured, there are still defects:

[0007] 1) It is necessary to construct a new replacement bracing structure before the horizontal bracing structure occupying the main space can be demolished, resulting in high construction costs and long construction periods.

[0008] 2) Leakage is likely to occur at the node positions where the horizontal bracing structure passes through the main structure. Currently, it is mainly dealt with by pre-embedding a water-stop structure in advance.

[0009] 3) If the originally designed horizontal bracing structure and replacement bracing structure are made of concrete materials, the demolished horizontal bracing structure cannot be reused, and problems such as a large amount of construction waste need to be disposed of, resulting in high construction costs. Summary of the Invention

[0010] The object of the present invention is to provide a construction method for steel pipe internal supports in foundation pit engineering that also serves as replacement bracing members, aiming to solve the problem of high construction costs in the prior art.

[0011] The present invention is implemented as follows. The construction method for steel pipe internal supports in foundation pit engineering that also serves as replacement bracing members includes the following construction steps:

[0012] 1). The foundation pit is provided with a vertical retaining structure on its outer periphery, and the vertical retaining structure is arranged around the outer periphery of the foundation pit; after the foundation pit is excavated to the bottom support position, two steel wales arranged facing each other are provided on the vertical retaining structure, and a steel pipe strut is arranged between the two steel wales;

[0013] 2). Excavate the remaining soil in the foundation pit until the foundation pit is excavated to the bottom of the foundation pit;

[0014] 3). Construct a main floor slab at the bottom of the foundation pit;

[0015] 4). Construct a main side wall on the main floor slab. There is a support interval between the main side wall and the inner side wall of the foundation pit. The top of the main measurement is lower than the steel pipe strut, and a front replacement bracing belt is provided in the support interval;

[0016] 5). Arrange steel replacement braces between the main side walls. The ends of the steel replacement braces are butted against the main side walls, and the steel replacement braces apply prestress to the main side walls;

[0017] 6). Remove the steel pipe strut;

[0018] 7). Remove the steel wales, and construct a rear replacement bracing belt in the support interval. The rear replacement bracing belt is located above the front replacement bracing belt;

[0019] 8). Construct a main roof slab on the main side walls. After the main roof slab is cured to the set time, remove the front replacement bracing belt and the steel replacement braces.

[0020] Further, in the construction step 1), a movable steel end is provided at the end of the steel pipe strut. After the steel wales are formed on the vertical retaining structure, the steel pipe strut is hoisted between the two steel wales, the steel end of the steel pipe strut is pressed against the steel wales, and the steel end is fixedly arranged. The steel pipe strut applies prestress to the vertical retaining structure.

[0021] Further, in the construction step 1), a steel anchor plate is constructed on the vertical retaining structure, and the steel wales are fixedly connected to the steel anchor plate so that the steel wales are fixed on the vertical retaining structure.

[0022] Further, in the construction step 1), a plurality of anchor bars are provided at the inner end of the steel anchor plate, and the plurality of anchor bars are embedded in the vertical retaining structure, and along the height direction of the steel anchor plate, the plurality of anchor bars are arranged at intervals up and down.

[0023] Further, in the construction step 2), the remaining soil in the foundation pit is excavated in zones until the bottom of the foundation pit is reached.

[0024] Further, in the construction step 2), after the remaining soil in the foundation pit is excavated to a set distance from the bottom of the foundation pit, manual bottom cleaning is carried out until the bottom of the foundation pit is cleared.

[0025] Further, formwork is supported at the bottom of the foundation pit to form a bottom plate formwork, a cushion layer and a steel bar framework are arranged in the enclosed area of the bottom plate formwork, concrete is poured in the enclosed area of the bottom plate formwork, the concrete covers the cushion layer and the steel bar framework, and after the concrete solidifies, the main bottom plate is formed.

[0026] Further, in the construction step 1), a horizontal bracing structure is provided in the foundation pit, the end of the horizontal bracing structure is butted against the vertical retaining structure, and the horizontal bracing structure is located above the steel pipe strut;

[0027] In the construction step 6), during the process of removing the steel pipe strut, adjust the prestress of the horizontal bracing structure and the prestress of the steel replacement strut.

[0028] Further, in the construction step 6), after the steel pipe strut is removed, the removed steel pipe strut is hoisted to the construction area where the steel replacement strut is to be arranged, and the removed steel pipe strut is arranged in the construction area to form the steel replacement strut.

[0029] Further, in the construction step 5), a middle section is formed in the middle of the steel replacement strut, a middle sleeve is sleeved on the outer periphery of the middle section, there is an annular middle interval between the middle sleeve and the middle section, and the middle interval is filled with a middle elastic ring; an end ring is formed at the end of the middle elastic ring, and the end ring is fixedly wound around the outer periphery of the middle section outside the middle interval formed by the end ring, and covers the end of the middle sleeve;

[0030] In the construction step 5), the two ends of the steel replacement strut respectively have end sections butted against the middle section, a plurality of outer rings are fixedly sleeved on the end sections, and the plurality of outer rings are arranged at intervals along the axial direction of the end section; there is an inter-ring interval between adjacent end sections, a plurality of butt joints are arranged in the annular interval, the ends of the butt joints are respectively butted against two outer rings, the plurality of butt joints are arranged at intervals around the circumference of the steel replacement strut, and there is an outer interval between the butt joints and the outer periphery of the steel replacement strut.

[0031] Compared with the prior art, the construction method of steel pipe internal support for foundation pit engineering provided by the present invention has the following advantages:

[0032] 1). By arranging the steel pipe struts first and then arranging the steel replacement struts during the construction of the main body side wall, there is no need to reserve holes or embed water stop steel plates in the main body side wall, and the steel pipe struts to be removed first can be used as components of the steel replacement struts, solving the problem of easy leakage of the main body side wall;

[0033] 2). The steel pipe struts have the characteristics of convenient and fast installation and removal and reusable. Under the condition of ensuring the safety of foundation pit construction, compared with the conventional process using concrete struts, the construction speed can be accelerated and the construction period can be saved;

[0034] 3). It avoids problems such as a large amount of construction waste that is difficult to dispose of and cannot be reused after the removal of concrete struts, has good environmental protection benefits, and greatly saves construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic flow chart of the construction method of steel pipe internal support for foundation pit engineering that also serves as a replacement strut component provided by the present invention;

[0036] Figure 2 is a front view schematic diagram of the construction of the main body floor slab in the foundation pit provided by the present invention;

[0037] Figure 3 is a front view schematic diagram of the arrangement of steel replacement struts in the foundation pit provided by the present invention;

[0038] Figure 4 is a front view schematic diagram of the construction of the main body roof slab in the foundation pit provided by the present invention;

[0039] Figure 5 is a front view schematic diagram of the removal of steel replacement struts in the foundation pit provided by the present invention;

[0040] Figure 6 is a front view schematic diagram of the connection between the steel collar beam and the foundation pit retaining structure provided by the present invention;

[0041] Figure 7 is a partial sectional view schematic diagram of the steel replacement strut provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0044] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings. This is only for the convenience of describing the present invention 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. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and should not be construed as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] Refer to Figure 1-7 As shown, it is a preferred embodiment provided by the present invention.

[0046] The construction method of the steel pipe internal support for the foundation pit project that also serves as a replacement bracing member is characterized by including the following construction steps:

[0047] 1) The foundation pit 101 is provided with a vertical retaining structure 100 on its outer periphery, and the vertical retaining structure 100 is arranged in a circular shape 501 around the outer periphery of the foundation pit 101; after the foundation pit 101 is excavated to the bottom support position, two steel wales 301 arranged opposite to each other are set on the vertical retaining structure 100, and a steel pipe strut 300 is arranged between the two steel wales 301;

[0048] 2) Excavate the remaining soil of the foundation pit until the foundation pit 101 is excavated to the bottom of the foundation pit 101;

[0049] 3) Construct the main floor slab 401 at the bottom of the foundation pit 101;

[0050] 4) Construct the main side wall 402 on the main floor slab 401. There is a support interval 403 between the main side wall 402 and the inner side wall of the foundation pit 101. The top of the main measurement is lower than the steel pipe strut 300, and a front replacement bracing belt 404 is arranged in the support interval 403;

[0051] 5) Arrange a steel replacement bracing 500 between the main side walls 402. The ends of the steel replacement bracing 500 are butt - jointed on the main side wall 402, and the steel replacement bracing 500 applies prestress to the main side wall 402;

[0052] 6) Remove the steel pipe strut 300;

[0053] 7) Remove the steel wale 301, and construct a rear replacement bracing belt 405 in the support interval 403. The rear replacement bracing belt 405 is located above the front replacement bracing belt 404;

[0054] 8) Construct the main roof slab 406 on the main side wall 402. After the main roof slab 406 is cured to the set time, remove the front replacement bracing belt 404 and the steel replacement bracing 500.

[0055] The construction method of the steel pipe internal support for the foundation pit project that also serves as a replacement bracing member provided above has the following advantages:

[0056] 1), By first arranging the steel pipe brace 300 and arranging the steel replacement brace 500 during the construction of the main body side wall 402, there is no need to reserve holes or embed water stop steel plates in the main body side wall 402, and the previously removed steel pipe brace 300 can be used as a component of the steel replacement brace 500, solving the problem of easy leakage of the main body side wall 402;

[0057] 2), The steel pipe brace 300 has the characteristics of convenient and quick installation and removal, and can be reused. Under the condition of ensuring the construction safety of the foundation pit 101, compared with the conventional process using concrete braces, the construction speed can be accelerated and the construction period can be saved;

[0058] 3), It avoids problems such as a large amount of construction waste that is difficult to dispose of and cannot be reused after the removal of concrete braces, has good environmental protection benefits, and greatly saves construction costs.

[0059] In this embodiment, in construction step 1), a movable steel end is provided at the end of the steel pipe brace 300. After the steel waling 301 is formed on the vertical retaining structure 100, the steel pipe brace 300 is hoisted between the two steel walings 301, the steel end of the steel pipe brace 300 is pressed against the steel waling 301, and the steel end is fixedly arranged, and the steel pipe brace 300 applies prestress to the vertical retaining structure 100. In this way, it is convenient for the docking and fixing between the steel pipe brace 300 and the steel waling 301, and it is also convenient for the steel pipe brace 300 to apply prestress.

[0060] In this embodiment, in construction step 1), a steel anchor plate 302 is constructed on the vertical retaining structure 100, and the steel waling 301 is fixedly connected to the steel anchor plate 302 so that the steel waling 301 is fixed on the vertical retaining structure 100. In this way, it is convenient for the connection between the steel waling 301 and the steel anchor plate 302, and it is also convenient for the steel waling 301 to be fixed on the vertical retaining structure 100.

[0061] In this embodiment, in construction step 1), a plurality of anchor bars 303 are provided at the inner end of the steel anchor plate 302, and the plurality of anchor bars 303 are embedded in the vertical retaining structure 100, and along the height direction of the steel anchor plate 302, the plurality of anchor bars 303 are arranged at intervals up and down. By arranging a plurality of anchor bars 303, the steel anchor plate 302 is firmly fixed on the vertical retaining structure 100.

[0062] In this embodiment, in construction step 2), the remaining soil in the foundation pit is excavated in zones until the bottom of the foundation pit 101 is excavated. The excavation can be carried out in accordance with the principle of "zoning, sectioning, and layering", and the earthwork excavation in the long side direction of the long strip foundation pit 101 should also be carried out in accordance with the above principle.

[0063] In this embodiment, in construction step 2), after the remaining soil of the foundation pit excavation reaches a set distance from the bottom of the foundation pit 101, manual bottom cleaning is carried out until the bottom of the foundation pit 101 is cleared. After the remaining soil of the foundation pit is excavated to 200 - 300 mm from the bottom of the pit, manual bottom cleaning is carried out to prevent the soil below the bottom of the foundation pit 101 from being disturbed. Subsequently, after the cushion layer, steel reinforcement cage, and bottom formwork are supported in sequence, concrete is poured to complete the construction of the bottom slab.

[0064] In this embodiment, formwork is supported at the bottom of the foundation pit 101 to form a bottom slab formwork. A cushion layer and a steel reinforcement cage are arranged in the enclosed area of the bottom slab formwork, and concrete is poured in the enclosed area of the bottom slab formwork. The concrete covers the cushion layer and the steel reinforcement cage. After the concrete solidifies, the main bottom slab 401 is formed.

[0065] In this embodiment, in construction step 1), a horizontal bracing structure is provided in the foundation pit 101. The end of the horizontal bracing structure is butted against the vertical retaining structure 100, and the horizontal bracing structure is located above the steel pipe strut 300; in construction step 6), during the process of removing the steel pipe strut 300, the prestress of the horizontal bracing structure and the prestress of the steel replacement strut 500 are adjusted.

[0066] During the process of unloading the steel pipe strut 300, closely monitor the lateral deformation development of the vertical retaining structure 100 of the foundation pit 101, and adjust the prestress of the remaining steel pipe struts 300 (or horizontal bracing structure) that have not started to be removed and the installed steel replacement struts 500 to ensure the safety of the foundation pit 101.

[0067] The horizontal bracing structure in the foundation pit 101 can be a steel pipe strut 300 or other bracing structures. As a preferred embodiment, the horizontal bracing structure is also a steel pipe strut 300.

[0068] In this embodiment, in construction step 6), after the steel pipe strut 300 is removed, the removed steel pipe strut 300 is hoisted to the construction area where the steel replacement strut 500 is to be arranged, and the removed steel pipe strut 300 is arranged in the construction area to form a steel replacement strut 500.

[0069] When the removed steel pipe strut 300 is hoisted to the construction area, if the working face is suspended, a hoisting device can be used for hanging, installed at the corresponding position of the steel replacement strut 500 and prestress is applied to complete the installation of all steel replacement struts 500. Finally, the remaining steel pipe struts 300 are removed and transferred out of the construction area.

[0070] In this embodiment, in construction step 5), a middle section is formed in the middle of the steel replacement strut 500. A middle sleeve 504 is sleeved on the outer periphery of the middle section. There is an annular middle interval between the middle sleeve 504 and the middle section, and the middle interval is filled with a middle elastic ring 505. An end ring 506 is formed at the end of the middle elastic ring 505. The end ring 506 is fixedly wound around the outer periphery of the middle section outside the formed middle interval and covers the end of the middle sleeve 504.

[0071] In construction step 5), both ends of the steel replacement strut 500 respectively have end sections docked with the middle section. A plurality of outer rings 501 are fixedly sleeved on the end sections. The plurality of outer rings 501 are arranged at intervals along the axial direction of the end sections. There is an inter-ring interval 503 between adjacent end sections. A plurality of docking bars 502 are arranged at intervals in a ring shape. The ends of the docking bars 502 are respectively docked with two outer rings 501. The plurality of docking bars 502 are arranged at intervals around the circumference of the steel replacement strut 500, and there is an outer interval between the docking bars 502 and the outer periphery of the steel replacement strut 500.

[0072] By arranging a plurality of middle sleeves 504, the middle sleeves 504 are elastically sleeved on the outer periphery of the middle section. In this way, the middle section can be provided with the characteristic of elastic strain, so as to improve the better support performance of the steel replacement strut 500. On the basis of maintaining sufficient strength support, elastic characteristic support can be formed in the middle section, which can achieve more stable support and buffer the vibration during the support process.

[0073] In addition, by arranging a plurality of outer rings 501 on the end sections, on the premise of interval reinforcement of the end sections, and forming docking bars 502 between adjacent outer rings 501, there is an outer interval between the docking bars 502 and the steel replacement strut 500. In this way, suspended support can be formed by using the plurality of docking bars 502, the stress can be evenly distributed in a circle, and the support stability can be enhanced.

[0074] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Construction method of steel pipe internal support for foundation pit engineering serving as a strut replacement member, characterized in that, It includes the following construction steps: 1). The foundation pit is provided with a vertical retaining structure on its outer periphery, and the vertical retaining structure is arranged around the outer periphery of the foundation pit; after the foundation pit is excavated to the bottom support position, two steel wales arranged facing each other are set on the vertical retaining structure, and steel pipe struts are arranged between the two steel wales; 2). Excavate the remaining soil of the foundation pit until the foundation pit is excavated to the bottom of the foundation pit; 3). Construct the main floor slab at the bottom of the foundation pit; 4). Construct the main side walls on the main floor slab. There is a support interval between the main side walls and the inner side wall of the foundation pit. The top of the main measurement is lower than the steel pipe strut, and a front replacement support belt is arranged in the support interval; 5). Arrange steel replacement struts between the main side walls. The ends of the steel replacement struts are butted against the main side walls, and the steel replacement struts apply prestress to the main side walls; 6). Demolish the steel pipe struts; 7). Demolish the steel wales, and construct a rear replacement support belt in the support interval. The rear replacement support belt is located above the front replacement support belt; 8). Construct the main roof slab on the main side walls. After the main roof slab is cured to the set time, demolish the front replacement support belt and the steel replacement struts.

2. The construction method of the steel pipe internal support for foundation pit engineering that also serves as a strut replacement member according to claim 1, characterized in that, In the construction step 1), a movable steel end is provided at the end of the steel pipe strut. After the steel wales are formed on the vertical retaining structure, the steel pipe strut is hoisted between the two steel wales, the steel end of the steel pipe strut is pressed against the steel wale, and the steel end is fixedly arranged. The steel pipe strut applies prestress to the vertical retaining structure.

3. The construction method of the steel pipe internal support for the foundation pit project that also serves as a strut replacement member as described in claim 2, characterized in that, In the construction step 1), a steel anchor plate is constructed on the vertical retaining structure, and the steel wale is fixedly connected to the steel anchor plate so that the steel wale is fixed on the vertical retaining structure.

4. The construction method of the steel pipe internal support for the foundation pit project serving as a strut replacement member as described in claim 3, characterized in that, In the construction step 1), a plurality of anchor bars are provided at the inner end of the steel anchor plate. The plurality of anchor bars are embedded in the vertical retaining structure, and along the height direction of the steel anchor plate, the plurality of anchor bars are arranged at intervals up and down.

5. The construction method of the steel pipe internal support for the foundation pit project that also serves as a strut replacement member according to any one of claims 1 to 4, characterized in that, In the construction step 2), the remaining soil of the foundation pit is excavated in zones until it is excavated to the bottom of the foundation pit.

6. The construction method of the steel pipe internal support for the foundation pit project serving as a strut replacement member as described in claim 5, characterized in that, In the construction step 2), after the remaining soil of the foundation pit is excavated to a set distance from the bottom of the foundation pit, manual bottom cleaning is carried out until it is cleared to the bottom of the foundation pit.

7. The construction method of the steel pipe internal support for the foundation pit project that also serves as a strut replacement member according to any one of claims 1 to 4, characterized in that, Form a bottom slab formwork by supporting formwork at the bottom of the foundation pit. Lay a cushion layer and a steel bar cage in the enclosed area of the bottom slab formwork, and pour concrete in the enclosed area of the bottom slab formwork. The concrete covers the cushion layer and the steel bar cage. After the concrete solidifies, the main floor slab is formed.

8. The construction method of the steel pipe internal support for the foundation pit project serving as a replacement strut member according to any one of claims 1 to 4, characterized in that, In the construction step 1), a horizontal bracing structure is provided in the foundation pit. The end of the horizontal bracing structure is butted against the vertical retaining structure, and the horizontal bracing structure is located above the steel pipe strut; In the construction step 6), during the process of demolishing the steel pipe struts, adjust the prestress of the horizontal bracing structure and the prestress of the steel replacement struts.

9. The construction method of the steel pipe internal support for the foundation pit project that also serves as a strut replacement member according to any one of claims 1 to 4, characterized in that, In the construction step 6), after the steel pipe struts are demolished, hoist the demolished steel pipe struts to the construction area where the steel replacement struts are to be arranged, and arrange the demolished steel pipe struts in the construction area to form the steel replacement struts.

10. The construction method of the steel pipe internal support for the foundation pit project that also serves as a strut replacement member according to any one of claims 1 to 4, characterized in that, In the construction step 5), a middle section is formed in the middle of the steel replacement strut. A middle sleeve is sleeved outside the middle section. An annular middle interval is provided between the middle sleeve and the middle section. The middle interval is filled with a middle elastic ring. An end ring is formed at the end of the middle elastic ring. The end ring is fixedly wound around the outside of the middle interval and covers the end of the middle sleeve on the outside of the middle interval formed by the end ring. In the construction step 5), end sections connected to the middle section are respectively arranged at two ends of the steel replacement strut. A plurality of outer rings are fixedly sleeved on the end sections. The plurality of outer rings are arranged at intervals along the axial direction of the end sections. An inter-ring interval is provided between adjacent end sections. A plurality of butt-joint bars are arranged at intervals in the annular interval. The end parts of the butt-joint bars are respectively butted against two outer rings. The plurality of butt-joint bars are arranged at intervals around the circumference of the steel replacement strut. An outer interval is provided between the butt-joint bars and the outer circumference of the steel replacement strut.

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