Large-diameter cable test model and closed space fire resistance test method thereof

Abstract

The invention discloses a large-diameter cable test model and a closed space fire resistance test method thereof.The model comprises a cable test model body composed of multiple cable strands, the size of the cable test model body is calculated through a set formula, the reduction proportion of the cable strands is consistent with that of the cable strands, and annular steel hoops are arranged at the two ends of the model body; a thermocouple is further pre-embedded in the model, the number of cable strands needing to be welded with the thermocouple is counted according to a preset target measuring point when the model is manufactured, and the thermocouple is welded to the surface of the cable strand measuring point; when the model is manufactured, the cable strands welded with the thermocouples are placed and positioned according to a preset sequence according to the measuring point positions, thermocouple wires are led out through cable strand gaps, and steel gaskets are additionally arranged on the surfaces, exposed out of the model, of the thermocouples to isolate flames; the surface of the model is provided with a fireproof anticorrosive coating, and the model is placed in a test furnace for a fire resistance test. According to the invention, the influence of the large-diameter cable on cable heat transfer and heat damage in different fire disasters, fire protection, fire time and the like is mainly researched, and the actual fire resistance of the fireproof material is verified.

Description

Technical Field

[0001] The invention relates to the technical field of fire testing of large-diameter cables for bridges, and in particular to a large-diameter cable test model and a closed space fire resistance test method thereof. Background Art

[0002] Cables are important force-transmitting components of bridge structures, usually composed of steel wire bundles, steel strands, etc. High-strength steel wires and steel strands are very susceptible to high-temperature damage in fires and are difficult to repair and replace. Therefore, the fire safety of bridge cables is facing major challenges.

[0003] Cables of large-span bridges generally have a larger diameter. Currently, the largest diameter of bridge cables in service can reach more than 1500mm. Therefore, when studying the heat transfer process and fire resistance of cables during fire, the influence of cross-sectional size should be considered, which will help to accurately simulate the actual fire conditions of large-diameter bridge cables. In addition, when a bridge catches fire, a large temperature gradient will be generated during the heat transfer process of the cable as the cross-sectional depth increases, further affecting the stress distribution inside the cable. Large-diameter cables will also produce more realistic evolution mechanisms and intuitive destruction mechanisms under the action of fire. At present, the evaluation of the fire resistance of large-diameter cables under fire is not accurate. Therefore, it is necessary to study the disaster of large-diameter cables under fire in enclosed spaces and establish a large-diameter cable and fire temperature field monitoring test system. The construction of this test system mainly involves the following issues:

[0004] At present, there is still a lack of systematic and mature test methods in the closed space fire test research of large-diameter cables. Conventional test methods usually test the cables after shrinking them. If the reduction ratio is too small, it is impossible to truly physically simulate the fire temperature field of the full-scale cable. Therefore, it is more meaningful to study the fire heat transfer process of large-diameter cables. If the reduction ratio is too large, for example, the diameter of the cable model is more than 1000mm, it is difficult to constrain the cable in the model making, and the danger increases. The existing test conditions are difficult to meet the test needs.

[0005] The porosity of the model has a significant impact on the physical heat transfer of the cable, and the size of the cable strand is one of the key factors affecting the porosity of the model. In addition, under the premise of large-diameter cables, a large number of thermocouples need to be arranged in the cross section of the model to accurately measure the cross-sectional temperature field of the model during the fire. The increase in thermocouples leads to a decrease in the porosity of the model. Therefore, the arrangement and positioning of the thermocouples in the cable and the determination of the cable strand size need to be optimized to ensure the accuracy of the model porosity.

[0006] At present, large-span bridge cable assembly uses large-scale cable extrusion machines and cable clamps to constrain the forming process. Due to the size of conventional fire furnaces in the laboratory, the length of cable fire-resistant models is generally short, with a maximum of about 2 meters. There is currently no dedicated cable extrusion and assembly equipment and supporting cable clamps, making it difficult to constrain and form large-diameter cables in the laboratory. Summary of the invention

[0007] In view of the above-mentioned technical deficiencies, the object of the present invention is to provide a large-diameter cable test model and a fire resistance test method for its enclosed space, which can not only meet the accuracy of physical simulation of the fire temperature field of large-diameter cables, but also achieve the convenience and safety during the assembly process of large-diameter cables.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a large-diameter cable test model, including:

[0010] A cable test model of the strand assembly type, the cross-sectional diameter of which is reduced in proportion according to the full-scale cable. The cable test model is composed of multiple strands that are parallel to each other, of the same length and aligned at both ends, and are locked and fixed by a number of annular steel hoops. The reduction ratio of the strands is the same as that of the cable test model, and the strands are formed by squeezing a number of fine wires into a round shape and are staggeredly tied and fixed at both ends and the middle position by steel straps;

[0011] Thermocouples, welded to the surface of the measuring points of several strands inside the cable test model, led out through the gaps between the strands, and the strands with welded thermocouples are arranged and positioned in sequence in the cable test model according to the target measuring point positions. Steel gaskets are installed on the surface of the thermocouples exposed outside the cable test model to isolate the flame;

[0012] Steel wires, wound around the surface of the cable test model.

[0013] Preferably, the minimum value of the diameter of the cable test model is within the allowable error range of 5%, and its diameter is not less than the result determined by the following formula:

[0014]

[0015] In the formula, R 0 is the minimum cross-sectional diameter of the cable test model (1), R is the diameter of the cable prototype, e is the natural constant, and 80mm ≤ R ≤ 1500mm.

[0016] In the second aspect, the present invention also provides a fire resistance test method for the enclosed space of a large-diameter cable test model, including the following steps:

[0017] Step 1, determine the diameter of the cable test model, use fine steel wires to make an appropriate number of strands, and each strand is tied several times at both ends and the middle with steel straps for squeezing and fixing the fine steel wires. The positions of the steel straps are arranged staggeredly, and the tying positions of different strands are staggered;

[0018] Step 2: Place a number of annular auxiliary devices in a straight line at both ends and the middle position of the preset cable test model to be made. The annular auxiliary devices at both ends are placed outside, and the annular auxiliary device in the middle position ensures that the overall cable test model is straight;

[0019] Step 3: Count the number of cable strands that need to be welded with thermocouples according to the preset target measuring point positions, and then weld the thermocouples on the surface of the cable strand measuring points;

[0020] Step 4: Place the cable strands in layers with the annular auxiliary device as a mold, and at the same time place the cable strands welded with thermocouples in the preset order according to the target measuring point positions for positioning, ensuring that the cable strands are parallel, the cable strands at both ends are flush, and the thermocouple wires of the thermocouples are led out of the cable test model through the gaps between the cable strands;

[0021] Step 5: After the cable strands are installed, fix both ends with annular steel hoops, and at the same time take out the made cable test model from the annular auxiliary device to complete the production of the cable test model;

[0022] Step 6: Wind steel wires on the surface of the cable test model, and install steel gaskets on the surface of the thermocouples exposed outside the cable test model to be made to isolate the flame;

[0023] Step 7: Place two steel-concrete fire-resistant supports in a closed test furnace, and adjust the placement direction and the distance between the two steel-concrete fire-resistant supports;

[0024] Step 8: Lift and install the cable test model on the steel-concrete fire-resistant supports, and use aluminosilicate cotton to cover the surfaces of both ends of the cable test model, the steel-concrete fire-resistant supports and the thermocouples for fire and heat insulation protection;

[0025] Step 9: After completing the fire protection of the ends of the cable test model and the thermocouple wires, close the furnace body, connect the thermocouple wires to the data acquisition instrument, and after the test preparation is completed, complete the test according to the specified fire environment and target fire exposure time.

[0026] Preferably, in Step 7, the steel-concrete fire-resistant support is formed by pouring square steel pipes and concrete, and includes an I-shaped bottom support. Two columns are provided on the bottom support, and a cross beam is fixedly connected between the two columns.

[0027] Preferably, in Step 8, fire protection is carried out on both ends of the cable test model using fire protection extended ends. The fire protection extended ends are sealed shells, and a steel-concrete support fire protection body for wrapping the steel-concrete fire-resistant support is also adapted at the bottom. Steel gaskets are installed on the surface of the thermocouples exposed outside the cable test model to isolate the flame, and the thermocouple wires of the thermocouples are led out of the furnace through the inside of the fire protection extended ends and the steel-concrete support fire protection body.

[0028] Preferably, in step 2, the annular auxiliary device comprises a base steel plate, the base steel plate is welded and fixed to the vertical annular cut steel plate, and a plurality of stiffening ribs are provided between the base steel plate and the vertical annular cut steel plate; the length of the base steel plate is greater than the outer diameter of the cable test model, and the width of the base steel plate is half of its length;

[0029] The vertical ring-cut steel plate is a square steel plate, and its side length is equal to the length of the base steel plate. The middle part of the vertical ring-cut steel plate is ring-cut into a hole according to the size of the cable test model. The upper part of the vertical ring-cut steel plate is opened from the center of the side length, and the opening size is larger than the outer diameter of the cable strand.

[0030] Preferably, in step five, the annular steel hoop is composed of two semicircular steel plates fixedly connected, and the cable test model has a plurality of annular steel hoops symmetrically arranged at both ends thereof and two adjacent annular steel hoops on the same side are arranged at a preset distance.

[0031] Preferably, in step six, when a cable fire resistance test is required, a removable fireproof and anti-corrosion layer is applied to the outer surface of the steel wire, and the removable fireproof and anti-corrosion layer is made of high temperature resistant aerogel felt.

[0032] Preferably, different fire environments and different target fire exposure times are set in the test to meet different fire conditions, and the test termination conditions include the steel surface temperature reaching a preset temperature and the test duration reaching the target fire exposure time.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention constructs the model by scaling down the cable strands in the same proportion as the overall model (error ≤ 5%), formulates the minimum diameter constraint, and arranges the cable strands in a layered manner to ensure that the diameter ≥ R 0 The temperature field of the full-scale cable can be accurately reconstructed under the premise of ; steel tie bands are used to stagger and fix the ends and middle of the cable strands, and the spatial dislocation distribution of the binding points of different cable strands is combined to make the model porosity close to the real porosity;

[0035] 2. The thermocouple is welded to the surface of the cable measuring point and reasonably led out. Steel gaskets are installed on the exposed part to isolate the flame. At the same time, fireproof and heat-insulating protection is provided for both ends of the cable test model, the steel-concrete refractory bracket and the thermocouple to prevent heat from entering from the end and the thermocouple wire from being burned, thus ensuring the accuracy of temperature data collection;

[0036] 3. The cable test model is equipped with a removable fire and corrosion resistant layer, which can be applied when the cable fire resistance test is required, thus enhancing the protection performance of the model and the diversity of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 Schematic diagram during the experiment of a large-diameter cable test model provided by an embodiment of the present invention;

[0039] Figure 2 Schematic diagram of the structure of a large-diameter cable test model provided by an embodiment of the present invention when placed on a steel-concrete fire-resistant support;

[0040] Figure 3 Cross-sectional schematic diagram of the cable test model provided by an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of the structure of the annular auxiliary provided by an embodiment of the present invention;

[0042] Figure 5 Schematic diagram of the structure of the annular steel hoop provided by an embodiment of the present invention;

[0043] Figure 6 Schematic diagram of the structure of manufacturing a cable test model on the annular auxiliary provided by an embodiment of the present invention;

[0044] Figure 7 Schematic diagram of the structure of the steel-concrete fire-resistant support provided by an embodiment of the present invention.

[0045] Explanation of reference numerals:

[0046] 1 - Cable test model; 2 - Annular auxiliary; 3 - Cable strand; 4 - Annular steel hoop; 5 - Steel wire; 6 - Thermocouple; 7 - Stiffening rib; 8 - Base steel plate; 9 - Vertical cutting steel plate; 10 - Bolt; 11 - Steel-concrete fire-resistant support; 12 - Bottom support; 13 - Column; 14 - Cross beam; 15 - Test furnace; 16 - Fire protection extended end; 17 - Steel-concrete support fire protection body; 18 - Detachable fire and corrosion protection layer. Detailed implementation manners

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0048] AsFigures 1 to 3 As shown in Figures 1 to 3 , this embodiment provides a large-diameter cable test model, hereinafter referred to as the model for short, including:

[0049] A cable test model 1 of the strand assembly type, whose size is proportionally reduced from that of a full-scale long-span bridge cable. The cable test model 1 is composed of multiple strands 3 that are parallel to each other, have the same length, and are aligned at both ends, which are locked and fixed by a number of annular steel hoops 4. The reduction ratio of the strand 3 is the same as that of the cable test model 1, and the strand 3 is formed by squeezing a number of fine steel wires into a round shape and is stagger-bundled and fixed at both ends and the middle position by steel straps to reduce the porosity of the cable test model 1 and make it close to the porosity of the real cable;

[0050] Thermocouples 6 are welded to the surface of the measuring points of the strand 3 and are led out through the gaps between the strands 3. Steel gaskets are installed on the surface of the thermocouples 6 exposed outside the cable test model 1 to isolate the flame; a number of thermocouples 6 are welded to the surface of the strands 3 inside the cable test model 1, and the strands 3 welded with thermocouples 6 are arranged and positioned in sequence in the cable test model 1 according to the target measuring point positions;

[0051] Steel wires 5 are wound around the surface of the cable test model 1 to prevent the flame from directly contacting the cable test model 1.

[0052] The minimum value of the diameter of the cable test model 1 is within the allowable error range of 5%, and its diameter is not less than the result determined by the following formula;

[0053]

[0054] In the formula, R 0 is the recommended minimum cross-sectional diameter of the cable test model 1, R is the diameter of the cable prototype, e is the natural constant, and 80mm ≤ R ≤ 1500mm.

[0055] This embodiment of the present invention also provides a method for the fire resistance test of the enclosed space of a large-diameter cable test model, including the following steps:

[0056] Step 1: Determine the diameter of the cable test model 1, and use fine steel wires to make an appropriate number of strands 3. Each strand 3 is respectively tied several times at both ends and the middle with steel straps for squeezing and fixing the fine steel wires. The positions of the steel straps are staggered, and the tying positions of different strands 3 are staggered to reduce the porosity;

[0057] Step 2: Place a number of annular auxiliary devices 2 on the same straight line at both ends and the middle position of the preset cable test model 1 to be made. The annular auxiliary devices 2 at both ends are placed outside for easy removal after cable formation, and the annular auxiliary device 2 at the middle position ensures the overall straightness of the cable test model;

[0058] See Figure 4, the annular auxiliary device 2 includes a base steel plate 8, the base steel plate 8 is fixedly welded to the vertical cutting steel plate 9, and several stiffening ribs 7 for reinforcement are also provided between the base steel plate 8 and the vertical cutting steel plate 9; the length of the base steel plate 8 is greater than the outer diameter dimension of the cable test model 1, and the width of the base steel plate 8 is half of its length to prevent the annular auxiliary device 2 from tilting;

[0059] The vertical cutting steel plate 9 is a square steel plate, the side length of which is equal to the length of the base steel plate 8, and the middle part of the vertical cutting steel plate 9 is cut into a hole according to the size of the cable test model 1. The upper part of the vertical cutting steel plate 9 is opened from the center of the side length, and the opening size is greater than the outer diameter of the cable strand 3.

[0060] Step three, count the number of cable strands 3 to which the thermocouples 6 need to be welded according to the preset target measuring point positions, and then weld the thermocouples 6 on the surfaces of these cable strand 3 measuring points;

[0061] Step four, lay the cable strands 3 in layers with the annular auxiliary device 2 as a mold, and at the same time place the cable strands 3 welded with thermocouples 6 in the preset order according to the target measuring point positions, ensuring that the cable strands 3 are parallel and the two end cable strands 3 are flush. The thermocouple wires of the thermocouples 6 are led out of the cable test model 1 through the gaps between the cable strands 3;

[0062] Step five, after the installation of the cable strands 3 is completed, fix both ends with the annular steel hoop 4, and at the same time take out the made cable test model 1 from the annular auxiliary device 2 to complete the main body production of the cable test model 1;

[0063] See Figures 5 - 6 , the annular steel hoop 4 is fixedly connected by two semi-circular steel plates. Two groups of annular steel hoops 4 are symmetrically arranged at both ends of the cable test model 1 and fastened with bolts 10 to squeeze and fix the cable strands 3. Each group is provided with several annular steel hoops 4 and a preset distance is set between adjacent two annular steel hoops 4 to adapt to the lifting equipment.

[0064] Step six, wind the steel wire 5 on the surface of the cable test model 1, and install steel gaskets on the surfaces of the thermocouples 6 exposed outside the cable test model 1 to isolate the flame;

[0065] Step seven, place two steel-concrete fire-resistant supports 11 in the closed test furnace 15, adjust the placement direction and the distance between the two steel-concrete fire-resistant supports 11 to ensure that the cable test model 1 can be installed on the cross beam 14 of the steel-concrete fire-resistant supports 11;

[0066] See Figure 7, the steel-concrete fire-resistant support 11 is formed by casting square steel pipes and concrete, and includes an I-shaped bottom support 12. Two columns 13 are provided on the bottom support 12, and a cross beam 14 is fixedly connected between the two columns 13. When the cross beam 14 supports the cable test model 1, it can ensure that its position is above the middle in the test furnace 15, so that it is uniformly heated during the test.

[0067] Step eight, hoist and install the cable test model 1 on the steel-concrete fire-resistant support 11, and use aluminosilicate cotton to wrap the surfaces of both ends of the cable test model 1, the steel-concrete fire-resistant support 11, and the thermocouple 6 for fire and heat insulation protection, which can prevent the thermocouple wire from being burned out and also prevent heat from entering from the ends, affecting the accuracy of the test results;

[0068] Use a fire-proof expansion end 16 to fire-proof both ends of the cable test model 1. The fire-proof expansion end 16 is a sealed shell, and a steel-concrete support fire-proof protection body 17 that can wrap the steel-concrete fire-resistant support 11 is also adapted at its bottom. A steel gasket is installed on the surface of the thermocouple 6 exposed outside the cable test model 1 to isolate the flame. The thermocouple wire of the thermocouple 6 is led out of the furnace from inside the fire-proof expansion end 16 and the steel-concrete support fire-proof protection body 17 to prevent the thermocouple wire from being damaged by high temperature.

[0069] Step nine, after completing the fire and heat insulation protection of the ends of the cable test model 1 and the thermocouple wire, close the furnace body. The thermocouple wire is connected to a data acquisition instrument to collect temperature data. After the test preparation is completed, the test is carried out according to the specified fire environment and target heating time.

[0070] Different fire environments and different target heating times can be set during the test to meet different fire conditions. The test termination conditions include that the steel surface temperature reaches 300 °C and the test duration reaches the target heating time.

[0071] When a cable fire resistance test is required, a detachable fire and corrosion protection layer 18 is applied to the outer surface of the steel wire 5, and the detachable fire and corrosion protection layer 18 is made of high-temperature resistant aerogel felt.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A large diameter cable test model, characterized in that: include: A cable test model (1) of cable strand assembly type, the cross-sectional diameter of which is proportionally reduced according to the full-scale cable, the cable test model (1) is composed of a plurality of cable strands (3) which are parallel to each other, of the same length and aligned at both ends, which are locked and fixed by a plurality of annular steel clamps (4), the reduction ratio of the cable strands (3) is consistent with the reduction ratio of the cable test model (1), and the cable strands (3) are formed by extruding a plurality of bundles of thin steel wires into a circle and are staggered and fixed at both ends and in the middle by steel tie bands; Thermocouples (6) are welded to the measuring point surfaces of a plurality of cable strands (3) inside the cable test model (1) and are led out through the gaps between the cable strands (3). The cable strands (3) welded with thermocouples (6) are arranged and positioned in sequence inside the cable test model (1) according to the target measuring point positions. Steel gaskets are installed on the surfaces of the thermocouples (6) exposed outside the cable test model (1) to isolate flames. The steel wire (5) is wound around the surface of the cable test model (1).

2. A large diameter cable test model as claimed in claim 1, characterized in that: The minimum value of the diameter of the cable test model (1) is within the allowable error range of 5%, and its diameter is not less than the result determined by the following formula: ， Where R0 is the minimum cross-sectional diameter of the cable test model (1), R is the cable prototype diameter, and e is a natural constant, 80 mm ≤ R ≤ 1500 mm.

3. A closed space fire resistance test method for a large diameter cable test model as claimed in claim 1, characterized in that: The following steps are involved: Step 1: determine the diameter of the cable test model (1), use thin steel wire to make an appropriate number of cable strands (3), and use steel tie bands to tie each cable strand (3) several times at both ends and in the middle to squeeze and fix the thin steel wire. The steel tie bands are arranged in a staggered manner, and the tying positions of different cable strands (3) are staggered; Step 2: placing a plurality of annular assistants (2) in the same straight line at the two ends and the middle of the preset cable test model (1), respectively, with the annular assistants (2) at the two ends being closer to the outside, and the annular assistants (2) in the middle ensuring that the cable test model (1) is straight as a whole; Step three, counting the number of cable strands (3) to be welded with thermocouples (6) according to the preset target measuring point positions, and then welding the thermocouples (6) to the surfaces of the cable strands (3) at the measuring points; Step 4: using the annular auxiliary device (2) as a mold, the cable strands (3) are placed in layers, and at the same time, the cable strands (3) welded with thermocouples (6) are placed and positioned in a preset order according to the target measurement point positions, ensuring that the cable strands (3) are parallel, the cable strands (3) at both ends are flush, and the thermocouple wires of the thermocouples (6) are led out of the cable test model (1) through the gaps between the cable strands (3); Step 5: After the cable strand (3) is installed, the two ends are fixed with an annular steel clamp (4), and the completed cable test model (1) is taken out from the annular auxiliary device (2), thereby completing the production of the cable test model (1); Step 6: Wrap the steel wire (5) around the surface of the cable test model (1), and install a steel gasket on the surface of the thermocouple (6) exposed outside the cable test model (1) to isolate the flame; Step 7, placing two steel-concrete refractory supports (11) in a closed test furnace (15), and adjusting the placement direction and the distance between the two steel-concrete refractory supports (11); Step 8: hoist and install the cable test model (1) on the steel-concrete fire-resistant support (11), and use aluminum silicate wool to cover the ends of the cable test model (1), the steel-concrete fire-resistant support (11) and the surface of the thermocouple (6) for fireproof and heat-insulating protection; Step nine, after completing the fire protection of the cable test model (1) end and the thermocouple wire, close the furnace, connect the thermocouple wire to the data acquisition instrument, and the test preparation is completed. Complete the test according to the specified fire environment and target fire exposure time.

4. A closed space fire resistance test method for a large diameter cable test model as claimed in claim 3, characterized in that: In step seven, the steel-concrete refractory support (11) is formed by casting a square steel pipe with concrete, and includes an I-shaped bottom support (12). Two columns (13) are provided on the bottom support (12), and a crossbeam (14) is fixedly connected between the two columns (13).

5. The closed space fire resistance test method of a large diameter cable test model according to claim 3, characterized in that: In step eight, a fireproof expansion end (16) is used to prevent fire at both ends of the cable test model (1). The fireproof expansion end (16) is a sealed shell and its bottom is also adapted to be equipped with a steel-concrete support fireproof protection body (17) that wraps the steel-concrete fire-resistant support (11). A steel gasket is installed on the surface of the thermocouple (6) exposed outside the cable test model (1) to isolate the flame. The thermocouple wire of the thermocouple (6) is led out of the furnace from the fireproof expansion end (16) and the steel-concrete support fireproof protection body (17).

6. A closed space fire resistance test method for a large diameter cable test model as claimed in claim 3, characterized in that: In step 2, the annular auxiliary device (2) includes a base steel plate (8), the base steel plate (8) is welded and fixed to the vertical annular cut steel plate (9), and a plurality of stiffening ribs (7) are provided between the base steel plate (8) and the vertical annular cut steel plate (9); the length of the base steel plate (8) is greater than the outer diameter of the cable test model (1), and the width of the base steel plate (8) is half of its length; The vertical ring-cut steel plate (9) is a square steel plate, the side length of which is equal to the length of the base steel plate (8). The middle part of the vertical ring-cut steel plate (9) is ring-cut into a hole according to the size of the cable test model (1), and the upper part of the vertical ring-cut steel plate (9) is opened from the center of the side length, and the opening size is larger than the outer diameter of the cable strand (3).

7. A closed space fire resistance test method for a large diameter cable test model as claimed in claim 3, characterized in that: In step five, the annular steel hoop (4) is composed of two semicircular steel plates fixedly connected, and the cable test model (1) is symmetrically provided with a plurality of annular steel hoops (4) at both ends thereof, and two adjacent annular steel hoops (4) on the same side are arranged at a preset distance.

8. The closed space fire resistance test method of a large diameter cable test model according to claim 3, characterized in that: In step six, when a cable fire resistance test is required, a removable fireproof and anti-corrosion layer (18) is applied to the outer surface of the steel wire (5), and the removable fireproof and anti-corrosion layer (18) is made of high temperature resistant aerogel felt.

9. A closed space fire resistance test method for a large diameter cable test model as claimed in claim 3, characterized in that: Different fire environments and different target fire exposure times were set in the test to meet different fire conditions. The test termination conditions included the steel surface temperature reaching the preset temperature and the test duration reaching the target fire exposure time.

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