A concrete model beam for high-temperature testing

Abstract

This application provides a concrete model beam for high-temperature testing. The concrete model beam includes concrete, reinforcing bars, and steel strands. The materials and structures of the concrete, reinforcing bars, and steel strands are consistent with those of the concrete, reinforcing bars, and steel strands in the prototype concrete beam. The concrete model beam is also provided with multiple temperature measuring points, which are distributed at different positions on the concrete model beam and are used to measure the temperature of the concrete, the temperature of the reinforcing bars, and the temperature of the steel strands, respectively.

Description

Technical Field

[0001] This application relates to the field of road and bridge testing technology, and in particular to a concrete model beam for high-temperature testing. Background Technology

[0002] Railways are a major public infrastructure vital to national security, the economy, and people's livelihoods; they are considered a lifeline project. As of now, the total operating mileage of railways in China has reached 159,000 kilometers, of which 45,000 kilometers are high-speed railways. my country's high-speed railways are largely constructed using the "bridge-instead-of-road" method, and the number of railway bridges has increased rapidly with the extension of railways, reaching a total of 92,000 bridges with a cumulative length of 31,000 kilometers.

[0003] my country's high-speed railways are mostly constructed using the "bridge instead of road" approach. Bridges account for an average of about 50% of the total length of existing high-speed railway lines, with the highest reaching 91%. Commonly used prestressed concrete simply supported beam bridges account for 94% of the total bridge length.

[0004] As the scope of railway construction and operation gradually expands, and the "eight vertical and eight horizontal" high-speed rail network is about to take shape, railway bridge operations face a complex environment, with various types of major disasters having a significant impact, among which fire is a major one. Prestressed concrete railway bridges, during their long service life, are highly likely to encounter extreme fire loads, leading to severe structural damage or even collapse, posing a serious threat to line operation and personal safety. This represents a significant challenge for prestressed concrete railway bridges in operation.

[0005] In recent years, fires have frequently occurred along railway bridges, which have seriously affected the structure of railway concrete bridges. Under the high temperature of the fire, the structure has suffered damage such as concrete spalling, concrete hollowing and cracking, exposed steel bars and exposed steel strands.

[0006] Under the high temperature of a fire, the strength, stiffness, and durability of the concrete, steel bars, and steel strands in the railway concrete box girder structure all degrade, resulting in a decline in the overall performance of the box girder structure. This affects the safety and serviceability of the structure, and in severe cases, it can lead to the collapse of the bridge structure. In general, railway concrete box girders will be damaged and need to be reinforced and repaired before they can continue to be used.

[0007] The high temperature of a fire is transferred from the surface of the beam to its interior through heat conduction. The superposition of multiple effects results in a very complex temperature field distribution inside the concrete box girder structure. Fire is an accidental and sudden disaster. Under high temperature, typical damage characteristics such as concrete spalling, exposed rebar, and exposed steel strands will appear. Due to the accidental nature of fire, it is impossible to monitor and test the temperature field and damage of the concrete, rebar, and steel strands inside the structure under the high temperature of a fire. Therefore, it is necessary to conduct high-temperature fire tests to test the material and structural performance after experiencing high temperatures, so as to scientifically analyze the damage of concrete beams after experiencing high temperatures and provide technical support for assessing the structural safety and durability of concrete beams after being exposed to fire.

[0008] On the other hand, due to the large size of concrete beam structures, conducting full-scale high-temperature fire tests on concrete beams requires enormous human, material, and financial resources, which has certain limitations. Summary of the Invention

[0009] This application provides a concrete model beam for high-temperature testing, which addresses the lack of technical solutions for post-fire assessment of concrete beam structures in the related art.

[0010] This application provides a concrete model beam for high-temperature testing. The concrete model beam includes concrete, reinforcing bars, and steel strands. The materials and structures of the concrete, reinforcing bars, and steel strands are the same as those of the concrete, reinforcing bars, and steel strands in the prototype concrete beam.

[0011] The concrete model beam is also equipped with multiple temperature measuring points, which are distributed at different positions on the concrete model beam and are used to measure the temperature of the concrete, the temperature of the reinforcing steel, and the temperature of the steel strand.

[0012] In one embodiment of the concrete model beam for high-temperature testing according to this invention, the effective prestress of the concrete model beam is greater than the maximum prestress of the prototype concrete beam.

[0013] In one embodiment of the concrete model beam for high-temperature testing of this utility model, the maximum prestress of the steel strand is greater than 1230 MPa.

[0014] In one embodiment of the concrete model beam for high-temperature testing of this utility model, the thickness of the concrete model beam's reinforcing steel cover is consistent with the thickness of the prototype concrete beam's reinforcing steel cover, and at least one temperature measuring point is provided near the reinforcing steel.

[0015] In one embodiment of the concrete model beam for high-temperature testing of this utility model, the distance from the bottom edge of the steel strand of the concrete model beam is consistent with the distance from the bottom edge of the steel strand of the prototype concrete beam, and at least one temperature measuring point is provided near the steel strand.

[0016] In one embodiment of the concrete model beam for high-temperature testing according to this utility model, the thickness of the concrete model beam's reinforcing steel cover is 35 mm, the same as that of the prototype concrete beam; and / or,

[0017] The distance from the bottom edge of the steel strands in the concrete model beam is 125mm, just like the distance from the bottom edge of the steel strands in the prototype concrete beam.

[0018] In one embodiment of the concrete model beam for high-temperature testing of this utility model, the concrete model beam is a railway bridge with a span of 32m.

[0019] In one embodiment of the concrete model beam for high-temperature testing according to this utility model, the concrete model beam is provided with stirrups and longitudinal bars, and the reinforcement ratio of the stirrups and longitudinal bars is consistent with the structure of the prototype concrete beam.

[0020] In one embodiment of the concrete model beam for high-temperature testing according to the present invention, the concrete model beam is further provided with at least two lifting rings, which are spaced apart. A portion of the lifting rings are anchored into the interior of the concrete model beam, while the other portion of the lifting rings are exposed on the exterior of the concrete model beam.

[0021] In one embodiment of the concrete model beam for high-temperature testing of this utility model, a portion of the lifting rings has a size greater than 150 mm; and / or, another portion of the lifting rings has a size greater than 50 mm. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0023] Figure 1 This is a structural schematic diagram of the concrete model beam used for high-temperature testing according to this utility model;

[0024] Figure 2 for Figure 1 Cross-sectional view at point AA;

[0025] Figure 3 This is a structural schematic diagram of the concrete model beam used for high-temperature testing according to this utility model;

[0026] Figure 4 for Figure 3Cross-sectional view at BB;

[0027] Figure 5 This is a schematic diagram of the internal structure of the concrete model beam used for high-temperature testing according to this utility model.

[0028] Figure 6 This is a schematic diagram of the concrete model beam of this utility model used for high-temperature testing, showing the high-temperature loading zone;

[0029] Figure 7 for Figure 6 Cross-sectional view at CC;

[0030] Figure 8 This is a schematic diagram of the concrete model beam for high-temperature testing according to the present invention, showing the cross-sectional location;

[0031] Figure 9 This is a schematic diagram of the concrete model beam used for high-temperature testing according to the present invention, which shows the testing device.

[0032] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments.

[0033] Explanation of reference numerals in the attached figures

[0034] 100. Concrete model beam; 101. Mid-span section;

[0035] 110. Concrete;

[0036] 120. Reinforcing steel bars; 121. Thickness of concrete cover for reinforcing steel bars; 122. Stirrups; 123. Longitudinal reinforcement;

[0037] 130. Steel strand; 131. Distance of steel strand from bottom edge;

[0038] 140. Temperature measuring point; 141. Reinforcing bar temperature measuring point; 142. Concrete temperature measuring point; 143. Steel strand temperature measuring point;

[0039] 150. Hanging rings;

[0040] 160. High-temperature loading zone

[0041] 170. Test apparatus; 171. Jack; 172. Load distribution beam; 173. Load sensor. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0043] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0044] In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0045] The terms "first," "second," "third," "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those illustrated or described herein.

[0046] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0047] This utility model discloses a concrete model beam 100 adapted for testing the mechanical properties of concrete beams after fire exposure. It can reflect the structural parameters and stress performance of concrete beams. By conducting high-temperature fire tests on it, the mechanical properties of concrete beams after fire exposure can be explored, providing technical support for the evaluation of the mechanical properties of actual beams after experiencing high-temperature fire exposure.

[0048] The present invention relates to a concrete model beam 100 for high-temperature testing, wherein the concrete model beam 100 includes concrete 110, reinforcing bars 120 and steel strands 130, and the materials and structures of the concrete 110, the reinforcing bars 120 and the steel strands 130 are the same as those of the concrete 110, the reinforcing bars 120 and the steel strands 130 in the prototype concrete beam.

[0049] The concrete model beam 100 is also provided with multiple temperature measuring points 140, which are distributed at different positions on the concrete model beam 100 and are used to measure the temperature of the concrete 110, the temperature of the reinforcing bar 120 and the temperature of the steel strand 130, respectively.

[0050] The concrete model beam 100 provided by this utility model can be adapted to the mechanical performance testing of concrete beams after being exposed to fire, including the following aspects.

[0051] First, the concrete model beam 100, adapted for testing the mechanical properties of concrete beams after fire exposure, contains materials such as concrete 110, reinforcing bars 120, and steel strands 130, which are consistent with the material type and strength grade of the original concrete beam. The structural parameters of the concrete model beam 100 are consistent with those of the prototype concrete beam, mainly including the thickness of the protective layer and the thickness of the protective layer of the steel strands 130. The stress performance of the concrete model beam 100 is consistent with the stress performance of the prototype concrete beam, mainly the stress of the concrete 110 at the bottom of the beam and the stress of the steel strands 130.

[0052] Second, when conducting high-temperature fire tests, it is necessary to clarify the temperature history of concrete 110, steel bar 120, and steel strand 130 at key locations, and arrange temperature measuring points inside the concrete model beam 100 to test the temperature of concrete 110, steel bar 120, and steel strand 130.

[0053] Third, after the high temperature of the fire, a bending performance test was conducted on the concrete model beam 100 and compared with the control component to compare the reduction of the mechanical properties of the concrete model beam 100 after the high temperature of the fire.

[0054] Fourth, after the concrete model beam 100 is subjected to high temperature in a fire, the beam is broken up, and material performance tests are carried out on the reinforcing bars 120 and steel strands 130 to obtain the material performance reduction of the test component after experiencing high temperature in a fire.

[0055] Regarding the design of concrete model beam 100, the stress performance of the prototype beam was analyzed. Based on the structural parameters of the precast post-tensioned prestressed concrete simply supported box girder of high-speed railway, a finite element model was established to analyze the stress performance of the prototype beam under operating loads.

[0056] Based on the structural parameters and load conditions of the 32m span prestressed concrete box girder of the high-speed railway, the final effective prestress of the steel strand system of the original beam was calculated. The results are shown in Table 1. The calculation results show that the final effective prestress of the prestressed system of the original beam is 968.06~1029.70MPa.

[0057] Based on the original beam structural parameters and load conditions, the stress at the bottom of the beam at the mid-span section 101 under the beam's self-weight, secondary dead load (160kN / m), and prestressing was calculated. The calculation results show that the compressive stress of the concrete 110 at the bottom of the beam at the mid-span section 101 under the beam's self-weight, secondary dead load (160kN / m), and prestressing is 5.35MPa.

[0058] The stress performance of the concrete model beam 100 was analyzed. Based on the beam dimensions, the dimensional parameters, stress of the steel strand 130, and structural stress performance of the beam were calculated. A comparison of the stress states at the mid-span section 101 of the original beam and the model beam is shown in Table 1, and a comparison of the structural parameters is shown in Table 2. The comparison results show that the thickness of the protective layer 121 for the ordinary steel reinforcement 120, the distance of the steel strand 130 from the surface, the stress of the steel strand 130, and the stress of the concrete 110 are all consistent with those of the original railway prestressed concrete 110 beam.

[0059] Table 1 Comparison of stress state at mid-span section 101 of the original beam and the model beam

[0060]

[0061] Table 2 Comparison of structural parameters between the original beam and the model beam

[0062]

[0063] In the design of the model beam structure, the strength grades of concrete 110, steel bars 120, and steel strands 130 in the test components are consistent with the corresponding material properties in the prototype beam; the concrete beam with steel bars 120 has a protective layer thickness of 35mm, a cross-sectional dimension of 250mm×250mm, and the reinforcement ratios of stirrups 122 and longitudinal bars 123 are consistent with the prototype concrete beam structure. Figure 1 This is a structural schematic diagram of the concrete model beam 100 used for high-temperature testing according to this utility model. Figure 2 for Figure 1 The cross-sectional view at point AA.

[0064] Model beam lifting point design, Figure 3This is a structural schematic diagram of the concrete model beam 100 used for high-temperature testing according to this utility model. Figure 4 for Figure 3 Cross-sectional view at BB, as shown Figure 3 and Figure 4 As shown, in the preparation of the verification model beam, two lifting rings 150 are arranged on the top surface. Both lifting rings 150 are made of 18mm diameter HRB400 grade steel bars 120. The steel bars 120 are embedded to a depth of 150mm, and the net clearance of the steel bars 120 exposed outside the lifting rings 150 is 50mm.

[0065] Regarding the high-temperature test of the concrete model beam 100, the high-temperature test can be designed according to the actual fire type. This utility model provides an example: the fire resistance performance scheme of the prestressed concrete beam is to carry out the fire resistance performance test under the action of the HC curve for the entire model beam. During the high-temperature loading process, the ambient temperature, concrete temperature, steel bar temperature, steel strand temperature, time and other parameters of the model beam are monitored. Figure 6 This is a schematic diagram of the concrete model beam 100 used for high-temperature testing according to this utility model, showing the high-temperature loading zone 160. Figure 7 for Figure 6 Cross-sectional view at CC.

[0066] HC curve temperatures were applied to the entire prestressed concrete beam. Five different working conditions were designed based on the typical damage characteristics of the railway concrete 110 bridge under actual fire conditions (see Table 3). The temperature history of concrete 110, reinforcing steel 120, and steel strand 130 was monitored and recorded throughout the process. A total of 16 model components were prepared for the high-temperature fire test.

[0067] Table 3 Fire resistance performance conditions of 120mm reinforced concrete model beam.

[0068]

[0069] During the high-temperature loading process of a prestressed concrete model beam, parameters such as ambient temperature, concrete temperature, reinforcing bar temperature, steel strand temperature, and time were monitored. Figure 5 This is a schematic diagram of the internal structure of the concrete model beam 100 used for high-temperature testing according to this utility model, showing the arrangement of measuring points at the mid-span section 101. Figure 8 This is a schematic diagram of the concrete model beam 100 used for high-temperature testing according to the present invention, showing the cross-sectional location.

[0070] In one embodiment, the thickness of the concrete model beam's reinforcing bar 120 protective layer is consistent with the thickness of the prototype concrete beam's reinforcing bar 120 protective layer, and at least one reinforcing bar temperature measuring point 141 is provided near the reinforcing bar 120.

[0071] In one embodiment, the distance from the bottom edge of the steel strand 130 of the concrete model beam is the same as the distance from the bottom edge of the steel strand 130 of the prototype concrete beam, and at least one steel strand temperature measuring point 143 is provided near the steel strand 130.

[0072] It also has 142 concrete temperature measuring points.

[0073] To simulate a real fire scenario for the prototype beam, the high-temperature loading of the fire high-temperature verification model involved applying high-temperature loading to three sides within a 2500mm range at the mid-span of the beam. Figure 6 This is a schematic diagram of the concrete model beam 100 used for high-temperature testing according to the present invention, showing the high-temperature loading zone 160; Figure 7 for Figure 6 Cross-sectional view at CC.

[0074] Regarding the high-temperature structural performance test, the railway concrete 110 verification model underwent the following three tests after high-temperature loading: First, the surface condition of the model beam was observed after high temperature, including the surface color of the concrete 110, the degree of breakage and cracking of the concrete 110, and the appearance of the exposed reinforcing steel 120; second, after observing the appearance of the component, the rebound value of the concrete 110 on the component surface was tested, and the rebound strength was tested without surface treatment; third, a static load test was carried out after the fire and high temperature to test the stress performance of the high-temperature reinforced concrete 110 and prestressed concrete 110 models, mainly testing the deflection and ultimate bearing capacity of the component during the static load test, and comparing it with the structural performance of the test component that did not experience the fire and high temperature. Figure 9 This is a schematic diagram of a concrete model beam 100 for high-temperature testing according to the present invention, which shows a test device 170, including a jack 171, a load distribution beam 172 and a load sensor 173.

[0075] Regarding the high-temperature material performance test, the test components were subjected to the following four tests after high-temperature loading: First, after observing the appearance of the components, the rebound value of the concrete 110 on the surface of the components was tested. The rebound was conducted under three conditions: the first was the value under the condition of no surface treatment, the second was the rebound value after removing the surface spalled concrete 110, and the third was the value after chiseling down to the fresh concrete 110 layer; Second, after the material components were broken after being subjected to high temperature, the surface condition of the steel strand 130 and the reinforcing bar 120 was observed and recorded, and the post-fire material performance of the reinforcing bar 120 and the steel strand 130 was tested.

[0076] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the utility models disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0077] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A concrete model beam for high temperature testing, characterized by, The concrete model beam includes concrete, reinforcing bars, and steel strands. The materials and structures of the concrete, reinforcing bars, and steel strands are the same as those of the concrete, reinforcing bars, and steel strands in the prototype concrete beam. The concrete model beam is also equipped with multiple temperature measuring points, which are distributed at different positions on the concrete model beam and are used to measure the temperature of the concrete, the temperature of the reinforcing steel, and the temperature of the steel strand.

2. The concrete model beam for high temperature test according to claim 1, characterized by, The effective prestress of the concrete model beam is greater than the maximum prestress of the prototype concrete beam.

3. The concrete model beam for high temperature test according to claim 2, characterized by, The maximum prestress of the steel strand is greater than 1230 MPa.

4. The concrete model beam for high temperature test according to claim 2, wherein The thickness of the concrete protective layer for the steel reinforcement of the concrete model beam is consistent with that of the prototype concrete beam, and at least one temperature measuring point is provided near the steel reinforcement.

5. The concrete model beam for high temperature test according to claim 4, characterized by The distance from the bottom edge of the steel strand of the concrete model beam is the same as the distance from the bottom edge of the steel strand of the prototype concrete beam, and at least one temperature measuring point is provided near the steel strand.

6. The concrete model beam for high temperature testing according to claim 5, wherein The concrete model beam has a reinforcement protective layer thickness of 35 mm, the same as that of the prototype concrete beam; and / or, The distance from the bottom edge of the steel strands in the concrete model beam is 125mm, just like the distance from the bottom edge of the steel strands in the prototype concrete beam.

7. The concrete model beam for high temperature testing of claim 5, wherein, The concrete model beam is a railway bridge with a span of 32m.

8. The concrete model beam for high temperature testing of claim 5, wherein, The concrete model beam is equipped with stirrups and longitudinal bars, and the reinforcement ratio of the stirrups and longitudinal bars is consistent with the structure of the prototype concrete beam.

9. A concrete model beam for high temperature testing according to any one of claims 1 to 8, characterised in that, The concrete model beam is also provided with at least two lifting rings, which are spaced apart. Some of the lifting rings are anchored into the interior of the concrete model beam, while others are exposed on the exterior of the concrete model beam.

10. The concrete model beam for high-temperature testing according to claim 9, characterized in that, One portion of the lifting rings has a size greater than 150 mm; and / or, another portion of the lifting rings has a size greater than 50 mm.

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