Lightweight flexible tunnel profile steel arch frame based on equivalent substitution principle

Abstract

The invention relates to the technical field of tunnel engineering, and discloses a lightweight flexible tunnel section steel arch frame based on an equivalent substitution principle, which comprises an arch section, the arch section comprises lightweight flexible section steel, the lightweight flexible section steel comprises at least two wing plates of which the upper and lower outer surfaces are parallel to each other, and a web plate is arranged between the two wing plates; at least one of the cross-sectional area and the strong-axis inertia moment Ix of the light-weight flexible profile steel is smaller than that of the standard part, and the change range of the maximum strong-axis bending moment Mx of the profile steel arch frame is + / -20% compared with that of the standard part; when the strength of the light-weight flexible profile steel is consistent with that of steel used by the standard part, at least one of the thickness of a web plate and the thickness of a wing plate is smaller than that of the standard part, and at least one of the section height and the section width is larger than that of the standard part; or the section height of the light-weight flexible profile steel is smaller than that of the standard part; or when the strength of the steel used by the light-weight flexible profile steel is larger than that of the standard part, at least one of the web plate thickness, the wing plate thickness, the section height and the section width of the light-weight flexible profile steel is smaller than that of the standard part.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering, and particularly relates to a lightweight flexible tunnel steel arch frame based on the principle of equivalent substitution. Background Art

[0002] In the initial support stage of tunnel engineering construction, the specifications and models of steel arch frames mainly come from I-beams in the national standard "GB / T706-2016 Hot-rolled Steel Sections" and H-beams in "GB / T 11263-2024 Hot-rolled H-sections and Split T-sections", and both the above I-beams and H-beams are standard parts. However, the following main problems currently exist:

[0003] (1) The current I-beam standard in China is a version introduced in the early days of the founding of the People's Republic of China and localized. Limited by the technical equipment level and concepts at that time, I-beams are a type of low-efficiency steel sections. More importantly, this standard has not undergone any substantial changes in the more than seventy years since its introduction. In addition, I-beams are essentially a general-purpose building steel section and are not specifically designed for the special working conditions of tunnel engineering. The structural defects of "thick limbs and short legs" with a narrow width and too thick plates result in the inability to fully utilize the material properties, causing waste of resources. Similarly, the national standard H-beams, also being general-purpose building steel sections, are not specifically designed for tunnel working conditions, and there are also problems of waste due to the incomplete utilization of material utility in actual applications.

[0004] (2) The state attaches great importance to the development of steel lightweighting and regards it as an important direction for the transformation and upgrading of the manufacturing industry and green and low-carbon development, emphasizing lightweight and high-strength technical measures and means. From the implementation of the several major sectors of steel products, namely plates, pipes, bars, sections, and wires, except for sections, steel with a strength level of 300-400 MPa has been widely used in other sectors, steel with a strength level of 500-600 MPa has also been widely promoted, and some industries have even started to use steel with a strength level of more than 1000 MPa. Abroad, high-strength steel sections with a strength of more than 600 MPa have become the market mainstream. However, from the information feedback by steel mills, in the production of section steel (here only referring to I-beams and H-beams), the production proportion of Q235 is as high as 70%-80%, and the remaining part is basically Q355. It is almost impossible to find higher-strength section steel products, which shows a significant gap from the requirements of national policies.

[0005] (3) The initial support arch of tunnel engineering is the main application scenario of I-beams and H-beams, especially the largest application field of I-beams. The design of tunnel engineering has significant particularities, and the accumulation of experience plays a dominant role. After decades of development, complete standard specifications have been formed for railway, highway, and municipal tunnels respectively, and a large number of engineering practices have proved that these specifications are highly safe and reliable. In the early days, Q235 material was the mainstream choice and was naturally incorporated into the standard specification system and has continued to this day. The current situation is that almost all Q235 I-beams are used in the general standards for railway, highway, and municipal tunnels, and high-strength steel has little use in this field. Many years ago, in response to the national call, a design institute simply upgraded the material to Q355 without making any adjustments to the specifications. On the surface, it seemed to comply with the national policy, but in fact, the material performance was excessive and there was a waste of resources. Eventually, it reverted to the original state due to opposition from various parties. The fundamental reason for the failure of this attempt was that when the material strength was increased, there was a lack of smaller-sized products that matched it.

[0006] (4) Currently, there are clear specification requirements for the selection of profiled steel in standard tunnels. The profiled steel used in non-standard tunnels belongs to the design self-selected standard parts and there is no clear specification. Due to reasons such as lack of experience, materials with too high rigidity are often misselected. Due to its high rigidity characteristics, it is extremely difficult to process it into a small-radius arch segment during the processing process. In the actual tunnel construction scenario, the processing requirement for small-radius arch segments is not uncommon, and the selection of high-rigidity standard parts seriously affects the construction progress and efficiency in this regard. More critically, when the arch is put into use later, due to its too high rigidity, it is extremely easy to have material deformation when facing the complex and changeable tunnel working conditions, causing the arch to buckle and deform, seriously threatening the stability and safety of the tunnel structure, and also causing the arch to be unable to play its due supporting role normally. In order to ensure the safe operation of the tunnel, it is necessary to maintain and replace the buckled arch, which undoubtedly greatly increases the later maintenance cost, manpower, and material input of the tunnel project, further exacerbating the waste of resources and the complexity of the project.

[0007] To sum up, the lightweight and high-strengthening of profiled steel products have a long way to go, and the flexibility is extremely urgent; therefore, it is urgent to design equivalent lightweight and flexible profiled steel that can be replaced one by one. Summary of the Invention

[0008] The present invention aims to provide a lightweight and flexible tunnel profiled steel arch based on the principle of equivalent substitution. On the premise of ensuring the equivalence of the maximum anti-bending moment of the strong axis of the arch, the lightweight and flexibility of the profiled steel arch are realized, the steel consumption is reduced, the flexibility performance is improved, and green and low-carbon are achieved to assist the national industrial upgrade.

[0009] To achieve the above object, the present invention adopts the following technical solutions: A lightweight and flexible tunnel steel arch frame based on the principle of equivalent substitution, including multiple arch segments with the same bending radius. The arch segment includes lightweight and flexible steel, and the lightweight and flexible steel includes at least two wing plates with parallel upper and lower outer surfaces, and a web is vertically provided at the middle position between the two wing plates. The cross-sectional area and the moment of inertia I of the strong axis of the lightweight and flexible steel x at least one is less than the replaced standard part, and the maximum bending moment M of the strong axis of the steel arch frame x compared with the standard part, the change range is ±20%; and it is achieved by any of the following methods:

[0010] When the steel used for the lightweight and flexible steel is the same as that of the standard part, at least one of the web thickness and the wing plate thickness of the lightweight and flexible steel is less than the replaced standard part, and at least one of the cross-sectional height and the cross-sectional width is greater than the replaced standard part; or the cross-sectional height of the lightweight and flexible steel is less than the replaced standard part; or

[0011] When the steel used for the lightweight and flexible steel has a higher strength than the replaced standard part, at least one of the web thickness, the wing plate thickness, the cross-sectional height and the cross-sectional width of the lightweight and flexible steel is less than the replaced standard part.

[0012] Further, the minimum bending radius R of the lightweight and flexible steel min ≤6m.

[0013] Further, at least one of the cross-sectional area and the moment of inertia I of the strong axis of the lightweight and flexible steel x has a reduction ratio greater than 10% compared with the replaced standard part.

[0014] Further, when the steel used for the lightweight and flexible steel has a higher strength than the replaced standard part, at least two of the web thickness, the wing plate thickness, the cross-sectional height and the cross-sectional width of the lightweight and flexible steel are less than the replaced standard part.

[0015] Further, at least three of the web thickness, the wing plate thickness, the cross-sectional height and the cross-sectional width of the lightweight and flexible steel are less than the replaced standard part.

[0016] Further, when the steel used for the lightweight and flexible steel is the same as that of the standard part, the difference range between the cross-sectional height of the lightweight and flexible steel and the standard part is 0-10%, and the difference range between the cross-sectional width of the lightweight and flexible steel and the standard part is 0-10%.

[0017] Further, the difference range between the cross-sectional height of the lightweight and flexible steel and the standard part is 0-8%, and the difference range between the cross-sectional width of the lightweight and flexible steel and the standard part is 0-8%.

[0018] Furthermore, the inner surfaces of the two wing plates have the same slope, and the slope range is 0-16.7%; the arc radius r at the connection between the wing plate and the web plate includes two cases, namely r=0 or r>0.

[0019] The principles of this solution are:

[0020] This scheme is based on the principle of equivalent substitution of bending moment, that is, the maximum bending moment M of the strong axis of the arch x Compared with the standard part replaced, the variation range is ±20%, where the variation range can be ±20%, ±15%, ±10%, ±5% or ±1%. The specific range is set according to the actual engineering design requirements, which will not be repeated here; where M x =W x f,W x is the strong axis section modulus W x =I x / (H / 2), f is the bending design strength of steel. The research purpose of this scheme is to study the maximum bending moment M of the strong axis. x In the equivalent case before and after replacement, materials are saved and / or the stiffness of the arch frame is reduced. Lightweighting is specifically manifested in the reduction of the cross-sectional area of ​​the steel arch frame, and flexibility is specifically manifested in the reduction of the moment of inertia of the strong axis of the steel arch frame:

[0021] When the strength of the lightweight flexible steel is the same as that of the steel used in the standard parts, M x =W x The three values ​​in f remain unchanged, but according to W x =I x / (H / 2),I x =∫y 2 dA, the theory of "wide limbs and thin walls" can be derived, that is: when the same maximum bending moment of the strong axis is achieved, the height is higher, the width is wider, and the thickness is thinner, which can save materials; according to the experimental data of Tables 1-3 and 5 of Example 1, it can be seen that under the premise of equivalent bending moment, the cross-sectional area of ​​the arch frame is reduced, and at least one of the web thickness and wing plate thickness of the lightweight flexible steel arch frame is reduced, while at least one of the height and width is increased, so as to achieve lightweight steel arch frame.

[0022] It can be seen from the experimental data in Table 4 in Example 1 that when only the cross-sectional height of the lightweight flexible steel is smaller than the standard part it replaces, although the cross-sectional area of ​​the steel arch frame is increased compared with the standard part, the strong axis moment of inertia of the steel arch frame is significantly reduced, that is, the stiffness of the steel arch frame is reduced and the flexibility is increased. While achieving bending moment equivalence, it better realizes flexible support and improves the stability of the tunnel steel support.

[0023] When the strength of the steel used in the lightweight flexible steel is greater than the standard part it replaces, according to the bending moment formula M x =W x f, bending moment M xRemain constant. When the flexural design strength f of the steel increases, the section modulus W of the strong axis x decreases in the same proportion as the relative flexural design strength f. Also, according to W x = I x / (H / 2), where I x = ∫y 2 dA, and from the experimental data of Example 2, it can be obtained that when at least one of the web thickness, flange thickness, section height, and section width of the lightweight flexible profiled steel is less than that of the standard part, W x can be reduced, and only in this way can the lightweight flexibility of the profiled steel arch be achieved on the premise of equivalent bending moment.

[0024] In this solution, the minimum bending radius of the lightweight flexible profiled steel is limited. It is required that R min ≤ 6m. 6m is the commonly used minimum bending radius in current tunnel engineering construction. If R min > 6m, it means that the performance index of this profiled steel arch is lower than that of the existing arch structure, and it cannot achieve equivalent replacement under the same tunnel working conditions.

[0025] The lightweight flexible profiled steel arch obtained based on the above technical principle has the following beneficial effects:

[0026] 1. The lightweight flexible profiled steel arch helps the transformation and upgrading of the national manufacturing industry and promotes the national development strategy of green and low-carbon:

[0027] Through the popularization and application of the lightweight flexible profiled steel arch, it is expected to greatly improve the current situation of steel application in low-level tunnel engineering in China, narrow the gap with advanced countries. Especially as China's transportation construction gradually focuses on the central and western regions with more mountainous areas, where the proportion of tunnels is high, the significance is even more significant.

[0028] 2. The lightweight flexible profiled steel arch saves steel consumption, reduces project costs, has significant economic benefits, and has great promotion prospects:

[0029] According to the experimental data of Example 1 and Example 2, the lightweight design reduces the cross-sectional area of ​​the steel arch frame, saves the material consumption, and the maximum reduction of steel can reach about 20%, and the weight reduction effect is very significant; after the arch frame uses high-strength steel, the unit price of the material will be more expensive, and its manufacturing cost will increase, but after actual measurement, it is found that the reduction in the cost of steel use is greater than the increase in the unit price of the material, and the overall cost reduction is still significant. The cost of steel use in large-scale projects is often hundreds of millions, and based on the current situation of meager profits or even losses in existing projects, according to Example 1 and Example 2, the lightweight and flexible steel arch frame of this scheme can reduce the project cost by about 5%-10%, which can save millions of costs. It is an extremely effective cost reduction method with significant economic benefits. Today, the amount of steel arch frames in highways, railways, municipal administration, subways, and water conservancy tunnels is huge, and the economic benefits are very considerable. The use of lightweight and flexible steel in this scheme saves costs for all parties, making this technical product very promising for promotion.

[0030] 3. The research on lightweight flexible steel arch frames has found a new direction for solving the world-class problems of tunnels in my country:

[0031] The construction of tunnels in soft, broken and large-deformation surrounding rocks with high ground stress is a recognized world-class problem. At present, the technologies in Japan and Europe are relatively mature and are gradually entering the Chinese market. Voestalpine in Europe and well-known Japanese companies have participated in major projects in my country, but they adopt the method of engineering general contracting, and the technical principles are not disclosed. Although my country has accumulated rich experience in the treatment of large deformation of soft surrounding rock tunnels in actual projects, its support theory and construction methods are still not mature enough. Once major deformation is encountered, the construction is always slowly advanced in the repetitive support "construction-destruction-replacement" process. Large deformation of weak surrounding rock is still one of the controlling problems of the entire tunnel and even the entire line.

[0032] During the research on lightweight, the inventor accidentally found that the use of high-strength steel not only reduces the cross-sectional area of the steel arch, but also leads to a decrease in the stiffness of the arch. The inventor was once frustrated. Later, the inventor collected a large amount of foreign materials, studied and pondered repeatedly, and boldly inferred that "reasonable strength and moderate rigidity and flexibility" of the arch are the main secrets of its support technology, and both of these two technologies have solutions in this scheme. According to the experimental data of Embodiment 1 and 2, using high-strength steel can significantly improve the flexibility while enhancing the strength, or by changing the height of the standard parts to improve the flexibility of the steel section. The decrease in stiffness obtained by the above optimization methods is exactly the need for flexible support and is a favorable indicator. However, at present, there is very little research on high-strength and flexible support of steel arch in China. In terms of the current situation, there are two extreme situations in the rigid-flexible support of steel arch: one is overly flexible, and the other is overly rigid; this reflects that the industry lacks in-depth understanding of the flexible support with moderate rigidity and flexibility, and there are also serious deficiencies at the practical level. Therefore, the research on the lightweight and flexible steel arch in this scheme has found a new breakthrough direction for solving the world-class problems of tunnels in China.

[0033] In actual application, in high in-situ stress soft rock tunnels, due to its own characteristics and the action of high in-situ stress, the surrounding rock has extremely large deformation and a long duration. However, the flexible steel arch in this scheme can slowly deform following the surrounding rock during the deformation process of the surrounding rock, continuously release the stress of the surrounding rock, reduce the surrounding rock pressure by 20%-30%, effectively avoid brittle failure caused by excessive rigidity, and greatly improve the safety and stability of the support structure. When crossing active fault tunnels, the flexible support in this scheme can absorb energy through its own elastic deformation when the surrounding rock deformation is caused by fault activities, maintain the integrity of the support structure, and ensure the safety of the tunnel. For urban shallow-buried tunnels, the flexible steel arch in this scheme, while ensuring the safety of the tunnel, its flexible deformation characteristics can better coordinate the deformation of the surrounding soil and reduce the impact on the surrounding environment.

[0034] 4. The lightweight and flexible steel arch can also significantly improve the seismic resistance of the tunnel:

[0035] Due to the unexpected discovery of the arch frame stiffness decrease and flexibility increase during the research process of this scheme, the inventor also unexpectedly discovered that it has a significant improvement in seismic performance. This discovery has been effectively verified in actual earthquake cases: in the Wenchuan earthquake, the tunnel was severely damaged; while in the earthquake in Japan, similar tunnels were slightly damaged due to the use of arch frame structures with corresponding characteristics. This scheme optimizes the design of steel materials and structures. In terms of materials, high-strength and high-toughness steel is selected to improve the overall strength and toughness of the structure, so that the flexibility of the steel arch frame is improved. When encountering seismic wave impact, the arch frame can rely on its flexibility to more flexibly produce a certain degree of deformation with the ground vibration, rather than hard resistance, which greatly reduces the degree of instantaneous stress concentration; in terms of structure, by optimizing the cross-sectional shape and size parameters, the natural frequency of the structure is adjusted to avoid the frequency range of vibration loads such as earthquakes, reduce the occurrence of resonance, and greatly improve the seismic performance of the tunnel support structure, providing a strong guarantee for the safety of tunnel projects in disaster environments such as earthquakes.

[0036] 5. Lightweight and flexible steel arches reduce tunnel damage during service life and reduce the cost of the tunnel throughout its life cycle:

[0037] The current service life of tunnels in my country is designed to meet the same standards as those in foreign countries, which can be up to 100 years. However, due to the limitations of the initial support of the tunnel, the steel arch frame is often the weak link, resulting in frequent defects in the tunnel. Defects such as landslides, water leakage, secondary lining cracking, and surface uplift are often related to damage to the arch support, requiring the tunnel to be closed for repairs or even large-scale replacements. Not only is the maintenance cost high, but traffic is also restricted.

[0038] This solution fundamentally improves the bearing capacity and durability of the tunnel support structure by optimizing the structural design of the steel arch and selecting high-performance steel. The optimized steel arch structure can distribute stress more evenly and reduce structural damage caused by local stress concentration. At the same time, high-performance steel has better corrosion resistance and can effectively resist the erosion of the complex environment in the tunnel (such as moisture, corrosive gases, etc.), delaying structural aging and damage. These factors work together to significantly extend the service life of the tunnel support structure, reduce the frequency of disease occurrence, reduce the subsequent maintenance costs and the impact on traffic, and improve the long-term economic and social benefits of the tunnel project.

[0039] 6. Lightweight flexible steel arch effectively assists in the efficient construction of non-standard tunnels and improves the support stability of non-standard tunnels:

[0040] Through optimization and improvement, the stiffness of the steel arch is reduced and its flexibility is enhanced in this solution, making it easier to process the small-radius arch section of the steel arch, improving the processing efficiency, and enabling the rapid progress of the entire project. More importantly, the working conditions of non-standard tunnels are complex and changeable, with extremely high requirements for the adaptability of the support structure. The lightweight and flexible steel arch shows its advantages in this regard. It can flexibly adjust its shape according to different geological conditions and stress distributions. When facing complex geological structures, it can adaptively deform more accurately according to the changes in surrounding rock pressure, effectively dispersing the pressure and avoiding buckling deformation caused by stress concentration, providing a stable support for the tunnel structure, and ensuring the safety during the construction and operation of the tunnel. At the same time, it also significantly reduces the need for maintenance and replacement, reduces the input of manpower and material resources, saves the maintenance cost, and avoids interfering with the normal operation of the tunnel, achieving a double harvest of economic and social benefits and ensuring the continuous and efficient operation of non-standard tunnels.

[0041] The present invention also provides another technical solution: a method for designing the cross-sectional dimensions of a lightweight and flexible tunnel steel arch, which is used to design the cross-section of the above-mentioned lightweight and flexible tunnel steel arch, and includes the following steps:

[0042] Step 1: First, determine the web height h and the outstretched width b of the flange, and then select the initial design values of the web thickness t1 and the flange thickness t2;

[0043] Step 2: According to H = h + 2t2 and B = 2b + t1, obtain the cross-sectional height H and the cross-sectional width B of the lightweight and flexible steel section;

[0044] Step 3: Substitute the web height h, the web thickness t1, and the cross-sectional height H of the lightweight and flexible steel section into the minimum bending radius formula

[0045]

[0046] where f y is the yield strength, with the unit of MPa, to obtain R min . If R min ≤ 6m, it meets the design index; if R min > 6m, reselect the values of the web thickness t1 and the flange thickness t2, obtain the new web thickness t1 and the cross-sectional height H of the lightweight and flexible steel section, and calculate the minimum bending radius R min again until R min ≤ 6m.

[0047] Further, when the steel strength of the lightweight flexible section steel is the same as that of the standard part, in step 2, the differences between the section height H and section width B of the lightweight flexible section steel and the replaced standard part should be within 10%. If the difference ranges of the section height H or section width B from the standard part exceed 10%, the web thickness t1 and flange thickness t2 need to be reselected, and step 2 is repeated to obtain the new section height H and section width B of the lightweight flexible section steel, so that the difference ranges of the section height H or section width B from the standard part are within 10%, and then the minimum bending radius R is calculated again min , and ensure that R min ≤6m.

[0048] Principle and beneficial effects of this solution:

[0049] In this design method, a new checking standard is designed for the section size, that is, the minimum bending radius R min ≤6m. 6m is the commonly used minimum bending radius in current tunnel engineering construction. If R min >6m, it means that the performance index of the steel arch is lower than that of the existing arch structure, and equivalent replacement under the same tunnel working conditions cannot be achieved. Through the minimum bending radius, it can be quickly and clearly judged whether the optimized section size of the steel arch meets the engineering reality.

[0050] Since there is little research on the minimum radius corresponding to cold bending of section steel in China at present, and there is no experience to talk about for non-standard section steel. The only research is limited to the theoretical level, and the calculation is complex and difficult to understand, and there is no simplified calculation formula suitable for engineering. Through cooperation and research with the cold bending machine factory, the inventor combines theory with practice and explores a fast calculation formula applicable to engineering, that is, the minimum bending radius formula in this application. This calculation formula intuitively expresses the relationship between R min and the web height h and thickness t1, the section height H of the lightweight flexible section steel, and the bending-resistant design strength f, making the process and results of section size optimization and improvement more directly and efficiently presented, and the overall calculation process is simpler, which has very important significance for engineering practical applications.

[0051] 1. This design method realizes the lightweight flexibility of the steel arch

[0052] This design method determines the web height h and the flange extension width b, then selects the initial design values of the web thickness t1 and the flange thickness t2 to obtain the section height H and the section width B of the lightweight and flexible section steel, and then checks through the minimum bending moment radius formula. In this process, the determination of the dimensions at each step is based on rigorous mechanical calculations and precise understanding of the structural performance. The thicknesses of the web and the flange are reasonably thinned to avoid material redundancy, thereby effectively reducing the section area and the overall weight of the section steel arch, achieving lightweight and flexibility. Moreover, when the relevant parameters do not meet the design conditions, the relevant steps are repeated for iterative optimization to ensure the achievement of the lightweight and flexible goal, minimizing the steel consumption to the greatest extent, continuously approaching the lightweight and flexible goal, reducing the project cost while ensuring the support effect, and realizing flexible support.

[0053] 2. This design method ensures the equivalent replacement of the bending resistance performance of the section steel arch under the same tunnel working conditions.

[0054] This design method utilizes the principle of equivalent bending moment substitution. By reasonably adjusting the section dimensions of the lightweight and flexible section steel and selecting appropriate steel, it ensures that while the section steel arch is lightweight and flexible, its bending resistance performance meets the tunnel support requirements. High-strength steel is selected. Combining with the bending moment formula M = W x f, while ensuring that the bending moment M x remains unchanged, the reasonable matching of the strong-axis section modulus W x and the steel bending design strength f is achieved. At the same time, based on W x = I x / (H / 2), by controlling parameters such as the strong-axis moment of inertia I x and others, the deformation of the arch crown is reduced, the settlement amount of the tunnel surrounding rock is effectively controlled, and it is ensured that when the steel consumption is reduced and the structure is lightweight and flexible, the bending resistance performance does not decrease, achieving performance equivalent replacement.

[0055] 3. This design method breaks the old industry standards.

[0056] In the traditional tunnel support industry, section steel arches are mostly made of low-grade steel (such as Q235 steel), and rely on increasing the support density to ensure strength, forming a fixed design and application mode. This design method abandons this traditional thinking, no longer limits to ensuring the support performance by increasing the material consumption, but starts from the optimization of the section size and material upgrade of the section steel arch, uses advanced mechanical principles and precise formula calculations to explore a new design path, provides an innovative idea for the industry development, and breaks the bondage of the traditional design concept. This design method proposes a series of technical indicators and calculation methods different from the traditional standards, including a specific minimum bending radius formula, and formulas for determining the sizes of the web and flange based on parameters such as the flexural design strength of steel, etc., provides a more scientific and more in line with the actual engineering requirements standard basis for the design, production and application of section steel arches, is expected to gradually replace the obsolete industry standards, lead the technical upgrade of the tunnel support industry, and promote the entire industry to develop towards high-end and scientific directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 FIG. is a schematic structural diagram of the section steel arch of the embodiment of the present invention.

[0058] Figure 2 FIG. is a schematic H-shaped cross-section of the lightweight flexible section steel of the embodiment of the present invention Figure 1 。

[0059] Figure 3 FIG. is a schematic H-shaped cross-section of the lightweight flexible section steel of the embodiment of the present invention Figure 2 。

[0060] Figure 4 FIG. is a schematic I-shaped cross-section diagram of the lightweight flexible section steel of the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0061] The following is further detailed through specific embodiments:

[0062] The reference numerals in the accompanying drawings of the specification include: section steel arch 1, lightweight flexible section steel 2, flange 3, web 4, cross-sectional height H of the lightweight flexible section steel, cross-sectional width B of the lightweight flexible section steel, web height h, outer extension width b of the flange, web thickness t1, flange thickness t2, arc radius r at the connection of the flange and the web, bending radius R of the section steel arch.

[0063] This application discloses a lightweight flexible tunnel section steel arch 1 based on the principle of equivalent substitution. As shown in the attached Figures 1-4 figure, it includes multiple arch segments with the same bending radius. The arch segments include lightweight flexible section steel 2. The lightweight flexible section steel 2 includes at least two flanges 3 with parallel upper and lower outer surfaces, and a web 4 is vertically arranged in the middle position between the two flanges 3.

[0064] The lightweighting of the steel arch in this application is reflected in the reduction of the cross-sectional area of the steel arch, that is, the cross-sectional area of the lightweight flexible steel is smaller than that of the replaced standard part, thereby reducing the weight of the steel arch. The flexibility is reflected in the reduction of the moment of inertia I of the strong axis of the steel arch, which reduces the stiffness of the steel arch and improves its flexibility performance. And the maximum bending moment M of the strong axis of the steel arch x decreases, reducing the stiffness of the steel arch and enhancing its flexibility performance. And the maximum bending moment M of the strong axis of the steel arch x (hereinafter referred to as bending moment M x ) compared with the replaced standard part, the change range is ±20%, and values such as ±20%, ±15%, ±10%, ±5% or ±1% can be taken. Specifically, it depends on the actual engineering design requirements and will not be elaborated here. The minimum bending radius Rmin of the lightweight flexible steel ≤ 6m. It is specifically achieved by any one of the methods described in Example 1 or Example 2 below.

[0065] In the field of tunnel engineering, standard parts such as hot-rolled ordinary I-beams in the national standard "GB / T 706-2016 Hot-rolled Steel Sections" and hot-rolled H-beams in "GB / T 11263-2024 Hot-rolled H-beams and Split T-sections" are the main steel materials used for steel arches. Among them, the height range of common steel section specifications is 100 - 350mm, and the width range is 50 - 300mm. In Example 1 and Example 2 of this application, the two endpoint values and the intermediate value of the height and width are selected as representative models for lightweight flexible improvement of the cross-sectional dimensions. Specifically, three models are selected: H-beam of H100×50, I-beam of 20a#, and H-beam of H350×300.

[0066] Example 1

[0067] In this example, the steel material strength of the lightweight flexible steel is the same as that of the standard part. At least one of the web thickness t1 and flange thickness t2 of the lightweight flexible steel is less than that of the replaced standard part, and at least one of the cross-sectional height H and cross-sectional width B is greater than that of the replaced standard part. Specifically, there are at least the following 9 optimization and improvement methods, but only the following 9 have practical engineering significance:

[0068] (1) Experimental groups 1 to 4 adopt the "single increase and single decrease" optimization and improvement method:

[0069] Experimental group 1: H↑, B→, t1↓, t2→;

[0070] Experimental group 2: H↑, B→, t1→, t2↓;

[0071] Experimental group 3: H→, B↑, t1↓, t2→;

[0072] Experimental group 4: H→, B↑, t1→, t2↓.

[0073] (2) Experimental groups 5 and 6 adopt the "single increase and double decrease" optimization and improvement method:

[0074] Experimental group 5: H↑, B→, t1↓, t2↓;

[0075] Experimental group 6: H→, B↑, t1↓, t2↓.

[0076] (3) Experimental groups 7 and 8 adopted the optimization and improvement method of "double increase and single decrease":

[0077] Experimental group 7: H↑, B↑, t1↓, t2→;

[0078] Experimental group 8: H↑, B↑, t1→, t2↓.

[0079] (4) Experimental group 9 adopted the optimization and improvement method of "double increase and double decrease":

[0080] Experimental group 9: H↑, B↑, t1↓, t2↓.

[0081] Tables 1, 2, and 3 were based on the H-shaped steel of standard part H100×50, I-beam 20a#, and H-shaped steel of H350×300 respectively, and carried out the optimization improvement and comparison of cross-sectional dimensions; among them, all standard parts and experimental groups in Tables 1 - 3 used Q235, and the flexural design strength f was 215 MPa.

[0082]

[0083]

[0084]

[0085] Based on the experimental data in Tables 1, 2, and 3, the following conclusions can be drawn:

[0086] 1. When the steel strength of the lightweight flexible profiled steel is the same as that of the standard part, at least one of the web thickness t1 and flange thickness t2 of the lightweight flexible profiled steel is less than that of the replaced standard part, and at least one of the section height H and section width B is greater than that of the replaced standard part, so that the cross-sectional area of the profiled steel arch is reduced compared with the replaced standard part, and the weight of the profiled steel arch is reduced, achieving the lightweight effect; and the maximum anti-bending moment M of the profiled steel arches obtained by all experimental groups x The change range compared with the replaced standard part is within ±20%, and the minimum bending radius is less than 6 m, meeting the flexural design requirements and realizing the moment equivalence under the same tunnel working conditions.

[0087] 2. The slope of the inner surface of the wing plate can be taken as 0 - 16.7%. Specifically, when the slope is 0, the cross-section of the lightweight flexible section steel is an H shape; when the slope is greater than 0, the cross-section of the lightweight flexible section steel is an I shape. Among them, the standard I-beam is optimized into a lightweight flexible I-beam or a lightweight flexible H-beam, and the standard H-beam is optimized into a lightweight flexible H-beam.

[0088] 3. The arc radius r at the connection between the wing plate and the web has two cases, namely r = 0 or r > 0; when r = 0, the steel arch is formed by welding; when r > 0, the steel arch is formed by hot rolling.

[0089] 4. As can be seen from Experimental Group 9 in Table 1-3, both the cross-section height H and the cross-section width B of the steel arch are larger than those of the replaced standard parts, and both the web thickness t1 and the wing plate thickness t2 are smaller than those of the replaced standard parts, which can achieve the best weight reduction effect. The reduction of steel is not less than 15%, and the lightweight effect is better. Moreover, the "double increase and double decrease" optimization and improvement method is the best choice for engineering practical applications, and it has great engineering significance.

[0090] Based on the fact that the steel strength of the lightweight flexible section steel is the same as that of the standard part in this embodiment, an engineering example is also provided. Its optimization method is that the cross-section height of the lightweight flexible section steel is smaller than that of the replaced standard part, and the cross-section width, the web thickness, and the wing plate thickness are all larger than those of the standard part; in this engineering example, the standard part is the H-beam of H294×200 in "GB / T 11263-2024 Hot-rolled H-beams and Split T-beams", and both the standard part and the steel in the experimental group use Q420, and its bending design strength f is 375 MPa. Table 4 optimizes and improves the cross-section dimensions of this standard part and makes a comparison.

[0091]

[0092]

[0093] The following conclusions can be drawn from the experimental data in Table 5:

[0094] 1. The changes in the differences between the cross-section height H and the cross-section width B of the steel arch and the replaced standard parts are both within 0 - 10%. That is, further reducing the difference ranges between the cross-section height H and the cross-section width B of the lightweight flexible section steel and the standard part to 0 - 8%, the steel arch can achieve a better lightweight effect, and the cross-section area is reduced by more than 15%, that is, the reduction of steel in the steel arch is not less than 15%; moreover, the lightweight flexible steel arch meets the bending design requirements and realizes the moment equivalence under the same tunnel working conditions; at the same time, it effectively improves the proportion balance of the cross-section height H and the cross-section width B of the lightweight flexible section steel, thereby improving the plate shape stability during the manufacturing process of the lightweight flexible section steel and reducing the overall instability rate during the processing of the arch.

[0095] 2. The difference between the sectional height H of the profiled steel arch and the replaced standard part varies within 0 - 10%, and the difference between the sectional width B and the replaced standard part varies within 0 - 10%. The weight reduction effect of the profiled steel arch is better, and the sectional area can be reduced by up to 20%, that is, the maximum reduction in steel consumption can reach 20%.

[0096] 3. Economic benefit analysis: Taking the experimental group 4 in Table 5 as an example, where the sectional area of the lightweight flexible profiled steel arch is reduced by 15.2%:

[0097] In engineering, the arch is usually measured by length, and the weight per unit length of the arch is called the weight per meter (= sectional area × length × steel density). After calculation, the weight per meter of the standard part arch is 27.9 Kg / m, and the weight per meter of the lightweight flexible arch is 23.7 Kg / m;

[0098] The cost per meter of the arch is called the price per meter. The price per meter of the standard part = the weight per meter of the standard part arch × the unit price of the standard part. The steel used for the standard part is Q235, and the unit price of the standard part is 3500 yuan / ton. The price per meter of the standard part is obtained as 97.6 yuan / m; The price per meter of the lightweight flexible profiled steel = the weight per meter of the lightweight flexible arch × the unit price of the lightweight flexible profiled steel. The steel used in the experimental group is Q235, and the cost unit price is 3900 yuan / ton (mainly due to the higher cost unit price caused by re - producing the mold). The price per meter of the lightweight flexible profiled steel is obtained as 91.3 yuan / m;

[0099] Furthermore, the cost saved per meter = the price per meter of the standard part - the price per meter of the lightweight flexible type = 6.3 yuan / m. Further, the cost saving ratio (= the cost saved per meter / the price per meter of the standard part) is 6.45%. For large - scale projects, using the lightweight flexible arch of this scheme can save at least millions of yuan in cost, and the cost reduction is very significant.

[0100] Example 2

[0101] In this example, the strength of the steel used for the lightweight flexible profiled steel is greater than that of the replaced standard part, and at least one of the web thickness t1, flange thickness t2, sectional height H, and sectional width B of the lightweight flexible profiled steel is less than that of the replaced standard part. Specifically, there are the following 15 optimization and improvement methods, all of which have practical engineering significance:

[0102] (1) The experimental groups 1 - 4 adopt the "single reduction" optimization and improvement form:

[0103] Experimental group 1: H↓, B→, t1→, t2→;

[0104] Experimental group 2: H→, B↓, t1→, t2→;

[0105] Experimental group 3: H→, B→, t1↓, t2→;

[0106] Experimental group 4: H→, B→, t1→, t2↓.

[0107] (2) Experimental groups 5 and 6 adopt the optimization and improvement method of "double reduction":

[0108] Experimental group 5: H↓, B↓, t1→, t2→;

[0109] Experimental group 6: H↓, B→, t1↓, t2→.

[0110] Experimental group 7: H↓, B→, t1→, t2↓;

[0111] Experimental group 8: H→, B↓, t1↓, t2→.

[0112] Experimental group 9: H→, B↓, t1→, t2↓;

[0113] Experimental group 10: H→, B→, t1↓, t2↓.

[0114] (3) Experimental groups 7 and 8 adopt the optimization and improvement method of "triple reduction":

[0115] Experimental group 11: H↓, B↓, t1↓, t2→;

[0116] Experimental group 12: H↓, B↓, t1→, t2↓;

[0117] Experimental group 13: H↓, B→, t1↓, t2↓;

[0118] Experimental group 14: H→, B↓, t1↓, t2↓.

[0119] (4) Experimental group 9 adopts the optimization and improvement method of "quadruple reduction":

[0120] Experimental group 15: H↓, B↓, t1↓, t2↓.

[0121] Among them, the steel used for the standard parts in Table 6 is Q235, and the steel used for all experimental groups is Q355; the steel used for the standard parts in Table 7 is Q355, and the steel used for all experimental groups is Q390; the steel used for the standard parts in Table 8 is Q390, and the steel used for all experimental groups is Q420.

[0122] Among them, the flexural design strength f of Q235 is 215 MPa, the flexural design strength f of Q355 is 305 MPa, the flexural design strength f of Q390 is 345 MPa, and the flexural design strength f of Q420 is 375 MPa.

[0123] The flexural design strength f of the steel used for the lightweight and flexible tunnel steel arch in this embodiment is not limited to the examples listed in this embodiment, and is specifically selected according to different design requirements.

[0124]

[0125]

[0126]

[0127] It can be seen from the experimental data in Table 6, Table 7, and Table 8 that:

[0128] 1. When the steel strength of the lightweight flexible profiled steel is greater than that of the replaced standard part, and at least one of the web thickness t1, flange thickness t2, section height H, and section width B of the lightweight flexible profiled steel is less than that of the replaced standard part, the cross-sectional area of the profiled steel arch is reduced compared with the replaced standard part, thereby reducing the weight of the profiled steel arch and achieving the lightweight effect; and the maximum anti-bending moment M of the profiled steel arch obtained in all experimental groups x The change range compared with the replaced standard part is within ±20%, and the minimum bending radius is less than 6 m, meeting the anti-bending design requirements and realizing the moment equivalence under the same tunnel working conditions.

[0129] 2. It can be seen from Experimental Group 15 in Tables 5-7 that when the section height H and section width B, web thickness t1 and flange thickness t2 of the profiled steel arch are all less than those of the replaced standard part, the best weight reduction effect can be achieved, and the steel reduction is not less than 20%, with a better lightweight effect; and the product obtained by this optimization and improvement has practical engineering significance and is the best choice for practical engineering applications.

[0130] 3. It can be seen from the experimental data in Tables 5-7 that the strong axis moment of inertia I of the lightweight flexible profiled steel arch obtained by the optimization method according to this embodiment x decreases. According to the bending stiffness = elastic modulus (E) × moment of inertia (I), the stiffness of the profiled steel arch decreases and the flexibility increases significantly; this result is regarded as a disadvantageous index under the traditional thinking, because in traditional thinking, once the arch deforms, it is often regarded as a dangerous signal that the tunnel support is about to fail, and the deformation may cause the support structure to be unable to continue to effectively bear the surrounding rock pressure, thereby triggering serious engineering accidents.

[0131] However, the applicant found from the actual application and monitoring results that the profiled steel arch with higher flexibility can better undergo elastic deformation when stressed, achieving good coordination with the deformation of the surrounding rock. Specifically:

[0132] In high-in-situ stress soft rock tunnels, the surrounding rock deforms extremely large and lasts for a long time due to its own characteristics and high in-situ stress. However, the flexible steel arch frame of this scheme can slowly deform along with the surrounding rock during the deformation process, continuously release the surrounding rock stress, reduce the surrounding rock pressure, effectively avoid brittle failure caused by excessive rigidity, and greatly improve the safety and stability of the support structure;

[0133] When passing through an active fault tunnel, the flexible support of this scheme can absorb energy through its own elastic deformation when the surrounding rock is deformed due to fault activity, maintain the integrity of the support structure, and ensure the safety of the tunnel;

[0134] For shallow urban tunnels, the flexible steel arch frame of this scheme can ensure the safety of the tunnel while its flexible deformation characteristics can better coordinate the deformation of the surrounding soil and reduce the impact on the surrounding environment.

[0135] 4. Based on the increased flexibility of the above-mentioned steel arch frame, the steel arch frame can better undergo elastic deformation when subjected to force and achieve good coordination with the deformation of the surrounding rock. The steel arch frame of this scheme can better dissipate vibration energy and load through flexible deformation, reduce resonance, and greatly improve the seismic performance of the tunnel support structure, providing a strong guarantee for the safety of tunnel engineering in disaster environments such as earthquakes.

[0136] 5. Economic benefit analysis: Taking the experimental group 15 in Table 8, the cross-sectional area of ​​the lightweight flexible steel arch frame is reduced by 20.2% as an example:

[0137] Arches are usually measured in length in engineering. The weight of an arch per unit length is called the meter weight (= cross-sectional area × length × steel density). The weight per meter of a standard arch is calculated to be 108 kg / m, and the weight per meter of a lightweight flexible arch is 86.4 kg / m.

[0138] The cost of arch frame per meter is called price per meter. Price per meter of standard parts = weight per meter of standard parts arch frame × unit price of standard parts. The steel used for standard parts is Q390, and the unit cost is 4100 yuan / ton, so the price per meter of standard parts is 442.8 yuan / meter. Price per meter of lightweight flexible steel = weight per meter of lightweight flexible arch frame × unit price of lightweight flexible steel. The steel used in the experimental group is Q420, and the unit cost is 4600 yuan / ton (the main reason for the higher cost is the re-production of molds and the improvement of materials), so the price per meter of lightweight flexible steel is 397.4 yuan / meter.

[0139] The cost saving per meter = standard part price per meter - lightweight flexible type price per meter = 36.7 yuan / meter, and the cost saving ratio (= cost saving per meter / standard part price per meter) is 10.25%. For large projects, the use of lightweight flexible arch frame of this solution can save at least one million yuan, which is a significant cost reduction.

[0140] The present solution also provides a method for designing the cross-sectional dimensions of a lightweight flexible tunnel steel arch, which is used to design the cross-section of the above-mentioned lightweight flexible tunnel steel arch, and includes the following steps:

[0141] Step 1: First, determine the web height h and the overhanging width b of the flange, and then select the initial design values of the web thickness t1 and the flange thickness t2;

[0142] Step 2: According to H = h + 2t2 and B = 2b + t1, obtain the cross-sectional height H and the cross-sectional width B of the lightweight flexible steel section;

[0143] Step 3: Substitute the web height h, the web thickness t1, and the cross-sectional height H of the lightweight flexible steel section into the minimum bending radius formula

[0144]

[0145] where f y is the yield strength, with the unit of MPa, to obtain R min . If R min ≤6m, it meets the design index; if R min >6m, reselect the values of the web thickness t1 and the flange thickness t2, obtain the new web thickness t1 and the cross-sectional height H of the lightweight flexible steel section, and calculate the minimum bending radius R min again until R min ≤6m.

[0146] When the steel used for the lightweight flexible steel section is the same as that of the standard part, in Step 2, the differences between the cross-sectional height H and the cross-sectional width B of the lightweight flexible steel section and the replaced standard part should be within 10%; if the difference range between the cross-sectional height H or the cross-sectional width B and the standard part exceeds 10%, then it is necessary to reselect the web thickness t1 and the flange thickness t2, repeat Step 2 to obtain the new cross-sectional height H and the cross-sectional width B of the lightweight flexible steel section, so that the difference range between the cross-sectional height H or the cross-sectional width B and the standard part is within 10%, and then calculate the minimum bending radius R min again, and ensure that R min ≤6m.

[0147] The above are only the embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the solution are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A lightweight flexible tunnel steel arch based on the principle of equivalent substitution, comprising multiple arch segments with the same bending radius. The arch segments include lightweight flexible steel sections, and the lightweight flexible steel section includes at least two wing plates with parallel upper and lower outer surfaces, and a web is vertically provided at the middle position between the two wing plates. It is characterized in that: The cross-sectional area and the moment of inertia I of the strong axis of the lightweight flexible section steel x At least one is less than that of the replaced standard part, and the maximum bending moment M of the strong axis of the steel arch frame x The change range compared with the standard part is ±20%; and it is achieved by any of the following methods: When the steel strength of the lightweight flexible section steel is the same as that of the standard part, at least one of the web thickness and flange thickness of the lightweight flexible section steel is less than that of the replaced standard part, and at least one of the section height and section width is greater than that of the replaced standard part; or the section height of the lightweight flexible section steel is less than that of the replaced standard part. Or When the steel strength of the lightweight flexible section steel is greater than that of the replaced standard part, at least one of the web thickness, flange thickness, section height and section width of the lightweight flexible section steel is less than that of the replaced standard part.

2. The lightweight flexible tunnel steel arch frame based on the principle of equivalent substitution according to claim 1, wherein: The minimum bending radius R of the lightweight flexible section steel min ≤ 6 m.

3. The lightweight flexible tunnel steel arch frame based on the principle of equivalent substitution according to claim 1, characterized in that: The cross-sectional area and the moment of inertia I of the strong axis of the lightweight flexible section steel x The reduction ratio of at least one item compared to the replaced standard part is greater than 10%.

4. The lightweight flexible tunnel steel arch frame based on the equivalent substitution principle according to any one of claims 1-3, characterized in that: When the steel strength of the lightweight flexible section steel is greater than that of the replaced standard part, at least two of the web thickness, flange thickness, section height and section width of the lightweight flexible section steel are less than that of the replaced standard part.

5. The lightweight and flexible tunnel steel arch frame based on the principle of equivalent substitution according to claim 4, wherein: At least three of the web thickness, flange thickness, section height and section width of the lightweight flexible section steel are less than that of the replaced standard part.

6. The lightweight flexible tunnel steel arch based on the equivalent substitution principle according to any one of claims 1-3, characterized in that: When the steel strength of the lightweight flexible section steel is the same as that of the standard part, the difference range between the section height of the lightweight flexible section steel and the standard part is 0 - 10%, and the difference range between the section width of the lightweight flexible section steel and the standard part is 0 - 10%.

7. The lightweight flexible tunnel steel arch frame based on the equivalent substitution principle according to claim 6, characterized in that: The difference range between the section height of the lightweight flexible section steel and the standard part is 0 - 8%, and the difference range between the section width of the lightweight flexible section steel and the standard part is 0 - 8%.

8. The lightweight and flexible tunnel steel arch frame based on the equivalent substitution principle according to any one of claims 1-3, characterized in that: The inner surfaces of the two flanges have the same slope, and the slope range is 0 - 16.7%; the fillet radius r at the connection between the flange and the web has two cases, namely r = 0 or r > 0.

9. A method for designing the cross-sectional dimensions of a lightweight and flexible tunnel steel arch, which is used to design the cross-section of the lightweight and flexible tunnel steel arch described in claim 7, and is characterized in that: It includes the following steps: Step 1: First determine the web height h and the outer extension width b of the flange, and then select the initial design values of the web thickness t1 and the flange thickness t2. Step 2: According to H = h + 2t2, B = 2b + t1, obtain the section height H and section width B of the lightweight flexible section steel. Step 3: Substitute the web height h, the web thickness t1, and the section height H of the lightweight flexible section steel into the minimum bending radius formula where f y is the yield strength in MPa, and R min is obtained. If R min ≤6m, it meets the design criteria; if R min >6m, reselect the values of the web thickness t1 and the flange thickness t2 to obtain the new web thickness t1 and the section height H of the lightweight flexible section steel, and recalculate the minimum bending radius R min until R min ≤6m.

10. A cross-sectional dimension design method for a lightweight and flexible tunnel steel arch as claimed in claim 9, characterized in that: When the steel strength of the lightweight flexible section steel is the same as that of the standard parts, in step 2, the differences between the section height H and section width B of the lightweight flexible section steel and the replaced standard parts should be within 10%; if the difference ranges of the section height H or section width B from the standard parts exceed 10%, then the web thickness t1 and flange thickness t2 need to be reselected, and step 2 is repeated to obtain the new section height H and section width B of the lightweight flexible section steel, so that the difference ranges of the section height H or section width B from the standard parts are within 10%, and then the minimum bending radius R is calculated again min , and ensure that R min ≤6m.

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