Quickly constructed pedestrian underground passage entrance and exit structure and construction method

Abstract

The invention discloses a fast construction pedestrian underground passage entrance and exit structure and a construction method, the fast construction pedestrian underground passage entrance and exit structure comprises a side wall, a top plate and a step ladder, the thickness of the side wall adopts a gradual change form, the thickness of the root is greater than that of the top, and the top is provided with a notch; the top plate is of a prefabricated assembled steel-concrete composite structure and comprises a prefabricated steel beam and a cast-in-place reinforced concrete plate, the prefabricated steel beam is installed in a notch in the top of the side wall and serves as a bottom die, and the cast-in-place reinforced concrete plate is poured; the step ladder is of a prefabricated assembly structure and comprises a prefabricated section and a cast-in-place section, and the two ends of the bottom of the step ladder are installed in channel bottom notches. The side wall of the structure is gradually changed, so that the support changing process is avoided. The top plate is of a prefabricated assembly steel-concrete structure, and full framing construction is omitted. The step ladder adopts a prefabrication and assembly process, so that the construction difficulty of pre-embedding of reinforcing steel bars is reduced, rapid and efficient construction is realized, traffic can be recovered as soon as possible, the step ladder can be put into use, and the influence on the surrounding environment is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground engineering construction, and more specifically, relates to a fast-constructed pedestrian underground passage entrance and exit structure and a construction method. Background Art

[0002] As an important part of urban transportation, pedestrian underpasses play an important role in achieving the separation of people and vehicles, improving vehicle traffic efficiency, and ensuring pedestrian safety. Therefore, pedestrian underpasses are widely set up in cities. The main passage of the pedestrian underpass crosses under the ground carriageway, and entrances and exits are set on both sides of the main passage. In order to facilitate pedestrian access, while considering increasing the usable space and reducing the cover load, the top plates of the entrances and exits on both sides of the passage are generally close to the ground. For the construction of conventional underpass structures, the side walls need to be replaced with support treatment, and the plain concrete needs to reach the design strength before the support can be removed. The process is complicated and the working hours are long. The top plates and steps of the entrances and exits are usually cast in place with full-height brackets, and the construction period is long. During the construction of the underpass, the road site is occupied, which affects the normal passage of vehicles and causes traffic congestion. The construction noise and dust also have a certain impact on the surrounding environment. Shortening the construction period of the underpass and reducing the occupation of the construction site can not only speed up the construction progress, restore traffic as soon as possible, and reduce the impact of construction on the surrounding environment, but also enhance the image of urban public services and improve social and economic benefits. Therefore, it is particularly important to develop a pedestrian underground passage entrance and exit structure that is fast to construct, has a stable structure, and reduces construction space. In the prior art, such as the patent document with application number CN202211121190.3, the invention patent proposes an assembled composite structure and process for the entrance and exit passage of an underground structure, including a retaining structure, a bottom plate, a prefabricated composite plate, and a prefabricated composite side wall. The prefabricated composite side wall includes a prefabricated side wall and a cast-in-place side wall cast between the prefabricated side wall and the retaining structure; a plurality of cup grooves arranged at intervals along the longitudinal direction are provided on the top surface of both ends of the bottom plate, and a plurality of embedded parts corresponding to the cup grooves are embedded on the bottom surface of the prefabricated side wall. The bottom surface of the prefabricated side wall is placed on the top surface of the bottom plate, and the bottom of the embedded part is inserted into the corresponding cup groove, and the cup groove is filled with grouting material. The present invention pours grouting material into the cup groove, places the bottom surface of the prefabricated side wall on the bottom plate, and inserts the exposed part of the embedded part at the bottom of the prefabricated side wall into the cup groove on the bottom plate, which can not only realize the positioning of the prefabricated side wall, but also realize the side wall without formwork, improve construction efficiency, and ensure the node strength of the prefabricated composite side wall and the bottom plate, and improve construction quality. However, the top plate of the structure of the invention adopts equal-section composite concrete, which cannot flexibly adjust the thickness to adapt to different stress conditions, and the material utilization efficiency is not high. In addition, the construction of the side wall involves the process of combining the prefabricated side wall with the cast-in-place side wall. Although formwork-free construction is possible, the construction steps are still relatively cumbersome. Summary of the invention

[0003] In view of the above defects or improvement needs of the prior art, the present invention provides a fast-constructed pedestrian underground passage entrance and exit structure and a construction method to solve the problems of complex construction procedures and long construction period of conventional underground passage entrance and exit structures.

[0004] To achieve the above object, according to one aspect of the present invention, the present invention provides a fast-constructed pedestrian underground passage entrance and exit structure, including side walls, a top plate and a step ladder, wherein:

[0005] The thickness of the side wall is in a gradual form, the thickness of the root is greater than the thickness of the top, a notch is provided at the top, and an embedded part connected to the top plate is provided at the bottom of the notch;

[0006] The top plate adopts a prefabricated steel-concrete composite structure, including a variable-section prefabricated steel beam and a cast-in-place reinforced concrete slab. The prefabricated steel beam is installed in the notch at the top of the side wall and serves as a bottom mold to cast the cast-in-place reinforced concrete slab.

[0007] The step ladder adopts a prefabricated assembly structure, including prefabricated sections and cast-in-place sections, and the two ends of the bottom of the step ladder are installed in the grooves at the bottom of the channel.

[0008] Furthermore, the gradient thickness of the side wall is calculated as follows:

[0009] t(h)=t 0 +αh

[0010] Among them, t 0 is the thickness of the top of the side wall, α is the thickness change rate, h is the depth of the side wall, and t(h) is the thickness of the side wall at the depth h;

[0011] The strength of the side wall should meet the force requirements, namely:

[0012]

[0013] Where σ(h) is the stress on the sidewall at depth h, b is the width of the sidewall, and f c is the compressive strength of the side wall material;

[0014] In order to optimize the calculation of the gradient thickness of the sidewall, it is necessary to find a suitable t 0 and α, so that the material usage of the side wall is minimized while meeting the strength requirements, and is optimized by the following formula:

[0015]

[0016] The constraints are:

[0017]

[0018] Where H is the total depth of the sidewall;

[0019] Solving the above optimization problem by the following formula can obtain t 0 Substituting the analytical solution of and α into the above-mentioned calculation formula of the side wall thickness t(h), the gradient thickness distribution law of the side wall is obtained;

[0020]

[0021] Furthermore, the variable cross-section design calculation of the prefabricated steel beam takes minimizing the material volume as the objective function, and the objective function is expressed as:

[0022]

[0023] Where V is the total material volume of the prefabricated steel beam, L is the total length of the steel beam, b(x) and h(x) are the functions of the width and height with position, respectively;

[0024] In order to ensure the safety and stability of the structure, set the constraints:

[0025] ①Minimum cross-sectional size: h(x)≥h min , b(x)≥b min ;

[0026] ② Maximum cross-sectional size: h(x)≤h max ,b(x)≤b max ;

[0027] ③ Local stability requirements: ensure that the flange and web will not buckle;

[0028] By introducing the Lagrange multiplier method to deal with the constraints, the new objective function becomes:

[0029] J=V+λ 1 (σ(x)-σ max )+λ 2 (w(x)-w max )

[0030] Where σ(x) is the stress at any location; w(x) is the deflection at any location; λ 1 and λ 2 is the Lagrange multiplier;

[0031] For the design variables h(x) and b(x), calculate the gradient of the objective function with respect to them; using the finite element analysis results, we can get:

[0032]

[0033] The design variables are adjusted according to the gradient direction, using the following iterative formula:

[0034]

[0035] Among them, η is the learning rate, which determines the step size of parameter adjustment in each iteration; h old (x) and b old (x) is the design variable value of the current iteration; h new (x) and b new (x) is the updated design variable value;

[0036] Set the convergence criterion and stop the iteration when the change of the objective function is less than a certain threshold:

[0037] |J new -J old |∈

[0038] Or when the maximum change of the design variable in several consecutive iterations is small enough, it is also considered convergence:

[0039] max(|h new (x)-h old (x)|,|b new (x)-b old (x)|)<δ.

[0040] Furthermore, the prefabricated steel beam adopts a variable cross-section design, and the beam height gradually decreases from the mid-span to both ends.

[0041] Furthermore, the prefabricated steel beam includes a full-length top plate, a web plate, a lower flange and a transverse stiffening plate, and a double row of shear nails are arranged on the top plate along the span direction for connecting the reinforced concrete cast-in-place slab and the prefabricated steel beam as a whole.

[0042] Furthermore, a vertical main reinforcement is reserved at the top of the side wall, which is extended to the top surface of the reinforced concrete cast-in-place slab and then bent, and the bending length must meet the anchoring requirements.

[0043] Furthermore, the main reinforcement of the cast-in-place reinforced concrete slab along the span direction extends to the outer edge of the side wall and bends downward, and the bending length needs to meet the anchoring requirements.

[0044] Furthermore, rubber plates are provided on the contact surfaces between the lower flanges at both ends of the prefabricated steel beam and the notches.

[0045] Furthermore, an embedded part for anchoring the prefabricated steel beam is provided at the lower part of the notch.

[0046] Furthermore, the step ladder is divided into a plurality of prefabricated sections at the center of the platform, and the cast-in-place section is arranged in the middle of the platform.

[0047] Furthermore, it also includes piers, which are arranged at the step ladder platform of the inlet and outlet bottom plates and are used to install prefabricated segments of the step ladder.

[0048] According to another aspect of the present invention, the present invention provides a construction method for a fast-constructed pedestrian underground passage entrance and exit structure, which is used to implement the fast-constructed pedestrian underground passage entrance and exit structure described above, and comprises the following steps:

[0049] S100: Determine the gradual thickness of the side wall, excavate the fertilizer trough, set up steel cement mixing piles and horizontal steel supports, install the side wall formwork, cast the side wall with gradual thickness, and reserve notches and vertical main reinforcement at the top;

[0050] S200: Prefabricated steel beams are manufactured in the factory and transported to the construction site. They are installed in sections in the notches at the top of the side walls and welded and assembled.

[0051] S300: After installing the prefabricated steel beam, tie the steel bars on the top of the prefabricated steel beam to install the formwork, pour the cast-in-place reinforced concrete slab to form the top plate, and anchor the top plate to the side wall with the reserved steel bars;

[0052] S400: Prefabricate stair segments in the factory, transport them to the site and install them on pre-set piers. Tie and connect the steel bars between the prefabricated stair segments, cast the cast-in-place segments to form a complete staircase, and complete the construction of the entrance and exit structure of the pedestrian underpass.

[0053] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0054] 1. A fast-constructed pedestrian underpass entrance and exit structure of the present invention adopts a side wall with a gradually variable thickness, a prefabricated assembled steel-concrete composite top plate and a prefabricated assembled step ladder. The prefabricated assembled steel-concrete composite top plate is firmly connected to the side wall through a notch and a cast-in-place reinforced concrete slab, and the prefabricated assembled step ladder is quickly connected by on-site pouring and splicing. No additional bracket is required during the entire construction process. The combination of the three structures simplifies the construction process of the pedestrian underpass entrance and exit, shortens the construction period, and can resume traffic and be put into use as soon as possible, reducing the impact on the surrounding environment.

[0055] 2. The steel in the prefabricated assembled steel-concrete composite top plate of the fast-constructed pedestrian underground passage entrance and exit structure of the present invention has a high tensile strength, while the concrete has a high compressive strength. By combining these two materials together, their respective advantages can be fully utilized to form a high-strength, high-rigidity structural system.

[0056] 3. The prefabricated assembled steel-concrete composite top plate of the pedestrian underground passage entrance and exit structure of the present invention, which is quickly constructed, adopts a variable cross-section design. The cross-section can be adjusted according to the actual stress conditions of the top plate, so that materials can be used more reasonably in different positions, which can reduce unnecessary material waste and reduce structural costs.

[0057] 4. The thickness of the side wall of the entrance and exit structure of a fast-constructed pedestrian underground passage of the present invention is in a gradual form. The root of the side wall is determined according to the force calculation under the maximum cantilever state, and a notch is provided on the top of the side wall for the later installation of the prefabricated steel-concrete composite top plate. This solution does not require the replacement of the support process. The side wall bears all the lateral earth pressure in the cantilever state, avoiding the problems of complex procedures and long construction period caused by the replacement of the support, simplifying the construction process and shortening the construction period.

[0058] 5. The top plate of the entrance and exit structure of a pedestrian underground passage of the present invention is a prefabricated steel-concrete composite structure. The prefabricated steel beams after welding and assembly can be used as the bottom formwork for casting reinforced concrete slabs. There is no need to use full-height bracket construction, which effectively saves construction time. The variable-section steel-concrete composite structure makes full use of material properties, which can reduce the thickness of the top plate and increase the usable clearance of the buried entrance and exit sections.

[0059] 6. The fast-constructed pedestrian underground passage entrance and exit structure step ladder of the present invention adopts a prefabricated assembly process, divides the step ladder into multiple prefabricated segments at the center of the platform, and casts the assembly segments between the prefabricated segments to form an overall step ladder structure, thereby solving the problem that the main reinforcement of the step ladder needs to be pre-buried along the line of the step ladder in the cast-in-place process, and the construction process is complicated and difficult, thereby realizing fast and efficient construction of the step ladder. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a schematic diagram of the structure of the buried section of a conventional pedestrian underground passage entrance and exit;

[0061] Figure 2 It is a schematic structural diagram of a side wall reinforced underground section of a pedestrian underground passage entrance and exit structure for rapid construction according to an embodiment of the present invention;

[0062] Figure 3 A schematic diagram of the structure of a top plate of a pedestrian underground passage entrance and exit structure for rapid construction according to an embodiment of the present invention;

[0063] Figure 4 This is a schematic structural diagram of a prefabricated steel beam facade of a top plate of a pedestrian underground passage entrance and exit structure that is rapidly constructed according to an embodiment of the present invention;

[0064] Figure 5 A schematic diagram of a structure of a fast-constructed pedestrian underground passage entrance and exit structure step ladder according to an embodiment of the present invention;

[0065] Figure 6 The present invention is a flowchart of a method for rapidly constructing an entrance and exit structure of a pedestrian underground passage according to an embodiment of the present invention.

[0066] In all the drawings, the same figure numbers represent the same technical features, specifically: 1-side wall, 101-notch, 102-embedded parts, 2-top plate, 201-precast steel beam, 202-cast-in-place reinforced concrete slab, 203-shear nails, 3-staircase, 301-precast segment, 302-cast-in-place segment, 4-pier, 5-passageway, 6-steel cement mixing pile, 7-steel support, 8-steel replacement support, 9-plain concrete. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0068] It should be noted that if there are directional indications (such as up, down, left, right, front, back, etc.) involved in the embodiments of the present invention, the directional indications are only used to explain the relative position relationship and movement of the components under a certain specific posture (as shown in the attached drawings). If the specific posture changes, the directional indication will also change accordingly. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0069] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0070] In the present invention, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "includes..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0071] Example 1

[0072] The embodiment of the present invention provides a pedestrian underground passage entrance and exit structure that can be quickly constructed, including a side wall 1, a top plate 2, and a step ladder 3. The side wall 1 is buried underground and serves as a supporting foundation for the entire structure. It extends vertically to provide the necessary stability and bearing capacity for the upper structure. The top plate 2 is installed on the top of the side wall 1 to form a closed space, and the step ladder 3 is arranged in the closed space. The three together constitute a stable, practical and efficient underground passage entrance and exit structure.

[0073] like Figure 1 As shown, it is a conventional buried section structure of the entrance and exit of the tunnel. The side walls of the buried section structure of the entrance and exit of the tunnel are of equal thickness. During the construction of the side walls, steel cement mixing piles 6 and steel supports 7 are used in combination with temporary support. When the construction reaches below the top plate, steel replacement supports 8 need to be set for replacement to ensure that the side wall structure can withstand the lateral soil pressure. When replacing the support, plain concrete 9 needs to be filled in the fertilizer trough. The support can only be removed after the plain concrete 9 reaches the strength requirement. The process is complicated and the construction period is long.

[0074] like Figure 2 As shown, the buried section structure of the entrance and exit of the side wall reinforcement channel, in the embodiment of the present invention, the side wall 1 adopts a gradual thickness form, the thickness of the root is greater than the thickness of the top, and the thickness of the side wall is changed according to the side wall force design to ensure that the resistance and force at different depths are more matched, without the need for a brace replacement process. A notch 101 is provided at the top of the side wall 1, and an embedded part 102 is provided at the lower part of the notch 101 for later installation and fixing of the top plate 2. The embedded part 102 should be cast and installed with the side wall 1, and ensure that the embedded part 102 is accurately positioned and the elevation is correct. Vertical main reinforcement for connecting the top plate 2 is also reserved at the top of the side wall 1.

[0075] The side wall gradient thickness is designed based on the force analysis of the side wall, and the specific calculation formula is as follows:

[0076] The side wall is mainly subjected to lateral earth pressure and water pressure in underground engineering. The force P(h) on the side wall at depth h is:

[0077] P(h)=Kγh+γ w h

[0078] Where, h is the depth of the side wall, K is the lateral earth pressure coefficient, γ is the soil density, and γ w The weight of water.

[0079] In order to match the thickness of the side wall with the force, the thickness of the side wall t(h) is:

[0080] t(h)=t 0 +αh

[0081] Among them, t0 is the thickness of the top of the side wall, and α is the thickness change rate.

[0082] The strength of the side wall should meet the force requirements, namely:

[0083]

[0084] Where σ(h) is the stress on the sidewall at depth h, b is the width of the sidewall, and f c is the compressive strength of the side wall material.

[0085] In order to optimize the calculation of the gradient thickness of the sidewall, it is necessary to find a suitable t 0 and α, so that the material usage of the side wall is minimized while meeting the strength requirements. This can be optimized using the following formula:

[0086]

[0087] The constraints are:

[0088]

[0089] Wherein, H is the total depth of the sidewall.

[0090] Solving the above optimization problem by the following formula can obtain t 0 Substituting the analytical solutions of and α into the above-mentioned calculation formula of the sidewall thickness t(h), the gradient thickness distribution law of the sidewall is obtained.

[0091]

[0092] Through the above formula, the design of the gradual thickness of the side wall can be optimized so that it can reduce the amount of material used while meeting the strength requirements, thereby improving the economy and safety of underground projects.

[0093] like Figure 3 and Figure 4 As shown, the top plate 2 adopts a prefabricated steel-concrete composite structure, including a prefabricated steel beam 201 and a cast-in-place reinforced concrete slab 202. The cast-in-place reinforced concrete slab 202 is cast on the top of the prefabricated steel beam 201, and together with the prefabricated steel beam 201, it constitutes the top plate 2.

[0094] The prefabricated steel beam 201 adopts a variable cross-section, which gradually decreases from the mid-span range to the two end beam heights. In the mid-span area with greater stress, a larger cross-sectional size is adopted to enhance the bearing capacity of the structure; while in the area with less stress, the cross-sectional size is reduced to reduce the deadweight and material consumption. It includes a top plate, a web plate, a lower flange and a transverse stiffening plate, and has a high bearing capacity and rigidity to adapt to different stress conditions. A double row of shear nails 203 are arranged on the top plate along the span direction to connect the reinforced concrete cast-in-place slab 202 with the steel beam 201 as a whole, thereby improving the integrity and stability of the top plate. The prefabricated steel beam 201 is installed in the notch 101 at the top of the side wall 1, and rubber plates are provided on the contact surfaces between the lower flanges at both ends of the prefabricated steel beam 201 and the notch 101. The size of the rubber plates is consistent with the size of the embedded parts 102, which are used to reduce the friction and collision between the prefabricated steel beam 201 and the side wall 1, and protect the prefabricated steel beam 201 and the side wall 1 from damage. The top plate of the prefabricated steel beam 201 has a hole partially opened at the beam end for the steel bars of the side wall 1 to pass through. After the prefabricated steel beam 201 is welded and assembled in sections, it can be used as a bottom mold for pouring the prefabricated steel beam 201, without the need for additional brackets, simplifying the construction process. Tie the steel bars on the top of the prefabricated steel beam 201 and pour concrete. During pouring, ensure that the concrete completely wraps the shear nails 203, and fill the beam end of the prefabricated steel beam 201 with concrete to ensure that the prefabricated steel beam 201 and the cast-in-place reinforced concrete slab 202 are firmly connected.

[0095] The variable cross-section design calculation of the prefabricated steel beam is as follows:

[0096] Where the steel beam is subjected to the maximum bending moment in the mid-span, the bending moment at both ends gradually decreases, and the shear force is relatively large. For the variable cross-section design of steel beams, that is, the changing rules of height and width.

[0097] The bending moment M(x) and shear force V(x) at any position of the steel beam affect the height h(x) and width b(x) of the section respectively. The specific relationship can be expressed by the following formula:

[0098] h(x)=h max -α·|M(x)

[0099] b(x)|=b min +β·|V(x)

[0100] Where x is the position coordinate along the length of the steel beam; h max is the maximum height at mid-span; b min is the maximum width; α and β are coefficients used to adjust the degree to which the cross-sectional size changes with internal forces; M(x) and V(x) are the bending moment and shear force values ​​at that position, respectively; b(x) and h(x) are functions of the width and height changing with position, respectively.

[0101] In order to ensure the safety and stability of the structure, some constraints need to be set:

[0102] ①Minimum cross-sectional size: h(x)≥h min , b(x)≥b min ;

[0103] ② Maximum cross-sectional size: h(x)≤h max ,b(x)≤b max ;

[0104] ③ Local stability requirements: Ensure that the flange and web will not buckle and meet the width-to-thickness ratio restrictions specified in relevant specifications.

[0105] Combining the above formulas and constraints, a comprehensive optimization model can be established with the objective function of minimizing the material volume while ensuring that the structure meets all mechanical performance requirements. The objective function can be expressed as:

[0106]

[0107] Where V is the total material volume of the prefabricated steel beam and L is the total length of the steel beam.

[0108] The gradient descent method is used to solve the total material volume V of the prefabricated steel beam, and the Lagrange multiplier method is introduced to deal with the constraints. The new objective function becomes:

[0109] J=V+λ 1 (σ(x)-σ max )+λ 2 (w(x)-w max )

[0110] Where σ(x) is the stress at any location; w(x) is the deflection at any location; λ 1 and λ 2 is the Lagrange multiplier.

[0111] For the design variables h(x) and b(x), calculate the partial derivatives (i.e. gradients) of the objective function with respect to them. Using the finite element analysis results, we can obtain:

[0112]

[0113] The design variables are adjusted according to the gradient direction, using the following iterative formula:

[0114]

[0115] Among them, η is the learning rate, which determines the step size of parameter adjustment in each iteration; h old (x) and b old (x) is the design variable value of the current iteration; hnew (x) and b new (x) is the updated design variable value.

[0116] Set the convergence criterion and stop the iteration when the change of the objective function is less than a certain threshold:

[0117] |J new —J old |∈

[0118] Or when the maximum change of the design variable in several consecutive iterations is small enough, it is also considered convergence:

[0119] max(|h new (x)-h old (x)|,|b new (x)-b old (x)|)<δ

[0120] Make sure that the new design after each update still meets all constraints. If some constraints are violated, corrections need to be made.

[0121] The variable cross-section design of the prefabricated assembled steel-concrete composite top plate formed by pouring can be adjusted according to the actual stress conditions of the top plate, so that the materials can be used more reasonably in different positions, which can reduce unnecessary material waste and reduce structural costs. Steel has high tensile strength, while concrete has high compressive strength. By combining these two materials together, their respective advantages can be fully utilized to form a high-strength and high-rigidity structural system.

[0122] The vertical main reinforcement reserved at the top of the side wall 1 extends to the top surface of the reinforced concrete cast-in-place slab 202 and then bends. The bending length must meet the anchoring requirements to improve the connection strength between the top slab 2 and the side wall 1. At the same time, the main reinforcement along the span direction of the cast-in-place reinforced concrete slab 202 also needs to extend to the outer edge of the side wall 1 and bend downward. The bending length also needs to meet the anchoring requirements to ensure that the top slab 2 and the side wall 1 are firmly combined. After casting and anchoring, the top slab 2 and the side wall 1 are connected as a whole.

[0123] like Figure 5As shown, the step ladder 3 adopts a prefabricated assembly structure, including a prefabricated segment 301 and a cast-in-place segment 302. The step ladder 3 is divided into multiple prefabricated segments 301 at the center of the platform. The cast-in-place segment 302 is arranged in the middle of the platform, and the cast-in-place process is adopted. The length of the cast-in-place segment 302 is 20 cm. The two ends of the bottom of the step ladder 3 are installed in the bottom notch of the channel 5, and no additional bracket is required. The inlet and outlet bottom plate is provided with a pier 4 at the platform of the step ladder 3, which is used to install the prefabricated segment 301 of the step ladder 3. This prefabricated assembly structure avoids the construction difficulty of pre-embedded or planted reinforcement of the main reinforcement of the step ladder, and at the same time, there is no need to set up a full-hall bracket, which simplifies the construction process and shortens the construction period.

[0124] In the structure of the embodiment of the present invention, after the construction of the side wall 1 is completed, there is no need to carry out the brace replacement process, and the prefabricated steel beam 201 is directly installed in the notch 101 at the top of the side wall 1. Then, the cast-in-place reinforced concrete slab 202 is cast on the top of the prefabricated steel beam 201 to form a prefabricated assembled steel-concrete composite top plate 2. The step ladder 3 adopts a prefabricated assembly structure, and the prefabricated segments 301 of the step ladder 3 are installed on the pier 4, and finally the cast-in-place segments 302 are cast to form a whole. The structure of the present invention does not need to adopt full-floor support construction, which simplifies the construction process and shortens the construction period. At the same time, the steel-concrete composite structure makes full use of the material properties, which can reduce the thickness of the top plate and increase the usable clearance of the buried section of the inlet and outlet. The prefabricated assembly process of the step ladder also avoids the construction difficulty of pre-embedded or planted steel bars, and further simplifies the construction process.

[0125] Example 2

[0126] like Figure 6 As shown, an embodiment of the present invention provides a construction method for a pedestrian underground passage entrance and exit structure that can be quickly constructed, including the following specific steps:

[0127] S100: Determine the gradual thickness of the side wall 1, set up steel cement mixing piles while excavating the fertilizer trough, set up transverse steel supports to provide temporary support for subsequent construction, install the side wall formwork, cast the side wall 1 with gradual thickness, and reserve notches 101 and vertical main reinforcements at the top to facilitate later structural connection;

[0128] S200: The prefabricated steel beam 201 is manufactured in the factory and transported to the construction site. According to the design drawings, the prefabricated steel beam 201 is hoisted in sections and firmly installed in the notch 101 at the top of the side wall 1, and is precisely welded and assembled to ensure the strength and stability of the overall structure.

[0129] S300: After the prefabricated steel beam 201 is successfully installed, a template system is installed by tying steel bars on the top of the prefabricated steel beam 201, pouring a cast-in-place reinforced concrete slab 202 to form a top plate 2, and anchoring the top plate 2 to the side wall 1 with reserved steel bars;

[0130] S400: Prefabricate the staircase segments 301 in the factory, transport them to the site and install them on the pre-set piers 4, tie and connect the steel bars between the staircase segments 301, and finally cast the cast-in-place segments 302 to form a complete staircase 3, completing the construction of the entrance and exit structure of the pedestrian underpass;

[0131] S500: Perform a comprehensive inspection on the construction quality and connection of the installed side wall 1, the top plate 2 and the step ladder 3 to ensure that they meet the design requirements. Perform necessary tests on the structure, such as bearing capacity test, anti-seepage performance test, etc., to ensure the stability and safety of the structure.

[0132] Through the steps in this embodiment, the entrance and exit structure of the pedestrian underground passage can be constructed quickly and efficiently, shortening the construction period and reducing the construction difficulty and cost.

[0133] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fast-constructed pedestrian underground passage entrance and exit structure, characterized in that: It comprises a side wall (1), a top plate (2) and a step ladder (3), wherein: The thickness of the side wall (1) is in a gradual change form, the thickness of the root is greater than the thickness of the top, a notch (101) is provided at the top, and an embedded part (102) connected to the top plate (1) is provided below the notch (101); The top plate (2) adopts a prefabricated assembled steel-concrete composite structure, including a variable-section prefabricated steel beam (201) and a cast-in-place reinforced concrete slab (202); the prefabricated steel beam (201) is installed in a notch (101) at the top of the side wall (1) and serves as a bottom mold to cast the cast-in-place reinforced concrete slab (202); The step ladder (3) adopts a prefabricated assembly structure, including a prefabricated segment (301) and a cast-in-place segment (302), and the two ends of the bottom of the step ladder (3) are installed in the bottom notch of the channel (5).

2. The pedestrian underground passage entrance and exit structure according to claim 1, characterized in that: The gradient thickness of the side wall (1) is calculated as follows: t(h)=t0+αh Where t0 is the thickness of the top of the sidewall, α is the thickness change rate, h is the depth of the sidewall, and t(h) is the thickness of the sidewall at the depth h; The strength of the side wall should meet the force requirements, namely: Where σ(h) is the stress on the sidewall at depth h, b is the width of the sidewall, and f c is the compressive strength of the side wall material; In order to optimize the calculation of the gradient thickness of the sidewall, it is necessary to find the appropriate t0 and α to minimize the material usage of the sidewall while meeting the strength requirements. The optimization is performed using the following formula: The constraints are: Where H is the total depth of the sidewall; By solving the above optimization problem through the following formula, we can get the analytical solution of t0 and α, and substitute it into the above calculation formula of the thickness t(h) of the side wall to get the gradient thickness distribution law of the side wall; 3. The pedestrian underground passage entrance and exit structure according to claim 2, characterized in that: The variable cross-section design calculation of the prefabricated steel beam (201) takes minimizing the material volume as the objective function, and the objective function is expressed as: Where V is the total material volume of the prefabricated steel beam, L is the total length of the steel beam, b(x) and h(x) are the functions of the width and height with position, respectively; In order to ensure the safety and stability of the structure, set the constraints: ①Minimum cross-sectional size: h(x)≥h min , b(x)≥b min ; ② Maximum cross-sectional size: h(x)≤h max ,b(x)≤b max ; ③ Local stability requirements: ensure that the flange and web will not buckle; By introducing the Lagrange multiplier method to deal with the constraints, the new objective function becomes: J=V+λ1(σ(x)-σ max )+λ2(w(x)-w max ) Where σ(x) is the stress at any location; w(x) is the deflection at any location; λ1 and λ2 are Lagrange multipliers; For the design variables h(x) and b(x), calculate the gradient of the objective function with respect to them; using the finite element analysis results, we can get: The design variables are adjusted according to the gradient direction, using the following iterative formula: Among them, η is the learning rate, which determines the step size of parameter adjustment in each iteration; h old (x) and b old (x) is the design variable value of the current iteration; h new (x) and b new (x) is the updated design variable value; Set the convergence criterion and stop the iteration when the change of the objective function is less than a certain threshold: |J new -J old |<∈ Or when the maximum change of the design variable in several consecutive iterations is small enough, it is also considered convergence: max(|h new (x)-h old (x)|,|b new (x)-b old (x)|)<δ。 4. The pedestrian underground passage entrance and exit structure according to claim 3, characterized in that: The prefabricated steel beam (201) comprises a top plate, a web plate, a lower flange and a transverse stiffening plate, and a double row of shear studs (203) are arranged on the top plate along the span direction for connecting the reinforced concrete cast-in-place slab (202) and the prefabricated steel beam (201) as a whole.

5. The pedestrian underground passage entrance and exit structure according to claim 4, characterized in that: Rubber plates are provided on the contact surfaces between the lower flanges at both ends of the prefabricated steel beam (201) and the notch (101).

6. A pedestrian underground passage entrance and exit structure according to any one of claims 1 to 5, characterized in that: A vertical main reinforcement is reserved at the top of the side wall (1), which is extended to the top surface of the reinforced concrete cast-in-place slab (202) and then bent, and the bending length must meet the anchoring requirements.

7. A pedestrian underground passage entrance and exit structure according to any one of claims 1 to 5, characterized in that: The main reinforcement of the cast-in-place reinforced concrete slab (202) along the span direction extends to the outer edge of the side wall (1) and bends downward, and the bending length needs to meet the anchoring requirements.

8. The pedestrian underground passage entrance and exit structure according to any one of claims 1 to 5, characterized in that: The step ladder (3) is divided into a plurality of prefabricated segments (301) at the center of the platform, and the cast-in-place segment (302) is arranged in the middle of the platform.

9. The pedestrian underground passage entrance and exit structure according to any one of claims 1 to 5, characterized in that: It also includes a buttress (4) arranged at the platform of the step ladder (3) on the inlet and outlet bottom plates and used for installing the prefabricated segments (301) of the step ladder (3).

10. A construction method for an entrance and exit structure of an underground pedestrian passage, applied to the construction of an entrance and exit structure of an underground pedestrian passage as claimed in any one of claims 1 to 9, characterized in that: The steps include: S100: Determine the gradual thickness of the side wall (1), excavate the fertilizer trough, set up steel cement mixing piles and transverse steel supports, install the side wall formwork, cast the side wall (1) with gradual thickness, and reserve a notch (101) and vertical main reinforcement at the top; S200: Prefabricated steel beams (201) are manufactured in a factory, transported to a construction site, installed in sections in the notches (101) at the top of the side walls (1), and welded and assembled; S300: After the prefabricated steel beam (201) is installed, a steel bar is tied to the top of the prefabricated steel beam (201) to install a template, a cast-in-place reinforced concrete slab (202) is cast to form a top plate (2), and the top plate (2) is anchored to the side wall (1) with reserved steel bars; S400: Prefabricate the stair segments (301) in the factory, transport them to the site and install them on the pre-set piers (4), tie and connect the steel bars between the stair segments 301, cast the cast-in-place segments (302) to form a complete stair (3), and complete the construction of the pedestrian underground passage entrance and exit structure.

Images