A steel-concrete composite trough beam and its design method

Abstract

The present invention discloses a steel-concrete composite trough beam and a design method thereof, belonging to the field of prefabricated building technology, comprising: a steel bottom beam, a steel cross beam, a trough main beam and a connecting tenon, wherein a plurality of steel bottom beams are connected to form a steel frame through a plurality of steel cross beams, and the trough main beam is placed on the top surface of the steel bottom beam and connected to the steel bottom beam through a connecting key. The present invention proposes a design iteration process based on the position of the plastic neutral axis, which optimizes the neutral axis position of the composite section by adjusting the cross-sectional area of ​​the steel bottom beam to ensure a balance between mechanical properties and functional use; through the steel-concrete composite structure, concrete is arranged in the compression zone and steel is arranged in the tension zone, giving full play to the mechanical properties of the two materials, and solving the problem of prestressing requirements or compressive instability of the steel structure caused by tension of the traditional trough beam bridge deck.

Description

Technical Field

[0001] The present invention relates to the technical field of prefabricated buildings, and in particular to a steel-concrete composite trough beam and a design method thereof. Background Art

[0002] A trough-beam bridge, with its deck located at the bottom between the main girders, is a through-type bridge. Trough beams are a bridge type designed to reduce the height from the bridge deck to the beam bottom, thereby increasing the clearance under the bridge. Trough beams offer excellent practicality: their greatest advantage is their low construction height, making them suitable for overpasses. While maintaining clearance requirements under the bridge, they can lower the elevation of the embankments at both ends, thereby reducing connection lengths and the amount of roadbed fill.

[0003] However, trough beams have significant mechanical disadvantages: the bridge deck lies below the neutral axis, subjecting the entire deck section to tension. Concrete trough beams require prestressing to resist tension. Alternatively, steel trough beams can be used, but the steel structure in the compression zone is prone to buckling.

[0004] The above problems need to be solved urgently. Therefore, a steel-concrete composite trough beam and its design method are proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to solve the problems existing in the existing trough beam technology, such as the bridge deck being located below the neutral axis and the entire section of the bridge deck being under tension, and a design method for a steel-concrete composite trough beam is provided.

[0006] The present invention solves the above technical problems through the following technical solutions, which include the following steps:

[0007] Step S1: Preliminary selection of the size and quantity of the steel bottom beams and the height h of the steel bottom beams s And calculate the cross-sectional area A of all steel bottom beams s :

[0008] A s =mA d ;

[0009] Among them, m represents the number of steel bottom beams, A d Indicates the cross-sectional area of ​​a single steel bottom beam;

[0010] Step S2: Based on the cross-sectional area A of all steel bottom beams s Based on the ultimate state design of bearing capacity and the principle that the plastic neutral axis is located on the top surface of the steel bottom beam, the cross-sectional area A of the trough main beam is calculated. c :

[0011]

[0012] Among them, fsd Indicates the tensile design strength of the steel bottom beam, f cd Indicates the concrete compressive design strength of the channel main beam;

[0013] Step S3: Based on the cross-sectional area A of the trough main beam c , determine the elastic neutral axis position h of the trough main beam c ;

[0014] Step S4: Calculate the neutral axis position h of the cross section of the combination formed by the channel main beam and the steel bottom beam z :

[0015]

[0016] Among them, h s Indicates the height of the steel bottom beam, h c Indicates the distance between the elastic neutral axis of the channel main beam and the top surface of the steel bottom beam. Indicates the elastic modulus E of the steel bottom beam s The concrete elastic modulus E of the trough main beam c The ratio of

[0017] Step S5: Compare h z With h s If h z Greater than h s If the cross-sectional area A of a single steel bottom beam exceeds the set value, d Increase; if h z Less than h s If the cross-sectional area A of a single steel bottom beam exceeds the set value, d reduce;

[0018] Step S6: Repeat steps S2 to S5 until the neutral axis position h of the cross section of the combination formed by the trough main beam and the steel bottom beam is z Height h from steel bottom beam s The ratio is within the set range.

[0019] Step S7: Calculate the bending bearing capacity of the cross-section of the trough beam designed in steps S1 to S6, and verify the bending bearing capacity to determine whether it meets the design requirements for bearing capacity. The bending bearing capacity calculation formula is as follows:

[0020]

[0021] Among them, M u It represents the bending bearing capacity of the composite section, and h is the height of the pre-planned trough main beam.

[0022] Furthermore, in step S1, the height h of the steel bottom beam is sThe initial value is 1 / 40 to 1 / 50 of the bridge span.

[0023] Furthermore, in step S3, the specific processing process is as follows:

[0024] Step S31: Calculate the static moment of the cross section of the trough main beam:

[0025]

[0026] Among them, S x dA is the static moment of the cross section of the trough main beam to the top surface of the steel bottom beam, c represents the differential of the cross-sectional area of ​​the trough main beam, and x represents dA c Distance to the top surface of the steel bottom beam;

[0027] Step S32: Calculate the distance between the elastic neutral axis of the trough main beam and the top surface of the steel bottom beam, that is, the elastic neutral axis position h of the trough main beam 3 c :

[0028]

[0029] Furthermore, in step S6, the setting range is 0.95≤h z / h s ≤1.05.

[0030] The present invention also provides a steel-concrete composite trough beam, which is designed using the above-mentioned design method and includes: a steel bottom beam, a steel cross beam, a trough main beam and a connecting tenon. Multiple steel bottom beams are connected to form a steel frame through multiple steel cross beams. The trough main beam is placed on the top surface of the steel bottom beam and is connected to the steel bottom beam through a connecting key.

[0031] Furthermore, the trough-type main beam is a prefabricated reinforced concrete structure with an open trough-type cross-section, including a bridge deck, a web, and a flange; the trough-type main beam is prefabricated in a factory; the bridge deck is provided with a notch, and mortise and tenon grooves are provided at the end faces of the bridge deck and the web, and the connection between two adjacent trough-type main beam segments is achieved by embedding a connecting tenon into the mortise and tenon grooves on both sides, and the cross-section of the connecting tenon is funnel-shaped.

[0032] Furthermore, the steel bottom beams are arranged at equal intervals along the transverse direction of the bridge, and the steel cross beams are arranged at equal intervals along the longitudinal direction of the bridge and are welded to the steel bottom beams.

[0033] Furthermore, the cross-section of the steel bottom beam is in the shape of an I, and the upper and lower flange areas are equal.

[0034] Compared with the existing technology, the present invention has the following advantages: a design iteration process based on the position of the plastic neutral axis is proposed, and the neutral axis position of the composite section is optimized by adjusting the cross-sectional area of ​​the steel bottom beam to ensure a balance between mechanical properties and functional use; through the steel-concrete composite structure, concrete is arranged in the compression zone and steel is arranged in the tension zone, so as to give full play to the mechanical properties of the two materials, and solve the problem of prestressing demand or compressive instability of steel structure caused by tension of traditional trough beam bridge deck; fully prefabricated components are used to reduce on-site wet work, and rapid assembly is achieved through connecting tenons, without the need for additional steel bars or prestressed tendons, which significantly improves construction efficiency; through the synergistic effect of the trough main beam and the steel frame, the building height is reduced and the functional use of the trough beam is guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 1 is an overall schematic diagram of a steel-concrete composite trough beam according to an embodiment of the present invention;

[0036] Figure 2 is a cross-sectional view of a steel-concrete composite trough beam according to an embodiment of the present invention;

[0037] Figure 3 is an overall schematic diagram of a trough-type main beam in an embodiment of the present invention;

[0038] Figure 4 Schematic diagram of the top surface of a steel-concrete composite trough beam according to an embodiment of the present invention;

[0039] Figure 5 Schematic diagram of the structure of the connecting tenon in an embodiment of the present invention;

[0040] Figure 6 Schematic diagram of calculation parameters for the design method of steel-concrete composite trough beams in an embodiment of the present invention.

[0041] In the picture:

[0042] 1-Steel bottom beam; 2-Steel cross beam; 3-Trough main beam; 4-Connecting tenon; 11-Connecting key; 31-Bridge deck; 32-Web plate; 33-Flange; 34-Tongue and groove. DETAILED DESCRIPTION

[0043] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0044] Example 1

[0045] like Figures 1 to 6As shown, this embodiment provides a technical solution: a steel-concrete composite trough beam, comprising a steel bottom beam 1, a steel cross beam 2, a trough main beam 3, and a connecting tenon 4. Several steel bottom beams 1 are connected to form a steel frame via several steel cross beams 2. The trough main beam 3 is placed on top of the steel bottom beam 1 and connected by a connecting key 11 to form a combined load-bearing structure.

[0046] In this embodiment, the steel bottom beam 1 is a hot-rolled steel with an I-shaped cross section and equal upper and lower flange areas (the steel bottom beam has a symmetrical cross section). Several beams are arranged in the transverse direction of the bridge at equal intervals.

[0047] In this embodiment, the steel cross beam 2 is a hot-rolled steel with an I-shaped cross section. It is arranged at equal intervals of 3 to 5 meters along the bridge direction and is welded to the steel bottom beam 1.

[0048] In this embodiment, the channel girder 3 is a prefabricated reinforced concrete structure with an open channel cross-section, comprising a deck 31, a web 32, and flanges 33. The channel girder 3 is prefabricated in a factory, with individual segments measuring 3 to 5 meters in length. Notches 35 are provided in the deck 31, and tongue and groove grooves 34 are provided at the end surfaces of the deck 31 and the web 32.

[0049] In this embodiment, the trough-shaped main beam 3 is placed on the top surface of the steel bottom beam 1 and arranged in sequence, and the connecting tenons 4 are placed in the tenon grooves 34 to realize the connection between the various sections of the trough-shaped main beam 3.

[0050] In this embodiment, the connecting tenon 4 is a cast iron part with a funnel-shaped cross section.

[0051] This embodiment also provides a design method for the above-mentioned steel-concrete composite trough beam, comprising the following steps:

[0052] Step S1: Preliminary selection of the size and quantity of the steel bottom beam 1, the height h of the steel bottom beam 1 s Initially take 1 / 40 to 1 / 50 of the bridge span and calculate the cross-sectional area A of all steel bottom beams 1 s :

[0053] A s =mA d ;

[0054] Where m represents the number of steel bottom beams 1, A d Indicates the cross-sectional area of ​​a single steel bottom beam 1;

[0055] Step S2: Based on the cross-sectional area A of the steel bottom beam 1 s Based on the ultimate limit state design of bearing capacity and the principle that the plastic neutral axis is located on the top surface of the steel bottom beam 1, the cross-sectional area A of the trough main beam 3 is calculated. c :

[0056]

[0057] Among them, f sd Indicates the tensile design strength of the steel bottom beam 1, f cd Indicates the concrete compressive design strength of the channel main beam 3;

[0058] Step S3: Based on the cross-sectional area A of the trough main beam 3 c , determine the size of the trough main beam 3 and the elastic neutral axis position h of the trough main beam 3 c ;

[0059] It should be noted that when the size of the trough main beam 3 is determined, the parameters such as the width, height h, and plate thickness of the trough main beam 3 are mainly set.

[0060] In this embodiment, the specific processing process of the above step S3 is as follows:

[0061] Step S31: Calculate the static moment of section of the trough main beam 3:

[0062]

[0063] Among them, S x dA is the static moment of section of the trough main beam 3 to the top surface of the steel bottom beam 1, c It represents the differential of the cross-sectional area of ​​the trough main beam 3, that is, a very small area. x represents the distance from the centroid of this very small area to the top surface of the steel bottom beam 1. x represents dA c Distance to the top surface of steel bottom beam 1;

[0064] Step S32: Calculate the distance between the elastic neutral axis of the trough main beam 3 and the top surface of the steel bottom beam 1, that is, the elastic neutral axis position h of the trough main beam 3 c :

[0065]

[0066] Step S4: Calculate the neutral axis position h of the cross section of the assembly consisting of the channel main beam 3 and the steel bottom beam 1 z :

[0067]

[0068] Among them, h s Indicates the height of the steel bottom beam 1, h c Indicates the distance between the elastic neutral axis of the trough main beam 3 and the top surface of the steel bottom beam 1, Indicates the elastic modulus E of the steel bottom beam 1 s The concrete elastic modulus E of the trough main beam 3 c The ratio of

[0069] Step S5: Compare h z With h sIf h z Greater than h s If the cross-sectional area A of the single steel bottom beam 1 exceeds the set value, d Increase; if h z Less than h s If the cross-sectional area A of the single steel bottom beam 1 exceeds the set value, d reduce;

[0070] Step S6: Repeat steps S2 to S5 until the neutral axis position h of the cross section of the combination formed by the trough main beam and the steel bottom beam is z Height h from steel bottom beam s The ratio is within the set range.

[0071] Step S7: Calculate the bending bearing capacity of the cross-section of the trough beam designed in steps S1 to S6, and verify the bending bearing capacity to determine whether it meets the design requirements for bearing capacity. The bending bearing capacity calculation formula is as follows:

[0072]

[0073] Among them, M u It represents the bending bearing capacity of the composite section, and h is the height of the proposed trough main beam.

[0074] Example 2

[0075] This embodiment provides a design method for a steel-concrete composite trough beam with a design span of 35 m and a bridge deck width of 5.5 m, comprising the following steps:

[0076] Step S1: The height h of the steel bottom beam 1 s Take 1 / 50 of the bridge span, that is, h s =35m / 50=700mm, the area of ​​a single steel bottom beam is A d =21148mm 2 , the number m = 3, calculate the cross-sectional area A of all steel bottom beams 1 s :

[0077] A s =mA d =3×21148mm 2 =63444mm 2 ;

[0078] Step S2: Based on the cross-sectional area A of the steel bottom beam 1 s , according to the principle that the plastic neutral axis is located on the top surface of the steel bottom beam 1, calculate the cross-sectional area A of the trough main beam 3 c :

[0079]

[0080] Among them, f sd Indicates the tensile design strength of the steel bottom beam 1, the steel grade used is Q345, f sd Take 270MPa; f cd Indicates the concrete compressive design strength of the channel main beam 3, the concrete grade is C50, f cd Take 22.4MPa;

[0081] Step S3: Based on the cross-sectional area A of the trough main beam 3 c , the size of the trough main beam 3 is proposed, the width is 5.5m, the height h is 1.4m, and the average plate thickness can be calculated as 97mm, and the elastic neutral axis position h of the trough main beam 3 is determined. c =220mm;

[0082] Step S4: Calculate the neutral axis position h of the cross section of the assembly consisting of the channel main beam 3 and the steel bottom beam 1 z :

[0083]

[0084] Among them, h s Indicates the height of the steel bottom beam 1, h c Indicates the distance between the elastic neutral axis of the trough main beam 3 and the top surface of the steel bottom beam 1, Indicates the elastic modulus E of the steel bottom beam 1 s =2.06×10 5 MPa and the concrete elastic modulus E of the trough main beam 3 c =3.45×10 4 The ratio of MPa, that is

[0085] Step S5: Compare h z With h s The size of the steel bottom beam 1 is used to determine whether the cross-sectional area A d Adjust the neutral axis position h of the combined cross section z Height h from steel bottom beam s Ratio: 0.95≤h z / h s =731 / 700=1.04≤1.05.

[0086] Step S6: The ratio is within the set range.

[0087] Step S7: The bending bearing capacity of the combined section of the channel composite beam designed in steps S1 to S6 is calculated according to the following formula:

[0088]

[0089] Among them, Mu It represents the bending bearing capacity of the composite section;

[0090] Then, the bending bearing capacity is verified to determine whether it meets the bearing capacity design requirements.

[0091] In summary, the steel-concrete composite trough beam and its design method in the above-mentioned embodiment adopt a fully prefabricated steel-concrete composite trough beam, and the amount of wet work on site is extremely small; the steel beam segments can be connected by directly placing connecting tenons, without the need for additional steel bars and prestressed tendons; it can achieve that the concrete is fully located in the compression zone and the steel is all located in the tension zone, while obtaining a lower driving height, and achieving a reasonable balance between mechanical properties and usage functions.

[0092] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A design method for a steel-concrete composite trough beam, characterized in that: The steel-concrete composite trough beam comprises a steel bottom beam, a steel cross beam, a trough main beam and a connecting tenon. The multiple steel bottom beams are connected to form a steel frame through multiple steel cross beams. The trough main beam is placed on the top surface of the steel bottom beam and connected to the steel bottom beam through a connecting key. The steel-concrete composite trough beam design method comprises the following steps: Step S1: Preliminary selection of the size and quantity of the steel bottom beams and the height h of the steel bottom beams s And calculate the cross-sectional area A of all steel bottom beams s : A s =mA d ; Among them, m represents the number of steel bottom beams, A d Indicates the cross-sectional area of ​​a single steel bottom beam; Step S2: Based on the cross-sectional area A of all steel bottom beams s Based on the ultimate state design of bearing capacity and the principle that the plastic neutral axis is located on the top surface of the steel bottom beam, the cross-sectional area A of the trough main beam is calculated. c : Among them, f sd Indicates the tensile design strength of the steel bottom beam, f cd Indicates the concrete compressive design strength of the channel main beam; Step S3: Based on the cross-sectional area A of the trough main beam c , determine the elastic neutral axis position h of the trough main beam c ; Step S4: Calculate the neutral axis position h of the cross section of the combination formed by the channel main beam and the steel bottom beam z : Among them, h s Indicates the height of the steel bottom beam, h c Indicates the distance between the elastic neutral axis of the channel main beam and the top surface of the steel bottom beam. Indicates the elastic modulus E of the steel bottom beam s The concrete elastic modulus E of the channel main beam c The ratio of Step S5: Compare h z With h s If h z Greater than h s And its ratio exceeds the set value, the cross-sectional area A of a single steel bottom beam d Increase; if h z Less than h s And its ratio exceeds the set value, the cross-sectional area A of a single steel bottom beam d reduce; Step S6: Repeat steps S2 to S5 until the neutral axis position h of the cross section of the combination formed by the trough main beam and the steel bottom beam is z Height h from steel bottom beam s The ratio is within the set range; Step S7: Calculate the bending bearing capacity of the cross-section of the trough beam designed in steps S1 to S6, and verify the bending bearing capacity to determine whether it meets the design requirements for bearing capacity.

2. The method for designing a steel-concrete composite trough beam according to claim 1, characterized in that: In step S1, the height h of the steel bottom beam is s The initial value is 1 / 40 to 1 / 50 of the bridge span.

3. The method for designing a steel-concrete composite trough beam according to claim 1, characterized in that: In step S3, the specific processing process is as follows: Step S31: Calculate the static moment of the cross section of the trough main beam: Among them, S x dA is the static moment of the cross section of the trough main beam to the top surface of the steel bottom beam, c represents the differential of the cross-sectional area of ​​the trough main beam, and x represents dA c Distance to the top surface of the steel bottom beam; Step S32: Calculate the distance between the elastic neutral axis of the trough main beam and the top surface of the steel bottom beam, that is, the elastic neutral axis position h of the trough main beam. c :

4. The method for designing a steel-concrete composite trough beam according to claim 1, wherein: In step S6, the setting range is 0.95≤h z / h s ≤1.

05.

5. The method for designing a steel-concrete composite trough beam according to claim 1, wherein: In step S7, the bending bearing capacity calculation formula is as follows: Among them, M u It represents the bending bearing capacity of the composite section, and h is the height of the pre-planned trough main beam.

6. The method for designing a steel-concrete composite trough beam according to claim 1, characterized in that: The trough-shaped main beam is a prefabricated reinforced concrete structure with an open trough-shaped cross-section, including a bridge deck, a web, and a flange; the trough-shaped main beam is prefabricated in a factory; the bridge deck is provided with a notch, and mortise and tenon grooves are provided at the end faces of the bridge deck and the web, and the connection between two adjacent trough-shaped main beam segments is achieved by embedding a connecting tenon into the mortise and tenon grooves on both sides, and the cross-section of the connecting tenon is funnel-shaped.

7. The method for designing a steel-concrete composite trough beam according to claim 6, characterized in that: The steel bottom beams are arranged at equal intervals along the transverse direction of the bridge, and the steel cross beams are arranged at equal intervals along the longitudinal direction of the bridge and are welded to the steel bottom beams.

8. The method for designing a steel-concrete composite trough beam according to claim 7, characterized in that: The cross section of the steel bottom beam is in the shape of an I, and the upper and lower flange areas are equal.

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