A thin steel bottom plate steel web u-shaped beam made of uhp concrete and a method for calculating the bending bearing capacity

Abstract

The application discloses a kind of thin steel bottom plate steel web UHPC combined I-beam and bending bearing capacity calculation method, including UHPC upper flange, UHPC lower flange, steel web, further including PBL shear key, thin steel bottom plate;PBL shear key is arranged on UHPC lower flange, and thin steel bottom plate is arranged above PBL shear key;The lower end of steel web is welded and fixed with the contact part of thin steel bottom plate;The connection strength of steel web and UHPC lower flange is strengthened by PBL shear key and thin steel bottom plate.Thin steel bottom plate and steel web, PBL shear key as a whole component, reliably connect with UHPC upper flange, UHPC lower flange, form whole, jointly resist external force, compared with traditional UHPC steel web I-beam, the thin steel bottom plate steel web UHPC combined I-beam proposed in the application has the advantages of large overall rigidity, small deformation, large bending bearing capacity etc..

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering technology, specifically relating to a UHPC composite I-beam with a thin steel base plate and steel truss web and a method for calculating its bending bearing capacity. Background Technology

[0002] Solid-web composite beams are widely used in bridge engineering, enabling prefabrication and assembly of bridges and significantly reducing construction time, thus showing great development potential. Specific structural forms include steel truss composite box girders (I-beams) and corrugated steel web composite box girders. With the rapid development of high-performance materials UHPC and ECC, steel truss UHPC composite beams and corrugated steel web UHPC composite beams have emerged. From the perspective of structural stress performance and span capacity, high-performance composite beams can meet the requirements of large spans and high durability, but some design details still need further improvement.

[0003] High-performance concrete composite beams with steel trusses have good spanning capacity and durability, but there are some problems with their local stress and failure modes. For example, at the joints of the steel trusses, they are often cast together with the bottom slab concrete through PBL shear keys to share the load. However, from the perspective of the weak points of structural failure, the joint between the PBL shear keys and the high-performance concrete is prone to tensile failure, which greatly weakens the load-bearing capacity of the structure. Summary of the Invention

[0004] This invention provides a UHPC composite I-beam with a thin steel base plate and steel truss web for bridges, aiming to solve the problem of localized damage at the connection between the shear key and high-performance concrete in the UHPC composite I-beam with a thin steel base plate and steel truss web.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] A composite I-beam of UHPC with thin steel bottom plate and steel truss web for bridges includes an upper flange of UHPC, a lower flange of UHPC, a steel truss web, and a reinforcing structure connected between the lower flange of UHPC and the steel truss web, thereby improving the connection strength between the steel truss web and the lower flange of UHPC.

[0007] Furthermore, the reinforcing structure consists of a PBL shear key and a thin steel base plate;

[0008] The PBL shear key is installed on the lower flange of the UHPC, and the thin steel base plate is installed above the PBL shear key; the lower end of the steel truss web is welded and fixed to the contact part of the thin steel base plate; the connection strength between the steel truss web and the lower flange of the UHPC is strengthened by the PBL shear key and the thin steel base plate.

[0009] PBL shear keys and thin steel base plates are all arranged on the lower flange of UHPC. The upper flange and lower flange of UHPC are cast in place using formwork and high temperature wet curing method. The formwork is removed after the concrete reaches the design strength and the concrete is poured to form an integral structure.

[0010] Furthermore, the diagonal bracing is made of H-beams, and the vertical bracing at the ends of the I-beams is made of box-shaped steel.

[0011] Furthermore, steel mesh is also tied to the upper and lower flanges of the UHPC. The steel mesh of the upper flange of the UHPC is tied together with the studs, and the steel mesh of the lower flange of the UHPC is tied together with the PBL shear key and the perforated steel bars to form a whole. The structure is combined into a whole through the steel mesh.

[0012] Furthermore, the design method for the flexural bearing capacity of I-beams is as follows:

[0013] b f ' is the effective width of the upper and lower flanges, h f ' is the thickness of the upper flange UHPC plate, h b 't' represents the thickness of the lower flange UHPC plate. s Where is the thickness of the thin steel base plate, h is the beam height, α is the angle between the diagonal web member and the chord member, and l is the span. d Width of a single main truss section; Based on the principle of equal shear deformation, the steel truss web is equivalent to a flat steel plate, then the equivalent flat steel plate thickness t w for:

[0014] (1)

[0015] Where: μ is the Poisson's ratio of steel, A f The cross-sectional area of ​​the web member;

[0016] Based on the different locations of the pressure zone height x, they are divided into the first category ( ) and second type T section ( The judgment conditions are as follows:

[0017] (2)

[0018] In the formula: A s f is the cross-sectional area of ​​the steel plate, including the equivalent flat steel plate and the thin steel base plate; cd Strength design value

[0019] G s and G s ' is the point of application of the resultant force of the steel plates in the tension and compression zones, x is the height of the compression zone, and h' is the beam height ignoring the concrete base slab, i.e., h' = h - h b ',y st y is the distance from the point of application of the resultant force of the steel plate in the tension zone to the lower edge of the beam. stty is the distance from the point of application of the resultant force of the steel plate in the tension zone to the neutral axis. sc y is the height of the compressed steel plate. sc / 2 is the distance from the point of application of the resultant force of the compressed steel plate to the neutral axis;

[0020] Based on the stress distribution at the ultimate limit state of the bearing capacity of the first type of composite beam, and according to the longitudinal force equilibrium condition, we can obtain:

[0021] (3)

[0022] Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows:

[0023] (4)

[0024] Where: M pu This refers to the flexural bearing capacity of the composite beam.

[0025] Based on the stress distribution at the ultimate limit state of the bearing capacity of the second type of composite beam, and according to the longitudinal force equilibrium condition, we can obtain:

[0026] (5)

[0027] In the formula: A sc This is the equivalent cross-sectional area of ​​a flat steel plate under compression.

[0028] Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows:

[0029] (6).

[0030] The beneficial effects of this invention are as follows:

[0031] 1. The thin steel base plate, steel truss web, and PBL shear key are integrated as a whole and reliably connected to the upper flange and lower flange of the UHPC to form a whole and jointly resist external forces. Compared with the traditional UHPC steel truss web I-beam, the thin steel base plate steel truss web UHPC composite I-beam proposed in this invention has the advantages of large overall stiffness, small deformation, and large bending bearing capacity.

[0032] 2. Embedding thin steel base plates in UHPC can significantly improve the bending resistance and durability of UHPC base plates. On the one hand, the thin steel base plate is closely integrated with the lower flange UHPC to share the load, thereby improving the bending load capacity of the base plate. On the other hand, the steel base plate embedded in concrete can play a role in corrosion prevention, thereby improving the overall durability of the structure.

[0033] 3. This invention enables the factory prefabrication of lightweight I-beams and rapid bridge construction. The thin steel base plate and steel truss web can be welded and installed in the factory, and then UHPC can be poured. When transported to the construction site, the prefabricated bridge deck can be assembled and the asphalt pavement can be poured on-site. Attached Figure Description

[0034] Figure 1 This is a structural schematic diagram of an existing conventional steel truss UHPC composite beam;

[0035] Figure 2 This is a schematic diagram of the UHPC composite I-beam with thin steel base plate and steel truss web of the present invention;

[0036] Figure 3 This is a schematic diagram of the I-beam girder web structure of the present invention;

[0037] Figure 4 yes Figure 3 Schematic diagram of the shear key structure in PBL;

[0038] Figure 5 yes Figure 3 A schematic diagram of the structure of component 8;

[0039] Figure 6 yes Figure 3 A schematic diagram of the structure of component 9;

[0040] Figure 7 This is a schematic diagram of the binding of the steel mesh on the upper and lower flanges of the I-beam of the present invention;

[0041] Figure 8 This is a schematic diagram of the concrete pouring and curing process for an I-beam UHPC (Ultra-High-Pressure Concrete) structure.

[0042] Figure 9 This is a construction sequence diagram of the present invention;

[0043] Figure 10 This is a schematic diagram of the equivalent flat steel web of a steel truss.

[0044] Figure 11 These are stress distribution diagrams of the ultimate bending capacity of two types of cross sections.

[0045] Figure 12 This is a schematic diagram of the cross-sectional dimensions of an embodiment of the present invention;

[0046] Figure 13 This is a schematic diagram of the finite element model of an embodiment of the present invention;

[0047] Figure 14 This is a schematic diagram of the model unit type in an embodiment of the present invention;

[0048] Figure 15 This is the UHPC constitutive model of an embodiment of the present invention;

[0049] Figure 16 This is a deformation diagram of the improved composite beam according to an embodiment of the present invention;

[0050] Figure 17 This is a deformation diagram of a conventional composite beam according to an embodiment of the present invention;

[0051] Figure 18 These are two types of combined I-beam load-deflection curves;

[0052] Figure 19 It involves calculating the geometric properties of two types of beam sections.

[0053] In the figure: 1-UHPC upper flange, 2- steel truss web, 3- UHPC lower flange, 4- stud, 5- truss web node plate, 6- thin steel bottom plate, 7- PBL shear key. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0055] 1. This invention proposes a UHPC composite I-beam with a thin steel base plate and steel truss web, comprising a UHPC upper flange 1, a UHPC lower flange 3, a steel truss web 2, and also includes a PBL shear key 7 and a thin steel base plate 6.

[0056] The processing method includes the following parts: (1) processing of steel truss web, including welding of H-beams, welding of thin steel base plates, processing of PBL shear keys and studs; (2) binding of steel mesh on the upper and lower flanges of the I-beam; (3) pouring and curing of UHPC concrete on the upper and lower flanges. The detailed processing method is as follows:

[0057] (1) Welding of H-beams for girder, welding of thin steel base plate, fabrication of PBL shear keys and studs.

[0058] I-beam truss structure, such as Figure 3 As shown, the diagonal bracing uses H-beams, and the vertical beam ends use box-section steel. Both the H-beams and box-section steel are welded. The lower sides of the diagonal and vertical bracing are welded to the thin steel base plate. The PBL shear key has the following cross-sectional form and connection method: Figure 4 As shown. Figure 5 The connection plate between the end vertical member and the chord member is constructed. Figure 6 The gusset plate is used to connect the diagonal members of the truss web to the chord members. The gusset web and the upper flange gusset plate and studs are welded together. The gusset web and the lower flange thin steel base plate and PBL shear key are welded together.

[0059] (2) Binding of steel mesh on the upper and lower flanges of the I-beam

[0060] To ensure coordinated operation between the upper and lower flanges of the UHPC I-beam and the truss web, steel mesh is tied to the upper and lower flanges of the I-beam, such as... Figure 7As shown, the upper flange steel mesh is tied together with the studs, and the lower flange steel mesh is tied together with the PBL shear key and the perforated steel bars to form a whole. The steel mesh is used to combine the structure into a whole.

[0061] (3) Curing of UHPC concrete for I-beams

[0062] The upper and lower flanges of the cast-in-place I-beams using UHPC concrete were cured with high-temperature wet curing. Formwork was removed only after the concrete reached its design strength. Figure 8 As shown.

[0063] 2. Calculation of Bending Capacity of UHPC Composite I-beam with Thin Steel Base Plate and Steel Truss Web

[0064] like Figure 10 This is a schematic diagram of a UHPC composite beam with a thin steel base plate and steel truss web, shown in figure b. f ' is the effective width of the upper and lower flanges, h f ' is the thickness of the upper flange UHPC plate, h b 't' represents the thickness of the lower flange UHPC plate. s Where is the thickness of the thin steel base plate, h is the beam height, α is the angle between the diagonal web member and the chord member, and l is the span. d Width of a single main truss section; Based on the principle of equal shear deformation, the steel truss web is equivalent to a flat steel plate, then the equivalent flat steel plate thickness t w for:

[0065] (1)

[0066] Where: μ is the Poisson's ratio of steel, A f Let be the cross-sectional area of ​​the web member.

[0067] When calculating the flexural capacity of composite beams, the following basic assumptions are introduced based on plasticity theory: ① The connection between the steel-concrete composite section is reliable and without slippage; ② The concrete below the neutral axis is no longer contributing, and the tensile force is entirely borne by the steel plate, neglecting the contribution of the longitudinal reinforcement in the tension and compression zones; ③ The stress distribution in the compression zone concrete is rectangular, and its stress is taken as the design strength value f. cd ④ In the tension and compression zones, the steel plate undergoes plastic deformation, and the stress is distributed in a rectangular pattern. Its strength is uniformly taken as f. d =f d When an I-beam reaches its ultimate bearing capacity, the concrete in the tension zone has ceased to function, and it can be designed and calculated as a T-beam. Based on the location of the compression zone height x, it is classified into the first category (…). ) and second type T section ( The judgment conditions are as follows:

[0068] (2)

[0069] In the formula: A sThe cross-sectional area of ​​the steel plate includes the equivalent flat steel plate and the thin steel base plate.

[0070] Based on the failure characteristics, when the composite beam reaches its ultimate limit state, the concrete in the tension zone ceases to function. Ignoring the contribution of the tensile reinforcement, the stress distribution in the section is as follows: Figure 11 As shown, Figure 11 (a) and 11(b) correspond to the first and second type T sections, respectively. In the figure, G s and G s ' is the point of application of the resultant force of the steel plates in the tension and compression zones, x is the height of the compression zone, and h' is the beam height ignoring the concrete base slab, i.e., h' = h - h b ',y st y is the distance from the point of application of the resultant force of the steel plate in the tension zone to the lower edge of the beam. stt y is the distance from the point of application of the resultant force of the steel plate in the tension zone to the neutral axis. sc y is the height of the compressed steel plate. sc / 2 is the distance from the point of application of the resultant force on the compressed steel plate to the neutral axis; combined with Figure 11 (a) The stress distribution at the ultimate limit state of the bearing capacity of the first type of composite beam can be obtained from the longitudinal force equilibrium condition:

[0071] (3)

[0072] Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows:

[0073] (4)

[0074] Where: M pu This refers to the flexural bearing capacity of the composite beam.

[0075] Combination Figure 11 (b) The stress distribution at the ultimate limit state of the bearing capacity of the second type of composite beam can be obtained from the longitudinal force equilibrium condition:

[0076] (5)

[0077] In the formula: A sc This is the equivalent cross-sectional area of ​​a flat steel plate under compression.

[0078] Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows:

[0079] (6)

[0080] 3. Comparison of Bending Performance between Thin Steel Base Plate Steel Truss Web UHPC Composite I-Beam and Traditional Composite I-Beam

[0081] like Figure 12The diagram shows a UHPC composite I-beam cross-section, simply supported at both ends, with a span of l=30m. Specific dimensions are shown in the figure. The steel type is Q345. The lower flange is reinforced with 15 Φ20 longitudinal reinforcing bars. Other non-reinforcing bars and distribution bars are selected according to structural requirements. The cross-sectional area of ​​the steel truss web is A. f =9000mm 2 According to the shear equivalent flat steel plate thickness t w =293mm; Models of thin-steel base plate steel truss UHPC composite I-beams and traditional UHPC composite I-beams were created using Abaqus finite element software, such as... Figure 13 As shown, the unit types used for the truss web, thin steel base plate, concrete, and reinforcing steel are as follows: Figure 14 As shown, the elastic modulus E of UHPC material c =45 GPa, Poisson's ratio μ c =0.22, the plastic stage adopts as follows Figure 15 The stress-strain relationship shown represents the elastic modulus E of the steel. s =206 GPa, Poisson's ratio μ s =0.3; Finite element deformation diagrams of two types of I-beams are as follows Figure 16 and 17 As shown, the corresponding load-deflection curve is as follows: Figure 11 As shown; using the calculation method of this invention, the flexural bearing capacity of two types of I-beams is calculated and compared, and the cross-sectional geometric parameters are as follows. Figure 12 As shown.

[0082] Depend on Figure 12-15 It can be seen that the bending bearing capacity of the UHPC composite I-beam with thin steel base plate and steel truss web is significantly greater than that of the traditional UHPC composite I-beam. The corresponding ultimate loads are 1151.9kN and 103.8kN, respectively, which is nearly 11 times higher. The corresponding ultimate deflections are 82cm and 37cm, respectively, which is about 2 times higher than that of the traditional UHPC composite I-beam. This indicates that the UHPC composite I-beam with thin steel base plate and steel truss web has a more significant bearing capacity and ductility than the traditional UHPC composite I-beam. It effectively utilizes the material advantages of the UHPC top plate's compressive strength and the steel base plate's tensile strength, and is easy to prefabricate in the factory and assemble on site. It has advantages in mechanical properties, construction convenience, and economy.

[0083] According to the material properties table, f d =270MPa, f cd =80MPa, b f =3500mm, calculate the bearing capacity of the composite beam with thin steel base plate and steel truss web, with cross-sectional dimensions as follows: Figure 19 As shown, the cross-sectional area A of the steel plate of the I-beam is... s =447480mm 2 (Including equivalent flat steel web and thin steel bottom plate); according to It is determined to be a second type of T-section; the cross-sectional area A of the compressed flat steel plate is obtained from equation (5). sc =130406.7mm 2 Therefore, the height y of the flattened steel plate can be obtained. sc =445mm, y stt =528.2mm; Substituting this into equation (6), the flexural bearing capacity of the improved truss composite beam is: .

[0084] Similarly, to calculate the flexural bearing capacity of a traditional steel truss composite beam, the cross-sectional dimensions are as follows: Figure 19 As shown, the equivalent flat steel web area A of the I-beam cross-section is... s =398480mm 2 (Only the equivalent flat steel web is included); according to It is determined to be a second type of T-section; the cross-sectional area A of the compressed flat steel plate is obtained from equation (5). sc =105906.7mm 2 Calculate the height y of the flattened steel plate under pressure. sc =361.5mm, the distance y from the point of application of the resultant force of the steel plate in the tension zone to the neutral axis. stt =499.3mm; Substituting this into equation (6), the bending bearing capacity of the traditional steel truss composite beam is: Compared with traditional steel truss web beams, the bending bearing capacity of the thin steel bottom plate steel truss web composite I-beam is increased by 21.7%.

Claims

1. A UHPC composite I-beam with thin steel bottom plate and steel truss web for bridges, comprising a UHPC upper flange, a UHPC lower flange, and a steel truss web, characterized in that, It also includes a reinforcing structure that connects the lower flange of the UHPC and the steel truss web to improve the connection strength between the steel truss web and the lower flange of the UHPC.

2. The UHPC composite I-beam for bridges with thin steel bottom plate and steel truss web as described in claim 1, characterized in that, The reinforcing structure consists of a PBL shear key and a thin steel base plate. The PBL shear key is installed on the lower flange of the UHPC, and the thin steel base plate is installed above the PBL shear key; The lower end of the steel truss web is welded and fixed to the contact area of ​​the thin steel base plate; the connection strength between the steel truss web and the lower flange of the UHPC is strengthened by PBL shear keys and the thin steel base plate. PBL shear keys and thin steel base plates are all arranged on the lower flange of UHPC. The upper flange and lower flange of UHPC are cast in place using formwork and high temperature wet curing method. The formwork is removed after the concrete reaches the design strength and the concrete is poured to form an integral structure.

3. A UHPC composite I-beam for bridges with a thin steel bottom plate and steel truss web, as described in claim 2, is characterized in that... The web of the steel truss includes diagonal members and vertical members. The diagonal members are made of H-beams, and the vertical members at the ends of the I-beams are made of box-shaped steel.

4. A UHPC composite I-beam for bridges with a thin steel bottom plate and steel truss web, as described in claim 2, is characterized in that... Steel mesh is also tied to the upper and lower flanges of the UHPC. The steel mesh of the upper flange of the UHPC is tied together with the studs, and the steel mesh of the lower flange of the UHPC is tied together with the PBL shear key and the perforated steel bars as a whole. The steel mesh is used to combine the structure into a whole.

5. The design method for UHPC composite I-beams with thin steel bottom plates and steel trusses for bridges according to any one of claims 1-4, characterized in that, The design method is as follows: b f ' is the effective width of the upper and lower flanges, h f ' is the thickness of the upper flange UHPC plate, h b 't' represents the thickness of the lower flange UHPC plate. s Where is the thickness of the thin steel base plate, h is the beam height, α is the angle between the diagonal web member and the chord member, and l is the span. d Width of a single main truss section; Based on the principle of equal shear deformation, the steel truss web is equivalent to a flat steel plate, then the equivalent flat steel plate thickness t w for: (1) Where: μ is the Poisson's ratio of steel, A f The cross-sectional area of ​​the web member; Based on the different locations of the pressure zone height x, they are divided into the first category ( ) and the second type T section ( The judgment conditions are as follows: (2) In the formula: A s f is the cross-sectional area of ​​the steel plate, including the equivalent flat steel plate and the thin steel base plate; cd Strength design value G s and G s ' is the point of application of the resultant force of the steel plates in the tension and compression zones, x is the height of the compression zone, and h' is the beam height ignoring the concrete base slab, i.e., h' = h - h b ',y st y is the distance from the point of application of the resultant force of the steel plate in the tension zone to the lower edge of the beam. stt y is the distance from the point of application of the resultant force of the steel plate in the tension zone to the neutral axis. sc y is the height of the compressed steel plate. sc / 2 is the distance from the point of application of the resultant force of the compressed steel plate to the neutral axis; Based on the stress distribution at the ultimate limit state of the bearing capacity of the first type of composite beam, and according to the longitudinal force equilibrium condition, we can obtain: (3) Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows: (4) Where: M pu This refers to the flexural bearing capacity of the composite beam. Based on the stress distribution at the ultimate limit state of the bearing capacity of the second type of composite beam, and according to the longitudinal force equilibrium condition, we can obtain: (5) In the formula: A sc This is the equivalent cross-sectional area of ​​a flat steel plate under compression. Point G of the resultant force of the steel plate in the tension zone s With the moment center as the equation, the moment balance equation is as follows: (6)。

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