Structure for improving ultimate bearing capacity of steel reinforced concrete beam

Abstract

A structure for improving ultimate bearing capacity of a steel reinforced concrete beam comprises a concrete column and the steel reinforced concrete beam, and the concrete column and the steel reinforced concrete beam are vertically connected in the axial direction. A section steel column is arranged in the concrete column, steel reinforced concrete beam inner section steel is arranged at the bottom of the steel reinforced concrete beam, and the section steel column is in rigid connection with the steel reinforced concrete beam inner section steel. The profile steel in the steel reinforced concrete beam is arranged downwards, so that the larger area of the profile steel in the steel reinforced concrete beam is located in a tension area of the steel reinforced concrete beam. According to the method, under the condition that the sagging moment of the midspan in structures such as a transfer beam in a complex building is large, the tension longitudinal bars on the lower portion can be optimized so as to meet the requirements of clear distance, cracks and the like of the steel bars. Under the condition that the section area of the section steel is not increased, the bending bearing capacity of the normal section of the composite beam is met, the consumption of the section steel is saved, and the manufacturing cost is saved.

Description

Technical Field

[0001] The invention relates to a structural method for improving the ultimate bearing capacity of a steel concrete beam, and belongs to the field of civil engineering. Background Art

[0002] Steel-concrete beams are widely used in the field of civil engineering, especially in complex buildings such as high-rise buildings and large-span industrial buildings. In structural design, designers usually place steel beams at the center of concrete beams. The role of steel beams in resisting positive bending moments at mid-span and negative bending moments at supports is roughly the same. However, in actual projects, especially in complex buildings, the bending moment of the transfer beam is usually large in the mid-span, the bottom reinforcement of the steel-concrete beam is large, and the steel bar arrangement is difficult to meet the requirements of reinforcement, cracks and structure.

[0003] The technical problems existing in the prior art are: 1. Conventional practice places the steel beam at the center of the concrete beam. The area of ​​the steel beam in the tensile zone of the concrete beam is small, and its effect on improving the positive bending moment bearing capacity is limited.

[0004] 2. When designing a structure, it is common to increase the cross-sectional size of the steel beam to obtain a greater positive moment bearing capacity. However, due to the limitations of the height-to-thickness ratio and width-to-thickness ratio of the steel beam, simply increasing the cross-sectional size of the steel beam will lead to an increase in the amount of steel used, which is not economical. Summary of the invention

[0005] The technical problem to be solved by the invention is: in view of the defects of the prior art, the present invention provides a structure for improving the ultimate bearing capacity of steel concrete beams.

[0006] The technical solution of the present invention is specifically as follows: A structure for improving the ultimate bearing capacity of a steel-concrete beam comprises a concrete column and a steel-concrete beam, wherein the concrete column and the steel-concrete beam are axially vertically connected to each other; a steel column is arranged in the concrete column, and a steel profile in the steel-concrete beam is arranged at the bottom of the steel-concrete beam, and the steel column and the steel profile in the steel-concrete beam are rigidly connected; the steel profile in the steel-concrete beam is placed downward so that a larger area of ​​the steel profile in the steel-concrete beam is located in the tension zone of the steel-concrete beam.

[0007] The inner steel section of the steel-concrete beam is located below the plastic neutral axis of the steel-concrete beam.

[0008] The inner steel of the steel concrete beam comprises an inner steel body, a top reinforcement is arranged on the top of the inner steel body, a bottom reinforcement is arranged on the bottom of the inner steel body, and a waist reinforcement is arranged in the middle of the inner steel body.

[0009] Longitudinal structural steel bars are symmetrically arranged on both sides of the steel section in the height direction of the steel concrete beam. The spacing between the longitudinal structural steel bars is not more than 200mm, and the cross-sectional area is not less than 0.1% of the cross-sectional area of ​​the beam web. The two longitudinal structural steel bars are tied together by tie bars.

[0010] The inner steel body is provided with second bolts, which are shear-resistant connectors. The second bolts are distributed on the upper flange, the lower flange or both the upper and lower flanges of the inner steel body.

[0011] The steel column comprises a steel column body, the upper and lower flanges of the steel column body are provided with first bolts, and the outer side of the steel column flange is welded with a mechanical sleeve; longitudinal reinforcement is arranged in the steel concrete beam, and when part of the longitudinal reinforcement meets the flange of the steel column, the longitudinal reinforcement is directly connected to the mechanical connection sleeve welded on the flange.

[0012] Stiffening ribs are provided on the steel columns at the positions of the mechanical connection sleeves, and holes are opened on the stiffening ribs to facilitate the pouring and vibration of concrete.

[0013] The steel-concrete beam is a cantilever steel beam section, which is connected to the next section of concrete beam via a connecting plate, on which friction-type high-strength bolts are arranged.

[0014] The beneficial effects of the present invention are: 1. The present invention can optimize the lower tensile longitudinal reinforcement to meet the requirements of steel bar clearance, cracks, etc. in the case of large positive bending moment in the mid-span of structures such as transfer beams in complex buildings.

[0015] 2. The present invention can meet the bending bearing capacity of the composite beam cross section without increasing the cross-sectional area of ​​the steel, thereby saving the amount of steel and the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a cross-sectional view of the steel-concrete composite beam of the present invention; Figure 2 This is the beam-column node diagram connecting steel concrete beam 2 and steel column 1. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0019] First, the present invention performs calculations based on the following basic assumptions: 1. The cross-sectional strain of the steel-concrete composite beam maintains the plane; 2. The tensile strength of concrete is not considered; 3. The ultimate compressive strain of the concrete at the compressed edge is taken as 0.003, and the corresponding maximum compressive stress is taken as the design value of the concrete axial compressive strength f c Multiply by the influence coefficient of concrete compressive stress in the compression zone α1; 4. The stress diagram of the steel web is a tensile and compressive trapezoidal stress diagram, which is simplified to an equivalent rectangular stress diagram during calculation; 5. The stress of steel bars and steel sections is equal to the product of the strain of the steel bars and steel sections and their elastic modulus, and its absolute value should not be greater than its corresponding strength design value; the ultimate tensile strain of longitudinal tensile steel bars and tensile flanges of steel sections is 0.01.

[0020] Based on the above assumptions, the bending bearing capacity of the steel-concrete composite beam's positive section comes from the following parts: ① The bearing capacity provided by the concrete in the compression zone; ② The bearing capacity provided by the steel bars in the compression zone; ③. Bearing capacity provided by the steel flange in the compression zone; ④. The bearing capacity provided by the steel web.

[0021] Among them, the bearing capacity provided by the steel web is the moment of the resultant axial force borne by the steel web on the resultant point of the steel tension flange and the longitudinal tension reinforcement.

[0022] According to the Code for Design of Composite Structures, the present invention adopts the limit equilibrium theory method. On the premise of satisfying the thickness of the protective layer of the steel beam and the clear distance of the lower longitudinal reinforcement arrangement, the present invention moves the inner steel 3 of the steel-concrete beam in the steel-concrete composite beam from the center position of the steel-concrete beam 2 to the bottom of the steel-concrete beam 2 (referred to as the steel beam lowering method), thereby increasing the height of the concrete compression zone, and further increasing the distance from the combined force point of the steel tension zone and the bottom tension longitudinal reinforcement to the tension edge of the cross section, so as to improve ① the bearing capacity provided by the concrete in the compression zone and ④ the bearing capacity provided by the steel web.

[0023] The purpose of moving the steel 3 in the steel concrete beam 2 downward is to make the steel web area more located in the tensile zone of the concrete beam, fully utilize the tensile strength of the steel material, and improve the bending bearing capacity of the cross section of the steel concrete composite beam. In addition, for cast-in-place floor slabs, the floor slab as the effective flange width of the beam has an impact on the beam stiffness and bearing capacity. The steel beam downward placement method can give full play to the compressive effect of the floor slab as the effective flange width of the beam, and improve the bearing capacity of the steel concrete composite beam.

[0024] like Figure 1 , Figure 2 As shown, a structure for improving the ultimate bearing capacity of a steel-concrete beam comprises a concrete column 5 and a steel-concrete beam 2, wherein the concrete column 5 and the steel-concrete beam 2 are axially connected to each other perpendicularly; a steel column 1 is arranged inside the concrete column 5, and a steel profile 3 inside the steel-concrete beam is arranged at the bottom of the steel-concrete beam 2, and the steel column 1 is rigidly connected to the steel profile 3 inside the steel-concrete beam. In this way, the present invention places the steel profile 3 inside the steel-concrete beam downward, so that a larger area of ​​the steel profile 3 inside the steel-concrete beam is located in the tensile zone of the steel-concrete beam. Without changing the cross section of the steel profile, only changing the position of the steel profile can greatly improve the bending bearing capacity of the positive section of the steel-concrete composite beam, thereby saving construction costs.

[0025] Furthermore, the steel section 3 in the steel concrete beam is located below the plastic neutral axis 4 of the steel concrete beam 2, and the height above the plastic neutral axis 4 is the height of the concrete compression zone.

[0026] The inner steel 3 of the steel concrete beam comprises an inner steel body, a top reinforcement 32 is arranged at the top of the inner steel body, a bottom reinforcement 33 is arranged at the bottom of the inner steel body, and a waist reinforcement 34 is arranged in the middle of the inner steel body.

[0027] Considering the impact of earthquakes, a stirrup reinforcement zone should be set at the beam end of the steel concrete beam 2. The stirrup reinforcement zone is located within 1.5 times the beam height of the steel concrete beam 2 from the support column. In the stirrup reinforcement zone, the diameter of the stirrup 35 is not less than 12mm, and the spacing is not greater than 100mm.

[0028] Longitudinal structural steel bars 36 are symmetrically arranged on both sides of the steel 3 in the steel concrete beam in the height direction. The spacing between the longitudinal structural steel bars 36 is not greater than 200 mm, and the cross-sectional area is not less than 0.1% of the cross-sectional area of ​​the beam web. The two longitudinal structural steel bars 36 are tied together by tie bars 37. The longitudinal structural steel bars 36 are spot welded to the web of the steel in the beam to facilitate the tie bar 37 tie construction.

[0029] The inner steel body is provided with second bolts 31 , which are shear connectors. The second bolts 31 are distributed on the upper flange, the lower flange, or both the upper and lower flanges of the inner steel body.

[0030] The outer edge of the flange of the steel section 3 in the tension zone of the steel concrete beam is 200 mm away from the outer edge of the concrete in the tension zone, which can meet the arrangement of the two rows of longitudinal tension steel bars in the lower part of the steel concrete beam 2, and can meet the requirement that one side flange of the steel section 3 in the steel concrete beam is located in the compression zone, and the other side flange is located in the tension zone.

[0031] The steel column 1 comprises a steel column body, the upper and lower flanges of the steel column body are provided with first bolts 11, and the outer side of the flange of the steel column is welded with a mechanical sleeve 12; longitudinal reinforcement is provided in the steel concrete beam 2, and when part of the longitudinal reinforcement meets the flange of the steel column 1, the longitudinal reinforcement is directly connected to the mechanical connection sleeve 12 welded on the flange. Preferably, a stiffening rib 13 is provided on the steel column 1 at the position of the mechanical connection sleeve 12, and a hole is opened on the stiffening rib 13 to facilitate concrete pouring and vibration.

[0032] Furthermore, the steel-concrete beam 2 is a cantilever steel beam section, and the steel-concrete beam 2 is connected to the next section of the concrete beam through a connecting plate 6, and a friction-type high-strength bolt 7 is provided on the connecting plate 6. As many longitudinal reinforcements as possible in the steel-concrete beam 2 pass through the beam-column node. When some longitudinal reinforcements need to pass through the connecting plate 6, a through hole should be reserved on the connecting plate 6. The through hole is prefabricated in the factory. During construction, the friction-type high-strength bolt 7 is also used as an installation bolt. After the steel in the beam is leveled and installed in place, it is connected by a fillet weld.

[0033] Furthermore, the cantilever steel beam section and the steel column 1 are connected by full penetration welds, and the weld quality grade is level one.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several changes and improvements can be made without departing from the overall concept of the present invention, which should also be regarded as the scope of protection of the present invention.

Claims

1. A structure for improving the ultimate bearing capacity of a steel concrete beam, characterized in that: The invention comprises a concrete column (5) and a steel-concrete beam (2), wherein the concrete column (5) and the steel-concrete beam (2) are axially connected to each other vertically; a steel column (1) is arranged in the concrete column (5), and a steel-concrete beam inner steel (3) is arranged at the bottom of the steel-concrete beam (2); the steel column (1) and the steel-concrete beam inner steel (3) are rigidly connected; the steel-concrete beam inner steel (3) is placed downward, so that a larger area of ​​the steel-concrete beam inner steel (3) is located in the tension zone of the steel-concrete beam (2).

2. A structure for improving the ultimate bearing capacity of a steel concrete beam according to claim 1, characterized in that: The inner steel section (3) of the steel concrete beam is located below the plastic neutral axis (4) of the steel concrete beam (2).

3. The structure for improving the ultimate bearing capacity of steel reinforced concrete beam according to claim 1, characterized in that: The inner steel (3) of the steel-concrete beam comprises an inner steel body, a top reinforcement (32) is arranged at the top of the inner steel body, a bottom reinforcement (33) is arranged at the bottom of the inner steel body, and a waist reinforcement (34) is arranged in the middle of the inner steel body.

4. The structure for improving the ultimate bearing capacity of steel reinforced concrete beams according to claim 1, characterized in that: Longitudinal structural steel bars (36) are symmetrically arranged on both sides of the steel-concrete beam along the height direction. The spacing between the longitudinal structural steel bars (36) is not greater than 200 mm, and the cross-sectional area is not less than 0.1% of the cross-sectional area of ​​the beam web. The two longitudinal structural steel bars (36) are tied together by tie bars (37).

5. The structure for improving the ultimate bearing capacity of steel reinforced concrete beam according to claim 1, characterized in that: A second bolt (31) is arranged on the inner steel body. The second bolt (31) is a shear connection piece. The second bolt (31) is distributed on the upper flange, the lower flange, or both the upper and lower flanges of the inner steel body.

6. The structure for improving the ultimate bearing capacity of steel reinforced concrete beams according to claim 1, characterized in that: The steel column (1) comprises a steel column body, first bolts (11) are arranged on the upper and lower flanges of the steel column body, and mechanical sleeves (12) are welded to the outer sides of the steel column flanges; longitudinal reinforcement is arranged in the steel concrete beam (2), and when part of the longitudinal reinforcement meets the flange of the steel column (1), the longitudinal reinforcement is directly connected to the mechanical connection sleeves (12) welded to the flange.

7. A structure for improving the ultimate bearing capacity of a steel-concrete beam according to claim 6, characterized in that: A stiffening rib (13) is provided on the steel column (1) at the position of the mechanical connection sleeve (12), and holes are opened on the stiffening rib (13) to facilitate concrete pouring and vibration.

8. The structure for improving the ultimate bearing capacity of steel reinforced concrete beams according to claim 1, characterized in that: The steel concrete beam (2) is a cantilever steel beam section. The steel concrete beam (2) is connected to the next section of concrete beam via a connecting plate (6). Friction-type high-strength bolts (7) are provided on the connecting plate (6).

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