Reinforcement design method for resisting progressive collapse of steel support

Abstract

The invention discloses an anti-progressive-collapse reinforcement design method for a steel support, belongs to the field of buildings, and solves the problem of how to design the steel support for progressive collapse. The method comprises the following steps: calculating a limit load beta max of a structure, and defining a critical load coefficient lambda as a ratio of a design load to the limit load; assuming that the number of the supports is k, the bearing capacity provided by a single support is (1-lambda) * (1.2 DL + 0.5 LL) / k; according to the method, a reinforced column and another adjacent column are dismantled at the same time, and the bearing capacity provided by a single support in different working conditions is calculated; the maximum bearing capacity max [(1-lambda) * (1.2 DL + 0.5 LL) / k] provided by a single support in all working conditions is obtained, and the axial force of the single support can be obtained according to a structural mechanics formula; and checking calculation and model selection are carried out on a single support section according to 'Steel Structure Design Standard' (GB 50017-2017).

Description

Technical Field

[0001] The invention belongs to the field of construction, and in particular relates to a steel support anti-progressive collapse reinforcement design method. Background Art

[0002] Progressive collapse refers to a chain reaction in which a partial or complete collapse of a building is caused by accidental factors such as explosions, vehicle collisions, and heavy impacts. It is a type of damage in which the initial damage state is disproportionate to the final damage state. Studies have found that adding steel supports can effectively improve the building's resistance to progressive collapse.

[0003] Steel braces can improve the progressive collapse resistance of frame structures (reinforced concrete frames, steel frames and steel-concrete frames), but brace design is usually based on seismic reinforcement or stability, and there is currently no steel brace design method for progressive collapse. Summary of the invention

[0004] The purpose of the present invention is to provide a steel support anti-progressive collapse reinforcement design method to solve the problem of how to design steel supports for progressive collapse.

[0005] The technical solution of the present invention is: a steel support anti-progressive collapse reinforcement design method, comprising the following steps: S1. Calculate the ultimate load of the structure using the incremental dynamic analysis method β max , define the critical load factor λ is the ratio of design load to ultimate load; S2. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load. Assuming that the continuous anti-collapse capacity provided by the frame and the support is independent of each other, the load to be borne by the support to be designed is (1−λ)×(1.2 DL +0.5 LL ); S3, instantly dismantle the reinforced column and an adjacent column at the same time; S4. Apply a force of magnitude of λ (1.2 ×DL +0.5 ×LL ) load, the maximum value of λ is 1, and it decreases in an arithmetic progression. The load applied to the remaining floors of the structure is 1.0×(1.2 ×DL +0.5 ×LL ) load, conduct nonlinear dynamic analysis and monitor the maximum displacement of the removed column position; S5. When the maximum vertical displacement of the column to be removed is greater than L / 5, indicating that the structure has collapsed. At this time, the bearing capacity provided by the support can be calculated as (1- λ )×(1.2 DL +0.5 LL ); S6. Assume that the number of supports is k , then the bearing capacity provided by a single support is (1- λ )×(1.2 DL +0.5 LL ) / k ; S7, repeating steps S3 to S6, respectively removing the reinforced column and another column adjacent to it at the same time, and calculating the bearing capacity provided by a single support in different working conditions; S8, obtain the maximum bearing capacity max[(1- λ )×(1.2DL+0.5LL) / k], the single support axial force can be obtained according to the structural mechanics formula; S9. When designing for compression support reinforcement, the single support cross-section shall be checked and selected according to Formula 7.2.1 of the "Standard for Design of Steel Structures" (GB50017-2017); when designing for tension support reinforcement, the single support cross-section shall be checked and selected according to Formula 7.1.1 of the "Standard for Design of Steel Structures".

[0006] As a further improvement of the present invention, in step S1, the incremental power analysis method includes the following steps: A. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load; B. Instantaneous removal of a single reinforced column; C. Apply a force of magnitude of β (1.2 ×DL +0.5 ×LL ) load, load factor β The minimum value is 1, and the value increases in an arithmetic progression. After the columns are removed, the failure span of the structure is monitored. The value of 1.0×(1.2 ×DL +0.5 ×LL ) loads to perform nonlinear dynamic analysis; D. When the maximum vertical displacement of the column removal position is L / 5 (collapse judgment standard), β=β max , indicating that the applied load is the maximum load that does not cause the structure to collapse after the column is removed. β max This is the ultimate load of the structure.

[0007] The beneficial effects of the present invention are as follows: the present invention proposes a simple and operable steel support anti-continuous collapse reinforcement design method, which can use both conventional design software and finite element software to carry out anti-continuous collapse reinforcement design of reinforced concrete frames, steel frames, and steel concrete frames, and has good reliability. The present invention provides reliable support through reasonable design, in order to ensure the overall stability of the building structure, improve the lateral stiffness and transmit the longitudinal horizontal force, the reinforced structure has better seismic performance and greater structural ductility. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a plan view of the framework structure of a specific embodiment of the present invention; Figure 2 is a load-deflection curve of a specific embodiment of the present invention; Figure 3 is a flow chart of the incremental power analysis method of the present invention; Figure 4 is a schematic diagram of a compression support according to a specific embodiment of the present invention; Figure 5 is a schematic diagram of a tension support according to a specific embodiment of the present invention; Figure 6 It is a force analysis diagram of a compression support according to a specific embodiment of the present invention; Figure 7 It is a force analysis diagram of a tension support according to a specific embodiment of the present invention; Figure 8 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0009] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0010] Embodiment 1, Take a 6-story frame structure as an example, the floor height is h, and the frame structure layout is as follows: Figure 1 As shown in the figure, the horizontal span of the frame structure is L, and the vertical span is H (assuming L>H).

[0011] S1. Calculate the ultimate load of the structure using the incremental dynamic analysis method β max ,like Figure 3 As shown, the specific steps are as follows: A. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load; B. Instantaneous removal of a single reinforced column, e.g. Figure 1 As shown, removal Figure 1 Layer 1 For axial frame columns, the column removal time is 10% of the remaining structure natural vibration period; C. Within the failure range of the removed column (i.e. Figure 1 In Range floor, involving the 2nd to 6th floor) the size of the application is β (1.2 ×DL +0.5 ×LL ) load, load factor β The minimum value is 1, and the number increases in an arithmetic progression with a common difference of 0.5 (i.e. β Take 1, 1.5, 2, 2.5, 3, 3.5... β max ), monitor the failure span of the structure after column removal (the vertical displacement of each measuring point of the beam is obtained to obtain the load-speed curve, such as Figure 2 As shown in the figure), the remaining floor slabs in the structure are applied with a size of 1.0×(1.2 ×DL +0.5 ×LL ) loads to perform nonlinear dynamic analysis; D. When the maximum vertical displacement of the column removal position is L / 5 (collapse judgment standard), β=β max , indicating that the applied load is the maximum load that does not cause the structure to collapse after the column is removed. β max is the ultimate load of the structure; Then define the critical load factor λ is the ratio of design load to ultimate load, where the design load is the actual load applied to the structure; λ Less than 1 means that the structure will collapse under the design load; When the axis frame column and its adjacent frame column, the remaining structure λ ≤1, therefore, the structure needs to be reinforced to resist progressive collapse.

[0012] S2. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load. Assuming that the continuous anti-collapse capacity provided by the frame and the support is independent of each other, the load to be borne by the support to be designed is (1−λ)×(1.2 DL +0.5 LL ).

[0013] S3, instantly dismantle the reinforced column and its adjacent column at the same time ( Axis frame column and Axis frame column), the column removal time is taken as 10% of the remaining structure natural vibration period.

[0014] S4, in the failure range (i.e. Figure 1 In Range floor, involving the 2nd to 6th floor) applies a magnitude of λ (1.2 ×DL +0.5 ×LL ) load, λ is taken as 1 at most, and decreases in an arithmetic progression (with a tolerance of 0.05) (i.e., λ is taken as 1, 0.95, 0.90, 0.85…), and the load applied to the remaining floors of the structure is 1.0×(1.2 ×DL +0.5 ×LL ) load, perform nonlinear dynamic analysis and monitor the maximum displacement of the removed column position.

[0015] S5. When the maximum vertical displacement of the column to be removed is greater than L / 5, indicating that the structure has collapsed. At this time, the bearing capacity provided by the support can be calculated as (1- λ )×(1.2 DL +0.5 LL ).

[0016] S6. Assume that the number of supports is k , then the bearing capacity provided by a single support is (1- λ )×(1.2 DL +0.5 LL ) / k .

[0017] S7, repeat steps S3 to S6, and simultaneously remove the reinforced column and another column adjacent to it (i.e., simultaneously remove Axis frame column and Axis frame column, Axis frame column and Axis frame column, Axis frame column and Axis frame column), calculate the bearing capacity provided by a single support in different working conditions respectively.

[0018] S8, obtain the maximum bearing capacity max[(1- λ )×(1.2DL+0.5LL) / k], the single support axial force can be calculated according to the structural mechanics formula.

[0019] S9. When the compression support (i.e. Figure 4 When designing the reinforcement of the steel structure (support shown in the figure), the cross section of a single support is selected and calculated according to Formula 7.2.1 of the "Standard for Design of Steel Structures" (GB 50017-2017). The stress analysis diagram of the compression support is as follows: Figure 6 As shown, the force on a single support is N=Pcosθ / 2, where P is the design value of the load borne by the failed column and θ is the angle between the support and the horizontal direction. Figure 5When designing the reinforcement of the support shown in the figure, the single support section is selected according to the calculation formula 7.1.1 of the "Steel Structure Design Standard". The stress analysis diagram of the tensile support is as follows: Figure 7 As shown, similarly, the single support force is N=Pcosθ / 2.

[0020] The method flow of the above steps S2 to S9 is as follows Figure 8 As shown, in the figure, i represents the working condition.

[0021] Through nonlinear analysis, it can be obtained that the steel support anti-progressive collapse design method proposed in the present invention can greatly improve the anti-progressive collapse capability of the structure.

Claims

1. A steel support anti-progressive collapse reinforcement design method, characterized in that The following steps are involved: S1. Calculate the ultimate load of the structure using the incremental dynamic analysis method β max , define the critical load factor λ is the ratio of design load to ultimate load; S2. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load. Assuming that the continuous anti-collapse capacity provided by the frame and the support is independent of each other, the load to be borne by the support to be designed is (1−λ)×(1.2 DL +0.5 LL ); S3, instantly dismantle the reinforced column and an adjacent column at the same time; S4, apply a magnitude of λ (1.2 ×DL +0.5 ×LL ) load, the maximum value of λ is 1, and it decreases in an arithmetic progression. The load applied to the remaining floors of the structure is 1.0×(1.2 ×DL +0.5 ×LL ) load, conduct nonlinear dynamic analysis and monitor the maximum displacement of the removed column position; S5. When the maximum vertical displacement of the column to be removed is greater than L / 5, indicating that the structure has collapsed. At this time, the bearing capacity provided by the support can be calculated as (1- λ )×(1.2 DL +0.5 LL ); S6. Assume that the number of supports is k , then the bearing capacity provided by a single support is (1- λ )×(1.2 DL +0.5 LL ) / k ; S7, repeating steps S3 to S6, respectively removing the reinforced column and another column adjacent to it at the same time, and calculating the bearing capacity provided by a single support in different working conditions; S8, obtain the maximum bearing capacity max[(1- λ )×(1.2DL+0.5LL) / k], the single support axial force can be obtained according to the structural mechanics formula; S9. When designing for compression support reinforcement, the single support section shall be in accordance with the "Steel Structure Design Standard" (GB 50017-2017) The selection shall be made in accordance with Formula 7.2.

1. When the design is based on the tension support reinforcement, the single support section shall be selected in accordance with Formula 7.1.1 of the Steel Structure Design Standard.

2. A steel support anti-progressive collapse reinforcement design method according to claim 1, characterized in that: In step S1, the incremental dynamic analysis method includes the following steps: A. The entire structure is loaded in a quasi-static manner with a load of (1.2DL+0.5LL), where DL represents the dead load and LL represents the live load; B. Instantaneous removal of a single reinforced column; C. Apply a force of magnitude β (1.2 ×DL +0.5 ×LL ) load, load factor β The minimum value is 1, and the value increases in an arithmetic progression. After the columns are removed, the failure span of the structure is monitored. The value of 1.0×(1.2 ×DL +0.5 ×LL ) loads to perform nonlinear dynamic analysis; D. When the maximum vertical displacement of the column removal position is L / 5, β=β max , which is the ultimate load of the structure.

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