Method and structure for early warning of overload collapse of concrete beamless floor underground garage

Abstract

The present invention provides a method and structure for early warning of overload collapse of underground garages with reinforced concrete beamless floor, and controls the destruction order of each component so that when the garage is overloaded and damaged and loses its use function, it will not collapse, and the destruction of the garage is accompanied by significant collapse signs. The present invention is different from the commonly used early warning: it is necessary to determine the early warning parameters, special instruments and equipment, and professional technicians. Since there will be obvious bending, cracks, falling concrete, and falling fill, ordinary people can know with common sense that the house is unusable and will collapse. The present invention is to first make the garage lose its use function, and then stop the overloading activity. Unless it is deliberately destroyed, it will not collapse when the overload damage forms an early warning. The present invention has a novel concept, a reasonable design, and a low cost. After implementation, it can reduce casualties and protect the lives of ordinary people.

Description

Technical Field

[0001] The invention relates to an underground garage with a reinforced concrete beamless floor, and in particular to a method and a structure for early warning of overload collapse of an underground garage with a concrete beamless floor. Background Art

[0002] In the field of construction engineering, the collapse of underground garages with beamless floors due to overload has occurred frequently. The reinforced concrete beamless floor structure, also known as the slab-column seismic wall structure, is composed of reinforced concrete columns, reinforced concrete walls, floor slabs and other components; because there are no reinforced concrete beams, it is called a beamless floor. The floor slab is divided into two types: with column caps and without column caps. The column cap floor slab is commonly used, and there are also many forms of column caps. The surrounding reinforced concrete retaining walls of underground garages with beamless floors often serve as seismic walls. There are also non-load-bearing decorative (material) components, such as fireproof partitions, etc., which are not related to this article. The current specification standard adopts the limit state design method under the probability theory, determines the material design value through probability statistical calculation, and determines the load effect partial coefficient; determines the structural importance coefficient according to the importance of the building, and determines the importance coefficient of each component according to the primary and secondary, which is basically the same as the structural importance coefficient, requiring that the resistance design value of each component is not less than the effect design value of the load effect combination, and the overall safety of the structure is guaranteed by the safety of each component. In the design of earthquake resistance, there are performance-based design, strong columns and weak beams, strong shear and weak bending, energy dissipation, strong earthquake resistance, and other conceptual designs. When determining the material design value, there is also the concept that the shear strength guarantee rate is greater than the tensile and compressive strength. The beamless floor has no beams and no beam-column joints. The seismic design requires that the seismic wall bears 100% of the seismic force. When the building height is not more than 12 meters, the slab columns and frame parts of each floor should be able to bear no less than 20% of the seismic shear force of this floor. Severe overload does not guarantee safety. Including high-performance concrete, high-strength steel bars, continuous collapse design when subjected to accidental effects, etc., all guarantee a certain degree of safety. Technical personnel in this industry have been committed to studying safety, controlling the probability of overload; controlling the probability of structural failure (destruction), and controlling the collapse of a major earthquake. It is believed that a very small probability of failure is acceptable. For reinforced concrete beamless floor underground garages, there are no beams, no beam-column joints, and the covering soil is prone to overload. Through several years of research and analysis, we have proposed a design method for reinforced concrete beamless floor underground garages that will not collapse under overload damage. Summary of the invention

[0003] To solve the above problems, the present invention provides a method and structure for early warning of overload collapse of a concrete beamless underground garage, which controls the destruction sequence of each component so that the garage does not collapse when it is overloaded and destroyed and loses its usability, and the destruction of the garage is accompanied by significant signs of collapse.

[0004] The object of the present invention is achieved in the following manner: a method for early warning of overload collapse of a concrete beamless floor underground garage is at least one of the following methods:

[0005] (I) (1) The steel bars of the end supports of the floor slab are fully anchored: the horizontal anchorage length of the steel bars of the end supports of the floor slab is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bar; (2) The steel bars of the middle supports of the floor slab are fully anchored: the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, or the different redundant steel bars on both sides of the middle supports are bent and anchored in the vertical direction at the same end supports or fully anchored in the horizontal direction; (3) Select high-quality steel bars and appropriate reinforcement ratio: Steel bar properties: total elongation ≥ 9%, ratio of measured tensile strength to measured yield strength ≥ 1.25, standard value of yield strength not less than 400MPa; reinforcement ratio 0.2 %~1.2%; (4) Punching shear does not damage first: the shear and punching bearing capacity of the support, reinforced concrete column or reinforced concrete wall is at least twice the punching shear calculation formula according to the current specification, and the bending resistance is implemented according to the current specification without reinforcement; the horizontal bearing capacity of the surrounding retaining wall of the floor slab is: when the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the surrounding retaining wall still does not fall sideways; at the same time, the above conditions are met, and other basic requirements of the current specification are met; when the overload reaches a certain degree, the steel bars are stretched first, and the middle part of the floor slab between the two supports or the support and the reinforced concrete wall sags or / and the floor slab has visible cracks, but the reinforced concrete wall and reinforced concrete column do not collapse or collapse;

[0006] (ii) Overload crushing points with a height of 100-250mm are set on the supports and reinforced concrete columns in the underground garage. The cross-sectional resistance of the preset crushing points is weaker than the cross-sectional resistance of other positions on the supports and reinforced concrete columns in the underground garage, and the cross-sectional resistance of the overload crushing points meets the requirements of the specifications. At least one side of the preset crushing points is in contact with the air. When the overload reaches a certain degree, the preset crushing points are crushed, and the crushed concrete falls, forming a collapse warning;

[0007] (III) The floor slab set at the place where the soil is piled up is set as an overloaded falling floor slab, and the other floor slabs around the overloaded falling floor slab and connected to the overloaded falling floor slab are the floor slab structure B: when the overload reaches a certain degree, the overloaded falling floor slab will partially fall off, and the overloaded falling floor slab will remain connected to the surrounding floor slab structure B part, thus forming a cavity, and the soil covering the cavity will fall off, forming a collapse warning.

[0008] The middle support reinforcement is through-length, which means that the reinforcement extending from the two ends of the middle support to the middle support is one reinforcement; the middle support reinforcement is through-length, welded, mechanically connected or overlapped as tensile reinforcement, which means that the reinforcement extending from the two ends of the middle support to the middle support is welded, mechanically connected or overlapped as tensile reinforcement; the different redundant reinforcements on both sides of the middle support are bent and anchored in the vertical direction or fully anchored in the horizontal direction at the same end support, which means that the reinforcement extending from the two ends of the middle support to the middle support has a horizontal anchorage length of greater than or equal to 0.6 times the basic anchorage length, and a vertical anchorage length of greater than or equal to 15 times the diameter of the reinforcement;

[0009] The horizontal bearing capacity of the surrounding retaining wall of the floor slab meets the following requirements: When the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the specific measures to prevent the surrounding retaining wall from collapsing are: thickening the concrete wall, increasing the area of ​​steel bars on the adjacent soil side, adding a vertical concrete wall in the vertical direction of the surrounding retaining wall, or adding a horizontal load-bearing beam on the top plate connected to the surrounding retaining wall.

[0010] The cross-sectional resistance at the preset crushing point is at least 10% smaller than the cross-sectional resistance at other locations on the reinforced concrete column in the underground garage.

[0011] The cross-sectional resistance of the preset crushing point is weaker than the cross-sectional resistance at other positions on the reinforced concrete columns in the underground garage. Specifically, within a unit volume, the total longitudinal cross-sectional area of ​​all longitudinal steel bars at the preset crushing point is at least 10% smaller than the total longitudinal cross-sectional area of ​​all longitudinal steel bars at other positions on the reinforced concrete columns in the underground garage; or the concrete strength at the preset crushing point is at least 10% smaller than the concrete strength at other positions on the supports and reinforced concrete columns in the underground garage; or a hollow body or a material with lower strength than concrete is embedded at the preset crushing point.

[0012] The overloaded floor structure is floor structure A. The connection between floor structure A and floor structure B is as follows: (1) At the connection on the side of floor structure B, the floor opening is designed according to the current specifications; (2) At the connection on the side of floor structure B, connecting steel bars I are provided to connect the upper and lower steel bars of the floor. Connecting steel bars I are tie bars. The tie bars are hooked at the intersection of the longitudinal and transverse steel bars of the outer steel bars of the upper and lower steel bars of the floor; (3) At the connection between floor structure A and floor structure B, among the connecting edges on the side of floor structure A: there is a direct connecting edge that can bear the weight of floor structure A; the remaining connecting edges of floor structure A are set as follows: between the upper and lower steel bars, in the concrete, a material that weakens the shear bearing capacity of the concrete is embedded. The weakening standard is that the shear bearing capacity is lower than that of other places by more than 10%, and at the same time, the safety degree of the current specifications is met when there is no overload.

[0013] The connecting edge of the direct edge that can bear the weight of floor slab A is: add connecting steel bar II within the 1 / 3 thickness range in the middle of the concrete thickness to form a strong connection.

[0014] The floor structure is in the shape of a cuboid.

[0015] The materials that weaken the shear bearing capacity of concrete are plywood and thin wood boards with a thickness of 2 to 10 mm. The materials that weaken the shear bearing capacity of concrete are placed obliquely.

[0016] For the early warning structure of overload collapse of concrete beamless floor underground garage, the early warning structure is at least one of the following structures:

[0017] (I) (1) The steel bars of the end supports of the floor slab are fully anchored: the horizontal anchorage length of the steel bars of the end supports of the floor slab is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bar; (2) The steel bars of the middle supports of the floor slab are fully anchored: the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, or the different redundant steel bars on both sides of the middle supports are bent and anchored in the vertical direction at the same end supports or fully anchored in the horizontal direction; (3) Select high-quality steel bars and appropriate reinforcement ratio: Steel bar properties: total elongation ≥ 9%, measured tensile strength value The ratio to the measured value of yield strength is ≥1.25, and the standard value of yield strength is not less than 400MPa; the reinforcement ratio is 0.2%~1.2%; (4) No pre-damage due to punching and shearing: the shear and punching bearing capacity of the support, reinforced concrete column or reinforced concrete wall is at least twice the punching and shearing calculation formula according to the current specification, and the bending resistance is implemented according to the current specification without reinforcement; the horizontal bearing capacity of the surrounding retaining wall of the floor slab meets the following requirements: when the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the surrounding retaining wall will not fall sideways; at the same time, the above conditions are met, and other basic requirements of the current specification are met;

[0018] (ii) Overload crushing points with a height of 100-250mm are set on the supports and reinforced concrete columns in the underground garage. The cross-sectional resistance of the preset crushing points is weaker than the cross-sectional resistance of other positions on the supports and reinforced concrete columns in the underground garage, and the cross-sectional resistance of the overload crushing points meets the requirements of the specifications. At least one side of the preset crushing points is in contact with the air;

[0019] (III) The floor slab set at the accumulation and covering soil is set as an overload falling floor slab, and the other floor slabs around the overload falling floor slab and connected to the overload falling floor slab are the floor slab structure B: when the overload reaches a certain degree, the overload falling floor slab falls, and the overload falling floor slab remains connected to the surrounding floor slab structure B part, thus forming a cavity, and the covering soil on the cavity falls, forming a collapse warning.

[0020] Compared with the prior art, the present invention is different from the commonly used early warning: it is necessary to determine the early warning parameters, special instruments and equipment, and professional technicians. Since there will be obvious bending, cracks, falling concrete, and falling fill, ordinary people can know with common sense that the house is unusable and will collapse. The present invention is to first make the garage lose its use function (destruction) and then stop the overloading activities. Unless it is deliberately destroyed, it will not collapse when the overloading damage forms an early warning. The present invention has a novel concept, a reasonable design, and a low cost. After implementation, it can reduce casualties and protect the lives of ordinary people. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a plan view of a beamless floor;

[0022] Figure 2 It is a schematic diagram of the cross section of a beamless floor;

[0023] Figure 3 It is a schematic diagram of the edge node of a beamless floor;

[0024] Figure 4 This is a schematic diagram of the floor structure A before it sinks;

[0025] Figure 5 This is a schematic diagram of the floor structure A after it sinks;

[0026] Figure 6 This is a cross-sectional diagram of scheme 1 without overload;

[0027] Figure 7 This is a cross-sectional diagram of the severely overloaded scheme 1;

[0028] Figure 8 It is a schematic diagram of the horizontal section of a reinforced concrete column;

[0029] Fig. 9 It is a vertical section diagram of a reinforced concrete column;

[0030] Fig.10 It is a vertical cross-sectional diagram of crushing failure at a preset crushing point under severe overload;

[0031] Fig.11 It is a cross-sectional schematic diagram of the connection between floor A and floor B;

[0032] Among them, 1 is a reinforced concrete column, 2 is a reinforced concrete column cap, 3 is a reinforced concrete top plate, 4 is a preset reinforced concrete failure hole, 5 is covering soil, 6 is a preset crushing point, 7 is steel bars, 8 is a reinforced concrete wall, 9 is a floor structure A, 10 is a floor structure B, 11 is a crack, 12 is a tie steel bar, 13 is plywood, wood boards and other materials, and 14 is a reinforced concrete retaining wall. DETAILED DESCRIPTION

[0033] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that this embodiment is only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical personnel skilled in the art can make some non-essential improvements and adjustments based on the above-mentioned contents of the present invention.

[0034] The top slab of the underground garage is covered with soil. Fill part of it first, and use loose materials with low adhesion such as silt, silt sand, fine sand, medium-coarse sand, coarse sand, etc. In the process of covering the soil, sometimes all the materials are piled up in one place, causing overload, and then causing the underground garage to collapse.

[0035] The overload of underground garages is gradual. The country has greening requirements. The roof of pure underground garages needs to be covered with soil and greened. The requirements for the thickness of soil covering vary slightly from place to place, such as not less than 1.2 meters, 1.5 meters, 3 meters, etc. Take the common two-way 8.0-meter column grid and 1.5-meter thick soil covering as an example. The soil covering in a column grid is 8.0x8.0x1.5=96 cubic meters, weighing about 96x16=1536kN (153 tons). The commonly used 2~10-ton soil trucks require 70~15 trucks, and the uncommonly used largest 50-ton trucks also require more than 3 trucks. The soil covering load of the underground garage roof is added little by little. The construction time of a project will last from several days to dozens of days. Overloading is a little bit of overloading, expanding from part to most, and overloading activities can be stopped at any time. The same is true for later use. The limit of road width, the limit of turning radius, the randomness of load, etc. Human activities are gradual.

[0036] The reinforced concrete beamless floor underground garage structure is composed of reinforced concrete columns 1, reinforced concrete walls 8, floor slab 3 and other components. The floor slab, top slab and floor slab are different names for the same structure.

[0037] The wall located around the garage and playing a retaining role is a retaining wall. The reinforced concrete wall 8 includes a reinforced concrete retaining wall 14. The reinforced concrete wall 8 located around the garage and playing a retaining role is a reinforced concrete retaining wall 14.

[0038] The support includes an end support and a middle support, and the reinforced concrete wall 8 and the reinforced concrete column 1 are both one type of the support. The middle support includes the reinforced concrete column 1.

[0039] The upper section of the reinforced concrete column may be provided with a column cap, and when provided with a column cap, the column cap is fixedly connected to the floor slab 3, and the column cap may be a reinforced concrete column cap 2. The floor slab may be a reinforced concrete top slab 3.

[0040] like Figure 1-Figure 11 As shown, the method for early warning of overload collapse of a concrete beamless floor underground garage is at least one of the following methods:

[0041] (I) (1) The steel bars of the end supports of the floor slab are fully anchored: the horizontal anchorage length of the steel bars of the end supports of the floor slab is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bar; (2) The steel bars of the middle supports of the floor slab are fully anchored: the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, or the different redundant steel bars on both sides of the middle supports are bent and anchored in the vertical direction at the same end supports or fully anchored in the horizontal direction; (3) Select high-quality steel bars and appropriate reinforcement ratio: Steel bar properties: total elongation ≥ 9%, ratio of measured tensile strength to measured yield strength ≥ 1.25, standard value of yield strength not less than 400MPa; reinforcement ratio 0.2 %~1.2%; (4) Punching shear does not damage first: the shear and punching bearing capacity of the support, reinforced concrete column or reinforced concrete wall is at least twice the punching shear calculation formula according to the current specification, and the bending resistance is implemented according to the current specification without reinforcement; the horizontal bearing capacity of the surrounding retaining wall of the floor slab is: when the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the surrounding retaining wall still does not fall sideways; at the same time, the above conditions are met, and other basic requirements of the current specification are met; when the overload reaches a certain degree, the steel bars are stretched first, and the middle part of the floor slab between the two supports or the support and the reinforced concrete wall sags or / and the floor slab has visible cracks, but the reinforced concrete wall and reinforced concrete column do not collapse or collapse;

[0042] (ii) Overload crushing points with a height of 100-250mm are set on the supports and reinforced concrete columns in the underground garage. The cross-sectional resistance of the preset crushing points is weaker than the cross-sectional resistance of other positions on the supports and reinforced concrete columns in the underground garage, and the cross-sectional resistance of the overload crushing points meets the requirements of the specifications. At least one side of the preset crushing points is in contact with the air. When the overload reaches a certain degree, the preset crushing points are crushed, and the crushed concrete falls, forming a collapse warning;

[0043] (III) The floor slab set at the accumulation and covering soil is set as an overload falling floor slab, and the other floor slabs around the overload falling floor slab and connected to the overload falling floor slab are the floor slab structure B: when the overload reaches a certain degree, the overload falling floor slab falls, and the overload falling floor slab remains connected to the surrounding floor slab structure B part, thus forming a cavity, and the covering soil on the cavity falls, forming a collapse warning.

[0044] According to the above method, the early warning structure of the reinforced concrete beamless floor underground garage for early warning of overload collapse includes at least one of the following structures:

[0045] Option 1: If Figure 3The steel bars of the end supports of the floor slab are fully anchored, not the current standard 0.4La or 12d or 0.35La (simply supported), La is the steel bar anchorage length, d is the steel bar diameter), but greater than the existing standard anchorage length, the horizontal anchorage length a is greater than or equal to 0.6La, and the vertical anchorage length b is greater than or equal to 15d. The steel bars of the middle supports are also fully anchored or full-length, the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, and the different redundant steel bars on both sides are bent and anchored at the same end supports or fully anchored horizontally (≥La), not the current commonly used "extending into the hidden beam 5 times the steel bar diameter and extending to the center line".

[0046] Specifically, the middle support steel bar is through-length means that the steel bars extending from the two ends of the middle support to the middle support are one steel bar; the middle support steel bars are through-length, welded, mechanically connected or overlapped as tensile steel bars, which means that the steel bars extending from the two ends of the middle support to the middle support are welded, mechanically connected or overlapped as tensile steel bars; the different redundant steel bars on both sides of the middle support are bent and anchored in the vertical direction or fully anchored in the horizontal direction at the same end supports, which means that the steel bars extending from the two ends of the middle support to the middle support on the middle support: the horizontal anchorage length is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bar.

[0047] The stress-bearing steel bars in the floor slab are high-strength, high-elongation, and high-bend-strength ratio construction steel bars. The standard value of steel bar yield strength is not less than 400Mpa, the total elongation of the steel bar is ≥9% and less than 25%, the ratio of the measured value of tensile strength to the measured value of yield strength is ≥1.25 (less than 2.0), and the standard value of yield strength is not less than 400MPa; the elastic modulus of steel bar Es = 200000~215000N / mm 2 Appropriate reinforcement ratio (0.2%~1.2%). Further ensure that when overload occurs, the steel bars are stretched first. And when overloaded, the steel bars are fully extended, forming an obvious sag in the middle of the floor slab and obvious cracks on the floor slab, so that it is easy for staff to observe the changes in the garage when overloaded before collapse, and the staff can stop the overloading activities in time and escape in time, reducing or even avoiding casualties.

[0048] In the underground garage, the shear and punching bearing capacity of the beamless floor is greatly improved at the support, reinforced concrete column 1 or reinforced concrete wall 8. For example, the shear and punching bearing capacity of the support, reinforced concrete column 1 or reinforced concrete wall in the underground garage is twice the punching calculation formula according to the current specification, and the bending resistance shall not be strengthened according to the current specification. For example: Figure 1 , reinforced concrete column grid 8m x 8m, cover 1.5m thick, live load 3.0 kN / m 2，Reinforced concrete columns are 550x550mm, column cap plane dimensions are 3000mm in both directions (the bottom bevel of the column cap expands 200mm at 45°), concrete strength grade is C30, the floor slab is 400mm thick except for the column cap, and the total thickness of the column cap is 400+300=700mm, which can meet the requirements of the current specifications. According to the current specification punching calculation formula, the concrete strength grade is changed to C40, the column cap thickness is changed to 400+500=900mm, and the bending reinforcement is calculated according to the modified column cap (becomes smaller). Other strengthening measures can also be taken, such as shear (punching) steel bars (steel), etc. Further ensure that when overloaded, the steel bars are stretched first, and there is no shear or punching damage to the concrete, and sudden collapse.

[0049] like Figure 1 (Right side) Strengthen the horizontal bearing capacity of the retaining wall around the underground garage to meet the standard of not falling over when the top plate cannot provide horizontal support. Strengthening measures include thickening the concrete wall, increasing the area of ​​steel bars on the side adjacent to the soil (the side of the retaining wall with soil is indoors and has no soil, and the side adjacent to the soil is the side in contact with the soil), adding vertical concrete walls in the vertical direction of the surrounding retaining walls, and adding horizontal load-bearing beams on the top plate connected to the surrounding retaining walls, etc. For example, the floor height is 3.5 meters, the upper cover soil thickness is 1.5 meters, there is no groundwater, and there is no large live load nearby (no more than 5.0kN / m 2 ), the surrounding retaining wall is usually 250mm thick, and the soil side is equipped with HRB400 steel bars, vertical, 12mm diameter and 120mm spacing, and horizontal steel bars, 12mm diameter and 150mm spacing. If only one measure of increasing the thickness of the surrounding retaining wall is adopted, the thickness of the surrounding retaining wall needs to be increased from 250mm to 350mm, and the vertical force-bearing steel bars on the soil side are changed to 18mm diameter and 100mm spacing, and the rest can remain unchanged. Avoid the collapse of the surrounding retaining wall when overloaded.

[0050] like Figure 6 When not overloaded, the above requirements do not violate the current national standards. The deflection of the beamless floor underground garage designed in this way meets the requirements of national standards: when the span is less than 7 meters, the deflection c is not greater than 1 / 200, when the span is greater than 9 meters, the deflection is not greater than 1 / 300, when the span is between 7 and 9 meters, the deflection is not greater than 1 / 250, and the cracks meet the requirements of national standards and are not greater than 0.3mm. The deflection cracks are not obvious, which is the case for ordinary civil buildings and underground garages. At this time, the stress of the steel bar is less than the tensile design strength, which is approximately the tensile design strength divided by the design sub-item factor, and the design sub-item factor is about 1.3~1.5.

[0051] As the load increases, the stress of the steel bar increases, the deflection and cracks increase, and the maximum stress of the steel bar gradually reaches the tensile design value. When the load increases further, the stress of the steel bar reaches the standard value of the tensile strength, which is about 1.1 times the design value. When the load increases further, the maximum stress of the steel bar approaches the standard value of the ultimate strength of the steel bar. Taking HRB400E steel bar as an example, the ultimate strength standard value is 1.5 times the design value. When the load increases further, the steel bar approaches the limit value. In the process of increasing steel bar stress, the strain of the steel bar increases (approximately in proportion) and the elongation of the steel bar increases; in this process, cracks and deflections increase significantly. When it gradually reaches a serious overload, such as Figure 7 , the deflection reaches 10~35 times the standard limit, and the 9% high elongation steel bar can make the deflection reach 1 / 6 of the span. For example, for a span of 8 meters, the standard limit of 1 / 250 is 32mm, and 10~35 times is 320~1120mm. People, including non-professionals, can see the danger; at the same time, the crack 11 also gradually reaches 2~10 times the standard limit of 0.3mm, to 0.6~3mm. Cracks below 0.05mm are invisible to the naked eye, 0.2~0.3mm are obvious cracks, and 0.5mm cracks can be seen by people from several meters away. People will see serious cracks and the house will collapse. Obvious signs can stop overloading activities.

[0052] High-strength steel bars make overload cracks larger than ordinary steel bars. High flexural strength ratio steel bars ensure that the stress of the steel bars is fully diffused along the steel bars. When not overloaded, the tensile stress of the steel bars at the bottom of the floor slab is the largest in the mid-span and less than zero at the support, resulting in a large difference in the stress of the steel bars when not overloaded. The upper steel bars in the concrete floor slab also have different sizes, gradually approaching or reaching the limit value, with more cracks, and the process from overload to collapse is longer and more obvious; the upper steel bars in the concrete floor slab correspond to the steel bars at the bottom of the floor slab. As the tensile stress of the steel bars approaches or reaches the limit value, if the support is not fully anchored, it will be pulled out and suddenly collapse will occur. At the same time, the surrounding retaining walls are strengthened to prevent the steel bars at the bottom of the floor slab from being pulled down due to tension, causing it to collapse. The appropriate reinforcement ratio (0.2%~1.2%) ensures that the steel bars are fully elongated rather than being crushed (squeezed) by the concrete.

[0053] During the gradual overloading process, the increase in deflection will affect the installation of horizontal equipment (water supply pipes, fire sprinkler pipes, heating pipes, cable trays, ventilation pipes, etc.) pipes (construction period). During use, the equipment pipes will be crushed, causing the building to be damaged and unusable.

[0054] The combination of sufficient anchoring of steel bars, selection of high-quality steel bars and appropriate reinforcement ratio, no pre-damage in punching and shearing, horizontal bearing capacity of the surrounding reinforced retaining walls, and other basic requirements in accordance with the current specifications ensure that the floor slab will not collapse when it is damaged. These conditions are indispensable. The current specifications only require the safety of a single component. For example, the bending safety of the floor slab is very high and meets the current specifications, and the shear safety just meets the specifications. At this time, the above signs will not appear. Customary practices often cannot meet all the requirements at the same time, or are not coincidental for this purpose. For example, the floor slab steel bars are full length to ensure the integrity of earthquake resistance, or the steel bars are full length due to temperature stress, etc. At present, there are also individual projects that strengthen observation and early warning during the construction stage (non-standard requirements), all of which require experienced professional technicians, professional tools or equipment. However, some design plans (construction drawings) professionals cannot see the signs, for example, safety without overloading, punching shear damage when overloading, little increase in deflection or even not exceeding the standard, and sudden collapse when concrete cracks (cracks do not exceed the standard). This industry is still mainly focused on controlling not to overload.

[0055] Option 2: Set a preset crushing point 6 on the reinforced concrete column in the underground garage. When the overload reaches a certain level, the preset crushing point is crushed. The cross-sectional resistance of the preset crushing point 6 is weaker than that of other positions, or other positions are stronger than the pre-destruction point 6, and the cross-sectional resistance here meets the requirements of the specification. At least one side of the preset crushing point is in contact with the air.

[0056] Under the premise of meeting the requirements of the specification, within the unit volume, the total longitudinal cross-sectional area of ​​all longitudinal steel bars at the preset crushing point 6 is smaller than the total longitudinal cross-sectional area 7 of all longitudinal steel bars at other reinforced concrete column positions of the column, or the concrete strength is lower, or a hollow body is embedded or a brick, wood and other materials with lower strength than concrete are embedded. It can be increased or decreased by 10%, for example: a column section of 500x500mm is embedded in the middle of a cube plywood hollow body with a side length of 160mm. The greater the difference, the more obvious the effect, but the higher the cost.

[0057] The size of the preset crushing point 6 in the height direction is 100-250 mm, that is, the distance from the lowest point to the highest point of the preset crushing point 6 in the height direction is 100-250 mm.

[0058] like Fig.10, the size of the preset crushing point in the height direction is controlled to be 100~250mm. After overloading, the preset crushing point 6 on the reinforced concrete column will show obvious concrete crushing, and part of the load will be transferred to the surrounding reinforced concrete columns or reinforced concrete walls (if concrete walls are arranged). After unloading part of the load, the damaged column can still play a supporting role and is not completely destroyed. Due to the crushing of concrete, obvious signs of collapse appear, and the overloading activity is stopped. In addition, since at least one side of the preset crushing point is in contact with the air, the crushed concrete falls, which is convenient for the staff to observe, and the overloading activity can be stopped in time, and the staff can escape in time, reducing or even avoiding casualties.

[0059] The current specifications do not allow overloading, column damage, or column crushing, and there is no customary practice of column crushing. Common designs have weak points that are not intended for this purpose, for example, the upper and lower stirrups must be denser due to earthquake-resistant requirements, etc.

[0060] Option 3: A special connecting floor is set up at the piled soil cover: floor structure A9, and the rest is called floor structure B10, such as Fig.11 There are four ways to connect floor structure A and floor structure B. The first three must be met at the same time, and the fourth can be selected:

[0061] 1. The connection on the B side of the floor structure can also be called the connection perimeter, and the floor opening design is based on the current specifications.

[0062] 2. At the connection of the floor structure side B, there is a connecting steel bar 12 connecting the upper steel bars 15 and the lower steel bars 16 of the floor. For example, the connecting steel bar is a tie steel bar 12, which hooks the outer steel bar at the intersection of the longitudinal and transverse steel bars (the outer steel bar is a common term in the construction industry. The upper and lower steel bars in the concrete floor or slab have two layers, one on the top and the other on the bottom, not a flat steel mesh; the outer steel bar refers to the upper steel bar of the upper part or the lower steel bar of the lower part, close to the steel bar outside the concrete), the spacing of the tie steel bars is the same as the horizontal spacing of the intersection of the longitudinal and transverse steel bars of each layer of steel bars, and the diameter of the tie steel bar is selected according to the diameter of the upper and lower steel bars and the shear force at the intersection of the longitudinal and transverse steel bars. The steel bar of 10~25mm is selected.

[0063] 3. At the connection between the floor structure A and the floor structure B: Among the connection edges on the side of the floor structure A: there is a direct connection edge that can bear the weight of the floor A; the remaining connection edges of the floor structure A are set as follows: between the upper steel bars and the lower steel bars, in the concrete, materials that weaken the shear bearing capacity of the concrete are pre-embedded. The weakening standard is that the shear bearing capacity is more than 10% lower than that of other places, and at the same time meets the safety level of the current specifications when not overloaded.

[0064] (4) The connecting edge of the direct edge that can bear the weight of the floor slab A can be: add connecting steel bar II in the 1 / 3 thickness range in the middle of the concrete thickness to form a strong connection, so that the weight of the floor slab A can be suspended without falling. The standard for hanging the weight of the floor slab A is that it does not fall, and the concrete thickness is in the vertical direction; for example: according to the weight of the floor slab A, a diameter of 6~20mm, a spacing of 100~300mm, and a length of 1.2 times the anchor length of the steel bars extending into the floor slabs A and B are selected to form a strong connection so that it will not fall after being damaged.

[0065] Between the upper and lower steel bars, in the concrete, a material 13 is embedded to weaken the shear bearing capacity of the concrete. This material is the dividing line between the floor A and the floor B, and is also the failure line of the vertical shear crack of the concrete. The weakening standard is that the shear bearing capacity is more than 10% lower than that of other places, and at the same time, it meets the safety degree of the current specifications when not overloaded. The material 13 that weakens the shear bearing capacity of the concrete can be ordinary plywood, thin wood board 13, etc. with a thickness of 2 to 10 mm. Generally, it is better to place it obliquely. For example, if the floor structure A is in the shape of a rectangular parallelepiped, it is set on the three sides with larger shear force. The weakening standard is that the shear bearing capacity is more than 10% lower than that of other places, and at the same time, it meets the safety degree of the current specifications when not overloaded. For example: Figure 1 For example, the column grid of the reinforced concrete column is 8m x 8m, the cover soil is 1.5m thick, the floor slab outside the column cap is 400mm thick, and the plane size (two-way) of the floor structure A is 2000mm. Place 2.5mm thick plywood in the three sides of the concrete slab of the floor structure A closer to the reinforced concrete column, with a height of 50mm and an inclination angle of 60°. Fig.11 13 of 13.

[0066] The floor A can also be designed as a polygon or other shapes, and the peripheral connection is the same as above. At the connection between the floor structure A and the floor structure B, among the connection edges on the side of the floor structure A: there is a direct connection edge that can bear the weight of the floor A, and the direct connection edge is: add connection steel bar II within the 1 / 3 thickness range in the middle of the concrete thickness to form a strong connection.

[0067] Engineering experience and conventional design show that the shear bearing capacity around floor A is relatively high and needs to be weakened to achieve option three. :

[0068] The underground garage reinforced concrete top plate 3 is provided with covering soil 5, which is filled first, and silt, silt sand, fine sand, medium coarse sand, coarse sand, and other loose materials with low bonding force are selected. Figure 1 , Figure 4 . Using the shear failure brittleness of concrete, when overloaded to a certain extent, such as Figure 5, concrete in floor structure A breaks, and then the steel bars break, and part of the connecting edge of floor structure A sinks and falls. The fill above or the crushed concrete between the steel bars falls from the cavity formed by the sinking of floor structure A, so that the staff can observe this phenomenon in time, stop the overloading activities in time, and escape in time, reducing or even avoiding casualties.

[0069] Even if the floor structure A sinks to form an obvious cavity 4, since the floor structure A is strongly connected to the surrounding floor structure B at least at one point, the floor structure A does not fall. Figure 5 The fill above the cavity falls from the cavity, making it impossible to increase the fill above the garage roof, so that it cannot continue to overload, thereby ensuring that it cannot be seriously overloaded and will not collapse. The connection around the pre-destroyed slab hole meets the requirements of the current specifications to ensure the safety of the building when it is not overloaded (i.e., conventional design). Under this condition, the shear bearing capacity is weakened, or the adjacent concrete is strengthened (reinforced reinforcement). Under the premise of meeting the specifications, the joint is the weakest and is destroyed first, achieving the purpose of unloading when the overload reaches a certain level.

[0070] In the above methods, if all the "signs" appear, the garage will lose its usability (destruction), requiring partial or complete rework or demolition and reconstruction. If it is not intentional, the overloading activities will not continue.

[0071] The above methods can be selected in one project based on specific circumstances. Each method can be set at every location or only at locations with high overload potential. For example, the overload potential of each location can be determined based on the construction organization intention (plan) and the location can be selected. It can also be set selectively in the plane based on factors such as the possibility of later transformation (e.g. Figure 1 ). In the same place of the same project, only one type should be selected, and at the same time, the other two types should not occur.

[0072] The configuration, size and quantity of the steel bars in the figure are determined based on actual conditions and are for reference only.

[0073] The present invention has novel ideas, reasonable designs, and low costs. After implementation, it can reduce casualties and protect the lives of ordinary people. The present invention does not involve sudden accidents such as explosions, civil air defense, rare earthquakes, and does not involve foundations, but the safety level is not reduced compared with the current national standards. If the foundation adopts the same beamless floor as the top plate, it needs to be strengthened according to the idea of ​​the first solution of the present invention. The content of the present invention, its purpose or the effect to be achieved is: if it is not intentional, it will not collapse when an early warning is formed due to overload damage. Because the garage has been damaged when the early warning is formed, the overload activity stops after the early warning is formed, so the collapse behavior will not occur. Therefore, the structure of the present application can achieve the effect of "no collapse due to overload damage", but it cannot avoid damage.

[0074] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. It should be pointed out that for those skilled in the art and any technician familiar with the technical field, without departing from the overall concept of the present invention, the technical solution and the inventive concept of the present invention are equivalently replaced or changed, and several changes and improvements are made, which should also be regarded as the protection scope of the present invention.

Claims

1. A method for early warning of overload collapse of an underground garage with a concrete beamless floor, characterized in that: At least one of the following methods: (I) (1) The steel bars of the end supports of the floor slab are fully anchored: the horizontal anchorage length of the steel bars of the end supports of the floor slab is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bar; (2) The steel bars of the middle supports of the floor slab are fully anchored: the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, or the different redundant steel bars on both sides of the middle supports are bent and anchored in the vertical direction at the same end supports or fully anchored in the horizontal direction; (3) Select high-quality steel bars and appropriate reinforcement ratio: Steel bar properties: total elongation ≥ 9%, ratio of measured tensile strength to measured yield strength ≥ 1.25, standard value of yield strength not less than 400MPa; reinforcement ratio 0.2 %~1.2%; (4) Punching shear does not damage first: the shear and punching bearing capacity of the support, reinforced concrete column or reinforced concrete wall is at least twice the punching shear calculation formula according to the current specification, and the bending resistance is implemented according to the current specification without reinforcement; the horizontal bearing capacity of the surrounding retaining wall of the floor slab is: when the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the surrounding retaining wall still does not fall sideways; at the same time, the above conditions are met, and other basic requirements of the current specification are met; when the overload reaches a certain degree, the steel bars are stretched first, and the middle part of the floor slab between the two supports or the support and the reinforced concrete wall sags or / and the floor slab has visible cracks, but the reinforced concrete wall and reinforced concrete column do not collapse or collapse; (ii) Overload crushing points with a height of 100-250mm are set on the supports and reinforced concrete columns in the underground garage. The cross-sectional resistance of the preset crushing points is weaker than the cross-sectional resistance of other positions on the supports and reinforced concrete columns in the underground garage, and the cross-sectional resistance of the overload crushing points meets the requirements of the specifications. At least one side of the preset crushing points is in contact with the air. When the overload reaches a certain degree, the preset crushing points are crushed, and the crushed concrete falls, forming a collapse warning; (III) The floor slab set at the place where the soil is piled up is set as an overloaded falling floor slab, and the other floor slabs around the overloaded falling floor slab and connected to the overloaded falling floor slab are the floor slab structure B: when the overload reaches a certain degree, the overloaded falling floor slab will partially fall off, and the overloaded falling floor slab will remain connected to the surrounding floor slab structure B part, thus forming a cavity, and the soil covering the cavity will fall off, forming a collapse warning.

2. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 1, characterized in that: The middle support reinforcement is through-length, which means that the reinforcement extending from the two ends of the middle support to the middle support is one reinforcement; the middle support reinforcement is through-length, welded, mechanically connected or overlapped as tensile reinforcement, which means that the reinforcement extending from the two ends of the middle support to the middle support is welded, mechanically connected or overlapped as tensile reinforcement; the different redundant reinforcements on both sides of the middle support are bent and anchored in the vertical direction or fully anchored in the horizontal direction at the same end support, which means that the reinforcement extending from the two ends of the middle support to the middle support has a horizontal anchorage length of greater than or equal to 0.6 times the basic anchorage length, and a vertical anchorage length of greater than or equal to 15 times the diameter of the reinforcement; The horizontal bearing capacity of the surrounding retaining wall of the floor slab meets the following requirements: When the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the specific measures to prevent the surrounding retaining wall from collapsing are: thickening the concrete wall, increasing the area of ​​steel bars on the adjacent soil side, adding a vertical concrete wall in the vertical direction of the surrounding retaining wall, or adding a horizontal load-bearing beam on the top plate connected to the surrounding retaining wall.

3. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 1, characterized in that: The cross-sectional resistance at the preset crushing point is at least 10% smaller than the cross-sectional resistance at other locations on the reinforced concrete column in the underground garage.

4. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 3 is characterized in that: The cross-sectional resistance of the preset crushing point is weaker than the cross-sectional resistance at other positions on the reinforced concrete columns in the underground garage. Specifically, within a unit volume, the total longitudinal cross-sectional area of ​​all longitudinal steel bars at the preset crushing point is at least 10% smaller than the total longitudinal cross-sectional area of ​​all longitudinal steel bars at other positions on the reinforced concrete columns in the underground garage; or the concrete strength at the preset crushing point is at least 10% smaller than the concrete strength at other positions on the supports and reinforced concrete columns in the underground garage; or a hollow body or a material with lower strength than concrete is embedded at the preset crushing point.

5. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 1, characterized in that: The overloaded floor structure is floor structure A. The connection between floor structure A and floor structure B is as follows: (1) At the connection on the side of floor structure B, the floor opening is designed according to the current specifications; (2) At the connection on the side of floor structure B, connecting steel bars I are provided to connect the upper and lower steel bars of the floor. Connecting steel bars I are tie bars. The tie bars are hooked at the intersection of the longitudinal and transverse steel bars of the outer steel bars of the upper and lower steel bars of the floor; (3) At the connection between floor structure A and floor structure B, among the connecting edges on the side of floor structure A: there is a direct connecting edge that can bear the weight of floor structure A; the remaining connecting edges of floor structure A are set as follows: between the upper and lower steel bars, in the concrete, a material that weakens the shear bearing capacity of the concrete is embedded. The weakening standard is that the shear bearing capacity is lower than that of other places by more than 10%, and at the same time, the safety degree of the current specifications is met when there is no overload.

6. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 5, characterized in that: The connecting edge of the direct edge that can bear the weight of floor slab A is: add connecting steel bar II within the 1 / 3 thickness range in the middle of the concrete thickness to form a strong connection.

7. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 5, characterized in that: The floor structure is in the shape of a cuboid.

8. The method for early warning of overload collapse of an underground garage with a concrete flat floor according to claim 5, characterized in that: The materials that weaken the shear bearing capacity of concrete are plywood and thin wood boards with a thickness of 2 to 10 mm. The materials that weaken the shear bearing capacity of concrete are placed obliquely.

9. An early warning structure for overload collapse of concrete beamless floor underground garage, characterized by: The warning structure is at least one of the following structures: (I) (1) The steel bars of the end supports of the floor slab are fully anchored: the horizontal anchorage length of the steel bars of the end supports of the floor slab is greater than or equal to 0.6 times the basic anchorage length, and the vertical anchorage length is greater than or equal to 15 times the diameter of the steel bars; (2) The steel bars of the middle supports of the floor slab are fully anchored: the steel bars of the middle supports are full-length, welded, mechanically connected or overlapped as tensile steel bars, or the different redundant steel bars on both sides of the middle supports are bent and anchored in the vertical direction at the same end supports or fully anchored in the horizontal direction; the full-length steel bars of the middle supports refer to the steel bars extending from the two ends of the middle supports to the middle supports as one steel bar; (3) Select high-quality steel bars and appropriate reinforcement ratio: Steel bar performance: Total elongation ≥ 9%, ratio of measured tensile strength to measured yield strength ≥ 1.25, standard value of yield strength not less than 400MPa; reinforcement ratio 0.2%~1.2%; (4) No pre-damage due to punching and shearing: shear and punching bearing capacity of supports, reinforced concrete columns or reinforced concrete walls shall be at least twice the punching and shearing calculation formula according to the current specification, and bending resistance shall be implemented according to the current specification without reinforcement; horizontal bearing capacity of the surrounding retaining wall of the floor slab shall meet the following requirements: when the top plate of the floor slab above the surrounding retaining wall does not play a horizontal supporting role, the surrounding retaining wall will not collapse; at the same time, the above conditions shall be met and other basic requirements of the current specification shall be met; (ii) Overload crushing points with a height of 100-250mm are set on the supports and reinforced concrete columns in the underground garage. The cross-sectional resistance of the preset crushing points is weaker than the cross-sectional resistance of other positions on the supports and reinforced concrete columns in the underground garage, and the cross-sectional resistance of the overload crushing points meets the requirements of the specifications. At least one side of the preset crushing points is in contact with the air; The total longitudinal cross-sectional area of ​​all longitudinal reinforcements at the preset crushing point within a unit volume is at least 10% smaller than the total longitudinal cross-sectional area of ​​all longitudinal reinforcements at other locations on the reinforced concrete columns in the underground garage; (III) The floor slab at the accumulation and covering soil is set as an overload falling floor slab, and the other floor slabs around the overload falling floor slab and connected to the overload falling floor slab are floor slab structure B: when the overload reaches a certain level, the overload falling floor slab falls, and the overload falling floor slab remains connected to the surrounding floor slab structure B, thereby forming a cavity, and the covering soil on the cavity falls, forming a collapse warning; The overloaded floor structure that fell is floor structure A. The connection between floor structure A and floor structure B is as follows: (1) At the connection on the side of floor structure B, the floor opening is designed according to the current specifications; (2) At the connection on the side of floor structure B, connecting steel bars I are provided to connect the upper steel bars and the lower steel bars of the floor. Connecting steel bars I are tie bars that hook onto the intersection of the longitudinal and transverse steel bars of the outer steel bars of the upper and lower steel bars of the floor.

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