Crack characteristics of reinforced concrete structures, what are the characteristics of crack spaci

There are many advantages of reinforced concrete structure, in addition to the reasonable use of the characteristics of steel and concrete, there are also the following advantages: (1) good moldability: the newly mixed concrete is moldable, and can be designed into various shapes and sizes of structures or components according to needs.

2) Good integrity: the cast-in-place reinforced concrete structure has good integrity, and has good anti-seismic, anti-explosion and anti-vibration performance when the design is reasonable. (3) Good durability:

The reinforced concrete structure has good durability. No regular maintenance or repairs are required under normal use conditions. (4) Good fire resistance:

Reinforced concrete structures have better fire resistance than steel structures. (5) Easy to take local materials: The sand and stone materials with large specific gravity used in reinforced concrete structures are easy to take local materials, and can effectively use industrial waste slag such as slag and fly ash to protect the environment.

Reinforced concrete structures have the following main disadvantages: (1) self-weight. The gravity density of reinforced concrete is about 25kN3, which is greater than the gravity of both masonry and wood.

Although less heavy than steel, the structure has a larger cross-sectional dimension, so its dead weight far exceeds the weight of a steel structure of the same span or height. (2) Poor crack resistance. As mentioned earlier, the tensile strength of concrete is very low, therefore, ordinary reinforced concrete structures often work with cracks.

Although the presence of cracks does not necessarily mean that the structure has failed, it does affect the durability and aesthetics of the structure. When the cracks are more numerous and wider, they can also create a sense of insecurity. (3) Brittle nature.

The brittleness of concrete increases with the increase of concrete strength grade. To sum up, it is not difficult to see that the advantages of reinforced concrete structures outweigh their disadvantages. Moreover, many effective measures have been worked out to overcome its shortcomings.

For example, in order to overcome the shortcomings of reinforced concrete's own weight, many lightweight, high-strength concrete and high-strength steel bars have been studied. In order to overcome the shortcomings of ordinary reinforced concrete, which is prone to cracking, prestress can be applied to it. In order to overcome the brittleness of concrete, fibers can be mixed into concrete to make fiber concrete.

The statistical analysis method was used to propose the corrected positive calculation formula for the average crack spacing, average crack width and maximum crack width of the axial tension member of 500MPa reinforced concrete

Ferroconcrete.

The crack width of the beam is at the maximum crack width limit or normal.

The presence of cracks is a common phenomenon in concrete structures. A large number of scientific research and practice have proved that cracks in concrete structures are inevitable, and the load is often 15% to 25% of the ultimate load.

Under the action of normal use load, reinforced concrete structure is generally working with cracks, and the crack range that is generally visible to the naked eye is, and the crack width is less than the harmless crack, and the influence on waterproofing, anti-corrosion and load-bearing can be negligible.

The crack width defined in the Code for Design of Concrete Structures refers to the crack width of the concrete on the side surface of the component at the level of the center of gravity of the tensile reinforcement.

In addition to the calculation of bearing capacity and deformation, crack resistance, crack width and stress verification according to the use conditions, the construction stages such as production, transportation and installation should also be checked according to the specific situation.

When the prestress is considered as a load effect, its design value is given in the calculation formula of the relevant section of this code. For the ultimate state of bearing capacity, when the prestress effect is favorable to the structure, the partial coefficient of prestress should be taken. It should be taken when it is unfavorable. For the serviceability limit state, the partial coefficient of prestress should be taken.

The crack width defined in the Code for the Design of Concrete Structures refers to: (b).

The crack width of the reinforced concrete beam is at the maximum crack width limit or is normal.

The presence of cracks is a common phenomenon in concrete structures. A large number of scientific research and practice have proved that cracks in concrete structures are inevitable, and the load is often 15% to 25% of the ultimate load.

Under the action of normal use load, reinforced concrete structure is generally working with cracks, and the crack range that is generally visible to the naked eye is, and the crack width is less than the harmless crack, and the influence on waterproofing, anti-corrosion and load-bearing can be negligible.

The beam cracks are not normal and can only be treated with reinforcement methods.

It should be within 1 to 3 millimeters.

The crack spacing of reinforced concrete components is mainly related to the following factors:

1.Determine the properties of bulk cavity materials: The properties of concrete, steel bars and other materials in reinforced concrete components will directly affect the generation and propagation of cracks. For example, the strength, toughness, shrinkage and other properties of concrete will directly affect the width and spacing of cracks.

2.Stress state: The stress state of reinforced concrete excavation components is also an important factor affecting the crack spacing, such as load size and form, support situation, etc.

When the force acts on the component, it will cause stress concentration, strain change and other conditions, which will lead to the formation and expansion of cracks.

3.Construction process: The quality of the construction process will also directly affect the crack spacing of reinforced concrete components. For example, the quality of concrete pouring, the welding process of steel bars, the support of formwork and other issues will affect the overall quality of the component, thereby affecting the generation and expansion of cracks.

4.Environmental factors: Environmental factors such as temperature, humidity, wind load, etc., can also affect the spacing and number of cracks. For example, in a high-temperature, dry environment, concrete is prone to dry cracking, which leads to the formation and propagation of cracks.

Therefore, the crack spacing of reinforced concrete components is not only related to the properties of the material, but also closely related to many factors such as its stress state, construction technology and environmental factors. In the actual project, it is necessary to comprehensively consider various factors to ensure the quality and safety of the components.

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Answer]: The maximum crack width of the incorrectly reinforced concrete component is not equal to the average strain of the reinforcement between the cracks multiplied by the maximum crack spacing.

Answer]: b, c, d, e

This question examines the prevention and control of structural cracks in reinforced concrete structures. Prevention and control measures for structural cracks in reinforced concrete structures: (1) Select high-quality cement and high-quality aggregates.

2) Reasonably design the mix ratio of concrete, improve the aggregate gradation, reduce the water-glue ratio, mix mixed materials such as fly ash, and add retarder; Under the condition that the working conditions can be satisfied, the concrete with a small water-glue ratio and a lower slump should be used as far as possible. (3) Avoid mixing concrete for a long time before using it. (4) Strengthen the construction quality of the formwork to avoid problems such as template movement and bulging.

5) The foundation and support should have good strength, stiffness and stability, and preloading measures should be adopted; Avoid bracket sinking, uneven settlement of the formwork and premature demoulding. (6) When pouring concrete, it should be vibrated sufficiently; After the concrete is poured, it should be maintained in time and the maintenance work should be strengthened. (7) Low-hydration bonded heating cement such as slag cement should be preferred for large-volume concrete; The cooling measures of the sunshade pergola were adopted to reduce the heat of hydration of concrete and delay the peak of heat of hydration. The temperature difference between different positions of the same structure should be within the allowable range of the design.