2.Concrete Material Strength Requirements and Mechanical Property Parameters in Structural Design

Minimum Strength Grade Requirements for Different Concrete Members
For plain concrete structures, the concrete strength grade shall not be lower than C20. For reinforced concrete structures, the concrete strength grade shall not be lower than C25; when reinforcement with a strength grade of 400 MPa and above is used, the concrete strength grade shall not be lower than C25. For prestressed concrete floor structures, the concrete strength grade is not recommended to be lower than C40 and shall not be lower than C30, while other prestressed concrete structural members shall have a concrete strength grade not lower than C40. When reinforcement with a strength grade of 500 MPa and above is adopted, the concrete strength grade shall not be lower than C30. For reinforced concrete members subjected to repeated loads, the concrete strength grade shall not be lower than C30.
Note: Plain concrete refers to concrete without load-bearing reinforcement; prestressed concrete improves crack resistance through pre-applied compressive stress. The above grade limits are specified in the referenced design specifications.

Standard Values of Concrete Axial Compressive and Tensile Strength
The characteristic values of concrete axial compressive strength and axial tensile strength are fundamental material indexes determined by standardized test methods and statistical principles, which reflect the basic mechanical performance of concrete materials. The values corresponding to each concrete strength grade are shown in the tables below.

Table 1 Characteristic Values of Concrete Axial Compressive Strength (N/mm²)

Table 2 Characteristic Values of Concrete Axial Tensile Strength (N/mm²)

Note: fck represents the characteristic value of concrete axial compressive strength; ftk represents the characteristic value of concrete axial tensile strength. The unit N/mm² is equivalent to MPa, and the definitions fully conform to the referenced standard provisions.

Design Values of Concrete Axial Compressive and Tensile Strength
The design values of concrete axial compressive strength and axial tensile strength are applied to the ultimate limit state calculation of structural bearing capacity, which are derived from characteristic values adjusted by material partial safety factors. The specific values for each strength grade are listed in the tables below.

Table 3 Design Values of Concrete Axial Compressive Strength (N/mm²)

Table 4 Design Values of Concrete Axial Tensile Strength (N/mm²)

Note: fc represents the design value of concrete axial compressive strength; ft represents the design value of concrete axial tensile strength. Design values are used for bearing capacity calculation, which is a general regulation of national concrete structure design standards.

Elastic Modulus and Deformation Parameters of Concrete
The modulus of elasticity of concrete under compression and tension shall be selected according to standard graded values. The shear modulus of concrete can be taken as 40% of the corresponding elastic modulus value, and the Poisson’s ratio of concrete can be taken as 0.2. The elastic modulus values for each concrete strength grade are shown in the table below.

Table 5 Modulus of Elasticity of Concrete (×10⁴ N/mm²)

Notes:

1. When reliable test data are available, the elastic modulus can be determined according to measured results.

2. When concrete contains a large amount of mineral admixtures, the elastic modulus can be determined according to measured data at the specified age.

Note: Ec represents the modulus of elasticity of concrete; Gc represents the shear modulus of concrete; νc represents Poisson’s ratio of concrete. The 40% ratio and 0.2 Poisson’s ratio are specified in the referenced standard provisions.

Disclaimer

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The data in this article are derived from publicly available industry standards and engineering experience. The viewpoints presented are for reference only. For specific schemes and data in actual engineering projects, adjustments shall be made in combination with the actual conditions of the project.

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