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Note: The calculation of the normal section bearing capacity in this section is based on the concrete strength rating of not more than C50. When the concrete strength rating exceeds C50, the relevant national standard “Code for Design of Concrete Structures†GB 50010 should be followed.
Second, the relative limits of the tension zone when the tension cold rolled ribbed steel and the compression zone concrete reach their strength design values ​​at the same time shall meet the following requirements:
(1) For reinforced concrete members, it is desirable that ξb = 0.37.
(2) For prestressed concrete members, the following formula should be calculated:
(2.1)
In the formula, b - the relative boundary pressure zone height;
Xb - the height of the boundary pressure zone;
H0 - the effective height of the section;
Fpy - the design value of the tensile strength of longitudinal prestressed steel bars shall be taken in accordance with Table 3.1.4 of this schedule;
σp0—The stress in the prestressed steel bar when the normal stress of the concrete at the resultant point of the longitudinal prestressed steel bar in the tension zone is equal to zero.
Note: The bending members of cold-rolled ribbed steel bars with different strength levels or different prestressing values ​​are arranged in the section tension zone. The relative compression zone height should be calculated separately and the smaller value should be taken.
3. The bent section of an inverted T-section with rectangular section or flange located in the tension zone shall have the flexural bearing capacity of the normal section in accordance with the following provisions (Figure 3.1):
M≤fcbx (h0-x/2)+fy′As′(h0-as′)-(σp0′-fpy′)Ap′(h0-ap′) (3.2-1)
Fig. 3.1 Calculation of the flexural bearing capacity of the flexural member with rectangular cross-section The height of the concrete compression zone should be determined according to the following formula:
Fcbx=fyAs-fy′As′+fpyAp+(σp0′-fpy′)Ap′(3.2-2)
The height of concrete compression zone should also meet the following requirements:
X≤ξbh0(3.2-3)
X≥2a′(3.2-4)
M in the formula - bending moment design value;
Fc—the design value of concrete axial compressive strength;
As—the cross-sectional area of ​​the normal rebar in the tension zone;
As′——the cross-sectional area of ​​the longitudinal normal rebar in the compression zone;
Ap—the cross-sectional area of ​​the longitudinal prestressed steel bars in the tension zone;
Ap′——the cross-sectional area of ​​the longitudinally prestressed steel bar in the compression zone;
b - the width of the rectangular section or the web width of the inverted T section;
H0—effective section height;
As' - the distance from the force point in the longitudinal compression zone to the edge of the cross section;
Ap′——distance from the resultant force point of the longitudinal prestressed steel bar to the pressure edge of the section;
a′——distance from the total longitudinal reinforcement point of the compression zone to the edge of the section under compression, when the compression zone is not equipped with longitudinal prestressed steel bars or when the longitudinal prestressed steel bar stress (σp0′-fpy′) of the compression zone is the tensile stress. , x in formula (5.1.3-4) is replaced by a' and as'.
Calculation of normal section bearing capacity of cold-rolled ribbed steel
Calculation of the normal section bearing capacity of cold-rolled ribbed steels 1. The basic assumptions for the calculation of the normal section bearing capacity of structural members are to comply with the relevant provisions of the current national standard “Specifications for design of concrete structures†GB 500l0.