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RF-CONCRETE Members Version 5

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3.6.6 Standard

Standard

The parameters in this tab depend on the standard set in the 1.1 General Data window (see Figure 3.2). Here, you can specify standard-specific reinforcement data, which is described in the following for EN 1992-1-1.

Use the [Default] button in the bottom right corner of this tab to restore the initial values of the selected standard.

Figure 3.39 Window 1.6 Reinforcement, tab EN 1992-1-1
Percentages of Reinforcement

The input field controls the general maximum percentage of reinforcement for the beam. EN 1992-1-1, 9.2.1.1 (3) recommends a value of As,max = 0.04 Ac for tension or compression reinforcement and refers to country-specific regulations. The National Annex for Germany defines the maximum value of the sum resulting from tension and compression reinforcement with As,max = 0.08 Ac, which must not be exceeded, even in zones of overlapping joints.

Various

If the concrete compression area is no longer able to absorb compression forces, a compression reinforcement is required. This occurs if the bending moment is exceeded, which results from the concrete edge's compression strain of - 3.50 ‰ and the strain εyd when reaching the yield strength of the reinforcing steel. For rebars of the material type 500, a related neutral axis depth of x/d = 0.617 arises. In case of continuous beams, horizontal beams of non-sway frames, and structural components mainly stressed by bending, you should not use this limiting bending moment to its full capacity in order to ensure a sufficient ability for rotation.

With the check box you can limit the depth of the compression area according to EN 1992-1-1, 5.6.3 (2). In this case, the maximum ratio is xd/d = 0.45 for concrete up to strength class C50/60 and xd/d = 0.35 for concrete starting from strength class C55/67.

Shear Reinforcement

The two input fields define the allowable range of the compression strut inclination. If there are user-defined angles beyond the allowed limits of the standard, a corresponding error message appears.

EN 1992-1-1 provides an integrated model for calculating the shear force resistance. For structural components with shear reinforcement perpendicular to the component's axis (α= 90°), the following applies:

VRd,s = Asws · z · fywd · cot θ

Equation 3.2 Shear force resistance

where

Table 3.1

Asw

: cross-sectional area of shear reinforcement

s  

: spacing of links

fywd

: design yield strength of shear reinforcement

z

: lever arm of internal forces (assumed as 0.9 ⋅ d)

θ

: inclination of concrete compression strut

The inclination of the concrete compression strut θ may be selected within certain limits depending on the loading. This way, the equation can take the fact that part of the shear force is resisted by crack friction into account. Thus, the virtual truss is less stressed. These limits are recommended in EN 1992-1-1, Eq. (6.7N) as follows:

1  cot θ  2.5  

Equation 3.3 Compression strut inclination

The compression strut inclination θ can vary between these values:

Table 3.2 Limits for compression strut inclination
Minimum inclination Maximum inclination

θ

21.8°

45°

cot θ

2.5

1

The National Annex for Germany allows for a flatter compression strut inclination of 18.4°.

1.0  cot θ  1.2 + 1.4 · σcdfcd1 - VRd,ccVEd  3.0  

Equation 3.4 Compression strut inclination NA Germany

A flatter concrete compression strut results in reduced tension forces within the shear reinforcement and thus in a reduced required area of reinforcement.

Factors

The upper input fields control the Partial safety factors according to 2.4.2.4 for concrete γc and reinforcing steel γs. The values according to EN 1992-1-1, Table 2.1N are preset for the load-bearing capacity. In the same way, the recommended values are preset for the serviceability. They can be adjusted as needed.

The Reduction factor α for considering long-term effects on the concrete strength can be specified separately for compression and tension loads. Again, a differentiation by design situations is possible. The values recommended in EN 1992-1-1, 3.1.6 are preset.

According to the National Annex for Germany, the reduction factor of the concrete compressive strength to be applied with αcc = 0.85 is the same as the one of the concrete tensile strength αct = 0.85. According to EN 1992-1-1, remark to 3.1.7 (3), the value η ⋅ fcd must be additionally reduced by 10 % if the width of the compression area decreases towards the compressed edge of the cross-section. If this condition is given, RF-CONCRETE Members will perform the reduction automatically.