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Overview

1 Introduction

2 Theoretical Background

3.6.6 Standard

Standard

The parameters in this tab depend on the standard set in Window 1.1 General Data (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*, *EN 1992-1-1* tab

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 A_s,max = 0.04 A_c 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 A_s,max = 0.08 A_c, 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 ε_yd 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 ensues. 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 x_d/d = 0.45 for concrete up to strength class C50/60 and x_d/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:

$V_{R d, s} = \frac{A_{s w}}{s} \cdot z \cdot f_{y w d} \cdot cot θ$

Equation 3.2 Shear resistance according to EN 1992-1-1, Eq. (6.8)

where

Table 3.1
A_sw	cross-sectional area of shear reinforcement
s	spacing of links
f_ywd	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 into account the fact that a part of the shear force is resisted by crack friction and the virtual truss is thus less stressed. These limits are recommended in EN 1992-1-1, Eq. (6.7N) as follows:

$1 \leq cot θ \leq 2.5$

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°.

$1.0 \leq cot θ \leq \frac{1.2 + 1.4 \cdot \frac{σ_{c d}}{f_{c d}}}{1 - \frac{V_{R d, c c}}{V_{E d}}} \leq 3.0$

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 γ_c and reinforcing steel γ_s. 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 for the concrete compressive strength to be applied is α_cc = 0.85, the one for the concrete tensile strength is also α_ct = 0.85. According to EN 1992-1-1, remark to 3.1.7 (3), the value η ⋅ f_cd must additionally be 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.

Parent section

3.6 Reinforcement