RF-CONCRETE Surfaces – Online Manual Version 5

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RF-CONCRETE Surfaces – Online Manual Version 5

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2.4.3 Determining the Statically Required Reinforcement

Determining the Statically Required Reinforcement

The stress-strain diagrams for concrete and reinforcing steel described in chapter 2.4.2 together with the allowable range of strain distributions (limit strains) represent the basis for determining the required longitudinal reinforcement for the previously determined design moments. This process is also documented in the design details.

Figure 2.39 Design details: Required longitudinal reinforcement

The first subentries for the required longitudinal reinforcement are the top and bottom side of the plate. There are main entries for the Bottom surface (+z) and Top surface (-z) that contain further details for each reinforcement direction.

Figure 2.39 shows that the reinforcement directions 2 and 3 only require very little to no reinforcement at the plate's bottom side.

Reinforcement Direction 1 is to be designed for the design bending moment mend,+z,φ1 = 35.89 kNm/m. The strains provide information about the determination of the longitudinal reinforcement.

The example shown in Figure 2.39 is checked for a dimensionless design procedure by means of a design table. The following input parameters are given:

  • Cross-section [cm]: rectangle w/h/d = 100/20/17
  • Materials: concrete C20/25 B 500 S (A)
  • Design internal forces: MEds = nsend,+z,φ1 ⋅ z+z,φ1 = 240.005 ⋅ 0.161 = 38.64 kNm/m
    NEd = 0.00 kNm/m

fcd = α · fckγc = 0,85 · 2,01,5 = 1,13 kN/cm2 

μEds = MEdsb · d2 · fcd = 3864100 · 172 ·1,13 = 0,1183 

For μEds = 0.1183, the following values can be interpolated from the design tables (e.g. [3] Annex A4):

ω1 = 0,1170 + (0,1285 - 0,1170) · (0,1183 - 0,11)0,12 - 0,11 = 0,1265 

σsd = 45,24 + (45,40 - 45,24) · (0,1183 - 0,11)0,12 - 0,11 = 45,37 kN/cm2 

With these values, the required longitudinal reinforcement can be determined:

As1 = ω1 · b · d · fcd + NEdσsd =0,1265 · 100 · 17 · 1,13 + 045,37 = 5,36 cm2/m 

Literatur
[3] Deutscher Beton-Verein e.V.: Beispiele zur Bemessung von Betontragwerken nach EC2. Bauverlag, Wiesbaden/Berlin, 1994.