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3.6.3 Reinforcement Layout
This tab defines how the reinforcement is inserted and which of the RFEM internal forces will be designed.
Both window sections are interactive with the option of whether to Design the provided reinforcement (see chapter 3.6): If the check box is selected, the covers refer to the edge distances c. They can be defined in the Concrete Cover section. If the provided reinforcement is not desired, the specifications refer to the dimensions of the rebars' centroidal axis u. They can be entered in the section Cover to Bar Centroidal Axis.
In the input field c-z(top), you can enter the concrete cover of the longitudinal reinforcement at the top; in the input field c+z(bottom), you specify the cover of the longitudinal reinforcement at the bottom. These values represent the nominal values of the concrete cover cnom (e.g. EN 1992-11, 220.127.116.11). Based on these specifications and taking into account the applied rebar diameters, RF-CONCRETE Members determines the lever arm of internal forces.
"Top" and "bottom" are clearly defined by the position of the local member axes in RFEM. The cover c±y(side) is needed for the equivalent wall thickness in the torsional design.
The position of the member axes is shown in the cross-section graphic to the right. In the RFEM work window you can display the local member axes by using the member's shortcut menu or the Display navigator (see Figure 3.32).
When entering the edge distances u for multilayer reinforcements, the distances must relate to the centroid of the entire reinforcement layer!
If you select the Minimum cover acc. to Standard check box, the default values of the selected design standard are set. It is also possible to [Edit] the parameters for determining the concrete cover. Clicking the button opens a dialog box with three tabs where you can adjust the specifications for the layouts individually.
The list contains a variety of possibilities how to arrange the reinforcement in the cross-section:
- top - bottom (optimized distribution)
- top - bottom (symmetrical distribution)
- top - bottom (define ratio As,top / As)
- top - bottom (define ratio As,tension / As)
- in corners (symmetrical distribution)
- uniformly surrounding
For the option -z (top) - +z (bottom) (optimized distribution), RF-CONCRETE Members also performs an optimization for biaxial bending load.
The reinforcement layout can also be defined by a user-defined Ratio of top reinforcement or tension reinforcement at the total reinforcement. You can enter the reinforcement ratio in the input field below. This enables you to analyze existing structural buildings.
For T-beams and I-sections, you can Distribute reinforcement evenly over complete slab width. With this option, the program releases a part of the rebars. It is also possible to reduce the distribution of the tension reinforcement over the effective width beff individually with a factor.
If a torsional reinforcement is required, it is distributed over the circumference by default.
Modifications to the reinforcement layout are shown dynamically in the graphic to the right.
In case of pure bending about the minor axis (My = 0; Mz > 0), increased reinforcement areas result for top - bottom reinforcement layouts: The design moment does not act in the specified distributing direction of the reinforcement. In this case, it is recommended to use the reinforcement layout In Corners.
All internal forces (axial and shear forces, bending and torsional moments) are taken into account for the design. This window section allows you to suppress particular internal forces in the performance of the design, for example, if very small torsional moments lead to problems in the shear analysis.
Modifying the default settings is the user's responsibility!