Reinforcement Distribution Areas
Three areas with different requirements for the required reinforcement cross-section per meter are defined. These areas are called distribution areas. The middle reinforcement area, which is assigned a width of 50 percent of the foundation side length perpendicular to the reinforcement currently being considered by the program during the design, is labeled "II" (Roman numeral two). The remaining two reinforcement areas are the so-called edge reinforcement areas. They are labeled "I" and "III" and are each 25 percent of the respective foundation side length wide.
Design strip
The foundation is divided into eight strips for each direction. The required steel cross-section per meter of each individual strip is shown below the slab. Each of these strips receives a different portion of the design moment for which the design is performed. The magnitude of the portions is determined using the so-called distribution numbers α1-4 according to Booklet 240, DAfStb [1] Table 2.9 for plate strips No. 1 to 4.
The required steel cross-section for the individual reinforcement areas is now determined. For the middle reinforcement area, this is always the required steel cross-section of the fourth plate strip. The largest steel cross-section to be covered for the edge strips depends on their width.
For the upper plate reinforcement, there is only one reinforcement area. Staggering would not be useful here because the required steel cross-section is the same in all plate strips.
Distribution Numbers
The distribution numbers are determined using the following quotients Q:
|
cx |
Column width in the x-direction |
|
cy |
Column width in the y-direction |
|
wx |
Foundation width in the x-direction |
|
wy |
Foundation width in the y-direction |
|
atx |
Top column allowance in the x-direction |
|
ttx |
Upper bucket wall thickness in the x-direction |
|
aty |
Top column allowance in the x-direction |
|
tty |
Top bucket wall thickness in the y-direction |
|
wx |
Foundation width in the x-direction |
|
wy |
Foundation width in the y-direction |
With these quotients, the distribution number for the respective strip can be determined according to the following table from DAfStb [1]:
| Q = 0.1 | Q = 0.2 | Q = 0.3 | |
|---|---|---|---|
| α1 | 0.07 | 0.08 | 0.09 |
| α2 | 0.10 | 0.10 | 0.11 |
| α3 | 0.14 | 0.14 | 0.14 |
| α4 | 0.19 | 0.18 | 0.16 |
| Sum | 0.50 | 0.50 | 0.50 |
If the determined quotient is less than 0.1, the values of α are determined from the column for a quotient of 0.1. If the determined quotient is greater than 0.3, a squat foundation is present, for which a staggered distribution of the design moment can be dispensed with. The distribution number α is then the same for all strips and is 0.125. If the determined quotient lies between the values of two columns, linear interpolation is performed.
The proportional design moment for a plate strip is then the design moment Mbottom (see chapter Determination of Design Moments ) multiplied by α.