RAM Concept - Modelling Reinforcement within Core Base Foundation

I've imported the core base mat foundation in to RAM concept and modelled the supporting Piles as Point spring supports. When inputting the bottom reinforcement (H25@150 c/c in both directions) I am getting the need for additional bars within the foundation. This appears to be dependent on the level of cover, I have initially assumed 75mm to account for the pile embedment resulting in the need for ~9H12 bars along the left side.

When cover is reduced to 60mm there are no additonal bars required.

I also checked the effect of upping the cover to 100mm which resulted in fewer total additonal bars being required (only 1xH12 along the left side) but in more locations.

By default the additional bars in both cases are added with approx 30mm cover.

If the additional bars were to control cracking I can't understand why the increase in cover would not result in more bars being required, is there any reason for the large discrepancies?

See below screenshots:

75mm cover: 

100mm cover:

  • Check the Design Status layer - Bottom Reinforcement Plan. Turn on the Visible Objects control for "Controlling Criteria" to confirm which code section dictates the need for the additional bars. 

    You probably do not want to use any span detailing provisions in your design strip properties since you have user defined compete reinforcement. Set it to "None".

    You can use the section audit to drill into the details if needed. The small change in 'd' must be significant.