RISAFoundation v12 now includes the ability to create a single layer of reinforcement anywhere in a slab. This improvement allows for a more straightforward design of thin, lightly loaded slab-on-grade where two layers of reinforcement (top/bottom) would be unnecessary. In order to add a single layer of reinforcement, users select Single Layer from the Rebar Options drop-down found in the Mat Slab tab of the Design Rules spreadsheet.
When a user selects Single Layer, only the inputs for Top Bar size and the Max/Min Top Bar Spacing are used. Additionally, the value of Top Cover found in the General tab is used to define the depth of the bar in the slab.
Note: When Mid-Depth Only is selected, the Bottom Bar size, the Max/Min Bot Bar Spacing and the Bot Cover are used.
The design of the slab will differ based on whether the reinforcement is placed above or below the mid-depth of the slab. When the single layer is placed above mid-depth, the slab will be designed according to slab-on-grade requirements found in ACI 360-R and ACI 223. These provisions focus mainly on design in response to crack control.
When the single layer is placed below mid-depth, the reinforcement is assumed to only resist moment in the bottom of the slab. If there is negative bending present, the top of the slab will be designed using the capacity of plain concrete.
After solution, the results are available in the Strip/Cut Results spreadsheet. You can also verify the that both a single layer of reinforcement and the appropriate cover is being used by evaluating the slab Detail Report.