RAM Concept: Span Detailer Producing more Reinforcement

Hi all,

Just a quick question about the span detailing which I have never quite understood. Why is it that the design strips' span detailer produces more reinforcement? 

I understand that the overall quantity will increase, as the lengths of bars may be extended to supports etc, but when viewing skyline plots for "with" or "without" span detailing, I don't understand why the peak requirements are different. 

I've looked in the manual, and can't find much besides a note that simply states: Note that the design strips' span detailer setting of code produces more reinforcement.

Thank you

  • Hi Seth,

    Any further developments regarding this matter?
  • Seth,

    I have turned off code minimum calculations, therefore clause 9.4.3 is not considered (I check this manually myself). I am also specifically looking at the Strength Rule Set Design, and the controlling criteria along the entire length says "Det/8.1" (Therefore, ductility clause 8.1.6 is not the issue here).

    Looking further, when set to Without Span Detailing, the required area of steel in the column strip in the skyline plot is 1260mm2. when set to With Span Detailing, the required area of steel becomes 1510mm2.

    Using the auditor tool, shows the Final Pass 1 strength designer of 1260mm2 (8.1), but then says 1600mm2 (9.4.1).

    My guess, the larger amount of 1600mm2 is required to satisfy the serviceability stress requirements in the bar, but I don't understand why this is happening in the strength rule set design, and why the results changes in the skyline plots where span detailing is being considered. Is RAM mistakenly considering Service Design in the Strength Rule Set Designer?

    If this is the case, when then does the official RAM Manual State "Note that the design stips' span detailer setting of code produces more reinforcement".

  • For AS 3600 2009 your bottom steel is probably controlled by section 8.1.6 or 9.4.3.2. For span detailing of RC and PT Two-Way Slabs - Figure 9.1.3.4 is implemented in support and span regions. Clause (b) says to use 75% of the area required by one of Clauses 9.4.3.3 to 9.4.3.5, as appropriate, and often controls. 

    In a test model, for short to moderate span lengths where 9.4.3.2 controls, I do see that As Bottom (Developed) without Span Detailing indicates a smaller amount of steel compared to AS Bottom (Developed) with Span detailing. I'm still investigating why our skyline plots work this way, but the larger amount which controls does seem to be correct. 



  • Hi Seth, Thanks for the quick response.

    The slab is being design to AS 3600, and is RC only. The area in question is for the bottom steel positive moment region in a span. I also note that not all strips show a difference in reinforcement quantity between with and without span detailing.

    Thank you.
  • What design code are you using? Is your slab pot-tensioned or mild reinforced? Is it the top steel or bottom steel that you see this for? (Or send over your file and let me know what strip you are looking at)