I have done all the training videos, read the manual, completed the exercises and now had my first attempt at doing a raft slab on springs in RAM Concept. I cannot get this software to give me a sensible answer so I am obviously doing something wrong. Have been trying for about 12 hours so need some help if anyone can spare a moment to have a look. I want to check the slab at 250mm thick with N12-200 EW T&B with 30mm cover.
1. Every load case I have entered is a ULS case yet I get a message saying the factors are not suitable for strength design.
2. Have I entered the reinforcing correctly, I feel like the software keeps adding in additional reo yet I want to use user defined and check it.
3. When I do a plot of maximum bearing pressure it tells me I have maximum & minimum values of 0kPa, why is this giving me such a strange result, is it related to the load factors RAM doesn't seem to like?
MY CLIENT IS SCREAMING FOR THIS SO A QUICK TURN-AROUND WOULD BE APPRECIATED. I have attached the Microstran file of the structure supported by this slab for information only.
Foundations rev 1.cptFree Roof.msw
Your soil is incredibly stiff, about 100,000 times the normal range, I think you might have a units error. This is likely the cause for some soil stress reporting issues.
Regarding load combinations. What I suggest to check the design combinations is to save a copy of the file, then "rebuild the combinations" (Criteria menu) and then compare to the saved file. If the differences are all intentional, i.e. you want a different load factor, then proceed with your combos. Some of the common issues are excluding the balanced or hyper-static loads from the combos, but if the slab is RC, that's irrelevant. Also make sure that the load type on your lateral loads is correct (i.e. is it wind-ultimate or wind-service?).
For the reinforcement, you might want to exclude the tiny strips from the edge column to the free edges (that's a very short span). With those design strips going right to the free edge you might have a rebar development length problem (or use anchored bars).
Some useful tips:
RAM Concept Loading FAQ
RAM Concept Design Strips TN
RAM Concept Reinforcement [FAQ]
The tips certainly helped clarify some issues but I still cannot get this model to work or produce a maximum bearing pressure plot. I had selected the wrong units hence why my soil was so stiff and have now corrected that issue but RAM Concept still will not plot maximum bearing pressure?
I also get a warning about there being net tension so I increased the iterations from 6 to 50 but this didn't help.
I now get a warning that the slab may be unstable and there is less than 25% contact area. This I find very strange, the uplift loads are tiny and I increased the slab to 400mm thick to see if this would remove the error (heaps of mass available) but it does not.
I am suspicious I have modelled something incorrectly but have no idea where to start looking as this is my first exposure to RAM Concept.
Also when I enter in the cover to reinforcing is it to the bar centre of gravity or to the outer surface, how can this be verified?
I have attached the current file for reference, any suggestions appreciated.
0777.Foundations rev 1.cpt
The problem here is stability, the first warning is
WARNING: The mat/raft is likely unstable. There is less that 25% contact area. Investigate Ultimate Wind LC: 0.9D + W Up North.
If you look at that load combination you'll see that the self-weight is not considered, but that self-weight is critical for stability.
When entering reinforcement cover in design strips, it's clear cover. With punching shear checks you specify the distance to the rebar group centroid, however.
5850.Foundations rev 1.cpt
That was an embarrassing oversight on my part, I thought it would happen automatically.
I have corrected it and the error messages have gone.
The only issue now is I still get zero on the Maximum Bearing Pressure, any idea why? Again I suspect I have entered something incorrectly but I don't know where to start looking to correct it!
Make sure you have at least one load combination with Active Rule Set - Soil Bearing Design (probably an unfactored service type combination).
Thanks Seth starting to get some useful results now.
For some reason RAM Concept keeps insisting I have anchored reinforcement in the solution but this isn't a possibility. I have attached two files:
1. Showing the solution with my main reinforcing mat "un-anchored" and you can see RAM Concept adds in anchored bars to obtain the solution.
2. Showing the solution with my main reinforcing mat anchored (not possible in reality) and you can see (other than 2 bars) RAM Concept is happy with the result.
How do I get around this issue, I cannot anchor these bars?
Central mat anchored.cptCentral mat un-anchored.cpt
In Australia we often use mesh to reinforce slab on ground, this is a Low Ductility product. I have added in the bar diameter from a couple of our standard mesh produces (SL82 & SL92) but there is nowhere to enter in the ductility.
As you can see in the screen capture low ductility reinforcing needs to be designed with a capacity reduction factor 0.65. What is being used by RAM Concept, I would assume the capacity reduction factor is being calculated in accordance with section (b)(i) of the table below not (b)(ii)? Where can I go in the report to verify what is happening?
AS 3600-2018 220.127.116.11 allows for a reduction in the development length where the full yield strength of the bar is not required. However, the reduced development length cannot be reduced below 12*db. As a result, RAM Concept considers the developed bar area to be 0 from the end of any bar to a distance 12*db away. In your model, I would edit support widths in the affected areas so that the support width is at least 12*db away from the slab edge to avoid the problem.
Regretfully, RAM Concept does not support Class L reinforcement. All reinforcement specified in RAM Concept is treated as Class N reinforcement.
The capacity reduction factor can be verified using the Cross Section Auditor as shown in the image below. See Chapter 33 in the RAM Concept Manual (Help - Manual) for information on using the Auditor.
I followed your advice and increased the supports to > 12 bar diameters, the solution still showed programme designated anchored reinforcement.
I then increased the support width to 500 mm so I was sure I had heaps of length to develop the bars, unfortunately the solution still provides programme designated anchored reinforcement.
This slab will have concrete placed tomorrow and they are installing reinforcing now so I am running out of time.
I am starting to regret using this software, I did it to try and get a better solution for my client now they are getting frustrated because it is taking so long and after all my effort I still don't have an answer I am confident with!
Hope to hear back quickly, I am running out of time fast, I have attached the adjusted file showing the above solution didn't work.Foundations rev 4.cpt
We called Ray yesterday and discussed why the anchored reinforcement was added. For others who come across this post, the program was extending reinforcement into the support and some of the strips were defined with the centerline of the support at the slab edge. See example below:
To eliminate the reinforcement, we pulled the end of the span segment off the slab edge and used a 0 support width. See below:
Another option would have been to keep the span segment modeled as-is and remove the support assignment at End 1. This would effectively make the strip a cantilever span.