Hello,
I am trying to design a basic concrete slab that includes a SLS Non-Linear Analysis task as well. My question is regarding the the design results that are stored in different design cases. Based on what I could understand from the various manuals this is what I have been doing.
The linear load combinations for ULS are run in ASE.
Task Design Parameters for Area Elements: Design Parameters for Area elements are set with min and max reinforcement. Crack width is specified
Task Design ULS for Area elements: Reinforcement is calculated for ULS design combinations (Type D) and reinforcement results are stored in Design Case 1. (This already includes the minimum reinforcement from Step 1)
Task Non-Linear Analysis in SLS: Using the base reinforcement of Design Case 1 (in step 3 above), a non linear analysis for a Quasi Permanent Combination (Type P) is carried out with appropriate creep and shrinkage factors. Any reinforcement, if increased to adjust stress levels is stored in Design Case 99. I am assuming that reinforcement values given here are the reinforcements combining that from both Step 3 and Step 4.
Task Design SLS for Area Elements: The Non Linear Load combination from Step 4 is used for this task and the base design case or minimum design case is 99 from Step 4 above. The results from this design task are then stored in Design Case 2.
Reinforcement values are then read in WinGraf for Design Case 2 as final values.
I would like to know if the procedure is correct or do I still need to insert this following code at the end for enveloping all the design cases.
+PROG BEMESS urs:52.1
HEAD
CTRL LCRI 1,2,99
LCR 11
END
I hope, I have been able to explain my question properly.
your explanations are correct. You don’t need to envelope all the design cases in the end. Although I would first run Task Design SLS Area elements and after that Task Non-linear Analysis in SLS. Reinforcement distribution 99 is usually only stored for graphical checks, unless steel stresses are checked with CHKR. So I would use it as the “final” reinforcement distribution and calculate the nonlinear analysis with the reinforcement distribution 2 from the SLS design. Nevertheless, it is also possible the other way round.
I had a chance to go through the tutorial mentioned by you which is well explained and quite detailed. However I have a conceptual question. As per the tutorial one must
Do a ULS design using “Uncracked” forces and store the reinforcement in DC10.
Do a SLS Design using “Uncracked” forces and DC10 and store it in DC15.
Do a Cracked SLS Analysis using DC15 and store in DC35.
I would like to ask if the following steps still makes sense.
Do a ULS design using “Uncracked” forces and store the reinforcement in DC10.
Do a Cracked SLS Analysis using DC10 and store in DC35.
Do a SLS Design using “Cracked” forces (from 2) and DC35 and store it in DC15.
And then read DC 15 as the final value.
I would assume that doing first the non-linear cracked analysis will give us the “actual” stress values which should then be used for doing the SLS design.
ULS uncracked:
Start off with this to get a quick estimate of actual reinforcement content.
The design calculations are straightforward and the assumed reinforcement does not influence results (too much).
SLS uncracked:
Iterative design calculations and the result is more heavily affected by the assumed reinforcement content.
The sectional forces are previously calculated in a linear analysis and the design reinforcement is calculated using ULS uncracked as a base line/first guess.
Under the hood the design calculations are iterative, since reinforcement content is an input to crack width calculations
SLS cracked
The entire analysis is non-linear and you want the first guess of the reinforcement content to be as correct as possible.
The calculations are theoretically more correct/complete, since you are considering the stiffness variations due to reinforcement content when calculating sectional forces/stresses.
Basically you want a good first guess for reinforcement content in SLS design either way, but:
SLS uncracked:
System calculation and design calculation are separate processes and only the design calculation is dependent on reinforcement content.
SLS cracked:
All calculations are non-linear and dependant on reinforcement content
→ More time consuming, i.e. you want a better starting guess here.