For beams and slabs:
SLS
1.) check stresses in concrete section and reinforcement
2.) calculate cracking widths
3.) calculate deflections with creeping and shrinkage effects
Modeling:
Create a beam that is bonded with a slab (T-section, "rib")
Thank you
čempres wrote:
For beams and slabs:
SLS
1.) check stresses in concrete section and reinforcement
Yes
2.) calculate cracking widths
Yes
3.) calculate deflections with creeping and shrinkage effects
Modeling:
Create a beam that is bonded with a slab (T-section, "rib")
http://forums.autodesk.com/t5/Robot-Structural-Analysis/Hollow-block-slab/td-p/4858886
I would like to do an simple egsample just to compare Robot and the program we are curently using.
Would it be a problem for you?
I was thinking of a simple rectangular beam 20/40cm, concrete c25/30, span 5,00m, selfweight +dead load of 5kn/m and live load of 8kn/m.
Generate a combination for ULS and SLS (quasi-permament)
creeping coeficient = 1,80
shrinkage coeficient = 0,0005%
Im very interested in how Robot presents all these results and checks (cracking width, stresses in concrete and steel, and deflection)
p.s. generating shinkage and creep effects with temperature isnt a calculation according to the CODE!
Shrinkage : According to which code you can't model using temperature loading?
What is your alternative method to model this effect?
Creeping, is usually taken into account with lower value for E.
Correct, creep only influences the E modulus of a materials.....so you can create a separate material for SLS ?
Shrinkage influences curvature of a member....so for egsample when using shrinakage coeficoefficient of 0,0005% how would you mimic this effect using temperatue?
When presenting SLS checks in ROBOT how does the program present the results?
In graphical view like presenting a diagram of cracking widths, steel stresses and concrete sresses for a member or something similiar?
Correct, creep only influences the E modulus of a materials.....so you can create a separate material for SLS ?
You can do that and have to model for general checking or seismic analysis for example (same problem when taking into account cracked inertia), you can also have a creep coefficient to check long term delfection (many posts do exist on this subject) but honestly I am not the expert I usually to design element that can be affected by this phenomenom)
Shrinkage influences curvature of a member....so for egsample when using shrinakage coeficoefficient of 0,0005% how would you mimic this effect using temperatue?
Sorry but this is incorrect, skrinkage is a strain -> if the strain is constant on the whole section then it doen'st influence curvature, it only shortens the element with the resulting traction is the extremeties are blocked. If water evaporates only from one side of the element THEN you will have a non constant strain that will affect curvature (for example slab with insulation and water barrier under or above it). This can be model with a temperature gradient (you heat or cool one face but not the other and this can be set in robot as a simple load case.
When presenting SLS checks in ROBOT how does the program present the results?
In graphical view like presenting a diagram of cracking widths, steel stresses and concrete sresses for a member or something similiar?
Please try ...
"You can do that and have to model for general checking or seismic analysis for example (same problem when taking into account cracked inertia), you can also have a creep coefficient to check long term delfection (many posts do exist on this subject) but honestly I am not the expert I usually to design element that can be affected by this phenomenom)"
So you have an option in ROBOT to asign an creep coefficient to a member?
"Sorry but this is incorrect, skrinkage is a strain -> if the strain is constant on the whole section then it doen'st influence curvature, it only shortens the element with the resulting traction is the extremeties are blocked. If water evaporates only from one side of the element THEN you will have a non constant strain that will affect curvature (for example slab with insulation and water barrier under or above it). This can be model with a temperature gradient (you heat or cool one face but not the other and this can be set in robot as a simple load case."
Sorry no, you are wrong!
The situation you are describing is a PEREFCT situation of a member wich is able toshrink withou any restrain. In concrete structures everything is restarined due to member interconecting with each other. Any yes for a simple single span beam wich isnt restarined anywere you still have to account for the reinforcement effect wich will generate axial stresse when concrete starts to shrink. This will always aply if you member has diferent reinforcement are in the top and the bottom. If the are the same, then your statement is correct, but only for a simply suported element wich can freely shrink.
So there is no graphical control in Robot when checking for SLS checks (crack widths, concrete ctresses reinforcement stresses)
File attached...you can see that max value permited is 0,3mm for cracks and in graphicaly view you can see the ratio wich is happening in your slab ....everything above ratio=1,00 is not satisfied....then you have aditional option of increasing reinforcement area in member or changing dimensions of a member
So you have an option in ROBOT to asign an creep coefficient to a member?
See attachment in my previous message
Sorry no, you are wrong!
The situation you are describing is a PEREFCT situation of a member wich is able toshrink withou any restrain. In concrete structures everything is restarined due to member interconecting with each other. Any yes for a simple single span beam wich isnt restarined anywere you still have to account for the reinforcement effect wich will generate axial stresse when concrete starts to shrink.
I confess I have never perform such a detailed calculation, I mean account for the restraining effect of rebars and the effect on the curvature in the case of a constant strain but with non symetrical reinforcement (and this is clearly the case for any horizontal element). But I am not sure this is governing the effort/deformation compared to element in which the water evaporates non symetrically.
This will always aply if you member has diferent reinforcement are in the top and the bottom. If the are the same, then your statement is correct, but only for a simply suported element wich can freely shrink.
My point wasn't particularly on "there will be effort or not to address the blocked strain", it was more to say skrinkage shortens more often than curves and when it curves is more likely because the relative humidity on one side is different than on the opposite.
Anyway, Robot or any other software is allows to model an estimation of this effect using uniform and gradient temperature load cases.
"See attachment in my previous message"
upppps, sorry. I didnt understand the text...this is france language right?
"I confess I have never perform such a detailed calculation, I mean account for the restraining effect of rebars and the effect on the curvature in the case of a constant strain but with non symetrical reinforcement (and this is clearly the case for any horizontal element). But I am not sure this is governing the effort/deformation compared to element in which the water evaporates non symetrically"
Whats there advanced aboth it?!
Its just basic stuff.
Wich design code are you based?
If you look at the Eurocode 2, section 7.4.3. point 6. you can clearly see the "S" value - first moment of area, that reinforcement has on the curvature of a member in bending. Nothing fancy here.
If you do a manual calculatin according to this standard you can clearly see how the reinforcement amount has an impact on the member deflection.
Ok.
I still didnt get the explanation how to simulate the skrinkage using a temperature in Robot?
EC 2 section 3.1.4. goes in detail how to caluclate these for you SLS checks but I would like to know how you do this without this option.
p.s. can anyone please attacj a photo , like I did in my previous post, just to see hoe you read the results of SLS checks.
Thanx!