Crack analysis in safe

[siham0700]

Do any one knows how SAFE apply crack analysis on slabs design, I did a sample calculations at the maximum deflection area in slab;
I calculate Mcr using modulus of rupture where Mcr= Fr*Ig/Yt , Fr=0.62*(sqr root of Fc')
found that Ma (From total DL+LL) < Mcr...thus mean that Ig will be used for total deflection calculations.
The value of deflection I calculated was very close to that obtained from safe model from linear analysis.
but when I defined the load cases for total deflection as nonlinear (cracked) with the true modulus of rupture value,the values for deflection became larger !!
It dose not make since unless the safe software is comparing the Mcr value with a different moment Ma value, probably the moment above columns !!am not sure what is the possibilities.

however I used the same procedure in the example at the below link:

https://wiki.csiamerica.com/display/safe/Cracked-section+analysis

 

[li0ngalahad]

Hi siham0700 I am having similar issues, I believe that the problem is in the Modulus of rupture used by SAFE which is much lower than that. In fact SAFE uses the following formula from ACI 435R-95 guidelines for deflection control in concrete structure) :

4*sqrt(f'c) [psi]
or
0.33*sqrt(f'c) [MPa]

which differs greatly from the formula you are using (which is also the one suggested in the ACI318-11 Eq 9-10) and from the formula used in AS3600-2009 (the code I use) which is 0.6*sqrt(f'c). This leads to much larger deflections. I prepared a spreadsheet that calculates long term deflections based on the Ian Gilbert suggested simplified method described on his book "Time-Dependent Behaviour of Concrete Structures", based on Bischoff formula for the effective second moment of area of section after cracking. The spreadsheet should be quite reliable (I checked it against RAPT software and values are never too distant one to each other) but the deflections I get in SAFE are much much larger. Introducing a custom value for the modulus of rupture in SAFE from the AS3600 formula, the value of the deflection becomes excessively low compared to my spreadsheet but much closer. However I am not too confident I can use this value.

In synthesis, the module of rupture is a pivotal value to use in the CSI SAFE cracked analysis, would be great if someone could give some suggestions or tips on its settings in particular for the use with AS3600.

HELP!

cheers

 

[JumanaMadi]

hello,

Does any of you know what these parameters are in crack width analysis of safe 12.

1- Parameter kt
2- Paramater k1
3- Parameter k2
4- Parameter k3
5- Parameter k4