Hello i need your help to understand this, iam using STAAD Foundation V9 Update 7.2.
Iam attaching STAAD File and SFA File having combined footing job and also MAT foundation jobs of the footings which could not be designed as combined footing in Combined footing job..
Footings cannot be designed in Combined job but in MAT foundation job it was designed.
0285.Structure1.STD
8272.Structure1_foundation.sfa
?
Few points to remember when you compare a combined footing model with a FE mat model.
1. For a combined footing job, the program will check a few conditions like gross bearing pressure below the footings, minimum contact area, sliding etc. If the foundation size is not meeting any of the above requirements, program reports as footing failed.
But, in the FE mat model, it does not check for these conditions, rather reports the bearing pressure, contact area % etc after a rigorous FE analysis. User should go through these results and make sure that the bearing pressure is within the allowable, or the contact area is within the limit, and so on. Even if these values are not within the limits, program does not give you a warning. User has to check these and increase the mat dimensions or other parameters accordingly.
2. In your combined foundation model, you have set the minimum percentage of contact area as 50% and program will try to increase the footing sizes to meet these criteria, whereas in your mat mode, the out of contact area is 65.20% and in this case you have to increase the mat sizes.
Same is true for bearing pressure,overturning and sliding checks.
Look at the screenshots from the mat analysis results
I have tried to ignore wood armer moment and my footing was designed and when i command the software to include wood armer moment my foundation fails.Now i would like to know when do we have to consider wood armer moment in footings and which factors can be used to ignore wood armer moment?
Wood Armer effects are considered to include the effect of twisting of the slab in the design for flexure. If the footing is short and thick, twisting is perhaps less likely. If it is long, wide and thin, twisting is more likely.
See the following documents if you need more information
https://www.concrete.org/Portals/0/Files/PDF/Previews/447R-18_preview.pdf
https://www.academia.edu/15396812/Twisting_Moments_in_Two_Way_Slabs_Design_methods_for_torsion_in_slabs_using_finite_element_analysis
Hello thank you Aswathi A , one last question.
When calculating subgrade modulus i have input parameters like bearing pressure, safety factor and allowable settlement, this allowable settlement i have to compare with which value shown in node displacement summary table, is it only Dy values? if yes then means my Dy value should not exceed that specified 25mm value? and for the case when i have Dy value as negative number what does that mean?
Compare it with Dy (the displacement normal to the surface of soil). Negative value for Dy means displacement is in the downward direction.
Thank you Aswathi, What if Dy has a positive value greater than settlement specified,how do we comment or make judgement in that scenario?