I am analyzing an existing structure. I have spread footings under frame columns. I have accounted for the self weight of the footing in my design, I strategically have not accounted for a surcharge. I have calculated the OSF and net uplift per the technical notes, and have been able to recreate the same values.
Two things:
1. Why is the uplift value only reported in some of the 'Spread Footing Design' reports for my frame columns, but not all?
2. I am getting this error on my frame columns even when my OSF > 1.0, why would this be?
1. The uplift check is omitted from the design report if there is not a net uplift force for any service load combination.
2. The overturning check is completed for the service load combinations. It is possible that there is a combination of large uplift and moment for a concrete load combination. If the resultant force for this load combination is outside the foundation, the program will not be able to determine the soil pressure distribution below the foundation and calculate the shear and moments to design the concrete.
Answer Verified By: Ashley Adams
Thank you for the timely response.
I have one question for clarification though. I have attached a design report as an example. You can see the error message at the top, the OSF > 1.0, the calculations for the concrete capacity are all good, and the soil capacity is calculated and good.
Are you saying that the excessive moment due to a concrete load combination is prohibiting the program to be able to analyze the reinforcement?
Additionally, how do I identify which concrete load combination is controlling this? (the combo listed for the OSF is a soil combination)