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RAM Concept - Overturning Instability

Mike Poulos — Tue, 22 Sep 2020 00:24:56 GMT

Hi:

I am working on a project where we sized the footings at our BRB frames like small mat foundations in RAM Concept. We sized them to stay within the maximum soil pressures given by the geotechnical engineer. We now want to use RAM Concept to determine the maximum load that footing that was previously design can resist before having an overturning instability. We have increased the loads to something crazy and never get an instability warning. where is this reported? OR how do you determine if one exist in Ram Concept.

Ram Concept Vibration Analysis

Mike Poulos — Fri, 15 Apr 2016 01:30:26 GMT

I am working on a hospital project with MRIs and Surgery. The vibration requirements we were given for the MRI is a maximum of 500mips. The slab is 13" thick PT slab on a 28'-0" by 32'-0" bay. The bays are consistent across the entire building. I ran it using the modal analysis option, with the default values, to get a feel of where we are at vibration wise. According to the results we were around 20,000mips. Well above the requirements for even a standard office. I am not a vibration expert, but there is no way that a 13" PT slab does not meet office vibration criteria for this bay spacing.

Some of the default values seemed a little bit off to me compared to what I have done with steel buildings. First a foot fall of 2.5 steps per seconds (150 per minute) seems extremely high. This match more closely to the rhythmic events (dancing) from AISC design guide 11. I would have expected something closer to 1 to 1.5 steps per second. Them damping value used, and the suggested values in the User Manual, also seem low. The weight of the person in Ram is 200lbs. Not sure what Ram does to convert this to the foot strike force, but for steel it is in the 65# to 85# range.

Does anyone have experience using the Vibration analysis in Ram Concept and have a comfort level with the results. This is the first concrete slab I have had to check for vibration.

Thanks

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RAM Concept - Overturning Instability

Ram Concept Vibration Analysis