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RAM Structural System self weight question

RAM Structural System self weight question

RAM Structural System self weight question

I am currently in the process of designing a simple steel framed, two-story building. The overall height is approximately 42 feet and the height from the ground elevation to the second floor elevation is approximately 15.5 feet. Whenever I run a lateral analysis for this structure, I am getting a second story drift of approximately 1.5 inches (not amplified per ASCE). This seems a bit high given the height and framing of the building. Additionally, the building is not in a high seismic region and we are using steel not specifically detailed for seismic design (R=3 and Cd=3). My project manager and I are stumped as to why we are getting such large seismic deflections. We looked at the weight of the floors (about 7400 square feet) and the second floor weighs 980 kips. However, when I calculate the weight by hand, I get approximately 550 kips.

Can someone provide some insight as to how RAM calculates the self weight of the structure? Or if there are any suggestions as to why I am getting such large deflections? Any help would be greatly appreciated!

RE: RAM Structural System self weight question

Are you including self-weight (mass) in the surface loads? If so, RAM may be calculating the mass while you are adding additional mass in the loads. To see if RAM is calculating the mass, I think you need to look in RAM Manager Criteria>Self Weight.

If self weight is not included in the surface loads, I would start by looking at the slab/deck definitions.

Note: with RAM, the weight for dead loads and the mass for seismic are defined separately. Also, when defining mass, just use the weight, don't try to convert it to slugs or any other real mass units.

RE: RAM Structural System self weight question

So after checking and re-checking and re-re-checking my calculations, I found my error. It turns out we had an applied line load (approximately 1.2 k/ft dead load) along the entire perimeter of the building. Once that is added into my numbers, I'm only a few kips off of the RAM model's numbers. Thanks for the help!

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