Frame Analysis
Frame Analysis
(OP)
Please see attached sketch for frames on existing equipment. I am looking for some general comments with regards to the analysis of the frame. Specification requirements typically reference AISC 9th or use basic allowables like 4 to ultimate and 2 to yield. There are some questions here because part of the frame is typicaly cast iron and part is steel so a consistent factor of safety is questionable. The main girder is analyzed as a simply supported beam, usually fastened to the columns with a single row of fasteners. The vertical columns are usually analyzed..depending on length which can range from 3 feet to 40 feet...using P/A or appropriate column formula. The vertical columns are usually structural tubing or cast iron. The frame is typically braced back to another row of frames or back to wall. So out of plane bending is not really an issue. The bracing also prevents sidesway in the plane of the frame. Is it approriate to analyze as mentioned or should a frame analysis be performed and the additional moments in the columns looked at. It appears that most of the original analysis paperwork does not perform a frame analysis. Loads are typically around 50-100 KIP. Past performance has not shown any problems. The equipment is part of a retrofit/upgrade and there is talk about replacing some of the items and possible redesign issues.






RE: Frame Analysis
Question yourself if any element is found to be under designed, you may need to check into older codes for such discrepancy.
RE: Frame Analysis
Bracing and connections would also be a concern.
RE: Frame Analysis
I would use a higher safety factor for the cast iron due to its potential non-homogeneity and brittleness.
RE: Frame Analysis
Best to assume frame analysis as a conservative case and then analyze cross beam as a simple span?
Some additional bracing is going to be provided for earthquake design as well. Main concern is in the lateral direction for sidesway.
RE: Frame Analysis
Yes, if this is single span beam with ends bolted.
You opening statement implies that this building, on top of materials, has some geometry irregularities. If lateral load effect is the concern, a frame analysis is justified and useful.