May 29, 2012

How Does RISAFloor Address Connection Eccentricity and Skip Loading on Columns?

RISAFloor v4 has the capability to automatically skip load columns. Skip loading is the process of determining the worst-case scenario of pattern loads which can be applied to a column. In order for this to be effective the column must be receiving moment from the beams which frame into it.

Typically this comes from the eccentricity between the centerline of the column and the location where a beam is shear connected. In the example below this value would be equal to [(d/2) + ec]. Whenever a steel beam is drawn in RISAFloor it is automatically assigned an offset equal to d/2. Additional eccentricity can be assigned through the Connection Rules.

Clearly if a column has beams framing into it from both sides, with equal end reactions and eccentricities, then the net moment on the column would be zero. However, if the live load reaction from one of the two beams were ignored there would be a moment on the column, which could result in a higher code check on the column. Because live load placement is unpredictable in practice, this case must be considered.

Column skip loading is enabled by default in the Global Parameters. During a solution the program checks every permutation of live load pattern at each floor for each column. The final code check and design of the column is based on the worst case, which may be viewed in the Column Detail Report.

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