How can I perform progressive collapse analysis (e.g. remove column and get dynamic response) in SAP2000?
SAP2000 can be used to model progressive collapse in the sense of studying how removing certain elements affects the structure. You can simulate this type of progressive collapse analysis with dynamic effects by running time history analysis as follows:
(1) Create "Model A" that contains the entire structure, including the column to be removed. Analyze Model A to obtain internal forces for the column to be removed.
(2) Create a "Model B" that does not contain the column to be removed. However, simulate the presence of column to be removed by applying end column forces obtained from Model A to the appropriate joints of the model. The column forces are essentially equivalent column loads.
(3) Run time history analysis to simulate the removal of the column by reducing the equivalent column loads to zero over a short period of time. This can be done by applying "column removal loads" that would be opposite to the equivalent column loads described in step 2 and whose magnitude would get increase from zero to full value in short time by using a ramp time function. How short (or long) the time should be would depend on how quickly the column is removed and you should use your judgment to decide this.
You can consider one of the following two approaches for applying the DEAD load:
- Apply the "DEAD" load together with the equivalent column load in a nonlinear static load case. Then the time history load case for column removal would start at the end of the said nonlinear load case and would remove the equivalent column load via a corresponding time function.
- Using a single time history load case, the "DEAD" load and the equivalent column load could be applied using one time function that would gradually ramp the loads to their full value and the column removal load could be applied via a separate time function with a later arrival time.
It is however important to remember that this type of progressive collapse analysis has certain assumptions and limitations. For example, it is not possible to model the effect of the collapsing structure hitting the structure that is still standing.
- Analytical Tools for Progressive Collapse Analysis by Robert Smilowitz
- Dynamic Analysis Procedure for Progressive Collapse by Elizabeth Agnew, and Shalva Marjanishvili; STRUCTURE Magazine, April 2006 - provides some SAP2000 specific information