Part 1 – Problem 08: The definition of existing structure is unclear. When replacing flexible with rigid diaphragms, does existing structure include only the first 10 stories, or all stories on the existing structure with the addition?

For this question, change the diaphragms from flexible to rigid for all the levels from the bottom floor up to the 10th floor (roof of the existing structure). Keep the diaphragms of the extension (11th floor to roof level of the addition) flexible. You are asked to compare mode shapes of this configuration to mode shapes of the structure with all flexible diaphragms.