Question
Is there a way to increase the mass participation factor in earthquake analysis?
I conducted an earthquake analysis on a structure composed of a two-story architectural steel frame and a two-story underground civil RC structure.
Despite specifying the mode order up to 1000, the mass participation factor is only 37% in the X-axis and 63% in the Y-axis.
How can I increase the mass participation factor to over 90%?
Answer
To secure the desired mass participation factor in a specific direction, it is necessary to check and proceed with additional conditions (boundary conditions, modeling simplification, etc.) to prevent the occurrence of unnecessary modes.
By managing boundary conditions and simplifying the model, you can prevent the occurrence of unnecessary modes and secure the desired mass participation factor in a specific direction.
To minimize unwanted local modes, you can adjust the stiffness of link conditions or arbitrarily set boundary conditions. Additionally, you can simplify the modeling by reducing the number of elements.
However, caution is needed as these changes might alter the behavior of the structure from the intended direction. Furthermore, the differences in results due to such changes fall under the designer's judgment, so they must be carefully decided so as not to affect the overall structural behavior.