| Square Root of the Sum of Squares (SRSS) |
This method estimates the peak response by the square root of the sum of the maximum modal responses squared.
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| Absolute Sum |
This method assumes that the maximum modal responses occur at the same time for all modes. It is the most conservative among the modal combination methods.
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| Complete Quadratic Combination (CQC) |
This method is based on random vibration theories. The peak response is estimated from the maximum modal values from the double summation equation.
where ρijis the cross-modal correlation coefficient and ξI and ξj are modal damping coefficients for modes I and j.
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| Naval Research Laboratory (NRL) |
The mode combination method recommended by the NRL takes the absolute value of the response for the mode that exhibits the largest response and adds it to the SRSS response of the remaining modes.
where
 represents the mode with the largest response among all modal responses.
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