Modal Graph plotting help

I have time and acceleration data from vibration of a beam in a data file that i imported into MATLAB. The values were used to plot the system response graph and analysed using FFT to plot frequency-amplitude data and find the resonating frequencies. I want to use these values to plot the mode shapes of the beam. How do I do this? I have the values of frequencies and amplitudes stored in the arrays as fvec and XReal respectively.