Temporal variations in B/P strength, P_s, defined as the maximum value of the median height of the stellar particles relative to the initial value. In our models, P_s increases gradually due to bar formation and enhancement in CMC and bar mass, except for model W00, which undergoes a buckling instability to increase P_s rapidly at ﹩t\sim 3.5\,\mathrm{Gyr}﹩.