In this paper, the behaviour and the strength of simply supported plates (aspect ratio α=1,2 and α=∞ (infinitely long plates)) under combined loads of biaxial compression and hydrostatic pressure are theoretically investigated following the previous studies. At the sametime, effects of aspect ratio of plates on the behaviour and the strength are also discussed from these results. Results obtained in this study are summarized as follows: 1) Carrying out the analyses based on basic equations deduced to pursue the elastic behaviour of plates under such combined loads, characteristics of behaviours including buckling phenomena are clarified. 2) The compressive strength of such a plate is calculated in the same way as the previous paper), and characteristics of the compressive strength and the collapse mode of the plates (α=1,2 and ∞) are clarified. 3) From above results, it is found that in the case of plates having the small value of compessive loads ratio P_y/P_x effects of aspect ratio of the plate on the behaviour including buckling phenomena and the compressive strength are generally similar to those in the case of P_y/P_x=0, while in the case of plates having the large value of P_y/P_x those are different and in the case of comparatively thin plates the compressive strength for the plate of α=∞ is remarkably low in comparison with those for plates of α=1,2.
