Iu the previous plastic analysis of bipod-type mests, the collapse of the mast had been treated to occure in the plane of the masts or perpendicular to the plane.
In this paper, the collapse by the loads of which direction has an arbitrary angle to the plane of the mast are dealt with by using two different yield condition i. e., a spherical and a polyhedral yield surface.
Experiments were carried out on twelve specimens and these results were compared with the theoretical results.
The following were obtained conclusively.
(1) The collapse load calculated by using a spherical yield surface is higher by about 10% than by using a polyhedral yield surface.
(2) Experimental collapse loads coincided well, except particular cases, with the theoretical results by using a spherical yield surface.
(3) As the collapse loads calculated by using a polyhedral yield surface are in the safety sice by about 10%, this surface may be adequate to the actual design, thinking that the calculation is simpler.
(4) It is clarified that the collapsing load of mast subjected to the load having skew angle, is not so less than that subjected to the parallel or perpendicular.