Generally, the structural steel satisfies the material strength specified in the standards. However, there are variations in the strength and stress-strain relationship. The purpose of this paper is to clarify the influence of the stress-strain relationship of the material on the strength behavior of simply supported plate under in-plane bending and compression by numerical analysis. The numerical analysis used consideration of the following four kinds of changes of the stress-strain relationship; (a)material strength, (b)Young's modulus, (c)the gradient of strain hardening, (d)the difference of gradient between elastic and plastic areas. Finally, this paper proposed the ultimate strength evaluation method of the simply supported plate under in-plane bending and compression.
