INTRODUCTION
In the following two chapters the strength and behavior of beam-column segments subjected to compression combined with biaxial bending are presented. As the name implies, here we are only concerned with short beam-columns for which the effect of lateral deflections on the magnitudes of bending moments is negligible. As a result, the maximum strength occurs when the entire cross section is fully plastic or yielded in the case of metal compression members or when the maximum strain (or stress) attains some prescribed value in the case of reinforced concrete members. This is known as stress problem of first order. Material yielding or failure is the primary cause of the strength limit of the member. This chapter presents methods of analysis in predicting this limiting strength, and simple formulas to enable designers to assess this strength. The elastic-plastic behavior of beam-column segments subjected to biaxial loading is the subject of the following chapter.
In determining maximum strength of beam-column segments subjected to axial load and biaxial bending, ideal nonlinear stress-strain relations for steel and/or concrete, conservation of entire plane sections or each of the thin-walled that plates of which the section is composed are usually assumed. In the case of reinforced concrete or composite members, no slip and no tension resistance by concrete are further assumed.
When the position of the neutral axis is known or assumed, the magnitude of the resultant axial force P and bending moments M x and M y
