ABSTRACT
The essential formulations of the author’s theory have been printed in two books (Obrębski, 1991, 1997). There is given theory of the first and second order, for statics and dynamics of straight bars with practically any type of cross-sections—including homogenous, composite, thin-walled and full. There, special attention is turned on stability problems of mentioned bars. Next, in period of time 1997 up to now, the theory was completed by e.g. uniform criterion for critical states of bar behavior and for geometrical unchengeability of structures, too. Moreover, were performed many numerical and experimental tests for better recognition of considered bars behavior. This paper presents more important observations and conclusions accumulated in the last years since SEMC 2013. Some examples shows critical ultimate surfaces for combined loadings, and critical izo-surfaces for longitudinal eccentric force. So, certain form of instability of single bars can occur not only by compressing of single bars including eccentric compression, but also by pure bending and by any combined loading. Instability of the bar is possible by tension of the bar, too.
