الفهرس | Only 14 pages are availabe for public view |
Abstract The fundamental property of the elastic critical load is that at critical load the frame, with its members remain elastic, offers no resistance to a small disturbing force or moment, for then the stiffness of the structure is equal to zero. In the static buckling analysis, the assumption is made that the stress remain within the elastic region and the material follows Hook’s Law. In general, to study the buckling strength of transmission towers, the joints are assumed rigid and the towers are treated as space frames. The transmission towers members are apparently slender and cannot resist safely the bending moments induced by rigid-joints. Thus, the analysis is not realistic. Also the computer capacity and the time consumed for the analysis are almost four times that of the space truss having pin-joints. Little attention has been paid to the actual stress-strain relationship above the proportional limit. The transmission towers are considered herein space trusses pinjointed. The members are of uniform cross sections and the loads are concentrated at joints. Beyond the yield stress, the relation between the change in stress and the change in the strain depends on the magnitude of the initial stress and is given by the slope of the compression test curve. An actual stress-strain curve of structural steel material is used for members stressed beyond the proportional limit to find formulas that relate the stress-strain and modulus of elasticity. Applications are performed for transmission towers made of structural steel in order to find their buckling strength. The towers were treated as rigid-joints space frames with its material follows Hook’s Law and as space trusses of pin-joints using an actual stress-strain curve. The results show that the buckling strength of the space frames are almost double that of the space trusses. It may be concluded that the buckling loads of the transmission towers being treated as space rigid-joints are not realistic. The analysis of post buckling behavior, introduced in this thesis, IS capable of predicting precisely the behavior and buckling strength of transmission towers. It offers significant aid for the design of structures. |