الفهرس 
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Abstract
Tubuler sections are extensively used in structures ranging from factory buildings and simple trusses to complex space frames and offshore structures. This is mainly due to their inherent advantage over other sections offered by their shape, such as superior strength to weight ratio. Their geometrical shape effectively resists torsion and out of plane forces. One of the difficulties encountered in practice, however, is to determine the ultimate load of such connections of different geometric configurations
Tubular sections (Hollow Structural Sections HSS) may be rectangular hollow section (RRS), square hollow section (SHS) or cricular sections Figure (1-1). A method of determining the ultimate load of tubular section as shown in Figure (1-2) is by treating the wall of this hollow section as thin rectangular plate loaded out of its plane. The yield line method of analysis is used because it provides an economical and effective means for predicting ultimate strength of plate laterally loaded.
The yield line method is a simple and efficient method to calculate the plastic collapse load of the plate. There are two approaches in the yield line theory; the virtual work method and the equilibrium method. Both methods lead to identical upper bound solutions. In the yield line method, a plastic collapse mechanism of the plate is assumed consisting of undeformed plate segments connected by plastic hinge lines, usually called yield lines. The mechanism must be kinematic ally admissible over the whole plate and at its boundaries.