Experimental study of concrete-filled multiplanar circular hollow section tubular trusses

This paper presents an experimental study on concrete-filled multiplanar tubular trusses made of circular hollow section (CHS) members. A total of four types of concrete-filled multiplanar tubular trusses including Triangular truss (TT), Inverse-Triangular truss (IT), Square truss (ST) and Trapezoid truss (TZ) were tested under static loading. The failure mode, load carrying capacity, overall deflection and strain intensity of all specimens are reported. The effects of top and bottom chord members, straight and diagonal brace members and lateral bracings on the load carrying capacity, flexural rigidity and ductility of all specimens were also investigated. The typical failure modes observed from the tests include the local buckling of straight brace members, the surface plasticity and shear failure of the bottom chord members, the weld fracture around tubular joints at the bottom chord members, and the end support failure of the top chord member. The load carrying capacity, flexural rigidity and ductility of different types of multiplanar tubular trusses made of identical CHS members are quite different due to the remarkable changes of the mechanical behaviour of CHS members. On the other hand, the lateral bracings play different roles under different load levels in enhancing the load carrying capacity of different types of multiplanar tubular trusses. It is demonstrated from the comparison that the Inverse-Triangular truss (IT) has optimum flexural rigidity, ductility and efficiency in practice.