Abstract
The behaviour of thin walled composite (TWC) filled beams with normal (NC) and lightweight volcanic pumice concrete (VPC), is described. Comprehensive series of tests provided information on the loaddeflection response, failure modes, stress-strain characteristics and effect of different modes of interface connections. The strength of the beam is limited by the compression buckling capacity of the steel plate at the top of the open box section. The enhancement of strength of such beams can be possible by stiffening the compression steel plates at the open end of box section with various modes interface connections. The design of such beams should consider local buckling of steel and interface shear bond characteristics.