STRUCTURAL DESIGN OF COMPOSITE CONCRETE-STEEL BEAMS WITH SPATIAL TRUSS REINFORCEMENT ELEMENTS

This paper deals with an atypical class of reinforced concrete beams, whose reinforcement is a steel truss structures. This typology of beams is quite unknown within the engineering community. Moreover they have been used for three decades in Italy, principally for industrial or special structures. Differently from traditional reinforced concrete beams, the steel trusses can bear their own weight and the weight of slabs and fluid concrete without any provisional support during a first dry assembly stage; after that, when concrete develop its own mechanical characteristics, they can collaborate with the cast in place concrete. Nowadays, interest for this technology is growing up in Italy, mainly because of some advantages it provides with respect to the traditional reinforced concrete beams. Nonetheless, neither in the current Italian nor in the European codes there are specific regulation for this class of reinforced beams. In order to achieve this goal, the main aim of this work is to illustrate possible mechanical models and verification principles to be used in designing these particular reinforced concrete beams when subject to static loads. Finally some practical design examples, done by using a specifically developed computer code, are presented to illustrate complete design procedures.