The model for a general composite section resulting from the introduction of composite dowels

A new form of shear connection, so-called composite dowels, first appeared in Europe in last decade. It enabled economic construction of steel-concrete composite bridges without an upper steel flange, using a direct connection between steel web and concrete slab. It finally resulted in new economic structural forms and composite sections that had not been used in bridge engineering before. In 2010 the European Commission launched an international project to build three different innovative bridges in three different European countries (Germany, Poland, Romania). Each bridge project was supported by a national consortium consisting of design office, general contractor and university. This economic technology has developed fast: by the end of 2016, at least 34 bridges using composite dowels had been constructed in Europe (13 in Germany, 11 in Poland, 4 in Czech Republic, 4 in Austria, 2 in Romania). These structures use different kinds of composite section that in many cases are not covered by standard design procedures for composite structures. The need for a consistent design method was evident. This leads to a clear design concept that covers the contribution of concrete slabs in transmitting part of the vertical force in composite sections and finally breaks with the concept of a “steel skeleton” constituting the fundamental part of the composite beam. The approach proposed here needs to be as simple and clear as possible, so it assumes some simplifications at this stage. It is intended to cover many types of composite section, externally reinforced section and conventional composite section.