Recent research developments in China on fatigue behaviour of welded joints of concrete-filled tubular trusses

Concrete-filled tubular steel trusses have been increasingly used in arch bridges in China in order to enhance the stability of arch trusses against buckling. This composite truss is usually made of hollow section braces and concrete-filled hollow section chords by welded connections between them. The fatigue problem of welded concrete-filled tubular joints is a new topic which needs to be investigated. This paper presents the current developments in China, particularly at Tongji University, of research on the fatigue behaviour of welded concrete-filled tubular joints. The research topics cover static experiments, finite element analysis and formulae for hot spot stress at the connection between a hollow section brace and concrete-filled hollow section chord, as well as the fatigue strength experiments. The types of composite joints investigated deal with T-type and K-type connections between CHS (circular hollow section) braces and concrete-filled CHS chords, as well as T-type and Y-type connections between CHS braces and concrete-filled SHS (square hollow section) chords. It is concluded that welded concrete-filled hollow section joints have a lower hot spot stress concentration and then higher fatigue strength than welded hollow section joints. The hot spot stress concept used in CIDECT guideline for welded hollow section joints can be adopted for the fatigue assessment of concrete-filled hollow section joints by means of an experimental S-N curve for the composite joints.