Structural behaviour and reliability of CFST trusses with random initial imperfections

Concrete-filled steel tubular (CFST) truss is a type of composite structure with CFST chords and hollow tubular braces. CFST trusses have been increasingly used in large-scale structures such as towers, bridge girders, piers and arch ribs. The compression and flexural behaviour of CFST trusses are greatly improved compared to hollow tubular trusses due to the concrete infill in chords. With the complex configuration, nonlinear material interaction and sophisticated construction process, initial imperfections may largely affect the strength and stability of a CFST truss structure. Relevant studies in the past mostly focused on one single type of imperfection with assumed magnitude in CFST member whilst in reality a variety of combinations of steel and concrete imperfection exist. This paper develops a nonlinear analysis formwork with the reliability analysis of CFST truss with random imperfections based on on-site measurement data and Monte-Carlo (MC) simulations. Advanced nonlinear finite element analysis (FEA) that can account for the material interaction and confinement in CFST trusses is established and validated by reported test data. The flexural behaviour of CFST trusses with deterministic and probabilistic initial imperfections are evaluated and compared, based on which the reliabilities and related system resistance factors in regards to random initial imperfections are proposed.