Flexural behaviour of concrete filled steel tubular (CFST) chord to hollow tubular brace truss: experiments

• Flexural behaviour of CFST trusses with or without a concrete slab was investigated.
• Failure modes and the effect of main parameters were discussed.
• Strain development of both the CFST truss and concrete slab was analysed.
• Simplified models for flexural stiffness and flexural strength of the trusses.

Concrete filled steel tubular (CFST) chord to hollow tubular brace truss (referred to as CFST truss for short) is a type of truss which uses CFST members as its chords and hollow tubes as its braces. A concrete slab can be provided on the CFST truss to form a hybrid CFST truss. The new type of trusses can be used in bridge structures and other large span structures. This paper reports a series of bending tests on CFST trusses and hybrid CFST trusses. Hollow tubular trusses were also tested for comparison. The main parameters investigated were the shear span ratio, the angle between the brace and chord, profile of the bottom chord, the existence of the infill concrete and the concrete slab. The influences of these parameters on the flexural behaviour and failure modes of the trusses were investigated and compared. The results showed that both the infill concrete and concrete slab improved the flexural performance of the truss notably. The strain development of the truss and the strain distribution along the mid-span section were also presented and discussed. Based on existing design codes, simplified models for the flexural stiffness and flexural strength of the trusses were suggested and verified, respectively.