Structural behavior of a continuous composite truss with a composite bottom chord

• Hybrid double composite truss bridge
• Experiments on a 30 m bridge model
• Flexural stiffness by lower composite chords and upper concrete slab
• Effective stiffness considering cracking
• Crack width

A continuous composite truss bridge combining steel box girders and composite truss girders was suggested to increase the span length of steel-concrete composite bridges. A bridge model with total length of 30 m was fabricated, and static tests were performed. Composite bottom chord members, comprising a concrete filled steel box section, increase the flexural stiffness of the composite truss section in the negative moment region, while cracking of the slab reduces the flexural stiffness of the composite truss section in the negative moment region. Before cracking at concrete slab, the longitudinal stress of top chord members was remarkably reduced due to the contribution of the concrete slab. After cracking, the effective stiffness of the concrete slab considering tension stiffening effects corresponded well with the measured deflection. Cracking and the crack width of the concrete slab were observed and measured. Crack width control by longitudinal reinforcing bars can be used for the serviceability design of concrete slab in tension.