Mechanical performance based rationalization research on steel-concrete double composite action

Casting an extra concrete bottom layer to a steel-concrete composite box girder in a hogging moment region can increase sectional stiffness and prevent steel buckling. However, a lower sectional neutral axis may not be favorable to concrete slab cracking and steel flange stress control. To this end, a double composite girder segment was proposed and investigated. Particularly, a static loading test on a large-scaled two-span continuous girder specimen with the double composite action in hogging moment region was conducted for mechanical investigation. Meanwhile, parametric analysis was carried out as well for a rational design scheme of the double composite section. The test results revealed that the load-carrying capacity of double composite section could be increased due to the contribution of extra bottom concrete layer. The transverse deformation of steel parts was favorably constraint. The parametric analysis results indicated that slab thickness that was 15% of steel girder height could provide most obvious contributions to the improvements of both sectional load-carrying capacity and cracking moment. Due to the additional reinforcement, the steel web thickness of double composite girder can be saved 16.7% and the steel bottom flange thickness only needs to meet the constructing requirement compared with common composite girder. Besides, the analysis also showed replacing the tub section with steel box section in the hogging moment region can reduce the stress on top flange by 24.4%. These results are an important basis for establishing a rational design scheme for the novel double composite section.This research is sponsored by the National Natural Science Founda-tion of China (No. 51978501) and the China Scholarship Council (No. 202106260050). The supports are gratefully appreciated.Peer ReviewedPostprint (author's final draft