In order to effectively prevent the occurrence of risky accidents during bridge construction, this study proposes a bridge construction risk assessment method based on variable weight theory and the cloud model theory. Firstly, the fishbone diagram was used to identify risk factors in constructing a bridge construction risk index system. Secondly, according to the cloud model theory, the comment cloud model of each risk index was established by using the forward cloud generator. Finally, the risk factor weights were quantified according to the intuitionistic fuzzy analytic hierarchy process (IFAHP). Combined with the variable weight theory, a zoning variable weight function was constructed and the weights were reallocated. Through the mutual aggregation of the comment cloud model and weights, the risk level of construction bridges was obtained. The method takes full account of the fuzziness and randomness existing in the evaluation process, optimizes the distribution of weight values of indicators, and uses Delphi iteration to effectively eliminate the subjective defects of individuals. A construction bridge in Changchun was used as an example for risk assessment, and the advance of the method was well verified. The results demonstrate that the method is highly feasible and effective after accuracy verification and sensitivity analysis.

The hybrid GFRP-concrete-steel double-skin tubular beams (DSTBs) are composed of the outer GFRP tube, the inner steel tube and the sandwich concrete between both tubes. They have attracted the attention of researchers owing to the high ductility, lightweight, corrosion resistance and convenient construction. However, there are few studies on the reinforced DSTBs under bending load compared with the unreinforced DSTBs. Eight circular cross-sectional composite beams are tested in this paper to investigate the flexural behavior, including five reinforced DSTBs, two unreinforced DSTBs and one solid reinforced concrete GFRP tubular beam. The main parameters include the longitudinal steel reinforcement ratio, the inner steel tube diameter, the GFRP tube thickness, and the concrete strength. The results show that all the composite beams exhibit ductile flexural failure, and the average displacement ductility factor of the reinforced DSTBs is 3.85. The arrangement of longitudinal steel bars significantly enhances the bearing capacity and reduces the mid-span deflection of the composite beam, and it is recommended to use a reasonable low steel ratio for the excessive steel reinforcement is adverse to the ductility. Increase of the inner steel tube diameter greatly improves the flexural capacity on premise of ensuring the stiffness and ductility. The outer GFRP tube provides moderate hoop confinement on the compressive concrete in the pure bending members, which limits the increasing extent of the flexural capacity. Reasonable confinement stiffness is suggested for the reinforced DSTBs to avoid insufficient or excessive constraint. Besides, concrete with sufficient compressive strength is recommended to be used in the hybrid DSTBs for it increases both the flexural capacity and the initial stiffness of the beam.