Computing model for influence of axial force on ultimate bearing performance of concrete segments

Taking into account the problems of small compressive depth and less than yielding strength for bars located in the compressive zone of concrete segments,a new computing model is proposed to evaluate the ultimate bearing per- formance of concrete segments. Under the actions of both axial force and bending moment,the concrete segment is sim- plified to column with eccentric compressive loading,and the expressions for force balance and bending moment bal- ance are derived. Based on the plane deformation assumption,the relationships between the stress of reinforced bars in the compressive zone and compressive depth in the concrete segment are proposed. Through two practical examples of underground tunnels lined by concrete segments,the influences of the axial force on compressive depth,the stress of reinforced bars and ultimate bearing performances of concrete segments are investigated. The computing results show that the ultimate bending moment of concrete segment increases with the increase of axial force,and the worst loading combination is the maximum bending moment with minimum axial force. The stress of reinforced bars in compressive zone cannot reach the yielding limit of material and are even in tensile state in some loading cases. The difference be- tween the assuming stress and practical stress for existing model is obvious. The proposed computing model can pre- cisely calculate the stress of reinforced bars in the compressive zone.