Mechanism and calculation theory of prying force for flexible flange connection

The flexible flange is a common connection for circular pipe structures, and the prying force appears when the flange bears tensile force or moment. Based on the load-carrying characteristics of T-shape steel plate connection under tensile force, a simplified model for prying force is built and the calculation theory is proposed, in which the factors of moment ratio α and moment arm x are assumed. The mechanical behavior of the connecting bolts for flange is analyzed, and the formula of bolt force and additional moment is derived. Meanwhile, three typical flexible flange connections are tested under tensile force and related FE analysis is implemented. The theoretical analysis is performed to investigate the effect factors of prying force in the tensile region of connection. The corresponding parametric analysis is conducted. It is proved that the ratio of outer to inner edge of bolts, and the flange plate thickness have a great effect on prying force. According to theoretical analysis and FEA results, a modified design formula is established in which the value of α is 1.0, x is 0.6a and β is 0.06, respectively. The calculation results fit the FEA results well and the proposed formula in this paper can be applied in practical engineering.