semi-rigid nodes;  steel frame;  system stiffness;  reliability;  P-△ second-order effect

Combining the gradient optimization method with the finite element method, the implicit functional function reliability algorithm is discussed, the main failure modes of the stiffness of semi-rigid and rigidly bonded steel frame systems are compared and analyzed by example, and the influence of joint rotational stiffness and P-△ second-order effect on the stiffness reliability of structural systems is discussed by PNET method. The results show that the main failure modes of the system stiffness of the semi-rigid joint and the rigidly connected steel frame are basically the same, and the large displacement between the layers forms the main failure mode of the stiffness of the structural system. The semi-rigid connection has a great influence on the stiffness reliability of the structural system, and increases the influence of the P-△ second-order effect.