Abstract: This paper describes the current status and reasons of decease scratch cracking in variable cross section continuous beam bridge and continuous rigid frame bridge and analyzes the current status of the calculation of external prestressed reinforced bridge. The deficiencies in the design calculations of reinforcement by single beam model, plane grillage model and solid model are point out, which leads to practical fine analysis of space grid model. The principle of detailed mesh model is introduced and the grid model of external reinforcement of continuous rigid frame bridge is analyzed. Then, the key longitudinal stresses before and after the reinforcement are compared. By analyzing the normal stress and in-plane principal tensile stress angle, the stress state of each longitudinal beam is improved by the reinforcement. The principal tensile stress is the synthesis of normal stress and shear stress, and the main stress in-plane is actively strengthened, which can reflect the strengthening effect.

Key words: road engineering, external prestressing, bridge strengthening, continuous girder bridge, spatial grid model, principal stress