Bonded steel plate has attracted extensive attention in the field of reinforced concrete structure, but the durability study of reinforced structure is rarely involved, especially the durability study of the coupling action of load and hydrothermal environment. In order to explore the durability and damage mechanism of reinforced concrete beams strengthened with bonded steel plates under the coupling action of load and hydrothermal environment, a steel plate bonded concrete reinforced with 7 bonded steel plates r was tested under hydrothermal environment. Considering the coupling action of no-load, static load and alternating load with hydrothermal environment respectively, the aging test was conducted in 15 days and 30 days under high temperature and humidity conditions. Finally, the mechanical test was performed to obtain failure mode, deflection, strain of steel plate and steel bar under the coupling action of different load and environment. After long term load and hydrothermal environment coupling, the mechanical properties of the reinforced structure was studied, as well as the damage of durability. Results showed that the mechanical properties of the reinforced beams with no load action were degraded after 15 days and 30 days. And the strengthened beams under the static load were more obvious. Especially for reinforced beams under the action of alternating load, the mechanical properties of the beams were most significantly degraded. Alternating load and hydrothermal action made the mechanical performance of reinforced beams decrease and the ultimate strength, flexural behavior and ultimate strain of steel plate were decreased by 17.26%, 17.21% and 41.92%, respectively, compared with the reference beam. The coupling of load and hydrothermal environment had an effect on the stress in beams, while did not have any significant effect on failure pattern. And the failure modes of reinforced beams under the coupling action of load and hydrothermal environment were divided into three stages of concrete cracking, crack development and steel plate peeling failure. The penetration of hydrothermal corrosion medium into reinforced concrete beams and bonding interface caused damage to durability and this effect was aggravated under the action of load.
