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The Q345qD bridge steels exposed to severe corrosion environments undergo mechanical property degradation, posing significant safety risks for sea-crossing bridges. Assessing the health of corroded bridge steel structures under load conditions in a manner that avoids causing damage can effectively prevent these intensifying safety hazards. To investigate the impact of corrosion on the mechanical performance of these steels, six sets of standard specimens underwent corrosion ranging from 0 to 896 h. Subsequently, during tensile testing, an image acquisition platform was established to utilize Digital Image Correlation (DIC) techniques for capturing and observing the tensile loading processes of various corroded specimens. Analysis of stress–strain curves and strain field evolution patterns provided insights into the deterioration of mechanical properties of Q345qD bridge steels after corrosion. For corroded bridge steel structures, defects caused by the corrosion pits can still result in localized strain concentration under low load levels. At higher load levels, mass loss due to corrosion or reduced cross-sectional dimensions of load-bearing elements are the primary causes of mechanical performance decline, precipitating overall structural failure. These findings provide some references for routine maintenance of steel structures of cross-sea bridges.

• The constant temperature liquid circulating system designed is reliable. • Synthetic seawater would severely reduce the fatigue life of the specimens. • Fatigue damage evolution can be described by strains versus fatigue cycles. In this study, a constant temperature liquid circulating (CTLC) system was designed and implemented to control the ion concentration, temperature, and pH value of a corrosive solution during the whole process of corrosion fatigue tests. A set of T-welded-joint specimens were manufactured from Q345qD steel and subjected to corrosion fatigue and fatigue tests. The experimental results show that the corrosive environment greatly reduces the fatigue life of the specimens. The mean reduction in the specimen lifetime is up to 47.7%. These tests also prove that the CTLC system designed in this study and described herein is both reliable and applicable. [ABSTRACT FROM AUTHOR]