Ultimate load-bearing capacity of prestressed T-girder bridges under typical explosion loads

To clarify the ultimate load-bearing capacity characteristics of prestressed concrete T-girder bridges under typical blast loads and address the technical difficulties in the residual load-bearing capacity evaluation of blast-damaged bridge structures, a two-stage test method combining blast damage test and post-blast static loading test is adopted in this study. A full-scale (1:1) prestressed concrete T-girder bridge specimen consistent with practical engineering structural parameters is taken as the test object to carry out large-equivalent field blast tests. Multi-stage graded static loading tests are further implemented on the blast-damaged specimen to obtain structural damage evolution features and deflection response data under post-blast service conditions. Based on the measured damage morphologies, deformation data and mechanical response laws acquired from physical tests, a refined three-dimensional finite element (FE) numerical simulation model for prestressed concrete T-girder bridges is established. Key structural characteristics including concrete and reinforcement strain-rate effects, material nonlinearity, prestress loss and structural contact interaction are fully considered in model establishment. The accuracy and reliability of the numerical model are validated through comparative calibration with experimental results. The validated model is subsequently employed to quantitatively investigate the ultimate load-bearing performance of bridges under three typical blast working conditions, including deck central contact blast, combined blast of deck central explosion and inter-girder internal explosion, and bilateral inter-girder internal explosion. The research results demonstrate distinct structural damage and bearing degradation characteristics under different blast scenarios. Contact blast acting on the bridge deck mainly induces local slab perforation failure and concentrated plastic deformation of deck concrete. For internal explosion occurring between main girders, structural damage presents a more severe and extensive pattern. In addition to concrete spalling and fragmentation on the bottom surface of the bridge deck, obvious outward bulging deformation, concrete crushing and local collapse failure occur on the webs and transverse diaphragms of T-girders. Among the three typical blast damage states, the combined blast condition with deck central explosion followed by secondary inter-girder explosion causes the most significant degradation of structural ultimate load-bearing capacity due to the superimposed synergistic damage effect. Reasonable optimization of live load layout effectively avoids severe damage areas of blast-affected bridges, eliminates the adverse influence of blast-induced structural defects, and achieves a remarkable improvement in the ultimate load-bearing capacity of damaged bridges. An integrated evaluation system covering the whole process from blast damage characterization to ultimate load-bearing capacity quantification is established in this research. The proposed evaluation method provides a systematic theoretical basis and feasible technical support for residual load-bearing capacity assessment, damage prediction and blast-resistant reinforcement design of prestressed concrete T-girder bridges suffering blast loads.