Ultimate load-bearing capacity of prestressed T-girder bridges under typical explosion loads
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摘要: 为明确典型爆炸作用下预应力T型梁桥的极限承载力，解决爆炸后桥梁承载力评估难题，采用“爆炸毁伤-静力加载”两步法，以1:1全尺寸预应力T型梁桥为靶标，开展了大当量爆炸试验和爆炸损伤后多级静力加载试验；根据试验结构破坏状态和挠度响应等数据，构建并校验了预应力T型梁桥精细化数值仿真模型，系统探究了桥面中心接触爆炸、桥面中心爆炸叠加梁间内爆、双侧梁间内爆3种典型爆炸工况下桥梁的极限承载力。结果表明：接触爆炸桥梁主要发生桥面破孔及塑性变形；梁间内爆除桥面发生层裂破碎外，T梁腹板及横隔梁发生侧凸、混凝土崩塌破坏；3种典型爆炸破坏状态中，桥面中心爆炸后叠加梁间内爆，极限承载力衰减最严重；合理选择荷载位置可有效规避爆炸损伤的不利影响，大幅提升桥梁的极限承载能力。Abstract: 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.
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图 11 静力加载时T梁桥损伤分布情况
Figure 11. Damage distribution in T-beam bridge under static loading
图 13 相同加载位置不同爆炸工况下极限承载力对比
Figure 13. Comparison of ultimate load-bearing capacity under different explosion conditions at the same loading position
图 14 相同爆炸工况不同加载位置下极限承载力对比
Figure 14. Comparison of ultimate load-bearing capacity with different loading positions under identical explosion condition
C0 C1 C2 C3 C4 C5 C6 e0a/MPa ρ0a/(kg∙m−3) 0 0 0 0 0.4 0.4 0 0.25 1.29 
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A/GPa B/GPa R1 R2 ω e0e/GPa D/(km∙s−1) ρ0e/(kg∙m−3) pCJ/GPa 373.8 3.747 4.15 0.9 0.35 6 6.93 1.63×103 21
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表 3 多级静载试验荷载
Table 3. Multistage static test loads
试验荷载分级 单级荷载/t 累计荷载/t 1 4.65 4.65 2 4.07 8.72 3 4.17 12.89 4 4.10 16.99 5 4.02 21.01 6 4.00 25.01 7 4.19 29.20 8 4.00 33.20 9 4.09 37.29 10 3.00 40.29 11 3.25 43.54
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表 4 试验挠度与仿真挠度
Table 4. Test and simulation deflection data
累计荷载/t wexp/mm wsim/mm 相对误差/% 4.65 0.700 0.685 −2.143 8.72 1.300 1.376 5.846 12.89 1.950 1.890 −3.077 16.99 2.610 2.475 −5.172 21.01 3.250 3.829 17.815 25.01 3.890 4.387 12.776 29.20 4.610 4.610 0.001 33.20 5.240 5.122 −2.252 37.29 5.980 5.941 −0.652 40.29 6.540 6.682 2.171 43.54 7.080 7.126 0.649
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表 5 不同爆炸工况下T梁桥的破坏模式
Table 5. Failure modes of t-beam bridge under different explosion conditions
序号 爆炸工况 TNT当量/kg 破坏模式 1 桥面中心
接触爆炸1000 在爆炸冲击波作用下桥面中心破孔，破孔周围翼缘板背部、T梁腹板和横隔板混凝土崩落、多根钢筋裸露。穿孔长1.89 m，宽1.98 m。 2 桥面中心爆炸后
梁4～5间内爆1000 （中心爆炸）
100（梁间内爆）二次爆炸使得爆炸冲击波作用下梁4、5的腹板发生严重破坏，混凝土崩落，钢筋从爆心截面失效折断，向外翻转变形。梁3迎爆侧腹板的混凝土崩落、钢筋裸露弯曲。爆心两侧的中横隔板、L/4横隔板完全破坏。 3 在梁1～2和
梁4～5间内爆2次均为100 爆炸冲击波作用下梁1～2、4～5的腹板发生严重破坏，混凝土破碎，钢筋从爆心截面失效折断，向外翻转变形。爆心处桥面向上隆起。梁3的腹板与顶板连接处出现开裂。爆心两侧中横隔板、L/4横隔板完全破坏。
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表 6 静力加载数值模拟结果
Table 6. Numerical simulation results under static loading
工况编号 桥梁情况 加载位置 极限承载力/t 衰减幅度/% 1 完整桥梁 位于梁4～5上方，中横隔板和L/4横隔板之间的桥面 949.97 0 2 桥面中心接触爆炸 位于梁4～5上方，桥梁跨中位置的桥面 811.96 14.528 3 桥面中心爆炸后，梁4～5间内爆 在横向上与爆坑中心处于同一断面，在纵向上位于梁1～2上方 671.61 29.302 4 桥面中心爆炸后，梁4～5间内爆 位于梁4～5上方，中横隔板和L/4横隔板之间的桥面，处在爆炸损伤的正上方 215.93 77.270 5 在梁1～2和梁4～5间内爆 位于梁4～5上方，中横隔板和L/4横隔板之间的桥面，处在爆炸损伤的正上方 363.80 61.704 6 在梁1～2和梁4～5间内爆 位于梁3上方，中横隔板和L/4横隔板之间的桥面 772.20 18.713
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