中、下承式拱桥悬吊桥面系强健性加固试验

为增强中、下承式拱桥悬吊桥面系的强健性，以无纵桥向加劲梁的中、下承式拱桥悬吊桥面系为研究对象，提出了一种采用钢管桁架加劲纵梁的悬吊桥面系强健性加固结构，对比分析了悬吊桥面系强健性加固前后吊杆断裂时剩余结构的动力响应；开展了钢管桁架加劲纵梁强健性加固结构模型试验和有限元分析，研究了吊杆断裂后加固结构的受力性能与破坏模式；讨论了精轧螺纹钢筋预紧力、开孔钢板厚度和材质对强健性加固结构受力性能的影响。研究结果表明:采用钢管桁架加劲纵梁加固悬吊桥面系后，长(短)吊杆断裂时桥面系最大竖向位移与应力分别降低了1.30(1.31)和3.31(1.99)倍，与断裂吊杆相邻的吊杆的最大索力降低了1.25(1.25)倍；在弹塑性阶段，钢管桁架加劲纵梁加固结构的开孔钢板发生弯曲变形，横梁下排植筋破坏，达到极限荷载时，中间下侧加劲钢板与开孔钢板间的焊缝发生断裂，随后下弦管与开孔钢板间的焊缝出现开裂而丧失承载能力；精扎螺纹钢筋合理预紧力为50 kN，开孔钢板合理厚度为20 mm；开孔钢板的材质从Q235提高至Q345时加固结构极限荷载增加了11.9%，说明提高开孔钢板的材质强度可有效提高加固构造的极限承载力。综上所述，采用钢管桁架加劲纵梁加固中、下承式拱桥悬吊桥面系可有效增强其强健性。 

Test on robustness strengthening for suspended deck system in half-through and through arch bridges

To enhance the robustness of the suspended deck system of half-through and through arch bridges, the suspended deck system of half-through and through arch bridges without a stiffening girder in the longitudinal direction of the bridges was taken as the research object, a robustness strengthening structure with a steel tubular truss (STT) stiffened longitudinal girder was proposed for the suspended deck system, and a comparative analysis was made on the dynamic responses of the remained structures at the moment of hanger fracture before and after the robustness strengthening of the suspended deck system. A test and a finite element analysis were conducted on the model of the robustness strengthening structure with an STT stiffened longitudinal girder, and the mechanical performance and failure mode of the strengthened structure after the hanger fracture were studied. The effects of the preload of finish-rolled screw-thread steel bar, the thickness of perforated steel plate, and the material on the mechanical performance of the robustness strengthening structure were discussed. Research results show that after the suspended deck system is strengthened by the STT stiffened longitudinal girder, the maximum vertical displacement and stress of the deck system reduce by 1.30(1.31) and 3.31(1.99) times, respectively, when the long (short) hanger fractures. The maximum cable force of the hanger adjacent to the fractured one reduces by 1.25 (1.25) times. In the elastic-plastic stage, the perforated steel plate of the structure strengthened by the STT stiffened longitudinal girder is subjected to bending deformation, and the embedded steel rebar near the bottom of the cross beam is damaged. When the ultimate load is reached, a crack appears on the weld between the middle-lower stiffened steel plate and the perforated steel plate. Then, a crack appears on the weld between the lower chord and the perforated steel plate, and the carrying capacity is thereby lost. The reasonable preload of the finish-rolled screw-thread steel bar is 50 kN, and the reasonable thickness of the perforated steel plate is 20 mm. The ultimate load of the strengthened structure increases by 11.9% when the material of the perforated steel plate is updated from Q235 to Q345. This indicates that enhancing the material strength of the perforated steel plate can effectively improve the ultimate bearing capacity of the strengthened structure. To sum up, utilizing the STT stiffened longitudinal girder to reinforce the suspended deck system in half-through and through arch bridges can effectively strengthen its robustness.