动力荷载下输电铁塔连接螺栓松脱及断裂机理与设计理论

Bolts loosening and fracture are easy to happen for transmission line towers subjected to dynamic loads due to the wind-induced vibration and conductors galloping. In the worst condition, the steel angle members will fail, and the towers will collapse. It is necessary to periodically fasten the bolts or replace them during the maintenance of transmission line. Howerver, there are short of researches on the mechanism of bolts loosening and fracture, and theoretical basis for maintenance. The dynamic load on connecting bolts and its calculation method will be investigated by analyzing the wind-induced vibartion of transmission tower-line system and conductors galloping. The pretightening force of bolts, stress state and load level will be selected as parameters, and the vibration tests of structural member and full-scale crossarm with C-class rough bolts will be carried out to study the behavior of bolts loosening and fracture. Besides, the influence rule of pretightening force on the bolts loosening and fracture and its reasonable values will be explored. Starting from the mechanical feature of bolts, stress changes on gearing faces between the srew threads, and the deterioration of self-locking performance, the mechanism of bolts loosening and fracture will be revealed. In addition, the simplified calculation model of bolts loosening and fracture and the life evaluation theory will be proposed. The verification tests and theoretical analysis of measures to prevent bolts loosening and fracture will be conducted. Lastly, the design method of bolts loosening and fracture for transmission line tower will be established. This study could provide the scientific theory of bolts loosening and fracture for the design, consturction and maintenance of transmission line towers, and prevent bolts loosening and fracture and towers’ collapse to promote the safety and reliability of transmission line.

风振及导线舞动等动力荷载下输电铁塔连接螺栓容易发生松脱及断裂，严重时可能导致构件失效和铁塔倒塌，线路运维需要定期紧固螺栓或替换，但国内外缺少铁塔螺栓松脱及断裂机理研究及运维的理论依据。通过输电线路塔线体系风振响应及导线舞动的模拟分析，研究连接螺栓上动力荷载及计算方法。以螺栓预紧力、受力状态、荷载水平为参数，开展输电铁塔用C级粗制螺栓连接部件和足尺横担真型结构的振动试验，考察螺栓松脱及断裂行为，探索预紧力对螺栓松脱及断裂特性的影响规律及合理取值。从受力特征、丝扣啮合面应力变化及自锁性能劣化入手，研究螺栓松脱及断裂机理，提出考虑受力状态、荷载水平的螺栓松脱及断裂计算模型和松脱寿命评价理论。开展螺栓防松脱及断裂技术措施的试验验证和理论分析，建立铁塔连接螺栓松脱及断裂设计方法。本课题研究为输电铁塔设计建设、运行维护提供科学理论依据，减少并防止螺栓松脱及断裂、铁塔倒塌事故，提高输电线路的安全可靠性。

本课题研究了风荷载及导线舞动下输电铁塔连接螺栓等效内力的计算方法，开展了单螺栓、螺栓群传力特性试验及量测，提出了连接螺栓内力计算方法，建立了连接螺栓动力等效荷载的计算理论及模型。开展了单双螺母紧固阶段螺栓丝扣的应力分布及接触力特性的非线性模拟，揭示了连接螺栓在紧固阶段、横向荷载作用下啮合丝扣传力机理及其紧固劣化失效的机制与影响因素。基于螺栓横向振动试验和非线性模拟分析，考察了不同紧固扭矩/预紧力、受力状态、荷载水平对螺栓松脱及断裂的影响规律，研究了动力荷载作用下输电铁塔用C级粗制螺栓的松脱及断裂机理，并探讨了螺栓群及其不同布置形式时螺栓的松脱及断裂性能，建立了连接螺栓松脱及断裂的计算模型及松脱寿命评价理论，分析了连接螺栓松脱断裂及疲劳断裂的判断准则。开展螺栓防松脱及断裂的技术措施试验研究，明确各种防松措施的放松效果，建立了输电铁塔连接螺栓松脱及断裂设计方法，可以指导输电铁塔节点连接设计及输电铁塔运行维护，减少并防止因连接螺栓松脱及断裂所引起铁塔失效及倒塌，提高输电线路安全运行的可靠性。本项目研究对输电线路运行维护、铁塔设计及施工安装提供科学的理论依据，确保输电铁线路运行安全可靠，具有重要的学术价值、科学意义和工程应用前景。