张弦桁架设计若干问题讨论

Discussion on issues of design of truss string structures

对张弦桁架设计过程中的若干问题进行了讨论。增加张弦桁架的矢高或垂距可减小结构跨中的挠度及弯矩,但增加矢高会加大结构支座处的水平反力,加大风荷载作用下结构表面的风载体型系数,减小预拉力作用下结构跨中的反拱值及反向弯矩,建议在设计时首先考虑使用增加垂距的方法来改善张弦桁架的受力性能。在反对称荷载作用下,张弦桁架中的拉索及撑杆无法为桁架提供有效支承,对有可能遭遇反对称荷载作用的张弦桁架应重视结构在该工况下的分析设计。张弦桁架传力路径较为单一,杆件的屈服有可能致使结构实际的失稳情形与弹性稳定分析结果不符,对该类结构进行弹塑性稳定分析是有必要的。将张弦桁架中的拉索设计成并行双索的形式将有助于提高结构的抗连续倒塌能力。

Some issues on the design of truss string structure are discussed. The mid-span displacement and bending moment of structure can be reduced by raising the vector high and cable-vertical distance, but raising the vector high will increase the horizontal support reaction force and wind-load shape coefficient, and reduce the structural inverted arch value and inverted bending moment under pre-stressing force. Compared to raising the vector high, to raise the cable-vertical distance is a better way to improve the mechanical properties of truss string structure. Cable and brace of truss string structure are invalid under anti-symmetrical distributed load, so structural analysis and design under this type of load should be taken seriously. Force transfer path of truss string structure is single, member yield may cause structure actual failure mode is different from the results of elastic stability analysis, so elasto-plastic analysis is necessary for the structure. Double-parallel cable design method can enhance the capacity of progressive collapse resistance capacity of truss string structure.