如何设计才能使网架具有延性?

How to Assure Ductility of Space Trusses

介绍了结构分层次的概念,即低一级结构的荷载-位移关系是上一级结构的本构关系。在平板网架中,压杆的压力-两端压缩位移的关系是网架简化为双向受弯板时受压区的本构关系。其中,压杆破坏具有脆性性质,类似于楼板中的混凝土,而网架下弦拉杆类似于楼板的受拉钢筋。对脆性破坏,可靠度指标是3.7,高于延性破坏的3.2,这要求对钢压杆应引入额外的抗力分项系数。为了避免脆性破坏,抗震设计中引入了能力设计法,通过强节点系数或强柱系数来实现,这也要求网架压杆引入强压杆系数,为此给出了强压杆系数取值建议。

Hierarchy of a structure is introduced,the force-displacement relation of a lower level is the constitutive relation of the upper level.In plate-like space truss,the compression-shortening relation of a chord is the constitutive relation of its compressed region when it is simplified as a plate.The compressed bars are of brittle nature,similar to concrete in a slab,while tension chord is similar to the tensile reinforcement.For brittle failure,the required reliability index is 3.7,greater than 3.2 for ductile failure,this implies that an addition safety factor is required for compression chords.For seismic design,brittle failure is prevented by capacity design technique,which is realized by strong column factor and strong joint factors in design check.This demands that a strong chord factor is necessary to achieve a ductile space truss.The paper proposes the value for this strong compression factor.