Due to the wide application of flat space trusses in practical engineering, the study on damage detection towords these structures becomes quite significant. Without the introduction of systematic error through the process of model-rebuilding, model-free damage identification theory is increasingly concerned, and has been applied in structural health monitoring for beam members. A novel kind of strain-modal-shape index is introduced in this paper, and then die method is used to identify damaged members in flat space frame structures. In the way of decreasing the cross-sectional area of some members in the model, the damage courses in these members are simulated, and five typical damage cases are analysed numerically by using FEM software. White noise is introduced into FEM analysis result data, and some members are difined as momitoring members. Analysis result shows that the strain-modal-shape index of those damaged members are higher than those of non-damaged members in the structure. Therefore, by comparing the index of each member,the damaged members, which are located in different parts of truss, such as top chords, bottom chords and web members, can be identified. Meanwhile, the index of the members around the damaged ones are higher than those of other non-damaged member, so that there is an index-notable area around the damage member. Additionally, when all the members are momitored, it turns out that strain-modal-shape index can also locate all the damaged ones in two or more damage cases.%平板网架结构在实际工程中应用广泛,针对此类结构的损伤识别研究显得尤为重要.由于避免了重新建模引入的系统误差,无模型的损伤识别理论正日益受到重视,并已被应用于梁式构件的健康监测.文中引入了一种应变模态指标,将无模型损伤识别理论应用于平板网架结构中.以折减杆件截面面积的方式来模拟杆件损伤,数值分析了5种具有代表性的损伤工况,在数值计算结果中引入了白噪声,并取部分杆件作为监测杆件.损伤识别分析结果显示,损伤杆件的应变模态指标为结构所有杆件中最高的.通过比对各杆件的应变模态指标,便能对发生在结构中上弦杆、下弦杆以及腹杆等不同位置的损伤进行识别.同时,损伤杆件周围杆件的应变模态指标也会比无损杆件的指标较大,在损伤点周围会出现一个损伤指标显著的区域.另外,当结构中两根或多根杆件同时损伤时,应变模态指标也能识别出全部损伤杆件.
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