Abstract: Smart film monitoring method has the capability of monitoring the important features of concrete structures effectively， such as occurrence，location，shape，length and development of initial crack． Aiming to monitor the crack width of concrete structures，the improved smart film adopted several groups of bunched magnetic wires which were horizontally placed． Each group of bunched magnetic wires was composed by a few of magnetic wires with different diameters，and each magnetic wire had different ultimate tensile strain． Therefore，the direct proportion between the ultimate tensile strain of magnetic wires and the crack width of structures was verified by the theoretical derivation and experiments． And the crack width can be indirectly calculated by the ultimate tensile strain of magnetic wires．

Key words: bridge engineering, structural health monitoring, crack width, smart film, ultimate tensile strain

摘要： 机敏网裂缝监测方法能够对混凝土结构的裂缝长度、位置和形状等进行长期有效监测。为实现对混凝土结构 裂缝宽度的监测，在实际的机敏网结构中增加多组横向的机敏线组，其中每一组横向机敏线组都由多根直径不同的 机敏线组成。由于不同直径的机敏线具有不同的极限拉应变，理论推导和实验均证明了机敏线的极限拉应变与结 构裂缝宽度成正比，因此可以通过机敏线的极限拉应变间接地计算出裂缝的宽度。

关键词: 桥梁工程, 结构健康监测, 裂缝宽度, 机敏网, 极限拉应变