Abstract: The collapse of building fires poses a serious threat to the safety of personnel. Research has shown that ground interference radar can be used for micro deformation monitoring and early warning of portal steel frames under fires. However, due to the fact that radar can only obtain deformation in the direction of the target line of sight, it is difficult to meet the multi-dimensional data requirements of early warning models. Therefore, it is urgent to study the three-dimensional deformation monitoring of building structural targets. On the basis of discussing the microwave signal model of the system, this article proposes a radar equivalent phase center estimation method based on distributed target imaging information, which achieves iterative optimization of the target's three-dimensional transformation matrix. Then, a scaled double span steel frame fire test is carried out to obtain the three-dimensional deformation component of the structural target under local coordinate system, and the monitoring results are compared with those of traditional wire displacement meters. The experimental results show that the combination monitoring of multiple ground-based interferometric radars can effectively obtain the three-dimensional deformation components of structural targets in real fire scenarios. The monitoring results conform to the deformation laws of existing portal steel frame structures under fire, and can provide effective data support for building collapse warning under fire.

Key words: ground based interferometric radar, steel portal frame, distributed monitoring, collapse deformation