In the composite structure of a concrete-filled steel tube (CFST), because the concrete is concealed inside the steel tube, subsurface cavities can occur and are difficult to identify. In this study, a thermal-driven method based on Brillouin fiber-optic sensors (BFOSs) was proposed to quantitatively identify subsurface cavities in CFSTs. By performing a thermodynamic analysis of subsurface cavities in CFSTs, a thermal model related to the relationship between the subsurface cavity size and the temperature rise at the top surface of the CFST was established for the first time. Then, a sensing scheme based on the BFOS was proposed, and its feasibility was evaluated through an experimental program. The experimental program involved the use of an active heating layer for inputting heat flow into the CFST structure and BFOSs for the distributed measurement of temperature to identify subsurface cavities in CFSTs. The experimental results indicated that the BFOSs can achieve real-time distributed measurements of the surface temperature of the CFSTs. According to the temperature anomalies in the temperature rise curves of the CFSTs, the subsurface cavities can be accurately located in the longitudinal direction of the CFST, and its length can be quantified. There is an obvious linear relationship between the temperature rise and the square root of the heating time, from which the equivalent heat absorption coefficient (EHAC) can be determined. Furthermore, according to the relationship between the subsurface cavity height and the EHAC in the thermodynamic theoretical analysis, the subsurface cavity height can be obtained quantitatively.

在钢管混凝土（CFST）的复合结构中，由于混凝土隐藏在钢管内部，因此会出现地下空腔，并且难以识别。在这项研究中，提出了一种基于布里渊光纤传感器（BFOS）的热驱动方法来定量识别CFSTs中的地下空腔。通过对CFSTs中的地下空腔进行热力学分析，首次建立了与地下空腔尺寸和CFST顶面温度升高之间的关系有关的热模型。然后，提出了一种基于BFOS的传感方案，并通过实验程序对其可行性进行了评估。实验程序包括使用主动加热层将热量输入CFST结构，并使用BFOS进行温度分布测量以识别CFST中的地下空腔。实验结果表明，BFOS可以实现CFST表面温度的实时分布式测量。根据CFST的温度上升曲线中的温度异常，可以准确地在CFST的纵向上定位地下空腔，并可以量化其长度。温度升高与加热时间的平方根之间存在明显的线性关系，由此可以确定等效吸热系数（EHAC）。此外，