轴压荷载下钢管混凝土损伤状态超声波检测

对3种壁厚的薄壁圆钢管高强混凝土短柱进行轴压试验，在加载过程中对柱中截面进行超声波检测，得到不同轴压荷载下的波形图，对波形图进行快速傅里叶变换，得到超声波通过钢管混凝土的频谱图.分别利用波形图、不同荷载作用下的波形最大幅值图和频谱图分析钢管内混凝土的损伤演变过程.试验结果表明:轴压荷载作用下钢管内混凝土的损伤呈3段式变化，分别为初期裂缝的扩展、套箍作用下的逐步密实和混凝土破坏.钢管外壁的应变分析发现其变化过程与超声波检测的波形和频谱分析的损伤过程一致.超声波技术可准确检测轴压荷载作用下钢管内混凝土的损伤状态.

Ultrasonic Wave Testing on Damage Condition of Concrete Filled Steel Tube Under Axial Loading

Axial compression tests were conducted on high-strength concrete-filled thin-walled steel tubular short columns with three kinds of wall thickness combined with ultrasonic testing on the middle cross section of the column. The waveforms under different axial loads were analyzed through fast Fourier transform to obtain the frequency spectrum when ultrasonic waves passing through the concrete-filled steel tube. The damage process of concrete in the steel tube can be reflected by the waveform， the maximum amplitude and the frequency spectrum of the waveforms under different loads. The experiment results showed that the damage process of concrete under axial loading takes on a three-stage characteristic， which can be divided into the extension of initial cracks， the compaction due to the hooping effect and the failure of the concrete. The strain changing on the outer wall of the steel tube agrees with the damage process reflected by waveform and spectrum analysis. The ultrasonic testing method can be applied to accurately measure the damage condition of concrete in the steel tube under axial loading.