Lee Changkye, Kee Seong-Hoon, Kang Jun Won, Choi Byong-Jeong, Lee Jin Woo
University Core Research Center for Disaster-free & Safe Ocean City Construction, Dong-A University, Busan 49315, Korea.
Department of Architectural Engineering, Dong-A University, Busan 49315, Korea.
Sensors (Basel). 2020 Oct 15;20(20):5838. doi: 10.3390/s20205838.
The main objectives of this study are to investigate the spectral responses of a fire-damaged concrete slab using Impact-echo (IE) testing, and to develop a simplified model for interpreting the frequency shift due to heat-induced concrete damage after the fire. For these purposes, a reinforced concrete slab specimen (1000 mm (width) by 5000 mm (length) by 210 mm (thickness)) was fabricated in the laboratory. Heat damage in the concrete slab specimen was induced by exposing the bottom of the specimen to the temperatures corresponding to the standard fire curve described in the ASTM E 119 for 3 h. Impact-echo testing was performed on the bottom surface of the concrete slab specimen before and after inducing the fire damage. It was observed that the spectral responses of the fire-damaged concrete were dominated by several non-propagating waves, which resulted in main peak frequencies around 4500 Hz and 5100 Hz. A discrete layered concrete damage model developed in this study was used to reconstruct the variation of the P-wave velocity with the depth of the fire-damaged concrete. It was demonstrated that the predicted P-wave velocity profile using the simplified model showed a good agreement with the measured values from the five core samples, which measured 100 mm (diameter) by 200 mm (height) cylinders, using ultrasonic pulse velocity (UPV) measurements at eight different depths. In addition, the peak frequencies predicted by the simplified model were consistent with the measured peak frequencies. The experimental results in this study demonstrated that IE testing is effective for evaluating the post-fire damage of reinforced concrete slabs. Particularly, the simplified model in this study can be effective for better interpreting the spectral responses of fire-damaged concrete slabs by IE testing.
本研究的主要目的是利用冲击回波（IE）测试来研究火灾受损混凝土板的频谱响应，并建立一个简化模型，用于解释火灾后热致混凝土损伤引起的频率偏移。为此，在实验室制作了一个钢筋混凝土板试件（宽1000毫米×长5000毫米×厚210毫米）。通过将试件底部暴露在符合ASTM E 119中描述的标准火灾曲线的温度下3小时，在混凝土板试件中诱导热损伤。在诱导火灾损伤前后，对混凝土板试件的底面进行了冲击回波测试。观察到火灾受损混凝土的频谱响应由几个非传播波主导，这导致主峰值频率在4500赫兹和5100赫兹左右。本研究开发的离散分层混凝土损伤模型用于重建火灾受损混凝土中纵波速度随深度的变化。结果表明，使用简化模型预测的纵波速度剖面与从五个芯样（直径100毫米×高200毫米的圆柱体）在八个不同深度处使用超声脉冲速度（UPV）测量得到的测量值显示出良好的一致性。此外，简化模型预测的峰值频率与测量的峰值频率一致。本研究中的实验结果表明，IE测试对于评估钢筋混凝土板的火灾后损伤是有效的。特别是，本研究中的简化模型对于通过IE测试更好地解释火灾受损混凝土板的频谱响应可能是有效的。
