In this paper, the damage characteristics of polyvinyl alcohol fiber-reinforced engineered cementitious composite (PVA-ECC) beams with high temperature damage under low velocity impact load were studied. A series of low speed impact tests were carried out to simulate the impact energy on the beam, and the impact response of the PVA-ECC beam with high temperature damage were compared with that without high temperature damage. The crack evolution and the wave attenuation were detected by the smart aggregate based active sensing method. The crack development was indicated by the energy of the wavelet packet of the received waves. The results showed that the impact resistance of PVA-ECC beam was significantly weakened after exposure to high temperature. The PVA reached its melting point at 230 °C and lost its function as reinforcement. Therefore, PVA-ECC lost its strength, toughness, and fatigue resistance after exposure to high temperature damage.

The lightweight steel column (LSC) plays an important role in resisting the combined action of fire and blast for lightweight steel structures. The material performance of LSC is more sensitive to these combined effects than other forms of steel structures. Thermal softening of the steel material under elevated temperatures makes the steel weaker under blasting loading. However, very limited researches have been conducted to analyze the anti-blast performance of LSC subjected to elevated temperatures, though these two issues have been systematically investigated separately. In this paper, anti-blast performance of LSCs with different cross-sections, namely H-type, rectangle and round sections, are numerically analyzed using ANSYS/LS-DYNA. Isothermal property is assumed under elevated temperatures and the blasting loading is applied on the side surface of the LSCs when establishing the finite element analysis (FEA) models. The failure mode and severity of the LSCs are investigated from the numerical results to study the performance of LSC due to different temperatures, blast loadings and cross-sections. Results show that the LSC with short side facing the blast, has the best anti-blast capacity in high temperatures while the LSC with circular section is the worst. The results from this study may provide useful reference for the design of the structures under the combined effect of elevated temperatures and blast loading.

Accidental impact of civil structures is a common type of damage in civil engineering. It may severely damage the structure, and further result in catastrophic losses. It is desirable to develop a non-destructive evaluation (NDE) system that is capable of detecting the impact damage and provide early warning to mitigate the damage. The main focus of this paper is the feasibility study of the detection of the impact damage in a beam structure using infrared thermography. The final intention is to detect the subsurface defects or cracks at the early stage after an impact event. In this study, a beam structure, made of polyvinyl alcohol fiber reinforced engineering cementitious composite (PVA-ECC), was investigated. A series of impact tests at constant impact energy were conducted. After each impact, infrared thermography was used for NDE of the structure. Sequences of images were acquired with starting and ending time sets so as to include all of the thermal evolution. An infrared thermography approach was developed to perform continuous monitoring during the entire process. The initiation and evolution of the impact damage altered the heat conduction along the beam’s surface, and then affected the heat distribution. Experimental results demonstrated that the proposed method is an innovative and effective approach to detect the impact damage.