Experimental Study on the Damage of Bridge Concrete in a Fire Environment Based on the Impact Echo Method

Abstract

Abstract To accurately assess the damage degree of bridge structures in a fire environment, fire damage test studies were conducted on the C30 and C50 concrete specimens at different temperatures (room temperature, 100°C∼700°C) based on the impact echo method. In addition, the variation rules of mass, impact echo signal, dynamic modulus of elasticity Ed, and static and dynamic modulus of elasticity ratios (Ec/Ed) with overfire temperature were obtained. The results show the following: (1) at ablation temperature ≤ 300°C, the main frequency of the impact echo signal is single, the peak value is obvious, the signal attenuation is fast, and the change is uniform; at ablation temperature > 300°C, the main frequency is frequent, there is more than one peak, and the vibration duration of the phenomenon is longer. (2) After fire damage, the specimen’s dynamic modulus of elasticity Ed is in a cubic relationship with the overfire temperature. (3) In engineering practice, the static and dynamic modulus of elasticity (Ec/Ed) ratio is classically based on Lydon and Balendran’s formula, which is usually used for derivation at room temperature. This article found that the formula can be extended to the rough estimation at lower temperatures (≤200°C), and the model proposed in this article can be used for the derivation of the static modulus of elasticity Ec and the dynamic modulus of elasticity Ed at high temperatures. In summary, the impact echo method can be used to quantitatively assess the damage state of bridges after fire. After the signal time-frequency domain conversion, a qualitative assessment of the degree of concrete damage can be made. Furthermore, a quantitative assessment of bridge concrete after fire damage can be made using the model proposed in this article.