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Reinforced concrete structures are currently under the threat of both fire and blast. The absence of theoretical methods demonstrates a drawback in the assessment of blast-resistant structures after exposure to fire. A modified layered-section method was developed in this article, which was not only able to determine the complete static resistance-deflection curves of fire-damaged reinforced concrete beams but also able to predict the responses of reinforced concrete beams subjected to blast after fire exposure. The hightemperature effects and the strain-rate effects were included in the concrete and steel material models in the proposed method. A corresponding calculation program FBBA was also compiled based on the explicit Newmark algorithm on the platform of Maple software. The developed method and program were validated by the existing test results. Analytical results showed that after fire exposure, the reinforced concrete beams show significant degradation in the residual bearing capacity, but increase in the ductility. The higher the steel reinforcement ratio, the more degradation the bearing capacity of reinforced concrete beams after fire exposure suffers. The blast resistance of the fired reinforced concrete beams was underestimated without considering the strain-rate effects or just considering the average strain-rate effects.

In this paper, the straight-wall-arch structure in the rock medium is taken as the research object, and the high-pressure plane charge loading test technology is adopted to study the anti-explosion performance of different types of structures under the explosion loading. Three types of structures, which are individually built with the high-performance reinforced concrete, the C30 reinforced concrete, and the C30 reinforced concrete with a foam concrete backfill layer as well, are tested, and the dynamic responses and damage characteristics of these structures are investigated. The test results show that under the condition of the same plane charge explosion loading, in the vault of the high-performance reinforced concrete test section appears a through-tensile crack with a largest transverse relative displacement between the two straight walls, and the composite structure test section only shows an intermittent crack at the arch foot, which represents a slight damage mode. Meanwhile the arch spring of the C30 reinforced concrete test section suffers a through-compression shear failure with a largest vertical relative displacement between the vault and the floor, which represents a moderate damage mode. Therefore, adopting the high-performance reinforced concrete, and the C30 reinforced concrete with the foam concrete backfill layer, can effectively decrease the damage degree of the rock structures. Compared with the C30 reinforced concrete, the high-performance reinforced concrete can improve the resistance of the structure by improving the structural strength and strengthening its capacity to absorb waves and energy dissipation, and the foam concrete backfill layer can significantly reduce the lateral and vertical relative displacement of the structural free surface and the peak stress of the structural inner layer. The composite structure test section of the C30 reinforced concrete with foam concrete backfill layer appears to be an excellent anti-explosion performance property.