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Lightning strike is one of the natural disasters to the roof components of ancient buildings. To investigate the causes and damage effects of lightning strikes on the roofing glazed tiles of ancient buildings, artificial lightning strike tests were carried out on glazed tiles. Based on the experiment results, a coupled electrical–thermal finite element model of mortar-containing glazed tiles was established and the Joule heat effect of lightning current was further investigated. The results show that when the lightning channel is attached to the surface of the enamel and body with a low electrical conductivity, the lightning current is mainly released in the form of surface flashover, and a minor damage is induced along the flashover path; when the lightning channel is attached to the mortar with a high electrical conductivity, the lightning current is injected into the mortar, resulting in significant tile damage. The spatial distributions of the temperature present clear gradient characteristics. The high-temperature area appears in the mortar while the high–thermal–stress area appears in the body connected to the grounding rail. As the peak of the lightning current increases, both the high-temperature and high–thermal–stress areas of the glazed tiles expand. The combination of the experiments and the numerical analysis results demonstrate that the damage mechanism of lightning Joule heat effect to glazed tiles may include two aspects. One is the internal explosive force generated from the sharp vaporization and expansion of the moisture inside the tiles due to rapid temperature increase, and the other is the thermal stress caused by the uneven temperature distribution.

Glazed roofing components play a very important role in Chinese ancient buildings. In this study, the artificial lightning strike test on a type of glazed roofing tile of ancient buildings in China was carried out to investigate the lightning damage mechanism of ancient buildings. A high-speed camera was used to observe the process of lightning striking the enamel, body and mortar of the glazed tiles. The highest propagation speeds of flashover channel are achieved on the enamel surface of the glazed tile, followed by one on the surface of the body and the mortar successively under the condition of the similar moisture content. The propagation speeds of flashover channels are generally positively related to the moisture content for the same material composition of the glazed tiles except mortar. The flashover channels are basically regular on the surfaces of the enamel and the body, while they are irregular on the surface of the mortar. For the enamel and the body of the glazed tile, the surface flashover is easier to develop along the rough body surface. The lightning current enters the glazed tile easily through the mortar position, which results in the fracture of the glazed tile. The reason might be related to the high porosity, high moisture content and good electrical conductivity of the mortar. So the mortar component of the glazed tiles should be important for the design of the lightning protection, which is helpful to decrease the lightning damage for the glazed roofing components.