Abstract
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.
Highlights
As a precious cultural heritage, ancient architecture has great scientific, artistic, and tourist value
The first 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 second is the thermal stress caused by the uneven temperature distribution
The following conclusions can be drawn: (1) Joule heat effect is the main damage cause of lightning strike, as the tile damaged significantly when lightning current attached to the mortar with high electrical conductivity, while only surface flashover was observed when attached to the surface of the enamel and body with low electrical conductivity
Summary
As a precious cultural heritage, ancient architecture has great scientific, artistic, and tourist value. Glazed tiles, which are key roof components of ancient buildings, present distinct characteristics of the period in which they were laid. They vividly and intuitively reflect the cultural and technical prowess of bygone times and play an important role in studying ancient architecture [1, 2]. Glazed tiles are non-renewable, and any man-made or natural damage is irreparable Because of their position, the lightning strike problems of buildings have been discovered for a long time in ancient time, e.g.in China [5], in Egypt [6], the protection measures were able to be implemented only after mid-eighteenth century based on the outcome of Benjamin Franklin [7]. It is very necessary to study the causes and damage effects of lightning strikes on the roofing glazed tiles
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