Arch ring
Arch ring is a building structure. Also known as coupon hole, law circle and law coupon. It not only has good bearing characteristics under vertical load, but also plays the role of decoration and beautification. Its shape is arc, and the form of arch ring changes slightly due to different building types. Semicircular arch ring is an important feature of ancient Roman architecture, while pointed arch ring is an obvious feature of Gothic architecture.
The arch ring of Islamic architecture is pointed, horseshoe-shaped, arched, trilobal, compound leaf and stalactite. Arch ring structure is one of Rome's greatest achievements. Arch ring technology appeared in the two river basins as early as 4000 BC, and was applied and developed in Babylon, Assyria, India and Rome.
Arch ring appeared late in China, and experienced several development steps such as hollow brick beam slab, pointed arch and folded arch, which was formed in the early Western Han Dynasty. At that time, the tomb was built with a cylinder arch or arch shell vault, and the tomb door was built with a circle. At first, the tube arch was made up of multiple coupons side by side, and later it developed into a vertical tube arch, with bricks and stones interwoven between coupons. The latter has strong integrity and many applications.
The tube arch used in Wang Jian's tomb during the Five Dynasties and Ten Kingdoms period was already very high. In order to strengthen the integrity of the circle, a layer of brick or stone is often laid on the circle according to its shape, which is called "pull back" in the "architectural style" of the Song Dynasty and "blessing" in the engineering practice of the Qing Dynasty. Several layers of coupons and volts can be stacked on a large coupon or bucket arch. The tower gate of Song Yue Temple Tower in Dengfeng, built in the Northern Wei Dynasty, has been using two coupons and two volts.
By the Ming and Qing dynasties, the number of coupons and the number of volts had become the symbol of the scale level of coupons, and the highest level was five coupons and five volts. The "Engineering Practices" of the Ministry of Industry and Commerce is also a practice of five coupons and five volts. The curvature of the arch is relatively gentle at the beginning, and the rise-span ratio is less than 0.5. Later, a semi-circular arch was adopted, that is, the height-span ratio was 0.5. In the Ming dynasty, most of them were "three-heart arches" with a height-span ratio greater than 0.5.
According to the engineering practice of the liquidation department, the face height is 0.55 of the span. The cylindrical arch of brick tombs in Han Dynasty and the arch ring on brick towers before Song Dynasty are mostly made of mud. Lime slurry existed in the Song Dynasty and was only used in the Ming and Qing Dynasties.