kōryō 虹梁

Lit. rainbow beam. A generic term for any curved, transverse tie beam. It is used almost exclusively in temple or shrine construction. Ordinary rainbow beams are large and usually span two bays. They function as tie beams which cross over the core *moya 母屋 of the building from pillar to pillar. They also bear much of the dead load of the roof structure and sometimes of the ceiling. The rainbow beam of the ancient period is characterized by a gentle curve from top to bottom, by rounded corners, by an inverted trapezoidal shape in cross-section, and by a lack of decoration. In the medieval period, with the introduction of the daibutsu style *daibutsuyō 大仏様 and Zen style *zenshūyō 禅宗様, changes occurred. Daibutsu style rainbow beams were huge and circular. Although comparatively straight on the underside, the upper side was sharply curved at both ends to enable them to be inserted into brackets or directly into the pillars themselves. Their extended ends were molded on the upper side and channeling was applied to the underside. Zen style rainbow beams were higher although overall they were thinner and rectangular in cross section. To enable insertion into a relatively small bracket complex, the ends were cut diagonally on the upper sides *sodekiri 袖切. Various decorative features were added to the underside including carved moldings on the lower edges *kakimayu 欠眉 and channeling on the underside *shakujōbori 錫杖彫. In addition to ordinary rainbow beams, there are a number of others named for their location, function, or shape:

1　Uchimuro kōryō 内室虹梁 are rainbow beams installed on the underside of an open roof *keshō yaneura 化粧屋根裏, when a ceiling is not installed.

2　Uchikōryō 内虹梁 are used on the underside of a roof in buildings that have no ceilings.

3　Sotokōryō 外虹梁 are placed on the outer side of a structure.

4　Tsumakōryō 妻虹梁 are rainbow beams used and exposed within the gable pediment of a gable roof *kirizuma yane 切妻屋根 or a hip-and-gable roof *irimoya yane 入母屋屋根.

5　*Mizuhiki kōryō 水引虹梁 is a rainbow beam which spans the distance between the outer pillars of a step canopy *kōhai 向拝 in a shrine or temple.

6　*Tsunagi kōryō 繋虹梁 are rainbow beams placed between the outer pillars of the aisles *hisashi 廂 and the pillars surrounding the core of the building *moya 母屋 or between the pent roof addition beyond the hisashi *mokoshi 裳階 and the moya pillars. They also connect the outer pillars of the step-canopy and the body of the building where they are attached above the head tie beams *kashiranuki 頭貫.

7　*Ebikōryō 海老虹梁, also written 蝦虹梁. Lit. a lobster or shrimp shaped rainbow beam. It is so-named because of the shape of its curve. It came into use in the hisashi of Zen style buildings or in hisashi influenced by the Zen style. At first, only the upper side was given a hump while the ends of the curved underside were inserted into the hisashi and moya pillars at the same height. Later, the beam was given such an exaggerated curve that the end inserted into the moya pillar was at a higher level than the end inserted into the hisashi pillar.