Typology and factors affecting the formation of architecture of historical bridges in Guilan province (with a look at bridges of Safavid and Qajar historical periods)

Due to rainfall and climatic conditions, Guilan province owns several bridges from past historical periods. The present study investigates the typology and recognition of factors affecting the formation of Safavid and Qajar historical bridges in Guilan province. The research seeks to answer the following questions; which factors have been effective in the formation of different types of Safavid and Qajar bridges in Guilan province? What are the differences between Safavid and Qajar bridges in Guilan in terms of structure, geometry, type of arch, materials and architectural decorations? Accordingly, based on library studies, the characteristics of 15 historical bridges of Safavid and Qajar eras in Guilan province were collected and in the next step, based on field studies, the factors affecting the formation of bridges were studied. For geometric analysis of bridges, manual drawing methods, PhiMatrix Professional, and Atris golden section software have been used. The research results show that religious and economic commonalities, development of Iran's political relations with the West, and the leisure of the Safavid kings were among the main factors in the formation of the Safavid bridges. Safavid bridges have three different types; single-span, two-span and four-span bridges. The use of sharp and slight panj-o-haft arches, multiple Karbandis, prominent brickwork, presence of accommodation space, circular-shaped buttress, two-stage sloping, rectangular-shaped bases and circular and rhombus breakwaters are common in Safavid bridges of Guilan. The most important factors in the formation of Qajar bridges include controlling the relationship and reducing tensions between the West and Iran, economic goals and establishing urban and rural connections. Qajar bridges include three different types of single-span, single central span and double side arches, and single central span and four side arches. The use of small arches, backward brickwork, single-sided slope and circular form in the breakwater, buttress and rectangular form in the bases and the lack of accommodation space, Minaret and Karbandi is common in Qajar bridges of Guilan province.