عوامل تأثیرگذار بر شکل‌گیری معماری پل‌های تاریخی ایران در مناطق ناهموار

As architectural elements, bridges have served as connective structures since old times. The functional value of bridges is a reason why researchers have paid insufficient attention to environmental and climatic factors despite the fact that bridges are directly affected by contextual conditions in terms of their form and structure. It is not surprising that before bridges, as architectural elements, were constructed to overcome natural obstacles and, in particular, to pass across rivers and valleys, our ancestors used to face serious barriers that limited the expansion of human civilizations to other places. For instance, bridges that are built in areas with rugged terrain are characterized by fundamentally different criteria which require detailed research. Conducted through a descriptive-analytical and historical-comparative method based on comparative research, the present study aims to explore the formation of bridges in areas with rugged terrain in terms of the three principles of function, form and structure. The findings suggest that in mountainous areas with rugged terrain, bridges are often built over valleys to facilitate transportation, hence, lacking any sign of decoration or embellishment in the formal aspect. In addition, maintaining a solid structure and strong foundation work via the use of stone and bricks are of special importance. In conclusion, special topographic features in mountainous areas lead to specific subtleties in the bridge structure. In terms of function, bridges in areas with rugged terrain are built, in the first place, to facilitate transportation across natural obstacles, which made it impossible or difficult to pass across. From the physical perspective, because bridges in areas with rugged terrain are mostly built for their function and role in communication, less attention is paid to decoration. After all, in terms of structure, foundation work, subgrade construction and reinforcement for resistance and durability are of crucial importance to make possible the transportation of vehicles and pedestrians, all of which require the application of solid materials in mountainous areas with rugged terrain.
Keywords: Bridge Construction, Architecture, Uneven Bed, Historic Bridges.
 
Introduction
As human beings, we bore tunnels through mountains and build bridges over valleys, rivers and cracks in the ground to overcome natural obstacles. The bridge structure has been constantly evolving as a man-made masterpiece that facilitates internal and external communication for societies. Considering Persia’s intermediary position for connecting the East and West through major trade route networks, especially the Silk Road, Persian architects had been dedicated throughout history to building bridges and tunnels that made possible passing across natural obstacles, facilitated transportation and served as strategic constructs during times of attack and defense. However, with the expansion of transportation vehicles, routes gained an especially critical value. It was then that Persian architects began experimenting with the bridge structure according to the requirements of time and climate and turned it into something that was no longer just a means of passage but also served secondary purposes. These globally unprecedented alterations to the bridge structure and its related amenities have been documented in various travelogues by visiting explorers.
Hypothesize of investigation is: that climate zone and type of terrain affect the formation of suburban bridges. Contrary to the principles governing the design of urban bridges, suburban bridges are subject to functionality and regional climate. In other words, the number of arches and the general shape of a suburban bridge are a function of component specifications, water flow conditions and the water discharge capacity of the bridge’s central and largest arch. However, before we can define an authentic theoretical framework to test this hypothesis in the case of historic bridges in Iran, it is necessity to study the different aspects of the formation and development of bridge structures after identifying and statistically categorizing them in climatic terms.
 
Identified Traces
- Function: Bridges are often built for making connections. The largest number of connective bridges have been built over rivers to link the two sides together. The bridges that were built in Mazandaran province in the first Pahlavi era were merely for railway transportation. In some cases, bridges were built on seasonal rivers which are currently dry.
- Form: Number and span: Our study of a large number of bridges in various climates shows that bridges built in warm and humid climate zones are characterized by the longest spans whereas those built in mild and humid climate zones are characterized by the shortest spans. However, in cold mountain climates, bridges are mostly short-spanned but their number is considerably higher, which is due to the special topography of such climates.
Arches: Most of Iran’s bridges have 1 or 3 arches with a pattern in which the central arch features a longer span and the two subsidiary arches have shorter spans.
Decoration: In bridge construction, decoration is much less a concern because the architect is mostly concerned with the strength and endurance of the bridge. Decorations often take the form of brickwork on the bridge façade.
- Structure: Bridge Construction Materials: Most of the materials used in the construction of bridges are stone and bricks. Bricks were used mostly for decorating. In the construction of bridge piers, stone, sarooj and lime mortar are common materials. In most cases, river rocks from the same area were cut for construction purposes. Arches were usually built with bricks and plaster. In cases where a bridge was built over a river, breakwaters were also embedded in the structure of the bridge. Triangular breakwaters were used for rivers with high discharge whereas semicircular breakwaters were used for rivers with low discharge. In some cases, bridges incorporated small rooms for guardianship or for passengers to rest. Bridge piers also included some overflow channels to allow for safe passage in times of flood.
 
Conclusion
In conclusion, it is important to identify the unique features of bridges built in areas with rugged terrain with special conditions as important elements of Iranian architecture and the climatic principles and indicators of the architecture of Iranian bridges in the past according to the three principles of architecture laid out above. In terms of function, bridges in areas with rugged terrain are built, in the first place, to facilitate transportation across natural obstacles, which made it impossible or difficult to pass across. From the physical perspective, because bridges in areas with rugged terrain are mostly built for their function and role in communication, less attention is paid to decoration. After all, in terms of structure, foundation work, subgrade construction and reinforcement for resistance and durability are of crucial importance to make possible the transportation of vehicles and pedestrians, all of which require the application of solid materials in mountainous areas with rugged terrain.