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ARCHITECTURAL ISSUES IN EARTHQUAKE REHABILITATION OF THE IRANIAN CULTURAL HERRITAGE (Related to topic No: I)

H. Arbabian,

PhD, MArch, BArch, ISCARSAH, ICOMOS, ISES,

Assist. Prof., School of Architecture,

Iran University of Science and Technology (IUST),

Narmak,Tehran, Iran     E-mail:  arbabian@iust.ac.ir

Abstract:

        Iran, like many other places, lives the curse of frequent, sometimes devastating earthquakes. So prevention and conservation of the Iranian building herritage should be a prime priarity not only at the national level but also internationally.  

While, a magor part of the 2800 Iranian Seismic Code is related to the architectural issues but there is nothing referring to the prevention and conservation of historical buildings.

The survival of Iranian historical buildings shows that such buildings possess the potential of resist earthquakes. In spite of the use of weak materials, which resulted in the collapse of many ordinary residential buildings in earthquakes, historical buildings present us with samples of appropriate design and construction methods.

To understand the characteristics of the historical and modern heritage, this paper will consider and describe the building construction process. It focuses on the material and ways in which construction operates and considers the environmental and socio-cultural conditions of the country and their effects on construction process. It also gives a few examples to demonstrate the potential and values, as well as the constrains and limitations to construction methods, from which we may learn possible lessons to rehabilitate rather than the changes in the context of the Iranian cultural heritage.

To some extent traditional building construction has always been in a state of change with new materials and developing techniques, but the most significant changes occurred with the changes to the physical forms of cities generally, and the development of new building materials such as steel and reinforced concrete. In Iran these changes were partly to introduction of modern construction methods by government action through imported building materials and the implementation of large scale construction programmes.

Unfortunately the changes occured without any detailed consideration of the existing techniques and the earthquake risk involved. One of the scope of this paper is to demostrate how, 'conventional' or modern construction methods in Iran are formed and developed and what are their problems.

Keywords:

Cultural Herritage, Earthquake, Prevention, Conservation, Conventional construction methods, Modern, Iran, Construction Process, Environmental Condition.

Introduction

It will be shown that traditional construction methods have changed. The change has been largely a shift to modern construction materials and methods, partly as a result of government policies but also based upon a multitude of individual decisions by small private builders. Unfortunately this change has occurred without any detailed consideration of the earthquake risks involved. There has been an earthquake code since 1962 but there was no attempt to implement it properly until after the North Earthquake in 1990. It may be argued that one factor encouraging the use of modern methods was because they were seen to be stronger and, therefore, to offer more security against earthquakes. Certainly rebuilding after the destruction of earthquakes has been a factor in the extensive use of modern construction materials. This, however, was not carried out through relevant methods by either proper detailing or proper building controls.

What is important, therefore, is to learn the lessons from the earthquakes and to look critically at those modern, ‘conventional’ methods of building construction to see what security they actually offer against earthquake destruction, to look at the kinds of details that should be adopted and to see what controls need to be put in place, and what other methods (such as adequate training) may be adopted to ensure that these recommendations are put into effect in construction. There are two aspects to this: one is the basic construction of the building, that is its basic structural fabric. The other, however, at least equally important, is the non-structural aspects of the building, such as partitions or surface finishes. These will be considered in detail.

As a preliminary to these detailed discussions of construction we need to look at the mechanisms of earthquake destruction that can be considered from two aspects. We can look at the theoretical behavior of buildings, considering the kinds of ground motions that occur and so the characteristics of construction that best resist these or we can consider the lessons from actual earthquakes. The latter will show not only the kinds of construction that offer the greatest security, but will also show the kinds of defects that occur in actual construction as a result of both faulty design and poor workmanship. In other words it shows the kinds of things which future legislation, education, training and system of building control should seek to prevent.

The ignored role of modern architect:

The earthquake resistance of buildings depends upon three quite different processes in design. There is the overall layout of the building which determines the magnitude of the forces which come onto the building and their distribution: a distribution which is important in the vertical direction as well as in plan. Then there is the ability of the various parts of the building to resist these forces, the strength of individual members and the connections between them. Thirdly there are those aspects of construction which are hardly regarded at all, the non-structural aspects of the building, the non-load bearing walls and the finishes. These may constitute a significant proportion of the mass of the building and their behavior may be quite independent from that of the main structural elements.

Within the ‘conventional’ design process in Iran most of the effort has been concentrated in the second of these, that is on detailed design. This is the area of design which is covered by the Earthquake Code, an area of design which is regarded as the province of the engineer who are trained to deal with the calculation of the forces and the design of elements to resist them. It is also to a large extent the area over which building control efforts may be exercised. Because this aspect of design has received most attention, it will be dealt with first. It is, however, the contention of this oaper that the other two aspects of construction, those that are conventionally within the control of the architect (at least within the formal sector of the industry) are at least as significant in determining the earthquake resistance of the buildings. A recognition of this would involve a considerable shift in the culture of design and the culture of building control such as legislation, and building codes. It will therefore be considered when the position regarding the engineering aspects of earthquake resistance have been dealt with.

It is possible to employ advanced techniques for the structural computation with a little effort, but it is not possible to remove poor workmanship easily. In this respect, Ghalibafian (1985, p. 207) pointed out:

For earthquake mitigation construction, we cannot claim that just by structural computation and without any attention to the execution problems such as workmanship, resistance to earthquake is possible.

An engineer himself, he argues that mathematical concepts of earthquake mitigation can not cover all factors such as construction principles, appropriate construction methods and workmanship. For the purpose of earthquake mitigation activity, the informal builders should be provided with some simple guidelines, construction detailing techniques and constrains to raise the quality of their workmanship.

The collapses of the 1990 Earthquake can be attributed to a number of causes. The 1988 Code, which would have been sufficient to prevent collapses of buildings designed in accordance with its provisions, had not been in force long enough to have had any significant effect on the building stock.  A number of buildings had, however, been designed after the introduction of the 1962 Earthquake Code and these should have survived the earthquake but did not.  Their collapse may be attributed to two possible causes. Possibly the Code itself was inadequate, that is the engineers who were responsible for drafting the Code had done a poor job and, therefore, they must take some of the responsibility for the collapses that occurred.  Even had the Code been adequate, there is still some concern about whether it would have been applied in practice by engineers designing particular buildings because there was no provision for its enforcement at the design stage.  This lack of control over construction also affected the standards of building, because there was no provision for inspection during construction.  We can assume that some of the collapses occurred in buildings which were adequately designed but which were poorly built.  We can see this from the experience of the Roodbar Hospital which was designed in accordance with the 1988 Code, should have resisted the earthquake.  As it was a public building we can be sure that the provisions of the code were observed in its design. If, therefore, the buildings were inadequate, it was because of the standards of construction and a contributing cause of this is likely to have been inadequate supervision.

Although there are a large number of Seismic Codes world-wide, most concentrate on structural elements and are written for engineers rather than architects. Few countries seem to have special codes of practice on this subject. Where such codes deal with architectural issues, the problem is that they are ignored and not regarded as the architects’ contribution to the earthquake resistance. This is one of the problems concerning implementation of the Iranian Seismic Code. The Turkish code, for example, deals with details of construction for ‘ordinary’ buildings but does not discuss the plan forms to be adopted. In the United States, until the 1973 edition of the Uniform Building Code (UBC), architectural aspects of shape and irregularity were not dealt with in a specific part of the Code (Arnold & Reitherman, 1982, p.6).

While much of the Iranian Code for Seismic Design is directly or indirectly related to the architectural characteristics and configuration of buildings, all activities in the field of earthquake mitigation are concentrated on the structural aspects and analytical calculations. Many houses, of course, particularly in small cities and rural areas, are not provided with any structural analysis or calculations, because their builders do not normally employ engineers.

There are three stages in ensuring adequate earthquake resistance.  First, there must be an adequate code to guide engineering designers.  There is of course nothing to prevent all buildings being designed from first principles but this is an unrealistic expectation.  Secondly, the provisions of the code needs to be incorporated into designs and this may require some means of checking and enforcing the design. Thirdly there must be some means of inspection to ensure that buildings are actually built according to appropriate designs and specifications.

If met, these three requirements, cover the engineering aspects of buildings.  They ensure that within the formal sector of the industry a building's structure will be adequate. They do nothing, however, to ensure that the architectural design is sensible and does not result in large forces with which the engineer has to cope, nor do they ensure that the non-structural components of the building will be designed with earthquake effects in mind nor do they do anything about those buildings put up by the informal sector of the Building Industry which are without an engineering input.

This gives us four problems to deal with.  It would be advisable to provide some guidance to architects so that they may be aware of the effect which their designs may have on the forces generated by an earthquake.  This may take the form of simple rules placing limits on certain design features. Some guidance needs to be provided for architects, when they are dealing with those aspects of the building which will not come under engineering scrutiny, for example, suspended ceilings or non-load-bearing partitions.  Some controls need to be exercised over the design of buildings in the informal sector of the Building Industry and measures need to be put in place to ensure adequate standards of construction in both the formal and informal sectors.

The architectural aspects of the earthquake performance of buildings are those features that are decided by the architect before the engineer makes his contribution or possibly without any contribution from the engineer. The overall form and configuration of building, for example, is an architectural issue which will have consequences with which the engineer will have to deal. On the other hand the architect may select or design non-structural elements or decide upon their configuration without reference to the engineer. Apart from the overall configuration of the building, this may include the specification of: architectural design, configuration of building, construction techniques, including non-bearing interior partitions, exterior infill walls (assuming there are not intended to contribute to structural rigidity), suspended ceilings, building contents and the like. Bearing this in mind, it could be said that the architectural aspects of earthquake performance of buildings means, their non-computational or non-structural aspects. Even when a structure is adequate, non-structural elements may cause by their destruction serious damage and risk to the occupants. These risks are serious even in a building in which the structure is safe. Earthquake resistance and prevention damage for the elements would consist of a lateral bracing, often at little additional cost.

These are what the architect conceives and controls and undoubtedly has a direct effects on earthquake performance of buildings.  In designing of the architectural aspects of building, architect influences the kinds of resistance systems that can be used and also be effective. Configuration p.5 and 49 Lagorio (1990, p.2) states that damage to the architectural elements, during an earthquake could cause major economic losses even with minor structural damage. He notes that the damage in the 1964 Alaska Earthquake, could account for up to 65 to 70 percent of a building’s repair costs.

As mentioned before, in the North 1990 earthquake many engineered buildings collapsed. The engineers responsible for drawing up the code did a poor job and the code was inadequate. One would say that these engineers were therefore responsible for the collapses. This failure of extensive analytical computation is an indication that, besides the structural calculations, there are other factors effecting the earthquake resistant requirements. The relatively high destruction of modern buildings during the North Earthquake constructed by engineers indicates the importance of non-computational aspects and the role of architects in earthquake performance of buildings. Therefore, it is important for architects to understand how earthquake forces are transmitted in buildings and how the buildings should behave in order to resist earthquakes.

In rural areas, where builders in the informal sector of the industry undertake building construction, there is no computational analysis of structure. The resistance of buildings, however, in the city of Masooleh, shows that informal builders can build resistant  buildings without any need for computation.. This suggests, therefore, that simple and easy rules may be provided which would be comprehensible by builders and which can effectively help earthquake mitigation in the informal sector of the industry in small cities and rural areas.

The overall form of a building is one the main aspects for determining the effects of earthquake motions upon it. As Perry (1990, p.72) has demonstrated, the effect of the basic weaknesses of building form in the Loma Prieta Earthquake in 1989, and consequent damage of many buildings in the earthquake, showed that the overall shape and form of buildings, which in turn is affected by the functional requirements, is one of main reasons for building failure. The North Earthquake also demonstrates a close relationship between form, function  and the building’s seismic performance.

Architects play a key role in determining the form and function of buildings, defining and balancing many different and often conflicting factors. One of these in areas subjected to earthquake, is the degree of coincidence between the centre of mass and the centre of resistance. While an engineer may understand these factors well, he can never fully overcome the effect of inappropriate building form. For this reason, the architect may have a more significant effect on the earthquake performance than the engineer and a close relationship between the two professions is usually necessary. Because earthquakes affect the whole building, earthquake resistance is a shared architectural and engineering responsibility. The importance of the effects of architectural aspects on earthquake performance of buildings is not a new concept. The concept has long been recognised by engineers who have been engaged with the problem. For example: Holmes (1976, p.827), has placed equal importance on the architectural aspects are the lateral design forces, and Degenkolb (1977, p.111), who pointed out that a poor engineering effort may not harm the building ultimate performance but a poor configuration can, are among them. With respect to the problems of inappropriate building configuration and its diverse effect on earthquake performance of buildings, In this respect, Arnold and Reitherman (1982) agree with those engineers who have placed equal importance on architectural aspects and lateral design forces.  

Survival of traditional buildings in Masooleh

It would be apposite to refer to examples here to demonstrate the resistibility of traditional buildings to earthquakes and the other which is a post earthquake reconstruction which is referred to application of traditional methods of building construction successfully. These examples are set out to show the earthquake resistance potential of traditional construction methods. It is about Masooleh in the North of Iran and the other is about reconstruction of Sighanchi in Afghanistan. Although  Sighanchi village is not in Iran, because it was a successful post-earthquake reconstruction project, there are some points in this experience which this study tries to draw some possible lessons for earthquake reconstruction in Iran particularly for informal sector of the industry.

Masoolehin the North of Iran demonstrates the robustness of the traditional building method. This city is located in the area which was affected severely by the 1990 Earthquake. This small city, 100 km. from the earthquake’s epicentre, is famous because of its 4,000 years history. Its architecture is based on the need for protection against environmental conditions (Niroomand-Rad, 1984) as well as earthquake resistance.

In this city architectural elements, local materials, and construction techniques have created a unique homogenous environment, a combined texture of houses and buildings with nature and culture. Perhaps, culture is the most dominant factor which has affected by the nature in the city. The natural sloping condition of Masooleh affected the building forms and methods of construction. Buildings in the city are generally of two or three stories and most of them are more than 100 years old and constructed with adobe and mud. Because of the sloping site of the city, the roof of every building forms the front surrounding of the house behind or is a path-way or bazaar. The roofs are heavy and constructed with strong wooden beams. Wooden beams, columns and ring ties are combined with thick adobe walls. Roofs are heavy and are comprised strong wooden beams located close to each other. What is notable is the ring tie system which are used in most of the buildings horizontally and vertically (Zandi, 1990).

At the time of the North 1990 Earthquake, the city of Masooleh suffered only minor damage in spite of having many old buildings. The earthquake magnitude in the city was estimated at six Richter, strong enough for the destruction of  sun-brick and mud buildings, but the buildings of this city had a high resistance to the earthquake (Zandi, 1990). What is very interesting, is the resistance of traditional buildings of this city during the earthquake. The reports presented by Building and Housing Research Centre (BHRC) indicate the ‘good’ behaviour of the traditional buildings in the city and elsewhere. BHRC states that ‘the behaviour of the traditional building in the earthquake is an evidence of satisfaction of knowledge of earthquake engineering in the past’ (BHRC, 1990, p.239).

In these buildings the designers paid attention to two main techniques of earthquake resistance. One considered the whole building as a single unit and the other considered the dissipation of ground motion . For the first technique, buildings are braced both vertically and horizontally and the wooden column used in the walls are anchored at the roof and at the foundations. The buildings are also braced at the corners with both vertical and horizontal wooden members, Figure 1. These are not timber frame buildings but could act as monolithic buildings in earthquakes.

Figure 1: Bracing system in building construction in Masooleh

For dissipation of ground motion, the role of the foundations is very important. For resistance to earthquakes, many traditional buildings in the North have been constructed on base-isolated foundations, Figure 2. These foundations have an important effect on the buildings’ resistance to earthquakes in the area. They have been designed and constructed in a way which allows the ground to move with the rolling movement of the building on the foundation. The foundation is constructed on layers of timber which can roll on each other and dissipate the earthquake forces.

Figure 2: Two sides of a foundation of buildings in Masooleh

The role of traditional architects,  mimars

Mimarsare the Iranian traditional architects. The Persian word mimar literally means architect but the word carries within it a concept of development and prosperity. For thousands of years mimars have achieved a balance between architecture and built-environment by the use of indigenous materials. The mimar decides on the scale, the use of materials, the use of space, ornaments and other design and constructional aspects of houses and other aspects of buildings such as earthquake resistance, based upon the clients’ or users’ safety, affordability, and taste.

On the basis of culture, climate, and available materials, the mimar, the senior architect (mimarbashi) and master mason (banna[1]), employed the locally available materials and labour and developed scientific and logical construction methods. They developed various techniques to create a space compatible with nature and culture which has withstood many natural disasters as well.

These achievements of Iranian (Persian) architecture came as a result of talents of individual mimars. Mimars, disciplined professionals, were educated in tradition and in current techniques. Their aesthetic was inspired by associated art forms and underpinned by the study of geometry and mathematics. Ostad[2] Ghiaseddin Jamshid Kashani[3], for example, was a mathematician who analysed the load behaviour of domes and arches (Golombek and Wilber, 1988, p.152). Iranian construction methods created an architecture displayed a great variety of both structural and aesthetic forms developed gradually and coherently out of previous traditions and experiences.

The survival of traditional historic buildings indicate that such buildings possess the potential to resist natural hazards. In spite of the use of weak materials, which resulted in the collapse of many ordinary residential buildings in earthquakes, historical buildings present us with samples of appropriate design and construction.

To understand the characteristics of the traditional buildings, this paper considers and describes the building tradition and its construction processes. It focuses on the materials and ways in which traditional construction operates and considers the environmental and socio-cultural conditions of the country and their effects on construction processes. It also gives a few examples to demonstrate the potential and values as well as constrains and limitations of traditional construction methods and from which we may learn possible lessons to improve ‘conventional’ construction methods in Iran.

Changes in the context of the Iranian building tradition

Changes which have occurred when introducing new methods in an effort to gain and use the benefits of modern construction have failed, because they have ignored traditional construction methods. This is both because of the ignorance of the potential and the values of existing methods of construction, and lack of knowledge of the new methods’ characteristics and requirements.

The role of the traditional architect, mimar, as well as the design and construction process and such implications, as the geometrical configuration of buildings which have a grate effect on resistance to earthquakes.

Iran has a long and continuous civilisation of more than 6,000 years (Pope, 1965, p9) and its traditional architecture is one of the brightest symbols of this civilisation. Indeed, the magnificent and unique traditional architecture of Persia has a system and style all its own example of which may be found at Persepolis, the architectural features of such cities like Yazd and Isfahan and their Islamic monuments, mosques, ancient palaces, and towers. At present there are still more than a dozen masonry buildings that have a history more than 1,000 years, in spite of many earthquakes. There is no denying that many buildings have been destroyed or that whole cities or villages have been wiped out, but many traditional buildings have been hit by earthquakes and have survived. The survival of these buildings raises these questions: how did these buildings resist so many earthquakes? How did the buildings perform during the earthquakes?

Traditional methods of construction need to be modified to meet growing needs, but they offer an important beginning. The goal of most research on traditional Iranian buildings has been the classification, listing, description of building types, and their spatial features. Little attempt has been made to link these special features to the way in which they are constructed. This author believes that the reason why traditional construction methods have not continued is that there is insufficient knowledge of their construction operation. It is not enough to say, for instance, that traditional buildings are built of adobe and mud. The traditional construction methods contain some remarkable techniques[4]in the use of bricks and mud which enable magnificent architectural masterpieces to stand up for hundreds of years but there is at the present time an insufficient understanding of the way in which adobe walls or those of similar construction, respond to earthquake loads and The question addressed here could be the way in which the adobe and sun-dried bricks construction have resisted so many destructive earthquakes. research on earthquake effects on Iranian traditional architecture is almost non-existent. The reason is twofold: modern engineers know very little of characteristic of traditional buildings and the architects who research traditional buildings are unfamiliar with earthquakes and structural dynamics

Drawing lessons from traditional construction techniques, and improving upon them could help their continuity which may in turn support modern ’conventional’ methods of building construction in the country. In the context of the use of new materials and the change in current methods, Wulff (1966) pointed out that:

 In the process of industrialisation, one fact is undeniable, namely that the country’s age-old tradition in industrial arts, always adaptable to new conditions, has been and will be of great help in this most significant change.

The resistance to earthquakes of traditional buildings and learning lessons from it, is of major concern. This lies in the role of the traditional profession and its architects (mimars), in the associated design and construction process and in the geometrical configuration of these traditional buildings.

Iranian traditional construction methods, gradually developed through a process of trial and error and are the result of a collaboration of traditional professions: the mimars, clients and users over the generations. Mimars created a co-ordination between architecture and the environment for thousand of years based upon the socio-cultural and geographical conditions of the country.

Opportunities for the development of the Building Industry and for changes in methods of construction inevitably depend upon the available materials and skills, and the existing administrative structure. None exists in isolation from the other, so that changes in one will commonly require or impose change upon others. A change in the materials of construction may thus necessitate a change in legislation and in the skills required. It may also involve changes in the process of construction and in the way in which materials and building components are distributed. Alternatively, changes in the regulations may implicitly demand changes in the methods of construction, for example, the change from mud roofs to the jack-arch and the joist-block as a result of Iranian Code for Seismic Design  Iran is a country with many climatic zones and different socio-cultural bases. Modern or conventional construction methods should not impose a uniform form of construction across the whole country.

Development of the ‘conventional methods’ of building construction in Iran is as a result of sudden changes of the use of new modern materials without preparation of the relevant skills is one of examples of the failure of, like failure of other rapid changes for fully industrialised dreams.

TheIranian traditional building code

The Iranian traditional building code is formed and developed on the basis of proportional design, standard measurement, and modular co-ordination (Falamaki, 1989). On this basis, the traditional construction methods may be adapted to industrial and modern construction methods (Wulff, 1966). Modular co-ordination which is one of the characteristics of industrial method,  is also one of the constituents of the traditional building code. The Iranian traditional building code is based on:

                                              ·          the elements of the environment,

                                              ·          the design process procedure,

                                              ·          geometrical order and modular co-ordination,

                                              ·          the six orders for design and construction.

The environmental elements

Iranian traditional architecture was inspired by Nature (Panaam). The traditional architect followed the ruling order of the Nature enhancing Nature’s potential and harmony. The architect, mimar, used to create buildings with the use of potential of Nature as much as he could (Rown).

Panaamand Rown are two principals of the attention to the manifestation of the use of elements of the Nature. The principles which basically refer to environmental design, determine both architectural and urban planning and design directions. According to the principles, any harmful effect to the Nature and environment is forbidden.

Mimarsthrough their practice made use of scientific principle draw directly from the resources of Nature.  A good example of this is the Badgir[5] (wind-catcher). The Badgir is a technological device. Its significance lies in its use of natural energies. Because of their attention to Nature, the mimars were knowledgeable about the use of such natural elements as: earth, water, light, view, wind, earthquake[6], together with their scientific effects and responses.

Wind, water and vegetation are the most important factors affecting the traditional Iranian architectural forms, particularly courtyard houses in the hot climate areas. For the best of use of wind, badgir, for example , which is an elements of most courtyard  houses, could cool inside properly.

Water , for example, plays an important part in the thinking of Iranian mimars. This practice partly stems from the Islamic belief that ‘everything is created by water’. Water has been used extensively in the design of houses both for visual delight and comfort. The result is that mimars developed skills in the handling of water in building. Unfortunately this led to an over-confidence in their skills in handling modern plumbing where they failed to see the conflict that occurs between plumbing needs and structural safety. The cutting of chases within the construction to accommodate modern piping has the effect of disrupting the structural continuity of walls, floors, and especially ring beams, which reduces the building’s resistance to earthquakes.

Design proces

The Mmars in traditional architecture used to conceptualise the design of the buildings using two processes simultaneously. One was analytic, the other geometric. They were given certain parameters to work with: the function of the building, its budget, often a schedule, and the scale of its most significant parts. Pirnia (1971) gave the following specification and has referred to the five stages of the traditional design process: gaz kardan (measuring), goftogoo (negotiation), barzeh (sketching), arayesh (approved plan), and Kast-afzood (changes to the provided sketch or as-built plans).

Gazkardan: can be regarded as site investigation. Goftogoo: the stage of determining the user’s requirements and the size of building/house as a result of negotiation and discussion. The term barzeh, implies that the user should accept by a process of discussion by the provided drawing of the plan and the layout of rooms and spaces. These are all arranged with gypsum planks on a board by the mimar. Arayesh, the final stage is related to the execution of construction including the determination of materials, details, construction methods and sequence of the work. kast-afzood are the changes to the design resulting from discussion and the barzeh presentation and rearrangement of final design.

In the geometrical process, the actual designing of the building was done theoretically to some extent regardless of the given scale. After the design had been drawn up on the basis of geometric proportions, the mimar returned to the analytic process. He selected one dimension within the design to serve a paymoon (module), which was either equivalent  to, or commensurate with gas[7]. Sometimes the thickness of the walls served as the paymoon. The paymoon was then subdivided  into smaller units, commensurate with it, and the minor details of the plan could be blocked out. These smaller units corresponded to the size of the brick plus a rising joint, so that the mimar could transmit measurements in real numbers, or even in terms of numbers of bricks, even though these measurements may have been worked out theoretically and often had irrational values. Appro -ximations of irrational numbers were also used (Golombek and Wilber, 1988).

That the two systems, analytic and geometric, were used by mimars is borne out by the analyses of actual buildings, for which both the proportional and modular systems have been deduced as modular co-ordination (gas-va-paymoon).

As for earthquake design construction, the configuration of building plays an important role in earthquake responses and the geometrical base of building form is considered here in order to understand the relation between form and resistibility to earthquake.

Geometrical bases

The Iranian traditional construction is based on a crystal form that is the intersection of two squares. The transversal points of squares make an octagonal geometric form. The equilateral octagon form is a popular form in Persian architecture. This form is used as a plan concept or a constructional measurement tool base. This two dimensional base for the plan, plus the symmetrical three dimension of the whole building form could effectively resist earthquake motions. The reason is that the square present an excellent but simple symmetrical shape which is resistant to earthquakes (Arnold & Reitherman, 1982).

Figure 3 :  The octagon which is originated from the ‘crossed squares’

The hashti[8] (octagon), forms  an entrance or lobby for the traditional courtyard houses. The octagon form can be found in many Iranian traditional buildings, for example, traditional gymnasia, public baths and religious buildings. The octagonal shape and ‘crossed squares’ (Shamseh-hasht) are also used in drawing, painting walls, and ceiling  decoration of kashicari (ceramic work) and Muqarnas ( stalactite). Figure 4,  shows the geometrical transition of a square to a octagon and ultimately to a circle by the use of ‘crossed squares’.

The ‘crossed squares’ is not merely a shape. It is also used for spanning the square

 form plan by use of a dome. Because the shape of dome is circular it would be easy to put it on a circle plan (the Roman rotunda), but where the plan is square, the problem is more complex and one which the Romans found impossible to solve. The essential problem of the dome constructed over a square plan, is how to manage the transition from a square plan to circle dome. In other words, the transition of square shape to circle base dome is the main concept of spanning a square plan by a dome. When a hemi-sphere rests on the corners of a square, it projects beyond the four sides of the square or when it rests on the sides, it projects in and falls short of the corners of the square: either form seems unpleasant. Mimars, the Iranian architects, for the first time in history solved this problem by changing the unpleasant condition of the transition to one of the most constructive and beautiful details in the Persian architecture. They used the ‘crossed squares’ as a base model of the transition of the square plan to circle form.

Figure 4 : The transition of a square plan to a circular dome

They considered the octagon as an intermediary form between square and circle. One or more polygons (multiples of eight) may be interposed between the square(s) and dome to decrease the incongruency of polygon and circle. For this it was necessary to intersect an assumed rotated equal square with the square plan. The crossed points of the ‘crossed squares’ make an octagon. Four sides of the octagon rest on the four sides of the square plan. The remaining four sides of the octagon which fall short of the corners of the plan, could rest on the bridged arches across each of the corners. If necessary, bridging arches could be repeated for the eight new corners. The arched corner is called sequnge (squinch), Figure 4, is known as the Persian method for spanning a non-circle plan by a dome. Sequnge as a geometrical born, is also used to be used in decorative ornaments. The use of stalactites or muqarnas decoration, for example, is a well known feature of Iranian traditional architecture.

Perhaps the reason for the selection of axial openings, that is se-dary and pange-dary (three and five doors room), was a matter of culture (Ardalan & Bakhtiar, 1975, p. 73). Culturally all existing things have zahir and batin. Zahir is appearance and form and batin is inside and function. Symmetry is one of the features of zahir. In a courtyard; garden, ivan, and a se-dary room are located on the axis of bagh (garden) symmetrically. Ardalan & Bakhtiar described that ‘the location of openings in its enclosing surfaces established the particular orientation and personality of a room’s space’ toward the bagh. The axis, from inside the se-dary room to the garden, passes through an opening. As Figure 4.5 shows, this opening is the middle doors in se-dary. The se-dary which is actually determined by culture, is modified structurally. The openings are arched and the middle one is sometimes, higher and wider.

 
          Figure 5 : Three opening/arch structure order   

Structurally, as the figure shows, the middle load bearing arched opening is supported from its sides by two other arches which act as buttresses. Because of this, it can be increased to five openings.

Openings, in traditional construction, have significant role not only in terms of culture, but also for structural stability. There is no opening on the external walls, apart from the entrance door, so the solid external walls act structurally. This feature of privacy or hejab, as well as the symmetrical building configuration which constitute the earthquake resistance function of traditional buildings shows the dominant of culture.

The six order of building design and construction

The six orders, are a set of basic principles for the design and construction of traditional buildings. The principles, first identified by Mohammed Karim Pirnia (1922-1997) an accomplished Iranian architect, make the design and construction of buildings easier and ensure the construction quality. To achieve a better understanding of traditional construction methods, the principles are briefly described below.

1) Mardomvary (being sympathetic to the People): This implies a compatibility of construction to the People’s needs and humanity regardless of their race and wealth. For either rich or poor there is an standard of living and a standard of space. Se dary, for example, is the smallest bed room, and the andaroony ( private zone of house) with biroony ( common zone) should exist in all houses. the house size and the number of rooms is determined by the number of occupants, irrespective of their wealth.

2) Khod basandegy (self sufficiency): the use of  boom avard (local availability). The materials and components must be provided from the site itself or from the local market. This reduces any sort of dependency from outside the area. The use of the excavated soil for foundation or basement, and building waste are the example of the best use of availability and the avoidance of waste of energy and materials..

3) Paymoon (modular co-ordination): Paymoon is a system of measurement for design and construction to standardise the building materials and its components. This is based on a system of modular co-ordination. It provides rules for determining the dimensions and proportions of building elements. Paymoon is based on equal units of gaz.

4) Daroon-graei ( inward looking): privacy is an inherent feature of Iranian traditional courtyard-houses (andarooni). Attention to the inside of the house is one of the most desirable principles in construction. This attitude existed even before the Islamic Period (Pope, 1976, p2)  p69 Memarzia.  The compatibility of this principle with the Islamic Philosophy of privacy or hejab is a reason not only for its acceptance but also for encouraging its development and growth. According to this principle, the whole concept of a house is one of a privately used commodity and as a consequence, there is nothing to display. Consideration is paid to the internal elements and courtyard facades, in contrast to the external facades on the streets which have no openings. The only opening in the external facade is the entrance door which opens only to the birooni courtyard and does not give direct access to the main part of the building. This feature of traditional house construction can be regarded as an earthquake resistant determinant factor because of the lack of openings.

5) Gange-o-banar ( the avoiding of unnecessary elements): this order refers to the optimisation of the use of land, materials and space. It encourages the avoidance of inappropriate size and useless decorations. One of the considerations of the gange-o-banar was avoiding excess dead loads all of which have an effect on the earthquake resistance of buildings. As the walls were very thick, they used to build castellated walls by openings of doors, windows, and also by  taghcheh (niche), raf, and ghatar bandy (the dented above the raf to the ceiling) to reduce dead loads. The order also refers to the reduction of construction cost and avoidance of waste in materials and labour.

6) Niaresh  (structural stability): this refers to all efforts made to construct the building structure in such a way that it could stand up. Niaresh is the way in which all the static and dynamic behaviours of building structure were determined.

Process and methods of construction

I have already referred to the mimar’s design and supervisory role. The mimarbashi (senior architect) who acted as a supervisor and the banna (master mason or mason), were also involved with construction works. In rural areas the banna acted as a builder. Bannas were permitted to design and build only the small dwellings.

In spite of specialist involvement in the construction process, it could be conducted with the involvement of ordinary people, families or communal groups, as direct workers (or those who provided food) in the form of a co-operative organisation. This was mainly practised in the erection of the buildings where such an erection needed much manpower. The custom of co-operative construction not only helps to overcome the problems of both simple and comple building constructions, but also has social implications. A clear manifestation of the way of life and belief of Iranian communities can be seen in the process of house construction. Occasions such as this were important in maintaining the close ties among citizens and giving to them a sense of belonging and identity.

The building construction process begins with the site selection of the house by careful observation of the site. After the site is selected, it is levelled and cleared. Building materials such as adobe-bricks were then made on the site. When the basic structural materials of the house were ready, the structure of the house was erected with the co-operative labour of the other families. The other components of the house such as doors and windows were then made and assembled to complete the house.

Building construction methods actually are the combination and assembly of materials and components. The way in which different parts and elements of buildings are constructed, illustrate the level of techniques and skills involved. To understand the characteristics of the Iranian traditional construction methods, the materials used and some of different elements of building construction are discussed in detail below.

In the past, materials used for building construction were gathered freely from the immediate surroundings and were usually taken directly from Nature. Available construction materials dictated most forms and methods of building construction. Local available materials played a crucial role in the development of construction technology. In the North, for example, on the coast of the Caspian Sea there is a high rainfall, and timber is abundant. In this area timber is used for structure, walls, windows, and doors. The structures were  usually timber frame with pitch roofs. Such resources are becoming scarcer today because of increased population and forest clearings for timber, agriculture and other development activities.

The building process for timber frame construction in the North resembles a modern prefabricated housing system where the components are first made on the ground and later assembled together on the site to form the house. This is an example in which modern methods of construction may directly parallel traditional methods, and the transfer from one to the other may be both simple and possible.

Clay, a readily available building material, has encouraged the developments of most of building construction techniques in other parts of the country. The most important primitive technique, is sun-dried compressed moulded clay (Khesht). The technique which was used in Iran from ancient times, is still common. The development of adobe and brick relies on the abundance of clay as the main source and lime as an adhesive and mortar.

Most Persian houses were made of mud-wall or adobe-brick construction, covered with domed or vaulted brick roofs. The maximum compressive strength of mud as a homogenous material was achieved through load bearing walls. But in many cases the clay available was often too sandy especially in rural areas and as a result produced walls and bricks of surprisingly low strength. Mud-straw was the main material where wood was scarce. Both bricks and mortar were made of a mixture of loam and straw.

Improvement and modification of traditional materials, because it is simple, easily available, and fast to construct, could benefit of those who are in need of shelter. The homogeneity of sun-dried brick construction in wall and to vault and dome roof, which used to create a single element, in compare to different materials used in modern methods, could be gained by the proper use of materials such as clay and mud-straw. There are a number of projects currently being undertaken in recent years on developing earth or mud buildings as a modern construction method and there is ‘a new appreciation of the technological achievements of traditional builders’ (Oliver, 1990, Mimar no. 38). Some more evidence of the modern earth method here for example Williams-Ellis, clough or Avebury experiments by Uk Government. in the provision of strength and resistance to earthquakes.

Sun-dried bricks and later burned- bricks were exist from the time that human learned to construct shelter outside the dug shelters.

Inventions mostly occur because of need and a number in inventions of materials and construction methods took place over the centuries during the development of Iranian architecture. Among them was the invention of flat rectangular bricks in the fourth millennium (Pope, 1965, p15 and Pope, 1976  Hajazi, civil. seminar, p218 , Ghirshman, 1954, p35), the invention of Sequnge (Squinch) - a transitional pattern of constructing a dome on a square plan, and the invention of an isolated building foundation of Takht-e-solaiman (or Takht-e-taqdis 618-628 AD) (Hejazi, 1996, p221). These examples, which result from the constrainly of a limited range of materials, indicate the need for a review of the traditional construction techniques for the purpose of learning useful lessons. The constraints encountered in the past played an important role in developing advanced construction techniques.

The way in which scarcity of materials affects architecture can be seen by looking at the effect of the availability of wood. In the North of Iran where wood is readily available it is used for even the simplest buildings. Further South, in the hot climate area, arches and domes are developed from soil and burned-bricks in construction of palaces, mosques and houses. There are many buildings which use these technique such as the Chuga Zanbil Ziggurat (1250 BC) (Hejazi, 1996, Civil engine. seminar) near Susa, which is famous for the materials and construction techniques used to span a space by means of dome for the first time during the Ashkani Empire (Soltanzadeh, 1986, p272). Tagh-e Kasra (about the second half of the third century AD) at Ctesiphon in Iraq, was the highest and widest spanning with a vault, at the time and for many years later(Hejazi, 1996, Civil engin. seminar, p221). Persepolis (330-560 BC) is the other example of the use of another advanced technique, with a mortar-less masonry construction method (Pope, 1976)(Hejazi, 219).

One of the reasons that these techniques are so developed is that the mimars were able to conserve materials because they had details and precise knowledge of the behaviour and characteristics of materials, not only in terms of cultural or climatic response of construction, but also in regard to building response to earthquake. For example, a few years after the 1780 earthquake in Tabriz, all new houses were intentionally built as low as possible with thicker mud walls and more wood, and the bazaars were covered only with a light wooden roof. For temporary shelters, the builders used the easy solution of erecting temporary timber-framed pavilions, the so called takht-e poosh shelters, in their gardens in case of emergency (Ambraseys, 1985, p25). This understanding tends to lead to clear solutions to the problems posed by earthquakes and the adoption of methods of construction.

Result

In addressing the role of traditional architects (mimars) and  the architectural aspects of earthquake performance of buildings, this paper has had three objectives: to show that earthquake construction has not been merely an engineering activity for structural engineers, it is an activity to be shared by both engineers and architects; to demonstrate the role that architectural aspects plays in determining the earthquake resistance of buildings and to emphasise the need for architects to understand the problems and nature of earthquake effects on buildings

This paper opened up an area of study of architectural issues in earthquake resistance in buildings and introduced a set of problems specific to ‘conventional’ construction methods and the robustness of traditional architecture in Iran. The justification for this lies in the general acceptance of the insufficiency of structural calculation alone in the earthquake resistance of buildings and the need for a combination of other issues, such as building form and configuration, materials and construction workmanship, with the structural aspects. These facts show that in the case of the majority of ordinary buildings in Iran, the problem is not the lack of structural analysis. Any improvement in architectural design change to configurations and methods employed in their construction operations, would go a long way in effecting the earthquake resistance of the buildings.
 

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[8]             Hashti which has an octagonal form in plan, means an entrance space.