SEISMIC PERFORMANCE OF ADOBE BUILDINGS IN CYPRUS

Vsevolod Levtchitch1, Yiannis Fessas2, George Nikitas3

ABSTRACT The aim of this study is to get an insight into old adobe practices and to obtain a better understanding of resources of these structures seismic resistance. Buildings which have already stood the test of time and managed to survive several low-to-moderate intensity earthquakes have been inspected, assessed and analysed. Basic structural wall arrangement, plan density, slenderness of buildings and walls, proportioning and location of openings, effect of floor and roof diaphragms, importance of collar beams, timber framing and bracing along with the properties of adobe materials and protection against water have been considered . Main principles of a good practice have been summarized. INTRODUCTION There is a rapidly growing interest in the oldest construction material: earth. In spite of the centuries of its massive use, the scientific backing or intellectual bottom has not been created yet. There is a critical core experience, but it was not aided by science. Too much reliance is placed on “rules of thumb”. Construction is the prime necessity and by its nature it heavily tends to be empirical. Traditionally it was a practical art and, for ages, the outcome was a function of a single factor: operations. Lack of knowledge had never stopped adobe construction. There were millions of successful builders who have never even heard of Young’s modulus, Mohr’s circle, Winkler’s sub-grade reaction, or D’Alambert’s inertia force principle. Common sense and collective historical wisdom have selected the safest forms and methods of construction using locally available and cheap materials. Trial and error method and hard lessons of numerous failures have helped to evolve the most reasonable construction practices. No one theory can disprove these techniques because they have passed the most rigorous testing: test of time. At the same time there were some practices which do not contribute to a general good performance under seismic loading. There was a continuous challenge and response but the intrinsic mysteries of randomly varying seismic forces could not be solved by observational experience only. Each earthquake has a nature of its own. Earthquakes do not repeat themselves and are never short of confusing surprises. Every strong earthquake reveals new weaknesses in our construction. Despite recent fantastic advances in earthquake engineering, the predictions are not yet possible. The renewed interest in earth materials does not mean focusing on the reinvention of the wheel. It is not due to the idle academic curiosity. Millions of people living in adobe houses are at the mercy of nature. Reduction of risk and mitigation of consequences are the major long term objective of the earthquake engineering. 1 Professor, Frederick Institute of Technology, Nicosia, Cyprus, savvas@research.fit.ac.cy 2 Manager, Proplan LTD, Nicosia, Cyprus, proplan@spidernet.com.cy 3 Manager, Geocratis LTD, Nicosia, Cyprus, geocrat@cytanet.com.cy

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Millions of people living in adobe houses are at the mercy of nature. Reduction of risk and mitigation of consequences are the major long term objective of the earthquake engineering. Adobe construction has some inherent seismic weaknesses. As we see it today, this is indeed a very poor choice for an earthquake prone areas. Adobe material is seismically deficient on many accounts. But it was used for centuries and an efficient practice has been filtered through ages. The tragic lessons from past earthquakes have helped to develop the practical “know-how” and to get from adobe the very best, what it could safely provide. If all physically possible structural capacities are jointly mobilised for a great occasion, a structure will stand up to an earthquake challenge. When all individually weak structural elements are tied together their simultaneous spatial response is much stronger than the simple sum of constituent components capacities. The capacity of a system as an integrated whole cannot be deduced by the simple summing up of apparent reserves of its parts. The system principle can be understood from Aristotle’s ( 350 BC) dictum: “ The whole is more than just the sum of components”. At present in Cyprus there is no new adobe construction. New materials hold a firm grip on the construction industry. New requirements and new financial possibilities leave virtually no chance for adobe. In 1996 in the Government controlled Southern part of Cyprus the reinforced concrete structures constituted 77% , masonry –14% and adobe – 9% of all existing buildings [1]. More than a half of all adobe buildings is located in Nicosia, the next quarter of them –in Larnaca and the remaining part – mainly in Famagusta region. The vast majority of them are older than 50 years. More than 70% of adobe buildings were constructed before 1947. The use of this material has stopped approximately in 1960. Since that time there was a construction boom and the rate of new construction was kept fast and steady. In 2003 the dwelling stock has increased by the healthy 2%. As compared to 2002 the investment in housing in real terms has increased by 20.6%. The average area per new dwelling was 172 m2 and the average number of rooms per new dwelling – 5.6. Practically all new dwellings are with solar water heaters (96.3%) and with central heating (82.2%) [2]. At the same time the allocations for the repairs constitute only 12.2% of the gross output. This is considerably lower than in other countries where the focus is steadily shifting on the old rather than on the new buildings. But when the both Southern and Northern parts of Cyprus are considered the cumulative number of adobe houses still makes approximately 9% of the total stock. The inhabitants of all adobe houses are elderly people who either have a strong emotional bond with their houses or do not have economical ability to move to a new dwelling. In cases when the financial side is not the decisive factor people are voluntarily willing to face a risk as a testimony of their nostalgic appreciation for the bygone days and things past. They have different perception of risk, consider themselves at a negligible risk and are strong believers in the effectiveness of old techniques and new methods of upgrading. The degree of risk awareness is conditional and involves some firm but illogical denials. Some projects of repairing, refurbishment, modification and seismic upgrading have been already done. These buildings send a clear message: adobe houses can be considerably upgraded (Fig.1,2). The perpetual fear of a total fall-out can be removed from the life. In spite of many un-tractable problems it is safe to say that these buildings lend themselves for a professional structural intervention. Some of them are in a dangerous structural state. In many cases there was no maintenance and no protection against the destructive effects of environment and at present there is a very slim chance that these structures will survive even under a small

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intensity earthquake. Many buildings have been abandoned and left to rot and decay. Adobe structures are much more seismically vulnerable than others. They cannot meet requirements of new codes of practice. Exposure therapy does not work. These buildings may be collectively classified as non-engineered. They were not specifically designed to resist seismic forces but in the course of their service-life the expectations are unrealistically higher than the available capacities. As a rule adobe structures are expected to do more than they are actually capable of. Adobe does not posses the key properties which allow to perform in a ductile, energy dissipative manner, to store strains and to redistribute stresses, to adapt to a random not clearly defined seismic vibration. Low shearing and tensile strengths make adobe structures an easy target for earthquake forces. This structures are sensitive to the differential settlement. Tilt or rotation greater than 1/500 results in serious damages. At the same time the visually noticeable values in buildings made of other materials are greater than 1 in 250. For comparison , in reinforced concrete structures a considerable structural damage is envisaged when the differential settlement value is greater than 1/150. The common limiting value of d/L to cause cracking in masonry walls and partitions is 1/300. A floor inclination of 2.5mm per meter (i.e.1/400) is usually considered as a defect in common residential buildings. So, from this view point the structural limitations of adobe buildings are close to the serviceability requirements. This is in a stark contrast to steel an reinforced concrete structures. In a simplified approach, each inclination of 2mm/m can be equated to a uniform 4% damage of building. This implies that the inclination of 1/20 means the complete damage. At present the inter-story drift is already universally adopted as a most reliable yard-stick for the assessment of buildings performance. For reinforced concrete structures the limit is set depending on the interaction between infill walls and columns. In buildings with clay brick masonry infill walls the serious damage is experienced when the inter-story drift exceeds 1/120 (i.e. 0.83%). But the convincing experimental evidence from laboratory testing of bare frames shows that the physical destruction of columns begins when the lateral drift is in excess of 3.5% , i.e. more than 4 times larger than the value defined from other considerations. In reality, the stability cannot be preserved under such a large drifts and the practical limitations set in codes of practice are drastically lower. Moreover they are expressed in terms of elastic displacements and the further additional large and separately assessed increases are recommended to account for the residual strains, cracking of concrete and inevitable reduction of actually available lateral stiffness. In adobe structures only the first component (conventionally elastic) can be taken into consideration. As a tentative bench mark a total lateral displacement of 1/1250 (e.g. 0.08%) can be considered. This is a much smaller value than those commonly recommended for reinforced concrete and steel structures but it is practically the same as those recommended for the glass partitions and the facing of walls with natural stones. For example, in Mexico and Chile for the load bearing frames with rigid connections of structural and non-load bearing elements, the elastic inter-story drift is restricted to 0.2%- 0.3% (but not more than 15mm). In New Zealand : 0.25%-0.50% and in USA: 0.50%. When non-structural elements are separated from the load bearing structures the drift can be increased 2…3 times. From this analysis it follows that the earth buildings are far more sensitive to deformations, displacements, differential settlements and, generally, to geometrical distortions than reinforced concrete, steel or timber structures. Earth materials have widely varying properties. There is virtually little chance of soil variability being reduced to negligible levels. Some striking assumptions are adopted while analysing soil materials. They are numerous and in dangerous conflict with real physical

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phenomena. But when combined all together they, in majority of practical cases, provide for the conservatively safe values. The classic works in Soil Mechanics, which are still in use, by Coulomb(1776), Darcy (1856), Rankine (1857), Winkler (1867), Boussinesq (1885), Terzaghi (1943) have all been based on the mind provoking assumptions of elastic, isotropic, homogeneous and orderly stratified earth medium. Of course, an exact solution cannot be based on flippant assumptions. The accuracy of mathematical modelling of real physical processes in earth materials is nowhere near. Up till now, in spite of the heavy involvement of the higher mathematics, it is a very approximate approach.

TYPICAL STRUCTURAL ARRANGEMENT OF ADOBE BUILDINGS IN CYPRUS. Fifteen old adobe houses have been inspected and assessed. Their age is between 60 and 80 years. Some of them have been abandoned and left to decay, degrade and disintegrate. Several buildings have been ruined to the extent of complete disrepair and recently they were demolished and gave space for a new construction. The prime cause of their demise can be easily pin-pointed: there was no maintenance and protection against water, wind and direct sun radiation. The third group of building has been designated for the repairing and seismic upgrading. Owners of these two buildings have a high hope that their buildings will get a new lease of life and bring them the peace of mind and joy for many years to come. All investigated buildings have identical structural arrangement. The rules of good practice have been followed consistently. Simple architectural planning provides for the regularity, uniformity and structural integrity. A cellular arrangement of load bearing walls in which lateral cross walls and longitudinal walls are rigidly joined together and create a rigid and stable cells of relatively small dimensions. In their turn these cells are joined with their neighbours and provide for the sharing of loads, their uniform distribution and dispersion between all structural elements (Fig.3,4,5). Floors and roof diaphragms have been rigidly fixed into the walls. The collar or bond beams under floor and roof structures created the lateral ties and, in general, provided a link for the box type structures which can be treated as the most appropriate shape. Free standing walls were not used. The main features of these buildings are summarised in Tab.1. Table 1. Typical characteristics of investigated buildings 1 2 3 4 5 6 7 8 9 10 11 16-25 m2, 1.2-1.7

0.20-0.30

0.75-1.75

7-9 3.0-3.5

8-11 0.15-0.35

0.10-0.20

1.0-1.5

≤1.1m ≤1.2m

1. Cell area = the plan area (m2) confined by walls of a structural unit, length/width

ratio. 2. Plan density = area of walls / area of cell floor 3. Building slenderness ratio = height / smaller plan dimension 4. Wall slenderness = height / thickness 5. Pier slenderness = pier height / thickness 6. Wall length / wall thickness (out of plane slenderness)

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7. Length of openings within a floor / length of a wall 8. Area of openings /area of a wall.

7. Pier width / height of opening (window) 8. Width of a single opening (m) 9. Distance from the corner to the opening and distance between openings (m).

These values are drastically different from those of reinforced concrete, steel and timber structures. Inherently poor mechanical properties of adobe material have been largely compensated by the selection of the most suitable forms of construction and good detailing practice. When the floor density factor is converted to the ratio of length of walls of one direction to the cell area this index translates into (48…72) cm/m2. For comparison, in low rise reinforced concrete frame structures with shear walls this index is commonly within the range 12….15 cm/m2. In Japan this ratio is substantially higher: 15…24 cm/m2. Adobe structures call for 4…5 times larger value. When the area of one direction walls is related to the cell floor area the ratio is within the range from 0.20 to 0.30. With the use of high strength materials the plan density has been reduced drastically. In contemporary reinforced concrete moment resisting frame structures the plan density is approximately 1.5%, while in braced frame structures it is even less than that. Taj Mahal in India constructed in 1630-1653 has he plan density of 50%, St Peter Cathedral (1506-1625)-25% and 445 m high Sears Tower constructed in 1974-only 2%. Building’s slenderness, which defines the mode of lateral displacement and regulates the magnitude of overturning moments, predetermines the forces in exterior load resisting vertical elements and generates the second order effects, is very small ( 0.75-1.75) as compared to corresponding values in reinforced concrete and steel structures. For common shearing type structures it is recommended to be between 3 and 4. Flexible structures are subjected to considerably smaller seismic loads than rigid ones, but stability requirements impose the clear cut restrictions. The compromise or a trade-off between these two conflicting factors is always needed. The Royal Concordia Hotel constructed in Manhattan in 1989 holds the world record for slenderness with the height-to-width ratio of 11.1. The majority of adobe buildings in Cyprus are ground floor houses, but there are ground floor plus one storey (Fig.1,2) and also a limited number of ground floor plus two storeys houses. In many cases several structurally identical adobe buildings have been clustered without separation joints. This goes against the well defined contemporary principle, but in case of small buildings the effect of clustering is to be assessed individually and in conjunction with an enhanced stability. In order to have less obstructed interior the spacing between lateral walls was increased with a corresponding provision of pilasters or buttresses (contra -forces) between walls (Fig.6). In this way the free length of walls has been reduced and the danger of out of plane failure was minimized. Again, this procedure needs an expert judgement. It can be counter- productive if the stiffness of buttresses is excessive. There were cases when buttresses were constructed from both exterior and interior sides of a wall. Buttresses are usually tapered at approximately 1:10 angle (Fig.4). Sometimes the exterior buttresses were only up to the mid-height of a wall and this cannot be treated as a reasonable solution. It introduces a much feared irregularity in stiffness distribution, buttresses perform as free standing structural

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elements and practically do not take part in seismic force resistance transferred by the floor diaphragm. The local incorporation of a stiff member which is not connected with the floor or roof diaphragm and not tied up with other vertical structural elements brings more harm than good.. Clay-silt and a lime mortar have been used as the bonding agents. Plinth masonry with the lime mortar has been used for the protection against water. In many cases the protection was not adequate or was omitted altogether and this resulted in a gloomy outlook and a serious degradation of repeatedly wetted and dried out walls. Water ingress, penetration and capillary rise are the principal trouble-makers. The very existence of adobe as a structural material depends on the moisture content. There were no adobe structures on the sites with a high ground water level. Water protection is of utmost importance. It can be singled out as the most influential factor. Rain water drains were usually provided around buildings and the seepage effects have been minimized. As a rule the bottom part of walls, up to the level of approximately 1m from the foundation, was made of un-coursed rubble stones. There is a documented evidence [3] that this practise goes as far back as to Frankish Period (1192-1489). As the bonding agents a clay-silt and a lime mortar have been used. Plinth masonry with the lime mortar has been used for the protection against water. In many cases the protection was not adequate or was omitted altogether and this resulted in a gloomy outlook and a serious degradation of repeatedly wetted and dried out walls. Adobe structures are very sensitive to differential settlement of foundations. The only answer to this problem is to provide a strong ,stable and durable foundation on a firm foundation bed. In Nicosia district soil conditions are rather good and the stresses induced by a common adobe building could not generate considerably uneven or unacceptably large settlements. But there are areas with clay soils which have been from time to time flooded and converted into temporary lakes. Highly expansive montmorillonite type clays, which prevail in some places, have caused numerous problems. The susceptibility of clays to shrinking-swelling and to long term consolidation settlements has been well known and was taken into consideration while selecting a building site. In the vast majority the foundations were of a simple strip type with a uniform width and depth. Loads were fairly uniformly distributed along the length of walls and transferred to foundations made of un-coursed rubble stones. The depth of founding was to the firm sub-soil strata, but in Nicosia region it was rarely deeper than 0.5m. In those cases the foundation was extended up to 0.5 – 1.0m above the ground. Actually it was a prototype or a variation of the trench foundation (or deep strip wall foundation) which is used in contemporary practice. Since the bearing capacity of soil substantially depends on the dept of founding this factor can influence the solution. Moreover, trench foundations reduce the substructure (underground) works considerably. The width of a foundation of this type was approximately 50% larger than the thickness of a wall resting on it. Under the buttresses, pilasters and chimneys incorporated into walls the foundations were extended beyond these elements on all sides to the same extent as they projected beyond the walls. In some cases these projections were somehow larger than those under the walls. When a strong soil stratum was deep the extended-base strip foundations were constructed. The base width was not less than the double wall thickness. It seems that the angle of stress dispersion within the base was taken approximately of 45 degrees. The thickness of a base was slightly larger or roughly equal to its projection beyond the upper part of a foundation and the wall. In this respect the principle of stiff foundations have been followed. The thickness of foundation extended bed was slightly larger or roughly equal to its

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projection beyond the upper part of a foundation and the wall. In this respect the principle of projection beyond the upper part of a foundation and the wall. In this respect the principle of stiff foundations have been followed. The material simply did not allow to make these bases flexible. In some exceptional cases the construction on sloping sites required the stepped foundations. Generally, this was not practiced. But during one demolition the foundation laid at two levels has been un-earthed. At the place of level change, the higher part was extended over the lower part for 1.5 times thickness of the foundation. This overlapping had been provided with the aim of a favourable transfer of loads and avoiding of stress concentration. It was corner-cutting in the name of reduction of cost. At present this practice in earthquake prone areas is strongly condemned. Foundations under the whole of a building are recommended to be at one level. INSPECTION OF ADOBE MASONRY There are two distinct seasons in Cyprus: summer and winter, or dry and rainy seasons. Transitional periods cannot be defined clearly. Central inland areas around Nicosia can be classified as semi-arid. The evaporation of water is approximately equal to the precipitation. The annual average rainfall from 30 years observations is as follows: Nicosia- 324mm , Larnaca – 344mm and Famagusta – 355mm. The temperature average maximums are: lowlands – 36 degrees C, coastal areas including Larnaca and Famagusta – 32 deg.C. But during the dry season there can be heat-waves which send temperatures to climb 6 – 9 degrees above the average maximums. For example, during 10 days in July 2000 the temperature had been kept above 40 degrees C with the maximum of 44.1 degrees C –the fourth highest temperature of the century. Temperatures changes are invariably accompanied by the relative humidity variations. In lowland areas the rise of temperature and the reduction of R.H. are taking part concurrently and inversely. For example, in 1999, in Nicosia the minimum recorded R.H. was 3%, there were 7 days with R.H. lower than 7%, and 38 days with RH less than 20% . But in Larnaca and Famagusta the RH does not decisively correlate with the temperature. In coastal areas the relative humidity is constantly much higher than in lowlands. This a bit long excurse to climatic conditions helps to understand a marked difference in adobe structures performance and durability in central lowland areas and in coastal regions. The degree of damage with time seems to correspond to the differences in environmental conditions, i.e. in relative humidity. The geometry of old adobe bricks with he reference to contemporary European Standard prepared by the Centre for he Development of Industry [5] can be classified as satisfactory. The bricks taken from the protected sides of walls were of regular dimensions with rectangular angles. Dimension variations are plus-minus 5mm for all: length, width, height. Both bed and laying faces were flat. The sweep of compression surfaces was not lager than 1 in 100. Chipped edges and corners did not exceed 12 mm and less than 7% in volume. Holes, cavities, splits, punctures and scratches did not exceed 7 mm in depth and did not affect the surface of more than 25%. The number of macro-cracks on each one surface was found to be less than 3. Macro-cracks were measured to be smaller than 45 mm in length, 10 mm in depth and 2mm in width. Flaking and efflorescence, generally, were not significant. On the exposed faces these defects were considerably larger. Surfaces were much more and friable The effect of environmental exposure can be decisive and cannot be ignored. crumbly

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Macro-cracks on exposed surfaces were up to 60mm in length, 15mm in depth and 5mm in width. The number of macro-cracks on the surface was up to 5. There were no large cracks which could considerably cause irregularities in the wall surface and to affect the wall’s structural integrity. If the erode-ability is to be defined depending on the depth of pitting in accordance to Frencham recommendation, the material is definitely to be identified as an erosive one [6]. The thickness of joints was found to be 10 – 15mm. According to Abram’s law the mortar is stronger when thicker. An old builder has told that in order to get a stronger mortar it should be sprayed during the first three days after placing. This is in common with the concrete technology, but still it needs a convincing explanation. They are horizontal, i.e. of the constant thickness over the wall length. The overlapping length in no case was less than 25% of the brick dimension. Superimposition of vertical joints was not detected. The deviation of vertical joints from the verticality was less than 10mm per storey height. ADOBE BRICKS COMPOSITION The constituent parts have varied from site to site. But it is of importance that deviations were not traumatic. Somehow it happened that the highly sensitive to water and excessively compressible montmorillonite clays were not used even at places of their natural deposition. It could be that buildings, in which they were used, simply did not survive. From the limited number of tests carried out so far, the content of clay and silt particles has been estimated to be within the range from 30% to 50%. Clay particles make the whole thing possible. They provide bond, plasticity and resistance to water penetration. The granular composition of clay particles is presented in Tab.2. Tab.2 Particle size distribution of clay particles. Particle size, mm

0.002mm and less (clay)

0.00625 (silt)

0.01 0.02 0.06 0.1 0.2 0.6

Content (%)

9-35 2-18 2-4 2-6 6-14 4-8 4-12 10-18

Plasticity limit: 15% - 20% with the average value of 17%. Liquid limit: 30%-42% with the average of 36% and this clay can be classified as of the intermediate plasticity. The corresponding index of plasticity: 15%-22%. According to Seed, Woodward and Lundgren the swelling potentials are very low if the index of plasticity is substantially smaller than 30%. At the same time a high value of the plasticity index (in soils with the same LL) means a better toughness , higher dry strength , lower permeability and due to this a lower rate of volume change under loading. Both compressibility and shear strength are directly related to the plasticity index. The weighed assessment and compromise are needed. The natural moisture content: 4%. The Proctor test has shown the maximum dry density of 1610 kg/m3 and the optimum water content of 21%. The mix had respectively: 1900kg/m3 and 11.5%. Approximately 65% of the clay minerals can be identified as illite, 25%-kaolinite and remaining 10% - montmorillonite. In coastal areas with marine deposits the illite is

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predominant and constitute more than 70% of the clay particles. Kaolins are mainly derived from the weathering of granites. Kaolins are the most stable clay minerals and preferable in construction. In montmorillonite group about one in six of the aluminium ions is replaced by magnesium. Penetration of water causes large volume changes within the crystals themselves. There is a drastic volume change between wet and dry season. Water absorption may continue until the complete dissociation of crystal sheets. For this reason this type of clay can create some serious problems. The remaining 50%-70% of the material was sand with the largest particle size of 2mm. Sand forms a stiff matrix which to some extent restricts volume changes but on the other hand the inclusion of rigid fractions is associated with the stress concentrations and implies a good bond between clay and sand. Regional variations in sand composition are very wide. In Larnaca region it consists mainly of quartz with some feldspar. Sands from the beach include calcitic sandstone, chert, quartz and igneous rocks. In some parts of Nicosia the dolomite component is prevailing. In some instances soil is contaminated with salts. Small amounts of salt can be found everywhere. Salts may be found in bedrock as layers or pockets. They exist in the form of dry salty crust in temporary lakes. Water soluble salts pose a real threat to adobe material. Their content should be controlled and limited. The quantity of soluble salts was found to be varying between 0.3% and 3.0%. The recommended limit is 1.0%. The organic matter was estimated to constitute up to 3%. The largest quantity has been encountered in coastal area, where skeletons of diatoms, uni-cellular marine organisms form the opal, a chemically reactive element. It is of interest that when PH is less than 9, opal is becoming to be soluble. The alkalinity of samples was between 5 and 9. The neutrality is thought to be desirable and the recommended value of PH is 7. When PH is larger than 13.7 all silica minerals become considerably soluble. The quantities of some basic chemical elements are shown in Tab.3. Tab.3 Chemical properties Element Chlorine

Cl Nitrare NO3

Sulphate SO4

Carbonate CO3

Phosphate PO4

Quantity, ppm

2420-2850 55-66 2810-4680 2360-2050 64-88

DEMOLITION OF OLD HOUSES. There was an opportunity to be present during the demolition of tree adobe houses. This experience has made a lasting impact. In one occasion we had a chance to advise the sequence of initial steps of this procedure. Unfortunately, in two other cases the operators were uncooperative and wanted to finish the job quickly and resolutely. Just in these two cases buildings were more structurally sound and could provide more information. When our participation was active , the building was practically without roof, i.e. without lateral tying diaphragm. Timber lintels also have been in a near collapse state. This building was abandoned for 11 years and became ruined beyond any feasible repairing. Unprotected

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walls were full of holes and cracks of various origin. Corners were the most affected parts of the walls. Walls have been repeatedly hit by the bursts of large volume rainfalls accompanied by strong winds. The erosion by removal of particles was evident. Water remained trapped in the holes and cavities and deterioration was continuing even after the rain. Although walls were practically free standing and were kept together only by weak remaining mutual connections at the corners and intersections they still could master a considerable resistance. There was no immediate collapse or collapse in one blow. In spite of the fact that joints at intersections have been badly affected the traces of spatial response were visible. The 80 horse power caterpillar had a difficulty when the force was applied axially along the cross wall at its base. Noticeable resistance was produced by the external corners. The weakest resistance was observed when the force was applied at the middle of the spacing between two lateral walls. So the out- of- plane performance can be decisive and there is a definite need to keep the unsupported length to wall thickness ratio lower than 10. The absence of a roof diaphragm has weakened walls enormously. It was clearly visible while changing the level of load application along the wall height. Before demolition of the other two buildings their roofs had been slightly damaged but basically they were intact. This has made a whole difference. Also the lintels were in a good condition. As long as the anchorage of roof structure was not destroyed, there was the spatial response of walls. The rooms were approximately square in plan and the maximum unsupported length of walls was 4.2m. The sequence of destruction shows that there was interaction and interdependence between walls. Cell principle of adobe walls arrangement seems to be the most reasonable. CONCLUSIONS

1. Adobe is seismically very weak material but in spite of that it can jump above its apparent capacities. Adobe structures can mobilise a respectful seismic resistance while getting the best what adobe can physically provide for.

2. Success does not depend on a single factor. There is no magic silver bullet and no patent formula for ruling out the risk, but there is a long list of measures, which added up, can practically solve the problem. Practical recommendations based on recognized experience provide adobe buildings with a reasonable defence mechanism.

3. The following features have decidedly contributed to the seismic survive-ability of adobe houses in Cyprus:

a) Stable stone strip foundation on a firm ground. Low and uniform contact stresses at the foundation base. Avoidance of sites with a high ground water level.

b) Orthogonal cell-type of wall arrangement, combined with tapered buttresses and pilasters. Slenderness of walls along the height of less than 8 and of not more than 9 in longitudinal direction.

c) The cumulative length of openings smaller than 1/3 of the wall length. Opening width smaller than 1.2m. The width of pier between openings and the distance of an opening fro0m the corner larger than 1.2m. Reliable lintels.

d) Water protection by the plinth masonry with lime mortar, stone bottom part of walls, rain water drains around the building, roof overhanging from all sides, strong plastering and painting.

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e) Timber wall plates anchored in walls and forming the upper collar beams with corner diagonals over all walls. Ring beam above the openings. Timber framing with diagonal bracing. Activation and involvement in seismic resistance of all walls throughout a building. The spatial performance and redistribution of stresses. Compatibility of displacements in all connected elements.

f) Uniform distribution of gravitational loads along all walls. Transfer of uniform and restricted stresses to the foundations.

ACKNOWLEGEMENTS We would like to thank the Research Promotion Foundation of Cyprus for providing the funds for this research. Our gratitude goes to former students of the Frederick Institute of Technology Andreas Andreou and George Antoniou who started this research as their student project.

EFERENCES

1. Hadjiloizi D, Toumazis A, Chrysostomou C, Pilakoutas K and Kyriakides Ch. 2002. Vulnerability and Retrofitting of Existing Buildings in Cyprus. 12th European Conference on Earthquake Engineering. London, UK.

2. Construction and Housing Statistics. 2003. Statistical Service, Series II, Report No26. Republic of Cyprus, Nicosia, Cyprus.

3. Koratzitou G, 1997. Dwellings in Akama. Architects + Engineers. Association of Civil Engineers and Architects of Cyprus. No43. Nicosia, Cyprus.

4. Ioannidou M, 1998. Reference to the Traditional architecture of Cyprus. I want to build. Association of Civil Engineers and Architects of Cyprus. Nicosia, Cyprus.

5. Compressed Earth Blocks Standards. 1998. Centre for the Development of Industry. CDI and CRATerre-EAG / ODA Guides. Brussels, Belgium.

6. Heathcote K, 1995. Durability of earthwall buildings. Construction and Building Materials. Vol 9, No3, pp 185-189. UK.

7. Marcial Blondet, Gladys Villa Garsia M, Svelana Brzev, 2003. Earthquake-Resistant Construction of Adobe Buildings. EERI / IAEE.

8. Affordable Efficient Housing. http//www.terra-ram.com/Advantages.htm 9. Evaluating Compressed Earth Blocks (CEB) Walls and Structural Performance.

http//www.terra-ram.com/structural_performance.htm 10. Adobe Brick Testing. http//www.claymineadobe.com/htm/adobetest.htm

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