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CT 5124 Timber Structures 2Delft University of Technology, The Netherlands

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Investigation of earthquake resistance of traditional timber buildingsin Turkey

S.H.J. van Es1, A. van Ham2, T. Hoekstra3, E. van Vliet4 1Delft University of Technology, Faculty of Civil Engineering, The Netherlands, [email protected]

2Delft University of Technology, Faculty of Civil Engineering, The Netherlands, [email protected]

3Delft University of Technology, Faculty of Civil Engineering, The Netherlands,

[email protected]

4Delft University of Technology, Faculty of Civil Engineering, The Netherlands, [email protected]

ABSTRACT

In Turkey all traditional buildings are partially constructed of timber frames. Differentconstruction methods can be distinguished where the infill between the timber frames is either bymasonry or timber laths with or without clay. Buildings fully made of timber logs also occur.These traditional construction methods have been applied widely up to about 1950. Since thenthe traditional construction has mostly been replaced with modern reinforced concrete structureswhich, according to a wide range of researches, perform worse in earthquake situations than theirtraditional equivalent.

In this study the different failure modes of traditional Himiş buildings are analysed. These failuremodes include minor damages (e.g. damaged plasterwork) and damages to a building that maybe dangerous to the structure itself or to their direct surroundings, including any present persons.For certain failure modes improvements can be made with simple methods which were notavailable when this building method was originally developed. In this way the earthquakeresistance of Himiş construction could be further improved.

The aim of this paper is to analyse different failure modes of the traditional Himiş constructionand suggest improvements where possible. In this way, traditional buildings can more easily bereintroduced in the Turkish building industry. To complete this study a similar research onreinforced concrete structures, as they are applied in Turkey, would be required.

INTRODUCTION

The traditional building method in Turkey is timber-framed construction. In contrary most newbuildings are built in reinforced concrete framework with infill masonry. However, in recentearthquakes traditional buildings have proven to be in general more resilient to earthquakes loadsin comparison with modern, reinforced concrete buildings. This paper contains a literature studyto the different traditional construction methods used in Turkey and the causes of their beneficialbehaviour in earthquakes.Finally some possible improvements will be mentioned.

BACKGROUND

Log houses

The oldest type of houses that have been built in Turkey are log houses where the logs have abearing and a separating function. Logs are laid down horizontally and can transmit vertical




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forces through contact pressure between the logs. Logs are only connected at the ends sohorizontal forces caused by earthquakes cannot be restrained. A recent development in theconstruction of log houses is the anchoring of logs to each other which could possibly make thelog houses more resistant to earthquake loading (Dogangün, Tuluk, Livaoglu, Acar, 2005).

Figure 1: Log house in Turkey (Kücükerman, Güner, 1995)

Hatil constructionThis type of construction consists of an overall masonry structure laced with horizontal timberelements. In Hatil construction the main bearing of the structure is done by the masonry walls,while the timber laces aid the structure to resist horizontal loads such as earthquakes. TheTheodosian city walls of Istanbul have a similar lacing system. The beneficial effect of theselacing elements is proven by an event occurring in 1999. When an earthquake struck in 1999, therestored parts of the wall collapsed while the original parts remained intact. The restorers had notcorrectly reapplied the laces in the wall (Langenbach 2010).

Figure 2: Hatil construction in Turkey (Dogangün, Tuluk, Livaoglu, Acar, 2005)

Himiş construction Himiş buildings consist of a load bearing timber frame with masonry infill. The infill can bestraightforward, or made up of difficult patterns (mainly for esthetical reasons, Fig. 4). The

masonry infill is mostly one brick in width, which is approximately equal to the width of thetimber frame. The masonry can be, instead of standard bricks, made up of sundried bricks. Inthat case the construction method is known locally as Yeğdene (Dikmen 2010). Thisconstruction method of timber framing with (mostly) masonry infill is also used in many otherparts of the world, for example: colombage in France, fachwerk in Germany and half-timber inBritain (Langenbach 2010).




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Figure 3: Himiş construction in Turkey (Dogangün, Tuluk, Livaoglu, Acar, 2005)

Figure 4: Special patterns for masonry infill (Gulkan, Langenbach, 2004)

Dizeme constructionThe Dizeme construction type in general is the same as the Bağdadi typology. Wood is used asfilling material instead of masonry (as in the Himiş type). It is particularly used in regions thatabound in wood. Short rough timber elements called as Dizeme are used as infill. In thisconstruction type, the infill is mounted as lightly nailed studs or horizontal framing. The purposeof wood infill use is to avoid the common early shear failure and falling out of the frame whichoccur in the case of masonry infill (Oztank, 2008). The dimensions of the wooden parts used forthe infill indicate the difference with the Bağdadi structures. When the width of these woodenstrips changes between 5 and 20 cm, the structures are called Dizeme (Dogan, 2010).

Figure 5: Traditional timber framed house with wood infill “Dizeme” construction(Oztank, N.)




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Bağdadi construction When the infill consists of wooden strips have a width of 2 to 4 cm, the construction type iscalled Bağdadi. The voids between these strips are filled with lighter materials or with trunk shells. The interior walls are covered by lath and plaster work of wood. The resistance againstlateral forces is improved because the use of a lighter filling material. The ductility and damping

capacity is increased by use of nails and laths prevent infill downfall (Akan, 2004). This type of construction is more prone to rot and insect attack.

Figure 6: Bağdadi construction in Turkey (Oztank, N.)

Comparison with concrete constructionThe more recent buildings in Turkey are made in concrete. This modern type of building couldbe more resistant to earthquakes than the traditional timber ones. However because they are notdesigned and constructed properly it is proven that they fail more often than their woodencounterparts. It appears that the entire building delivery process; design, construction andinspection fails. The traditional timber buildings are built using a crafted technique, shaped bycenturies of trial and error. When reinforced concrete is used in the same non-engineered way of

workmanship, the essential aspects of earthquake design are not taken into account. This is themain reason for the bad performance of modern reinforced concrete dwellings compared with thetraditional timber building (Gulkan, Langenbach, 2004)

RESPONSE TO EARTHQUAKE OF HIMIŞ CONSTRUCTION

As already mentioned in the introduction of this paper, the traditional timber construction typesin Turkey are very efficient to withstand an earthquake load case, this in contrary to the moremodern techniques. However, the most vulnerable building type in case of an earthquake is theHimiş construction. The lateral accelerations acting in an earthquake cause large stresses due tothe high mass of the masonry infill.

Figure 7 : Collapse of masonry infill of Himiş building (Akan, 2004)




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Masonry structures in general show brittle shear failure during the event of an earthquake. InHimiş construction the masonry panels are separated by the timber framing, preventing thecollapse of the structure caused by local failure of the masonry. Another important failuremechanism is the collapse of the heavy walls due to weak connections between the perimeter and

orthogonal partition walls. Separation occurs and the thick perimeter walls collapse in the out of plane direction, this is called dislodgement of the masonry infill (Dikmen, 2010). The mass of the building is often even more increased by the application of heavy roofs. This is done forreasons of thermal insulation in Turkish warm climate (Akan, 2004).

This general failure of the masonry infill consists of the following symptoms (Dikmen, 2010)(with increasing severity):

1. Cracking and falling of plaster2. Crack of mortar3. Dislodgement of the masonry infill

The following failures will most likely occur after the first failures (cracking of plaster andmortar) have already occurred:

4. Loosening or failure of connections5. Large lateral displacements6. Failure of connection to foundation

Finally, some failures are not directly related to the construction method but can cause partial ortotal collapse:

7. Failure of chimneys8. Collapse of other buildings upon it

Important in the behaviour of Himiş construction exposed to an earthquake is that the infillmasonry walls respond to the stress of the earthquake by “working” along the joints between theinfill and the timber frame. The straining and sliding of the masonry and timbers dissipate asignificant amount of the energy of the earthquake (Akan, 2004).

Another beneficial factor is the type of connections that are used. In principle all timberconnections are nailed connections. According to local inhabitants this is not coincidence.Nailed connections are chosen on purpose for their ability to absorb and lower the movementscreated by earthquakes (Dikmen, 2010).

SOLUTIONS

Failures (1) and (2) are, while not desirable, unavoidable. First of all it would be verycomplicated to decouple the movement of the structure and the building finishes (in this case: theplasterwork). Secondly, removal of the plaster may be necessary after the earthquake anyway, toinspect and assess damage to the structure.

Dislodgement of the infill (3) can be a problem if the entire panel would fall out, thereby leavingthe timber frame „on its own‟. If this would occur during the early stages of the earthquak e thiscould cause problems with both structural integrity of the construction and possibly the safety of people inside or close to the building. The integrity could be affected because the infill can now

no longer perform its energy dissipated task, while falling pieces of masonry could fall onfleeing people close to the building. A regular placing of wooden laths could act as a safety net




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to prevent falling out of the masonry. This of course does have its influence on the aestheticappeal of the building. This adaption combines Himiş construction with other constructionmethods as Bağdadi or Dizeme. Perhaps this method could even lead to larger allowable spacingof the timber frame. If the aesthetical appeal of the building is very important it could also beconsidered to integrate this kind of safety nets in the masonry. This would seriously complicate

the building method, while in our opinion esthetics might not be that important.

Figure 8: Possible solution to the dislodgement problem

Failure and loosening of the connections (4) can only occur after heavily damaging the masonryinfill, as large deformations are needed. While Dikmen points this out as a failure mechanism, inthe same paper he argues that nailed connections are deliberately constructed weak to dissipatesufficient energy. In our opinion it would therefore not be wise to prevent this failure mode as itprevents total collapse. Failure of the connection to the foundation (6) may only occur in thesame way that other connections fail (i.e. large displacements accompanied with energydissipation), but total separating of elements should be avoided. Therefore, while not evident atfirst sight, foundation connections should also be capable of taking up a certain tensile load toprevent the building from lifting up. This is especially important when the building is

significantly lightened due to falling out of the masonry (3).

Figure 9: Examples of used foundation connections (Oztank, 2008)




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In Fig. 9 different foundation connections are shown. Most of those connections can be designedto take up tensile forces but are not able in their current layout. A possible adaption of aconnection (in this case connection „A‟ from Fig. 9) is shown in Fig. 10.

Figure 10: Possible adaptation of foundation connection

Large lateral displacements (5) can also only occur after the aforementioned failure mechanismsare already acting. While it may not be desirable, the fact that the large lateral displacementsoccur also ensures that the building is not acting “too stiff”.

Unreinforced masonry chimneys are particularly susceptible to eartquake damage. Failure of thechimneys (7) can cause damage to the roof and wall of the structure below. Also, damagedchimneys may be dangerous in aftershocks following the intitial earthquake. According to theCWC, the Canadian Wood Council, damage can be prevented in future earthquakes by bracingchimneys or using chimneys from lighter materials. (CWC, 2004) However, ABAG, the regionalplanning and services agency for San Francisco Bay Area, advises the following: „Retrofittingmasonry chimneys with bracing or strapping is not an effective safety measure because manybraced or strapped masonry chimneys typically will still fall when exposed to violent shaking.‟(ABAG, 2004). While these advices are not intended for traditional Turkish masonry chimneys,they will behave the same.

Figure 11: A collapsed chimney of traditional building during the 2003 Buldan earthquake (Kaplan, 2003)




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Therefore the best results can be achieved by using lighter materials. Constructing chimneysfrom lighter material can be done with metal-stud systems for example. Also insulated thinplated steel chimneys can be used. These can be covered with wood for instance. (Fig. 12)

Figure 12: Example of lightweight structure for chimney (GG, 2011)

Collapse of other buildings on the structure (8) can of course not be prevented with structural

adaptions to the considered structure. This problem can be prevented by making sure allbuildings are sufficiently safe, but the total assessment of all buildings lies out of the scope of this paper. In general it can be stated that this kind of damage cannot be prevented, provided thatthe collapsing building is heavy enough to damage the considered (traditional) structure.

DISCUSSION / CONCLUSION

While the traditional construction methods used in Turkey generally behave good in earthquakesituations there are some points which could be improved. Some improvements can easily beexecuted within the knowledge of traditional building. The „safety net‟ for the masonry (Fig. 8)closely resembles the Dizeme and Bağdadi construction methods. Improvement of the chimneys

and foundation structures could require some more advanced technology in comparison with theoriginal building method. However, the required materials and construction are relativelycommon in today‟s construction.

Therefore, by implementing simple adjustments the traditional construction can be furtherimproved making them more durable in earthquake regions than they already were. Thereforethey can be very competitive with modern reinforced concrete structures, especially in low risebuildings. To make a good comparison between traditional timber and modern concretestructures a similar research to the weaknesses of reinforced concrete structures is necessary.

REFERENCES

ABAG, (2004) Website of the Association of Bay Area Governments, the regional planning andservices agency for the nine-county San Francisco Bay Area. Consulted: 15-3-2010:http://www.abag.ca.gov/bayarea/eqmaps/fixit/chimneys.html

Akan, Asli er., (2004) Some observations on the seismic behaviour of traditional timberstructures in Turkey. http://cires.colorado.edu/~bilham/Duzce.html

CWC: Canadian Wood Council. (2004) “Wood-frame construction: meeting the challenges of earthquakes”, Building Performance Series No. 5




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Dikmen, N., (2010) An investigation on traditional timber-framed buildings in Çankiri provinceof Turkey. http://fbe.trakya.edu.tr/tujs

Dogan, M. (2010) Seismic analysis of traditional buildings: Bağdadi and Himiş. In: Anadolu

University journal of science and technology, ed. Arastirma Makalesi

Dogangün, A., Tuluk, O., Livaoglu, R., Acar, R., (2005) Traditional wooden buildings and theirdamages during earthquakes in Turkey. http://www.sciencedirect.com

GG, (2011) Figure found on website which is a report of people building their own house.Consulted: 15-03-2011: http://goinggreenoffthegrid.wordpress.com/page/5/

Gülkan, P., Langenbach, R., (2004) The earthquake resistance of traditional timber and masonrydwellings in Turkey. 13

thWorld Conference on Earthquake Engineering

Kaplan H, Inel M, Senel M, Toprak S, Kayhan, A, Özsoy I., Yazar E, Yılmaz, S. (2003) “A

preliminary engineering report on the Buldan/Denizli Earthquake of 23–26 July 2003:”,Pamukkale University, Denizli Turkey

Kücükerman, Ö., Güner, S., (1995) Turkish houses in Anatolian heritage. Book for ministry of Turkish culture.

Langenbach, R., (2010) Earthquake Resistant Traditional Construction is Not an Oxymoron.http://www.conservationtech.com

Oztank, Nimet, (2008) Traditional Timber Turkish Houses and Structural Details. World

Conference on Timber Engineering (WCTE) 2008, Miyazaki, Japan.

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