seismic behaviour of vernacular masonry buildings during 2010 and 2011 earthquakes in turkey

9th International Masonry Conference 2014 in Guimarães

9th International Masonry Conference, Guimarães 2014 1

Seismic Behaviour of Vernacular Masonry Buildings During 2010 and 2011 Earthquakes in Turkey

KURUSCU, ALI OSMAN1; GÜNEY, DENIZ2; ARUN, GÖRÜN3

ABSTRACT: Unreinforced masonry has traditionally been the primary construction method of rural

areas in Turkey till 1960s. Though reinforced concrete was introduced late 19th century, the rural houses using brick, adobe, stone and concrete blocks and unskilled labour continued to be constructed. Recent earthquakes showed that the performance of traditional unreinforced construction were generally poor. The seismic performance of masonry structures depend on the performance of their walls and the walls play major role on the seismic response of the whole structure for they are the basic resisting elements to horizontal seismic actions. The material used in the wall construction, and configuration of the wall material affects the vulnerability severity level of the building. Site investigations and researches after the earthquakes add to the knowledge on the behavior of masonry buildings and traditional construction methods.

In this paper, the correlation between damage level and physical properties of masonry walls were studied according to data obtained from March 2010 in Elazığ and October 2011 and November 2011 in Van earthquakes. In the region, there are many houses and public buildings constructed with stone, brick, adobe and concrete blocks. Some of them were heavily affected where some had slight damages. The observation of the buildings and assessment of the failures were made by eye inspection and collecting data by photos. The overall data obtained from site has been evaluated according to the parameters playing important role on the performance of the buildings.

Keywords: Masonry walls, vulnerability, seismic performance, damage, earthquake

NOTATION Hw height of wall; Lw length of wall; tw wall thickness;

1 INTRODUCTION

Elazığ and Van earthquakes were reported to be on the left lateral strike slip of the East Anatolian Fault (EAF) which is shown to be consistent with the distribution of the aftershocks. The East Anatolian Fault System is one of the most active fault systems in Turkey. Because of the northward movement of Arabian and African plates, the Anatolian Block has a westward extrusion.

Earthquake Department at Disaster and Emergency Management Presidency (DEMP), reported a moderate earthquake of magnitude of 6.0 on Richter scale in the high seismicity region on Eastern

1) Dr, Yildiz Technical University, Department of Architecture, [email protected] 2) Associate Prof. Dr, Yildiz Technical University, Department of Architecture, [email protected] 3) Prof. Dr, Yildiz Technical University, Department of Architecture, [email protected]

Kuruscu, A.O.; Güney, D.; Arun, G.


Anatolian Fault System, in the Karakocan district of Elazığ on March 8th of 2010 at 04:32am (1:32 GMT). Its epicentral coordinates as 38.7665N, 40.0712E were located in Kovancılar town of Elazığ city and with shoal hypocenter depth of about 5 km (Figure 1).

The impact of the earthquake was catastrophic especially in Okcular, Yukari Kanatli, Yukari Demirci, Gocmezler, and Kayalik Village, which are located within approximately 100 km from the Elazig city center and approximately 30 km from Elazig`s Kovancilar Town. The nearest station to the epicentre was Palu station having an epicentral distance of 12 km. The epicentral distances of the buildings with heavy damages were ranging from 4.8 km to 10.0 km. The earthquake was also mildly felt in Bingol, Tunceli, Diyarbakir, Erzincan, and Batman.

The duration of the earthquake is another important factor affecting the level of the structural damages during the strong motion. According to the Palu station records, the earthquake lasted for 15.52 sec in the NS direction [1]. Due to the earthquake, 42 people were killed, 137 people were injured and 14 113 buildings were damaged [2, 3].

In 23 October 2011, Van city in Eastern Turkey was hit by a large an earthquake at 13:41 (10:41 GMT), on Sunday afternoon of magnitude 7.2. This earthquake had a shoal hypocenter depth of about 10 km. The Van earthquake, where epicenter was about 16 km north of Van city at Tabanlı village, between Ercis Town and Van city, devastated the area (Figure 1). Ercis Town, 90km away from Van city, was mainly affected by earthquake. Effective duration of the earthquake according to Muradiye station records, was 20s, according to Bitlis station records was 18s. During this earthquake 644 people died, 2608 people injured and 2307 buildings totally collapsed.

In 9 November 2011, the second Van-Edremit centered earthquake occurred at 21.23 (18.23 GMT) of magnitude 5.6. The epicenter of the earthquake was near the Edremit town south of Van (Figure 1). Effective duration of the earthquake according to Van station records was 18s, according to Van-Edremit station records was 23s. During the second earthquake 40 people died. The buildings previously having slight or medium damage in Van city center now totally collapsed or were heavily damaged [4, 5].

Figure 1. March 8, 2010 Elazığ, October 23, 2011 and November 9, 2011 and Van Earthquakes

https://www.researchgate.net/publication/49611859_2010_Karakocan-Elazig_earthquake_and_masonry_structures?el=1_x_8&enrichId=rgreq-01263423-f1da-467a-9638-9364c34d3861&enrichSource=Y292ZXJQYWdlOzI2NzQ0MTQ2NjtBUzoxNTcyMDQ1MTQ2MTUyOTZAMTQxNDQ5MTg4NTExOA==

https://www.researchgate.net/publication/258685950_Van_earthquakes_23_October_2011_and_9_November_2011_and_performance_of_masonry_and_adobe_structures?el=1_x_8&enrichId=rgreq-01263423-f1da-467a-9638-9364c34d3861&enrichSource=Y292ZXJQYWdlOzI2NzQ0MTQ2NjtBUzoxNTcyMDQ1MTQ2MTUyOTZAMTQxNDQ5MTg4NTExOA==



2 SEISMICITY OF THE REGION

Turkey is one of the most seismically active regions in the world and lies within the Mediterranean part of Alpine-Himalayan belt that extends from Azor islands to Southeast Asia. The compressional motion between Europe and Africa produced the Alpine orogeny, whereas the Himalayan orogeny has resulted from the India-Asia collision. African, Eurasian, and Arabian plates are three major plates surround Turkey, and two generally acknowledged minor plates are Aegean and Anatolian [6].

The North Anatolian Fault Zone (NAFZ), Aegean Graben System (AGS), East Anatolian Fault (EAFZ) and Southeast Anatolian Thrust (SAT) are the most important faults in Turkey and also they are quite active faults (Figure 2). The North Anatolian Fault Zone extends East-West direction at the Northern part of Turkey and accepted as a dextral strike slip fault of the relative motions between the Anatolian block and Eurasian plate. This region is at the intersection of the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault Zone (EAFZ). One important segment is the Yedisu segment and it has not slipped since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly [7].

The focal depths of the earthquakes in Turkey are shallow except for the ones in the Mediterranean Sea. So, when the magnitude of earthquake is larger than, about 5.5, usually considerable loss and building damage result.

The Ministry of Public Works and Settlement published Earthquake Hazard Zoning Map of Turkey in 1996, based on maximum acceleration value that has calculated with probabilistic method. It assumes that a normal construction, which has 50 years of economic life, may not be exposed larger than these expected maximum acceleration values with 90 percent probability. Here, the whole country divided into the 5 different hazard zones where zone 1 is the severest. Accordingly, Elazığ is situated in 2nd, Van is situated in 1st and 2nd earthquake zones.

Figure 2. North and east Anatolian Faults at Anatollia [8]



Due to its orogenic system, geology, topography and climate, Turkey is exposed to various natural disasters. There have been 74 major destructive earthquakes during the period of 1903 - 2013, which collectively have killed more than 150,000 people and destroyed about 450,000 buildings.

In the area of Lake Van and further east, tectonics is dominated by the Bitlis Suture Zone (in eastern Turkey) and Zagros fold and thrust belt (toward Iran). The October 23, 2011 earthquake occurred in a broad region of convergence beyond the eastern extent of Anatolian strike-slip tectonics. The focal mechanism of today's earthquake is consistent with oblique-thrust faulting similar to mapped faults in the region. Given its tectonic history, a major earthquake in Anatolia is by no means an unusual event and other major earthquake events are to be expected in the region as the central block continues to be squeezed westwards and lateral movement occur along the fault complexes of both North and east Anatolian Faults (Figure 2).

In the region, Major earthquakes occurred in the year 1111 causing major damage and having a magnitude around 6.5-7. In the year 1646 or 1648, Van was again struck by magnitude of 6.7 quake killing around 2000 people. In 1881, magnitude of 6.3 earthquakes near Van killed 95 people. Major earthquakes in the region are shown in Table 1.

Table 1. Number of Damaged buildings and Died People at the latest Earthquakes at the region [9]

Year Earthquake Location Magnitude (Ms)

No. of Heavily damaged buildings

Died

2011 Van EQ 7.2 2307 644

2010 Elazığ EQ 6.0 14113 42

2003 Bingöl EQ 6.4 1602 177

1992 Erzincan EQ 6.8 8057 653

1983 Erzurum-Kars EQ 7.1 3240 1400

1976 Çaldıran-Muradiye EQ 7.5 9232 3840

1971 Bingöl EQ 6.8 9111 878

1967 Plümür- Tunceli EQ 5.9 1282 97

1966 Varto- Muş EQ 6.9 20007 2396

1952 Hasankale- Erzurum EQ 5.8 701 41

1949 Karlıova- Bingöl EQ 6.7 3500 450

1946 Varto- Hınıs EQ 5.9 3000 839

1943 Çorum EQ 7.2 2554 618

1941 Erciş- Van EQ 5.9 600 430

1939 Erzincan EQ 7.9 116720 32968

3 SEISMIC BEHAVIOR OF MASONRY BUILDINGS

Although seismic performance of unreinforced masonry structures is considered poor, many masonry buildings have survived major and moderate earthquakes and were resistant enough against exerted forces and had good seismic behavior. The researches and studies on seismic performance of masonry structures indicate that walls are the most important structural elements affecting vulnerability severity. If these walls remain undamaged or slightly damaged, life losses can be minimized.

Typical modes of masonry building failure subjected to earthquake loads are in-plane shear cracking, out-of-plane overturning of the walls, separation of walls at the corners. Separation of floors/roofs from the walls is result of the other types of failures, and in most cases, leads to collapse. Cracking is almost certain to occur during major seismic ground motions as the stresses in the wall exceed the tensile capacity of the material.



As the cracks propagate, during earthquake, friction across the cracks limits the in-plane wall displacements. However, in walls without adequate horizontal constraints, crack size increases during reversing cycles of ground motion and the wall frequency decreases (Figure 3a). When the cracks intersect each other, each wall becomes an assemblage of irregularly shaped wall segments as the independent cracked blocks. In-plane wall motions and gravity loads may lead to progressive damage as the broken sections of the wall slide out (Figure 3b).

The out-of-plane motion of walls often results in horizontal cracking at the bottom of the wall. The vertical location of these horizontal cracks depends upon the loads induced by the weight of the wall or other tributary loads. Vertical or diagonal cracks at the wall intersections may be due to the out-of-plane motion of the walls that cause excessive bending and tension reactions at these locations. Non-load bearing walls that don’t carry floor/roof joists often are the first to collapse when there is no restraint provided at the roof or floor connections. The bearing walls carrying the floor/roof joists may also collapse, and the effect of their collapse may be catastrophic. Inadequate connection between roof or floor beams and the wall top can cause a load bearing wall to progressively move out from under the beams. The primary factors affecting the out-of-plane stability of a masonry wall during the earthquake are its absolute thickness, its slenderness ratio (height/thickness ratio), and the degree of restraints that may limit the deflection at the top and added gravity loads from roof or floor framing. The restraints at the top of the walls provide continuity throughout the loading cycles and some restoring force near the extremes of the block motion.

Chapter 5 of “2007 Specification for Buildings to be built in Earthquake Zones”, published by the Ministry of Public Works and Settlement Government of Republic of Turkey is on Earthquake Resistant Design requirements for Masonry Buildings [10]. In this chapter, maximum number of stories permitted for the masonry buildings is 2 floors in 1st seismic zone, 3 floors in 2nd and 3rd seismic zones. The minimum wall thicknesses of the load-bearing walls, on ground floor has to be 50cm stone, 30 cm brick or 60 cm adobe, on first floor 20cm brick and 40cm adobe. Stone wall is not permitted on 1st floor. The unsupported length of a load bearing Wall between the connecting wall axes in the perpendicular direction shall not exceed 5.5 m. in the first seismic zone and 7.5 m in other seismic zones. The unsupported length of an adobe wall shall not exceed 4.5m. The specification also has restrictions about the size of the door and window openings and their distance to the corners and between the openings.

According to the previous investigations on number of adobe and brick walls that have withstood repeated strong motion EQs, vertical slenderness ratio less than 5,( Hw/tw <5) for adobe and less than 10 ( Hw/tw <10)for brick, ratio between the unsupported length of the wall to wall thickness less than 9 ( Lw/tw <9) for adobe and less than18 ( Lw/tw <18) for brick behaved well during EQs [11].

a) b)

Figure 3. Inadequete horizontal constraints of the walls

Van 2011 Elazığ 2010



4 CONSTRUCTION SYSTEMS AT THE REGION

Unreinforced masonry has traditionally been the primary construction method of rural areas in Turkey till 1960s. Though reinforced concrete was introduced late 19th century, the rural houses using local material and unskilled labour continued to be constructed. Buildings in the cities are generally of RC frame structural systems with masonry partition walls.

Until 2011, National Construction Control and Supervising Law was not a mandatory regulation in the region [12]. Therefore the buildings in the region didn’t have any engineering assistance. Most of the houses used different construction materials and systems in the same building (Figure 4). The use of different building materials in the same load bearing element caused irregularities in the structure.

Traditional masonry buildings in the villages of Van city are mostly of adobe and concrete blocks, and rarely of stone with cement or mud mortar binders. Adobe and stone buildings had heavy earthen roofs or metal roofs placed on one directional irregular wooden beams. Some buildings with concrete blocks had vertical and horizontal RC tie elements and RC floors.

5 EARTHQUAKE DAMAGES IN THE REGION

The damages during both earthquakes are due to unskilled labor and uncontrolled construction. Use of heavy earth roofs, use of earth mortar as binder, improper connection of perpendicular walls to each other were main causes of the failures.

Use of heavy earth roofs in the region significantly increases earthquake forces. Besides, degradation of soil over time, snow and rain water opening hollows and filling these hollows to level the soil every year increased the thickness of the roof, so that the load on the roof has increased.

The use of earth mortar as binder significantly decreased the shear resisting capacity of structural walls due to harsh environmental conditions. The earth mortar with low compressive strength had reduced adherence between the units. The frost and thaw events during very cold winter in the region caused the earth mortar to disintegrate. Besides, the walls having large stones on the outer surface and small stones on the inside behaved in very brittle manner.

Especially on three leafed walls, not connecting the two outer leafs with the intersecting walls made the unsupported length of the outer leaf more than inner leaf. As a result, the out-of-plane failure risk was considerably increased for the effective thickness of the wall was decreased.

Figure 4. Use of different construction materials and systems

Elazığ 2010 Elazığ 2010



Performance of unreinforced masonry construction during numerous earthquakes in Turkey has generally been poor. The studies on seismic performance of masonry structures indicate that walls are the most important structural elements affecting vulnerability severity level. Below, the failures at the region are compiled according to the failure modes.

5.1. Out-of-Plane failures of masonry wall

Lateral loads perpendicular to the Wall plane cause flexural cracks. Load bearing walls that carry floor/roof beams resist the lateral loads better than non-load bearing walls for the beams tie the two parallel walls and floor/roof loads are tributary. The slenderness ratio and connection of floor/roof to the Wall is effective.

Out-of-plane wall separation failures are seen mostly on non-load bearing walls that don’t carry floor/roof beams (Figure 5). The out-of-plane lateral loads cause bending on the Wall. The horizontal cracks at the lower level and out-of-plane displacement occurred in these walls are due to the wall not having any vertical support, not tied to the floor/roof joists and not having proper connection to the adjacent perpendicular walls. As the EQ motions increased, these walls are demolished.

On long walls that have good connection with the adjacent walls vertical cracks occurred in the middle part. On some long walls, the out-of-plane loads caused horizontal cracks at the bottom, diagonal and vertical cracks close to the intersecting wall. As ground motions increased, such walls were demolished.

According to the thickness and length of the wall and the way wall’s connection to the floor/roof or adjacent walls, so the form of the flexural cracks during lateral loads perpendicular to the wall may differ. In general, the horizontal cracks were at the middle of and close to the bottom on slender, high and long walls (Figure 6). Such cracks are also seen on free standing yard walls.

Figure 5. Out-of-Plane wall separation




5.2. In-plane failures of masonry wall

Lateral loads parallel to the Wall plane cause diagonal shear cracks for masonry material has very low tensile strength. Such cracks also develop in areas of high stress concentrations as the corners of the door and window openings. On the walls with high slenderness ratio, at the top and bottom of the masonry between the openings, horizontal cracks may be observed (Figure 7).

5.3. Failures at the Corners

On intersecting walls, the sway of the Wall that receives perpendicular lateral loads and rigid behavior of the other Wall that receives lateral loads parallel to its plane and the weak connection between the walls caused vertical cracks and the separation of the walls (Figure 8). Such cracks are mostly on the slender walls.

Figure 6. Out-of Plane flexural cracks

Figure 7. In-Plane failures of masonry wall

Van 2011




5.4. Floor/roof failure

The collapse of floors/roofs from the walls is result of the other types of failures. Inadequate form and connection of one-directional roof or floor beams to the wall at the top can cause beams to move out as the wall underneath moves (Figure 9). Use of heavy roofs receives more earthquake loads.

6 CONCLUSIONS

Elazığ earthquake on March 8th of 2010 with magnitude of 6.0 on Richter scale and Van earthquakes on October 23rd of 2011 with magnitude of 7.2 and November 9th of 2011 with magnitude of 5.6 were reported to be on the left lateral strike slip East Anatolian Fault (EAF). These shallow earthquakes caused loss of many lives and properties.

Unreinforced masonry has been the primary construction method of rural areas in this region. These were built with poor material and labor, without following any construction principles and

Figure 8. Failures at the corners

Figure 9. The collapse of floors/roofs

Van 2011 Van 2011

Elazığ 2010 Elazığ 2010

Van 2011



regulations. However some masonry buildings have survived these earthquakes, while many have suffered considerable damage.

Seismic deficiencies of masonry construction are caused by the heavy weight of the structures, their low strength, and brittle behavior. The primary factors affecting collapse of a masonry wall are its absolute thickness, its slenderness ratio, and the degree of restraint at the top. Like in other rural areas, masonry buildings and walls of this area lacks connection between the walls and roof/floor and adjacent perpendicular walls which in turn caused damage in most buildings during earthquake. Not having appropriate restraints as horizontal tie beams made it impossible to maintain structural integrity and caused out-of-plane failure of the walls. The use of heavy soil-roofs increased the adverse effects of earthquake and use of different building materials and systems in the same building caused irregularities in the structure.

The collapse resistance of a masonry building can be greatly improved by construction details that continue to hold the elements of the building together and that provide structural continuity after cracks have fully developed. Adequate connection between the walls and floor/roof system is essential to prevent overturning. The restraints at the tops of walls can improve the out-of-plane rocking stability of a wall and provide significant additional redundancy to the structural system.

If appropriately constructed, masonry buildings do not necessarily behave in a non-ductile, brittle manner, even though they are made from a low-strength, non-ductile, brittle material.

REFERENCES [1] Cetinkaya N.: 2010 Karakocan-Elazig earthquake and masonry structures, Nat. Hazards Earth

Syst. Sci., 11, 11–16, 2011.

[2] Kalafat D., Zülfikar D., Vuran E., Kamer Y.: 08 Mart 2010 Başyurt-Karakoçan (Elazığ) Depremi Raporu, Boğaziçi Üniversitesi Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü, March 2010.

[3] Baykal B., Miyake H., Yokoi T.: Source Model of the 2010 Elazığ Kovancılar Earthquake (Mw=6.1) for Broadband Ground Motion Simulation, 15WCEE, Lisboa, 2012

[4] Disaster and Emergency Management Directorate (AFAD) Report,: Press Bulletin on the 23 Oct. and 9 Nov. 2011 Van eq. (in Turkish), 24 November 2011.

[5] Guney D.: Van earthquakes (23 October 2011 and 9 November 2011) and performance of masonry and adobe structures, Nat. Hazards Earth Syst. Sci., 12, 3337-3342, 2012

[6] Bayrak Y., Öztürk S., Koravos G. Ch., Leventakis G. A., and Tsapanos T. M.: Seismicity assessment for the different regions in and around Turkey based on instrumental data: Gumbel first asymptotic distribution and Gutenberg-Richter cumulative frequency law, Nat. Hazards Earth Syst. Sci., 8, 109–122, 2008.

[7] Ozener H., Arpat E., Ergintav S., Dogru A., Cakmak R., B. Turgut, U. Dogan,: Kinematics of the eastern part of the North Anatolian Fault Zone, Journal of Geodynamics, 49, 141–150, 2010.

[8] http://en.wikipedia.org/wiki/File:Anatolian_Plate.png, January, 2014.

[9] http://www.koeri.boun.edu.tr/sismo/Depremler/tLarge0.htm, January, 2014.

[10] Ministry of Public Works and Settlement Government of Republic of Turkey is on Earthquake Resistant Design requirements for Masonry Buildings,: 2011, Ankara, Turkey

[11] Salekzamankhani, J., Arun G. (2010),: ”Seismic Behavior of Adobe Masonry Walls in 2006 Earthquake Silakhor, Iran”, proceedings of 8th International Masonry Conference, 4-7 July 2010, Dresden, Germany

[12] Taskin, B., Sezen, A., Tugsal, Ü.M, Ayfer Erken, A.: (2013) “The aftermath of 2011 Van earthquakes: evaluation of strong motion, geotechnical and structural issues”, Bull Earthquake Eng. (2013) 11:285–312, DOI 10.1007/s10518-012-9356-9

seismic behaviour of vernacular masonry buildings during 2010 and 2011 earthquakes in turkey

Documents