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PERFORMANCE OF NON-STRUCTURAL COMPONETS IN THE 2012 VARZAGHAN-AHAR EARTHQUAKE

Tariq MAHDI1

ABSTRACT

On August 21st, 2012 two earthquakes struck the northern part of East Azerbaijan Province, Iran with a magnitude 6.2 and 6.0. The earthquake affected three medium-size city centers; Varzaghan, Ahar and Heris. Most urban buildings in the stricken area had suffered minor or moderate structural damages combined with major non-structural ones. Many of the essential facilities (e.g. hospitals) in the stricken areas were damaged and were not operable after the earthquake.

The major failure modes of non-structural elements involved, cracking and collapse of infill walls, separation of facades from back walls, and failure of suspended ceilings. Damages to exterior architectural elements, parapets, partitions and internal walls, stair wells, building contents and other non-structural components were also observed in these events. Generally, the poor performance of non-structural components has been caused by improper construction and installation practices.

INTRODUCTION

East Azerbaijan Province is a high-risk seismic zone to the northwest of Iran and has frequently experienced major earthquakes for centuries, with the City of Tabriz having a long history of destruction, as a result of these natural disasters (Zaré et al., 2012). On August 21st, 2012 two earthquakes struck the northern part of this region with a magnitude 6.2 and 6.0. The first event had a maximum PGA of about 478 cm/s/s. Only 11 minutes after the first event, the second earthquake occurred. The maximum PGA for the second event was recorded of about 534 cm/s/s (ISMN, 2012). In this later event, long-period velocity pulse components were clearly identified with a maximum speed beyond 30 cm/s recorded (ISMN, 2012). The main impacts were felt around the towns of Varzaghan, Ahar and Heris. In these two events, it has been reported that more than 330 people lost their life. The significant amount of death toll was the results of the failure of adobe and non reinforced masonry buildings in rural areas (Miyajima et al., 2012). Furthermore, 4500 had been injured and 72,000 directly affected due to complete or partiall destruction of their properties (Fallahi, 2013). According to the IFRC report, 399 villages and five cities had been affected. The total number of the houses with 60% or more destruction was 11,908 (IFRC, 2012). In a later report published by the Housing Foundation, it had been stated that around 18400 rural residential units had sustained 30% or more destruction, while only 9500 of those units sustained more than 60% or more destruction. Furthermore, from the total of 25700 urban residential units that affected by these events, around 4750 planned to be reconstructed (Housing Foundation, 2012).

1 Assistant Professor, BHRC, Tehran, mahdi@bhrc.ac.ir

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GENERAL DAMAGE OBSERVATIONS

Buildings in the stricken area experienced different levels of damages. In rural areas, most of the collapsed and damaged houses were adobe and unreinforced masonry buildings, as shown in Fig. 1. The main failure modes of these types of building are failure of heavy roofs, out of plane failure of walls, and separation of cross walls from each other's. In general, performance of the brick masonry buildings was noticeably better than of adobe ones (EERI, 2012). Furthermore, confined masonry buildings that were constructed according to The Iranian Seismic Code - IS 2800 had sustained little or no damages. Most urban buildings in the stricken area had suffered minor or moderate structural damages combined with major non-structural ones. In some steel structures and due to the absence of lateral systems, some damages had occurred.

The two main hospitals in the stricken area; in Heris and Ahar, were highly damaged and were not operable after the earthquakes. Both hospitals were two-storey concrete buildings. The Heris hospital building sustained different degrees of structural damages, while Ahar's hospital sustained no such damages. Furthermore, the two earthquakes did great damage to the non-structural parts and the facilities (IIEES, 2012).

In these two events, it had been reported that some of the observed damages were directly related to site and/or topography effects. According to the observations made by Zaré, buildings founded either on soft sediments or on hills had suffered more damages than similar buildings elsewhere (Zaré et al., 2012). Examples of these effects are shown in Fig.2.

Figure 1. Collapse of buildings in rural areas. A complete destruction of adobe houses (left), and failure due to

the absence of confinements in unreinforced masonry buildings (right)

Figure 2. An example of buildings found on or near hills. Failures of adobe buildings located in steep hillsides

(left), Deep cracks occurred in Ershad Building-Ahar, located on hillock (right)

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INFILL WALLS

Different types of masonry units were used in the earthquake stricken area. Masonry units; like burnt clay and sand-lime bricks, produce heavy-weight infill walls that usually attract high lateral forces. On the other hand, using lighter masonry infill walls similar to the perforated clay blocks would have adversely results. In the present events, many of these infill walls had collapsed due to weak bond between units, as shown in Fig. 3. This was resulted due to the small contact area and the poor quality of mortar.

The damage observed in moment resisting frames with URM infill walls varied from small cracking to severe damage and collapse. In most cases, and due to the lack of adequate restraints in the direction perpendicular to the infill plane, infill masonry walls were damaged. Furthermore, some of the columns experienced shear cracks and diagonal cracks observed in some of the beams next to the column joint. In most cases, the absence of suitable frame-infill connection details and the lack of special design to protect columns against shear failures; were the main reasons for such phenomena. A sample of a concrete bending frame with URM infill walls is shown in Fig. 3. However, in some other cases and by breaking the large masonry infill wall panels into smaller ones using steel members in vertical and horizontal directions, less damage had occurred, as shown in Fig. 4.

Figure 3. Collapse of infill walls with perforated clay blocks (upper left and right). Typical diagonal cracks in infill walls (lower left), and shear failure of a column due to the presence of infill wall (lower right).

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Figure 4. Typical buildings with confined infill walls

The practice of infill wall separation from the frame at the interface had been also used, as was the case of Heris hospital building. The 10 cm thick non-structural walls were separated from both sides and attached to upper and floor beams. Furthermore, double angles were used at both edges of the wall, as shown in Fig. 5. To prevent out-of-plane failures, additional mid-span double angles were used for long span walls. Despite these measures, that had been designated to provide stability to the walls and insured pure bending behavior of the frames, many cracks had appeared near the frame-wall regions leading to spall of plaster there. This phenomenon was observed near the mid-span double angles as well, as shown in Fig. 5. The absence of gaps or the use of small gaps between walls and frames were the main reason for such a failure. Furthermore, the use of heavy masonry units and thick plaster coatings did great damage to the infill walls (Consulting Engineers of Fadak, 2013).

Figure 5. Double angles at the edge of infill wall (left) and spall of plaster at the middle of infill wall showing the

mid-span angles used there (right) (Consulting Engineers of Fadak, 2013)

EXTERIOR ARCHITECTURAL ELEMENTS

Exterior wall systems must securly protect buildings from wind and weather, noise and fire. However, they need to be anchored directly to the supporting structures. Examples of the losses occurred to curtain walls due to the lack of connections between these walls and the structural components are shown in Fig. 6. Furthermore, due to the big drifts, most of these walls were affected by the quakes.

In the earthquake stricken region, a special type of exterior walls in the form of U-shaped perimeter walls were used. Those walls were constructed outside the frames but their wings were

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either connected to the columns or infill walls. Examples of these walls are shown in Fig.6. Usually the potential vulnerabilities of these walls are very high due to story drifts and lack of improper connections with the main structure. In other cases, many deep vertical cracks had been observed in these walls, especially in the nearby of their corners.

Despite the existence of general provisions for non-structural walls in the IS 2800, no official connection details were available for exterior walls. Providing such details was largerly ignored by the engineering community, as well.

Figure 6. Typical buildings with exterior walls. Thick masonry curtain walls not connected to the columns (left).

Collapse of the U-shaped exterior wall (middle), and cracks in the U-shaped wall (right)

FACADE

Two types of façades were observed in the earthquake stricken region. In both types, the façade units were placed after construction of the back wall. Thus, the most important item in such façade systems is their connection details.

The first type of façade was based on traditional methods of construction. For such methods, IS 2800 provide some provisions in this respect. In these provisions, the back wall needs to be attached to façade bricks by using some bars. Then, the free ends of the bars need to be placed inside the mortar beds of façade bricks. Similarly, the back wall need to be attached to façade stones using clamps or other suitable type of attachments (BHRC, 2003). According to the observations made by the author during his visits to the earthquake stricken areas, the above mentioned standard provisions were mostly not observed. Consequently, buildings in the area had sustained different types of damage, as shown in Figure 7. Furthermore, it had been noticed that little or no mortar had been used between façade units and back walls, an issue led to the collapse of some of the façade bricks. This was particularly the case when the façade was subjected to forces normal to its plane.

In the second type of facade, sheets with a thickness of 2 to 3 cm of plastofoam as insulation material had been used between walls and facades. Although the number of the bars used in this process was quite sufficient and the end of these bars were mostly well embedded into facade, these bars had been separated from the main structure due to the absence of complementary horizontal elements in the walls and the lack of good fixing details, as shown in Figure 7. It can be concluded that this type of façades was neither able to withstand normal forces nor in-plane forces. It worked as a thin wall in the normal direction while its connections made little resistance against in-plane forces.

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Figure 7. Failure of façade bricks (upper left). Failure of façade stones (upper right). Improper fixing details of façade, insulating layer, and the back wall (lower left and right)

PARAPETS

In an earthquake, parapets are weak against all those forces perpendicular to their plane. In some circumstances, the development of cracks in these walls makes them more vulnerable to failure. The lack of lateral supports for such a parapet caused its partial failure. On the other hand, by providing some kind of restraint by providing vertical and horizontal steel members around the parapet, better performance had been obtained. Examples of these parapets are shown in Fig. 8.

Figure 8. Failure of a parapet with little restraint (left), and good performance of a restrained parapet (right)

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GLASS DOORS, WINDOWS, AND GLAZING

In recent years, the use of glass panels becomes a common architectural feature in large and small cities in Iran. Mostly, these panels have been used without providing proper connections to the structural components. In these events, many of the large glass panels had been broken or thrown out, causing the glasses to be shuttered. Others with smaller size had escaped the events. Examples of these panels are shown in Fig. 9.

Figure 9. Dislodgement of large glass panels (left), and relative good performance of a window (right)

PARTITIONS AND INTERNAL WALLS

Usually, interior walls are vulnerable to out of plane forces. In these events, the lack of proper connections between such walls and the main structure was one of the main reasons that caused their failure. Furthermore, the high intensities and the relatively long durations of the two big earthquakes with the many aftershocks followed them, had contributed to that failure. An example of such failure was that of walls constructed above suspended ceilings but below structural roof levels. For various reasons, including the use of ducts, pipes, canals and other facilities under the level of structural roofs, these walls were not connected to the roof. As a sequence of the earthquakes, the failure of materials from the upper parts of the wall had caused minor to moderate damage to the suspended ceilings. Even with partitions having full height, the traditional details commonly used for connecting walls with roofs were found inadequate in these events.

INTERIOR WALL FINISHES

Substantial cracking and spall of interior wall finish materials was observed in many buildings. This was more noticeable at the corners of perpendicular walls, at column-wall joints, and at beam-wall connection zones, as shown in Fig. 10. In some walls, the use of thick layers of plaster was an additional reason for this kind of failure.

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Figure 10. The spall of interior wall finish materials

SUSPENDED CEILINGS

Many buildings had experienced some damage related to suspended ceilings. Although the structural performance of these buildings was as intended, the suspended ceilings were unable to accommodate the induced lateral accelerations. In these events, the failure of suspended ceiling systems was one of the most common types of non-structural failure.

The most commonly used suspended ceilings are those of metal meshes coated by plasters. According to the traditional practices, ceilings were built without providing perimeter angles and attached directly to the walls. In most cases, no gap was provided between walls and ceilings. During earthquake tremors, metal meshes and plasters of the ceilings were under lateral pressure from the walls that caused buckling, deformation and local failure, as shown in Fig. 11.

Among other types of suspended ceilings were metal ceilings. These ceilings were also attached directly to the walls with no gap. Similarly, and because of lateral pressures applied by the walls, failure of some ceiling units had occurred, as shown in Fig.11.

Another type of failure was that caused by the collapse of walls constructed above suspended ceilings but below structural roof levels. This kind of failure was discussed before.

BUILDING CONTENTS

Another source of damage during these earthquakes was the tumbling of building contents. Buildings contents were displaced, overturned and caused damages as a result of these events. In many hospitals, the displacements and the fallings of medical equipments and oxygen capsules were among the main reasons led to the stoppage of their services. In all cases, furniture in different buildings had not been fastened to the walls to prevent overturning. Accordingly, this kind of damage was quite common.

MECHANICAL AND ELECTRICAL COMPONENTS

Overturning of medical equipments was also observed as one of the major failure modes in some hospitals (EERI, 2012 and Zare et al, 2012). On the other hand, none of the mechanical and electrical equipments found in the basement of the main hospital of Heris was affected by the quake, as shown in Fig.12. In spite of the shortcomings observed in the restrained systems, all these equipments had met the "Operational Non-structural Performance Level".

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Figure 11. Failure of suspended ceilings. Failure of metal meshes coated by plasters (upper right and left), and Failure of metal ceilings (lower left and right)

Figure 12. Mechanical and electrical equipments in main hospital of Heris

ELECTRICITY NETWORK

Electricity network of 25 villages were totally damaged. The total damage in these villages had be estimated to be around 0.6 million US Dollars. As result of these events, some of electrical feeders were gone out of circuits and reconnected after half an hour. Furthermore, electricity towers located on fault has fallen but the rest of them in further distances from the fault remain intact.

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TELECOMMUNICATION SYSTEMS

Some Insufficiencies were reported in telecommunication antennas. There were some difficulties in phone contact to the earthquake stricken areas because of heavy traffic in calls.

GAS AND WATER SYSTEMS

Damage to gas distribution network had been reported in residential areas because of buildings collapse (Miyajima et al., 2012). Moreover, there were signs of seriously damaged gas valves as well (IIEES, 2012). Furthermore, it has been reported that some gas leakages caused fire in some villages of the area (IIEES, 2012 and Miyajima et al., 2012). The gas system of Ahar and Heris started working again after a couple of hours and in Varzaghan it took a day to be back in service (IIEES, 2012). On the other hand, no structural damages were observed in the gas stations in the affected area.

In these events, some problems in the water network had been also faced. The severity of the damage was more in villages due to topographic and soil condition. However, the problems in water network were mostly fixed in the few days followed the events (Kalantari, 2012).

NON-STRUCTURAL COMPONENTS AND SEISMIC CODES

The Seismic Iranian code, known as IS2800, was published in 1991 and revised twice in 1999 and 2004. This code has specifies a horizontal ground acceleration of 0.3g for the northern part of East Azerbaijan Province. For low-rise buildings of high importance (e.g. hospitals), with fundamental periods around 0.63 located on medium compacted soils, the design base shear would be a little bit more than 0.1 of the building weight (Consulting Engineers of Fadak, 2013). The fourth edition of the IS 2800, that suppose to be published in 2014, is expected to maintain the same design base acceleration value of 0.3g for this region (BHRC, 2013). Although a detailed discussion is needed on the provisions of this code, experience has shown that buildings that met the minimum code requirements had survived past earthquakes. However, failure of non-structural systems is still a big problem in Iran.

As shown in these events, buildings that remained structurally sound after the earthquakes lost their operational capabilities due to damages to their non-structural components. Although International codes have moved forward to bridge this gap by utilizing all the information collected on the performance of non-structural components during past earthquakes to upgrade their regulations, IS 2800 has not revised its regulations on this subject for the last few years. However, stricter and more detailed regulations for the design of non-structural components are expected in its coming fourth edition (BHRC, 2013).

CONCLUSIONS

In this earthquake, the poor performance of non-structural components has been caused mainly by improper construction and installation practices. Furthermore, the lack of clarity of the present specifications, the inadequacy of the procedural rules that govern their design and construction, and the lack of proper supervision were among the other reasons that caused extensive damages to these components.

In past earthquakes, it was common practice to blame the non-engineered buildings for most of the losses. In this earthquake, this also was the case. However, and since this earthquake had stricken urban centers, the safety of infrastructures and essential facilities had become a major concern for the society. The losses occurred in the main hospitals in the region had caused an increase in the number of fatality in this earthquake. This issue was quite alarming for both the government and the people. Furthermore, and in comparison to previous earthquakes, urban buildings sustained less structural damages. This favorite development had turned the attention toward the performance of non-structural components, an issue neglected in the past and hopefully it would not be forgotten in the future.

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REFERENCES

BHRC (2013) Final Draft Regulations for Seismic Design of Buildings: IS 2800-92 (in Persian) BHRC (2003) Iranian Code of Practice for Seismic Resistant Design of Buildings, Standard No 2800, 2nd Ed.-

1999 Consulting Engineers of Fadak (2013) A Comprehensive Evaluation Report on Imam Hussein (AS) Hospital in

Heris city (in Persian) EERI (2012) The Mw 6.4 and Mw 6.3 Iran Earthquakes of August 11, 2012 Fallahi A (2013) “Technical report- sheltering, from relief to reconstruction: One year after the 2010 East

Azerbaijan Province Earthquake,” International Journal of Architectural Research, 7(3):122-129 Housing Foundation (2012) Iran-Azarbaijan Sharghi Province Earthquake Situation Report No. 4 IFRC (2012) Iran: Earthquake, Information Bulletin No. 9, WWW.ifrc.org IIEES (2012) Varzaghan- Ahar Earthquake IIEES Report, , www.iiees.ac.ir ISMN (2012) Ahar – Varzaghan Earthquake of 11th August 2012,

http://www.bhrc.ac.ir/portal/Default.aspx?tabid=1209 Kalantari A (2012) Private Communications Miyajima M, Fallahi A, Sadeghi A, Ghanbari E, Soltani H, Amiraslanzadeh R, Vakilazadsarabi A, Forouzandeh

FJ, Sheikhalizadeh R (2012) Site Investigation of the Ahar-Varzeghan Earthquake in NW Iran of August 11, 2012, http://committees.jsce.or.jp/eec205/system/files/Quick%20Report%20of%20Iran%20EQ.pdf

Zaré M, Kalantari A, Ansari A, Haghshenas E, Davoodi M, Mostafazadeh M (2012) Preliminary Reconnaissance Report on Dual Varzaghan-Ahar Earthquakes www.iiees.ac.ir (in Persian)