Discussion 11

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Journal of Earthquake Engineering

ISSN: 1363-2469 (Print) 1559-808X (Online) Journal homepage: http://www.tandfonline.com/loi/ueqe20

Damage to Cultural Heritage Structures and Buildings Due to the 2015 Nepal Gorkha Earthquake

Satish Bhagat, H. A. D. Samith Buddika, Rohit Kumar Adhikari, Anuja Shrestha, Sanjeema Bajracharya, Rejina Joshi, Jenisha Singh, Rajali Maharjan & Anil C. Wijeyewickrema

To cite this article: Satish Bhagat, H. A. D. Samith Buddika, Rohit Kumar Adhikari, Anuja Shrestha, Sanjeema Bajracharya, Rejina Joshi, Jenisha Singh, Rajali Maharjan & Anil C. Wijeyewickrema (2018) Damage to Cultural Heritage Structures and Buildings Due to the 2015 Nepal Gorkha Earthquake, Journal of Earthquake Engineering, 22:10, 1861-1880, DOI: 10.1080/13632469.2017.1309608

To link to this article: https://doi.org/10.1080/13632469.2017.1309608

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Damage to Cultural Heritage Structures and Buildings Due to the 2015 Nepal Gorkha Earthquake Satish Bhagata, H. A. D. Samith Buddikaa, Rohit Kumar Adhikaria, Anuja Shresthaa, Sanjeema Bajracharyaa, Rejina Joshia, Jenisha Singha, Rajali Maharjanb, and Anil C. Wijeyewickremaa

aDepartment of Civil and Environmental Engineering, Tokyo Institute of Technology, Tokyo, Japan; bDepartment of International Development Engineering, Tokyo Institute of Technology, Tokyo, Japan

ABSTRACT Cultural heritage structures are an integral facet of the irreplaceable cultural heritage of a nation and have been constructed several hun- dreds and even thousands of years ago. In this paper, based on a field reconnaissance of the highly damaged areas of Kathmandu Valley and Sindhupalchowk district, damage to cultural heritage structures due to the 2015 Nepal Gorkha earthquake and its impact on Nepal are reported. Damages to engineered and non-engineered buildings are also discussed. The damage patterns observed and discussed will be useful for the prevention of damage to cultural heritage structures and other buildings in seismically active countries.

ARTICLE HISTORY Received 10 February 2017 Accepted 27 February 2017

KEYWORDS Cultural Heritage Structures; Earthquake Reconnaissance Survey; Engineered and Non-Engineered Buildings; Structural Damage; 2015 Nepal Gorkha Earthquake

1. Introduction

An earthquake of momentous magnitude ðMwÞ 7.8 occurred in the central region of Nepal on April 25, 2015, at 11:56 Nepal Standard Time. The epicenter (28.147°N, 84.708°E) of the earthquake was located in the village of Barpak, Gorkha district, which is approxi- mately 78 km northwest of the capital city, Kathmandu (Fig. 1), and its focal depth was 15 km [USGS, 2015]. Over 472 aftershocks with Mw greater than 4.0 have been recorded as of October 2016 [NSC, 2016], with some significant seismic events having Mw 6:7 on April 26, 2015, and Mw 7:3 on May 12, 2015 (Fig. 1). The earthquake resulted in a Maximum Mercalli Intensity of IX (Violent) with about 8790 deaths, and 22,300 people injured [NPC, 2015]. Significant damages to many public and private buildings were reported. In addition, many cultural heritage structures were also damaged, ranging from moderate damage to total collapse. It was reported that 2900 structures with a historical and religious significance were affected [NPC, 2015], of which 133 had collapsed, 95 were partially collapsed and 515 were partly damaged [DOA, 2015].

The cultural heritage of a nation depicts the social beliefs, customs, and traditions that connect people and provide a sense of unity and belonging to a nation. Cultural heritage structures (i.e. tangible cultural heritage) also serve as tourist attractions but are vulnerable to strong ground shaking due to seismic events, as these structures were obviously built before structural design guidelines were established. The traditional materials used for the

CONTACT Anil C. Wijeyewickrema [email protected] Department of Civil and Environmental Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ueqe.

JOURNAL OF EARTHQUAKE ENGINEERING 2018, VOL. 22, NO. 10, 1861–1880 https://doi.org/10.1080/13632469.2017.1309608

© 2018 Taylor & Francis Group, LLC

construction of cultural heritage structures need proper maintenance at regular intervals to maintain structural integrity. Lack of regular maintenance and deterioration of con- struction materials can lead to significant damage to these structures, even under minor ground motion intensity levels.

Damage to cultural heritage structures in Italy are discussed in detail by Parisi and Augenti [2013]. Protection of cultural heritage structures is always a matter of concern and has gained significant attention in many European countries [Kappos et al., 2007; Milani and Valente, 2015]. In Nepal, the Ancient Monuments Preservation Act empowers the Department of Archeology to be responsible for all heritage sites in the country. Inadequate resources and mechanisms to implement projects and protect heritage sites, and conflicting interests of multiple stakeholders involved in conservation and mainte- nance of heritage structures, have led to a situation where there are problems with the implementation of regular maintenance of all cultural heritage structures [Chapagain, 2008]. This resulted in extensive damage to cultural heritage structures due to the 2015 Nepal Gorkha earthquake.

Many engineered and non-engineered buildings were also damaged due to the 2015 Nepal Gorkha earthquake. A total of 498,852 buildings were fully damaged and 256,697 buildings were partially damaged [NPC, 2015]. This includes both engineered and non-engineered buildings. Damage to buildings due to the 2015 Nepal Gorkha earthquake have been reported in many studies [for e.g. Adhikari et al., 2015; Sun and Yan, 2015; Goda et al., 2015; Shakya and Kawan, 2016; Sharma et al., 2016]. These studies mainly focused on damage to

Figure 1. Location of the mainshock and two major aftershocks of the 2015 Nepal Gorkha earthquake [modified from Parajuli and Kiyono, 2015]. Note: Kathmandu Valley consists of Kathmandu, Lalitpur, and Bhaktapur districts.

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reinforced concrete buildings highlighting some of the major causes such as weak column- strong beam mechanism, lack of confining reinforcement, low-quality construction materi- als, and poor reinforcement detailing. Parajuli and Kiyono [2015] investigated damage to stone masonry structures. However, these studies do not discuss damage to cultural heritage structures, which are one of the most valuable cultural assets of a nation.

In the last few decades, shortly after the occurrence of a major seismic event, many reconnaissance surveys have been carried out by different groups of researchers. The reconnais- sance surveys mainly focusing on structural damage can be broadly categorized as focusing on (a) damage to building structures [e.g. Tsai et al., 2000; Eberhard et al., 2010; Kawashima et al., 2010; Romão et al., 2013; Parajuli and Kiyono 2015; Lukkunaprasit et al., 2016; Yazgan et al., 2016]; (b) damage to cultural heritage structures [e.g. Leite et al., 2013; Sorrentino et al., 2014; Adami et al., 2016] (c) seismic pounding of buildings [e.g. Kasai and Maison, 1997; Cole et al. 2012]; and (d) damage to bridges [e.g. Kawashima et al., 2009; Schanack et al. 2012].

The present paper reports the findings of the earthquake reconnaissance after the 2015 Nepal Gorkha earthquake, where the focus is on the damage caused to cultural heritage structures and the resulting impact on Nepal. A field reconnaissance of the highly damaged areas of Kathmandu Valley (which consists of Kathmandu, Lalitpur, and Bhaktapur districts) and Sindhupalchowk district (Fig. 1) was conducted by a team from the Tokyo Institute of Technology, Japan from June 1 to 8, 2015. In addition, damage to engineered and non- engineered buildings located in areas where there were a large number of casualties is also discussed. The observations and related discussions provided in this paper would be useful when formulating plans to preserve cultural heritage structures and other buildings from future earthquakes in seismically active nations.

2. Characteristics of Nepalese Heritage Structures

Kathmandu Valley has seven monument zones included in the list of UNESCO World heritage sites, revealing a wide range of historic and artistic achievements over the centuries. These monument zones include the Durbar Squares of Kathmandu, Patan, and Bhaktapur, the Buddhist stupas of Swayambhu and Boudhanath, and the Hindu temples of Pashupatinath and Changu Narayan [UNESCO, 2016]. All these cultural heritage structures have unique features and depict the traditions and culture of Nepal. Besides this, the design approach, materials, and craftsmanship adopted during the construction of these structures represent the ancient remarkable architectural typologies. Most of these cultural heritage structures are built using stone masonry and brick masonry bonded with mud mortar or lime mortar, which easily deteriorate with time (in a few of these structures the main frame is made of timber), thus making them susceptible to damage under lateral shaking. In general, Nepalese temples can be broadly grouped into three categories based on their architectural pattern: Pagoda style, Stupa style, and Shikhara style, all of which vary from each other in their construction methods.

3. Seismicity of Nepal

Since Nepal lies in the vicinity of the active plate boundary between the Indo-Australian and Eurasian plates, there is always a risk of a major earthquake. Nepal is divided into three tectonic zones from south to north, viz., the Main Central Thrust (MCT), the Main Boundary Thrust (MBT), and the Himalayan Frontal Thrust or the Main Frontal Thrust (MFT). The major and

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minor earthquakes in Nepal are associated with these active thrusts. Some of the major earth- quakes in Nepal up to 2016 and their locations are shown in Fig. 2. The 1934 Nepal-Bihar earthquake was the most devastating seismic event that led to 8514 fatalities in Nepal, of which 4296 fatalities were in Kathmandu Valley alone [Pandey and Molnar, 1988]. It is noted that the April 25, 2015 earthquake occurred near the MFT, between the subducting Indo-Australian plate and the overriding Eurasian plate, moving at a relative rate of approximately 45 mm/year towards the north-northeast [USGS, 2015] region. The acceleration time histories of East-West (EW), North-South (NS), and vertical (UD) components for the ground motion recorded at the KATNP station during the mainshock of April 25, 2015 are shown in Fig. 3. The EW, NS, and UD components had peak ground acceleration (PGA) of 0.158, 0.164, and 0.186 g, respectively. The response spectra of the acceleration time histories are shown in Fig. 4, where the EW component has a predominant period of 4.55 s and the NS component has two predominant periods at 0.43 and 4.85 s. The predominant period of the UD component is 0.08 s. Hence, both low- and high-rise structures are expected to have more damage due to the NS component of the ground motion, while the EW component is expected to cause more damage to taller structures with a longer fundamental period. However, 40- to 50-story high-rise buildings (corresponding to buildings with a fundamental period approximately in the range of 4.0–5.0 s) have not yet been constructed in Kathmandu Valley. The tallest building in Kathmandu Valley when the earthquake occurred was an 18-story high-rise building.

Ms 7.7 Nepal-Tibet August 28, 1916 Darchula district

Mw 6.8 Nepal-Bihar August 21, 1988 Udayapur district

Ms 8.0 Kathmandu-Bihar August 26, 1833 Rasuwa

Mw 6.9 Nepal-Sikkim September 18, 2011 Taplejung district

Mw 8.1 Nepal -Bihar January 15, 1934 Udayapur district

Ms 6.5 Kathmandu July 7, 1869 Kathmandu district

Mw 7.8 Nepal-Gorkha April 25, 2015 Gorkha district

Ms 6.3 Nepal-India July 27, 1966 Bajhang district

Ms 6.5 Nepal-Pithoragarh July 29, 1980 Bajhang district

Mw 7.3 Nepal-Dolakha May 12, 2015 Dolakha district

B A

district

Figure 2. Map of Nepal showing the major earthquakes up to 2016. Note: Mw = moment magnitude; Ms = surface wave magnitude. (A) Kathmandu Valley (Kathmandu, Lalitpur, and Bhaktapur districts) and (B) Sindhupalchowk district.

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4. Damage to Cultural Heritage Structures

The devastating earthquake caused enormous destruction to historic centers in Nepal, resulting in irreparable damage to the cultural legacy of the country. Major destruction was observed in most of the cultural heritage sites in Kathmandu Valley. Of the nearly 750 damaged or destroyed monuments, about 450 were located in Kathmandu Valley and 20 were located in Sindhupalchowk district. Most of the Nepalese temples and monuments were constructed during the 14th–19th centuries, without considering proper seismic resistance requirements. Some of the inherent structural characteristics of Nepalese monuments, such as symmetrical

0 20 40 60 80 100 120 -0.2

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Figure 3. Ground motion recorded at Kantipath station (KATNP), Kathmandu on April 25, 2015 [Source: USGS, 2015].

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Figure 4. Response spectra for ground motion recorded at Kantipath station (KATNP), Kathmandu on April 25, 2015.

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construction, multi-level plinth, and conical mass distribution resulted in an enhanced seismic performance. However, the lack of vertical structural continuity, lack of rigid connections between various structural components, and heavy roof structures make these structures more vulnerable to strong ground motions.

4.1. Temples

During the earthquake reconnaissance survey carried out by the authors in June 2015, it was observed that some of the temples constructed with brick masonry and a timber frame sustained less damage than those constructed without a timber frame. Additionally, it was also observed that the construction materials used in most of the damaged monuments were already deteriorated, highlighting the need for appropriate repair and maintenance programs. Damages to these cultural heritage structures are discussed using the photo- graphs taken during the field survey.

Figure 5 shows the Nautalley Durbar (which means nine-story Palace), located in Kathmandu Durbar Square, that was damaged during the earthquake. This structure was built in 1768 AD to commemorate the victory of King Prithvi Narayan Shah of Nepal. The lower three stories were constructed in the Newari farmhouse style, while the upper six stories (four tiers) were constructed in the Pagoda style. The brick

Figure 5. South face of Nautalley Durbar located in Kathmandu Durbar Square viewed from Basantapur Dabali: (a) before earthquake, (b) after earthquake, (c) load path discontinuity in Nautalley Durbar, and (d) damage to white masonry building next to the Durbar. The upper three stories (two tiers) of the Nautalley Durbar collapsed due to the earthquake. The white masonry building next to the Durbar suffered severe damage and the entire front part of the building (south face) was destroyed.

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masonry and timber structural elements used in the four-tiered roofs contributed to the heavy weight at the top, causing collapse of the upper three stories (two tiers). In addition, the lack of continuous vertical structural elements (i.e. load path discontinu- ity) from the base to the roof in the pagoda style construction of the Durbar as seen in Fig. 5(c) resulted in toppling of the upper floors in this structure. Moreover, the lack of proper connections between struts, purlins, joists, and load bearing walls witnessed during the field survey, was another factor to undermine the seismic strength. The masonry building next to the Nautalley Durbar was also heavily damaged as seen in Fig. 5(d). The damage to this building was due to deterioration of the bricks and mortar used for the construction, as well as seismic pounding of the building with the adjacent Nautalley Durbar, as seen in Fig. 5(d).

The pre- and post-earthquake photographs of the pagoda-style Maju Dega temple and Narayan temple constructed in the late 17th century, also located in Kathmandu Durbar Square, are shown in Fig. 6. The massive multi-level plinth supported the Maju Dega temple above it, while the plinth of the Narayan temple was relatively lower in height (Figs. 6(a) and (b)). The walls used for the main structures are constructed over the inner timber beams (Fig. 6c), where a firm connection between the brick walls and the wooden beams at the top level of plinth could not be observed. The timber column stands over a timber beam on a base with a pin inserted into the base stone. The connection between

Narayan temple

Maju Dega temple

Narayan temple

Maju Dega temple

Inner beams

External beams

Base stone

Figure 6. Pagoda style Maju Dega temple and Narayan temple located in Kathmandu Durbar Square: (a) before earthquake, (b) after earthquake, and (c) close-up view of the connection of Narayan temple after damage. The lack of a rigid connection between the base and the superstructure led to the collapse of the temple.

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the timber column and the base stone is also described in Shakya et al. [2014]. The lack of a rigid connection between the base and the superstructure led to the collapse of the superstructure of these two temples. A similar collapse occurred at the Fasidega temple that was also supported on a multi-level plinth located in Bhaktapur Durbar Square is shown in Fig. 7. This temple was rebuilt after it was fully damaged in the 1934 Nepal- Bihar earthquake.

In contrast to the collapse of the Maju Dega temple and the Fasidega temple (Figs. 6 and 7), some temples that had a wide plinth sustained no damage and performed well during the earthquake. The Taleju Bhawani temple located in Kathmandu Durbar Square (constructed in 1549 AD) and the Nyatapola temple located in Bhaktapur Durbar Square (constructed in 1702 AD), shown in Figs. 8(a) and (b), did not suffer any damage, while a small temple located in front of the Taleju Bhawani temple collapsed completely.

The brick masonry walls on the ground floor of the pagoda-style Changu Narayan temple located in Bhaktapur district suffered severe damage as shown in Fig. 9. The temple was originally built in the 4th century and was rebuilt in 1702 AD after a major fire damaged the temple. Local residents confirmed that frequent repairs and maintenance of the temple used to be carried out. The vertical layers of brick walls built with mud mortar, were not well interconnected and could not withstand large displacement demands and resulted in out-of- plane failure as seen in Fig. 9(b). During the field survey, it was observed that the temple was extensively supported by shores, to carry out necessary repair and retrofitting works (Fig. 9(a)). However, there were no signs of tilting or out-of-plumb of the timber frame that supports the entire structure.

Another type of temple that was damaged during the earthquake was the Shikhara style temples with a superstructure composed of a tall curvilinear or pyramidal tower. These are slender structures, constructed using brick masonry with lime mortar or mud mortar. They are brittle in nature, and their slenderness makes them more susceptible to damage

Figure 7. Fasidega temple located in Bhaktapur Durbar Square: (a) before earthquake and (b) after earthquake. The lack of a rigid connection between the base and the superstructure led to the collapse of the temple.

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under large lateral displacements. Some of the Shikhara style temples located in Bhaktapur Durbar Square that sustained damage are shown in Figs. 10–12. The pinnacle of the Siddhi Laxmi temple that was built in 1702 AD tilted, but the rest of the temple was intact (Fig. 10). Only the upper part of the Shiva temple that was constructed in 1674 AD collapsed (Fig. 11), but the entire Vatsala Durga temple that was constructed in 1696 AD had collapsed (Fig. 12). The smaller size of columns in the Vatsala Durga temple and added weight above it (Fig. 12(a)) resulted in failure of the columns leading to total collapse. The deterioration of the construction materials is clearly visible in Fig. 11(c), and lack of regular maintenance was the reason for collapse.

Figure 8. Temples with wide plinth that sustained no damage due to the earthquake: (a) Taleju Bhawani temple located in Kathmandu Durbar Square and (b) Nyatapola temple located in Bhaktapur Durbar Square. Rubble in front of Taleju Bhawani temple is from a small temple in the vicinity that collapsed completely.

Figure 9. Changu Narayan temple located in Bhaktapur district: (a) shores used to support the temple after the earthquake and (b) out-of-plane failure of the corner brick masonry walls at the main entrance. The timber frame that supports the entire structure was intact. ((b) source: http://rubinmu seum.org/page/then-and-now-changu-narayan).

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4.2. Landmark Tower

The failure of the 203 foot (61.88 m) tall Dharahara tower, which is made of brick masonry with lime mortar and mud mortar, is shown in Fig. 13. The tower had been constructed with thick walls to make the structure stable and capable of withstanding gravity loads and to accommodate an internal spiral stairway (Fig. 13(c)). The increased weight of the structure due to the thick walls and absence of reinforcing bars resulted in a brittle mode of failure, which prevented people from evacuating, leading to the deaths of 180 people. Since April 25, 2015 was a Saturday, there

Figure 10. The Shikhara style Siddhi Laxmi temple located in Bhaktapur Durbar Square: (a) before earthquake and (b) after earthquake. The pinnacle was tilted due to the earthquake.

Figure 11. The Shikhara style Shiva temple located in Bhaktapur Durbar Square: (a) before earthquake, (b) after earthquake, and (c) deterioration of bricks used for construction exposed after the earthquake. The upper part collapsed due to the earthquake.

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were many people who were visiting the Dharahara tower and were using the internal spiral stairway. Most of the people who lost their lives or were injured were on the internal spiral stairway of the Dharahara tower.

5. Damage to Engineered and Non-Engineered Buildings

5.1. Damage to Engineered Reinforced Concrete (RC) Buildings

The 2015 Nepal Gorkha earthquake caused damage to many reinforced concrete (RC) buildings. Damages to residential buildings, school buildings, factories, and apartment

Figure 12. The Shikhara style Vatsala Durga temple located in Bhaktapur Durbar Square: (a) before earthquake and (b) after earthquake. The temple was completely destroyed.

Figure 13. The historic landmark tower known as Dharahara: (a) before earthquake and (b, c) after earthquake. The spiral stairway is visible in (c).

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buildings were observed during the survey. Inadequate seismic design (and not obtaining approval from the relevant authority prior to the construction of buildings), use of low quality construction materials, and poor workmanship were the major reasons for damage to RC buildings. Here, an overview of the performance of RC buildings and some of the major causes for damage in Kathmandu Valley and Sindhupalchowk district surveyed by the Tokyo Tech team in June 2015 are discussed.

5.1.1. Inadequate Seismic Design, Low-Quality Construction Materials, and Poor Workmanship Evidence of inadequate seismic design is shown in Figs. 14 and 15. Buildings where the size of columns required to resist the lateral forces due to the earthquake was insufficient are shown in Figs. 14(a) and (b), and the close-up view of a damaged column is shown in Fig. 14(c). The absence of stirrups at beam-column joints (Fig. 15(a)) and wide spacing of stirrups at beam-column joints (Figs. 15(b) and (c)) were observed in collapsed and severely damaged buildings.

A severely damaged building where low-quality construction materials had been used for the structural members is shown in Fig. 16. Although the size of columns and the amount of rebars required to sustain the load of the superstructure may have been sufficient during the design phase, the use of low quality concrete during the construction

Figure 14. Inadequate seismic design—insufficient size of columns: (a) fully collapsed building, (b) tilted building, and (c) close-up view showing the size of columns.

Figure 15. Inadequate seismic design—stirrup issues: (a) no stirrups at the joint, (b), and (c) wide spacing of stirrups at the beam-column joint.

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led to the failure. The rebars that were used were already corroded, and the concrete used did not have proper grading of aggregates.

Figure 17 shows an example of poor workmanship during construction, where it is clear that there is inadequate cover concrete in the beam (Fig. 17(a)) and improper concreting at the beam-column joint (Fig. 17(b)), which resulted in corrosion of the exposed rebars.

5.1.2. Soft Story Collapse of a School Building The Jana Jagriti Higher Secondary School with three main buildings, located in Sindhupalchowk district, was inaugurated in October 2005 but suffered damage due to the earthquake as shown in Fig. 18. Figure 18(b) shows the complete collapse of the first story of the four-story building. The circular columns with 300-mm diameter had six 16- mm rebars, but the stirrups were placed at 150 mm spacing, which was inadequate. However, the two-story building in the same school compound constructed about 5 m away from the collapsed building suffered only minor structural damage (Fig. 18(c)), while the three-story building located about 30 m from the collapsed building sustained only

Figure 16. Low-quality construction materials used for structural members: (a) crushing of core concrete and (b) failure of column.

Figure 17. Poor workmanship during construction: (a) insufficient cover concrete in beam and (b) improper concreting of beam-column joint.

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non-structural damage (Fig. 18(d)). The four-story building was constructed at the edge of a slope, while the other two buildings had no such slopes nearby. Evidence of differential settlement could be observed as indicated by the inclination and cracks on the first floor slab as seen in Figs. 18(e) and (f). However, lack of stirrups due to inappropriate spacing at the joints (Fig. 18(b)) was also one of the causes of failure.

5.1.3. Structural Failure Due to Addition of Stories to Existing Buildings In some buildings that were severely damaged, the building facade indicated that addi- tional stories had been added to the existing building. The increase in the weight of the

Cantilever slab

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Figure 18. Damage to a school building in the Sindhupalchowk district: (a) plan view of the three main buildings in the school compound, (b) collapse of the first story of the 4-story building, (c) minor structural damage to the 2-story building, (d) non-structural damage to the 3-story building, (e), and (f) cracks and inclination in the first floor slab.

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building resulted in increased story shear demands during the earthquake, and resulted in pancake failure of the fourth floor (Fig. 19(a)). Although the building in Fig. 19(b) did not collapse, it is almost impossible to repair or retrofit the building, as there is complete failure at the column joint of the first story.

5.2. Damage to Non-Engineered Unreinforced Masonry (URM) Buildings

Several non-engineered unreinforced masonry (URM) buildings built without any con- sideration of seismic performance had partially collapsed or fully collapsed. Most of these URM buildings were made of brick masonry bonded with cement mortar, lime mortar, or mud mortar with timber joist floors. In the case of mud mortar, the mortar hardens with time, leading to shrinkage and separation of joints in masonry structures. The most common damage patterns observed in such structures are: (a) curtain fall collapse of the side walls (partial or full) (Figs. 20(a) and (b)); (b) vertical cracks on walls along the mortar joint (Fig. 20(c)); (c) diagonal cracks across the walls due to the inability of the wall to resist tensile stresses (Fig. 20(d)); and (d) collapse of the entire structure (Fig. 20(e)). Similar damage to URM buildings was also observed during the 2011 Sikkim-Nepal earthquake [Shakya et al., 2013]. The main cause of damage to these URM buildings is due to: (a) strength deterioration of the construction materials; (b) lack of regular maintenance; (c) lack of proper connections at the corners; and (d) excessive weight in the upper part of the building.

6. Performance of Restored Structures and Seismically Retrofitted Structures

Some of the cultural heritage structures that had been restored prior to the earthquake were unaffected by the earthquake, while some suffered only minor damage. The Bhimsen temple located in Patan Durbar Square, the Palace of Fifty-Five Windows and Chyasilin Mandap located in Bhaktapur Durbar Square, and the Pashupatinath temple were restored

Figure 19. Structural failure due to insufficient load carrying capacity: (a) pancake failure of 4th floor due to addition of extra story on the top and (b) insufficient load carrying capacity of lower floor columns due to the addition of extra upper floors.

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before the earthquake and survived with only very minor damage. Restored cultural heritage structures performed remarkably well during the earthquake and are also dis- cussed in the EERI report [EERI, 2016].

A total of 160 public schools in Kathmandu Valley, which were part of an Asian Development Bank (ADB)–supported school safety program that included seismic retrofit, withstood the earthquake and its aftershocks [ADB, 2015]. A number of hospitals, which were seismically retrofitted as a core part of a preparedness plan under a World Health Organization initiative, provided continuous service after the earthquake [UNISDR, 2015].

Partially damaged structures must undergo seismic performance assessment to evaluate the remaining seismic capacity, followed by retrofitting work. Restoration and retrofit of cultural heritage structures have been done in many seismically active countries such as Chile, Greece, Italy, Japan, New Zealand, and Turkey. The techniques adopted in these countries can be useful for the restoration and seismic retrofit of cultural heritage structures in Nepal and other countries that have not yet implemented such plans in a comprehensive manner.

7. Impact of Damage to Cultural Heritage Structures on Nepalese Society

Cultural heritage structures are crucial to the tourism industry in Nepal, and are one of the major sources of income for the country. Damage to cultural heritage structures due to the 2015 Nepal Gorkha earthquake has caused a large reduction in the number of tourists

Figure 20. Damage observed in non-engineered URM buildings: (a) and (b) curtain fall collapse of the side wall, (c) vertical disintegration of brick joints, (d) cracks along the walls due to excessive tensile stress, and (e) collapse of the entire building.

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and resulted in a significant reduction in the revenue generation of the country. A decline in the number of tourists from 790,118 in 2014 to 583,970 in 2015 was reported as a consequence of the earthquake [MOCTCA, 2015]. A loss of 600 million Nepalese rupees (NPR) (approximately 6M USD) was expected due to the decline in revenue generated from ticket sales at cultural heritage sites in Kathmandu Valley [NPC, 2015]. The decline in the number of tourists visiting Nepal after the earthquake has also affected the employ- ment of local people who mainly depend upon the tourism industry for their livelihood.

In addition to the economic impact, damage to cultural heritage structures has affected the social and cultural aspects of the Nepalese society. Cultural heritage structures are not only the pride of the nation but also the inseparable part of daily life of the people. These cultural heritage structures include a number of temples that many people visit on a daily basis for religious reasons. Cultural heritage sites are also a place for social and cultural interactions where traditional events are organized on a frequent basis. Sudden destruc- tion of these structures has lowered the morale of the people, as well as disrupted their daily lives.

The estimated total loss due to the damage caused to the physical assets and infra- structure at the cultural heritage sites is 16.9 billion NPR (approximately 169M USD) [NPC, 2015]. These direct and indirect losses may be recovered with proper restoration of the damaged cultural heritage structures and the reconstruction of collapsed structures. The National Planning Commission of Nepal estimates that about 21 billion NPR (approximately 210M USD) and a period of six years will be required for the restoration and reconstruction of these cultural heritage structures, and for seismically retrofitting the structures [NPC, 2015].

8. Summary

The magnitude 7.8 Nepal Gorkha earthquake, which occurred on April 25, 2015, caused widespread damage to cultural heritage structures as well as engineered and non-engi- neered buildings in Nepal. The damage was exacerbated by two significant aftershocks of Mw 6:7 on April 26, 2015, and Mw 7:3 on May 12, 2015. In the present paper, the damage levels in Kathmandu Valley and Sindhupalchowk district are discussed, as these areas had the largest number of casualties. Valuable lessons can be learned from the damage that was observed.

The damage to cultural heritage structures was mainly due to the magnitude of the seismic event, the deterioration of construction materials, and lack of maintenance. Major damage may have been prevented if there was a planned schedule of restoration and seismic retrofit, followed by routine maintenance of these structures. Seismic vulnerability assessment of cultural heritage structures that were partly damaged or not damaged should be carried out, followed by appropriate restoration and seismic retrofit with minimal disturbance to the original structural features. In addition, the connection of the timber framing with the brick masonry walls must also be investigated, as many temples have a timber main frame. Since these structures must be preserved for posterity, scheduled inspections should be carried out, and repairs should be done immediately, if required.

Damage to engineered buildings was mainly due to inadequate size of columns necessary to resist lateral forces, large spacing of stirrups at the beam-column joints,

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and insufficient concrete cover leading to corrosion of the rebars. Considering the con- struction materials and construction quality, structural damage should have been expected following the occurrence of a major seismic event. It is important that appropriate seismic design, good-quality construction materials and approved construction methods are used to minimize damage to engineered buildings.

Since non-engineered URM buildings were constructed using brick masonry with cement mortar or lime mortar, such buildings are not capable of withstanding large lateral deforma- tions due to its brittle nature. Reinforcing these structures will ensure that these buildings will be capable of sustaining large deformations and prevent major structural damage.

Adopting proper design and engineering practices to build resilient structures will ensure the operability of structures right after an earthquake. Besides this, seismic mon- itoring of cultural heritage structures and important buildings could be done to observe the dynamic behavior during a seismic event.

Policymakers and government officials in seismically active countries, especially develop- ing countries, should recognize the threat to cultural heritage structures and develop appro- priate plans to safeguard the irreplaceable, cultural heritage structures from seismic events.

Acknowledgments

The authors thank Professor Junichiro Niwa, Dr. Jiro Takemura, and Professor Akihiro Takahashi of the Department of Civil Engineering, Tokyo Institute of Technology for their kind support and encouragement of the field visit. They convey special thanks to Professor Prem Nath Maskey of the Institute of Engineering (IOE), Tribhuvan University (TU) for providing useful suggestions and assisting with the field visit in Nepal. They also extend thanks to Professor Gokarna Bahadur Motra, Dr. Basanta Raj Adhikari and Mr. Nagendra Raj Sitaula of IOE, TU, and Dr. Ramesh Guragain, Deputy Executive Director of NSET-Nepal for their kind cooperation and suggestions relevant to the field visit.

The authors acknowledge the anonymous review comments that have improved the manuscript.

Funding

Partial financial support from the Department of Civil Engineering and the Civil Engineering Alumni Association of the Tokyo Institute of Technology for the field visit is gratefully acknowledged.

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