Damage scenario of reinforced concrete buildings in the

2015 Nepal earthquakes

Rohit Kumar ADHIKARI1, Satish BHAGAT1

and Anil C. WIJEYEWICKREMA2 1Graduate Student, Tokyo Institute of Technology, Japan

adhikari.r.aa@m.titech.ac.jp, bhagat.s.aa@m.titech.ac.jp 2Associate Professor, Tokyo Institute of Technology, Japan

wijewickrema.a.aa@m.titech.ac.jp

ABSTRACT

The Gorkha earthquake of April 25, 2015 and its aftershocks caused extensive damage

to hundreds of thousands of building structures in Nepal. A reconnaissance survey was

carried out in the most affected areas to assess the damage to buildings due to the

earthquakes. It was found that many old as well as modern reinforced concrete

buildings including residential, school and high-rise apartments sustained minor to

major damage including collapse. Most of the well-designed reinforced concrete

buildings sustained minor or non-structural damage. From the field observation, some

of the main reasons of such a vast damage to building structures are found to be the

lack of maintenance of old structures, negligence of building codes, and poor design

and construction practices. This paper summarizes the damage to reinforced concrete

buildings with specific focus on the causes and types of damage due to the earthquakes.

Most of the collapsed reinforced concrete buildings were seen to have soft-first story

failure mechanism. Non-structural damage mainly included heavy damage to the brick

masonry infill walls. Suggestions and research needs are also identified to improve the

seismic performance of reinforced concrete buildings in Nepal.

Keywords: earthquake reconnaissance survey, reinforced concrete buildings, seismic

damage, 2015 Nepal earthquake

1. INTRODUCTION

A magnitude 7.8 earthquake occurred in the central region of Nepal on April 25, 2015 at

11:56 AM (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 approximately

77 km north-west of the capital city Kathmandu (Figure 1) and its focal depth was 15

km (USGS, 2015). The earthquake resulted in a maximum Mercalli Intensity of IX

(Violent) and more than 8,700 deaths and over 22,300 injuries were reported. Some

casualties were also reported in the adjoining areas of India, China, and Bangladesh.

Over 350 aftershocks with magnitude greater than 4.0 have occurred, with some

significant ones having a magnitude of 6.7 on April 26 and 7.3 on May 12 (Figure 1).

More than 500,000 houses were totally collapsed and over 200,000 houses were

partially damaged leaving over two million people homeless. Although Kathmandu and

Sindhupalchowk districts were far away from the epicenter, severe damages were

observed in these areas.

October 2015, Kathmandu, Nepal

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Reconnaissance survey of the heavily affected regions (Kathmandu valley and

Sindhupalchowk district) were conducted by a team from Tokyo Institute of

Technology, Japan to assess the extent and nature of damage to building structures

caused by the earthquakes (Wijeyewickrema et al., 2015).

This paper summarizes the cause and nature of the structural damage to RC buildings

due to the earthquakes. Some suggestions for improving the performance and future

research needs in the area of seismic design and construction practice of RC buildings

in Nepal are also presented. Since, the investigation was based on the visual inspection

without the information on actual design and construction details, there is a possibility

that the interpretation of the failure mechanism might not be accurate.

2. SEISMIC DESIGN AND CONSTRUCTION PRACTICE IN NEPAL

In recent years, reinforced concrete framed structures are common construction practice

in Nepal (JICA, 2002). Low-rise reinforced concrete buildings are designed using the

seismic design code NBC-105 (DUDBC, 1994) whereas high-rise buildings are

designed following the guidelines provided by the Indian seismic code IS1893 (BIS,

2002). Detailing for ductility is based on Indian standard IS 13920 (BIS, 1993).

Although various guidelines are prevailing for the seismic design of buildings in Nepal,

most of the low-rise structures do not follow the design codes. Owners themselves

compromise with the quality of construction materials, design and construction process

due to economic reasons. The construction practice in most of the cases is based on

thumb rules and the masons are not well trained. Due to the increasing urbanization and

skyrocketing population in the Kathmandu valley, the owners opted for addition of

stories in the old construction, which were not well designed. These are some of the

weaknesses of the current building design and construction practice in Nepal.

Chaulagain et al. (2013) studied the seismic vulnerability of common RC buildings in

Nepal and found that the buildings constructed using current construction practice and

designed with Nepal Building Codes (NBC) are highly vulnerable to earthquakes.

Figure 1: Locations of the mainshock and major aftershocks. (Source: USGS)

Damage scenario of reinforced concrete buildings in 2015 Gorkha Earthquake

3. DAMAGE TO REINFORCED CONCRETE STRUCTURES

Reinforced concrete moment-resisting frame buildings performed poorly in the 2015

Gorkha earthquakes. Many low-rise reinforced concrete buildings in the affected area

were either collapsed or sustained heavy damage. Most of the poorly designed

buildings not confirming to design standards suffered severe damage. But well-

designed reinforced concrete buildings suffered only minor non-structural damage. The

damaged reinforced concrete buildings included mostly residential buildings as well as

school and high-rise apartment buildings. Most of the high-rise apartment buildings

were subjected only to damage in the non-structural elements and are livable after

repairing.

3.1 Damage to residential buildings

Many poorly designed residential buildings collapsed or suffered heavy damage due to

the earthquakes. All the reinforced concrete framed constructions in Nepal have heavy

brick masonry infill walls increasing the seismic weight of the buildings. Typical

damage scenario of reinforced concrete residential buildings in the Kathmandu valley

and Sindhupalchowk district are reported here.

Photo 1 shows a completely collapsed RC building. The failure is due to the

insufficient size and poor detailing of columns, beams and structural joints resulting in a

pancake failure.

Photo 1: Collapsed residential RC frame building in Sitapaila, Kathmandu.

Photo 2: Pancake failure of buildings in Gongabu, Kathmandu.

2 stories collapsed 4 stories collapsed

October 2015, Kathmandu, Nepal

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The buildings in Photo 2 lost their lower 2 stories and 4 stories due to the soft story

pancake failure. The heavy load of brick masonry infill walls and the cantilever

projection as seen caused the failure of columns. Photo 3 shows the pounding damage

between two adjacent building ‘A’ and ‘B’. Photo 4 shows the collapsed building with

fractured reinforcement of the columns, which is due to the poor ductile detailing. The

first story columns of the 3 storied building (Photo 5) failed in shear in which the upper

2 stories were added recently on top of the original single story building.

Photo 3: Pounding damage between two adjacent building ‘A’ and ‘B’ in Lamosanghu,

Sindhupalchowk.

Photo 4: Collapse of a 3 storied RC building in Lamosanghu, Sindhupalchowk. Note

that all the longitudinal reinforcing bars of the column shown have fractured.

A B

Damage scenario of reinforced concrete buildings in 2015 Gorkha Earthquake

Photo 5: Damage to the first story of the 3 storied building in Chautara, Sindhupalchowk,

in which upper 2 stories are added recently.

3.2 Damage to school buildings

More than 8,000 school buildings were destroyed due to the earthquake and its

aftershocks. Fortunately, the schools were closed on the day when main shock and its

major aftershocks occurred. Temporary shelters have been constructed to conduct

classes in the Kathmandu valley as well as in remote areas. The damage to one of the

reinforced concrete school building in Sindhupalchowk district is reported here.

Photo 6: (a) Collapsed building of the Shree Jana Jagriti Higher Secondary School,

Sangachowk, Sindhupalchowk and (b) Shear failure of columns.

Photo 6 shows a school building damaged heavily due to the earthquakes. Circular

columns in this 3-story building had 300 mm diameter with 6 no. of 16 mm main bars,

while square columns had 300 mm x 300 mm size with 4 no. of 16 mm and 4 no. of 12

(a) (b)

October 2015, Kathmandu, Nepal

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mm bars as longitudinal reinforcements. Both circular and square columns had 5 mm

stirrup with 150 mm spacing which is not sufficient (Photo 6(b)).

Photo 7: Heavily damaged brick masonry infill wall.

3.3 Damage to high-rise apartment buildings

Many high-rise apartment buildings in Kathmandu valley suffered mostly non-structural

damage. Only minor structural damage was observed in some buildings. None of the

high-rise apartment buildings collapsed and almost all are usable after repairing.

Damage to one of the apartment buildings (Sunrise Apartment) at Nakkhu in

Kathmandu valley is shown in Photos 8 and 9.

Photo 8: Diagonal cracks in the masonry infill walls.

Damage scenario of reinforced concrete buildings in 2015 Gorkha Earthquake

Photo 9: Diagonal shear failure of a beam at the basement leading to seepage of water.

4. CONCLUSIONS AND RECOMMENDATIONS

As reported in this paper, many reinforced concrete buildings in the affected areas

suffered either collapse or severe damage due to the 2015 Gorkha earthquakes. Most of

the collapsed buildings suffered soft-first story failure. Similarly, the non-structural

damage mainly included the heavy damage to brick masonry infill walls. Besides some

of the exceptional cases in which the earthquake effects exceeded the design limits due

to geological, site effects etc., the primary reasons of such a vast damage to reinforced

concrete buildings are negligence of seismic design codes and poor construction

practices. As observed by the authors, insufficient member size, inadequate shear

reinforcement, poor ductile detailing, strong-beam weak-column combination, weak

beam-column joints, large cantilever projections, heavy masonry infill walls were

among the most common reasons for such a massive damage to reinforced concrete

structures.

There are many factors to be considered for improving the seismic performance of

reinforced concrete buildings in Nepal. The first and foremost step is to strictly

implement the building codes for the seismic design. The owners, contractors,

engineers, workers must be educated about the earthquake resistant constructions. The

seismic design code of Nepal is to be revised to include current practices and

developments in earthquake resistant constructions around the world. Lightweight

construction should be preferred. Use of reinforced concrete shear walls should be

promoted for better seismic resistance. Seismic strengthening and retrofitting works

should be implemented to old and partially damaged constructions.

Future research work is needed to improve the frame-infill wall connection to reduce

the non-structural damage as well as the replacement of masonry infill walls with

lightweight materials. Seismic resistance of stone masonry walls should be studied as

these are economical construction materials in developing countries.

October 2015, Kathmandu, Nepal

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REFERENCES

Chaulagain, H., Rodrigues, H., Jara, J., Spacone, E., & Varum, H. (2013). Seismic

response of current RC buildings in Nepal: a comparative analysis of different

design/construction. Engineering Structures, 49, 284-294.

IS 13920: 1993. Ductile detailing of reinforced concrete structures subjected to seismic

force – code of practice. Bureau of Indian Standards, New Delhi, India.

IS 1893 (Part1): 2002. Criteria for earthquake resistant design of structures. 5th

revision, Bureau of Indian Standards, New Delhi, India.

JICA (2002). The study on earthquake disaster mitigation in the Kathmandu valley,

Kingdom of Nepal, Japan International Cooperation Agency (JICA) and Ministry of

Home Affairs, His Majesty’s Government of Nepal.

NBC-105: 1994. Seismic design of buildings in Nepal, Nepal National Building Code,

Government of Nepal, Ministry of Physical Planning and Works, Department of Urban

Development and Building Construction, Kathmandu, Nepal.

Wijeyewickrema, A. C., Samith Buddika, H. A. D., Bhagat, S., Adhikari, R. K.,

Shrestha, A., Bajracharya, S., Singh, J., Maharjan, R., 2015. Earthquake reconnaissance

survey in Nepal after the magnitude 7.8 Gorkha earthquake of April 25, 2015. Field

Investigation Report. Department of Civil Engineering, Tokyo Institute of Technology,

Japan.