International Journal of Modern Research in Engineering & Management (IJMREM) ||Volume|| 1||Issue|| 5 ||Pages|| 22-32 || May 2018|| ISSN: 2581-4540
Failure Study of Reinforced Concrete Buildings of Kathmandu Valley In Gorkha Earthquake 2015 Dr Rajan Suwal Asst, Professor, Institute of Engineering, Pulchowk Campus, Tribhuvan University, Nepal
------------------------------------------------------ABSTRACT---------------------------------------------------Nepal lies in earthquake prone zone. There are different fault zones in Nepal. Active fault of in this region causes several earthquakes in Nepal. In the recent, an earthquake of M7.8 occurred in 77 km NW of Kathmandu (in the boarder of Gorkha and Lam Jung) at 11:56 on 25 April 2015 with shallow depth of 15 km with maximum Mercalli Intensity of IX, lasting approximately thirty seconds. Nepal faced continued aftershocks throughout the country at the intervals of 15–20 minutes, with one shock reaching a magnitude of 6.7 on 26 April at 12:54:08. And another major earthquake of 7.3 (as per USGS report) occurred in 18 km south-east of Kodari and epicenter is in boarder of Dolkha and Sindhu pal chowk district at 12.51 on 12 May 2015. This article is concentrated to study of damages of reinforced concrete buildings only which are in Kathmandu valley in Gorkha Earthquake 2015. Effect of earthquake in reinforced concrete frame structures in Kathmandu valley are considered. Height of buildings is taken from two storied to ten storied. In this study it is discussed about the types of failures of reinforced concrete structures, observations and causes of structural failures, tilting of building, fully collapsed buildings, sandwich type failure of buildings, soft story failure of buildings, column failures, crushing of concrete failure of column, shear and bending failure of columns, shear failure of beams and beam-column joint failure, failure due to reinforcement deficiency, poor quality of concrete and infill wall failure. It is found that soil exploration in building site is not done in most of the failed building area so foundation failure in excessive settlement and tilting are observed, Configuration of buildings are not regular. It is observed the lack of structural design and not properly structural designed of buildings. In addition to this it is found that not proper reinforcement detailing of building elements and lack of quality control of construction materials. So, it is recommended that in the stage of soil exploration, planning, design and supervision of buildings, building norms should be strictly fulfilled. Technical expertise should be used in all process of work.
KEYWORDS: Failure study, damages of reinforced concrete buildings, type of failures, poor quality of concrete, crushing of concrete. ----------------------------------------------------------------------------------------------------------------------------- ---------Date of Submission: Date, 15 April 2017 Date of Accepted: 23 April 2018 --------------------------------------------------------------------------------------------------------------------------------------I. INTRODUCTION Nepal lies in earthquake prone zone. There are different fault zones in Nepal. They are Main Frontal Trust(MFT), the Main Boundary Trust(MBT), Main Central Thrust(MCT) and South Tibet Detachment (STD). The MFT lies in southern part of main Himalayas. The border between outer and lesser Himalaya; and lesser and higher Himalayas are known as MBT and MCT respectively. The south Tibetan detachment (STD) lies between the higher and Tethys Himalayas. Due to these because Nepal is always vulnerable in earthquake disaster. Active fault of in this region causes several earthquakes in Nepal which were reported in 1255, 1810, 1866, 1934, 1980 and 1998(Pandey 1995)1. In the earthquake of 1934(great Bihar-Nepal Earthquake) with the maximum intensity of X (Rana 1935)2, caused intensive damage in eastern part of Nepal. It was recorded 8500 deaths. In the earthquake of August 21, 1988, with the magnitude of 6.6, shaken eastern part of Nepal and killed 721 people, injured 6553 people. It was recorded that damaged or collapsed buildings were 66,541(Thapa, 1998)3. In the recent, an earthquake of M7.8 occurred in 77 km NW of Kathmandu (in the boarder of Gorkha and Lampung) at 11:56 on 25 April 2015 with shallow depth of 15 km with maximum Mercalli Intensity of IX, lasting approximately thirty seconds. Nepal faced continued aftershocks throughout the country at the intervals of 15–20 minutes, with one shock reaching a magnitude of 6.7 on 26 April at 12:54:08. According to the USGS, the temblor was caused by a sudden thrust, or release of built-up stress, along the major fault line where the Indian Plate is slowly diving underneath the Eurasian Plate4.
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Failure Study of Reinforced Concrete Buildings of Kathmandu… Kathmandu, situated on a block of crust approximately 120 km (74 miles) wide and 60 km (37 miles) long, reportedly shifted 3 m (10 ft) to the south in a matter of just 30 seconds. 5 And another major earthquake of 7.3 (as per USGS report) occurred in 18 km south-east of Kodari and epicenter is in boarder of Dolkha and Sindhu pal chowk district at 12.51 on 12 May 2015. Hundreds of thousands of people were made homeless with entire villages flattened in Dolakha, Sindhupalchowk. Severely affected is in Kathmandu valley and across many districts of the country. It was recorded that officially 8,857 and in total 8964 people dead and 21,952 injured 6 . Mainly very old buildings were destroyed at UNESCO world heritage sites in the Kathmandu Valley including some at the Bhaktapur Durbar Square, the Kathmandu Durbar Square, the Patan Durbar Square, the Changu Narayan Temple and the Swayabhunath Stupa.
II.
SCOPE OF THE WORK
Most of the old masonry buildings, which were not constructed properly were damaged severely. It can be seen number of reinforced concrete buildings which are damaged in different places of Kathmandu valley. The buildings are damaged in different level. This article is concentrated to study of damages of reinforced concrete buildings only which are in Kathmandu valley in Gorkha Earthquake 2015. Effect of earthquake in reinforced concrete frame structures in Kathmandu valley are considered. Height of buildings is taken from two storied to ten storied. Types of Failures of Reinforced Concrete Structures: There are several types of failure of reinforced concrete frame structures. Building might be failed in different ways. For example, failure of foundation, column, beam, column beam joint, staircase, slab, infill wall. Building might fail due to weak story, soft story also. Certain buildings may collapse fully due to different causes. Observations and Causes of Structural Failures 4.1. Tilting of Building: Certain buildings which are not collapsed, not damaged but tilted which are shown in fig 1.1. Buildings are tilted due to soil settlement (fig 1.1a). Even though this building is not damaged and tilting but it can be used. Another type of buildings which are tilted due to soft soil of foundation and slender buildings (fig 1.1b and fig 1.1c). These can be used with certain rectification. Building shown in fig 1.1d, is tilted due very weak soil of foundation and unequal settlement of soil. This building cannot be used and needs dismantling. Fully Collapsed Buildings: Fully collapses of buildings are shown in fig 1.2. Most of the collapsed buildings are not structurally designed. Some of them are not properly designed. Sections of columns are smaller than required. Longitudinal and transverse reinforcements seem less than needed. It is seen that certain buildings were constructed in poor quality of concrete. Sandwich Type Failure of Buildings: Sandwich type failure of reinforced concrete frame structure occurs when columns of building are weaker than beams. It means “Weak column –strong beam”. Four storied departmental stores were collapsed due to heavy beam and slab but weak columns (fig 1.3a). Building has less infill wall using for shopping area in ground and first floor, bank in second floor and residence for top floor. Load in roof was increased due to gardening with soil layer. Another building in Sisupala (fig 1.3b) was being used as shopping area in ground floor and residence in upper floors, also collapsed in sandwich type (fig 1.3b) Soft Story Failure of Buildings: Soft storied failure occurs when ground floor is weak stiffness with respect to lateral stiffness of above stories. Buildings are classified as having a "soft story" if that level is less than 70% as stiff as the floor immediately above it, or less than 80% as stiff as the average stiffness of the three floors above it. This type of failure occurs where ground floor is being used for parking, shopping and open hall without considerable shear walls and infill walls. Some of the soft story failures of buildings are shown in fig 1.4. Residence building with shopping purpose in ground floor failed in ground level which is shown in fig 1.4a. Ground floor weakens due to open area for shopping purpose. In fig 1.4b it is shown weak floor of ground due to weak stiffness in ground floor and due to it building failed. Another example of soft story failure of store building in ground floor near Propmaker building in Kathmandu is shown in fig 1.4c. Similar type of failure is occurred in building of Gongobu shown in fig 1,4d.
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌ Column Failures Crushing of concrete failure of column: Crushing of concrete of column occurs when column is subjected heavy dynamic axil load as well as lateral loads. It might happen due to weakness of column in terms of concrete grades and not enough reinforcements. Some examples of column failure in crushing of concrete are shown in fig 1.5. Column failed due to more slenderness and low quality of concrete of the building of Lubhu is shown in fig 1.5a. Due the heavy load of five storied building load, failure of corner column in residence building near Kalanki is shown in fig1.5b. Failure of columns in heavy load of six storied building are shown in fig 1.5c and fig 1.5d. Similarly, column of four storied residence building in Gongabu is given in fig 1.5e. Six storied office building columns fail due to heavy dynamic vertical load, which is given in fig 1.5f. Shear and bending failure of columns: Due to small size column and less shear reinforcement in buildings, shear failure of columns occurs. Some pictures of shear failure of columns are shown in fig 1.6. It is seen that most of the building columns have not enough resistance for shear. In fig 1.6a shows the crack of column due to excessive shear force and bending moment in bottom columns. And in fig 1.6b, shear failure at mid height of column near the place of opening. In fig 1.6c and 1.6d, it is shown the failure of columns where building works as soft story. Shear Failure of Beams and Beam-Column Joint Failure: Shear failure of beam is shown in fig 1.7a. It happens when either concrete section is not enough or shear reinforcements are not sufficient. In the fig 1.7b, it is seen that the beam column joint failure occurs due to poor quality of concrete. Failure due to Reinforcement Deficiency: Buildings that were not designed properly, deficiencies of longitudinal and transverse reinforcement are observed. In addition to that, detailing of reinforcements is not correct. Fig 1.8a shows the less longitudinal reinforcements as well as transverse reinforcement. In fig 1.8b also, it can be seen that less number of reinforcements in longitudinal and transverse direction for four storied building loads. The spacing of transverse reinforcements is more than 150 mm which is the one of the main cause of column failure. Poor Quality of Concrete: Most of the buildings, which are damaged, not because of only design problem, reinforcing detailing problems but also due to inferior quality of concrete. Concrete strength is not good enough; vibration of concrete is not done properly. Some poor quality of concrete of school buildings of Chabahil, Kathmandu are shown in the fig 1.9 Infill Wall Failure: It is observed that there are lot of infill wall failure in most of the reinforced concrete buildings due to earthquake. Some pictures of infill wall failure are shown in fig 1.10. The causes of infill wall failure are no concrete band in infill masonry wall and no connection of wall with columns. Others: There are other several causes of failure of building. Some of the building failed due to irregular shape of it, that means architectural planning problem. Some of the building fails due to the construction in sloppy ground area. In the sloppy land, foundations are laid in different level and some of them are in infill soil, so due to unequal settlement of building, it damaged. In most of the cases, soil exploration is not done. Staircase of some of the buildings is damaged due to long span of staircase and not enough thickness of staircase waste slab. Some of the building failed due to ponding effect.
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
b)
d)
Fig 1.1. Tilting of buildings: a) Residence building in Kaushal tar, Bhaktapur; b) Residence building in Sitapaila outside ring road; c) Residence building in Byasi, Bhaktapur; d) Residence building in Panipokhari, Kathmandu (Photo Source: Rajan Suwal)
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
b)
d)
e)
f)
g) h) Fig 1.2. Collapses of buildings: a) Residence building in Duwakot, Bhaktapur; b) College building in Tokha road, Kathmandu; c) Residence building in Kuleshov, Kathmandu; d) Church and school buildings) in Sitapaila, Kathmandu e) Residence building in Tripureswor, Kathmandu; f) Residence building in Khusibu, Bishnumati, Kathmandu; g) Residence building in Jagati, Bhaktapur; h) Shopping building in Sanobh aryang, Shwoyambhu, Kathmandu (Photo Source: Rajan Suwal)
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
Fig 1.3. Sandwich type failure of buildings: a) Departmental store in Sanobharyang, Swoyambhu, Kathmandu; b) Residence building in Sitapaila (near Chetan Marg), Kathmandu; (Photo Source: Rajan Suwal)
a)
b)
Fig 1.4. Soft story failure of buildings: a) Residence with shopping in ground floor in Sitapaila chowk, Kathmandu; b) TU VC office building in Kirtipur, Kathmandu c) Residence building with store and shopping in ground floor near Paropakar (Lhuhiti), Kathmandu; d) Residence building with shopping shutter in ground, Mitranagar Marg, Gongabu, Kathmandu (Photo Source: Rajan
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
c)
Fig 1.5. Crushing of columns of buildings: a) Residence building in Lubhu, Lalitpur; b) Residence building near Kalanki Chowk, Kathmandu; c) Press building in Kuleswor, Kathmandu; d) Press building in Kuleswor, Kathmandu; e) Residence building in Mitranagar Marg, Gongabu, Kathmandu; f) Office building in Balkhu, Kathmandu (Photo Source: Rajan Suwal)
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
b) d) Fig 1.6. Shear failure of columns: a) Office building in Balkhu, Kathmandu; b) Residence building in Swoyambhu, Kathmandu; c) and d) Residence building in Lazimpat, Kathmandu (Photo Source: Rajan Suwal)
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
Fig 1.7. Failure of beam and beam-column joint failure: a) Shear failure of beam of school in Panchakumari near Sitapaila, outside of ring road, Kathmandu; b) Beam-column joint failure of school building in Panchakumari, Sitapaila outside Kathmandu (Photo Source: Rajan Suwal)
Fig 1 .8. Failure of column due to deficiency of longitudinal and transverse reinforcements: a) Residence building near Sitapaila, outside ring road, Kathmandu; b) School building in Chabahil, Kathmandu (Photo Source: Rajan Suwal)
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
a)
b)
Fig 1.9: Failure due to low quality of concrete a) Tie beam -column joint of school building in Chabahil, Kathmandu, b), c) and d) Column failure in different height due to poor quality of concrete of school building in Chabahil, Kathmandu.
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Failure Study of Reinforced Concrete Buildings of Kathmandu‌
Fig 1.10: Infill wall failure a) Residence building in Swoyambhu; b) Residence building in outside Sitapaila, Kathmandu.
III.
CONCLUSION AND LESSON LEARNT
In the Gorkha Earthquake 2015, reinforced concrete buildings of Kathmandu valley failed due to the major following causes. Some of them are as follows: a) b) c) d) e)
Soil exploration in building site is not done in most of the failed building area so foundation failure in excessive settlement and tilting are observed. Configuration of buildings are not regular due to it, different type of failures of elements of building are observed. Lack of structural design and done not proper structural analysis and design. Lack of reinforcement detailing in building elements. Poor quality of construction material and lack of quality control.
So, it is recommended that in the stage of soil exploration, planning, design and supervision of buildings, building norms should be strictly fulfilled. Technical expertise should be used in all process of work.
REFERENCES: 1. 2. 3. 4. 5. 6. 7.
Pandey MR, Tandukar RP, Avouac JP, Lave J, Massot JP (1995) Inter seismic strain on the Himalayan crustal ramp (Nepal). Geophys Res Lett 22(7):751–754 Rana BJB (1935) Nepal ko Maha Bhukampa (Great earthquake of Nepal). Jorganesh Kathmandu Thapa N (1988) Bhadau Panch Ko Bhukampa (in Nepali). Central Disaster Relief Nepal Howard, Brian Clark (25 April 2015). "Nepal Earthquake Strikes One of Earth's Most Areas". National Geographic. Retrieved 27 April 2015. Joel Achenbach (27 April 2015). "Kathmandu shifts three metres in 30 seconds". Sydney Herald (Washington Post). Retrieved 28 April 2015. http://www.thehindu.com/news/international/over-250000-buildings-damaged-in-nepalquake/article7161808.ece https://en.wikipedia.org/wiki/April_2015_Nepal_earthquake
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accumulation Press, Committee, Quake-Prone Morning
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