Authors’ info:

PRAKASH SITIKHU ,BE Civil Engineering, MSc. in Structural Engineering:sitikhup@gmail.com

BHARAT PRADHAN ,BE Civil Engineering, MSc. in Structural Engineering:bharat.pradhan@unipa.it

Abstract
Nepal is seismically active country. After the earthquake in 2015 (Mw 7.8), many buildings were damaged fully or partially and URM buildings were the most damaged type throughout the country. This article presents the damage prognosis of URM buildings in Nepal.

Key words: URM (Unreinforced Masonry), DG (Damaged Grade)

Introduction

After the earthquake, Nepal government conducted the survey of the damaged buildings in 31 districts. Out of the 876520 houses surveyed in 14 most affected districts, 92.6 percent (811,344) of the houses were damaged by the earthquake to some extent and only 7.4 percent (65,176) houses were found not damaged by the earthquake. Among the 176,428 houses surveyed in 17 districts, 96.4 percent (170,017) of the houses were found damaged by the earthquake to some extent and only 3.6 percent (6,411) houses were not damaged by the major earthquake. Figure 1 shows the districts hit by major earthquake, seven districts from mountainous region were severely affected. Figure 2 shows the type of buildings that were damaged by earthquake, masonry buildings were the highly affected ones.

This article presents the damage prognosis made for such URM building using the 3muri software. Damage prognosis indicates that the large number of buildings of this type are vulnerable in medium to large shaking earthquakes.

Case study of a Masonry Building

Seismic assessment of the numbers of URM buildings [1-2] were performed. An example of a building from Bhaktapur is kept here. The building has flexible floor system i.e. timber is used as structural member with mud compacted over it. The building is 4 storied with 40 cm thick wall on the ground floor, 40 cm exterior and 20 cm interior walls on the other floors. The schematic drawing of the building is shown in the figure 3. The building was constructed in 1960.

Nonlinear analysis of the building was performed in 3Muri.The material properties for the masonry structure and timber are shown in table 1. Soil type C was taken for the analysis according to EC8 as the building was from Kathmandu Valley. The buildings were subjected with the peak ground acceleration of around 160 cm/s². The non linear pushover analysis of the building was performed taking into account the first mode equivalent frame model.

Building reached its maximum displacement of 38.35 mm at base shear value of 391.41 KN in X direction and ultimate displacement of 42.55 mm at 412.88 KN. European Macro-Seismic Scale (EMS) was used for the classification of damage grade of masonry structure. The outcome from the pushover analysis was compared in every step and appropriate damage grade was assigned. Following figure gives the clear view of the different level of damage grade attained with increasing displacement.

3muri shows the failure of different elements in the building. Bending damage was found in different piers and spandrel beam of the building with about damage grade 5 in the top floor sill and lintel. The damage level obtained was similar to the damage observed during the earthquake, the building failed in sill and lintels of the top floor

Conclusion

Nonlinear analysis on number of URM buildings of Nepal built in a traditional style shows that they are highly vulnerable in future earthquakes. Numerical tools can be helpful for understanding their structural behaviour for minimizing the losses during such impending disasters.

Note: This article is written based on the MSc. thesis of Prakash Sitikhu. Mr. Sitikhu is a graduate of structural engineering from Bauhaus University Weimar, Germany

1. Nepal, “Central Bureau of Statistics.” [Online]. Available: http://www.cbs.gov.np/. [Accessed: 12-Jun-2018].
2. Nepal – Household Registration for Housing Reconstruction Survey 2016-2017.” [Online]. Available: http://cbs.gov.np/nada/index.php/catalog/69. [Accessed: 11-Jun-2018].
3. H. R. Parajuli, “Determination of mechanical properties of the Kathmandu World Heritage brick masonry buildings,” in Proc. of the 15th World Conference on Earthquake Engineering, Lisboa, 2012.