Investigation of Retrofitting Technique for RC School buildings in Nepal

Abstract

The Gorkha earthquake (25th April 2015) and its aftershocks had a significant impact on the education sector in Nepal. The earthquakes destroyed 3,552 schools in the 14 most affected districts. Large-scale structural integrity and damage assessment of school buildings were done on those heavily damaged districts. The need for rapid retrofitting activity for damaged School buildings in Nepal was felt. So, this investigation is done to get a Reliable Retrofitting technique for school buildings subjected to seismic action that were constructed following the “Type Design Model”. Therefore, the basic purpose of this investigation is to determine the Best Retrofitting Technique; carry out pushover analysis; develop the Strut modeling, determine the fragility Curve, and observe its results and parameters. Four- “Type Designed” School models are selected based on Aspect ratio, number of damaged schools, and number of floors. Non-destructive Test Data were used for the 3-D modeling and analysis for retrofitting. The FEM model method was used to observe the effect of Seismic forces on selected Building models. The models are analyzed using, Non-linear Static Pushover analysis, and the results obtained such as Base shear, displacement, Performance Point, etc. were used to develop the Fragility curve and to develop an equivalent diagonal Strut model for better result interpretation. Our investigation shows that failure in the selected building due to seismic action is mostly due to column failure. In most of our cases, Jacketing of the Column is sufficient to meet the demand of seismic Forces as per IS 15988:2013 code requirement. Combined use of Shear walls and Retrofitted columns were found to be Timeconsuming and un-practical. The introduction of the shear wall provided no significant contribution in reducing the number of columns to be retrofitted. So the use of a shear wall is taken out of the equation for this research purpose and Jacketing of Column and Beam (if required) is put forward as the best option for Retrofitting Selected School buildings.

The Gorkha earthquake (25th April 2015) and its aftershocks had a significant impact on the education sector in Nepal. The earthquakes destroyed 3,552 schools in the 14 most affected districts. Large-scale structural integrity and damage assessment of school buildings were done on those heavily damaged districts. The need for rapid retrofitting activity for damaged School buildings in Nepal was felt. So, this investigation is done to get a Reliable Retrofitting technique for school buildings subjected to seismic action that were constructed following the “Type Design Model”. Therefore, the basic purpose of this investigation is to determine the Best Retrofitting Technique; carry out pushover analysis; develop the Strut modeling, determine the fragility Curve, and observe its results and parameters. Four- “Type Designed” School models are selected based on Aspect ratio, number of damaged schools, and number of floors. Non-destructive Test Data were used for the 3-D modeling and analysis for retrofitting. The FEM model method was used to observe the effect of Seismic forces on selected Building models. The models are analyzed using, Non-linear Static Pushover analysis, and the results obtained such as Base shear, displacement, Performance Point, etc. were used to develop the Fragility curve and to develop an equivalent diagonal Strut model for better result interpretation. Our investigation shows that failure in the selected building due to seismic action is mostly due to column failure. In most of our cases, Jacketing of the Column is sufficient to meet the demand of seismic Forces as per IS 15988:2013 code requirement. Combined use of Shear walls and Retrofitted columns were found to be Timeconsuming and un-practical. The introduction of the shear wall provided no significant contribution in reducing the number of columns to be retrofitted. So the use of a shear wall is taken out of the equation for this research purpose and Jacketing of Column and Beam (if required) is put forward as the best option for Retrofitting Selected School buildings.