Current Science

Durgesh C. Rai ¹, Vaibhav Singhal ¹, S. Bhushan Raj ¹, S. Lalit Sagar ¹

Affiliations
1 Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, IN

Abstract

The M 7.8 earthquake of 25 April 2015 was a significant event in the long seismic history of the Eastern Himalayas, which caused more than 8000 casualties; widespread destruction of residential, commercial and cultural heritage structures, surface fissures and landslides in the western and central regions of Nepal. It was followed by a strong aftershock of M 7.3 after 17 days of the main event which caused further damage. These events provided a unique opportunity to study the vulnerability of the built environment and reassess the risk exposure of the region which is undergoing rapid urbanization without adequate preparedness for seismic safety. A field trip was undertaken covering the affected regions of Nepal and adjoining Indian states of Uttar Pradesh and Bihar. This article discusses the general observations in the earthquake affected regions, with special emphasis on the seismic performance of residential structures in the Kathmandu valley region.

Keywords

Earthquake Effects, Reinforced Concrete Frame, Seismic Vulnerability, Unreinforced Masonry.

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Durgesh C. Rai ¹, Sudhir K. Jain ², C. V. R. Murty ³, Dipanshu Bansal ⁴

Affiliations
1 Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, IN
2 Indian Institute of Technology Gandhinagar, Ahmedabad 382 424, IN
3 Indian Institute of Technology Jodhpur, Jodhpur 342 011, IN
4 Department of Civil Engineering, State University of New York at Buffalo, US

Abstract

The earthquake simulation on full-scale civil engineering structures in a pseudo-dynamic testing facility provides an affordable and practical means to understand the seismic behaviour of structures as it provides accurate information about their real time response of inelastic behaviour up to failure. One such pseudo dynamic testing facility is nearing completion at IIT Kanpur, which has 15 m × 10 m L-shaped and 10.5 m high reaction wall and 1.2 m thick top slab of the box girder for the strong floor. The anchor points are located in the wall and floor in a square grid of 0.6 m with each point has load capacity of 1.7 MN in tension and 1.0 MN in shear. The 2 m thick posttensioned wall using Freyssinet 12K15 cable system in a novel configuration can resist an overturning moment of 12.7 MNm per metre of the wall. The capacity of the reaction assembly depends upon number of loads applied, combination of loads and interaction between different components of the reaction assembly structure. A methodology based on 'influence coefficients' was developed to estimate the worst load combination for describing load rating of the reaction structure. Finite element analyses in ABAQUS environment were conducted to compute the influence coefficients matrix whose elements can be added linearly to find out the maximum loading effect on the reaction structure which can be used to determine the limiting load for a particular case of load application.

Keywords

Pseudo-Dynamic Testing Facility, Reaction Wall, Seismic Behaviour, Load Rating.

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Durgesh C. Rai ¹, Vaibhav Singhal ², Tripti Pradhan ³, Anu Tripathi ⁴

Affiliations
1 Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, IN
2 Department of Civil and Environment Engineering, Indian Institute of Technology Patna, Bihta 801 103, IN
3 Mueser Rutledge Consulting Engineers, 14 Penn Plaza, 225 West 34th Street, 6th Floor, New York, NY 10122, US
4 Department of Civil, Environment, and Geo-Engineering, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, US

Abstract

Buddhist monasteries in the Sikkim region have conserved and portrayed the art of Tibetan and Chinese architectural style through centuries. These historic structures have sustained varied degrees of damage due to earlier earthquakes. Their performance in the recent Sikkim earthquake of M 6.9 on 18 September 2011 shows their high seismic vulnerability. A quick seismic assessment using certain simplified indices suggests higher vulnerability of damage for these heritage structures. A post-earthquake ambient vibration test established these monastery temples as shortperiod structures with fundamental period of 0.23 to 0.37 s. A finite element analysis of one of these temples has been done to study its dynamic behaviour. The response spectrum and static nonlinear pushover analysis highlighted vulnerable portions of stone masonry walls and provided useful insights for proper retrofitting to mitigate damage in future earthquakes.

Keywords

Ambient Vibration, Finite Element Analysis, Monasteries, Seismic Vulnerability, Stone Masonry.

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Durgesh C. Rai ¹, Hemant B. Kaushik ², Vaibhav Singhal ³

Affiliations
1 Department of Civil Engineering, IIT Kanpur, Kanpur 208 016, IN
2 Department of Civil Engineering, IIT Guwahati, Guwahati 781 039, IN
3 Department of Civil and Environmental Engineering, IIT Patna, Bihta 801 103, IN

Abstract

The M 6.7 Imphal Earthquake of 4 January 2016 caused devastation in Manipur state and adjoining areas. This event presented another opportunity to understand the earthquake risk of the affected region as well as of the North-Eastern Himalayan region, which have similar patterns of seismicity, built environment and construction practices. Many dramatic collapses and damages, especially to publicly-funded buildings were disproportionate to the observed intensity of shaking. This was primarily due to poor compliance with seismic codes, inferior quality of raw materials and shoddy workmanship. Consequently, the seismic risk in the region is growing at an alarming pace with increasing inventory of vulnerable construction. This article discusses seismic performance of three publicly-funded buildings in the recent earthquake and highlights the vulnerability of such inventories along with the below par preparedness of the government agencies in dealing with such calamities. This event should be regarded as a preview of what is likely to happen in the event of a greater shaking expected for the region and should hasten the community to take necessary steps to identify seismic vulnerabilities and improve construction practices through effective intervention.

Keywords

Earthquake Effects, Reinforced Concrete Frame, Seismic Vulnerability.

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