Vaibhav Singhal

Reconnaissance of the effects of the M7.8 Gorkha (Nepal) earthquake of April 25, 2015

The M7.8 earthquake of 25th April, 2015 caused widespread damage in the Nepal region by destroying many residential, public, religious and cultural heritage buildings and roads due to intense shaking, surface fissures and landslides. This earthquake provided an opportunity to study the vulnerability of the built environment and reassessment of the risk exposure of the region. The reconnaissance trip was aimed at surveying the Kathmandu valley region in Nepal and adjoining districts of Bihar state in India due to their high population density and rapid urbanization. The observed damage in Kathmandu and the northern districts of Bihar were consistent with the intensity reported in these regions. Complete collapse was observed in RC buildings and old unreinforced masonry buildings due to inherent structural defects in regions of MM intensity VIII and IX. Significant number of cultural heritage structures suffered partial to complete collapse. These observations provide a perspective on the widespread lack of preparedness even when the seismic hazard of the Himalayan region is well established. This letter cites some of the poor construction practices that are followed in the Kathmandu valley region which make the built environment vulnerable to unacceptable levels of damage under expected design levels of shaking.

Suitability of Half-Scale Burnt Clay Bricks for Shake Table Tests on Masonry Walls

AbstractExperimental small-scale modeling of clay brick masonry for behavior up to failure under earthquake-type loads poses many challenges, such as manufacturing of small-scale bricks and creating masonry that not only meets necessary similitude laws but also accommodates the requirement of artificial mass for shake-table tests. In addition, the stress and modulus ratios should be unity for model and prototype masonry in all loading conditions. The suitability of the half-scale bricks, produced in the same manner as the prototype, was studied through several material tests on brick units and masonry assemblages. Tests for compressive strength, water absorption, and initial rate of absorption were conducted on brick units. Axial compression, shear, tension bond, flexure, and diagonal compression tests were performed on brick masonry assemblages. A reasonable agreement in strength and stiffness properties of model and prototype masonry was observed, despite the difference in compressive strengths of model...

Reconnaissance report of the M6.9 Sikkim (India–Nepal border) Earthquake of 18 September 2011

The M6.9 Sikkim Earthquake of 18 September 2011 caused widespread devastation in the state and adjoining areas from disrupting the road network to damaging structures of commercial, public, and religious values. This event presented another opportunity to further the understanding of 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. The general pattern of damage to structures, landslides, rockfalls, etc. was consistent with the shaking associated with this event. However, collapses of many buildings and damages to structures were disproportionate to the observed intensity of shaking, 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. The current event provides a preview of what is likely to happen in the event of a larger earthquake which the Himalayan region has witnessed in the past. This article discusses the construction practice in Sikkim Himalayas and their seismic performance in the recent earthquake, highlighting the vulnerability of inventories and suggests steps to mitigate the seismic risk for future events.

Role of Toothing on In-Plane and Out-of-Plane Behavior of Confined Masonry Walls

AbstractLoad-carrying capacity of confined masonry walls in the out-of-plane direction after being damaged is crucial for overall stability and is affected by the type of interface present at the wall edge and column, such as toothing. Shake table tests were conducted to investigate the effectiveness of a toothed connection on the out-of-plane behavior of damaged confined masonry walls. Four half-scale clay brick masonry walls were subjected to a sequence of slow cyclic in-plane drifts and shake table–generated ground motions in the out-of-plane direction. Specimens included one regular RC infill frame and three confined masonry panels, two with different densities of toothing and one with no toothed connection. The specimen with the infill panel demonstrated a higher risk of out-of-plane collapse, whereas the other three confined masonry wall specimens maintained structural integrity and out-of-plane stability even when severely damaged. The confined masonry walls with or without toothing enhanced the in...

Sub-Paneling of Masonry Walls Using Precast Reinforced Concrete Elements for Earthquake Resistance

Some traditional designs of masonry structures have shown acceptable structural performance during past earthquakes. In these structures, a grid of horizontal, vertical, and/or diagonal elements divide a large wall into smaller wall areas and provide confinement to masonry panels. In addition, grid elements provide a definite shearing plane along which masonry blocks can slide adding to deformability and energy-dissipation capacity. Inclined elements significantly add to lateral stiffness and strength depending on whether they can develop a complete truss action for lateral loads. Cyclic tests were conducted on five half-scaled wall specimens with different sub-paneling schemes using RC precast grid elements. Experimental results and finite element studies were used to develop simplified predictive relations for strength and stiffness response based on a confinement factor representing the grid element density. These relations can be used to configure the grid elements for desired performance levels with additional inputs about the global behavior.

Diagonal Shear and Out-of-Plane Flexural Strength of Fabric-Reinforced Cementitious Matrix–Strengthened Masonry Walletes

AbstractStrengthening of unreinforced masonry walls is essential to mitigate their brittle failure during natural hazards like earthquakes. An experimental program was conducted to evaluate the dia...

Behavior of Confined Masonry Walls with Openings under In-Plane and Out-of-Plane Loads

Six half-scaled wall panels were tested to investigate the effect of openings on their load-carrying capacity; these walls were subjected to a sequence of slow cyclic in-plane drifts and shake table–generated out-of-plane ground motions. Two specimens were masonry-infilled frames with and without openings. The other four specimens were confined-masonry (CM) walls, with one solid wall and three walls with openings bounded by reinforced-concrete (RC) confining elements on all sides. The infill walls demonstrated higher risk of out-of-plane collapse, whereas the CM walls maintained structural integrity and out-of-plane stability. The test results clearly indicate the necessity of confinement all around the openings for good seismic performance. The confining scheme with no continuous horizontal bands was ineffective in confining wall piers at large drifts, and piers remain vulnerable to out-of-plane collapse due to severe damage. However, the wall with continuous horizontal bands at the lintel and sill levels was not only able to compensate for deficiencies in strength due to the presence of openings, but also achieved a better overall behavior due to more distributed damage and greater ductility.