Hemant B. Kaushik

Code Approaches to Seismic Design of Masonry-Infilled Reinforced Concrete Frames: A State-of-the-Art Review

Masonry infill (MI) walls are remarkable in increasing the initial stiffness of reinforced concrete (RC) frames, and being the stiffer component, attract most of the lateral seismic shear forces on buildings, thereby reducing the demand on the RC frame members. However, behavior of MI is difficult to predict because of significant variations in material properties and because of failure modes that are brittle in nature. As a result, MI walls have often been treated as nonstructural elements in buildings, and their effects are not included in the analysis and design procedure. However, experience shows that MI may have significant positive or negative effects on the global behavior of buildings and, therefore, should be addressed appropriately. Various national codes differ greatly in the manner effects of MI are to be considered in the design process from aseismic performance point of view. This paper reviews and compares analysis and design provisions related to MI-RC frames in seismic design codes of 16 countries and identifies important issues that should be addressed by a typical model code.

Landscape Changes in the Andaman and Nicobar Islands (India) after the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami

Lifeline systems in the Andaman and Nicobar islands performed poorly during the December 2004 Great Sumatra earthquake and tsunami. Several power stations and transmission lines were damaged by the ground shaking, affecting the electric power supply to parts of the islands. Telecommunication services were severely affected because of destruction of several telephone exchanges. These services were restored quickly by government agencies. The dams and reservoirs, which supply potable water, sustained minor damage from ground shaking. However, segmented pipelines connecting the dams and reservoirs to various storage sites broke at several places, which significantly affected the water supply for a few days. Ground shaking damaged several elevated as well as ground-supported storage tanks. Damage related to tsunami waves was substantial in the 500–1,000-m strip immediately next to the coastline.

Masonry Infill RC Frames with Openings: Review of In-plane Lateral Load Behaviour and Modeling Approaches

Un-reinforced masonry walls are commonly used as infills in reinforced concrete (RC) buildings. These build- ings have high in-plane stiffness and strength, and therefore, the lateral load behaviour of such RC frames is different than that of the frames without infill walls. Openings in walls significantly reduce the lateral strength and stiffness of RC frames, and alter their failure modes. Past researchers have tried to find out experimentally and analytically the influence of several parameters, like opening size and location, aspect ratio of openings, connection between frame and infill wall, ductile detailing in frame members, material properties, failure modes, etc. on behavior of masonry infill RC frames. Ac- cordingly, several analytical models have been proposed in the literature and seismic codes of some countries to model the stiffness and strength properties of infill walls. Most of the past studies and seismic codes recommend modeling the infills as equivalent diagonal struts, and cross-sectional area of the struts are reduced appropriately to account for openings in the walls. Analytical methods have also been proposed to estimate the possible mode of failure and lateral load carrying ca- pacity of infill frames with and without openings. The current article is intended to review and compare past relevant stud- ies and seismic codes of different countries on in-plane lateral load behaviour and modeling approaches for masonry infill RC frames with openings. The comparative study may help designers and code developers in selecting and recommending suitable analytical models for estimating strength, stiffness, failure modes, and other properties of infill RC frames with openings.

Performance of Structures in the Andaman and Nicobar Islands (India) during the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami

The damage sustained by buildings and structures in the Andaman and Nicobar islands area was due to earthquake shaking and/or giant tsunami waves. While damage on Little Andaman Island and all the Nicobar Islands was predominantly tsunami-related, damage on islands north of Little Andaman Island was primarily due to earthquake shaking even though tsunami waves and high tides were also a concern. In general, the building stock consists of a large number of traditional and non-engineered structures. Many traditional structures are made of wood, and they performed well under the intensity-VII earthquake shaking sustained along the islands. However, a number of new reinforced concrete (RC) structures suffered severe damage or even collapse. Also, extensive damage occurred to the coastal and harbor structures in the Andaman and Nicobar islands.

Evaluation of Nonlinear Material Properties of Fly Ash Brick Masonry under Compression and Shear

AbstractThis paper reports nonlinear stress-strain characteristics and failure mechanisms of fly ash brick masonry and its constituents (fly ash brick units and mortar) obtained under compression and shear. Based on the experimental results, simple relations were proposed to evaluate the modulus of elasticity of fly ash brick masonry prisms in terms of the compressive strength of masonry prisms. Shear strength and shear modulus of masonry were evaluated by testing two different sizes of masonry wallettes, and a parametric study was carried out to evaluate the effect of the compressive strength of brick units, mortar cubes, and masonry prisms on the shear strength of masonry wallettes. The compressive strength of masonry prisms and fly ash brick units was found to be less than that of the mortar cubes. Fly ash bricks exhibited a very weak and soft nature in comparison with that of burnt clay bricks.

The Effect of the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami on Transportation Systems in India's Andaman and Nicobar Islands

Boats and ships are the major modes of transportation among the Andaman and Nicobar group of islands. The Andaman Trunk Road also forms an important part of the transportation system in the Andaman Islands north of Port Blair. The harbor structures in the islands were the most affected during the ground shaking; the result heavily disrupted the lives of the island residents. These transportation systems are expected to be in working condition after a major disaster, to facilitate the search and rescue operations and the relief work in the affected areas. A reconnaissance team surveyed the damage that the 2004 earthquake and tsunami caused to the transportation structures in the islands. Damage was observed in all transportation systems, including harbors, highways, airports, and hangars.

Assessment of Seismic Vulnerability of Structures in Sikkim, India, Based on Damage Observation during Two Recent Earthquakes

AbstractRecently, two earthquakes (MW=5.3 on February 14, 2006, and MW=6.9 on September 18, 2011) struck the mountainous region of Sikkim, one of the most seismically active regions in India. The 2006 event, though of lesser magnitude, clearly showed the high seismic vulnerability of different structures in Sikkim, especially in the state capital, Gangtok. Damage observed in buildings in and around Gangtok was disproportionately high during the 2006 event, considering the small size of the earthquake. It was expected and hoped that the 2006 event would act as a wake-up call to all stake holders in the society to improve the construction practices in the region. However, the bigger earthquake of 2011 not only affected the older structures but also severely damaged a large number of new structures. Comparison of observed damage with structures in Sikkim during these two earthquakes clearly demonstrates an alarming rise in seismic vulnerability of structures in Sikkim.

Seismic Fragility of Reinforced Concrete Frames with Vertical Irregularities

Seismic fragility functions are essential for performance-based seismic design of structures. It is a common practice in the past to consider global demand parameters, such as peak roof displacement or drift in a building to estimate its seismic fragility. However, such global demand parameters may not suffice in case of buildings with vertical irregularities, where maximum demand is mostly concentrated at the level of irregularity. To investigate the matter, reinforced concrete frames with and without vertical irregularity (soft storey) are considered in the current study. Nonlinear dynamic analysis of the frames subjected to ground motions scaled-up for different PGA is carried out to estimate the local and global drift demands, also known as engineering demand parameters (EDPs). Seismic fragilities developed for the frames based on both the local and global EDPs are presented. Finally, the importance of component-based fragilities for irregular frames is emphasized.

Component Level Fragility Estimation for Vertically Irregular Reinforced Concrete Frames

ABSTRACT Seismic fragility functions are essential for performance-based seismic design of structures. Global demand parameters, such as peak roof displacement or maximum drift over the height of the building, are commonly used to estimate seismic fragility. However, in case of buildings with vertical irregularities, the global demand parameters may not suffice since maximum demand in such building is mostly concentrated at the level of irregularity. The current study focuses on one of the most common forms of vertically irregular reinforced concrete (RC) buildings, known as open ground story buildings, where irregularity lies at the ground story. Nonlinear dynamic analyses of RC frames subjected to a number of ground motions, each scaled-up for different PGA, are carried out to estimate the component level and global drift demands, also known as engineering demand parameters (EDPs). Seismic fragilities developed for the frames based on both the component and global EDPs are presented. Finally, the importance of component-based fragilities for estimation of seismic fragility of irregular frames is emphasized. The component level EDP-based fragility is found to be effective in predicting the actual damage scenarios in such buildings observed during past earthquakes.

Non-linear Behavior of Weak Brick-Strong Mortar Masonry in Compression

Non-linear (stress-strain) properties of masonry form a pre-requisite in carrying out the non-linear analysis of structures. A detailed study on the non-linear behavior of strong burnt clay brick masonry was carried out by Kaushik et al. (J Mater Civ Eng 19:728–739, 2007), whereas non-linear stress-strain characteristics for weak brick-strong mortar was not available. To evaluate the same, fly ash bricks whose compressive strength was lesser than the strength of mortar were selected. Prisms with three different grades of mortar: strong (cement:sand 1:3), intermediate (1:4) and weak (1:6) were constructed to evaluate the non-linear behavior of weak brick-strong mortar, and to assess the influence of strength of mortar on masonry prisms. Specimens were instrumented with strain measuring instruments and tested under monotonic compressive loading using servo controlled hydraulic actuator. Stress-strain curves for weak brick-strong mortar masonry were plotted and the results were compared with strong brick-weak mortar masonry (Kaushik et al. J Mater Civ Eng 19:728–739, 2007). From the results, it was observed that strength of weak brick-strong mortar masonry was lower when compared to strong brick-weak mortar masonry, but the failure strain observed in case of weak brick-strong mortar masonry was significantly higher when compared to strong brick-weak mortar masonry.