Sekhar Chandra Dutta

Augmenting Strength of Collapsed Unreinforced Masonry Junctions: Principal Damage Feature of Walls Damaged by Moderate Indian Earthquakes

AbstractFrequently occurring moderate earthquakes in the Indian subcontinent have extensive impact on the nonengineered shelters of the local people inhabiting them because these shelters generally consist of unreinforced masonry walls. Through a reconnaissance-based damage survey of two such earthquakes in the Eastern Himalayas and that of another in the plains, the present paper identifies the absence of proper connections at masonry junctions as the principal cause of damage. To augment junction strength subjected to reversible lateral loading, the survey proposes reinforcing with L-shaped steel dowels or encasing with polypropylene bands, which incurs a minimal cost increase. The results from shaking table tests show that such measures may lead to a quantifiable increase in the lateral strength of the junctions, which helps in evolving empirical design guidelines at the artisanal level.

Investigating Compressive and Cleavage Strengths of an Indian Bamboo Species

AbstractDepleting timber resources has generated interest in bamboo, a traditional sustainable building material of the tropics. However, dearth of strength data has been a major hindrance in its engineered application. The present paper reports experimentally verified compressive and cleavage strengths of an Indian bamboo species that is considered suitable for structural applications. The investigated compressive strength is well comparable with that of equivalent timber. The paper reports lesser strength of split bamboo specimens than round ones, which contradicts the provisions of some codes. The paper also observes that compressive strength of bamboo generally increases along its culm length, gradually from bottom to top. The paper further identifies a factor, which when multiplied by the density of a given specimen, yields corresponding permissible compressive strength. Low values of coefficients of variation and skewness of the experimental data indicate its reliability. This paper may be considere...

Influence of dynamic soil-pile raft-structure interaction: an experimental approach

Traditionally seismic design of structures supported on piled raft foundation is performed by considering fixed base conditions, while the pile head is also considered to be fixed for the design of the pile foundation. Major drawback of this assumption is that it cannot capture soil-foundation-structure interaction due to flexibility of soil or the inertial interaction involving heavy foundation masses. Previous studies on this subject addressed mainly the intricacy in modelling of dynamic soil structure interaction (DSSI) but not the implication of such interaction on the distribution of forces at various elements of the pile foundation and supported structure. A recent numerical study by the authors showed significant change in response at different elements of the piled raft supported structure when DSSI effects are considered. The present study is a limited attempt in this direction, and it examines such observations through shake table tests. The effect of DSSI is examined by comparing dynamic responses from fixed base scaled down model structures and the overall systems. This study indicates the possibility of significant underestimation in design forces for both the column and pile if designed under fixed base assumption. Such underestimation in the design forces may have serious implication in the design of a foundation or structural element.

Strongest cyclone of the new millennium in the Bay of Bengal: strategy of RVS for nonengineered structures

Coastal areas of the Indian subcontinent are familiar with aftermaths of severe tropical cyclones. Nonengineered structures of the common people are major casualties of these natural disasters. The present paper documents features of damages due to the 2007 Cyclone Sidr, the strongest cyclone in the Bay of Bengal portion of the Indian Ocean in the new millennium. A critical analysis of the documented damages is followed by suggestions regarding the adoption of relevant remedial measures during future constructions in the coastal regions compatible with the socioeconomic situation. In the absence of any rapid visual screening (RVS) procedure for cyclones, the paper further discusses strategies for evolving RVS procedures for cyclone-affected nonengineered structures as part of a quick and easy vulnerability assessment. The application of the proposed RVS methodology, consisting of 11 visually identifiable parameters and basic scores for eight different types of nonengineered or semiengineered buildings, is cross-checked for two cases whose RVS scores strongly match those of the proposal.

Performance of Sidr Affected a Few Typical Non-engineered Buildings at the Ganges Delta

A tropical cyclone of velocity more than the Basic Wind Speed recommended by the Indian Wind Code, slammed the Bangladesh coast around 100km east of the Sagar Islands, India in the evening of 15th November 2007, affecting the lives of millions of people. The vulnerability of the Ganges Delta to large storm surges, due to its minimal topography was demonstrated after the passage of the Cyclone Sidr. Such devastations give one a rare scope to study their impact, especially on the non-engineered building elements, which constitute shelter for major segment of the population. This paper reports some of the major and prominent findings of two reconnaissance based vulnerability and damage surveys undertaken at the Sagar Islands, India and the Khulna and Barisal Divisions of Bangladesh.