Abstract

This paper proposes a novel method of integrating planning with Monocular Simultaneous Localization and Mapping (SLAM) systems. Monocular SLAM, typically referred to as VSLAM systems in literature consists of recovering trajectory estimates of the camera and stationary world features from a single moving camera. Such VSLAM systems are significantly more difficult than SLAM performed with depth sensors, such as using an accurate Laser Range Finder (LRF). When the camera motion is subject to steep changes in orientation, tracked features over the previous instances are lost, making VSLAM estimates highly unreliable, erroneous that cannot be recovered. Most often a complete breakdown occurs, which entails a new sequence of images to be captured from a fresh camera trajectory. Herein we propose an optimization based path planning formulation for such VSLAM systems that reduces occurence of such errors through paths that are not subject to high orientation changes. Further we plan a velocity profile over the path that prevents features from getting significantly displaced over successive images, often considered a critical criteria for robust feature tracking. The velocity profile is computed using the novel concept of non linear time scaling proposed in our earlier work. The VSLAM system is also sufficiently innovated to provide for dense mapping over planar segments. The efficacy of the formulation is verified over real experiments on a camera mounted robot.

Abstract

Depth information has been shown to affect identification of visually salient regions in images. In this paper, we investigate the role of depth in saliency detection in the presence of (i) competing saliencies due to appearance,(ii) depth-induced blur and (iii) centre-bias. Having established through experiments that depth continues to be a significant contributor to saliency in the presence of these cues, we propose a 3D-saliency formulation that takes into account structural features of objects in an indoor setting to identify regions at salient depth levels. Computed 3D saliency is used in conjunction with 2D saliency models through non-linear regression using SVM to improve saliency maps. Experiments on benchmark datasets containing depth information show that the proposed fusion of 3D saliency with 2D saliency models results in an average improvement in ROC scores of about 9% over state-of-the-art 2D saliency models.

Abstract

Visual localization in crowded dynamic environments requires information about static and dynamic objects. This paper presents a robust method that learns the useful features from multiple runs in highly crowded urban environments. Useful features are identified as distinctive ones that are also reliable to extract in diverse imaging conditions. Relative importance of features is used to derive the weight for each feature. The popular Bag-of-words model is used for image retrieval and localization, where query image is the current view of the environment and database contains the visual experience from previous runs. Based on the reliability, features are augmented and eliminated over runs. This reduces the size of representation, and makes it more reliable in crowded scenes. We tested the proposed method on data sets collected from highly crowded Indian urban outdoor settings. Experiments have shown that with the help of a small subset (10%) of the detected features, we can reliably localize the camera. We achieve superior results in terms of localization accuracy even when more than 90% of the pixels are occluded or dynamic.

Abstract

Analysis and design of high-rise buildings for lateral load such as wind load and earthquake are the major issues which are playing significant role in recent decades. This paper describes a recent application of the computational fluid dynamics technique for wind analysis. Conventional wind analysis suggests wind tunnel experiment for arriving at the wind forces for a given structural form. As a case study a regular 38-story high-rise building (Jamieson place, Calgary Canada1) made of concrete with shear wall, built in downtown Calgary 2010 is selected. It is assumed that the building is located in highly seismic area. The design objective was to develop most cost-effective structural system while meeting building functionality goals and adhering to code requirement. The main structural design issues considered in this building are reviewed: Static analysis, Dynamic Analysis, Wind Analysis and Stability Analysis. Initial static and dynamic analysis is conducted in SAP and later wind analysis is conducted in Ansys as opposed to wind tunnel experiments. The building model is modeled in Ansys workbench and then the mesh file is imported to Ansys CFX for CFD simulation and analysis. After CFD analysis the wind forces on the building model are extracted in Ansys CFX-Post and imported to the structural model in SAP 2000 for the structural analysis.

Abstract

For the assessment of risk of any area three components are necessary viz., Hazard, Exposure and Vulnerability. While most of the times Exposure and Vulnerability are easy to obtain compared to Hazard. For Hazard estimation, real ground motions are required. However, in highly seismic areas with less number of recorded ground motions, artificial ground motions are quite helpful. The estimation of strong ground motion parameters for a particular region can be done either by analytical methods or by numerical methods. Present work illustrates a comparative study of real and artificial ground motion generated for Uttarkashi earthquake. Midorikawa technique is used for generating strong ground motions at different locations. Ground motions records are considered at 13 stations during Uttarkashi earthquake. The synthetic ground motions are compared with recorded accelerograms at stations. The results of the analyses with both artificial and real accelerograms were compared in terms of site-transfer function, acceleration response spectrum and several strong motion parameters.

Abstract

Lifeline structures like dams should always be designed for highest safety, resisting worst forces of nature. However, events that took place across the world proved how devastating an earthquake could be, particularly near-field. Landers (1992 – Mw 7.3), Northridge (1994 – Mw 6.7), Hyogoken-Nanbu (1995 – Mw 6.8) and few more events with near-field effects caused damage to different range of structures. Notable damage to Koyna dam due to Koyna earthquake (1967 – Mw 6.5), India and Shih-Kang dam due to Chi-Chi earthquake (1999 – MW 7.6), Taiwan, proved effects of near-field earthquakes can cause damage even to dams. In India there are several dams constructed near the active faults, which might suffer moderate to severe damage in an event of near-field earthquake. In this concern, a proper study should be done to understand the behavior of concrete gravity dam subjected to near-field earthquake caused by fault motion near the dam site. In the proposed study, a concrete gravity dam is selected from the National Importance Dams of India. Structure-1(S1) as a concrete gravity dam with foundation and structure-2 (S2) as a concrete gravity dam with foundation and soil strata are numerically modeled using Applied Element Method (AEM). Displacement is given at the base to generate reverse fault effect on the dam. Behavior of dam is studied by direct and sub-structure methods. In the direct method, the effect of fault motion on dam is studied in S2, by modeling dam at different locations on foot wall and hanging wall. In sub-structure method, free-field accelerations are recorded at different locations on foot wall and hanging wall while only the sub-structure is subjected to fault motion. The recorded accelerations on the surface are used as input to analyze super structure S1. Comparison is later drawn between S1 and S2.

Abstract

Recent ground-motion observations suggest that there is a considerable difference in surface-rupturing earthquakes and earthquakes due to buried faults. Near fault records for buried as well as surface fault earthquakes, in the distance range of less than 100 m from the faults are not available except for few cases. Therefore numerical simulation of ground motions for such near-fault situations for buried and surface fault earthquakes is necessary. In this paper the difference in ground motion due to buried faults and surface faults has been studied using 3D Applied Element Method. For the surface fault when the fault intersects the surface, a remarkable concentration of large ground acceleration in a very narrow region around the fault trace has been seen. The presence of the low velocity layer tends to reduce the particle velocity and rupture speed leading to the reduction in ground motion. The ground motion due to buried fault contains low frequency content there by giving greater response to long period structures. It has been seen that there is increase in peak ground acceleration value on the surface with the increase in the stiffness of the bedrock layer where the rupture takes place and increase in the strong ground motion with the decrease in the rise time of the slip applied at the base of the fault plane. This study explains some of the features of the buried fault earthquakes.

Abstract

The Indian Seismic Code IS: 1893-2007 indicates that about 60% of India’s land area is under threat of moderate to severe earthquake shaking. Also according to census 2011, number of houses exposed such high hazard is almost 80%. This is due to uneven population distribution. In order to find out the potential risk to housing for a city, it is necessary to evaluate Hazard (H), Exposure (E) and Vulnerability (V). Since, vulnerability of a building is combination of many factors like, planning, design, execution and maintenance; it is very difficult to assess the same for entire city. As a case study, a 3-storey RC framed building has been selected in the Union Territory of Chandigarh, which lies in high seismic area; and vulnerability of the same to nearby earthquakes is studied. Building vibration sensors (accelerometers) have been installed at appropriate locations on the building and data acquisition is done. In companion paper, data is acquired first by using micro-tremor observation system and later by using permanent sensors. In this paper, event accelerations recorded at the ground were normalized to earthquakes in zone IV and zone-V areas and response of the building is studied. Fragility curve has been developed for the building area.

Abstract

The Indian Seismic Code IS: 1893-2007 indicates that approximately 60% of India’s land area is under the threat of moderate to severe earthquake shaking. According to census 2011, number of houses exposed such high hazard is almost 80%. This is due to uneven population distribution. In order to find out the potential risk to housing in a city, it is necessary to evaluate Hazard (H), Exposure (E) and Vulnerability (V). Since, vulnerability of a building is a combination of many factors like, planning, design, execution and maintenance; it is very difficult to assess the same for entire city. As a case study, a 3-storey RC framed building, which lies in a highly seismic area, has been selected in the Union Territory of Chandigarh and its vulnerability to nearby earthquakes is studied. Building vibration sensors (accelerometers) have been installed at appropriate locations on the building and data acquisition has been done. In this paper, we present a comparison of Fourier amplitude spectrums generated from the data acquired using a micro-tremor observation system and permanent sensors. The companion paper presents a study of the response of the building to the acceleration data, recorded at ground, normalized to the earthquakes in zone IV. We then propose a potential risk model to the scenario earthquake by analyzing the fragility curve developed for the building area.

Abstract

The post earthquake study of the structures reveals that the interaction of soil and foundation plays a major role in the damage/response of structure. In this regard a literature survey has been done on Frame structures supported on various foundations like isolated footings, mat foundations, combined footings or pile foundations. Persual of literature reveals that very few investigations were done on frame structures supported on pile foundations. So in this paper, an attempt is made to implement the prominent investigations on soil structure interaction analysis of framed structures supported on pile foundations. It also covers the analytical methods to predict lateral deflections of pile foundations alone (single and Group piles).