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).

Abstract

Abstract: Pipeline generally extends over long distances traversing through wide variety of different soils, geological conditions and regions with different seismicity. Most analytical models developed in the past for pipeline fault crossing are of limited usage as models developed were useful only for strike slip fault. Incorporating the large geometric changes in analytical study is a tricky task; however pipeline subjected to the fault motion itself is a phenomenon of large geometric changes, especially when pipeline subjected to compression in addition to material deformation, it also undergoes local buckling with bending. With computational advancement in numerical modelling, pipes under compression can also be studied. In this paper, a 3D FE-based numerical model is suggested to carry out pipeline performance of buried pipeline subjected to fault motion including material non-linearity and large geometric deformations. A 3D FE programme is developed using MATLAB. Displacement controlled arc-length technique is implemented to solve the non-linear behaviour.

Abstract

Recent earthquakes, 18 Sep 2011, Sikkim earthquake, M6.9 and 1 May 2013 Doda earthquake, M5.8 produced two major effects, namely on buildings and on hill slopes. The maximum intensity of ground shaking experienced during these earthquakes was only about VI or less on the MSK scale. Considering the low intensity of ground shaking inthe affected areas, the damage attributed was disproportionately higher. It ismainly due to high amplification in local site areas. In this regard, a research is carried out to understand the performance of buildings on hill slopes. In this paper, the study of the behavior of a G+3 building on varying slope angles i.e., 15°, 30°, 45°and 60° is studied and compared with the same on the flat ground. Building is designed as per IS 456 and later subjected to earthquake loads. It was observed that as the slope angle is increasing, building is becoming stiffer. Two types of analyses were conducted viz., lateral load analysis and incremental dynamic analysis. It was observed from the initial results that the columns on the higher side of the slope i.e., short columns were subjected to more shear force then longer columns on the lower side. Finite element method is used to study the static behavior where as Applied Element Method (AEM) is used to perform incremental dynamic analysis.

Abstract

Recorded large earthquake show that different sigment may reputre at different velocities.