Abstract

Understanding earthquakes and its prediction is most challenging tasks. Even though the earthquakes have been understood clearly, the prediction of earthquakes would take more time to come into reality. For this, collection of earthquake data and its interpretation plays a vital role. Its importance continues for few more decades in understanding the various aspects of earth structure and tectonic plate interactions. India, the second largest populous country of the world has experienced and is continuing to experience both inter and intra plate earthquakes, claiming life loss as well as damage to built environment. Apart from earthquakes, India has also experienced Tsunamis in both the directions; eastern tsunamis from Sumatra and western tsunamis from Makran. In this paper using past earthquake data, Indian plate interactions with its neighboring major (Eurasia, Africa & Australia) and minor plates (Arabia, Burmese & Sunda plate) have been understood. Upon clearly observing seven interactions, it is clear that interaction types, their lengths and thickness of plate play a great role in the occurrence of major to great earthquakes.

Abstract

Most seismic design codes allow structure to be designed for lesser force than elastic force, thus allowing structure to damage at appropriate locations. Indian seismic code IS 1893-2002 divides seismic design of structures into three categories; Ordinary moment resisting frame, Intermediate moment resisting frame and Special moment resisting frame. The classification differs based on reinforcement detailing and response reduction factor. It is expected that the performance of ductile detailed building would be better than non ductile detailed building and the capacity shall be more and damage is less compared to non ductile detailed building. This paper compares the performance of structure designed considering non ductile detailing and ductile detailing, in terms of capacity, damage, response reduction factor and drift. As a case study, a 5 storey building designed for Gravity loads as well as lateral load as per IS: 1893-2002 for seismic zone III is considered. Static Non Linear (Pushover) analysis and fragility analysis are performed for estimation of post damage yielding behavior of structure. The change in non linear behaviour of structure based on assumed load patterns in pushover analysis is done. This paper also provides other important conclusions on seismic design provisions, response reduction factor and interstorey drift.

Abstract

The Chi-Chi earthquake (M7.6) was triggered on 20th September 1999 at 17:47:12 UTC in Chi-Chi, Taiwan. This was the largest inland earthquake occurred in Taiwan region. Chelungpu fault was the main cause for this earthquake and the fault was ruptured over 100 km. The ground motions were recorded at more than 600 stations. This study presents simulation of near field ground motions of 1999 Chi-Chi earthquake. For this purpose, 3 stations on foot wall side and 7 stations on hanging wall side are selected to generate ground motions using semi-empirical approach. The ground motion characteristics of the earthquake are calculated at 10 stations. It is found that the distribution of peak ground acceleration (PGA) obtained from semi-empirical approach, similar to real PGA distribution. Higher frequencies of simulated ground motions match with frequencies of real ground motions.

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 in the near-field areas. Landers earthquake (1992 – Mw 7.3), Northridge earthquake (1994 – Mw 6.7), Hyogoken-Nanbu earthquake (1994 – Mw 6.8) and few more earthquake events caused damage due to near-field effects. Notable damage to Koyna dam due to Koyna earthquake (1967 – Mw 6.5), India and Shih-Kang DamdueChi-Chi earthquake (1999 – MW 7.6), Taiwan proved earthquakes and near-field effects 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 earthquake in near-field areas. In this concern, a proper study on behaviour of concrete gravity dam subjected to near-field ground motions should be performed. In the proposed study, a concrete gravity dam is selected from the National Importance Dams of India (NRLD-2009) and numerically modeled using Applied Element Method (AEM). Fault normal and fault parallel components of 5 near-field ground motion are considered as input. The behaviour of dam subjected to near-field ground motions is then studied by understanding the displacement response, and stress distribution on upstream and downstream side of the dam body.

Abstract

Understanding the mechanism behind the tectonic plates in collision area, which may propagate into the subduction-collision transition zone is of great interest. At the locations of high-pressure metamorphism, some places form huge crustal deformations like between Indian-Eurasian plates, and subduction at other places like Indian-Burmese plates. In either of the cases deformation is a continuous, dynamic process. To understand the process, a study has been carried out using two dimensional finite element modeling. With the availability of computing technology (Parallelization), advanced numerical models (FEM, XFEM) and material models (Elastic, Visco-elastic), it would be an easy task to know the parameters effecting the transition from collision to subduction process between different tectonic plates. In this paper, Arc-collision model is used to study subduction-collision transition zone. Visco-elastic material rheology is considered for all the tectonic plates. Effect of parameters such as geometry of plates, friction at the interface, length of the plates and type of loading are studied.

Abstract

Seismic resistant design philosophy incorporates the non linear response of the structure by using appropriate Response reduction factor (R). The value of R is directly related to the ductility level provided in the structure. Greater the assumed value of R, grater will be the ductility in the structure. The non linear response of structure will be more than the linear response because of material non linearity, factor of safety in load combinations, structural redundancy and ductility. Use of higher values of R is encouraged because of significant reduction in base shear leading to more economic structure. Value of R for reinforced concrete structure depends on the type of framing system. Proposed IS 1893 draft classifies framing into three categories i.e. 1) Ordinary Moment Resisting Frame (OMRF), 2) Intermediate Moment Resisting Frame (IMRF), and 3) Special Moment Resisting Frame (SMRF). In the paper, study is done to compute the value of R, component wise of a G+4 storey building designed for all seismic zones, considering ductile and non ductile design provisions and the same is compared with the assumed R to check the safety of the structures. R provided is computed from the obtained pushover curves.

Abstract

Past response analyses of structures under earthquake excitations revealed that both the maximum displacement and the number of inelastic excursions cause higher damage to the structure. However, it is observed that the quantification of damage is a difficult task. In the paper, a new methodology is proposed for the quantification of damage of reinforced concrete framed structure. This method is based on the nonlinear energy dissipated by the structure along the complete displacement path. Three methods have been proposed to assess the global damage state of the structure, for any deformation level. In these proposed methods, the damage index is expressed as the ratio of nonlinear dissipated energy at an instant, to the total non-linear energy capacity of the structure. To calculate the energy, pushover curve is plotted between base shear versus displacement at C.G of external force profile, which provides consistent meaning for work done by external forces. The area under the curve represents the energy dissipated by the structure. To illustrate the proposed concept, two cases i.e., G+5 and G+9 story structures have been considered. Keywords: Pushover analysis, expended energy, total energy, damage index.

Abstract

Reconnaissance reports of past earthquakes states that the open ground storey is one the most common problems, causing severe damage in the structural members of ground storey. In majority of the buildings, it was observed that even after proper ductile detailing, there is severe damage to the structure. This is mainly attributed to the presence soft storey. In this paper, a study is carried out to improve the seismic performance of a 5 storey open ground floor building with ductile detailing. The seismic performance is improved by: (a) providing wall infill in some portion, (b) increasing the moment carrying capacity of ground storey columns, and (c) combinations of the above two. The proposed methods can be used for new structures by incorporating the effect in design philosophy or can be implemented in the strengthening of existing structures. The performance of the structure is determined with the help of Non Linear Pushover analysis. The main parameters investigated are interstorey drift and lateral displacement. The study shows, with increase in design moments as per seismic codes for the columns having open ground storey will not improve the performance of the structure significantly. Also the open ground storey columns are severely damaged making their repairing difficult and costly. It is suggested that seismic performance of the structure can be improved more significantly by combination of constructing wall infill and higher design moments in columns; if damage occurs in wall only, it can be reconstructed and structure can be repaired easily. Keywords: Open ground storey, pushover analysis, retrofitting, design provision

Abstract

The use of unreinforced brick masonry as infill material in reinforced concrete frames is inevitable even in higher seismic zone areas. With increasing demands for architectural features in buildings, the provision of soft storey is a common practice in many multi storeyed structures throughout the world, for parking. The standard code of practice in many countries suggests higher design forces for the columns present in the soft storey. In order to understand the affect of increase in design seismic forces on the columns in a structure present in higher seismic zone areas, a study is carried out by taking pushover analysis as a tool for obtaining capacity of the structure. A comparative study between three types of arrangements; type I: structure with infill walls in all floors, type II: structure with open ground storey, type III: structure with open ground storey and columns designed for increased forces. It is observed that there is an increase in maximum load carrying capacity for the type III structure as compared to type II structure with no considerable change in behaviour of the two types of structures. It can be concluded that the increase in design forces of the columns at open ground storey may not lead to the safety as of structure type I. Keywords: Unreinforced brick masonry (URM), multi storeyed structures, higher seismic zone areas, soft storey, pushover analysis

Abstract

According to current seismic zone map around 60% of India’s land area is prone to moderate to severe earthquakes. And earthquake losses, in terms of life and property in last 2 decades have been high, with housing contributing to over 95% of life loss; this failure attributed to improper design and construction practices of housing.Thus, all the three factors influencing earthquake risk of houses in India are above danger levels in many districts of India – hazard, exposure and vulnerability. This paper classifies housing risk in the entire country into four groups; about 47% of population is living in the highest risk. Gigantic effort is required to mitigate the risk. The paper also suggests some steps to move forward to reduce earthquake risk to housing in India.