Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Author: search.filters.author.Shreyasvi, C.

Search Results

Now showing 1 - 10 of 10
  • No Thumbnail Available
    Item
    Seismic Hazard Estimation for Southwest India
    (Springer, 2020) Shreyasvi, C.; Venkataramana, K.
    The objective of the study is to understand the seismicity of the Western coast and its adjoining regions whose seismic potential has not been evaluated so far. The study area encompasses a major portion of Karnataka and Northern part of Kerala and Goa. The approach incorporated in the study is probabilistic in nature and attempts to capture the uncertainty involved in various phases of hazard estimation. The seismic sources in the study region are mostly diffused in nature and are modeled as areal sources with uniform seismicity within a source zone. Regionally, adaptable ground motion prediction equation constitutes the ground motion modeling. The epistemic uncertainty involved in the selection of ground motion models is addressed by adopting a logic tree approach. The seismic source model and the ground motion model are combined together to produce hazard curves for the study region. Most of the ground motion prediction equations are developed for hard rock conditions (Vs > 800 ms−1). However, most of the built environment rests on the soil and there is a necessity to estimate the hazard values at the surface level. Based on the site topography, it was observed that majority of the study area belongs to NEHRP site class C and D. The hazard values were estimated for the boundary site condition CD (310 < VS (30) < 520 ms−1) using a nonlinear site amplification model. Seismic hazard maps produced from this study are believed to be of immense use for building planners and designers. © 2020, Springer Nature Singapore Pte Ltd.
  • No Thumbnail Available
    Item
    Influence of Variabilities of Input Parameters on Seismic Site Response Analysis
    (Springer, 2020) Shreyasvi, C.; Badira Rahmath, N.; Venkataramana, K.
    The seismic waves originating from an earthquake source undergoes significant amplification on its way toward the surface. The dynamic properties of the soil such as shear modulus/stiffness degradation and damping play a major role in amplifying the seismic waves. In the present study, two sample bore logs from Calicut have been taken for one-dimensional equivalent linear ground response studies. The bore logs represent clayey and sandy deposits and the shear wave velocity (Vs (30)) of these sites are in the range of 300–360 ms−1(NEHRP C). The uncertainty in the soil properties has been addressed by randomizing the soil profile using Monte Carlo simulation on STRATA. Similarly, the influence of the number of ground motions on the site response has been analyzed by considering different ground motion suites. The regional seismic hazard consistent ground motions have been considered for the analysis. The variation of Peak Ground Acceleration (PGA) along the depth of the soil profile is studied to understand the influence of local soil profile in modifying the wave properties. The influence of variability associated with the input parameters has been assessed through numerical experiments considering multiple numbers of realizations (Vs profile) and ground motions. The study reveals the variability associated with the ground motions to be high when compared to soil property. It can be concluded that the uncertainty in the input motion has a significant impact on the overall outcome of site response analysis. © 2020, Springer Nature Singapore Pte Ltd.
  • No Thumbnail Available
    Item
    Influence of tectonic regime in the selection of ground motions for seismic site response analysis
    (International Association for Earthquake Engineering, 2021) Shreyasvi, C.; Chopra, S.; Venkataramana, K.
    The common practice in seismic site response simulation is to use the ground motion records consistent with the tectonic regime. In other words, for sites located in a stable continental region, ground motions recorded in a region with the same tectonic setup is used in computing the site response. In the present study, an attempt has been made to test the applicability of different ground motions in the simulation of local site response for a stable continental region. The numerical study was performed by using 140 ground motions recorded in stable continental areas and 150 ground motions recorded in active areas. The earthquake events with magnitude in the range of MW 5-8 and distance 1-300km (active) and 1-500km (stable) were chosen. The magnitude range was further categorized into various magnitude bins with a variation of 0.5 and distance bins with a variation of 50km. The ground motions were selected in such a way that there exist at least 5-7 ground motions in each combination of the magnitude and the distance bin and recorded at a site with VS > 760ms-1. The soil profile was chosen from Gandhinagar, Gujarat, Western India, which is an intraplate region. The seismic site response of this site was studied in the form of predominant period and the amplification. The variation of these parameters in different scenarios was evaluated. The spectral amplification observed for ground motions from both the tectonic regimes has been compared. The results reveal that the predominant frequency of the soil deposit varies between 0.3-0.4s depending on the induced strain by the input motion. Also, the difference in the performance of the soil deposits to the ground motions is evident in the amplitude. Overall, the present study is an attempt to address the merits and demerits of using ground motions of the active tectonic regime in a stable continental region. © The 17th World Conference on Earthquake Engineering.
  • No Thumbnail Available
    Item
    Estimation of Local Site Effects in Indian Scenario: Lessons from Past Earthquakes, Current Practices, and Future Trends
    (Springer Science and Business Media Deutschland GmbH, 2022) Shreyasvi, C.; Venkataramana, K.
    The incorporation of local site effects in seismic hazard analysis has evolved radically over the last few decades. Initially, the whole site characterization was expressed by a single scalar quantity known as soil factor. The advancement in technology has paved the way for more sophisticated techniques in estimating the site response. The new-age techniques of site characterization involve field investigation as well as laboratory testing of the soil samples. The study sites are modeled in more than one dimension, and the complex phenomena of site response such as basin effects and resonance in a valley are computationally simulated. The present article outlines the state-of-the-art practices in characterizing site/soil response to tectonically induced ground shaking. The article briefs about the different methods and provides a detailed description of the computational methods for estimating the site response. The existing methodologies, their applicability, and pitfalls are presented. Additionally, the scope for future work and the direction toward improving the existing methods have been discussed. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
  • No Thumbnail Available
    Item
    Role of Uncertainties in Site Response Analysis and Their Incorporation in Seismic Hazard Workflow
    (Springer Science and Business Media Deutschland GmbH, 2023) Shreyasvi, C.; Venkataramana, K.
    The inherent randomness in the underlying geotechnical and geological formations makes its characterisation highly site-specific. While mapping the hazard at a larger scale, the site characteristics sampled at individual locations are collectively used to represent an entire region. Maps representing local geology, soil amplification, and hazard of a region are created through spatial interpolation of the site-specific estimates. Since the half-space is highly unpredictable, the estimates are probabilistic with a certain amount of uncertainty. This uncertainty can be partly modelled during the computation of site response while a fraction of it will remain as a standard error or deviation of the estimated values. The latter is known as aleatory uncertainty while the former is known as epistemic uncertainty. When the uncertainties are systematically partitioned and accounted for in the hazard integral, an ergodic approach (conventional PSHA with no site-specific information) transforms to a non-ergodic (completely site-specific) and partially non-ergodic approach (partially site-specific). The present article outlines the scope of a non-ergodic PSHA in the Indian scenario and the existing practices in capturing the uncertainties introduced by the site component. The authors believe that the article can provide insight towards improving the existing site-specific PSHA practices in the country. © 2023, Indian Society of Earthquake Technology.
  • No Thumbnail Available
    Item
    Nonlinear Soil Amplification Models for a Moderately Active Seismic Zone in India
    (Springer Science and Business Media Deutschland GmbH, 2021) Shreyasvi, C.; Venkataramana, K.
    The dynamic stiffness and damping of the soil material, depth of the soil profile, impedance between the soil and the underlying bedrock and soil nonlinearity are the factors influencing the local site response. The important parameter in assessing the site response is the “amplification factor,†which is usually correlated to Shear Wave velocity in the top 30 m (Vs(30)). Though using VS(30) as an index for amplification is simple and robust, it is not recommended for site-specific applications. In the present study, two distinct soil types i.e. “Sand†and “Clay†with the same value of VS(30) demonstrated variable amplification characteristics. Hence, distinct site amplification models were derived for the two soil types considering the intensity of the input bedrock motion as the primary independent variable. The borehole data from nearly 50 locations in North Kerala, an intraplate region in the Southern part of India was collected. The ground response was simulated in 1-dimension considering equivalent linear behavior of soils on the SHAKE 2000 platform. The ground motions used in the simulation were scaled to the target spectrum obtained from the regional seismic hazard assessment. The average spectral amplification observed is 5 for “Clay†and 3.5 for “Sand†in the study region. The soil profiles categorized as “sand†exhibits nonlinear behavior. “Clay†deposits reveal sustained amplification at longer periods and hence, can significantly influence ground response during longer duration ground shaking. The empirical amplification equations developed from the study can be used to modify the generic ground motion prediction models to region-specific applications. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
  • No Thumbnail Available
    Item
    Seismic Performance of Infilled RC Frames by Pseudo-Optimization Method
    (Springer Science and Business Media Deutschland GmbH, 2023) Priyusha, G.; Shreyasvi, C.; Venkataramana, K.
    In the present situation, most of the structures are made of Reinforced Concrete (RC) because of readily available raw materials, expertise, and most cost-effective construction. Any building/infrastructure located in seismic zone III or higher has to follow the ductile detailing procedure outlined by IS 13920 (2016) to resist the seismic effects. As earthquakes are highly unpredictable, it is the role of the structural engineer to take care of seismic effects while designing a multi-storey building. The main concept behind earthquake resistant design of structures is to utilize the ductile capability of the materials and the structural members. However, the linear behavior cannot capture the performance of the structure beyond its yield limit and hence, nonlinear analysis is commonly used. On the other hand, nonlinear analysis can be computationally expensive and time-consuming. Hence, the objective of the present study is to optimize the analysis and seismic design by applying pseudo optimization technique. The technique makes use of existing linear structural analysis models with some improvements in the design process based on modal energy. The pseudo optimized design is a three-step procedure that is cost-effective and time-saving. It can be easily implemented by practitioners in their structural design without much of a disruption in the existing workflow. In the current research, finite element model based structural analysis software is used to model and analyze the building. To evaluate its seismic performance pushover analysis is done. The study highlights the merits of the pseudo optimization technique through the application of the methodology. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.
  • No Thumbnail Available
    Item
    Studies on Seismic Performance of RC Framed Buildings Using Pseudo-optimization Method
    (Springer Science and Business Media Deutschland GmbH, 2024) Priyusha, G.; Shreyasvi, C.; Venkataramana, K.
    Most of the RC framed buildings which are designed for seismic prone regions have to follow the ductile detailing procedure outlined in earthquake resistant design code IS 13920(2016) while the infill wall in the RC frames must follow the procedure outlined in IS 1893 (Part 1): 2016. Earthquake resistant design aims to completely utilize the ductile behaviour of the members and it’s constituent materials. Nonlinear analysis is frequently used to explore the ductile behaviour of the structure which is visible only beyond the yield limit/the linear range of the material behaviour. However, nonlinear dynamic analysis can be time consuming and resource intensive. Therefore, the goal of the present study is to utilise the material strength to full potential while keeping the analysis simple and robust. Hence, a pseudo optimization technique was adopted to improve the existing analysis and seismic design methods. The adopted method employs linear models of a structure whose seismic design has been enhanced and optimised based on modal energy. The pseudo-optimized design is a three-step process. The first step is to perform Pushover analysis to evaluate the seismic capacity of the existing building. In the next step, the variation of storey stiffness, storey strength and modal energy shall be examined along the height of the building considering the in-plane stiffness and strength of unreinforced masonry (URM) infill walls. As a last step, based on the modal energies observed in various structural members, the design is optimised. This method is practitioner friendly and has potential for industry level applications. © 2023, Springer Science and Business Media Deutschland GmbH. All rights reserved.
  • No Thumbnail Available
    Item
    Probabilistic Seismic Hazard Assessment of Mangalore and Its Adjoining Regions, A Part of Indian Peninsular: An Intraplate Region
    (Birkhauser Verlag AG, 2019) Shreyasvi, C.; Venkataramana, K.; Chopra, S.; Rout, M.M.
    The Southwestern part of India investigated in the present study mainly comprises of states such as Goa, north Kerala and a major portion of Karnataka. A comprehensive regional seismic catalog has been compiled spanning over 190 years apart from a few prehistoric events from the early 16th century. The classical Cornel–McGuire approach has been incorporated in the estimation of seismic hazard. The seismic sources are modeled as area sources and the entire study region is divided into four seismogenic source zones. The uncertainties involved in the formulation of the seismic source model and ground motion prediction model has been discussed in detail. Further, the procedure for selecting appropriate GMPEs involves the evaluation of multidimensional (M, R, T) ground motion trends and performance against observed macroseismic data. The epistemic uncertainty in the estimation of seismicity parameters and ground motion prediction equations (GMPEs) has been addressed using logic tree computation. The results of the hazard analysis demonstrate that the existing seismic code underestimates the seismic potential of seismic zone II (BIS 1893) areas. The de-aggregation of the predicted seismic hazard revealed earthquakes of magnitude range (Mw) 4–6 occurring within a distance of 35kms to be most influential for any given site of interest. Sensitivity analysis has been performed for crucial input parameters in the formulation of seismic source and ground motion models. Site amplification study has been carried out using topographic slope as a proxy to shear velocity in the top 30 m (Vs30). A maximum of 60% to 80% amplification has been observed in the study area. The seismic hazard maps in terms of PGA have been plotted for the seismic hazard estimated at the bedrock level as well as the surface level for 2% and 10% probability of exceedance in 50 years. The hazard estimation specifically for the southern part of the west coast is the first of its kind. The investigation suspects mining-induced seismicity in Bellary and Raichur districts though there is no mention of this in the prior literature. © 2019, Springer Nature Switzerland AG.
  • No Thumbnail Available
    Item
    Local site effect incorporation in probabilistic seismic hazard analysis – A case study from southern peninsular India, an intraplate region
    (Elsevier Ltd, 2019) Shreyasvi, C.; Venkataramana, K.; Chopra, S.
    The inclusion of local site effects into seismic hazard analysis is an important issue and has been attempted previously in both deterministic and probabilistic manner. The present study is an attempt to combine the local site response with the standard probabilistic seismic hazard analysis. The site response was computed by performing an equivalent linear analysis in the frequency domain. The input soil profiles for the analysis were taken from the borehole data of the North Kerala region (one of the Southerly states in India). The uncertainty in estimating the shear velocity profile (VS) has been addressed by applying multiple VS–N correlations. The variability in the choice of input motions has been reduced by selecting multiple ground motions representing distinct hazard levels (return period of 50–2000 years). The uniform hazard spectrum developed for the host reference site conditions has been adjusted to the target region and the input motions are scaled accordingly. The analyzed soil profiles were categorized into three distinct soil types namely ‘Sand’, ‘Clay’ and ‘All soil’ based on the predominant soil content. The empirical amplification equation as a function of input rock spectral acceleration (Sa r) was developed for each soil type. ‘Sand’ exhibits nonlinear behavior for Sa r > 0.1 g whereas ‘clay’ demonstrates sustained amplification at longer periods. The average spectral amplification observed is 3 for ‘All soil’, 5 for ‘clay’ and 3.5 for ‘sand’ in the study region. The regionally developed amplification function aids in transforming a Ground Motion Prediction Equation (GMPE) from generic to site-specific. The modified GMPE is integrated with the regional seismic source model to estimate site-specific probabilistic seismic hazard. The study produces site-specific spectrum and surface hazard maps which can be of direct use to planners and designers in creating a seismic resilient built environment. © 2019 Elsevier Ltd