Faculty Publications
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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.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.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.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.Item Dynamic Behaviour of Bridge Pier Due to Direct Vehicle Collision(Springer Science and Business Media Deutschland GmbH, 2022) Rahman, P.A.; Reddy, G.R.; Venkataramana, K.Bridge is the structure that is expected several normal and postulated dynamic loads. Vehicle collision with the bridge pier is one of the postulated dynamic loads considered in the design provisions. The Indian code IRC-6 consider the vehicle collision load as equivalent static load, whereas European standards EN 1991-1-7 gives provisions for both static and dynamic analysis. However the both codes don’t give a simplified mathematical model for the dynamic analysis. The Finite element analysis (FEA) is the popular method used for analysis of pier subjected to the collision load. However, the finite element analysis requires a combination of vehicle and concrete structure modeling which is a tedious process. This analytical study includes calculation of dynamic load on the bridge pier as per Eurocode EN 1991-1-7 and its dynamic responses, due to the direct vehicle collision with pier. In this article a simplified model the pier is discussed. Since majority of mass located at the top of the pier and the collision load is acting at bottom part of the pier, pier is modelled as a Two Degrees of Freedom System and the Lumped mass approach is adopted. The dynamic responses of the pier are calculated by Newmark’s Beta Linear Acceleration Method. The dynamic analysis of vehicle collision load also gives the load transferred to the superstructure and its components like bearings. Comparison study of the effect of the impact of the vehicle having 30 tonnes mass and 300 kN/m stiffness with speed 130, 90, 70 and 50 km/h as per EN 1991-1-7: 2006, shows that there is no significant difference in response of the pier for hard impact when vehicle speed varies from 50 to 130 km/h. This may be due to the peak intensities of dynamic actions affect the structure over such a short time in which the structure cannot properly respond to them. However, acceleration response is significantly high when the velocity of impact increases. And vehicle impact load never fails to induce a considerable amount of base shear in the column which is more than the equivalent static loading suggested IRC-6. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Dynamic Behaviour of Road Bridge Deck When a Truck Moves Along the Irregularities of the Road Profiles(Springer Science and Business Media Deutschland GmbH, 2022) Rahman, P.A.; Reddy, G.R.; Venkataramana, K.Bridge is the structure that is seen several dynamic loads unlike other structures. Ministry of Road Transport and Highways (MORTH) said that 10,876 people were killed due to potholes in the year 2015, which denotes the lack of proper maintenance of road pavements. When a vehicle moves along these surface irregularities, it not only causes uncomfortable to the passenger but also causes dynamic loads on the components like deck slab, bearings. Since the road surface irregularities like unevenness, potholes, etc., are unavoidable, we should understand the dynamic effect on the structure due to such undulations. IRC-6, standard to find the loads and load combinations on the road bridges, doesn’t talk about the dynamic load induced by surface irregularities with respect to the different classes of road profile as per ISO: 8608. On the other hand, IRC-6 only gives provisions of static analysis in the case of the vertical dynamic effect produced by moving vehicles. This study aims to generate road profiles having different degrees of unevenness as per ISO: 8608 and to propose a conservative method to find the vertical dynamic load on the bridge deck and its vertical response. A bridge deck is modeled as a Single Degree of Freedom system and the vertical dynamic responses of the bridge deck are found by Newmark’s Beta Linear Acceleration Method. It is found that the dynamic response, almost doubles when road profile quality changes from one class to the very next class. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Seismic Response of Buildings Resting on Geosynthetics Reinforced Sand Bed(Springer Science and Business Media Deutschland GmbH, 2023) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.An earthquake is a significant disaster that destroys structures all over the world. The structure must be designed to resist the impacts of the earthquake. The present study analyzes the efficacy of an Ultra-High Molecular Weight Polyethylene (UHMWPE) liner to lower the amount of seismic energy conveyed and the dynamic response of buildings. Finite element simulation of the transient response of an integrated soil isolation-building system in which buildings are resting on a raft in medium dense sand beds, with and without a soil-seismic isolation system, has been performed with the help of a recorded accelerogram of the El Centro (1940) earthquake. Two sets of space frame building models (two and three storey) of single bay reinforced concrete frames have been considered to estimate seismic response. UHMWPE thickness has been varied from 0.0064 m to 0.15 m to investigate its impact on peak acceleration at building roof levels. The analysis results indicate that earthquake vibration energy transmission to the superstructure is limited by the use of a UHMWPE liner, as a soil isolation medium and the thickness of the soil isolation liner significantly influences the building response during an earthquake ground motion. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.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.Item Experimental investigation on dynamic characteristics of structures founded on a dispersive soil(2008) Jayalekshmi, B.R.; Lohith, K.; Shivashankar, R.; Venkataramana, K.The objective of this paper is to evaluate the Soil-Structure-Interaction (SSI) effects on the seismic response of structures founded on Shedi soil of Dakshina Kannada. Shedi soil, which is a dispersive type of soil is highly vulnerable to dynamic loading in the saturated condition. Experimental investigations have been carried out on 1:10 scaled single bay three dimensional multistorey building models made of aluminium with its foundation resting on locally available Shedi soil (classifying as sandy silt) and sand in the saturated and dry conditions. The combined system of Soil-Foundation-Structure models is subjected to dynamic loading. The response of the model is measured at each floor level. This structural response is compared with that of a fixed base model to isolate the effect of soil structure interaction. The variations in natural frequency with various parameters such as different types of soil, degree of saturation of soil, number of storeys and the stiffening effect of walls are evaluated. The experimental results are presented and the modifications in dynamic characteristics due to the incorporation of soil flexibility are studied. Free vibration analysis of the three dimensional finite element model of the soil foundation structure system is carried out and the results are compared with the experimentally obtained values.Item Shake table tests to investigate the effi cacy of geomembranes for soil isolation in a space frame with isolated footing(2011) Jayalekshmi, B.R.; Shivashankar, R.; Venkataramana, K.; Ramesh Babu, R.; Reddy, G.R.; Parulekar, Y.M.; Patil, S.J.; Gundlapalli, P.Generally a base isolator shifts the natural period of the building away from that of the predominant period of the most probable earthquakes and provides additional damping to absorb the energy. The present study focuses on the effi cacy of soil, geofi bre reinforced soil and a layer of smooth geosynthetic membrane placed in soil in reducing the seismic response of a structure. Shake table tests are carried out in a tri-axial shaker system on a 1/3rd scaled model of a single storey, single bay RC space frame. A steel tank fi xed to the shake table is used as a container for soil and reinforced soil. The structure with different base conditions is subjected to sine sweep tests and the motion corresponding to the response spectrum of Zone III as per IS 1893(Part1):2002. Analysis of results shows that smooth geomembrane in sand can be effectively used to reduce the seismic response of the structure.