Papers by Ishwer Datt Gupta
Worldwide networks of seismic recording instruments mostly record only translational ground motio... more Worldwide networks of seismic recording instruments mostly record only translational ground motion in two or three orthogonal directions. Rotational component of earthquake is not commonly recorded. Several theories are available to estimate a torsional component from recorded translational components of ground motion. In this paper detailed investigations are made to study the relative performance of some available methods. This paper suggests a practical approach for obtaining true SH (S-wave having particle motion in horizontal direction) component from two recorded horizontal components of ground excitation. This new approach will help to obtain optimum torsional time histories from translational time histories.
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IJASE, 2010
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Bulletin of the Indian Society of Earthquake Technology, 1996
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Bulletin of the Indian Society of Earthquake Technology, 1993
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Soil Dynamics and Earthquake Engineering, 1998
ABSTRACT Several investigations have been concerned with the statistics of peaks in the seismic r... more ABSTRACT Several investigations have been concerned with the statistics of peaks in the seismic response of multi-degree-of-freedom (MDOF) structures when all the peaks are arranged in decreasing level of amplitude. The present paper suggests improvements in the probabilistic formulation adopted in such studies. With these improvements, the probabilistic spectrum superposition approach becomes more accurate and convinient to use in practical applications. By computing the response of a five-story example building excited by several real accelograms with differing frequency and nonstationary characteristics, it is shown that the probabilistic approach is able to predict accurately the amplitudes of several significant response peaks, corresponding to the strong-motion stationary part of input excitation.
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Engineering Structures, 2000
ABSTRACT Investigations have been conducted to study the characteristics of the seismic response ... more ABSTRACT Investigations have been conducted to study the characteristics of the seismic response of structures to stationary and nonstationary random excitations. Exact transient response to stationary excitation is evaluated for several SDOF structures subjected to a wide variety of input motions. For structures with low damping ratio and natural frequency very different from the predominant frequency of the input, the response is dominated by free-vibrations up to several response cycles. For narrow-band excitations, such transient response amplitudes even overshoot the final steady state response. Therefore, to get realistic results, it is proposed to carry out the exact solution for the response to stationary excitations. The nonstationarity of input motion is commonly defined by a stationary process multiplied with a deterministic envelope function. The response amplitudes to such an excitation are influenced by both the subjectively chosen envelope function and the PSDF of the associated stationary excitation. Because the actual nonstationarity in design accelerograms cannot be represented by such simplifying idealizations, the conventional analysis for nonstationary excitations does not provide reliable information for practical use in design applications.
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Earthquake Spectra, 2006
Seismic hazard maps have been prepared for Northeast India based on the uniform hazard response s... more Seismic hazard maps have been prepared for Northeast India based on the uniform hazard response spectra for absolute acceleration at stiff sites. An approach that is free from regionalizing the seismotectonic sources has been proposed for performing the hazard analysis. Also, a new attenuation model for pseudo-spectral velocity scaling has been developed by using 261 recorded accelerograms in Northeast India. In the present study, the entire area of Northeast India has been divided into 0.1° grid size, and the hazard level has been assessed for each node of this grid by considering the seismicity within a 300-km radius around the node. Using the past earthquake data, the seismicity for the area around each node has been evaluated by defining a and b values of the Gutenberg-Richter recurrence relationship, while accounting for the incompleteness of the earthquake catalogue. To consider the spatial distribution of seismicity around each node, a spatially smoothed probability distribut...
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Evaluation of soil amplification effects is of fundamental importance for arriving at site-specif... more Evaluation of soil amplification effects is of fundamental importance for arriving at site-specific strong ground motions for the purpose of earthquake resistant design of structures. It has long been recognized that local site conditions has significant influence on earthquake ground motion, which depends on the geometry and material properties of the subsurface materials, on site topography, as well as on the characteristics of the input motion. Over the years, a number of different methods with varying degree of simplification have been proposed by various investigators for ground response analysis. Engineers have traditionally evaluated such influence with reasonable success using simple models based on a one-dimensional description of local soil profile and seismic wave propagation. Some of the commonly followed theoretical techniques are analyzed here for typical soil profiles and the results are compared critically to suggest the best possible practical approach to evaluate soil amplification for practical engineering applications.
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International Journal of Geotechnical Earthquake Engineering, 2014
The inhomogenieties of the foundation can be modeled explicitly in standard FEM procedure, howeve... more The inhomogenieties of the foundation can be modeled explicitly in standard FEM procedure, however, the results vary significantly with the extent of foundation block modeled and mechanism of applying the input earthquake excitation. The substructure approach provides mathematically exact solution but assumes average properties for the entire foundation as viscoelastic half space. This paper has carried out detailed investigations with varying impedance contrasts and different size of foundation block to show that the results, with suitably deconvoluted free-field ground acceleration time-history applied at the base of foundation block in the FEM approach, are in good agreement with the substructure approach. However, the other variants of the FEM approach may lead to erroneous and overestimated stresses in the dam body. As the foundation of gravity dams can generally be approximated as an equivalent homogeneous half-space, the more accurate and efficient substructure approach can b...
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International Journal of Rock Mechanics and Mining Sciences, 2002
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Current Science, 2005
Seismic hazard maps have been prepared for Northeast India in the form of uniform hazard contours... more Seismic hazard maps have been prepared for Northeast India in the form of uniform hazard contours for pseudo-spectral acceleration at stiff sites. These maps are for the horizontal component of ground motion and for different values of exposure time, confidence level and natural ...
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Acta Geophysica, 2010
Rockbursts are minor earthquakes induced due to mining operations. The seismic signals recorded u... more Rockbursts are minor earthquakes induced due to mining operations. The seismic signals recorded using geophones in the near field are generally saturated and are not suitable for estimating the true magnitudes. The strong-motion accelerograms recorded due to rockbursts are therefore used to obtain the Wood-Anderson synthetic seismograms for getting accurate and reliable values of the local magnitudes. Using several typical strong-motion accelerograms of rockbursts in the mines of Kolar Gold Fields, the magnitudes have been computed in the present study. Correlations of peak ground acceleration and peak ground velocity with the magnitude, studied for the rockbursts vis-à-vis the natural earthquakes in the Koyna dam area, suggest the mechanical similarity between the two different types of events. The results and findings are described in this paper.
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The seismic hazard analysis is concerned with getting an estimate of the strong-motion parameters... more The seismic hazard analysis is concerned with getting an estimate of the strong-motion parameters at a site for the purpose of earthquake resistant design or seismic safety assessment. For generalized applications, seismic hazard analysis can also be used to prepare macro or micro zoning maps of an area by estimating the strong-motion parameters for a closely spaced grid of sites. Two basic methodologies used for the purpose are the "deterministic" and the "probabilistic" seismic hazard analysis (PSHA) approaches. In the deterministic approach, the strong-motion parameters are estimated for the maximum credible earthquake, assumed to occur at the closest possible distance from the site of interest, without considering the likelihood of its occurrence during a specified exposure period. On the other hand, the probabilistic approach integrates the effects of all the earthquakes expected to occur at different locations during a specified life period, with the associ...
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The paper investigates the validity of the [Max +30%] rule by comparing the results for a typical... more The paper investigates the validity of the [Max +30%] rule by comparing the results for a typical six-story steel building with the exact results based on the response spectrum in the principal direction and, the critical response spectrum providing an upper bound to the multi-directional component response. Three different sets of real earthquake ground motions with widely differing characteristics are used. It has been found that the [Max + 30%] rule, which is included in IS 1893 (2016) may not lead to realistic results in all the cases.
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Advances in Indian Earthquake Engineering and Seismology
This paper reviews the response spectrum superposition methods to estimate the maximum amplitudes... more This paper reviews the response spectrum superposition methods to estimate the maximum amplitudes of various response quantities at different levels of multi-degree-of-freedom structures for earthquake-resistant design applications in a very convenient way. The available methods are based on varying degrees of assumptions and idealizations, leading to widely varying errors in the results. The recent methods considering modal interaction effects more accurately and also considering the contribution of high-frequency rigid modes by quasi-static response need to specify additional parameters like exact spectrum velocity amplitudes and the peak ground acceleration, which are generally not available readily. The various approximations and need of specifying additional parameters are eliminated in the stochastic method described in the paper. A large number of numerical results are computed to analyze the relative performance of the commonly used response spectrum superposition methods.
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Papers by Ishwer Datt Gupta