Online material : Data files for seismogenic source zones (polygons), smoothed-gridded seismicity models, and hazard curves at 0.2° regular grid spacing over the study region.

Earthquake disasters occur mainly due to the collapse of buildings and structures triggered by ground motions. It is, therefore, important to predict ground-shaking levels in order to determine appropriate building code provisions for earthquake-resistant design of structures. This involves extensive analyses and development of appropriate seismological models; namely, seismogenic sources, seismic site conditions, and ground motion predictions. The hazard products, viz . data and maps, constitute important tools for framing public policies toward land-use planning, building regulations, insurance, and emergency preparedness.

View this table:

Table 1 
Major Earthquake Casualties during 1900–2008 in India and Adjoining Regions



In India, several events during the last 100 years, as listed in Table 1, indicate that even moderate earthquakes ( MW < 7.0) can cause significant devastation. On one hand, ongoing urbanization and unprecedented population growth have considerably aggravated the prevailing seismic risk. On the other hand, the available seismic hazard maps covering the entire country are about a decade old. Consequently an updated seismic hazard model for the country is imperative and necessitated by new data, recent findings, and methodological improvements. In the present study, we make a case for new probabilistic seismic hazard analysis (PSHA) of India. The fundamental studies have been carried out to deliver the hazard components, including seismogenic source zonation and seismicity modeling in the Indian subcontinent (Thingbaijam and Nath 2011), assessment of site conditions across the country (Nath, Thingbaijam, Adhikari et al. 2011), and a suitability test for the ground-motion prediction equations in the regional context (Nath and Thingbaijam 2011). These components are integrated to deliver a preliminary model consisting of spatial distributions of peak ground acceleration (PGA) and 5%-damped pseudo spectral acceleration (PSA).

Initial attempts at …

/pdf/probabilistic-seismic-hazard-assessment-of-india-46hsn804y2.pdf

Probabilistic Seismic Hazard Assessment of India

Ground motion prediction equation considering combined dataset of recorded and simulated ground motions

Proper selection and ranking of Ground Motion Prediction Equations (GMPEs) is critical for successful logic-tree implementation in probabilistic seismic hazard analysis. The present study explores this issue in predicting peak ground accelerations at the rock sites in India. Macroseismic intensity data complemented with limited strong ground-motion recordings are used for the purpose. The findings corroborate the possible conformity between the GMPEs developed for tectonically active shallow crust across the globe. On the other hand, the relevant GMPEs in the intraplate regions cluster into two different groups with the equations of lower ranks catering to higher ground motions. The earthquakes in the subduction zones have significant regional implications. However, affinity in the ground-motion attenuations between the major interface events (MW > 7.4) in Andaman-Nicobar, Japan and Cascadia, respectively, is noted. This can be also observed for the intraslab events in the Hindukush and Taiwan respectively. Overall, we do not observe any significant advantage with the equations developed using the regional data. These findings are expected to be useful in probabilistic seismic hazard analysis across the study region.

Peak ground motion predictions in India: an appraisal for rock sites

Many older unreinforced masonry (URM) buildings feature timber floors and solid brick masonry. Simple equivalent frame models can help predicting the expected failure mechanism and estimating the strength of a URM wall. When modelling a URM wall with an equivalent frame model rather than, for example, a more detailed simplified micro-model, the strengths of the piers and spandrels need to be estimated from mechanical or empirical models. Such models are readily available for URM piers, which have been tested in many different configurations. On the contrary, only few models for spandrel strength have been developed. This paper reviews these models, discusses their merits, faults and compares the predicted strength values to the results of recent experimental tests on masonry spandrels. Based on this assessment, the paper outlines recommendations for a new set of strength equations for masonry spandrels.

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Review of strength models for masonry spandrels

The seismic performance of stone masonry buildings is known to be generally poor with respect to other structural typologies. However, significant differences can be observed for different architectural configurations, structural details and masonry mechanical properties. In particular, the seismic vulnerability of existing stone masonry structures is often governed by local failure modes, typically consisting of out-of-plane overturning of structural portions or crumbling of outer wythes in multi-leaf walls. In buildings with an adequate masonry quality, an overall behaviour controlled by the in-plane capacity of walls can develop and govern the global failure mode, provided that proper connections between perpendicular walls and between walls and floors are effective in contrasting the activation of early local failures. In these cases, the in-plane stiffness of diaphragms (typically vaults and timber floors/roofs) can play a significant role in coupling the response of the different walls, hence controlling the global building capacity. Recent experimental testing campaigns carried out in different laboratories have focused on several aspects of the seismic response of stone masonry buildings and on the effect of several strengthening techniques. The availability of such experimental results allowed validation and improvement of analysis tools and procedures for the assessment of the seismic capacity of existing stone masonry structures. In order to make them available to all practitioners, the research achievements need to be incorporated in codes and guidelines for the assessment and strengthening of existing stone masonry buildings. The procedures currently proposed in several codes are already based on a rational approach, which starts from the acquisition of an adequate structural knowledge level and allows for using nonlinear analysis procedures. They could straightforwardly include new research findings and practical developments.

Seismic assessment of existing and strengthened stone-masonry buildings: critical issues and possible strategies

Seismic Performance of Reinforced Concrete Buildings on Hill Slopes: A Review

Cloud analysis has emerged as a popular tool for the seismic demand/fragility assessment of structures. The output of cloud analysis is a seismic demand model which relates an Engineering Demand Parameter (EDP) indicative of structural distress to an Intensity Measure (IM) signifying the severity of ground shaking. IMs commonly used for probabilistic seismic demand assessment are quite heterogenous with respect to their “efficiency”, i.e. their degree of correlation with a specific EDP. This feature has serious implications on the number of ground motion records that must be used to perform cloud analysis on a given structure in order to accurately describe the distribution of the EDP at various IM levels. In the current study, demand models for maximum interstorey drift (?max), based on a wide spectrum of IMs, are developed from the cloud analyses of a five-storey RC bare frame structure using a suite of fifty unscaled natural ground motion records. The method of bootstrap resampling is used to investigate the convergence of the regression coefficients in the demand model with the size of the bootstrap subsamples, each comprising of a limited subset of records drawn from the original suite with repetitions allowed. This procedure helps determine the minimum number of ground motion records necessary for the calibration of demand models without compromising its accuracy in predicting the drift demands. Results from the study indicate a strong correlation between the efficiency of various IMs and the optimal number of records required to produce reliable seismic demand models.

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On the choice of ground motion intensity measure and the number of records for cloud analysis-based seismic demand assessment

Corrigendum to “Investigation of in-plane and out-of-plane interaction in unreinforced masonry piers by block-based micro-modeling” [Structures, 46(2022) 1327–1344]

Under seismic loading, a structure may be subject to simultaneous in-plane and out-of-plane actions. Existing simplified methods like the storey-shear mechanism to determine the shear capacity of masonry structures neglect the out-of-plane effects leading to a non-conservative seismic assessment. In this paper, an analytical model is developed to evaluate the in-plane shear capacities of unreinforced masonry (URM) walls, in the presence of additional out-of-plane displacement. Results from this paper demonstrate that the additional out of displacements alter both the in-plane shear capacity and failure mechanism of the wall. The sensitivity of the interaction to the axial load on the wall is also studied. The proposed model is validated with non-linear finite element analysis. The developed model can be used to determine the reduced shear capacity of URM walls if the mid-height out-of-plane displacement is known. The biaxial interaction of URM walls is also studied dynamically. The model is extended to the framework of the storey-shear mechanism to study the effect of out-of-plane displacements at the global level.

Biaxial Effects in Unreinforced Masonry (URM) Load-Bearing Walls

In the last decades, the devastating effects of seismic events in India have been raising the awareness about the high exposure of the population, especially in crowded urban areas. The daily gathering of believers in temples has been indeed identified as one of the most risky conditions, especially because of the high vulnerability of these historical temple structures. This paper presents the first outcomes of a joint project between EUCENTRE (Pavia, Italy) and IIT Madras (Chennai, India), aiming to reduce the seismic risk of selected architectural heritage structures both in Italy and India, by means of post-tensioning. Two sites were selected and recognized as cultural heritage both for their architectural features and their historical value, as representative of the respective structural typologies. The results of this study can be hence directly applicable to many other similar structures. The paper describes the characteristics of the two temples, in terms of geometry and material, identified based on literature data and results of in-situ investigations on both structural and soil properties. The results of a probabilistic seismic hazard analysis, which was combined with fully stochastic site response analyses at the Indian site, in order to define the expected seismic input, are also presented. The results of this preliminary study are necessary for the design of representative prototype specimens that will be tested on shaking table within this joint project. The numerical model of the temples will be validated against experimental results and will allow future studies on similar structures and improved retrofitting techniques.

Arun Menon

Papers

Seismic Performance of Reinforced Concrete Buildings on Hill Slopes: A Review

On the choice of ground motion intensity measure and the number of records for cloud analysis-based seismic demand assessment

Corrigendum to “Investigation of in-plane and out-of-plane interaction in unreinforced masonry piers by block-based micro-modeling” [Structures, 46(2022) 1327–1344]

Biaxial Effects in Unreinforced Masonry (URM) Load-Bearing Walls

Reduction of seismic risk of roman and hindu temples