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.

/pdf/review-of-strength-models-for-masonry-spandrels-31cqrj3c2b.pdf

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

Prior to implementing retrofitting measures for seismic action, it is necessary to evaluate the global capacity of unreinforced masonry (URM) buildings. Even with simplified assumptions, equivalent frame (EF) modeling adequately captures global responses and failure mechanisms in existing buildings, making it a popular modeling strategy among structural engineers. However, macro‐elements employed in the EF modeling of URM walls consider in‐plane (IP) and out‐of‐plane (OP) behaviors separately by decoupling their interaction and require independent verification for OP failure involving limit analysis. Such decoupling of interaction is justifiable if proper wall‐wall/wall‐floor connections and rigid‐diaphragm action of slabs are ensured; however, OP failure is likely a result of inadequate connections. Multiple components of ground motion excitation and plan eccentricity in buildings can activate bidirectional interaction in such circumstances. Due to OP damage, the interaction reduces the full IP strength of a URM wall, resulting in overestimating its lateral capacity. This paper proposes a frame‐like 3D macro‐element incorporating the effect of OP action on the IP shear response of URM piers under static and monotonic lateral loads. Only two parameters modifying IP shear stiffness and capacity are required to account for the interaction. Analytical expressions for the interaction parameters are proposed from a detailed micro‐modeling study. The paper also demonstrates, within the EF modeling, the applicability of the proposed macro‐element for seismic analysis of regular URM shear walls with openings.

A macro‐element with bidirectional interaction for seismic analysis of unreinforced masonry walls

Determination of the causative mechanism of structural distress in the presidential palace of India

Sri Kedarnath temple, located in the Central Seismic Gap in Himalayan region in India is an ancient Hindu temple, which represents India’s rich history of culture, religion, science and technology. The temple structure is composed of concentric enclosures with the innermost sanctum sanctorum roofed with corbelled dome and tapering tower. Multi-leaf, dry stack stone masonry constructions with strong irregularities in plan and elevation along with the uncertainties related to the material and geometric characteristics of the temple pose various challenges to systematic seismic verification. Role of diaphragms to resist the lateral load is another area of concern. In addition, the selection of a unique seismic analysis strategy was a challenge. On the other hand, the effectiveness of non-linear dynamic analysis depends largely on selection of ground motion records, apart from the challenge of high computational demand. The current study addresses these issues by analyzing the outcomes of a comprehensive parametric study. Non-linear static and dynamic analyses have been performed on the 3D numerical model by considering the uncertainties in material parameters such as Elastic modulus of stone, Friction angle and compressive strength of stone joints. Synthetic ground motion records with PGA varying from 0.2 g to 1.0 g were used for TH analysis. The study reveals that the tapering tower above the sanctum is susceptible to collapse due to sliding shear failure.

Arun Menon

Papers

A macro‐element with bidirectional interaction for seismic analysis of unreinforced masonry walls

Determination of the causative mechanism of structural distress in the presidential palace of India

Seismic Vulnerability Assessment of Sri Kedarnath Temple in India

Traditional construction in high seismic zones: A losing battle? The case of the 2015 Nepal earthquake

Effect of out-of-plane displacements on the in-plane capacity of lightly precompressed rocking unreinforced masonry piers