Effects of stiffness degradation on ductility requirements for multistorey buildings

The effect of stiffness degradation in reinforced concrete structural members on the inelastic response of multistorey buildings to earthquakes is investigated. In particular, the following question is examined. How do the ductility requirements for multistorey systems with degrading stiffness behaviour compare with those for structures with ordinary bilinear hysteretic property? Inelastic dynamic responses of two idealized multistorey buildings, one having a long and the other a relatively short fundamental period, to an ensemble of twenty simulated earthquakes representative of moderately intense ground motions in California at moderate epicentral distances on firm ground, are analysed for ordinary bilinear hysteretic behaviour and for bilinear hysteretic behaviour with stiffness degradation property. The conclusions deduced from the results of this investigation include the following (1) It is, in general, not possible to predict the maximum response of a degrading stiffness system from results for the corresponding ordinary bilinear system (2) The differences in ductility requirements due to stiffness degradation are generally smaller than those associated with probabilistic variability from one ground motion to another (3) Stiffness degradation has little influence on the ductility requirements for flexible buildings, but it leads to increased ductility requirements for stiff buildings.     

A simplified model for analysis and design of asymmetric-plan buildings

A new simplified model for analysis and design of multistorey buildings is developed. The model is based on a single super-element per building storey capable of representing the elastic and inelastic properties of the storey. This is done by matching the stiffness matrices and ultimate yield surface of the storey with that of the element; this surface relates storey shear and storey torque. For practical convenience, these surfaces are parametrized in terms of seven important physical parameters controlling the seismic response of asymmetric structures. Several numerical studies showed that the accuracy of the super-element model is satisfactory for most design purposes; the errors in peak responses are expected to be less than 20 per cent for most practical structures. Among the important advantages of this simplified model is that the time required in formulating, analysing and interpreting the structural model and its response is at least an order of magnitude smaller than for any conventional 3-D inelastic model. This enables the engineer to try different structural configurations and, thus, produce designs that have the desired seismic behaviour and are cost-effective. Furthermore, it has been shown through a multistorey building example that the super-element model is a powerful tool for conceptual design of a building. In spite of its simplicity, the model uses an accurate representation of the storey-shear and torque surfaces, which enables it to capture the fundamental features controlling the inelastic behaviour of the building.     

Frequency response functions for arch dams: Hydrodynamic and foundation flexibility effects

The linear response of a selected arch dam to harmonic upstream, cross-stream or vertical ground motion is presented for a wide range of the important system parameters characterizing the properties of the dam, impounded water, reservoir boundary materials and foundation rock. Based on these frequency response functions, the hydrodynamic and foundation flexibility effects in the dynamic response of arch dams are investigated.     

On the oscillation of Balat river,district Khasi and Garo Hills,Meghalaya

Balat River has abandoned its westerly course and followed an old course to the east during the recent past. This has lead to the recognition of an oscillation pattern for this river with its periodic shift where the course if confined to the zone bounded by the two channel courses.     

Earthquake response of structures with partial uplift on winkler foundation

The effects of transient foundation uplift on the earthquake response of flexible structures are investigated. The structural idealization chosen in this study is relatively simple but it incorporates the most important features of foundation uplift. In its fixed base condition the structure itself is idealized as a single-degree-of-freedom system attached to a rigid foundation mat which is flexibly supported. The flexibility and damping of the supporting soil are represented by a Winkler foundation with spring-damper elements distributed over the entire width of the foundation. Based on the response spectra presented for several sets of system parameters, the effects of foundation-mat uplift on the maximum response of structures are identified. The influence of earthquake intensity, structural slenderness ratio, ratio of foundation mass to structural mass, foundation flexibility and p-δ effects on the response of uplifting structures is also investigated.     

Morphotectonic analysis in Anandpur Sahib area,Punjab (India) using remote sensing and gis approach

Anandpur Sahib area of Rupnagar district (Punjab) was investigated using an integrated multi-disciplinary approach of geomorphological, structural, drainage and morphotectonic analysis through satellite data and GIS. Most commonly used geomorphic indices viz., channel sinuosity, drainage basin asymmetry, basin elongation ratio, mountain front sinuosity and valley floor to valley width ratio index have been used to identify the geomorphic indicators of active tectonics in the area. Existence of fluvial anomalies viz., abrupt changes in flow direction, flow against gradient, beheaded streams and river terraces reflect the strong structural control on the fluvial features. Asymmetric nature of drainage basin, elongated nature of the sub-watersheds, straight to curvilinear mountain fronts and narrow incised valley floors further substantiate the role of active tectonics in the region.     

Effect of photoelectric emission on blunt probe conductivity measurements in the stratosphere

Two identical planar blunt probes of stainless steel material, biased with a bipolar ramp voltage, are used to measure the stratospheric polar conductivities to altitudes of 34 km. One probe (DP) is mounted closer to the gondola, looking downwards and shielded from sunlight, while the other (SP) is mounted looking sideways, away from the gondola. The daytime observations of positive ions in the 29–34 km altitude range with SP, and of negative ions at 34 km with DP, show photoelectric contaminations induced by solar UV radiations in the 190–230 nm band. These contaminations are found to be due to photoemissions from the SP probe steel surface and from the carbon paint that coats the surface of the gondola, respectively. It is found that, a segment of the photocurrent contaminated I–V curve, recorded with SP at higher negative probe potentials, is linear, and it can give the ambient positive polar conductivity.     

Study of crustal structure and geological implications of southwestern margin of Northeast India

It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average V_P/V_S ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38–45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of V_P/V_S ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson’s ratio (1.69–1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of V_P/V_S ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins.