Mathematical models for the dynamic analysis of concrete gravity dams

The results from field tests on Pine Flat Dam near Fresno, California, are described. The results are then used in the formulation of a three-dimensional mathematical model of the dam and a two-dimensional mathematical model of one of the taller monoliths. The significance of these mathematical models in relationship to the behaviour of concrete gravity dams during earthquakes is also discussed.     

Earthquake resistance of buildings with a ‘soft’ first storey

The dynamic, bi-linear response behaviour of a series of eight storey shear buildings subjected to simulated earthquake excitation is studied. The specific objective of the investigation is to determine under what conditions a yielding first storey can adequately protect the upper storeys from significant yielding. Two classes of buildings are considered: stiff (0.5 sec period) and flexible (2.0 sec period), and the basic parameters considered in the yielding first storey are the yield force level and the bi-linear stiffness. The results demonstrate that a very low yield force level and an essentially perfectly plastic yielding mechanism are required in the first storey to provide effective protection to the superstructure. Moreover, the required displacement capacity of such an effective first storey mechanism is found to be very large.     

Estimation of seismic demands on isolators in asymmetric buildings using non‐linear analysis

A procedure based on rigorous non‐linear analysis is presented that estimates the peak deformation among all isolators in an asymmetric building due to strong ground motion. The governing equations are reduced to a form such that the median normalized deformation due to an ensemble of ground motions with given corner period T_d depends primarily on four global parameters of the isolation system: the isolation period T_b, the normalized strength η, the torsional‐to‐lateral frequency ratio Ω_θ, and the normalized stiffness eccentricity e_b/r. The median ratio of the deformations of the asymmetric and corresponding symmetric systems is shown to depend only weakly on T_b, η, and Ω_θ, but increases with e_b/r. The equation developed to estimate the largest ratio among all isolators depends only on the stiffness eccentricity and the distance from the center of mass to the outlying isolator. This equation, multiplied by an earlier equation for the deformation of the corresponding symmetric system, provides a design equation to estimate the deformations of asymmetric systems. This design equation conservatively estimates the peak deformation among all isolators, but is generally within 10% of the ‘exact’ value. Relative to the non‐linear procedure presented, the peak isolator deformation is shown to be significantly underestimated by the U.S. building code procedures. Copyright © 2003 John Wiley & Sons, Ltd.     

Integrated resource study for conservation and management of Ropar wetland ecosystem, Punjab

Integrated resource study in Ropar wetland ecosystem was undertaken to analyse physiography, drainage, landuse and vegetation status. Various thematic maps have been prepared using black and white aerial photographs on 1:20,000 scale and IRS 1A LISS-II (FCC) on 1:50,000 scale. The Ropar wetland ecosystem is comprised of six major landforms i.e. Siwalik hills, Valley, Piedmont plain, Alluvial plain, River terraces and River courses. The study area show high drainage density with sub dendritic and sub parallel drainage. The area has poor vegetative cover which results in extensive erosion and sedimentation of Ropar lake. The water spread and. qualitative turbidity level in the notified wetland area was also monitored. Anthropogenic pressure, industrial pollution, sedimentation, eutrophication, illegal fishing and flooding have been identified as major threats to the wetland. Keeping in view the threats to Ropar wetland, the conservation measures have been suggested.     

A note on the avulsion of Ghagghar river in the alluvial plains of Punjab and Haryana,North-West India

Ghagghar river in the alluvial plains of Punjab and Haryana, north-west India exhibits the phenomenon of avulsion in its middle and lower reaches. Study of aerial photographs shows that it has abandoned a 25 km long meander belt between Badshahpur and south of Jaswantpura which lies to the north of the present channel. The present channel course lies at a lower elevation on the flood plain away from the levee deposits which acted as an alluvial ridge.     

Earthquake analysis of a class of torsionally-coupled buildings

An effective procedure is summarized without derivation for estimating the maximum response of a class of torsionally-coupled, multi-storey buildings due to earthquake ground motion characterized by response spectra. The analysis procedure is shown to be efficient and to provide insight into torsional coupling effects because the maximum response of such a torsionally-coupled, N-storey building in its njth mode of vibration is determined exactly by analysing (i) the response in the jth vibration mode (j = 1,2, N) of the corresponding torsionally-uncoupled, N-storey system; and (ii) the response in the nth vibration mode (n = 1, 2 for a one-way symmetric plan) of an associated torsionally-coupled, one-storey system. It is also demonstrated that an earlier, simpler approach in which the total (considering all vibration modes) response of the building is determined from the total response of the two simpler systems is strictly valid only under restrictive conditions, which are identified, but the simpler approach leads to results that are accurate to a useful degree.