IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

GENERAL

Department Of Civil Engineering

Journal of Structural Engineering (Madras)

Structural distress of the corbelled vaults in the Ta Prohm temple of Angkor Wat

An analytical method using a cone model is developed to evaluate the impedance functions of pile foundations in a layered soil medium. The dynamic behaviour of piles depends on the nature of the interaction between the piles and the surrounding soil. The soil-pile interaction effect modifies the stiffness of the piles and generates damping through energy radiation to infinity. This modified complex stiffness is called the impedance function. A physical model called a cone frustum is developed to represent the layered soil medium. It is capable of incorporating the complexity of layered soil media and the complicated behaviour of propagating waves. The analytical tool is developed based on wave propagation principles.

Geotechnique

Dynamic behaviour of pile foundations in layered soil medium using cone frustums

Beam column joint in reinforced concrete (RC) frames is a crucial zone, the integrity of which is essential for the satisfactory performance of the whole structure. A new analytical model has been proposed to identify the shear behaviour of joint panel zone. Joint panel zone has been idealised as 2D element subjected to in-plane shear and normal stresses. The shear response of the joint core has been characterised by shear stress - shear strain (deformation) relationship established by softened truss model theory. Inelastic behaviour associated with the slip of longitudinal reinforcement anchored in the joint is represented through bar slippage model. The effect of cyclic load on the total response of the structure is obtained through proper hysteretic modelling of beam, column and joints. The behaviour of joints has been studied by carrying out non-linear dynamic analyses on experimental sub-assemblages under cyclic loads. Good correlation between predicted and test results were obtained.

Analytical model for beam column joint in RC frames under seismic conditions

Optimization gives a new facet to design and development of tires. A new approach to the tire profile optimization is proposed in this study. The optimization procedure is integrated with a simple shell-spring finite element model for faster evaluation. In the shell-spring model, the shell elements represent the tire carcass, whereas the tread is represented by the spring elements. This is applied for the optimization of the tire contour for better maneuverability. The genetic algorithm, an evolutionary optimization procedure that is robust and efficient in solving complex optimization problems, is chosen. A new tire contour is obtained that improves tire maneuverability by increasing the sidewall belt tension.

Tire Science and Technology

Application of a shell-spring model for the optimization of radial tire contour using a genetic algorithm

The critical step in the substructure approach for the soil-structure interaction (SSI) problem is to determine the impedance functions (dynamic-stiffness coefficients) of the foundations. In the present study, a computational tool is developed to determine the impedance functions of foundation in layered soil medium. Cone frustums are used to model the foundation soil system. Cone frustums are developed based on wave propagation principles and force-equilibrium approach. The model is validated for its ability to represent the embedded foundation in layered medium by comparing the results with the rigorous analysis results. Various degrees of freedom, such as, horizontal, vertical and rocking are considered for this study. © 2002 Elsevier Science Ltd. All rights reserved.

Soil Dynamics and Earthquake Engineering

Embedded foundation in layered soil under dynamic excitations

The paper describes a methodology for estimation of reliability of fixed offshore structures with respect to fatigue and extreme stress. The failure criteria for fatigue are formulated using fracture mechanics principle and that for extreme stress using API Code. Advanced Second Moment method is used to find the reliability index. The total life of the structure is divided into a set of stationary sea-states, occuring during storms and described by directional power spectrum. The method has been illustrated through application to a typical jacket platform. Usefulness of the methodology for planning in-service inspections has been highlighted.

Ocean Engineering

Fatigue reliability analysis in time domain for inspection strategy of fixed offshore structures

Reliability analysis of offshore structures, a useful tool for planning in-service inspection of offshore platforms and for checking design and certification, is gaining importance. The paper presents a methodology for estimation of reliability of fixed offshore structures with respect to fatigue. Fracture mechanics principle is used to formulate the failure criteria. Advanced Second Moment method is used to find the reliability index. Formulation for reliability updating, incorporating results of in-service inspection has been described. The method has been illustrated through application to a typical jacket platform.

Fatigue reliability analysis and inspection strategy of jacket structures

Most of the practical optimization procedures are based on fixed, component level, code safety factors and hence are almost deterministic in nature. Reliability-based structural optimization (RBSO) procedures use component and system level reliabilities as explicit design constraints and thus enable the designer to arrive at real optimum solutions by balancing / compromising the total cost and the safety level. The RBSO formulations can be made attractive to professionals by reducing the computational complexities and making the structural modeling as realistic as possible at the same time. This paper makes an attempt towards such a goal, by reconstituting the RBSO formulation using genetic algorithms. The genetic modeling and penalty-based unconstrained formulations are discussed in the case of pin jointed structures. Target reliability-based optimization strategies are proposed, considering the limit states pertaining to both service and collapse stages. Advanced First Order Second Moment (AFOSM) method is used for reliability assessment. Two examples are presented to demonstrate the robustness and efficiency of the proposed methodology in arriving at optimum solutions with the prescribed target reliability levels. The results are compared with those available in literature where mathematical optimization techniques were used for RBSO.

Genetic algorithms-based methodology for reliability-based structural optimization

Closed-form expressions and comprehensive numerical solutions are presented for the transfer functions of surface-supported, rigid, rectangular foundations excited by horizontally polarized, incoherent shear waves for which the motions are parallel to one of the foundation sides. The free-field ground motion is specified stochastically in terms of a local power spectral density function and an orthotropic incoherence function which decays exponentially with the square of the excitation frequency and the separation distance. The response quantities examined include the lateral and torsional components of the foundation motion. Displayed graphically, the results elucidate the effects and relative importance of the numerous parameters involved. For vertically incident incoherent wave fields, the lateral transfer function of a rectangular foundation is related to that of a judiciously selected square foundation, and the interrelationship of the results is examined.

Earthquake Engineering and Structural Dynamics

Transfer functions for rigid rectangular foundations

A study of soil-structure interaction for seismically excited simple structures is made considering both kinematic and inertial interaction effects. The information and concepts presented elucidate the nature and relative importance of the two effects and make it possible to assess readily the influences of the more important parameters. The response quantities examined are the ensemble means of the peak values of the lateral and torsional components of the foundation input motion and of the associated structural deformations. The results are evaluated over wide ranges of the parameters involved and are compared with those obtained for no soil-structure interaction and for kinematic interaction only. Simple, physically motivated interpretations are given for the observed differences. For the important special case of vertically incident incoherent waves, simple closed-form approximate expressions are presented for the transfer functions of circular massless foundations. © ASCE.

World University root node

Journal of Structural Engineering (United States)

Seismic interaction of structures and soils: Stochastic approach

Comprehensive analyses are made of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses also are evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. The results are displayed graphically in the form of response spectra for absolute maximum displacement employing dimensionless parameters that are easy to interpret and use. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this approach. A particularly simple approximation is included for the hydrodynamic modal damping values of multi degree freedom, stick like systems.