• N Gopalakrishnan

      Articles written in Sadhana

    • Enhancement of damage indicators in wavelet and curvature analysis

      B K Raghu Prasad N Lakshmanan K Muthumani N Gopalakrishnan

      More Details Abstract Fulltext PDF

      Damage in a structural element induces a small perturbation in its static or dynamic displacement profile which can be captured by wavelet analysis. The paper presents the wavelet analysis of damaged linear structural elements using DB4 or BIOR6.8 family of wavelets. An expression is developed for computing the natural frequencies of a damaged beam using first order perturbation theory. Starting with a localized reduction ofEI at the mid-span of a simply supported beam, damage modelling is done for a typical steel beam element. Wavelet analysis is performed for this damage model for displacement, rotation and curvature mode shapes as well as static displacement profiles. Damage indicators like displacement, slope and curvature are magnified under higher modes. Instantaneous step-wise linearity is assumed for all the nonlinear elements. A localization scheme with arbitrararily located curvature nodes within a pseudo span is developed for steady state dynamic loads, such that curvature response and damages are maximized and the scheme is numerically tested and proved.

    • SSI analysis of a massive concrete structure based on a novel convolution/deconvolution technique

      J Rajasankar Nagesh R Iyer B Yerraya Swamy N Gopalakrishnan P Chellapandi

      More Details Abstract Fulltext PDF

      Investigations conducted based on seismic soil-structure interaction analysis of a massive concrete structure supported on a raft foundation are presented in this paper. Linear transient dynamic analysis is carried out using finite element method and imposing transmitting boundary conditions at far field of layered elastic half-space. Analysis is conducted in two phases, namely:

      free-field analysis of the layered half-space and

      seismic analysis of the structure by including soil-structure interaction effects.

      In the first phase, a simple and novel technique is used to establish free-field excitation at a depth in the half-space. In the second phase, seismic soil-structure interaction analysis of the structure is carried out for the free-field excitation determined in phase-I. Stress resultants experienced by the raft and the stresses at the interface between the rock and raft are evaluated. Critical examination of the results indicates tensile stresses of considerable magnitude at few locations in the rock-raft interface. Typical stress responses at the interface are presented and discussed in the paper.

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