• B K Raghu Prasad

      Articles written in Sadhana

    • Fracture Mechanics of Concrete - FOREWORD

      B K Raghu Prasad

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    • Enhancement of damage indicators in wavelet and curvature analysis

      B K Raghu Prasad N Lakshmanan K Muthumani N Gopalakrishnan

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      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.

    • Modelling heterogeneity of concrete using 2D lattice network for concrete fracture and comparison with AE study

      R Vidya Sagar B K Raghu Prasad

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      In this paper, numerical modelling of fracture in concrete using two-dimensional lattice model is presented and also a few issues related to lattice modelling technique applicable to concrete fracture are reviewed. A comparison is made with acoustic emission (AE) events with the number of fractured elements. To implement the heterogeneity of the plain concrete, two methods namely, by generating grain structure of the concrete using Fuller’s distribution and the concrete material properties are randomly distributed following Gaussian distribution are used. In the first method, the modelling of the concrete at meso level is carried out following the existing methods available in literature. The shape of the aggregates present in the concrete are assumed as perfect spheres and shape of the same in two-dimensional lattice network is circular. A three-point bend (TPB) specimen is tested in the experiment under crack mouth opening displacement (CMOD) control at a rate of 0·0004 mm/sec and the fracture process in the same TPB specimen is modelled using regular triangular 2D lattice network. Load versus crack mouth opening displacement (CMOD) plots thus obtained by using both the methods are compared with experimental results. It was observed that the number of fractured elements increases near the peak load and beyond the peak load. That is once the crack starts to propagate. AE hits also increase rapidly beyond the peak load. It is compulsory here to mention that although the lattice modelling of concrete fracture used in this present study is very similar to those already available in literature, the present work brings out certain finer details which are not available explicitly in the earlier works.

    • Size effect in self consolidating concrete beams with and without notches

      H Eskandari S Muralidhara B K Raghu Prasad B V Venkatarama Reddy

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      The aim of this study is to obtain the fracture characteristics of low and medium compressive strength self consolidating concrete (SCC) for notched and un-notched plain concrete beams by using work of fracture $G_F$ and size effect model $G_f$ methods and comparing them with those of normal concrete and high performance concrete. The results show that;

      with an increase in compressive strength, $G_F$ increases and $G_f$ decreases;

      with an increase in depth of beam, the decrease in nominal stress of notched beam is more when compared with that of a notchless beam.

    • Influence of interface properties on fracture behaviour of concrete

      G Appa Rao B K Raghu Prasad

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      Hardened concrete is a three-phase composite consisting of cement paste, aggregate and interface between cement paste and aggregate. The interface in concrete plays a key role on the overall performance of concrete. The interface properties such as deformation, strength, fracture energy, stress intensity and its influence on stiffness and ductility of concrete have been investigated. The effect of composition of cement, surface characteristics of aggregate and type of loading have been studied. The load-deflection response is linear showing that the linear elastic fracture mechanics (LEFM) is applicable to characterize interface. The crack deformation increases with large rough aggregate surfaces. The strength of interface increases with the richness of concrete mix. The interface fracture energy increases as the roughness of the aggregate surface increases. The interface energy under mode II loading increases with the orientation of aggregate surface with the direction of loading. The chemical reaction between smooth aggregate surface and the cement paste seems to improve the interface energy. The ductility of concrete decreases as the surface area of the strong interface increases. The fracture toughness (stress intensity factor) of the interface seems to be very low, compared with hardened cement paste, mortar and concrete.

    • Foreword

      B K Raghu Prasad

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    • Modified Adomian decomposition method for fracture of laminated uni-directional composites

      B K Raghu Prasad P V Ramana

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      In this paper, the well-known Adomian Decomposition Method (ADM) is modified to solve the fracture laminated multi-directional problems. The results are compared with the existing analytical/exact or experimental method. The already known existing ADM is modified to improve the accuracy and convergence. Thus, the modified method is named as Modified Adomian Decomposition Method (MADM). The results from MADM are found to converge very quickly, simple to apply for fracture(singularity) problems and are more accurate compared to experimental and analytical methods. MADM is quite efficient and is practically well-suited for use in these problems. Several examples are given to check the reliability of the present method. In the present paper, the principle of the decomposition method is described, and its advantages form the analyses of fracture of laminated uni-directional composites.

    • Residual strength evaluation of concrete structural components under fatigue loading

      A Rama Chandra Murthy G S Palani Nagesh R Iyer Smitha Gopinath B K Raghu Prasad

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      This paper presents methodologies for residual strength evaluation of concrete structural components using linear elastic and nonlinear fracture mechanics principles. The effect of cohesive forces due to aggregate bridging has been represented mathematically by employing tension softening models. Various tension softening models such as linear, bilinear, trilinear, exponential and power curve have been described with appropriate expressions. These models have been validated by predicting the remaining life of concrete structural components and comparing with the corresponding experimental values available in the literature. It is observed that the predicted remaining life by using power model and modified bi-linear model is in good agreement with the corresponding experimental values. Residual strength has also been predicted using these tension softening models and observed that the predicted residual strength is in good agreement with the corresponding analytical values in the literature. In general, it is observed that the variation of predicted residual moment with the chosen tension softening model follows the similar trend as in the case of remaining life. Linear model predicts large residual moments followed by trilinear, bilinear and power models.

    • Handling large variations in mechanics: Some applications

      K Balaji Rao M B Anoop S Muralidhara B K Raghu Prasad

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      There is a need to use probability distributions with power-law decaying tails to describe the large variations exhibited by some of the physical phenomena. The Weierstrass Random Walk (WRW) shows promise for modeling such phenomena. The theory of anomalous diffusion is now well established. It has found number of applications in Physics, Chemistry and Biology. However, its applications are limited in structural mechanics in general, and structural engineering in particular. The aim of this paper is to present some mathematical preliminaries related to WRW that would help in possible applications. In the limiting case, it represents a diffusion process whose evolution is governed by a fractional partial differential equation. Three applications of superdiffusion processes in mechanics, illustrating their effectiveness in handling large variations, are presented.

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