B Nageswara Rao

Biaxial voided slab is an innovative slab system which results in a self-weight reduction of up to 50% in comparison with solid slabs. In this paper, the effect of voids of various shapes on flexural behavior of reinforced concrete (RC) square slabs was studied through experimental investigations. Five full-scale slab specimens under a 16-point load were tested with two different shapes of voids, such as sphere and cuboid. The results obtained for solid and voided slab specimens were compared and found that the ultimate flexural capacity is almost the same. However, the presence of voids influences flexural stiffness. While such influence accounts for a marginal deviation of the post-cracking flexural stiffness, the initial stiffness of solid slabs is observed to be 37% higher than that of voided slabs. Furthermore, the flexural load-carrying capacity was estimated based on the yield line method with tensile membrane action and compared with experimental results. For this, the experimental results of the present study (five specimens) and test data collected from the literature (seven specimens) were compared with predictions. It was found that the beneficial effect of tensile membrane action is applicable for biaxial voided RC slab in enhancing the flexural load-carrying capacity. Furthermore, through the comparison of experimental and analytical results, it is found that the 16-point load can be adopted to simulate uniformly distributed loading condition.

The exponential growth of computational power during the last few decades has enabled the finite element analysis of many real-life engineering systems which are too complex to be analytically solved in a closed form. In the traditional deterministic finite element analysis, system parameters such as mass, geometry and material properties are assumed to be known precisely and defined exactly. However, in practice most of the data used in the solution process of many practical engineering systems are either collected from experiments or acquired as empirical data from the past, which are usually ill defined, imprecise and uncertain in nature. This work presents a practical approach based on High Dimensional Model Representation (HDMR) for analyzing the response of structures with fuzzy parameters. The proposed methodology involves integrated finite element modelling, HDMR based surrogate model, and explicit fuzzy analysis procedures.

Abstract.: In this paper, a unit cell based approach is followed, where a unit cell consisting of one aggregate surrounded by mortar matrix is used for numerical simulation of mechanical response of cement concrete. Unit cell approach is a simple mathematical approximation that helps us to simplify the simulation of mechanical response of multi-phase composites. To model the failure of matrix, brittle cracking model is used, where the entire fracture zone is represented by a band of micro cracked material. Current study involves; (a) failure analysis of the concrete unit cell when it is subjected to tensile loads, and (b) parametric study of variation of peak strength with shape and volume fraction of aggregate. In this study, circular and square aggregates at various orientations are modelled. The simulation results predict that the peak tensile stresses are not very sensitive to the volume fraction of aggregates, when the unit cell is subjected to tensile loads. This paper effectively demonstrates the power of unit cell model in simulating the nonlinear mechanical response of cement concrete when it is subjected to tensile loading. © 2011 Indian Academy of Sciences.

A common observation is that flexural load carrying capacity of reinforced concrete slab from yield line analysis is lower than that from an experimental study. This capacity difference arises due to tensile membrane action developed at the post-yield stage. The orientation of reinforcement also plays a significant role in enhancing load carrying capacity, since the fracture moment exceeds moment capacity estimated using yield line analysis. It happens only when reinforcement in orthogonal directions is compelled to yield by diagonal fracture line. The present study investigates the load enhancement due to tensile membrane action and orientation of reinforcement in solid and biaxial voided slabs. Experimental results of 10 specimens (6 solid and 4 biaxial voided slab) were taken from literature. Two-way flexural capacity of those specimens was estimated by yield line analysis in conjunction with Indian code provisions (IS 456: 2000). Results from the experimental study are comparable with yield line analysis after considering the effects due to tensile membrane action and reinforcement orientation.

This study proposes and verifies a numerical framework that can efficiently quantify non-uniform corrosion penetration depth along the perimeter of the rebar in concrete exposed to chloride environment. Moreover, this framework considers the effects of rebar size and location on the process of chloride ingress into concrete and evaluates the non-uniform corrosion states that correspond to two scenarios of corrosion penetration depth: corrosion of segment of the rebar and uneven corrosion along the rebar perimeter. Qualitative comparisons of the evaluated non-uniform corrosion states with the variety of available laboratory and field data show good agreement.

This paper presents fractal finite element based continuum shape sensitivity analysis for a multiple crack system in a homogeneous, isotropic, and two dimensional linear-elastic body subjected to mixed-mode (modes I and II) loading conditions. The salient feature of this method is that the stress intensity factors and their derivatives for the multiple crack system can be obtained efficiently since it only requires an evaluation of the same set of fractal finite element matrix equations with a different fictitious load. Three numerical examples are presented to calculate the first-order derivative of the stress intensity factors or energy release rates. © 2009 Elsevier Ltd. All rights reserved.

Purpose: To develop a new computational tool for predicting failure probability of structural/mechanical systems subject to random loads, material properties, and geometry. Design/methodology/approach: High dimensional model representation (HDMR) is a general set of quantitative model assessment and analysis tools for capturing the high-dimensional relationships between sets of input and output model variables. It is a very efficient formulation of the system response, if higher order variable correlations are weak and if the response function is dominantly of additive nature, allowing the physical model to be captured by the first few lower order terms. But, if multiplicative nature of the response function is dominant then all right hand side components of HDMR must be used to be able to obtain the best result. However, if HDMR requires all components, which means 2N number of components, to get a desired accuracy, making the method very expensive in practice, then factorized HDMR (FHDMR) can be used. The component functions of FHDMR are determined by using the component functions of HDMR. This paper presents the formulation of FHDMR approximation of a multivariate limit state/performance function, which is dominantly of multiplicative nature. Given that conventional methods for reliability analysis are very computationally demanding, when applied in conjunction with complex finite element models. This study aims to assess how accurately and efficiently HDMR/FHDMR based approximation techniques can capture complex model output uncertainty. As a part of this effort, the efficacy of HDMR, which is recently applied to reliability analysis, is also demonstrated. Response surface is constructed using moving least squares interpolation formula by including constant, first-order and second-order terms of HDMR and FHDMR. Once the response surface form is defined, the failure probability can be obtained by statistical simulation. Findings: Results of five numerical examples involving structural/solid-mechanics/geo-technical engineering problems indicate that the failure probability obtained using FHDMR approximation for the limit state/performance function of dominantly multiplicative in nature, provides significant accuracy when compared with the conventional Monte Carlo method, while requiring fewer original model simulations. Originality/value: This is the first time where application of FHDMR concepts is explored in the field of reliability and system safety. Present computational approach is valuable to the practical modeling and design community, where user often suffers from the curse of dimensionality. © Emerald Group Publishing Limited.

The structural reliability analysis in the presence of mixed uncertain variables demands more computation as the entire configuration fuzzy variables needs to be explored. Moreover the existence of multiple design points deviate the accuracy of results as the optimization algorithms may converge to a local design point by neglecting the main contribution from the global design point. Therefore, in this paper a novel uncertainty analysis method for estimating the membership function of failure probability of structural systems involving multiple design points in the presence of mixed uncertain variables is presented. The proposed method involves Multicut-High Dimensional Model Representation technique for the limit state function approximation, transformation technique to obtain the contribution of the fuzzy variables to the convolution integral and fast Fourier transform for solving the convolution integral. In the proposed method, efforts are required in evaluating conditional responses at a selected input determined by sample points, as compared to full scale simulation methods. Therefore, the proposed technique estimates the failure probability accurately with significantly less computational effort compared to the direct Monte Carlo simulation. The methodology developed is applicable for structural reliability analysis involving any number of fuzzy and random variables. The accuracy and efficiency of the proposed method is demonstrated through three examples. © 2012 World Scientific Publishing Company.

This paper deals with the simultaneous identification of road roughness and vehicle parameters, considering the effect of vehicle-structure interaction. The proposed technique avoids the use of bridge response data (which has practical implementation difficulties along with the high chances of corruption with environmental noises) and utilizes the vehicle response data (which is relatively easier to record). Further, vehicle calibration is not needed as the roughness is estimated simultaneously. The identification is carried out by the coupling of an unbiased minimum variance estimator with an optimization scheme. This study considers a quarter-car vehicle model and a half-car vehicle model, instrumented to measure the vehicle vibration data. The unbiased minimum variance estimator (MVE) allows a linear temporal evolution of the state variables, incorporating the roughness as an unknown input term such that the need for linearization is avoided, unlike the traditional nonlinear filters. The optimization scheme helps in choosing a set of optimal solutions for the vehicle parameters as designed in the coupled scheme. The best split of the available measurement data to be used in the two schemes (MVE and optimization scheme) is discussed. The effect of different objective functions is also studied. The proposed technique is successful in terms of simultaneously estimating the vehicle parameters, roughness profile and vehicle responses (states) accurately.