Pradeep Bhargava

Investigation of Dispersion of Compression in Bottle-Shaped Struts

A bottle-shaped strut in a strut-and-tie model can form when load is applied to a relatively small area, and the resulting stresses disperse as they flow through the strut. The directional changes of the dispersing stresses give rise to transverse tensile forces that have an important influence on the behavior of bottle-shaped struts. This study examines the dispersion of compression in a bottle-shaped strut from first principles and compares the theoretical model with experimental results. ACI 318-05 recommendations for modeling of the dispersion of compression in a bottle-shaped strut have been critically reviewed. The results indicate that the dispersion of compression is significantly influenced by the bearing area of the applied load. The proposed expression for the dispersion of compression enables the estimation of the magnitude of the transverse tensile force for different loading conditions. This in turn is essential for design and detailing of transverse reinforcement in bottle-shaped struts. The ACI 318-05 recommended 2:1 fixed dispersion model will result in highly conservative estimates of the transverse tensile force for concentration ratios exceeding 0.33. The results from this study can be used for obtaining the values of the slope of angle of dispersion of compression in these cases.

VIBRATION AND BUCKLING ANALYSIS OF LAMINATED SANDWICH PLATE HAVING SOFT CORE

Free vibration and buckling of laminated sandwich plate having soft core is studied by using an efficient C0 continuous finite element (FE) model based on higher-order zigzag theory (HOZT). In this theory, the in-plane displacement field for both the face sheets and the core is obtained by superposing a global cubically varying displacement field on a zigzag linearly varying displacement field with a different slope in each layer. The transverse displacement is assumed to be quadratic within the core while it remains constant in the faces beyond the core. The proposed model satisfies the condition of transverse shear stress continuity at the layer interfaces and the zero transverse shear stress condition at the top and bottom of the plate. The nodal field variables are chosen in an efficient manner to overcome the problem of C1 continuity requirement of the transverse displacement. Numerical examples on free vibration and buckling covering different geometric and material features of laminated composite and sandwich plates are presented. Many new results are also presented which should be useful for future research.

Probabilistic failure analysis of laminated sandwich shells based on higher order zigzag theory

The probabilistic failure analysis of laminated composite and sandwich shells is studied first time by using an efficient C0 2D finite element model based on higher order zigzag theory incorporating all three radii of curvatures. The proposed model satisfies transverse shear stress continuity at each layer interface besides higher order theory features, hence predicts better transverse shear stresses. The present 2D finite element model predicts failure loads close to 3D elasticity solutions. The model can not only analyze normal curvature shells like cylindrical but also cross curvature shells like hypar shells. Elastic moduli and ultimate strength values are considered as basic random variables. The present study is to find probability of failure of composite/sandwich hypar and cylindrical shells using Monte Carlo simulation and response surface method. The study reveals that Monte Carlo simulation takes 18,500 finite element simulations for one composite/sandwich shell problem whereas RSM takes only 168 finite element simulations to achieve the same accuracy.

Characterization of Recycled Aggregate Concrete

The effects of using crushed waste concrete as coarse aggregates upon fresh and hardened properties of concrete were investigated through series of testing concrete cylinder specimens to failure. The coarse recycled concrete aggregate (RCA) used in this investigation was sourced from the tested concrete specimens like cubes, cylinders, prisms and beam specimens originally tested for various purposes in the concrete testing laboratory of IIT Roorkee. Total six numbers of concrete mixtures were prepared. These mixtures were differing only in amount of coarse RCA used. The mixture without any RCA was referred as control mixture. Considerable effect of replacement level on compressive strength was observed. Moreover increase in peak strain and significant decrease in static modulus was observed. Stress-strain curves generated during testing were utilized to evaluate normalized toughness and ductility index. Higher value of replacement level found decreasing normalized toughness and ductility index.

Efficient Failure Analysis of Laminated Composites and Sandwich Cylindrical Shells Based on Higher-Order Zigzag Theory

AbstractAn efficient failure analysis of laminated composite and sandwich cylindrical shell is done for the first time using an efficient C0 finite-element (FE) model based on higher-order zigzag theory (HOZT). The FE implementation based on HOZT to study the failure of composite and sandwich shells incorporating all three radii of curvature is presented. The proposed two-dimensional (2D) FE model satisfies the interlaminar shear stress continuity at the layer interfaces and also ensures zero transverse shear stress conditions at the shell top and bottom. The problem of C1 continuity associated with the HOZT is circumvented by using an appropriate C0 FE formulation. The piecewise parabolic shear stress variation across thickness of each layer is considered and hence, shear deformation is accurately modeled for composites and sandwich shells. The failure load results for laminated composite and sandwich shells obtained by using the present 2D FE model are quite close to the 3D elasticity results. Many new ...

Vibration analysis of laminated composite skew cylindrical shells using higher order shear deformation theory

A C0 finite element (FE) formulation based on higher order shear deformation theory (HSDT) is developed for free vibration analysis of composite skew cylindrical shells. The problem of C1 continuity associated with the HSDT has been overcome quite efficiently in the present FE model. The curved isoparametric element used in the model consists of nine nodes with seven nodal unknowns per node. Use of shear correction factor is avoided by assuming a realistic parabolic variation of transverse shear strain through the shell thickness. The transverse shear stresses are taken as zero at the shell top and bottom. Sander’s approximations are considered in the FE formulation to include the effect of three curvature terms in the strain components of composite shells. Since there is no result available in the literature on the problem of skew composite cylindrical shell based on HSDT, the present results are validated with some results available on composite plates/shells. Many new results are presented on free vibration response of laminated composite skew cylindrical shells considering different geometry, boundary conditions, ply orientation and skew angles.

Static and Dynamic Control of Smart Composite Laminates

An efficient C0 continuous two-dimensional finite-element model has been presented in this paper for the control of laminated composite and sandwich plates embedded/surface-bonded with piezoelectric layers and subjected to mechanical loading as well as electric potential. The problem of modeling of smart laminates involves the coupling between mechanical and electrical fields. The structural component is modeled by an efficient equivalent single-layer plate theory, which ensures interlaminar shear-stress continuity and zero transverse shear-stress conditions at the top and bottom of the plate surfaces. Moreover, this theory contains unknowns defined at the reference plane (i.e., midplane) only. The electric field is modeled using layerwise theory, which contains the unknowns at each layer interfaces. The proposed combine model, which may be called a refined hybrid plate model, is implemented to analyze the coupled problem of piezoelectricity in laminated composites and sandwich plates.

HALF TUNNELS ALONG HILL ROADS OF HIMALAYA - AN INNOVATIVE APPROACH

Abstract ‘Half tunnels,’ which are excavated as overhangs within steep slopes of hard rocks, have an advantage over conventional full tunnels or open excavations in that they involve less cost and time. However, due to a lack of interest and their uncommon occurrence, the design and analysis of half tunnels have remained by and large unexplored. In the present paper, an effort has been made to study some of the half tunnels in the Middle and the Higher Himalaya in India. In addition to studying the geology of half tunnels, rock mass properties pertaining to Q and RMR for the rocks exposed around the half tunnel have been evaluated. The Markland test has been carried out to assess the probability of plane or wedge failures along the slopes in the half tunnel area. The results obtained have been again confirmed by analyzing the data with the help of a computer program uwedge . Both analyses suggest that the wedges are stable and that all the half tunnels analyzed are safe. Finite element analyses for different slopes and spans of half tunnels have been carried out to study the distribution of stresses around half tunnels. The range of maximum tensile stress concentration in the roof of half tunnels for different slopes is suggested.

Thermal Analysis of Reinforced Concrete Structural Elements

The paper presents a comparative study of thermal properties of reinforced concrete structural elements. A total of 2 beams and 2 columns were selected from literature [1-3]. Thermal profiles of these elements were predicted using different thermal properties and were compared with the experimental results. The thermal analysis is carried out numerically using finite element analysis package, ABAQUS [4]. Comparisons of different analyses results have been made with the main focus laid on the effect of the boundary conditions i.e. prescribed temperature boundary condition, convection and radiation. During the heating phase, there was slight difference in the temperatures predicted using the two boundary conditions, whereas during cooling phase, there was a significant difference: the convective and radiation boundary condition yielded better results. A reduction in discrepancy between the simulated and experimental result was observed on using thermal properties as per the formulation in Eurocode2 which took into account the moisture content.

An efficient hybrid plate model for accurate analysis of smart composite laminates

An efficient C0 continuous two-dimensional finite element model for the accurate analysis of laminated composite plates embedded and/or surface bonded with piezoelectric layers and subjected to mechanical loading and/or electrical potential has been presented in this article. The problem of smart laminates involves the coupling between mechanical and electrical fields. The mechanical/structural component is modeled by an efficient equivalent single-layer plate theory, which ensures interlaminar shear stress continuity and zero transverse shear stress conditions at the top and bottom of the plate surfaces. Moreover, this theory contains unknowns at the reference plane (i.e. the mid-plane) only. The electrical field is modeled using layer-wise theory, which contains the unknowns at each layer interfaces. In order to calculate the accurate through-the-thickness transverse shear stress variations, a simple approach based on least square error method is applied to the three-dimensional equilibrium equations of the plate problem at the postprocessing stage, after in-plane stresses are calculated using the finite element model based on the above-mentioned refined plate theory and layer-wise theory. The proposed combine model, which may be called as a refined hybrid plate model, is implemented to analyze the coupled problem of piezoelectricity in laminated composites and sandwich plate bending.