# Saravanan UmakanthanIndian Institute of Technology Madras | IIT Madras · Department of Civil Engineering

Saravanan Umakanthan

PhD

## About

53

Publications

7,150

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328

Citations

Introduction

**Skills and Expertise**

Additional affiliations

August 2018 - present

**Indian Institute of Technology Madras**

Position

- Professor

Education

August 2001 - June 2005

August 1999 - August 2001

July 1995 - June 1999

## Publications

Publications (53)

The creep behavior of concrete is usually studied using tests carried out on the spring-loaded creep frame recommended by ASTM C512-15. Recent studies 1 have shown that the creep strains observed in a test carried out using the spring-loaded creep frame has interference effects and is a function of the frame component stiffness. A method to deduce...

When straight material filaments do not remain straight after deformation, the strain varies spatially. These spatially varying strain fields arise because of (1) non-uniform distribution of boundary traction, (2) presence of residual stress in the reference configuration, (3) the body being inhomogeneous. The strain measured using devices such as...

Magnetostrictive materials that couple mechanical and magnetic domains have been widely explored for use in sensors and actuators. These materials often exhibit a nonlinear material response under applied magnetic fields, which limits the use of linear constitutive models. Furthermore, the nonlinear constitutive relations tend to be implicit in nat...

A thermodynamic framework is proposed to capture the dissipative response of metals. In contrast to the conventional practice, a stressed reference configuration is assumed instead of a stress-free configuration. The second law of thermodynamics is converted into equality by prescribing a non-negative rate of dissipation function. Stress in the ref...

Time-dependent strains in reinforced concrete (RC) members are usually estimated using approximate algebraic methods. This paper presents an exact method for estimating the time-dependent strains in RC members subjected to concentric axial compression, using creep compliance and shrinkage strain information for the corresponding plain concrete. The...

We develop a methodology for solving truss problems involving viscoelastic materials where, of all the member forces that satisfy the nodal force equilibrium equation and nodal displacements that satisfy the displacement boundary conditions, those member forces and nodal displacements that satisfy the constitutive relation are sought. Since a rate...

Here the possibility of developing a better three dimensional model for rubber when Hencky strain is written as an explicit function of the Cauchy stress is examined. Based on the experimental evidence, vulcanized unfilled rubber is assumed to be isotropic, incompressible, and deforming from a stress-free reference configuration. Vulcanized unfille...

The test method of ASTM C512 (ASTM. 2015. Standard test method for creep of concrete in compression. ASTM C512/C512M. West Conshohocken, PA: ASTM) dictates the use of a spring-loaded creep frame to perform a creep test on concrete. The main thesis of the study is that tests performed using these spring-loaded frames is not a creep test in the sense...

The validity of some of the assumptions made during systematic development of constitutive relation – homogeneity, isotropy, and non-dissipative response – is examined experimentally by testing plain concrete cylinders in the circumferential displacement controlled uniaxial compression tests. The tested cylinders indicate that the surface strains a...

This work documents the formulation of an axial element that could handle implicit constitutive relations. This formulation uses nodal displacements, member forces, and reaction forces as primary unknowns. For some assumed values of these primary unknowns satisfying the nodal equilibrium equations, the computed stretch and stress in the members nee...

Knowing the current state of a bridge is of interest for a variety of reasons. Some parameters that determine the current state of a bridge are the material properties and boundary conditions. Using strain measurements obtained from a slow-moving vehicle on a bridge, the boundary condition and material properties are determined through a mechanisti...

This paper reports a bridge weigh‐in‐motion system, for railways, when dynamic analysis is not required to determine the displacement response of the structure with reasonable accuracy. It is also assumed that the mechanism of resisting the axle loads is through bending action and the loads transferred to the bridge girder can be assumed to be poin...

Here mixture theory is used to capture the changes in cement concrete exposed to sodium sulfate till cracks develop. Toward this, the mixture is assumed to be made of eleven constituents of which the sodium sulfate and water move relative to themselves and the remaining nine solid constituents. The nine solid constituents constrained to move togeth...

The AASHTO:TP-79 (2010), Standard method of test for determining the dynamic modulus and flow number for hot mix asphalt using the asphalt mixture performance tester (AMPT) stipulates the test procedure for the measurement of dynamic modulus of bituminous mixtures. In this test, the stress–strain–time data for different frequencies (from 25 to 0.01...

A methodology for obtaining implicit constitutive representations involving the Cauchy stress and the Hencky strain for isotropic materials undergoing a non-dissipative process is developed. Using this methodology, a general constitutive representation for a subclass of implicit models relating the Cauchy stress and the Hencky strain is obtained fo...

Recently, a thermodynamically consistent non-linear constitutive equation has been developed to describe the large deformation cyclic response of viscoelastic polyamides (see [17]). In this paper, two boundary value problems within the context of the above model, namely the stress relaxation of a right circular annular cylinder subject to twisting,...

Major challenge in heart valve tissue engineering for paediatric patients is the development of an autologous valve with regenerative capacity. Hybrid tissue engineering approach is recently gaining popularity to design scaffolds with desired biological and mechanical properties that can remodel post implantation. In this study, we fabricated align...

Concrete exposed to sulfates deteriorates. Here, an attempt is made to see whether the framework of mixture theory can be used to model the changes that occur in concrete exposed to sodium sulfate. Toward this, diffusion and reaction of sulfates with concrete is modeled within the framework of mixture theory. Appropriate choices are made for the He...

It is customary to use a displacement-based formulation to seek solutions to boundary value problems for its computational efficacy. In displacement-based formulations, it is convenient to prescribe the constitutive relation for stress as an explicit function of displacement gradient. However, from a general theoretical point of view, the stress an...

Using a custom built experimental setup, biaxial and uniaxial extension tests are performed on the same specimen. In biaxial tests, the stretch ratio along y direction is held constant and the stretch ratio in the perpendicular x direction is increased gradually from 1 to 1.4. Stored energy function is obtained from seven different biaxial tests pe...

Many bodies of biological and engineering interest have a fibrous and layered structure. Hence, it is believed that these bodies are inhomogeneous and made up of anisotropic material. Classical mechanical experiments used to find the required material symmetry in the constitutive relation cannot distinguish inhomogeneous bodies made of isotropic ma...

The mixing temperature for binders is normally chosen by the pavement engineer based on a specific ‘viscosity’ required during hot mix asphalt production. Majority of the unmodified binders exhibit Newtonian behaviour at the mixing temperature and hence the determination of the same is straight-forward. However, when modified binders are used, expe...

All bodies are inhomogeneous at some scale but experience has shown that some of these bodies can be idealized as a homogeneous body. Here we examine which bodies can be idealized as a homogeneous body when they are subjected to a non-dissipative mechanical process. This is done by studying circumstances in which an inhomogeneous body admits pure s...

Practically all experimental measurements related to the response of nonlinear bodies that are made within a purely mechanical context are concerned with inhomogeneous deformations, though, in many experiments, much effort is taken to engender homogeneous deformation fields. However, in experiments that are carried out in vivo, one cannot control t...

The current binder testing protocols in the oscillatory domain use peak stress–strain data for material characterisation. The viscoelastic linearity limits are also based on such data. For a rigorous characterisation of the viscoelastic response of the binder, it is necessary that one records the complete waveform of the material response during os...

The confidence level in the determined residual life of an existing civil infrastructure depends on the reliability of its inferred current state. Of the various techniques available to determine this current state, the robustness of using strain measurements obtained from slow moving vehicle loads on a statically determinate bridge is studied. The...

This paper studies the classical problem of extension, inflation, and circumferential shearing of an annular cylinder for a new class of compressible elastic bodies wherein the left Cauchy-Green deformation tensor is given as a function of the Cauchy stress tensor. We use a semi-inverse method to study the problem by assuming forms for both the def...

We formulate and study inflation of radially prestressed incompressible spheres and annular spherical shells. We find that radially prestressed Neo-Hookean spheres subjected to tensile radial component of normal stress at the outer boundary admit deformations fields such that a cavity forms at the center of the sphere and that for a critical value...

Plastic zone method of advanced analysis, which uses shell elements to model the entire structure, is the most accurate method available to predict the ultimate strength and behavior of steel frames. The disadvantage of such full shell plastic zone models is that it is computationally expensive and hence its use is limited to small structures. Beam...

Using a special model that belongs to a new class of elastic bodies wherein the Cauchy–Green stretch is given in terms of the Cauchy stress and its invariants, within the context of the spherical inflation of a spherical annulus, we show that interesting phenomena like the development of “stress boundary layers” manifest themselves. We consider two...

The mechanical properties of bitumen vary with the nature of the crude source and the processing methods employed. To understand
the role of the processing conditions played in the mechanical properties, bitumen samples derived from the same crude source
but processed differently (blown and blended) are investigated. The samples are subjected to co...

Details about custom built experimental set up to perform inflation tests at constant length on blood vessels are presented.
Using this displacement controlled set up we can apply and measure pressures up to 100 kPa and axial loads ranging up to 100
N. The surface deformation is determined from tracking twelve markers in 3D space using 2 CCD camera...

We show that even when the constitutive relations for the elastic response of compressible bodies satisfy the empirical, Baker–Ericksen and ordered forces inequalities and ellipticity restrictions, they could result in physically unrealistic response. We pick a constitutive relation that satisfies the above inequalities and is also globally ellipti...

We formulate and study inflation, extension and twisting of prestressed cylindrical shells that are isotropic in the stress free configuration. We establish that if the prestresses vary only radially in the annular cylinder then a deformation field of the form r=r^(R), θ=Θ+ΩZ, z=λZ is possible in annular cylinders made of any incompressible materia...

In this article, the appropriateness of modelling asphalt using linear viscoelastic constitutive relations is explored. Towards this, a rate-type nonlinear viscoelastic model recently proposed by Santoshreddy et al. (2011) is used and it is shown that the stress relaxation and creep response of asphalt are influenced by the type of experiment, init...

Asphalt for highway and runway construction is processed by either air blowing or blending with different petroleum streams. In the blending process, petroleum pitch, a by-product of solvent deasphalting of the vacuum residue is mixed with heavy extract to produce asphalt of the desired specifications. The rheological response of blended asphalt he...

In this article, details about state of art custom built experimental set up to perform biaxial tests on thin sheets made of polymers or soft biological tissues is presented. This displacement controlled set up can apply and measure loads ranging from 0.01 N to 100 N. Then, the uniform or non-uniform surface deformation is determined from tracking...

There are several problems wherein it would be convenient to have representations for the stress from a stressed configuration as reference. We assume that the body undergoes finite elastic deformations (i.e., non-dissipative processes) from a stressed reference configuration but it is possible that a dissipative (inelastic) process could be the ca...

We study several simple boundary value problems for a special class of inhomoge- neous, isotropic, compressible elastic solids: in∞ation of a spherical shell; bending, stretching and shearing of a rectangular block; and straightening, stretching and shearing of a sector of a hollow cylinder. The purpose of the study is two-fold: to es- tablish new...

Here we investigate whether the deformation observed in an experiment in which the porcine circumflex coronary artery is subjected to inflation at constant length included in the class, \(r\)
\(=\)
\(r(R)\), \(\theta\)
\(=\)
\(\Theta\), \(z\)
\(=\)
\(\Lambda Z\). We find that this is not the case and discuss its implications in the study of the mec...

All real bodies are inhomogeneous, though in many such bodies the inhomogeneity is “mild” in that the response of the bodies
can be “approximated” well by the response of a homogeneous approximation. In this study we explore the status of such approximations
when one is concerned with bodies whose response is nonlinear. We find that significant dep...

We study the inflation, extension, torsion and shearing of an isotropic inhomogeneous compressible annular right circular cylinder. Current approaches to homogenization that appeal to an equivalence of the stored energies could lead to serious errors in the estimate for stresses in a inhomogeneous body as stresses depend on the derivatives of store...

It is quite common to approximate “mildly” inhomogeneous bodies as homogeneous bodies belonging to a certain constitutive class in view of the simplification that such an approximation provides. In this study, we investigate the consequences of such an assumption, and we show that it is clearly inappropriate for many classes of inhomogeneous bodies...

In this paper, a methodology to control the surface error on a Doppler antenna using the concept of a variable geometry truss structure is proposed. A genetic algorithm is used to find the optimal location and number of actuators with the objective to minimize the construction and runtime costs. The optimization also takes into account the limitati...

Details about custom built experimental set up to perform uniaxial and biaxial tests on planar soft tissues are presented.
This displacement controlled set up can apply and measure loads ranging up to 100 N. The surface deformation is determined
from tracking markers in 3D space using 2 CCD cameras. Discarded valve tissue from patients undergoing v...

In finite elasticity, while developing representation for stress, it is customary to require the reference configuration to be stress free. This study relaxes this requirement and develops representations for stress from a stressed reference configuration. Using the fact that the value of Cauchy stress in the current configuration is independent of...