Computational Mechanics Civil, IISc

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Studies on structural topology and shape optimization

A study on the shape optimization of reinforced concrete flexural members has been undertaken. A natural velocity field method was employed for shape optimization of the member. The change in shape of an initially rectangular cross-section in addition to variation of the breadth and depth along the length of the member has been permitted. The required shape changes have been computed using a sequential quadratic programming technique. A genetic algorithm has been employed to optimize the diameter and number of main reinforcement bars. Constraints based on limit state design principles on the permissible flexural and shear stresses and deflection were employed. This study has also been extended to the optimization of the shape of initially rectangular prestressed concrete girders and prestressed box girder-deck slabs structures. The optimization of structural truss systems which is particularly complex as the load sustained by these members is directly dependent on the member connectivity and the nodal locations, has also been studied.


Studies on the distribution factors for live load moments

An evaluation of existing procedures employed to estimate the live load bending moment distribution in concrete slab on steel girder composite bridges has been undertaken. The composite action between the slab and the girder has been modeled using multi-point constraint relationships between the slab and the top flange of the girder. The effect of transverse diaphragms (number and spacing), the stiffening effect of railings, parapet and continuity of the decks and the skew in the bridge has also been considered in the study.


Linear / Nonlinear  finite element analysis of Adhesively bonded joints

Adhesive bonded joints are the most common types of joints in aerospace applications. However, their application is gradually increasing in Civil Engineering applications as well. The aim of the adhesive bond is to transfer the load smoothly from one adhere to the other minimizing the peak shear stress and peel stress in the adhesive layer. This requires a superior understanding of the adhesive bonding and a rational reliable analytical process that will provide quantitative estimation of the stresses and strains within a wide range of adhesive bonded joints in use across a broad spectrum of manufacturing processes. Both material nonlinearities in the form of a visco-plastic formulation of the constituent materials and a geometric nonlinearity have been incorporated into the finite element formulation.


Development of elements based on the integrated force method (IFM)

An integrated force method (IFM) approach, wherein the internal forces in the element are the unknowns, has been employed to develop a family of plate bending finite elements. Studies are underway to assess the performance of these IFM plate elements with available benchmarks reported in the literature.


Applications of continuum damage mechanics in FRP composites

Research has been initiated in the department in the area of continuum damage mechanics (CDM) with reference to Ductile Damage modeling.  In contrast to Fracture Mechanics, which considers the process of initiation and growth of micro-cracks as discontinuous phenomena, CDM uses a continuous variable, which is related to the density of these defects, to describe the deterioration of the material before initiation of micro-cracks.  The damage variable based on the "effective stress concept" represents average material degradation, which reflects the various types of damage at the micro-scale level (like nucleation and growth of voids, cavities, micro-cracks and other microscopic defects).  To model isotropic damage processes, it suffices to consider scalar damage variable, whereas tensor valued damage variables are required to account for anisotropic damage.  Isotropic damage formulations are extensively employed in literature because of their simplicity and adequacy for many practical applications.   Three isotropic ductile damage models have been developed and integrated with elasto-plasticity in the framework of Nonlinear Finite Element Analysis.  Effort has also been put to develop efficient computational algorithms.  Preliminary studies have been made to bring out the potential of CDM in structural integrity assessment.  Research is in progress to apply CDM to study progressive failure in FRP composites with reference to Civil Engineering Applications.