Articles written in Sadhana

    • Evaluation of micro-mechanical properties of nonlinear cementitious composite using large-displacement transient nanoindentation analysis


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      Nanoindentation technique is employed for evaluation of mechanical properties of homogeneous materials at micro-level. Many engineering materials, especially cement and concrete composites, which are extensively used as building materials, exhibit phase heterogeneity and are highly porous. The presence of pores highly influences the response obtained from nanoindentation tests. In this study, mechanical properties of Calcium-Silicate-Hydrate (C-S-H), the primary binding agent in cementitious composites, are investigated using a simulated nanoindentation technique. The influence of presence of pores and its geometrical distribution on the non-linear response of C-S-H phases and the stress distribution are critically analysed.

    • Seismic performance evaluation of GLD beam–column sub-assemblages of three different scenarios


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      Gravity load designed (GLD) structures exhibit poor seismic performance due to inadequate reinforcement to cater for the seismic forces, lack of confinement, poor joint strength, improper anchorage, presence of weak column and strong beams. These structures are also susceptible to environmental impact leading to corrosion of reinforcement which would further degrade their seismic performance. In RC structures, beam–column joints are crucial members and dissipate the seismic energy imparted to the structure. Hence in this study, two typical cases of GLD (i) uncorroded GLD and (ii) corrosion affected GLD (corroded) exteriorbeam–column sub-assemblages subjected to reverse cyclic loading are investigated and compared. Reinforcement corrosion of one of the GLD specimens is accelerated by the impressed current technique. Based on theinvestigation on uncorroded GLD and corrosion affected GLD beam–column specimens, it is noted that the corrosion has significant effect on the seismic performance in terms of loss of energy dissipation, strength- andstiffness- degradation. To improve the seismic performance of uncorroded GLD specimens, a low invasive single steel haunch upgradation scheme (SHUS) is proposed in this study. The maximum load carried by steel haunch upgraded GLD specimen is about 30% higher than that of GLD specimen. Hence, it is noted that by implementing the proposed upgradation scheme for GLD beam–column sub-assemblage, remarkable improvement in the seismic response can be achieved. The present study provides insight into the behaviour of steel haunch upgraded GLD specimen and would also pave the way for formulating seismic upgradation of even corroded GLD beam–column sub-assemblage.

    • Evaluation of longitudinal force in railway bridges: comparative evaluation of codal provisions with comprehensive field investigations


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      The present paper focusses on the critical examination of the existing provisions in the current International- and National- Standards for longitudinal force (LF) evaluation in railway bridges during braking and tractive effort from train formation. During the comparative evaluation among the codes, the prevailingstipulations for the allowable vertical load are considered, followed by the same vertical load for bringing the uniformity in the comparison in LF arrived using the codes. It is found that the predicted values are widely different and the disparity is more pronounced when the bridge span is longer than 30 m. Since no wellacceptable strategy is available for evaluation of LF in railway bridges, detailed field investigations are carried out. Five different types of bridges (steel plate girder, prestressed concrete girder, prestressed slab and masonry arch) are considered for field investigations. For each case, the innovative arrangement is conceptualised and designed to capture the developed LF during plying of fully loaded test train formation on the bridge spans. Prior to the massive tests, field level calibration studies are carried out for understanding the dispersion of LF at rail level to the girder level and based on that, the instrumentation and test method is established. During field studies, the instrumentation is carried out from wagon coupler level (or rail level as suitable) to girder level to experimentally estimate the force flow. It is found that the developed schemes are able to provide the critical information on the LF at different levels of the bridge. Further, the magnitude of induced longitudinal force depends on the type of the bridge and the braking case is found to be not as critical as tractive effort. It is also noted that the evaluated LF, though varying from case to case, is 25–40% of the predicted values. The present study emphasized the need for an efficient and elaborate method(s) for evaluation of LF in railway bridges.

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