BITS Faculty Publications

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Author: search.filters.author.Singh, Shamsher BahadurSubject: search.filters.subject.Civil Engineering

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    Performance of concrete made using sintered fly ash lightweight aggregate-a review
    (India Concrete Journal, 2023) Singh, Shamsher Bahadur; Barai, Sudhir Kumar
    Current work summarizes research done on potential of sintered fly ash lightweight aggregate based concrete and its suitability as an aggregate. The manuscript presents physical and chemical parameters of ingredients such as fly ash as well as binders adopted in manufacturing process covering effect of these materials on parameters related to pelletization like duration, angle of inclination and rotation speed and its subsequent effect of aggregate characteristics. The impact of sintering temperature and its duration on aggregate characteristics is also discussed. The physio-chemical and mechanical characteristics of sintered fly ash aggregate is briefly presented. The review of literature suggests that specific gravity and water absorption of sintered fly ash lightweight aggregate is low and high respectively as compared to conventional aggregate. The use of additives such as alkaline activators, styrene-butadiene rubber, quick lime etc. and additional treatments such as coating or vacuum impregnation has shown potential for reducing water absorption. The mechanical performance of sintered fly ash lightweight aggregate in concrete is different from normal concrete. Factors affecting compressive strength, flexural strength and modulus of elasticity apart from the characteristics of manufactured sintered fly ash lightweight aggregate are cement content, supplementary cementitious materials, additives used, treatment done to aggregate, aggregate content, shape index of aggregate etc. Studies have indicated no direct relationship between factors affecting concrete durability such as water absorption, mechanical perfromance, cement content, water penetrability and freeze-thaw resistance of sintered fly ash lightweight concrete.
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    Experimental and Nonlinear Finite Element Simulation of Compressive Behavior in Natural FRP-Concrete-Steel Double-Skin Rectangular Tubular Columns
    (Springer, 2024-06) Singh, Shamsher Bahadur; Barai, Sudhir Kumar
    This study addresses the research gap regarding using natural fibre-reinforced polymers (FRPs) to construct hybrid Double-Skin Tubular Columns (DSTCs). Experimental testing on twelve rectangular specimens revealed critical failure mechanisms primarily due to the rupture of FRP tubes under excessive stress. This rupture led to the loss of lateral support for the concrete, resulting in severe crushing and localized buckling of the inner steel tube. The experimental results also showed an 18% increase in axial stress and 18 times enhancement in axial strain within confined concrete specimens compared to unconfined concrete specimens because of the effective confinement provided by the outer natural FRP tube (hemp fibre). By integrating experimental and nonlinear finite element simulations, this study highlights the structural performance of these hybrid DSTCs under axial compression, with an average deviation of 1% at the peak axial load, demonstrating the effectiveness of the numerical simulation model. Additionally, a parametric study using validated nonlinear finite element analysis (NLFEA) models to investigate the influence of outer tube cross-sectional aspect ratio, inner steel tube shape, and outer FRP tube thickness on the confined concrete in rectangular DSTCs has been carried out. The finding highlighted that rectangular DSTCs with thicker FRP tubes exhibit higher ultimate axial stress and strain in the confined concrete. Moreover, rectangular DSTCs with square inner steel tubes showed notably lower ultimate axial stress and strain in the confined concrete than rectangular DSTCs with circular inner steel tubes. This comprehensive study emphasizes the importance of stress–strain models, offering valuable insights for the design and construction of hybrid rectangular DSTCs.
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    Present day status and numerical modelling of heritage masonry bridges of Kalka-Shimla Mountain Railways
    (Inder Science, 2022-05) Singh, Shamsher Bahadur
    This study is conducted on two masonry arch skew bridges located on UNESCO recognised Kalka-Shimla Mountain Railways, India, built in the year 1905 with stone masonry located in seismic zone IV as per Indian Standard Code 1893 (2016). Hence, the present day assessment and seismic performance evaluation of the bridges is necessary for conservation. In this study, field measurement of the bridges is conducted using ambient vibration testing (AVT) and operational modal analysis (OMA) with sensitive accelerometers and data acquisition system. Further, modal parameters have been extracted using frequency spatial domain decomposition (FSDD) technique from recorded data. Furthermore, the measured response of the bridges is compared with the developed initial numerical model to estimate the present day status of the bridges in terms of material degradation. A reliable model is then developed adopting modal updation trial and error procedures. At last, the study is concluded towards understanding status of material degradation and preparation of reliable numerical models of the heritage bridge structures
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    Test Methods for Characterizing the Properties of Fiber-Reinforced Polymer Composites at Elevated Temperatures
    (MDPI, 2022-04) Singh, Shamsher Bahadur
    Recent research trends focus on developing bio-based (derived from agricultural byproducts) fiber-reinforced polymer (FRP) composites for structural applications. Fire resistance is one of the key issues that need to be addressed for the use of these FRP materials in buildings. The thermal and mechanical properties of the constituent materials essentially determine the fire performance (and the fire resistance rating) of a structural member, and these properties vary with temperature. Further, the properties of composite materials such as the FRP are highly influenced by the composition and type of fibers and matrix, and these thermo-mechanical properties also vary significantly with temperature. Due to this variation, the fire resistance of FRP materials (both conventional and bio-based) poses a major concern for use in buildings. Currently, very few standardized test procedures are available for evaluating the high-temperature material properties of FRP composites. In this paper, a review of testing protocols and procedures for undertaking tests on FRP materials at various elevated temperatures for evaluating their properties is carried out. Recommendations are provided on the most suitable test methods, specimen conditions, testing regime, and other issues associated with testing at elevated temperatures. In addition, the applicability of the proposed test methods is illustrated through a case study on conventional FRP specimens. Further, the applicability of the recommended test procedures for measuring high-temperature properties of bio-based FRP composites is highlighted
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    Effect of ECC layer thickness and reinforcement ratio on the load carrying capacity of steel-reinforced composite beams
    (Wiley, 2023-02) Singh, Shamsher Bahadur
    The present study investigates the effect of Engineered Cementitious Composites (ECC) layer thickness against various reinforcement ratios on the flexural performance of reinforced ECC–concrete composite beams. In total, 20 reinforced composite beams are selected from the literature to predict their flexural response using Finite Element (FE) analysis. In addition to the FE analyses, a detailed analytical study is performed using the strain compatibility procedure to predict the flexural strength of ECC–concrete composite beams. The results from the FE analyses are compared against the experimental results and are found to show a close agreement. Using the validated FE models, detailed parametric studies are conducted to determine the effectiveness of different design parameters such as (a) ECC height replacement for a reinforcement ratio, (b) reinforcement ratio for an ECC height replacement, and (c) adequate reinforcement ratio for effective strengthening. The results of the parametric study show that the use of 0.4 ECC height replacement ratio and 1.70% steel reinforcement ratio exhibit better load-carrying capacity in ECC–concrete composite beams. The effective tensile reinforcement ratio for the ECC–concrete composite beams from minimum to maximum varies in the range of 0.92%–1.85%, respectively. The moment capacities predicted from the section analysis is in good agreement with the experimental and numerical moment capacities.
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    Effect of Fiber Volume Fraction on the Mechanical Properties of NFRP Composites
    (Springer, 2024-06) Singh, Shamsher Bahadur
    Natural fibers are gaining popularity at present because they are readily available in nature and biodegradable. This study aims to determine how fiber content affects the mechanical characteristics of natural fiber-reinforced polymer (NFRP) composites. Three types of laminates are manufactured using the hand-layup technique by considering the flax, hemp, and jute fibers as reinforcement and epoxy resin and hardener as a matrix. The impurities on surface of fibers are cleared by treating them with a 2% NaOH concentration. All the laminates are fabricated using 40 and 50% fiber volume fractions to identify their effect on mechanical properties. Mechanical performance of the composites is investigated by performing the tension and compression tests on composite coupons following ASTM standards along several fiber directions of 0°, 90° and 45°. This study shows that composite materials with a fiber volume fraction of 40% perform better in terms of elastic characteristics. The composite made with a fiber volume proportion of 50% has served better regarding strength properties
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    Effect of Mercerization on Mechanical Properties of Jute/Flax/Hemp Fiber Reinforced Polymer Composites
    (Nanoworld Journal, 2023) Singh, Shamsher Bahadur
    The primary goal of this study is to examine the impact of mercerization over elastic and strength properties of jute/flax/hemp fiber-reinforced polymer composites. Bast fibers such as flax, jute and hemp fibers were selected as a reinforcement in the composite, and epoxy was considered for the matrix. Using the Hand Lay-up method, the composites are manufactured with a 40% fiber volume fraction and a 60% matrix volume fraction. To enhance the fiber matrix interface, all fibers are chemically treated by the process of mercerization. The natural fibers are treated with an alkaline solution (2% NaOH; sodium hydroxide). Tensile and compressive tests on composite coupons were carried out using the ASTM standards to investigate the material properties along various fiber directions of 0°, 90°, and 45°. Based on the results of mechanical properties, it was observed that the chemical treatment had mixed results over the composite properties. The mercerization had a positive impact on the composite’s properties along the fiber direction, whereas the mercerization had a negative impact along the transverse direction of the fiber.
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    Fire Resistance Evaluation of Concrete Beams and Slabs Incorporating Natural Fiber-Reinforced Polymers
    (MDPI, 2023-02) Singh, Shamsher Bahadur
    This paper presents a numerical study to evaluate the fire resistance of concrete beams and slabs incorporating natural fiber-reinforced polymers (FRP). A validated finite element model was applied to carry out a series of numerical studies on fire-exposed reinforced concrete (RC) beams and slabs strengthened with conventional and bio-based FRP composites. The model calculates the temperature-dependent moment–curvature relationship for various segments of the member at each time step, which are then used to calculate the moment capacity and deflection of the member. The variables in the beams and slabs include different strengthening techniques (externally bonded FRP and near-surface mounted FRP), different fiber composites, and fire insulation schemes (uninsulated and insulated). The results from the study indicate that the bio-based FRP-strengthened RC members undergo a faster degradation in moment capacity and also experience higher deflections under fire exposure. This leads to a lower fire resistance in RC members with bio-based FRP composites compared to beams and slabs with conventional FRP-strengthened concrete members. The addition of fire insulation to the bio-based FRP-strengthened members can enhance their fire performance and help achieve the required fire resistance ratings for use in building applications. In this study, the NSM CFRP-strengthened RC beams were found to have a fire resistance of 3 h without any fire insulation; however, the bio-based FRP-strengthened beams required a layer of vermiculite–gypsum-based fire insulation material (of about 25 mm) to achieve similar fire resistance.
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    Integrating Response Surface Methodology and Finite Element Analysis for Model Updating and Damage Assessment of Multi-Arch Gallery Masonry Bridges
    (IAS, 2024) Singh, Shamsher Bahadur
    This article presents a sophisticated approach to updating the finite element model of two historical arch masonry bridges located in the challenging terrain of Kalka Shimla mountain railway, using vibration testing results. To estimate the dynamic characteristics of the bridges, ambient vibration testing was carried out. Next, initial finite element models of the bridges were developed based on geometrical survey data. Sensitivity analysis was used to determine which parameters needed to be modified for the bridges. The response surface method and global optimization techniques were employed to identify the optimal values of structural parameters that would result in a satisfactory agreement between the numerical and measured natural frequencies of the heritage bridges. Ultimately, the methodology provided a surrogate mathematical model to represent the relationship between structural parameters and dynamic response, and could predict the damage status of the historical bridges.
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    Effect of Curing Temperature on the Mechanical Properties of Hemp Fiber Reinforced Polymer Composites
    (Springer, 2024-01) Singh, Shamsher Bahadur
    The main objective of this study is to investigate the effect of curing temperature on the mechanical properties of hemp fiber reinforced polymer (HFRP) composites. In this study, hemp fiber was considered as a reinforcement and epoxy resin with hardener as a matrix. The mercerization process was used to remove contaminants from the fiber surface. The overall volumetric fraction used was 40% fiber and 60% matrix. One composite sample was cured at open temperature (27 ± 3 °C) for 15 days and others at elevated temperatures such as 80, 120 and 160 °C for various durations such as 1, 2, and 3 h (h). Different mechanical tests were performed under ASTM standards to examine the mechanical performance of HFRP composites. The tensile and compressive properties such as Young’s modulus, tensile and compressive strengths are higher in the specimens cured at 120 °C for 3-h. The flexural strength and stiffness are maximum in the composites cured at 80 °C for 3-h. The maximum interlaminar shear strength representing the composite's resistance to delamination is observed at 120 °C for 3-h curing condition. The Fourier transform infrared (FTIR) study identifies that the chemical treatment has reduced the impurities present on the fiber surface. Scanning electron microscopic (SEM) studies indicate better fiber/matrix adhesion in specimens cured at elevated temperatures than those cured at open temperature. Finally, this study emphasizes that curing at elevated temperature (120 °C for 3-h) improves the mechanical performance of the NFRP composites.