Now showing 1 - 10 of 14
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    Development of strut-and-tie models for RC bridge pier caps subjected to asymmetric loading
    (01-01-2016)
    Geevar, Indu
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    Reinforced concrete (RC) bridge pier caps are subjected to concentrated loads from the superstructure. These are deep members where strain distribution is non-linear and traditional flexural theory cannot be used. Strut-and-tie method can be used to design and detail such regions which idealises the pier cap domain into struts and ties capable of transmitting the loads to the pier. The loads on pier caps can be asymmetric due the effect of live loads, unequal spans and possible curvature of the superstructure. This paper attempts to develop strut-and-tie models for symmetric pier caps subject to asymmetric loading. The possible strut and tie models (STM) for load cases with one side subjected to a heavier load with respect to the other are presented. The ratio between heavier and lighter load is considered as a parameter in this study. The optimised strut and tie model is chosen from the possible models for a particular load case based on minimum tension load path (sum of product of force and corresponding length of the tension members). A solution algorithm is presented for the development of strut and tie models.
  • Placeholder Image
    Publication
    Development of strut-and-tie models for rc bridge pier caps subjected to asymmetric loading
    (01-01-2016)
    Geevar, Indu
    ;
    Reinforced concrete (RC) bridge pier caps are subjected to concentrated loads from the superstructure. These are deep members where strain distribution is non-linear and traditional flexural theory cannot be used. Strut-and-tie method can be used to design and detail such regions which idealises the pier cap domain into struts and ties capable of transmitting the loads to the pier. The loads on pier caps can be asymmetric due the effect of live loads, unequal spans and possible curvature of the superstructure. This paper attempts to develop strut-and-tie models for symmetric pier caps subject to asymmetric loading. The possible strut and tie models (STM) for load cases with one side subjected to a heavier load with respect to the other are presented. The ratio between heavier and lighter load is considered as a parameter in this study. The optimised strut and tie model is chosen from the possible models for a particular load case based on minimum tension load path (sum of product of force and corresponding length of the tension members). A solution algorithm is presented for the development of strut and tie models.
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    Improved design guidelines for slender rectangular RC beams
    (01-01-2011)
    Girija, K.
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    Behaviour of slender reinforced concrete (RC) beams is different from that of normally propotioned beams, on account of slenderness effects which introduce susceptibility to lateral torsional buckling. Highly slender beams are prone to sudden instability mode of failure. Moderately slender beams are also susceptible to slenderness effects and they may undergo flexural failure at moment values less than their flexural capacities corresponding to material failure (Muf). Concrete design codes presently do not provide any procedure to evaluate the critical buckling moment (Mcr), and also do not account for the capacity reduction in moderately slender beams on account of slenderness. The existing recommendations are limited to prescriptions of limiting slenderness ratios, which are semi-empirical in nature. The experimental results carried out in the present study clearly show reduction in moment capacity in beams with slenderness ratios well below the critical values given in various codes and in literature. Based on the experimental and theoretical studies conducted, new design guidelines are proposed for slender rectangular RC beams.
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    Assessment of Strut-and-Tie Methods to Estimate Ultimate Strength of RC Deep Beams
    (01-01-2017)
    Adrija, D.
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    Geevar, Indu
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    Reinforced concrete (RC) deep beams are structural members characterized by relatively small shear span to depth (a/d) ratios. Sectional analysis as well as design procedures are not valid for these members due to the complex interaction of flexure and shear. The strut-and-tie method (STM) has been widely accepted and used as a rational approach for the design of such disturbed regions (D regions) of reinforced concrete members, where traditional flexure theory cannot be used. The flow of stress is idealized as a truss consisting of compressive struts (concrete) and tension ties (reinforcing steel) transmitting the loads to the supports. Usually, STM considers only equilibrium. Hence, there is no unique solution for a given system, as one can find more than a single truss geometry admissible for a given force field. Therefore, the model which gives the maximum capacity can be considered as the most appropriate one. This paper attempts to predict the ultimate strength of deep beams failing in diagonal compression as well as tension, from the experimental database available in literature based on STM. A modified approach has been used, considering the crushing and splitting failures of the diagonal strut separately. Crushing failure of the diagonal strut has been predicted using a plastic Strut-and-tie model with varying compression zone depth. A localized STM has been considered to predict the splitting failure of the diagonal strut.
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    Reliability based seismic performance evaluation of open ground storey buildings
    (01-12-2013)
    Padhy, Tushar K.
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    Open Ground Storey (OGS) buildings are the popular building typ\ology seen in the urban areas as they provide the much-needed parking space to the users. Due to their inherent seismic vulnerability owing to vertical irregularity, much of the damage occurs in the first few stories of such buildings. In the aftermath of Bhuj earthquake, the revised version the Indian seismic code (IS 1893) makes a criterion for strengthening/stiffening of such structures. An open ground storey building designed as per IS 1893 is evaluated using a multi-level reliability based approach. An alternative to the code-prescribed approach is proposed wherein the drift at the first floor is estimated and a simplified direct displacement-based method of analysis is followed to arrive at the equivalent lateral load profile for the OGS buildings.The seismic performance of such OGS building conforming to the proposed approach is assessed subsequently using SAC-FEMA method. © 2013 Taylor & Francis Group, London.
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    Pushover analysis of gfrg-ogs building systems
    (01-01-2018)
    Gouri, Krishna S.R.
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    Glass Fibre Reinforced Gypsum (GFRG) panels have been in use in our country since a decade. These panels, with the advantages of rapidity, sustainability and affordability, are best suited to meet the mass housing requirements of India. However, the present design of GFRG buildings needs the walls to start from the foundation itself as the walls are load bearing. This denies the provision of ground storey parking which is a feature of high demand in multi storey constructions especially in urban areas, where the land is scarce. The proposed solution to cater this issue is to raise the GFRG building system over a frame structure in ground storey comprising of Reinforced Concrete (RC) columns, beams and slabs. The present study evaluates the behaviour of GFRG Open Ground Storey (OGS) structure subjected to gravity and lateral loads using pushover analysis.
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    Creep and shrinkage effects on reinforced concrete walls: Experimental study
    (01-01-2018)
    Shariff, Najeeb
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    Prediction of long-term strains, due to creep and shrinkage, is important to ensure adequate safety and serviceability throughout the life of the structure. Mathematical models are developed based on tests done on prismatic elements, which are applicable for columns. The present study investigates the be¬haviour of RC walls with regard to long-term effects. Further, the applicability of currently popular models, to predict the behaviour of walls is examined. This paper reports the test done on an RC wall panel under sustained load in ambient environment for a period of 8 months. It was observed that the ACI, B4 and CEB-fib MC10 prediction models underestimate the strains in walls, while B3 overesti¬mates. EC2 and GL2000 model predict the final strains in a satisfactory manner. However, the initial trends are overestimated by all prediction models, except ACI. Further, the influence of reinforcement on long-term strains is not included in the prediction models. This study emphasis the need to refine the prediction models to make them applicable for RC walls.
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    Seismic fragility of open ground story buildings in India
    (01-12-2010)
    Robin, Davis P.
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    Padhy, Tushar K.
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    Open ground storey' (OGS) framed buildings are very common in urban areas in countries like India. In design practice, the influence of the infill stiffness in the upper stories of the building is usually ignored, and unless the ground storey columns are specially designed for enhanced bending moments and shear forces, OGS framed buildings is seismically vulnerable due to vertical irregularity. In this study, the seismic fragility of existing OGS buildings in India are evaluated and compared with the corresponding fragility curves for building frames without infill (bare frames) and with full infill in all storeys. The inter-storey drift at the ground storey is treated as the demand variable using a power law model, considering a soft-storey failure mechanism. A regression analysis is performed to estimate the parameters of the demand model, from the peak responses estimated from nonlinear dynamic analyses of OGS buildings using an ensemble of 30 ground motions that represent the seismicity of the region. The probability distributions of the capacities are assumed to be lognormal. The OGS frames are found to be significantly more fragile compared to the fully infilled frames at all limit states, and in general, the fragility increases with increase in number of storeys, but decreases when a large number of bays are involved.
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    Yield line analysis of RC grid slab systems
    (01-01-2016)
    Balakrishnan, Bijily
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    Reinforced concrete (RC) grid slab systems are commonly used to cover large column free spaces. This system of slabs and grid beams is predominantly subjected to flexure, shear and torsion under the action of uniformly distributed gravity loads. Conventionally, the design of the slab portion is done using the simplified moment coefficients prescribed in various codes, assuming the supports to be non-deflecting (rigid supports), considering appropriate boundary conditions at the four edges of each slab panel (continuous or discontinuous). The supporting beams are analysed, assuming load transfer from the slab panels using tributary area concepts. The failure pattern typically assumed for the slab corresponds to a ‘slab-alone failure’ mechanism, for which the collapse load can be estimated using yield line theory; enhancement in the actual collapse load observed in experiments is attributed mainly to tensile membrane action. When the supporting beams are flexible (as in a waffle slab), the system is usually analysed (under factored loads) using linear elastic theory (as in standard finite element softwares). This paper shows how the yield line theory can be applied to all beam-slab systems, accounting for the relative flexibilities and flexural strengths of slab and beam components. The failure mechanism can occur either by ‘slab-alone failure’ or by ‘combined beam-slab failure’. The latter involves yielding of the longitudinal tensile reinforcement in the beams which intercept the yield lines. The focus of the paper is on developing a formulation to predict the collapse load of simple rectangular beam-supported slab systems; this can be extended to larger rectangular grid systems. The results have been validated with experiments reported in the literature on square beamsupported slabs.