Now showing 1 - 8 of 8
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    Displacement-controlled nonlinear analysis of RC frames and grids
    (01-12-2015)
    Shariff, M. Najeeb
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    This paper presents details of a nonlinear analysis program capable of tracing the complete load-deflection response of reinforced concrete (RC) beams, frames and grids. The program has been developed in MATLAB using a displacementcontrolled algorithm. The program is capable of handling geometric nonlinearity by using a geometric stiffness matrix in conjunction with a primary stiffness matrix that is constantly updated iteratively. Material nonlinearity is accounted for by making use of prescribed moment-curvature formulations. Stiffness degradation due to cracking of concrete, yielding of steel, tension-stiffening, strain softening and P-A effects is incorporated. The program is computationally efficient and requires only minimal input from the user. The proposed methodology has been validated against experimental data. It is seen that the numerical results generated using the proposed algorithm are in good agreement with the experimental results reported in the literature. Further, the method has been extended to RC grids and RC columns in tension.
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    Estimation of critical buckling moments in slender reinforced concrete beams
    (01-03-2006)
    Revathi, P.
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    At present, there are no recommendations in codes such as ACI 318 and BS 8110 to estimate the critical buckling moment in slender concrete beams. It is assumed that if the slenderness ratios of the beams are limited to the values prescribed by the codes, the failure moment of the beam will be dictated by flexure and not by buckling. Experimental studies carried out as part of the present study, however, show that the specified slenderness limits are not reliable, and failure by lateral instability can occur in slender beams designed according to the code. It is also shown that the existing formulations to predict critical buckling moments in beams, suggested by various researchers, grossly overestimate the capacities in the case of under-reinforced beams. In this paper, a modified formulation is proposed to predict theoretical buckling moment, and it is found to agree very closely with experimental results for both under-reinforced and over-reinforced beams. Copyright © 2006, American Concrete Institute. All rights reserved.
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    Seismic retrofit strategies of buildings
    The Department of Civil Engineering, Indian Institute of Technology Madras, has developed a Handbook on Seismic Retrofit of Buildings under the sponsorship of the Central Public Works Department and under the aegis of Indian Buildings Congress. The Handbook contains seventeen chapters covering different aspects of seismic retrofit The first chapter is a stand-alone chapter that explains the concepts of seismic design and retrofit in a language suitable for the lay person. Besides the introductory chapters, there are chapters on evaluation and retrofit of various types of buildings. The types of buildings cover non-engineered, masonry, reinforced concrete, steel buildings and historical and heritage structures. The geotechnical seismic hazards and retrofit of foundations are placed as separate chapters. Retrofit using fibre reinforced polymer composites, energy dissipation and base isolation devices are introduced. A chapter on quality assurance and control is included. This paper presents the content of the Handbook and two case studies briefly.
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    Reduction in flexural strength in rectangular RC beams due to slenderness
    (01-08-2011)
    Girija, K.
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    This paper presents the results of 15 experimental tests on rectangular slender reinforced concrete (RC) beams. The results reveal limitations in existing theoretical formulations to estimate the failure moment capacity and mode of failure. An improved theoretical formulation is proposed here to predict the critical buckling moment including effects related to nonlinearity and cracking of concrete. Also, following the trends in steel design, an improved measure of slenderness ratio is proposed. Based on a study of 72 test results, it is shown that there is an interaction between flexural tension and instability modes of failure in moderately slender beams. To avoid lateral instability failure, it is suggested that the slenderness ratio be limited to unity. A 'moment reduction factor' is also proposed to account for slenderness effects in RC beams. © 2011 Elsevier Ltd.
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    Experimental Studies on Creep and Shrinkage Behavior of Reinforced Concrete Walls
    (01-05-2020)
    Shariff, M. N.
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    This paper presents experimental studies on four reinforced concrete (RC) walls subject to sustained axial compressive load for 1 year under ambient environmental conditions. The reinforcement percentage and concrete strength have been varied, and their influence on the time-dependent behavior studied. It is observed that the percentage of steel, concrete grade, and age of loading have a significant influence on the time-dependent strains. The evolution of time-dependent strain was also numerically simulated using six prediction models, in conjunction with analysis accounting for the restraining effect of steel. It is demonstrated that although these models have been empirically derived based on tests done on plain concrete cylinders, they are also applicable to large planar elements such as walls, having low volume to surface area. The ACI 209 model for creep and shrinkage is found to yield good results, when applied to RC walls.
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    Moment-curvature relationships to estimate deflections and second-order moments in wind-loaded RC chimneys and towers
    (01-01-1998)
    Second-order moments of considerable magnitude arise in tall and slender RC chimneys and towers subject to along-wind loading, on account of eccentricities in the distributed self-weight of the tower in the deflected profile. An accurate solution to this problem of geometric nonlinearity is rendered difficult by the uncertainties in estimating the flexural rigidity of the tower, due to variable cracking of concrete and the 'tension stiffening' effect. This paper presents a rigorous procedure for estimating deflections and second-order moments in wind-loaded RC tubular towers. The procedure is essentially based on a generalised formulation of moment-curvature relationships for RC tubular towers, derived from the experimental and theoretical studies reported by Schlaich et al. 1979 and Menon 1994 respectively. The paper also demonstrates the application of the proposed procedure, and highlights those conditions wherein second-order moments become too significant to be overlooked in design.
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    Short-term deflections in two-way RC slabs using deflection coefficients
    (01-10-2008)
    Govind, Maidhily
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    Sarkar, Pradip
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    Estimation of deflections in RC slabs is important in the limit state design approach, as deflection control is often the governing condition for slab thickness. Unlike the case of one-way slabs, there is presently no simple procedure available in design codes as well as in the published literature to estimate maximum deflections of RC two-way slabs. The present study attempts to address this problem, with regard to estimation of short-term deflections in RC two-way slabs for which deflection coefficients are available. A modified Branson's formulation is proposed to assess the flexural rigidity of the two-way slab in order to account for the complex effects of cracking and tension stiffening. The empirical formulation is based on 16 experimental load-deflection data sets reported in literature for uniformly loaded rectangular panels on unyielding supports with simply supported and restrained edges.
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    Design of RC beam-column joints under seismic loading - A review
    (01-02-2007)
    Sarkar, Pradip
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    Agrawal, Rajesh
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    A beam-column joint is a very critical element in reinforced concrete (RC) framed structure where the elements intersect in all three directions. Joints ensure continuity of a structure and transfer forces that are present at the ends of the members. The present provisions in IS 13920:1993 are inadequate, in terms of (i) minimum column width, (ii) column/beam flexure strength ratio, (iii) estimation of shear demand, (iv) assessment of shear strength, design and detailing of shear reinforcement, and needs to be upgraded regarding the beam-column joint under seismic loading. This paper reviews the design procedures for the RC beam-column joints under seismic loading reported in literature, with a special emphasis on three international codes of practice viz. ACI 318M-02, NZS 3101:1995 and prEN 1998-1:2003. It is pointed out that although there is a need for continuing research to resolve various disparities, there is an urgent need to revise IS 13920 suitably, in the interest of structural safety.