Now showing 1 - 10 of 25
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    Assessment of shear strength of circular reinforced concrete beams
    (01-11-2016)
    Balakrishnan, Bijily
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    Hussain, Shehbaz
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    Reinforced concrete (RC) members with circular cross sections are sometimes preferred over rectangular cross sections in members such as columns, piers, and piles, because of their identical strength properties in all directions. In practice, the shear strength of a circular section is generally based on an equivalent rectangular section, using the formulation provided in ACI 318-14. This paper establishes the need to introduce an additional correction factor of 2/π to the shear strength estimation of circular stirrups, using the formulation applicable for rectangular stirrups. Use of this modified formula is validated in the experimental results of 30 tests on RC circular beams, reported in this paper, as well as 27 test results reported by Ang et al. (1989) and Jensen (2010). The theoretical predictions of shear strength have been based on ACI 318-14 and IS 456-2000.
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    Analysis of the ASTM C512 Spring-Loaded CREEP Frame
    (01-10-2019)
    Shariff, Mohammad Najeeb
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    Rajagopal, Kumbakonam R.
    The test method of ASTM C512 (ASTM. 2015. Standard test method for creep of concrete in compression. ASTM C512/C512M. West Conshohocken, PA: ASTM) dictates the use of a spring-loaded creep frame to perform a creep test on concrete. The main thesis of the study is that tests performed using these spring-loaded frames is not a creep test in the sense that the force acting on the specimen is not held constant while the specimen undergoes time-dependent strain. Analysis of this frame is performed using a linear viscoelastic model to represent concrete and isotropic Hooke's law to represent the steel rods and springs. The internal force and displacement in concrete and steel rods at any given instant of time is found using equilibrium equations and compatibility conditions. It is observed that the force transmitted to the concrete does not remain constant throughout the test duration but is a function of the spring and rod stiffness and the viscoelastic properties of the concrete. Hence, a drop in the magnitude of the force transmitted to the concrete specimen occurs in experiments when a spring-loaded creep frame is used. Experimental validation is also carried out by comparing the response of a spring-loaded creep frame with theoretical results. In this work, optimal spring and rod stiffness values to minimize the drop in the force transmitted to the concrete specimen are established. Thus, this study could be used to determine the linear viscoelastic properties of concrete in a creep frame.
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    Reliability analysis and design of cantilever RC retaining walls against sliding failure
    (01-04-2011)
    Sujith, M. S.
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    Among the various modes of failure of reinforced concrete (RC) cantilever retaining walls, the sliding mode of failure is invariably seen to be the critical mode governing the proportions of the wall. Traditionally, a constant factor of safety (usually 1.5) is adopted in the design of cantilever retaining walls against sliding and overturning instability, regardless of the actual uncertainties in the various design variables. This paper presents the stability analysis of cantilever retaining walls, accounting for uncertainties in the design variables in the framework of probability theory. The first order reliability method (FORM), second order reliability method (SORM) and Monte Carlo simulation (MCS) method are used as alternative ways to evaluate the probability of failure associated with the sliding failure of retaining walls of various heights (ranging from 4 to 8 m). Sensitivity analysis has shown that the angle of internal friction (Φ) and the coefficient of friction below the concrete base slab (μ) are the most sensitive random variables. It is shown that cantilever retaining walls, optimally proportioned to achieve a factor of safety of 1.5 against sliding failure, can have significant variations in the reliability index (or probability of failure). In order to achieve consistently a 'target' reliability index (β = 2.5 or 3.0), the factor of safety must be appropriately chosen, accounting for uncertainties, especially with regard to Φ and μ. In this paper, easy-to-use design tables have been developed for this purpose.
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    Calibration of a hysteretic model for glass fiber reinforced gypsum wall panels
    (01-01-2014)
    Janardhana, Maganti
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    Robin Davis, P.
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    Ravichandran, S. S.
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    Glass fiber reinforced gypsum (GFRG) wall panels are prefabricated panels with hollow cores, originally developed in Australia and subsequently adopted by India and China for use in buildings. This paper discusses identification and calibration of a suitable hysteretic model for GFRG wall panels filled with reinforced concrete. As considerable pinching was observed in the experimental results, a suitable hysteretic model with pinched hysteretic rule is used to conduct a series of quasi-static as inelastic hysteretic response analyses of GFRG panels with two different widths. The calibration of the pinching model parameters was carried out to approximately match the simulated and experimental responses up to 80% of the peak load in the post peak region. Interestingly, the same values of various parameters (energy dissipation and pinching related parameters) were obtained for all five test specimens. © 2014 Institute of Engineering Mechanics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg.
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    Yield line analysis and testing of reinforced concrete rectangular slabs with primary and secondary beams
    (01-01-2019)
    Balakrishnan, Bijily
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    The application of yield line analysis to carry out strength design of reinforced concrete (RC) slab systems is mostly limited to solid slabs without beams. In an earlier paper on isolated rectangular beam-slab systems, the authors had demonstrated that such analysis, considering plastic hinges in the beams along with yield lines in the slabs, can result in rational and economical designs. In this paper, it is shown that such yield line analysis can be further extended to beam-slab systems with secondary beams, and the predictions have been validated by tests carried out on four rectangular RC beam-slab systems (each comprising four symmetric grid units), supported at the four corners on pillars. Six possible collapse mechanisms have been investigated. It is established that the critical collapse mechanism is governed primarily by the beam-slab relative strength. It is shown how an economical and rational design can be achieved, making use of the proposed yield line analysis.
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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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    Comparison of force-based and displacement-based methods for seismic design of buildings
    (01-04-2012)
    Varughese, Jiji Anna
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    Displacement-based design (DBD) methods are emerging as the latest tools for performance-based seismic design and as a viable alternative to conventional force-based design method (FBD). FBD starts with an estimation of base shear force, which is calculated based on the fundamental period and ductility capacity of the structure. This base shear force is distributed to the various floor levels based on the fundamental mode shape, and the structure is designed for these lateral loads. Unlike FBD, DBD method requires explicit consideration of displacements. Typically, DBD determines a target displacement demand and then calculates the required base shear capacity to achieve this demand. In this method, the lateral loads at various floor levels are obtained based on an assumed inelastic displacement profile. This paper presents the findings of a study that uses the FBD method and DBD method to design a typical four-storeyed and a nine-storeyed regular frame. The performances of the frames were assessed using nonlinear time history analysis and their relative performances are reported.
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    Vertical geometric irregularity in stepped building frames
    (01-08-2010)
    Sarkar, Pradip
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    Stepped building' frames, with vertical geometric irregularity, are now increasingly encountered in modern urban construction. This paper proposes a new method of quantifying irregularity in such building frames, accounting for dynamic characteristics (mass and stiffness). The proposed regularity index' provides a basis for assessing the degree of irregularities in a stepped building frame. This paper also proposes a modification of the code specified empirical formula for estimating fundamental period for regular frames, to estimate the fundamental time period of the stepped building frame. The proposed equation for fundamental time periods is expressed as a function of the regularity index. It has been validated for various types of stepped irregular frames. © 2010 Elsevier Ltd.
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    Strength of reinforced concrete pier caps-experimental validation of strut-and-tie method
    (01-01-2019)
    Geevar, Indu
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    The strut-and-tie method (STM) is commonly used to design reinforced concrete (RC) pier caps, where the traditional methods of shear and flexural design cannot be used due to nonlinear strain distribution. This paper presents experimental studies on scaleddown pier cap specimens subject to four concentrated loads, to study the influence of various parameters and the applicability of STM. The STM prescribed by ACI 318 and AASHTO are found to give reasonably conservative results only when the beneficial effect of triaxial confinement near the bearing node is invoked; otherwise, the predictions are overly conservative. Variations in bearing plate size, distributed reinforcement, and loading eccentricity did not have much influence on the load capacity, but distributed reinforcement was seen to be beneficial in limiting crack widths. The formation of the assumed STM is validated using strain measurements in concrete and steel, and it is observed that this develops only after significant cracking.
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    Earthquake-resistant design of open ground storey RC framed buildings
    (01-06-2010)
    Davis, Robin
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    Prasad, Meher
    Open ground storey (OGS) buildings are known to be vulnerable under seismic loading due to early formation of collapse mechanism in the ground storey RC columns. The estimation of design forces in such buildings has not been adequately addressed in existing design codes and the literature. In the present study, four different methods are proposed, ranging from rigorous nonlinear dynamic analysis (NDA) of the infilled frame to simplified equivalent static analysis of the bare frame. All the methods proposed are found to result in similar estimates of the design forces in the ground storey columns. The linear analysis (static/dynamic) methods proposed are particularly simple to apply in practice, and will result in designs that are rational and economical, compared to the existing code-based methods.