Devdas Menon

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.

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.

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.

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.

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.

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.

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.

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.

Use of rapid techniques for timely delivery of construction projects by adopting fast methodologies and alternate building materials is necessary in India, given the tremendous housing shortage. Further, the construction has to be affordable and also sustainable. The construction technique proposed in this paper, by making use of Glass Fibre Reinforced Gypsum (GFRG) panels (with reinforced concrete infilled cavities) to build homes, promises such a solution for rapid affordable mass housing in India. GFRG building system is a rapid building technology composed of prefabricated wall panel load bearing system. GFRG is also an eco-friendly building material which can be manufactured out of either natural or industrial gypsum. In India, these panels have been manufactured from the fertilizer by-product waste. As an outcome of the research done at IIT Madras on the feasibility of using these panels for affordable mass housing in India, a two-storeyed GFRG building of 184 square meter area was built at IIT Madras campus, as a demonstration of the suitability of this technology. This is described in this paper.

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.