Meher A Prasad

Most of the practical optimization procedures are based on fixed, component level, code safety factors and hence are almost deterministic in nature. Reliability-based structural optimization (RBSO) procedures use component and system level reliabilities as explicit design constraints and thus enable the designer to arrive at real optimum solutions by balancing / compromising the total cost and the safety level. The RBSO formulations can be made attractive to professionals by reducing the computational complexities and making the structural modeling as realistic as possible at the same time. This paper makes an attempt towards such a goal, by reconstituting the RBSO formulation using genetic algorithms. The genetic modeling and penalty-based unconstrained formulations are discussed in the case of pin jointed structures. Target reliability-based optimization strategies are proposed, considering the limit states pertaining to both service and collapse stages. Advanced First Order Second Moment (AFOSM) method is used for reliability assessment. Two examples are presented to demonstrate the robustness and efficiency of the proposed methodology in arriving at optimum solutions with the prescribed target reliability levels. The results are compared with those available in literature where mathematical optimization techniques were used for RBSO.

Glass fibre reinforced gypsum (GFRG) wall panel, a composite walling product, is made essentially of formulated gypsum plaster, reinforced with glass fibres. The behaviour of such wall panels under earthquake loading merits investigation. The hollow cores inside the walls can be filled with reinforced concrete to increase the strength and lateral load resistance. The results of experimental test on a full-scale GFRG wall panel, filled with reinforced concrete, and subjected to axial and in-plane reverse cyclic load, are presented in this paper. The experimental specimen is 1.02 m wide and 2.85 m high. Hysteretic behaviour of the wall panel, acting as a shear wall, is discussed. © 2008 Taylor & Francis Group.

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.

Beam column joint in reinforced concrete (RC) frames is a crucial zone, the integrity of which is essential for the satisfactory performance of the whole structure. A new analytical model has been proposed to identify the shear behaviour of joint panel zone. Joint panel zone has been idealised as 2D element subjected to in-plane shear and normal stresses. The shear response of the joint core has been characterised by shear stress - shear strain (deformation) relationship established by softened truss model theory. Inelastic behaviour associated with the slip of longitudinal reinforcement anchored in the joint is represented through bar slippage model. The effect of cyclic load on the total response of the structure is obtained through proper hysteretic modelling of beam, column and joints. The behaviour of joints has been studied by carrying out non-linear dynamic analyses on experimental sub-assemblages under cyclic loads. Good correlation between predicted and test results were obtained.

Performance based design is an emerging area in earthquake engineering in which damage modeling of structural components plays an important role in achieving the performance objectives. Past researches in damage index evaluation indicated no obvious shear dependent trends on cyclic combined shear and flexure. Paper focuses in finding a simple and realistic indicator, which gives a reliable measure of the structural damage, and use it in the design stage calculations of medium and long period structures. Experiments consisting of monotonic and cyclic tests were conducted on a variety of concrete beams. Two available models for damage indices in the literature, namely Park and Ang model and the model suggested by Rao et al. (1998), were used to predict the damage indices. A simple set of relationships connecting damage index to the failure cyclic ductility ratio, shear span to depth ratio and cyclic amplitude have been derived. The above relationships have been validated on the test data generated during the present investigation. A procedure to evaluate the demand-monotonic ductility ratio at failure corresponding to a given state of damage and the shear span to depth ratio has been developed from the proposed curves.

Near fault earthquakes are common in recent years and are known for the unique strong ground motion characteristics. Dynamic behavior of liquid storage tanks during strong ground motion requires lot of research attention and sloshing is one of the major concerns in the design of liquid storage tanks. Simulated experimental investigations using 3D shake tables are rare in this field and the nonlinear dynamic behavior of the structure is of interest, especially during near fault earthquakes. The paper presents an experimental investigation under simulated conditions on a fixed base rectangular container with water. The tank has been designed to suit experimental requirements and the dimensions were selected to fit the structure in 2m- tri axial shaking table. The behavior of the system is identified during dynamic loading using harmonic excitation and simulated earthquake studies were carried out further on the 3D shaking table. Higher dynamic pressures on the walls and increased dynamic loads on the tank due to the pulse characteristics of ground motion have been verified during the investigation. Computational modeling has been carried out on the experiments conducted and the results are discussed. Dynamic free surface flow is simulated using moving mesh interface and the fluid motion is modeled with incompressible Navier-Stokes formulation.

In this paper, uncertainty analysis of Advanced Heavy Water Reactor (AHWR) subjected to an accidental pressure is carried out using a computational tool based on High Dimensional Model Representation (HDMR) that facilitates lower dimensional approximation of the original high dimensional implicit limit state/performance function. The method involves response surface generation of HDMR component functions, and Monte Carlo Simulation. HDMR is a general set of quantitative model assessment and analysis tools for capturing the high dimensional relationships between sets of input and output model variables. It is a very efficient formulation of the system response, if higher order variable correlations are weak, allowing the physical model to be captured by the first few lower order terms. Once the approximate form of the original implicit limit state/performance function is defined, the failure probability can be obtained by statistical simulation. Reliability estimates of AHWR Inner Containment subjected to an internal pressure exceeding the design pressure, considering four stages of progressive failure prior to collapse are presented. © 2009 Elsevier B.V. All rights reserved.

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.