Asian journal of civil engineering
Volume:9 Issue: 5, October 2008

In this work a robust optimum design for mechanical parameters of linear Tuned MassDamper devices is proposed. In this field, standard approaches are based on the implicitassumption that all system parameters are deterministically known quantities. When thishypothesis is removed, a robust optimum design criterion for Tuned Mass Damper should be developed, where robustness is obtained by finding solutions which are less sensitive tovariation of system parameters, originated by the uncertainty.In this study the load condition for the analysed system is represented by a stationarystochastic process which models the base acceleration, and here modelled by the Kanai- Tajimi stochastic process. The main system, which is equipped by a single Tuned Mass Damper, is described by a system with a single degree of freedom: system mass and stiffness are assumed to be affected by uncertainty, and then are represented by random-bounded variables. The ratio between the protected and unprotected main system covariance displacement is assumed as Objective Function, and then its mean and standard deviation are evaluated. Robust optimum design is formulated as a multi-objective optimization problem, in which both the first and the second statistical moments are minimized simultaneously, with different weights. In this way,optimal Pareto fronts are obtained: after that a sensitivity analysis is carried out in order toassess the variation of robust solution with respect to some parameters, and moreover in order to evaluate the differences with respect to conventional deterministic solution.

The development of Self Compacting Concrete marks an important milestone inimproving the product quality and efficiency of the building industry. Self CompactingConcrete is a recently developed concept in which the ingredients of the concrete mix are proportioned in such a way that it can flow under its own weight to completely fill theformwork and passes through the congested reinforcement without segregation and selfconsolidate without any mechanical vibration. Several studies in the past have revealedthe usefulness of fibres to improve the structural properties of concrete like ductility,post crack resistance, energy absorption capacity etc. Fiber reinforced self compactingconcreting combines the benefits of self compacting concrete in fresh state and shows animproved performance in the hardened state due to the addition of fibers. In thisinvestigation Cem-FIL anti-crack high dispersion glass fibres were added to selfcompacting concrete and Glass Fibre Reinforced Self Compacting Concrete wasdeveloped. An attempt has been made to study mechanical properties and stress-strainbehaviour of self compacting concrete and glass fibre reinforced self compactingconcrete. A strength based mix proportion of self compacting concrete was arrived basedon Nan-Su method of mix design and the proportion was fine tuned by using Okamura’sguidelines. Five self compacting concrete mixes with different mineral admixtures like flyash, ground granulated blast furnace slag and rice husk ash were taken for investigationwith and without incorporating glass fibres. A marginal improvement in the ultimatestrength was observed due to the addition of glass fibres to the self compacting concretemix. Also incorporation of glass fibres had enhanced the ductility of self compactingconcrete. Complete Stress-Strain behaviour has been presented and an empirical equationis proposed to predict the behaviour of such concrete under compression.

This paper presents a detailed experimental investigation on the acid resistance of ternaryblended concrete immersed up to 32 weeks in sulfuric acid (H2SO4) and hydrochloric acid(HCl) solutions. The results are compared with those of the control and binary blendedconcrete. ASTM class F fly ash was considered to develop the binary blended concrete atthe replacement level of cement as 20% by weight. Then silica fume was considered todevelop the ternary blended concrete and the replacement of cement in the ternary system by silica fume was suggested as 8% of total powder content by weight. The variable factors considered in this study were concrete grades (M20, M30 and M40) and curing periods (28 days and 90 days) of the concrete specimens. The parameter investigated was the time in days taken to cause 10% mass loss and strength deterioration factor of fully immersed concrete specimen in a 5% H2SO4 and 5% HCl solutions. The investigation indicated that the ternary blended concrete prepared by 20% fly ash and 8% silica fume performed better acid resistance than the ordinary plain concrete and binary blended concrete.

In this paper the influence of the unit cost of steel, concrete and formwork and thecharacteristic strengths of steel and concrete on the optimum design of reinforced concrete flat slab buildings is investigated. Size optimization of flat slab buildings according to the British Code of Practice is carried out. The objective function is the total cost of the building including the cost of floors, columns and foundations. The total cost of the building includes the cost of material and labour for concrete, reinforcement and formwork. Excavation cost is also considered in the cost of foundations the optimization process is handled in two levels.In the first level the optimum cross-sectional dimensions of reinforced concrete elements isdetermined using a hybrid algorithm based on genetic algorithm. In the second level anexhaustive search is applied to seek the optimum size and number of steel bars for eachindividual type of structural elements. A practical example is given to demonstrate theachieved cost saving and sensitivity of the optimum design to unit cost items and thecharacteristic strengths of steel and concrete.

The objective of the experimental work is to study the influence of Fly ash mixed with lime having varying percentage of hair fibres on California Bearing Ratio values. The randomly oriented hair fibres were, 1.00, 1.50, 2.00 and 2.50% of cement by weight respectively. Thermal power plants generated different types of Fly ash. Fly ash is the most abundant of all the residues and its disposal not only needs enormous land, water and power resources but it also causes serious environmental hazards. In India about 82 such Power Plants produce nearly 106 million tons of Fly ash per year [1] and the Figure is likely to soar. This alarming increase in the production of Fly ash and its disposal in ecologically suitable manners has lately become a global concern. Efforts are being made to increase the use of Fly ash in every possible way.In this struggle scientists and engineers especially civil engineers are playing a remarkablerole. A number of studies have been carried out to determine the influence of fibres on the physical properties of soil and Fly ash with and without Lime. However, no study has been found so far in the literature to investigate the effect of randomly oriented hair fibres on Fly ash mixed with lime. In this paper, results of an experimental study have been presented to determine the effect of randomly oriented Hair fibres in Fly ash and lime on the value of California Bearing Ratio and found encoraging.

Wavelet analysis is a new mathematical technique and in the recent years enormous interest in application of engineering has been observed. This new technique is particularly suitable for non-stationary processes as in contrast to the Fourier transform. The wavelet transform allows exceptional localization, both in time and frequency domains. The application of the wavelet transform to earthquake engineering is rare. In this paper the wavelet transform capability to give a full time–frequency representation of the earthquake record isdemonstrated. In this method, the time series of the earthquake record, breaking at the tropical coral reefs and mechanically generated waves in the wave flume demonstrates the ability of the wavelet transform technique to detect a complex variability of these signals in the time–frequency domain. Various spectral representations resulting from the wavelettransform are discussed and their application for earthquake record is shown.

A study has been carried out to determine the optimum configuration of a multistoreybuilding by changing shear walls location. Four different cases of shear wall position for a25 storey building have been analyzed as a space frame system using a standard packageETAB subjected to lateral and gravity loading in accordance with UBC provisions.It is found that columns and beams forces are found to increase on grids opposite to thechanging position of shear wall away from the centroid of the building. Twisting momentsin members are observed to be having increasing trend with enhancement in the eccentricity between geometrical centroid of the building and shear wall position. Stresses in shear wall elements have more pronounced effect in elements parallel to displaced direction of shear wall as compared to those in perpendicular direction.The lateral displacements of the building is uniform for a zero eccentricity case. On thecontrary, the drift is more on grids on one side than that of the others in case of eccentric shear wall position. It is concluded that the shear wall should be placed at a point by coinciding center of gravity and centroid of the building.

In this paper, the behavior of masonry columns under working load has been studied. Theeffect of cracking on compression area of column or variation of moment of inertia ofcolumn along its height has been considered. The analytical solution for the critical load anddeflection of the column is presented. A numerical example is presented to illustrate the method. The proposed approach has provided more realistic behavior of the masonrycolumns and proved to give an optimized critical load. The implications of the proposedstudy on the Indian code have also been presented.