Asian journal of civil engineering
Volume:12 Issue: 1, Feb 2011

In this paper, a large plasticity deformation finite element modeling is presented for threedimensional dynamic analysis of unsaturated soils with special reference to the failure of lower San Fernando dam under the 1971 earthquake. The finite element method is applied to the governing equations for the spatial discretization, followed by a generalized Newmark scheme used for the time domain discretization. Time stepping scheme is used in the fully implicit coupled method and a direct solution procedure is used for the coupled equation system. The framework of generalized plasticity is presented and the numerical results of unsaturated soils are demonstrated based on the Pastor-Zienkiewicz model (Int. J. Numer. Analyt. Meth. Geomech., 14: pp. 151–190, 1990), Bolzon-Schrefler-Zienkiewicz model (Geotechnique, 46: pp. 279–289, 1996), and enhanced-BSZ model (Transport in Porous Media, 65: pp.1–30, 2006). Finally, 3D dynamic analysis of the failure of lower San- Fernando dam is presented based on the modified Pastor-Zienkiewicz plasticity model.

A series of experiments on composite beams reinforced with Prefabricated Cage System isreported. The experiments include eleven series of composite beams. The tests reported were used to ascertain the flexural strength of the beams and to validate the theoreticalpredictions. Companion specimens of concrete cylinders and cubes were tested forcompressive strength and elastic modulus properties. Specimens of cold formed steelsheeting coupons were tested in tension to ascertain their yield strength and young’smodulus. Failure shown is occur in pure bending region. In this study, the effects of concrete strength and confinement on flexural ductility of PCRC beams have been evaluated in terms of a parameter known as the ductility factor and this gives an indication of the ability of a structural member to deform. The results reveal that PCRC beams show better ductile performance and maintain their loading upto the loading. There was good agreement between the results obtained from the analytical model and those obtained from the test programme.

In statically indeterminate prestressed concrete structures, prestressing force producessecondary moment in addition to primary moment due to eccentricity. This condition isdifferent from statically determinate structures where there is no secondary moment effect and the moment due to prestressing is due to primary moment only, i.e., prestressing force times eccentricity. With the presence of secondary moment, prestressing force design becomes more complex, because the secondary moment is a function of prestressing force and the geometry of the structures. In addition, considering that in general the cable profile is parabolic or another type of curves, which also occurs at continuous supports, the load balancing method may not be used. To cope with this problem moment due to prestressing force is assumed to be the prestressing force times a β coefficient. In statically determinate structures the β coefficient equals the cable eccentricity to the center of gravity of the section. Therefore, the β coefficient can be considered as a statically indeterminate eccentricity. By assigning that the moment due to prestressing force as a function of prestressing force and by considering the allowable stress requirements at top and bottom fibers, equations can be derived to compute the prestressing force in statically indeterminate structures. From the derived equations, the upper and lower bounds of prestressing force can be determined if the section satisfy the requirements. If the optimum prestressing force is needed, the difference of lower and upper bounds should be minimum. Nevertheless, the difference of lower and upper bounds can be considered as a safety level. At the end of thepaper examples are presented to show the application of the proposed method.

This paper offers a method to use deterministic attenuation relationships in probabilisticseismic hazard analysis (PSHA). For a given magnitude and epicentral distance,deterministic attenuation relationships evaluate strong ground motion definitely, so analyzer must assume a standard deviation for the attenuation relationship in the PSHA. This study proposes a PSHA method which can apply the attenuation relationship without standard deviation. Required uncertainty for PSHA is obtained through the uncertainty in magnitude. Seismic source is modeled as a convex combination of three Gaussian distributions. The method is tested for Milad tower site and the results are in accordance with previous studies.

In the event of sudden fire break out, the concrete elements such as columns, beams etc. are subjected to extreme temperatures. The assessment of their performance after fire becomes necessary to decide upon its fitness and required repair measures. Hence, it is important to understand the changes in the concrete properties due to its exposure to extreme temperatures. It is important to know the effect of elevated temperature on the properties of concrete. This paper investigates the effect of sustained elevated temperature on the properties of ordinary concretes of M40 grade, containing different types of cements and cured by two different methods. The specimens were heated to150C, 300C and 450C for 1 hour duration in a muffle furnace. They were tested for compressive strength after air cooling to the room temperature. The variables considered in the study include type of cementing material, temperature and method of curing. The comp. strength of concrete and weight of concrete decreased with increasing temperature. Specimen subjected to conventional water curing performed relatively better than those of membrane curing.

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