INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
Year:2008 | Volume:6 | Issue:2|Papers Count:6

In the present investigation, the cyclic load deformation behavior of soil-fly ash layered system is studied using different intensities of failure load (I = 25%, 50% and 75%) with varying number of cycles (N = 10, 50 and 100). An attempt has been made to establish the use of fly ash as a fill material for embankments of Highways and Railways and to examine the effect of cyclic loading on the layered samples of soil and fly ash.The number of cycles, confining pressures and the intensity of loads at which loading unloading has been performed were varied. The resilient modulus, permanent strain and cyclic strength factor are evaluated from the test results and compared to show their variation with varying stress levels. The nature of stress-strain relationship is initially linear for low stress levels and then turns non-linear for high stress levels. The test results reveal two types of failure mechanisms that demonstrate the dependency of consolidated undrained shear strength tests of soil-fly ash matrix on the interface characteristics of the layered soils under cyclic loading conditions. Data trends indicate greater stability of layered samples of soil-fly ash matrix in terms of failure load (i) at higher number of loading-unloading cycles, performed at lower intensity of deviatoric stress, and (ii) at lower number of cycles but at higher intensity of deviatoric stress.

Solute transport in unsaturated porous media can be viewed as a coupled phenomenon with water and heat transport, together with mechanical behaviour of media. In this paper, solute transport is formulated mathematically considering heat and water flow in deformable porous media. Advection, dispersion and diffusion of chemical species in the liquid phase are considered. Convection and conduction for heat flow is taken into account. Water flow is considered in both vapour and liquid phases. Equilibrium equation, energy conservation, mass conservation and linear momentum for water, gas and solute are written and solved simultaneously using finite element method. The developed model is validated by solving some examples and comparing results with the results of experimental observation.

In this paper shear behavior of two calcareous sands having different physical properties are investigated using drained and undrained triaxial tests. The investigated sands are obtained from two different zones located in Persian Gulf, Kish Island and Tonbak region. Analysis based on energy aspects show that friction angle in these soils, having crushable particles, is formed of three components: substantial internal friction angle, dilation and particle breakage angle. Dilation component is available in the two investigated sand. Particle breakage component is a function of grains hardness, structure and geometry shape. Particles breakage decreases the volume of sample during drained tests and creates positive pore water pressure during untrained tests. Two investigated sands show different amount of dilation and particle breakage under similar conditions. Simultaneous dilation and particles crushing and different amount of them result in different shear behavior of the two studied sands. Energy aspects are used to determine the effect of particle crushing on the shear strength. There is a suitable compatibility between relative breakage of grains and consumed energy ratio for particle breakage.

Presence of risks and uncertainties inherent in project development and implementation plays significant role in poor project performance. Thus, there is a considerable need to have an effective risk analysis approach in order to assess the impact of different risks on the project objectives. A powerful risk analysis approach may consider dynamic nature of risks throughout the life cycle of the project, as well as accounting for feedback loops affecting the overall risk impacts. This paper presents a new approach to construction risk analysis in which these major influences are considered and quantified explicitly. The proposed methodology is a system dynamics based approach in which different risks may efficiently be modeled, simulated and quantified in terms of time, cost and quality by the use of the implemented object oriented simulation methodology. To evaluate the performance of the proposed methodology it has been employed in a bridge construction project. Due to the space limitations, the modeling and quantification process for one of the identified risks namely “pressure to crash project duration” is explained in detail.

Large capacity cylindrical tanks are used to store a variety of liquids. Their Satisfactory performance during earthquake is crucial for modern facilities. In present paper, the behavior of cylindrical concrete tanks under harmonic excitation is studied using the finite element method. Liquid sloshing, liquid viscosity and wall flexibility are considered and additionally excitation frequency, liquid level and tank geometry is investigated. The results show a value for wall thickness to tank diameter ratio which may be used as a guide in the consideration of wall flexibility effects.

The nonlinear static pushover analysis technique is mostly used in the performance-based design of structures and it is favored over nonlinear response history analysis. However, the pushover analysis with FEMA load distributions losses its accuracy in estimating seismic responses of long period structures when higher mode effects are important. Some procedures have been offered to consider this effect. FEMA and Modal pushover analysis (MPA) are addressed in the current study and compared with inelastic response history analysis. These procedures are applied to medium high-rise (10 and 15 storey) and high-rise (20 and 30 storey) frames; efficiency and limitations of them are elaborated. MPA procedure present significant advantage over FEMA load distributions in predicting storey drifts, but the both are thoroughly unsuccessful to predict hinge plastic rotations with acceptable accuracy. It is demonstrated that the seismic demands determined with MPA procedure will be unsatisfactory in nonlinear systems subjected to individual ground motions which inelastic SDF systems related to significant modes of the buildings respond beyond the elastic limit. Therefore, it’s inevitable to avoid evaluating seismic demands of the buildings based on individual ground motion with MPA procedure.