Journal of the Structural Engineering and Geotechnics
Volume:3 Issue: 4, Autumn 2013

The induced cracks on the concrete lining of the intake pressure tunnels may cause the water seep into the surrounding media leading to develop a hydro pressure on the external surface of the lining. In the common design practice, the lining can be designed to tolerate with this pressure using the Schleiss method. However, when the tunnel is constructed above the underground water, the seepage may cause the strength of the ground to reduce the amount of which may be considerable in some water sensible soils.
In this paper, the finite element package of PLAXIS has been used to do the non-linear analysis of an intake pressure tunnel located inside a mudstone soil. The stress-strain model for the lining is taken linear elastic and for the soil is the elasto-plastic Mohre-Columb. The analysis is carried out by developing a 2D numerical model for an area of 100X73 meters. Consequently, the optimum lining is designed while the soil strength reduction occurs due to the seepage of water through the cracks in the lining. The results of numerical analysis are compared with that obtained from Schleiss common method of designing. Finally, a series of parametric studies are carried out and some important points and comments are suggested for designing of intake pressure tunnels facing the same condition.

This paper employs one-dimensional numerical ground response analysis models to investigate seismic response of shallow cohesive and non-cohesive soil deposits on vertical propagation of horizontal shear waves. Soil response is modelled by traditional equivalent-linear (EL) frequency-domain analysis using DEEPSOIL software and nonlinear (NL) time-domain analysis using OPENSEES software. The analysis is performed on soil columns of different heights to account for depth dependency of responses. Input rock outcropping motions are selected from far-field and near-field time histories and scaled to various shaking levels to evaluate soil nonlinearity level. The results show that the shallow soil deposits have capability of amplifying the input motion considerably. Moreover, With increasing soil depth, greater damping and shifting in the dominant periods of the computed spectra occur and maximum value of spectrums increases. These results for shallow soil deposits, highlight the need to consider the full depth of the soil column to perform local ground response analysis.

Thin walled cylindrical shells are important components of industrial structures such as liquid storage tanks, silos, etc. Shell buckling is usually a major failure mode of thin walled shells under extreme loads such as earthquakes. Longitudinal and radial stiffeners are generally used in order to increase buckling capacity of thin walled shells. During an earthquake, cylindrical shells may experience global shear and suffer shear buckling. Buckling of thin walled shells is highly dependent to imperfections. In this study buckling of imperfect cylindrical stiffened tanks due to global shear and seismic loads are studied. To this end nonlinear FE static analyses have been performed in order to estimate buckling capacity of imperfect cylindrical stiffened tanks due to global shear. Herein cylindrical tanks of a constant height and different height to diameter (H/D) ratios were considered. Different arrangements of stiffeners were considered for each tank. Random patterns of imperfection with moderate imperfection amplitude were considered in all tanks. Design relations have been presented based on the results of numerical analyses. Finally, time history analyses were performed in order to evaluate the validity of suggested design relations for buckling of cylindrical stiffened tanks due to seismic loads.

The important criteria for designing in the most of hydrologic and hydraulic construction projects are based on runoff or peak-flow of water. Mostly, this measure and criterion is calculated or estimated by stochastic data. Another feature of these data that are used in watershed hydrological studies is their impreciseness. Therefore, in this study, in order to deal with uncertainty and impreciseness, based on Buckley’s estimation method, a fuzzy logic method of evaluating hydrological measures is developed. The method introduces triangular shape fuzzy numbers for different measures in which both of the uncertainty and impreciseness concepts are considered. Finally, to illustrate the methods more explicitly, the two algorithms are tested on a real case data.

A new challenge which the world will face in near future is the reduction of water resources regarding to global climate changes. Climate change is one of the phenomena which will threats future of the universe. Iran locates in an arid and semi-arid region and has limited water resources. Based on global and Intergovernmental Panel on Climate Change (IPCC) board database and the statistics of some selected synoptic stations (Tabriz, Bilghan, Mashhad) to obtain an appropriate spatial distribution in northern part of the country, we have considered the climate change and its effects on Iran`s water resources. Based on IPCC scenarios the temperature will grow 1-2 degrees in these regions till 2020 and precipitation will decline to 20%, this will directly influence the condition of water resources of these regions and new challenges. This procedure and its changes will be considered through statistical analysis and graphical description of data gathered through selected synoptic stations databases. Regarding climate changing effects on water resources, studying the karst water resources of Northern Khorasan indicated a significant reduction among the spring's discharge in these resources.

Developments in the field of Structure and Earthquake Engineering and also consequences of earthquakes have been led to develop some continually changes and improvement of seismic regulations around the world. In regards to seismicity of Iran, it is necessary and also possible to review and edit the Seismic Regulations of Iran and compare it with the other countries; so it seems that a comparative study of relations of the fundamental period based on various regulations is required. This debate is regarded to change all kinds of structures; for example, here the irregular structures with varieties of irregularities on height can be mentioned. The irregular structures are more observable than the other ones because of their unique form and creative ideas of architectures. Then, in regards to extend and grow of usage these structures around the country we shall collect and present a correct study based on an accurate planning because investigation of the fundamental period of irregular steel frames on height is required. By this research the investigation of the fundamental period of three-opening irregular steel frames with divergent bracing along with irregularities on height is studied. Models of three-bay frames with 2-15 storeys have been modeled by Etabs Software; also a series of short, middle and high frames have been modeled by Opensses Software, and then they are compared together, finally the analyzed periods have been compared with the different relations in Regulation; then by the use of MATLAB-2013 Software some coefficients of formula of the fundamental period have been determined for three-bay frames with one-sided-stepped on the height and divergent bracing.