نشریه سد و نیروگاه برق آبی ایران
پیاپی 20 (بهار 1398)

In this research, the effect of nonlinear behavior of concrete on seismic performance of roller compacted concrete (RCC) is discussed. Nonlinear behavior of material shows the behavior close to reality due to use of all structural capacity and it is considered the most appropriate method for design. So in this paper, by using the appropriate definition of nonlinear behavior of RCC, the Ansys software based of finite element method is used for modeling and analysis considering dam-reservoir-foundation interaction. Consider to behavior of roller concrete dam, two-dimensional model is selected and the dynamic analysis is carried out in time domain applying the Northridge earthquake components for linear and nonlinear cases. For evaluation of the effect of nonlinear behavior on the output results, the maximum hydrodynamic pressure, dam crest displacement, tensile stress in heel and compressive stress in the toe of dam are selected as critical responses. Finally, for accurate evaluation of the effect of nonlinear behavior on output responses, the results has been obtained as time history curves for both linear and nonlinear cases and the difference of responses has been determined.

The present study investigate the effects of mechanical properties of the rock layers in the foundation of concrete gravity dam on the seismic response of gravity dam–reservoir –foundation systems. The mutual effects of different domains are considered in the present research. As a case study the biggest section of Shafarud dam in the north of Iran is modeled two dimensionally using ABAQUS software and its response to the may 1940 El–Centro California earthquake is considered.Four different ratio of elasticity modulus of foundation to the elasticity modulus of concrete of dam body are applied in the analysis obtained results show a significant effect of the foundation material properties on the crest displacement of dam and stress distribution in the dam bodywhich highlight the importance of detailed survey in order to identify the features of the site before construction.

Limit equilibrium method, strength reduction method and Finite Difference Methods are the most prevalently used methods for soil and rock slope stability analysis. However, it can be mention that those have some limitations in practical application. In the Limit equilibrium method, the constitutive model cannot be considered and many assumptions are needed between slices of soil and rock. The strength reduction method requires iterative and continual calculations and does not give the slip surface directly. For slope stability analysis a new method based on the numerical Manifold method and Graph theory is this research developed that can directly calculate the potential critical slip surface and minimum safety factor according to the stress results of numerical simulation. This method is based on current stress state and can overcome the disadvantages mentioned above in those three traditional methods.

In this work, a research carried out on a project by Shahid Abbaspour dam in Khuzestan province, was used to improve the epoxy paint used in staining the dam. Nanoparticles of titanium oxide contaminated with tin and then polymerized with polypyrrole were added to the paint used in the dam with various weight percentages of 0.1 to 1% by weight, and it was observed that if 0.5% of nanoparticles in paint is used, the epoxy fastness to corrosion increases significantly. In this field research, all materials used in the dam, including pipe, paint, and water from pipes and intrusive walls were used. An electrochemical method was used to conduct a corrosion test, one of the electrodes of which were pieces of tubes used in the dam, painted with normal epoxy and enhanced epoxy with nanoparticles. Meanwhile, for electrolyte used in tubes, various water samples taken from different points of the dam were used.

Today to design large hydraulic structures like dams, application of dynamic analysis in time domain seems very interesting due to its benefits. For applying such analysis, appropriate earthquake records that are compatible to site conditions are necessary for designer. Such information is rarely recorded for a dam site during an earthquake and usually the amount of recorded data is not sufficient for a non-uniform analysis. In this study using … stochastic vibration method, artificial earthquake records compatible to site conditions are generated and effects of distance from source and corner frequency is investigated. It is shown that increasing in corner frequency, caused to complicating simulated acceleration pattern and also the magnitude of maximum acceleration is increased. It is shown that increasing in distance caused in decreasing amplification effects at site. With increasing distance over 100 kilometers the amount of maximum acceleration is approached to each other in two conditions (with and without amplification effects) so we can ignore the effects of amplification. But in closer distances the combination of site amplification effect and distance parameters and the path have significant effect on earthquake records.

Performance based earthquake engineering approach has been under evolution for seismic safety assessment of structures. Qualitative and quantitative definition of seismic performance levels is major challenge of concrete gravity dams. The main purpose of this article is damage patterns and failure scenarios prediction of structure while they prepare a suitable basement to determine dam seismic limit-states. Therefore nonlinear incremental dynamic analysis has been applied to dam-reservoir-rigid foundation system of Pine Flat gravity dam as a case study under the pulselike near-fault records. Then the critical zones of dam body have been recognized using a new way and a series of potential crack paths has been found. The mentioned above paths have been validated through comparing with authoritative published reports. We observed that the structure is damaged in certain patterns under near-fault records. Also formation of full crack in dam body is possible only in four paths before the possibility of total collapse. Hence three failure scenarios of concrete gravity dam have been defined in this research, in addition to damage patterns prediction. The results show that the safety level of concrete dam is increased substantially when the crest displacement response or drift ratio is limited to the conservative value.

Location of floating piles is one of the main factors influencing on their optimal performance with respect to slope stability improvement. Many studies have been devoted to this concern using different analytical methods. Due to the importance of this issue in seismic conditions, still more studies are necessary and therefore, the location of floating piles has been investigated in this research using finite element method under seismic conditions. Three parameters including soil arching, crest settlement and pile bending moment has been considered in investigations. Using load transfer factor, soil arching can be suitably quantified and then utilized in numerical analyses. A comprehensive coupled numerical analysis has been carried out in order to examine the optimal location. With the purpose of considering soil's increasing elasticity modulus in depth, a FORTRAN code was developed. To obtain authentic results, modeling has been verified by comparing numerical results with an experimental research which was performed previously. The results showed that the optimal location which causes the highest stability level is the first middle of up-slope (XP/LH = 0.5 - 0.75).