Journal of Numerical Methods in Civil Engineering
Volume:5 Issue: 1, Sep 2020

In present study, the effect of reservoir length on seismic performance of concrete gravity dam has been investigated. Monte Carlo probabilistic analysis has been used to achieve a sensitivity of the responses to variation of truncated reservoir length in finite element model. The ANSYS software based on finite element method is applied for modeling and analysis. The Pine Flat dam in California, under components of El Centro, San Fernando and North Ridge earthquake, is modeled as a case study to evaluate the effect of reservoir length on seismic behavior and optimization. The foundation flexibility has been considered in modeling and Sommerfeld boundary condition has been used for reservoir truncated boundary condition. In Monte Carlo probabilistic analysis, the reservoir length has been considered as input variable and maximum dam crest displacement, maximum hydrodynamic pressure in reservoir and maximum tensile principal stress in heel and compressive principal stress in toe of dam have been selected as output parameters. The Latin Hypercube sampling method has been applied with unique distribution function for input variable.  Obtained results show the sensitivity of output responses to variation of reservoir length. Considering sensitivity results, it is possible to select the optimum length of reservoir for finite element model.

Pre-stress techniques tend to increase cross-sectional capacity and optimize design. Such features have made these techniques rather popular. Over time, these structures tend to fail, and the reduction of pre-stress force over the lifetime of the structure is said to be one of the most significant destructive factors in these structures. This decrease in force occurs due to various reasons. In majority of cases, a cracking of pre-stressed concrete beams appears due to the reduction of pre-stress strength. Where there is permanent monitoring by the sensors buried within pre-stressed tendons, the force of the tendons can be investigated. But given the high cost of this procedure, such monitoring cannot be implemented in many structures. Nevertheless, it is possible to determine changes in pre-stress forces through investigating the dynamic behavior of structures. This paper examines the changes in the dynamic behavior of a pre-stressed beam experiencing a variety of pre-stress force levels. The idea is to monitor force changes in the pre-stressed tendons via examining certain dynamic characteristics of the beam (namely, modal damping and resonance frequency) and carry out repair prior to fail. The results show that with increasing the prestressing force, the system frequency increased and the system damping decreased.

Recently, global warming problems with rapid population growth and socio-economic development have intensified the demand for water and increased tensions on water supplies. This research evolves the Multi-Objective Coronavirus Optimization Algorithm (MOCVOA) to obtain operational optimum rules of Voshmgir Dam reservoir under the climate change conditions. The climatic variables downscaled and predicted by the Bias Correction Spatial Disaggregation (BCSD) method of MIROC-ESM model, was introduced into the Extreme Learning Machine (ELM) modelto evaluate the future runoff flowing into the reservoir. The model objective functions included minimizing vulnerability and enhancing reliability indices during baseline and climate change periods. Results revealed that under climate change conditions, the river flow would decrease by 0.17%, increase the temperature up to 2°C and decrease the rainfall by 23.8%, corresponding to the baseline period. Moreover, the extent of vulnerability index variations in the baseline and climate change conditions were also determined as 20-38% and 13-40%, respectively. The reliability index changes under the baseline and climate change conditions obtained were, 57-85% and 40-91%. Therefore, the vulnerability index was also measured at 33% and 30% for baseline and climate change conditions, respectively, with 80% of reliability index. Finally, the comparison of reservoir performance in meeting the water needs of downstream lands at the Pareto point of 80% reliability under both conditions indicated that the reservoir release rate would be more in line with the demand in the climate change conditions.

The overturning potential of rocking soil-structure systems subjected to near-fault pulses is investigated in this paper. An extensive parametric study is conducted, including medium-to-high-rise buildings with different aspect ratios based on shallow raft foundation allowed to uplift considering the effects of nonlinear soil-structure interaction.  The considered parameters are (i) ground motion characteristics, (ii) structural properties of the superstructure, and (iii) foundation design parameters. Mathematical directivity and fling pulses are used as input ground motion. The superstructure is assumed to predominantly showcase first-mode characteristics. Two-dimensional overturning spectra of buildings of various geometrical, as well as dynamic characteristics, are derived. Evidently, the prevalent pulse period (Tp) is a key parameter governing the rocking response of the system. It is also observed that fling pulses are more destructive than directivity pulses of the same magnitude with respect to overturning potential. On the other hand, the lower frequency parameter (p) of the more large-size buildings is a quantity that indicates higher safety margins against toppling with respect to small-size buildings of the same aspect ratio.

Seismically induced slope movements have imposed severe damage on the pile-supported structures located on soil slopes during past earthquakes. Consequently, evaluation of the lateral seismic response of pile-slope systems is an important measure towards safe design of pile groups. However, since the codes and techniques used in seismic design of pile groups for engineering purposes are neither practical nor easily accessible, it is difficult to employ them consistently in design procedures. Therefore, simplified approaches are required for pile design application. This paper presents a novel approach that practitioners can use to quickly evaluate the seismic displacements of pile-groups in soil slope. Such an approach is based on the reasonable and practical relationship found between the pseudo-static safety factor of pile-slope system and seismic displacements of pile groups. In order to explore this relationship, a parametric study was performed and a dimensional analysis was carried out to study  the results of the relationship and achieve the dimensionless chart. Thus, the conclusions of this study are intended to provide practitioners with some practical guidelines such as low calculation efforts, and to incorporate the relationship between slope safety factor and pile group displacements into the design process.

In the present paper, a hybrid analytical/numerical method capable of integrating singular logarithmic functions, as an essential part of the Boundary Element Method (BEM) process, is presented. The proposed scheme provides a more practical approach through the reduction of the computational effort of the analytical method. For this purpose, the singular function is divided into two parts of singular and non-singular. The non-singular part is numerically integrated, while the singular part is analytically integrated and the result of both parts is combined. The capabilities and accuracy of the proposed scheme are investigated through various elemental and potential examples. The results of numerical comparisons indicate the ability of the proposed scheme to reduce the computational effort of the analytical solutions, which develops an appropriate alternative for the simple analytical solution of the potential problems that can be used in practical modeling problems such as heat transfer.