نشریه مهندسی عمران فردوسی
سال سی و ششم شماره 4 (زمستان 1402)

In recent years, the use of smart numerical search techniques in active control of structure has been considered by researchers. Genetic algorithm is one of these methods that is based on natural evolution patterns. Here, the genetic algorithm is used to minimize the constrained objective function of the structure and determine the appropriate control forces. By connecting the sensor to the degrees of freedom of the structure, nodal displacement is monitored at each time step and genetic algorithm determines the proper control forces by using constrained objective function and solving dynamic equation of the structure. Choosing appropriate constrained objective function according to the structure conditions has a great impact on the efficiency of the proposed method. This function is obtained by combining the structural constraints and the assumed weighting factors for each constraint. Then, the weighting factors are calculated from the optimization methods. Such a process, leads to achieve a new active control method based on using genetic algorithm. The efficiency and accuracy of the proposed algorithm are investigate by controlling the oscillations of several structures. The results show that the proposed method is able to reduce structural oscillations effectively.

In this paper, the non-linear response spectra of elastoplastic systems with constant ductility for three accelerograms which were obtained by linear interpolation method of excitation and also by using cubic spline function are compared with each other. Non-linear response spectra were calculated for ductility of 1, 1.5, 2, 4 and 8. For a more detailed analysis, the time interval between the accelerogram points was divided into 2, 5, 10, 20, 50 and 100 equal parts, respectively, and new accelerograms were produced once using linear interpolation and once using spline interpolation, and the non-linear response spectra of these two types of accelerograms were compared. The results of the work indicated that the maximum and minimum values had significant values. In addition, in most cases, the maximum value of the difference was greater than the absolute value of the corresponding minimum difference. Also, in most periods, the spectral values did not differ much, but in small periods, which are related to stiff structures, the amount of difference was significant.

In this research, the behavior of concrete rectangular ground tanks equipped with lead-rubber base isolators has been investigated under the simultaneous excitation of transitional and rotational components of earthquakes, using nonlinear time history analysis including water-structure interaction. For this purpose, first, the rotational component of three earthquakes was generated using the wave propagation and classic elasticity theories simultaneously. Then, the tanks equipped with appropriate number of base isolators were modeled in two volumes of 500 and 1000 m3 and three states of water level. In modeling the finite elements of the isolators, a model consisting of one-dimensional elements is proposed; whose hysteresis behavior is equivalent to the behavior of the three-dimensional model of the isolators.The results of the research show that the decreasing or increasing effect of the rotational component of the earthquake on the seismic response of these tanks in the full and half-full state is less than 10%, and in general, its effect on the seismic response of the rectangular ground tanks can be ignored. Also, the presence of isolators in these types of tanks has increased the response of the tanks in all states. So that the base shear force has increased up to 4 times and the normal stress has increased between 8 and 23 times, which can be attributed to the increase in the period of ground tanks from the initial range of the response spectrum to the constant acceleration region of the spectrum due to the presence of the base isolators.

Micropiles are one of the most widely used components in civil engineering to strengthen foundations or improve the soil. These elements are also used in wind turbines. In addition to the vertical force resulting from the weight of the turbine, these tall structures are also affected by significant lateral force. This paper aims to investigate the behavior of a square micropiled foundation with the dimension of 20 cm under lateral loading. For this purpose, the reinforced foundation with 2, 4, and 8 micropiles with lengths of 40 and 60 cm in the sandy soil has been modeled experimentally and subjected to static lateral load. Also, the effect of vertical surcharge load on lateral bearing capacity has been investigated in different conditions. The results of the tests revealed that this type of reinforcement has improved the bearing capacity up to 6 times in some cases. Studying micropile collective behavior unveiled that, distant from collapse, micropile length minimally affected individual lateral capacity. In the extreme scenario (8 micropiles, 15% overload), this discrepancy was 30%. Varying micropile numbers near collapse produced two contrasting behaviors: amplification in one and reduction in another case. The determining factor in both instances was the micropile quantity, leading to a remarkable 200% role increase in the most extreme conditions.

Numerical modeling of unsaturated soils has become increasingly popular in recent years. The Discrete Element Method (DEM) is a powerful tool for modeling granular materials by focusing on particle interactions. In this study, the behavior of unsaturated granular soil was investigated using two-dimensional DEM by considering meniscus formation among particles. Unlike previous studies that simply considered particle shapes as circular or spherical, this study used more realistic polygonal particles shape that forming meniscus can be examined in different pores with respect to the geometry and arrangement of the particles. However, because of symmetry in circular and spherical particles, the shape of the meniscus among these particles depends only to the size of the particles. To this end, using a program based on the DEM was developed and a soil sample were simulated under different suction values and confining pressures. The results showed that the shear strength of the sample augments by increasing suction until a specific value and then, decreased with further suction increases. It was also observed that the effect of meniscus force on increasing shear strength decreased with increasing confining pressures. Modeling particles of different sizes also showed that the effect of meniscus force is greater for smaller particles and decreases with particle size.

Evaluation of mechanical behavior of the soil-structure interface has been the focus of many researchers as an effective factor on the strength performance and deformation of the structure. Since the interaction of the structure and the soils around it will have a great impact on the soil bearing capacity, it is important to study the physical conditions. In this study, taking into account the curing time, effect of using Persian gum and the roughness of the steel on the behavior of the soil-structure interface using large-scale direct shear test have been investigated. The Persian gum was used in three amounts of 0.3, 0.6 and 0.9% on three smooth, rough and geotextile covered surfaces. Based on the results, by injecting Persian gum into the soil-candle interface, the adhesion between soil and contact surface increases by about 20 times and the internal friction angle increases by one degree. The rate of increase of strength parameters decreases with increasing curing time.