نشریه مهندسی عمران فردوسی
سال سی و دوم شماره 4 (زمستان 1398)

Under small strains, the shear-wave velocity (Vs) and its resultant maximum shear modulus (Gmax) are important parameters in geotechnical engineering soil dynamics analyses. In this regard, the evaluation of the influences of soil particle size on the dynamic behavior of soils during wave propagation has been an important issue in geotechnical engineering. According to the relevant literature, the influences of grain size on shear wave velocity of soil were completely different in various research studies. This research aims to experimentally examine the effects of a wider range of particle sizes, on maximum shear modulus in dry sandy soils, using a bender element apparatus embedded in a triaxial cell. The results indicated that maximum shear modulus of sand was considerably affected by changes in grain size so that in a particular range of grain size, shear modulus increased as the diameter of soil grains rose, while, in the other range, maximum shear modulus diminished with increasing grain diameter.

Nowadays the researchers and experts are interested in steel plate shear wall throughout the world particularly in the regions with high frequency of earthquakes. There has been a number of numerical and experimental studies to get more information about the behavior of this system.to make more use of the capacity of inelastic behavior of the systems and structures it makes necessary to apply Non-linear methods in designing structures. As this method is rather time-consuming the static linear technique is used instead of it, designing elastic is not economical, so it is replaced by coefficient behavior. In this study, the seismic coefficient for the reinforced concrete moment frame with the thin steel plate shear wall is carried out using incremental nonlinear dynamic analysis. Three 7-story, 15-story, and 30-story buildings with different near fault and far fault records were analyzed. The ductility factor, additional strength, and coefficient behavior of the structure were calculated as 4.24, 2.48,9 respectively. The result of this study show that the coefficient behavior, and ductility factor of this system is decreased as the height of the structure goes up but it leads to the increase in the strength Factor.

In this study, the transportation of sediment in sewer flumes is predicted using a hybrid model. On the other hand, the hybrid model (ANFIS-GA) using Adaptive Neuro-Fuzzy Inference Systems (ANFIS) and Genetic Algorithm (GA) for prediction of the Froude number of three-phase (air, water and sediment) flow is developed. In this study, the genetic algorithm is used to increase the ability of ANFIS by tuning the membership functions and subsequently minimize the error. The genetic algorithm (GA) is a meta-heuristic inspired by the process of natural selection that belongs to the larger class of evolutionary algorithms (EA). Then, the 127 hybrid models were defined using input parameters. For the superior model, the Mean Absolute Percentage Error (MAPE) and Root Mean Square Error (RMSE) were computed equal to 5.529, 0.315, respectively.

A huge amount of money is spent every year on designing and constructing of asphalt pavements due to an increase in the number of vehicles and, consequently, a higher demand for constructions of new roads. In addition, overtime, different factors such as severe climates and roads traffic conditions create cracks on the road surface that also require spending money on roads maintenance. Thermal cracking is one of the major distress types in the cold regions. Further propagation of such cracks may occur because of tensile thermal stresses induced by temperature fluctuations which can result in pure mode I fracture mechanism in the asphalt pavement. This study aims to determine fracture toughness ( ) as a fundamental parameter for estimating the load bearing capacity of cracked pavements against crack propagation under mode I cracking in low temperatures. To this end, the asphalt mixtures were manufactured with AC 60/70 bitumen. Semi-circular bending (SCB) specimens with effective crack length (a=23 mm) have been prepared in three thickness (35, 50 and 65 mm). We collected data with conducting the fracture tests at three subzero temperatures (-5°C, -15°C and -25°C) and calculating the fracture toughness values using fracture loads. The results indicated that, in general, increasing speciments thickness and decreasing temperature increase fracture toughness. Finally, using MATLAB software, a model was developed to estimate the asphalt fracture toughness according to the two parameters of temperature and specimens thickness. It was determined that the proposed model can predict the values of fracture toughness in asphalt mixtures prepared on present study at the temperature and thickness range of the research.

Marls are among sedimentary deposits that generally contain 35 to 65 percent of clay minerals and calcium carbonate. The presence of clay minerals in marls has significant effect on reduction of slake durability index of marls. Hence, marls stabilization is important. Furthermore, the presence of carbonate as one of the main components of marls has drastic influence on engineering behavior of soils. Heat, both in transient or constant forms, results in physical, mechanical and microstructural alternation of soils, especially the engineering properties of clay soils. Accordingly, the purpose of this study is to investigate the effect of heat treatment on strengthening parameters of marls, microstructural perspective. Impression of heat treatment on behaviors of marls, using macrostructure tests (Unconfined Compressive Strength, Atterberg Limit, Granularity, Slaking, Water Absorption and Linear Shrinkage) and microstructural tests (pH and X-ray diffraction) have been assessed. For this purpose, the specimens are exposed to heating surfaces (25 to 900 °C). examinations with emphasize on microstructural alternations of marls on specified temperatures and effect of temperature variations on mechanical and strengthening specifications of soil, have been conducted. According to the results, on 700°C marl soils have the best compressive strength of 27.69 Kg/cm2 and durability against moisture.

In performance-based seismic engineering, conservatism in acceptance criteria has increased the cost of rehabilitation. Considering of uncertainties can reduce the conservatism and the cost of rehabilitation. In this study, reliability of rehabilitated structure with steel shear wall has been discussed and study of reliability index has been performed on probabilistic variables. The studied structure is nine-story steel moment frame that has been analyzed pre-and post-rehabilitation. The results have indicated that yield strength of steel shear wall has the greatest effect on the structural response of other probabilistic variables. According to results, the rehabilitation of the structure has decreases probability of failure and consideration of uncertainties of rehabilitated structure has increased probability of failure and therefore existing conservatism has been decreased.

In the present study, a combination of delayed dams in the upstream basin with the coastal dike in the downstream of residential area of the Kan river was studied, so that for this combination, the cost of constructing the structures is minimized and the reduction of flood peak is maximized. For this purpose, multi-criteria decision method and TOPSIS method were used and the best option was determined. This research showed that for the best combination, if 3 delayed dams with coastal river dike are constructed, the peak of output flood reduce to 31.5%. In addition, the diffusion and elongation of the output hydrograph in the superior state were significant and the time of concentration of flood increase.