نشریه مهندسی عمران فردوسی
سال سی و سوم شماره 3 (پاییز 1399)

The aim of this study is to investigate the effect of aleatory and epistemic uncertainties on seismic performance of an intermediate steel moment frame. For this reason, generalized incremental dynamic analysis is employed. To model record-to-record aleatory uncertainties, 40 far-field ground motion records are utilized. Also, to model important epistemic uncertainties, 5 parameters of plastic hinge behavior are uncertainly modeled and statistical parameters are considered for these models. Then, by using effective simplified models of random variable production, 50 combination of these 5 parameters are produced and for each one of these models a bin of IDA curves are extracted. Results show that parameters with epistemic uncertainty affect fragilities of IO limit state more than other limit states. In other words, for CP and GI limit states fragilities of mean of models yield acceptable results even when incremental dynamic analysis cannot be conducted for all the 50 models. However, For IO level, the effect of epistemic uncertainties cannot be neglected.

Study of immediate settlement of a rectangular foundation with the task of transferring structural forces to the ground, is one of the important factors in the design of structures. Due to its heterogeneous and anisotropicnature, soil parameters have highuncertainties, the omission of which in estimating the settlement of foundation, creates challenges in the analysis of structural stability. Therefore, the use of reliability methods with the ability to accept uncertainties and reliable stability analysis of geotechnical issues are welcomed today. In this study, in order to estimate the probability of failure due to settlement of rectangular foundation, first-order and second-order reliability methods as well as Monte Carlo simulations were used and the relevant analysis were performed in RT and @Risk software.The results indicate a high probability of failure related to the foundation settlement (9.5%). The second-order methods and Monte Carlo simulations provide more accurate results due to the non-linearity of the limit state procedure. In addition, the sensitivity analysis of random variables based on sensitivity vectors showed that thecontact stress (qo), has an important role in the probability of failure, and then the Poisson’s ratio is important.

The high energy impinging on the outflow through the overflows is controlled by the design of the energy absorber structures in the downstream or downstream relaxation pool. However, the occurrence of downstream local scour is one of the major threats to the stability of the overflows. In the present laboratory research, first, by conducting control experiments (unimpeded shot) at different landing numbers, the geometry of the scour pit was investigated, then by providing a basic block-height protection method in three geometric shapes (Rectangular, Semicircular, Triangle), four mounting positions proportional to the total Lb/Lf shot length (0.2, 0.4, 0.6, 0.8) and also, to concave the installation of blocks, the dimensions of the scour pit are measured and Dimensional analysis was performed using Pie-Buckingham method. The results showed; The use of block base on the slope of the shot in all the models tested has an effect on the dimensionality of the scour and has always reduced the dimensions of the scour pit. In summary: 1. The depth and final length of the scour increases with the increase in the number of upstream landing overflows. 2. In the series of upward concave tests, blocks always have lower values ​​of scour dimension than low facing concave. 3. By decreasing the installation distance of the blocks from the overflow claw, the scour depth and length decrease. So that at position (Lb/Lf = 0.8) the highest energy damping occurred at other positions. And under different conditions the flow decreases between 15 to 61.2% of the depth of the scour pit. 4. In position (Lb/Lf = 0.6), semicircular and rectangular blocks with low upward concavity and also in position (Lb/Lf = 0.8) triangular block with high upward concavity, with average yield 38/1 to 73/4% had the highest decrease during scour compared to other states. 5. By increasing the number of downstream currents, the relative damping energy of the current in the shoot paw decreases.

In recent years, several constitutive models have been proposed to predict soil behavior under thermomechanical loads. On the other hand, it is important to study the behavior of energy piles and their adjacent soils under thermomechanical loads and by using constitutive models in which soil behavior changes due to temperature changes are considered. In this study, a thermomechanical constitutive model was added to the Abaqus finite element software to be used to evaluate the performance of energy piles. Results obtained from numerical modeling of Triaxial test show that the code written for the given constitutive model is capable of predicting soil behavior under thermomechanical conditions. Also, the results obtained from the analysis of energy pile using mechanical constitutive models of Drucker-Prager, MCC and thermo-mechanical constitutive model Tourchi show that in the analysis of energy pile, although the choice of constitutive model has a significant impact on the results, but there is no difference between choosing a mechanical or thermomechanical constitutive model for the adjacent soil.

The type of contact surface has a significant impact on the frictional resistance. Experimental evaluation of the effect of contact surfaces on bolt connections has been conducted in current research. The purpose of this study is to study the effect of different levels of contact surface on the frictional resistance and propose a new method for increasing frictional resistance. Contact surfaces used in this research are as follow: non sand-blasted, sand-blasted, coating with 20 μ thickness, coating with 40 μ thickness, triangular corrugated surface and squared corrugated surface. The results indicate that, the highest and the lowest bearing capacity were captured according to corrugated surface and 40 μ coated surface, respectively.

Skirted foundations are expanding as a new type of alternative foundations for other prevalent foundations in onshore and offshore structures. The study of skirted foundations performance is essential for evaluating the effect of foundation geometry and soil specification. In this research, the bearing capacity and settlement of circular skirted foundations resting on sand under vertical compression loading was studied by physical modeling and numerical analysiswith consideration of the effect of different parameters including skirt depth, foundation diameter, sand density and surface roughness of the foundation models. The performance of skirted foundations was compared with common types of surface, semi-deep and embedded foundations. Analysis of results showed that the behavior of skirted foundation models compared to the surface foundations has been improved significantly in terms of the enhancement in the values of bearing capacity and subgrade reaction modulus, as well as the reduction of settlement amounts. Improvement in the performance of skirted foundations was increased by increasing the skirt depth and surface roughness of models, and also, reducing the density of the sand. The comparison of the bearing capacity results of the skirted foundations with the corresponding values of the semi-deep foundations showed that the load- bearing behavior of the skirted foundations is close to those of semi-deep foundations with the same depth and diameter. Comparison of the skirted foundations performance relative to embedded surface foundations represents a further reduction in the settlement amounts of surface foundations due to the skirt existence underneath foundation instead of its embedment in depth, as well as the further improvement of bearing capacity by increasing the surface roughness of the skirt.