نشریه مهندسی عمران فردوسی
سال بیست و هشتم شماره 1 (بهار 1395)

Mechanism and factors influencing on creep behavior of clay soil have not been understood yet due to its complex structure. In this paper, to investigate the affecting parameters on the creep behavior of the clay soils such as stress level, over consolidated pressure and water pressure, odeometr test are performed in states of single stage, stepwise and overloaded-unloaded and the creep mechanism are explained with considering the effect of sliding of clay particles at their contacts and deformation of particles. Since the conducting of some creep tests may last for months, therefore the prediction of a new method to accelerate the creep tests is necessary. The results show that in overloaded-unloaded test, the time required to reach the specified porosity is lower than the single stage, and this process accelerates the creep.

Development of new methods in seismic analysis and increasing application of performance based seismic design necessitate the study of the seismic performance of structures designed based on Iranian regulations. In this study the seismic performance of steel moment-resisting frames designed based on the tenth code of the Iranian national building regulations is investigated. Frames are different in number of stories, seismic loads, span length and gravity loads. Fragility curves of the frames are depicted for different performance objectives and their seismic vulnerabilities are examined. Results indicates that satisfying life safety performance level would ensure the proper performance of frames for other performance levels and also the performance of taller frames is more critical than shorter frames.

In order to investigate the structural behaviour of Persian brick masonry domes, three types of semi-circular, (drop, ordinary and raised) four-centred and (drop, ordinary and raised) pointed domes have been studied. The three-dimensional non-linear finite element method using the ANSYS code has been used for analysis. Domes with different thicknesses and spans have been subjected to monotonic concentrated loads up to local failure. Vulnerable zones have been stiffened by FRP strips. Stiffened domes have been again subjected to monotonic loads until local failure. FRP strips with different dimensions and patterns have been used. They have been placed at the one-third and two-third of dome height. Appropriate failure criteria have been used for prediction of brick and FRP failure. In this paper, obtained results including failure loads of domes, the effect of dimensions and patterns of FRP strips, and that of the shape and span of domes on failure load are presented.

The use of polymer composite (FRP) as a reinforcement material for the repair and strengthening of important components of reinforced concrete structures, particularly columns, has found wide spread. In this study, the effect of intermediate layer on improving the confinement behavior of reinforced concrete columns has been investigated. To achieve the objectives of the study, 14 cylindrical reinforced concrete specimens with 150 mm diameter and 500 mm height were tested under pure axial load. The columns have been classified into four groups and were reinforced by one or two layers of carbon fibers and then to investigate the research topic, confinement with intermittent CFRP strips was performed in both traditional (Without intermediate layer) and modern method examined in the present study and the results were compared together and with the results of loading columns with internal reinforcement and without external reinforcement (the control sample). The new method involves using a thin layer of galvanized sheet (thickness 0.13 mm) which is mounted under the FRP sheet to prevent the transmission of stress concentration induced cracking concrete to FRP Sheets.The middle layer reduces the transfer of biaxial stress to FRP sheettoo. The results suggest that specimens reinforced with FRP and galvanized sheets have higher strength and ductility than specimens reinforced with FRP and without Galvanized.

In many structures, the applied lateral loads are comparable with gravity loads. These types of piles which are subject to high lateral load are usually divided into two categories including long and short piles. The general methods to estimate lateral bearing capacity of short and long piles are based on ultimate bearing capacity and allowable horizontal displacement respectively. In the present research, in order to evaluate lateral bearing capacity of piles subjected to horizontal loads, steel pipes which were embedded in sand soil to simulate piles in the laboratory. A wide range of laboratory tests were performed to investigate the behavior of long piles with different lengths and diameters. The test results were compared with three different theories including Modulus of Subgrade Reaction, Elastic and khmax approaches. The experimental results reveal that khmax approach is more suitable for determination of horizontal displacement and also estimation of lateral bearing capacity for long piles.

Due to widespread application of reinforced soil media and the crucial need to understand and anticipate its actual behavior, in addition to the fact that direct numerical analysis of reinforced masses is a difficult and time-consuming procedure, homogenization methods have been introduced. In this study, multiphase approach which is considered as a new framework in homogenization methods is developed. This development is done using the Duncan-Chang hyperbolic model for simulating the behavior of soil in a reinforced medium. In this study, efforts have been made to propose a new multiphase model for analyzing reinforced soil media, based on assigning the Duncan-Chang constitutive model to soil and elastic-perfectly plastic behavior to reinforcements. A developed multiphase model is used to simulate a full-scale reinforced soil wall. The wall has been analyzed by means of both direct and homogenization approaches, using Duncan-Chang constitutive model and the developed multiphase model, respectively. After comparing the results of the analyses, sufficient accuracy of homogenization approach using proposed multiphase model has been approved. It is also observed that in contrast to its simplicity, the Duncan-Chang hyperbolic model presents a suitable estimation of behavior of the reinforced soil wall in case of implementing direct analysismethod.