فصلنامه رویکردهای نوین در مهندسی عمران
سال پنجم شماره 4 (زمستان 1400)

Purpose of this study is Assessment and review of time - lag factors in a Bridge. The execution of development projects such as bridges, due to the importance and critical role of the structure in the system of transport and traffic control, aims at achieving the goals of development plans and its impact on the development and evolution of human activities, distribution of services and reducing traffic volume, as compared to other development projects. It is essential to study the factors of time delay in the construction process, and thus making significant savings in the construction and implementation of other similar development projects, thus making significant savings on the financial and temporal dimensions. In this study, after accurate identification and introduction of case study , three main indices of project delay , each consisting of several sub - branches , are prepared in the majority of questionnaires and are weighted by a number of experts , indicators and sub - indices of project delay. In this way, the most important parameters which have the maximum contribution to the delay in the project implementation process are introduced. In the following, using the classification and gathering points and the results of the questionnaire, the most important factors for delay in the project will be identified and introduced. It should be noted that the responses obtained from the questionnaire in this study will be AHP method. According to the results of the present study, one of the most important factors affecting the time delay regarding the bridge has been classified into three main indicators related to financial factors, regulatory factors and executive management factors. Therefore, the most important sub - indicator of the delay was due to the three indicators of financial , monitoring and implementation, respectively, lack of price list nonuse of new engineering contracts such as BOO , BOT , EPC  and lack of Article 53 of the General Terms of treaty.

Due to the seismicity of Iran and the occurrence of irreparable human and financial losses during the past years and in order to reduce these losses due to lateral loads, control methods can be used. Vibration control is a low-cost method among various methods of improving the seismic behavior of structures, which leads to a reduction in the response of the structure under dynamic loads. Control systems are divided into four categories: inactive, active, semi-active and combined. In this research, for the accuracy of modeling, an analytical article conducted by other researchers is used and the results are compared. Then 6 frames without damper and 6 frames with viscous damper with the same number of floors, under the title of short level 3, 5, medium level 7, 10 and high level 12, 15 floors in Itbus software according to 360-AISC- regulations, sixth and tenth topic National building regulations are loaded, designed and controlled. The results show an increase and improvement in the performance of the structure with a viscous damper compared to a normal structure. Reducing the displacement of floors can help reduce issues such as the seam allowance of two buildings as well as the comfort of residents in the event of an earthquake. Reducing floor drift can help improve the behavior of non-structural components and joinery. The presence of viscous dampers has reduced the displacement and drift of floors by even 90%. The presence of a viscous damper makes the drift of the floors more uniform. The presence of a viscous damper reduces the forces applied to the members and increases the capacity of the structure. As a general conclusion, the use of viscous dampers has acceptable results in structural responses and has increased the behavior and capacity of the structure.

The use of control methods in the design of structures has received more attention. Separators, reduce damage by reducing the vibration transmitted to the structure. In this research, modeling of 7 and 11 story steel flexural frames with and without separators has been used and the effects of separators on the structural safety have been measured using nonlinear time history analysis. The modeling was performed under the record of the El-centro earthquake and the results show that the isolators are very effective in reducing the shear and acceleration parameters. With 67% reduction of the base shear in the middle structure and 44% reduction in the high structure, using this control system, reduces the possibility of damage due to relative displacement. Also, according to the study of the process of plastic joint formation in the models, structures with separators mostly remained in the elastic stage. Plastic joints formed in unseparated structures were also in the range of life safety. The isolators, have a good effect on the process of reducing the floor shear, acceleration and relative displacement.

In this study, firstly, the 12-story 3D structure with hybrid system of buckling restrained brace and moment frame with 6 states such as 1) whole stories with buckling restrained brace system, 2) the first 6 stories with buckling restrained brace system and the second one with moment frame, 3) the first 5 stories with buckling restrained brace and the 7 stories with moment frame, 4) the first 7 stories with buckling restrained brace and the 5 stories with moment frame, 5) the first 3 stories with buckling restrained brace and the 9 stories with moment frame, 6) the first 9 stories with buckling restrained brace and the 3 stories with moment frame. Then, using Opensees software, the side axle frame is modeled subjected to incremental nonlinear static analysis and incremental nonlinear dynamic analysis (IDA) with the intensity parameter (IM) corresponding to the maximum relative displacement and the DM response parameter corresponding to the first mode spectral acceleration Sa (T1, 5%)and the level of collapse prevention performance (CP) has been evaluated. In the following, fragility curves and modification factor are presented. By investigation of the results, it is observed that the frame with more braces, at a constant seismic intensity level, is less likely to fail than other frames. Therefore, increasing the percentage of brace use leads to a higher modifaction factor and less probability of failure than other cases, and by reducing the ductility of the frames, the probability of their failure also decreases.

Behavior coefficient is one of the important parameters in calculating the loads affecting the structure in structural analysis. In this research, different aspects of behavior coefficient have been identified and have been raised as the main issue of the present study. Eccentric Bracing Frames (EBF) braces are also used as a useful tool in steel structures. One of the important issues in steel structures with EBF braces is the problem of link beams. The main purpose of this study is to investigate the coefficient of behavior of steel frames with link beams and different heights by considering the effect of soil-structure interaction, which were studied based on increasing nonlinear static analysis in four, eight and twelve floor structures. The variable of link beam length along with the effect of soil-structure interaction has been evaluated. In the study of the effect of soil-structure interaction on the cover curve, it was observed that considering the effect of soil-structure interaction, the displacement in the pushover curve increases but the base shear force decreases. It is also observed that the values of behavior coefficients decrease in the presence of the effect of soil-structure interaction, which can be due to the decrease in base shear values and increase in displacement values. The general trend of determined graphs has been to increase the values of the coefficient of behavior due to the increase in the length of the link beam. Also, the values of behavior coefficients have been reduced by considering the effect of soil-structure interaction.