فصلنامه رویکردهای نوین در مهندسی عمران
سال هفتم شماره 1 (بهار 1402)

In order to prevent damages caused by the extraordinary energy of water at supercritical speeds and to eliminate the additional kinetic energy in such water, it is generally necessary to use special structures called (Energy dissipators) that are made downstream.In addition to removing water energy, these structures are also a mean of controlling and restraining hydraulic jump and creating conditions for its occurrence in a specific location.In this research, which has been compiled by descriptive research method, after introducing and recognizing hydraulic jump and resting basin, researches on the geometric arrangement of resting ponds were investigated and finally three different expansion ratios and five different heights of overflow edges were investigated.

Today, concrete is used as the main material in the construction of structures in our beloved country of Iran. Therefore, various types of concrete have been researched by different researchers in terms of behavior, weight, and resistance, and have been an important concern of researchers for a long time. Lightweight concrete, high-strength concrete, porous concrete, self-compacting concrete, etc. are examples of this research in the field of civil engineering, which has been held in various competitions in recent years. The present research has been discussed in the field of mixing design of a specific type of relatively light and relatively resistant concrete. The main goal of this article is to optimize the cubic concrete mixing design (5x5 cm) using artificial neural network models. The experiment program in this research started with 200 mixing designs in the field of cubic concrete and preparing a database and it was modeled by using various perceptron multilayer neural network structures. The evaluation indices used in this research include the regression coefficient (R) and the mean square error (MSE), which have been used to introduce the optimal structure of the artificial neural network. The results of the modeling based on the laboratory tests showed that the correlation coefficient for most of the models is more than 85%, which indicates the appropriate efficiency of the artificial neural network based on the Schmidt criterion. Also, pseudo-neuron with double hidden layer of 8 neurons with an average correlation coefficient of 93% in three sets of learning, training and evaluation and an average error index of 0.182 has been selected as the optimal structure in the set of structures used.

Contractors play the main role in the success or failure of construction projects, therefore, it is very important to determine the qualifications and selection of contractors in order to succeed in projects and reduce costs. This article was done with the purpose of evaluating and selecting construction contractors. This research is a non-experimental (descriptive) based on the objective, practical and based on the method of data collection, which was conducted in a cross-sectional survey. The target community included experts, experts and decision makers in the field of contractor evaluation in organizations and companies in Semnan. Sampling was done by targeted method and finally 10 people participated in this study. To analyze the data, the combined method of DeMetal, the process of network analysis and the best-worst were used. The findings of the research showed that the criteria of quality, management ability, financial index, technical ability, reputation and health, safety and environment are in the first to sixth priority respectively. The findings of the best-worst method have shown that quality, management ability and financial index, technical ability, safety and environment and reputation are in the next ranks. Finally, suggestions were made based on the research findings.

In this literature a case study that includes surcharge and prefabricated vertical drains (PVDs) was introduced and verified using finite element program Geostudio 2018R2. Based on the verified model, the lateral displacement and horizontal strains were calculated. It was shown that the safe zone for this special case study is 40 m that is approximately equal to the length of the constructed embankment. In urban areas as a result of the existence of water and wastewater pipes, optical fibers, oil and gas transition lines or trenches and excavations, these infrastructures are in serious danger due to the lateral displacements and horizontal strains. The same case is true for constructions in industrial areas. Since the mentioned infrastructures do have special importance in passive defense doctrine, exclusive attention should be considered by the owners, consultants and contractors in such projects all phases including preliminary investigation, during the construction and after the compilation of the treatment process in the case of permanent embankment. It was shown that due to the obstacles related to surcharge and PVDs treatment, this method is not suitable in urban areas.

In the present paper, the effects of viscoelastic dampers and lead-rubber bearing (LRB) isolators on the seismic behavior of irregular steel buildings at height have been investigated. To this aim, a number of steel frames with flexural frame bearing system were modeled as 5, 9 and 13 stories and their seismic performance was evaluated in three modes: (1) without damper and isolator, (2) equipped with viscoelastic damper and (3) equipped with rubber core lead separator. After modeling the buildings in PERFORM-3D finite element software, by performing nonlinear static (pushover) and nonlinear dynamic (nonlinear time history) analyzes, the effect of damper and separator on the behavior of irregular steel buildings has been investigated. The results showed that the viscoelastic dampers and LRB isolators improve the seismic performance of steel buildings; The use of viscoelastic dampers in steel buildings with flexural frame system has increased the rigidity of the building and consequently the base shear force compared to single flexural frame and buildings equipped with LRB isolators. The results also showed that in all buildings, the base shear created in the isolated structure is much less than other control methods, which is due to the nature of seismic separation, ie reducing the force applied to the building.