نشریه مهندسی سازه و ساخت
سال دهم شماره 1 (پیاپی 66، فروردین 1402)

Bridges are exposed to various micro and small damages during their service life. Due to the importance and role of these structures in transportation on roads, timely detection of damages in them has a special place. This research presents an innovative and efficient method for diagnosing and estimating micro and small damages to bridges. The proposed method is based on the combination of spectral finite element and modal strain energy-based damage index to determine the location of damages in the first step. Then the support vector regression technique is used to estimate the severity of damages in the second step. A new eight-node element with spectral finite element characteristics is defined in OpenSees software. Then, micro and small damages are modeled in a single-span beam and a double-span steel beam with spring supports. In the first step, after modal analysis of the structures, the modal strain energy-based damage index is calculated to determine the location of the damages. In the second step, using the modal strain energy-based damage indices calculated in the previous step, the support vector regression networks are trained to estimate the severity of the damages. The results show very high accuracy and optimal performance of the proposed method.

Lack of correct understanding of the final product of projects is one of the most important causes of cost overrun in the construction industry, which is the source of many differences between the main elements of projects. The use of new technologies has helped developed countries control the cost of projects. Virtual reality is one of the latest technologies which has entered many industries such as the construction industry in recent years and has positive effects in different areas of project management such as cost management. According to the critical capabilities of these projects in the field of creating a correct understanding of the final product, as well as the strong influence of the finishing on increasing the cost of construction projects, the present study is limited to investigating the effect of virtual reality on cost reduction in the finishing stage of residential projects. Firstly, to achieve the study's objectives, 39 causes of increasing the cost of construction projects were extracted by studying the previous literature. Rework, design changes during execution, and fluctuations in material prices were identified as the most influential factors in growing joinery projects' costs. Then, ten experienced experts validated the accuracy of the results using a questionnaire. Second, a platform was designed to implement virtual reality to provide a correct image of the project product and management information. Then, by an interview, the effect of virtual reality on reducing the cost of finishing residential projects was measured. Finally, by merging the first and second steps of the research, the results showed that virtual reality through reduction of design changes during implementation, rework, and mistakes in virtual reality design have a significant impact on reducing project costs. Also, 25 factors that have not impacted this technology and five other factors that have experienced minimal impact were separated.

In recent decades , the vibration control of the structures subject to some loads , such as winds and earthquakes , etc . , has been widely expressed. Vibration control, which intends to keep the behavior of a structure within a permissible limit , is utilized in several structures , like bridges , tall buildings , wind turbines , foundations with additional vibrations in industry , and even ordinary structures. In this paper , some of the recent studies on optimal control of the structures are reviewed. In other words , a comprehensive review of articles on the optimal design of different known control systems of each category i.e. , Tuned Mass Dampers (Active , Passive , and Semi - active) , Viscoelastic Dampers and Base Isolation (Passive and Semi - active) , Fluid Viscous Dampers (Passive and Semi - active) and the active Tendons , with special attention to studies performed in the past decades, are presented. Also , due to simplicity , reliability , and maximum energy dissipation of the friction dampers as an energy dissipation device , especially for seismic amplification of the engineering structures , a brief overview of the optimization of the friction dampers is discussed.

One way to reduce seismic force is to use knee bracing systems. In this method, the diagonal limbs of the brace are connected to the knee joint. The duty of the brace is to create stiffness and the duty of knee member is to create ductility like a yielding damper. In this method, some novel results are achieved by combining Y type bracing with the knee members. In this regard, three samples of the proposed frame were tested in the laboratory of structure based on the ATC24 loading protocol. The results show that this seismic system has a good performance in energy absorption and stability. At lower frame displacements, the knee element begins the absorb energy process faster. The use of a knee bracing system can be a good alternative to the brace system due to its ease of replacement. The behavior of the hysteresis (force-displacement) curves obtained from the experimental tests show good results in force balancing. Moreover, due to relatively lower initial stiffness and strength, the proposed frame will perform well in low-intensity earthquakes. It was observed that the failure mechanism of the structure has an acceptable ductility in the plastic part of the system. In addition, it was shown that by moving the middle node towards the corner of the frame and increasing the eccentricity of this point, the stiffness of the frame decreases and as a result, the natural vibration period and system displacement increases under constant load.

Understanding the behavior of the pile group near the slope is an important factor in designing a structure adjacent to the slope. There are very little research on the vertical capacity and efficiency coefficients of pile group near slope, so the study about the behavior of pile group adjacent of the slope is very important. The purpose of this study is to investigate and compare the bearing capacity and efficiency coefficient of vertical pile group under axial loading in the near sandy slopes in two modes of free horizontal movement and no free horizontal pile movement by testing the physical model of pile group. Also in the this study, horizontal force applied to the pile group with free lateral movement is investigated with the FLAC3D software. For this purpose, a series of experiments were performed on the physical model of 2 × 2, 2 × 1, 3 × 1 and 3×3 pile groups adjacent to the dry sandy slope without horizontal displacement and the results were obtained with previous research of other researchers in which the lateral displacement of the pile group has been free, compared. The results of the physical model tests show that the bearing capacity and efficiency coefficient of the pile group is dependent on the pile distance, the pile group configuration, and the liner pile-group direction relative to the slope direction. Also, the results of the physical model tests show that the bearing capacity and efficiency coefficient of the pile group with free lateral movement have higher values than the pile group without lateral movement. Numerical analysis results show that the lateral force applied to the pile group decreases by increasing the spacing of the piles, and the ratio of horizontal force to axial force in the linear pile group decreases with increasing number of piles.

Today, due to existing economic issues, optimization and maximum use of materials are highly regarded. Due to the wide range of parameters, the use of mathematical methods is not logical. For this reason, meta-heuristic methods have expanded. In the field of structures, weight optimization using various methods is of great interest. Due to the importance of truss, in this paper, the optimization of truss has been done using a hybrid algorithm of harris hawks and genetics. The harris hawks algorithm is one of the newest algorithms in the field of optimization, which is derived from the natural behavior of animals. In the harris hawks algorithm, the mutation process, which belongs to the genetic algorithm, is used. The optimization is constrained; therefore the constraints of stress and displacement have been selected. Four trusses, planer 10-bar truss, spatial 25‑ bar truss, spatial 72‑ bar space truss and planner 200 bar truss have been selected for optimization. The implementation of harris hawks algorithm has been done in MATLAB software. The results obtained from harris hawks-genetic algorithm are compared with other available sources. The study shows the acceptable performance of this hybrid algorithm for truss. The harris hawks-genetic hybrid algorithm has faster convergence speed.

Temporary soil improvement methods have always been a concern of geotechnical engineers. Today, the use of methods such as nailing and anchorage is one of the common methods in Iran, while in developed countries, new methods such as artificial ground freezing are also used. The reason for the increasing use of artificial ground freezing, in addition to technical, economic and environmental benefits, is its ability to be used in all boundary conditions and all types of soils. Due to the insignificant laboratory study on the behavior of frozen clay, in this paper, after conducting initial experiments, over 130 unconsolidated-undrained triaxial experiments have been performed on clay samples prepared from the Shurabil Lake site (located in Ardabil). In these triaxial experiments, the effect of freezing, temperature decrease, strain rate increase and confining pressure increase on stress-strain behavior of saturated clay samples has been completely investigated. The results of this study show that decreasing the temperature significantly increases the shear strength and modulus of elasticity of frozen clay samples. Also, due to the presence of ice matrix in the structure of frozen clay, the effect of strain rate is to a large extent, which leads to an increase in shear strength and modulus of elasticity of the samples. Also, all samples showed strain hardening behavior and none of the samples showed brittle rupture. Therefore, the use of artificial ground freezing method in clay soils can be used.

In recent years, the use of steel bracing system in reinforced concrete structures has expanded. The bracing system can also be used effectively to improve existing concrete structures. Considering the soil -structure interaction in the analysis of the structure compared to the case where the soil of the substructure is considered rigid causes a change in the behavior of the structure during seismic excitation. The present study is the result of a realistic approach to the problem of soil effects on the seismic behavior of concrete structures with steel bracing. In this research, considering the 6-story concrete structure, improved with X-bracing on three types of soil C, D and E according to ASCE7-16 standard, under appropriate earthquake records, the effect of soil-structure interaction has been investigated. In modeling, nonlinear behavior is assumed for structure and linear and nonlinear behavior is assumed for soil and nonlinear dynamic analysis of soil -structure interaction is performed using direct method and two-dimensional geometric modeling in Opensees software and the response of structure by considering two The rigid base and the flexible base are compared. The results show that considering the soil -structure interaction in models improved by steel bracing according to the type of soil, increases the period in some cases up to about 72% and reduces the base shear to about 49% compared to the rigid bed in the structure.

This study explores multiple mathematical models for estimating house prices in Tehran, Iran. Estimation of house prices is vital from various perspectives. Estimated prices can be used in the planning, design, and construction of residential building projects. Based on the estimated future prices of residential units, investors and constructors can conduct an investment analysis and mitigate the risk of the financial failure of residential projects. Reducing the investment risk of residential projects can lead to jobs creation and economic growth. Several factors such as previous house prices, population changes, house construction costs, and seasonal effects can significantly affect house prices. In this research, first, the macro and microeconomic factors that affect house prices were reviewed, and relevant data were collected. The next step was data preparation and pre-processing. Then, the data was used to train several models using regression and time series analysis models, namely Autoregressive Integrated Moving Average and Vector Autoregression. The current house prices can be estimated using the regression model based on a set of independent variables such as the age of the building. The ARIMA model receives the output of the regression model and estimate house price in the subsequent year. Alternatively, the Vector Autoregression model can be used independently to estimate future prices. To compare the performance of the models, their error was measured by two methods Mean Absolute Percentage Error and Relative Standard Error. The error of the Autoregression model is less than the combination of regression and ARIMA models because in the Autoregression model, the effect of independent variables is directly applied in the model. The models developed in this research can help decision-makers, investors, developers, homebuyers, and financial institutes obtain appropriately estimated prices and make informed decisions in construction projects.

Nowadays, start-ups are one of the most effective factors in the economic development of developed societies. On the other hand, the existence of some shortcomings has made the formation and promotion of these businesses face great challenges. Therefore, the present study has been done by analyzing the theoretical foundations of the stages of formation of startups, identifying various environmental factors in the development of startup start-up businesses in the field of construction and exploring the application of project management science in this field. The main purpose of this study is to explain the conceptual model of startup implementation using a project management approach based on the PMBOK standard with emphasis on the Iranian construction industry. The present study is applied in terms of purpose and descriptive-analytical in nature and method, which has been done using qualitative analysis method and strategy of data foundation theory. In this regard, twenty experts in the field of construction startups were purposefully selected. After studying the theoretical foundations and conducting semi-structured interviews, the data were analyzed in three stages of open, axial and selective coding. After reviewing their validity and reliability, the final model was explained and finally approved by ten experts in the field of construction. Research findings show that startup formation can be considered a project whose primary sources and data, initial idea and output, innovative product or new service and startup development. In fact, the proposed conceptual model, using the project-based thinking and also the project-based project management approach in general and the standard in particular, can effectively promote start-up businesses (pre-seed, seed, scale up, expansion, IPO) in the construction industry; in line with resilience and achieving the desired excellence, in order to help the activists in this field in today's dynamic, competitive and complex work contexts.

In this paper, for the first time, a nonlinear analysis of the dynamic instability of a relatively thick curved structure equivalent to a composite wing layer is performed. For this purpose, the wing structure of the aircraft is considered as a relatively thick curved beam and modelling has been done using first-order shear theory. Van Carmen's large non-linear strain relationships have been used in strain components in a curved line environment. One of the most complex instability modes is axial excitation of the curved beam under a harmonic dynamic load despite a static constant value. These static loads (positive or negative) and dynamic harmonic load coefficient have a significant relationship with static buckling load. Considering the dynamic axial load, the dynamic equations governing the system and the equations of the boundary conditions are obtained using the Hamilton principle and the method of calculating the changes, and to solve them, the generalized numerical differential squaring method is used. Also in this paper, for the first time, by solving the final algebraic nonlinear equations, the stability region of a relatively thick curved beam is determined as changes in the excitation frequency in terms of dynamic load. To determine the effects of different parameters on natural frequencies, critical buckling load and beam stability range, different modes including different linear and nonlinear kinematic models, different values of static load, length to beam thickness ratio and radius of curvature along with beam types Flat and curved composite layers have been considered. As one of the most important results, the results show that considering different combinations of fibbers, the amount of curvature as well as the geometric nonlinearity of the material is important and will have a great impact on the predicted responses for the dynamic instability region.

Staggered truss system is one of the types of lateral bracing systems in steel structures. In this system, lateral forces are transmitted through the rigid floor diaphragm between adjacent trusses. The columns of the staggered truss system are placed only in the outer walls and the middle columns are removed. Hence, a large open space without columns is achievable, which is architecturally appropriate. In this paper, the effect of geometric characteristics of staggered truss systems such as the ratio of the opening length, the type and arrangement of the side trusses in seismic performance is investigated using ETABS software. For this purpose, the ability of the analytical model was first validated to estimate the available experimental results. It was observed that the analytical result is in good agreement with the results of the Experimental model. Then, by examining several different models, the effect of the length of the middle opening was investigated on the seismic parameters of the Staggered truss system. The results showed that the ratio of the length of the middle opening is very important in seismic performance; So that this ratio can have a direct effect on the ductility and stiffness of the structure. Finally, the effect of truss type used in side openings was evaluated on the best span ratio based on the best level of seismic performance. In this paper, three types of structures are used: short, medium and high.