نشریه مهندسی سازه و ساخت
سال نهم شماره 9 (پیاپی 62، آذر 1401)

Concrete beam-column joint perform an important role in structural ductility, energy absorption and delaying breakdown. In this study, the effect of engineered cementitious composites containing carbon nanofibers (CNF-ECC) on the behavior of T-shaped concrete beam-column connections under cyclic loading is investigated. The tensile strain hardening behavior of ECCs has made a powerful material with high energy absorption and high cracking potential before failure. Since ECC is a relatively new material, much of the research has focused on understanding the nature of these materials, their different constituents, different mixing ratios, the stress-strain curve relationships, the invention of new composites. Research has also been done on its practical applications in structures. But these studies are not as extensive as research on the behavior of materials themselves, and require a great deal of analytical ad laboratory work. In this study, three concrete joints were tested, one of which was replaced as a reference specimen and the other two joints were replaced with ECC and CNF-ECC. The main parameters considered include hysteresis Moment curves - relative drift, energy absorption capacity, and crack distribution. Experimental models were subjected to cyclic loading at the end of the beam with displacement control. The loading continued until the load reduction reached more than 30-40% of the maximum load. The results show that by using these high- performance materials, the ductility and energy absorption of these joints are effectively improved. The results showed that using these powerful materials, the ductility and energy absorption of these joints were effectively improved and the cracks created in the connection spring as a dense network of micro-cracks with very shallow depth and width. respectively.

Today, with the advancement of analysis and structural design, various lateral force resisting systems have been proposed to take advantage of each of the existing systems simultaneously. Among bracing systems, Eccentrically Brace Frames are the top priority. The application of energy dissipation, such as friction dampers and shear panels, reduces seismic responses to earthquake and wind. In the present paper, a system consisting of an Eccentrically brace frames with a steel shear panel and a rotation friction damper has been proposed based on numerical modeling and its performance is based on different levels of Hazard level. Hazard level, with average return periods of 72, 475 and 2475 years, has been studied by dynamic analyzes of nonlinear time history. The Optimum slip moment is determined based on the minimum value of the seismic performance index, in three levels of danger, once separately and once by considering the level of intermediate Hazard level, with a return period of 1200 years. To investigate the seismic performance of the proposed structural system, the structural responses are estimated at three hazard levels based on the optimal slip moment determined by the two states. The results showed that considering the Optimum slip moment corresponding to each Hazard level separately, improves the seismic responses of the proposed structural system. But naturally, the Optimum slip moment shared different hazard levels will provide conservative results . It was also found that the damper, at higher hazard levels, has a better performance in improving the response and seismic behavior of this hybrid system.

Earthen dams have a significant impact on the lives of surrounding communities, so the need for continuous monitoring during the construction and safe operation of these structures when applying dynamic loads, especially explosive loads due to possible sabotage and firefighting has always been considered. The effects of explosive loading, assuming the conditions affecting the performance of earth dams, can be measured using several parameters, the most important of which are the dimensions of the pit caused by the explosion and the stability coefficient of the slopes of the structure. Therefore, in the present study, according to the researches done in the field of dynamic loading of earth dams, while selecting the model and its characteristics, in order to validate the simulation process and apply dynamic loading, the results of numerical solution with the article A reference is compared that provides acceptable consistency. Then the dynamic loading of the explosion in the form of finite element software is simulated in certain parts of the structure and after analysis, the results show that by increasing the explosive charge and increasing the water level of the dam reservoir and also reducing the density of constituents Of the body; The depth and dimensions of the hole created by the explosion in the crown of the dam will increase, which will also indicate local damage. Finally, to investigate the dynamic stability of the slopes, the results are transferred from finite element software to the slope stability analysis software, and the model under pseudo-analysis Static and dynamic, and finally stability analysis. The results indicate that under an explosive charge of 800 kg , the reliability coefficient of slope stability is higher than the reliability coefficient introduced by the publication 624, which indicates no serious damage and instability of the dam structure

The concrete structures exposed to the earthquake have the potential of cracking and reduction in stiffness and strength. Because of their low deformability, there would be some cracking and plastic hinging in the moment-resisting frame. The utilization of dampers is a solution to improve the behavior of the constructed structures. Dampers play a crucial role in improving structural performance level and bearing capacity. In the present study, 9 concrete frames were tested, and steel yield dampers have been used for the seismic rehabilitation of the concrete moment-resisting frames. The yield dampers elements are ADAS dampers (Added Damping and Stiffness) connected to the concrete frame using steel braces. The concentric-type steel braces connect the dampers and concrete beams. Furthermore, to investigate the influence of the braces on the structure’s strength and behavior three concentrated braces have been installed in the structure. The structure in which ADAS dampers was employed demonstrated more strength and less recorded damages than the simple moment-resisting frame. In the present study, the effect of braces and dampers have been investigated in the behavior of the structure, cracking, and strength. The strength of the frames was increased by 48% and 21% by employing steel braces and yield dampers in the concrete frames, respectively, comparing the control frame.

Wind load is one of the influential lateral loads in the design of cylindrical storage tanks. In the static method, one of the parameters in calculating the wind force entering the structure, which depends on the geometry of the tank, is the pressure coefficient. Ways to find this coefficient are using wind tunnel tests or using numerical modeling in software based on computational fluid dynamics (CFD). Accurate estimation of these pressure coefficients in the whole surface of the tank is very important for calculating the buckling load and controlling other design criteria. In this paper, wind pressure coefficients on cylindrical storage tanks with height to diameter ratios of 0.25, 0.5, 1 and 1.5 using wind tunnel testing and numerical modeling based on computational fluid dynamics using ANSYS software have been obtained. Comparing the results of wind pressure coefficients, it is observed that with increasing the ratio of height to tank diameter, the maximum value of negative air pressure coefficient (suction) increases. The maximum negative pressure at ɵ= 90o was equal to 2.2 and the maximum positive pressure at ɵ= 0o (against wind) was 1. In this research, the equation governing wind pressure coefficients on the environment of storage cylindrical tanks is presented, which can be used in the design of storage tanks. The pressure coefficients on the storage tank made using corrugated sheets are also presented.

One of the main concerns of project based organizations in construction projects is to manage multiple projects in a portfolio simultaneously. Construction Portfolio management determines the best time and condition of starting and selling each project according to the financial need of the stakeholders. This paper aims to optimize the cash flow in construction portfolios considering market indices using meta-heuristic algorithms from the organization’s point of view. In this research, a model was presented to simulate the conditions of the project portfolio and was optimized using genetic algorithm (GA) and particle swarm optimization (PSO). The inflation rate of construction and real estate during recession and expansion was considered to make the situation more real as well. To evaluate the model, a portfolio including five real selected projects in advance by an organization is optimized by the model. The results showed that the model and the optimization algorithms used in the model had an effective role in the arrangement and balancing of the portfolio. Moreover, conditions of the organization such as cash flow and market indices such as project construction inflation and real estate inflation during periods of recession and boom were also considered, which is almost impossible in traditional project portfolio management. Both algorithms came up with the same solution which showed that the result is valid, but the performance of the particle swarm optimization algorithm was better than the genetic algorithm in terms of program execution speed and speed of the final result. In comparison to an expert decision on balancing the portfolio, the algorithms found the solution with 33% better objective function values.

The use of steel beam connection system to reinforced concrete columns has been used as an alternative to steel bending frames in medium and high-rise buildings. In high-rise buildings, because the rigidity of the structure controls the design, the use of concrete columns with more rigidity compared to steel columns makes the design economical. In this study, the seismic behavior and energy-dissipation of steel beam to reinforced concrete column connection with double-skin steel tubular are investigated using numerical methods. This system improves the hysteresis behavior and performance of traditional steel beams to reinforced concrete column connection. To evaluate the steel beam's hysteresis behavior and energy absorption to reinforced concrete column connection with double-skin steel tubular system, parametric studies were performed. Parametric studies have been performed applying the nonlinear finite element (MFE) procedure to investigate the improved models. The parametric studies comprise examining the parameters of thickness and cross-section shape of an inner tube. Also, the accuracy of finite element models was evaluated by comparing test results that showed the good accuracy of finite element models in predicting the specimens' hysteresis behavior and failure modes. The results indicated that the thickness of the inner tube of improved models has a considerable influence on determining the ultimate capacity, performance, and energy dissipation. Also, the results show that the details of the construction of the internal tube were a considerable effect on the performance and hysteresis behavior of steel beam to reinforced concrete column connection with double-skin steel tubular.

After contract between public sector organizations and contractors, events often occur that can cause project cost overrun from a system’s perspective. The purpose of this paper is to study the causes of project cost overrun from a system’s perspective, with an exploratory and confirmatory factor analysis approach. This study is practical in nature and is considered as a descriptive-exploratory correlation study. The required data were collected through the distribution of questionnaires among 270 people who employed in the public sector and contracting companies in three cities of Tehran, Uremia and Sanandaj. The results of exploratory factor analysis led to the discovery of four factors: poor contract planning and supervision, lack of effective coordination among the contracting parties, weak institutional and economic environment of projects, changes in contract and processes. The first-order confirmatory factor analysis indicated the correct measurement of the four latent variables identified. The second-order confirmatory factor analysis shows that the effects of each of the latent variables are significant and their rank in terms of their impact on the formation of the main construct are: lack of effective coordination among the contracting parties (0.70), poor contract planning and supervision (0.48), changes in contract and processes (0.31), lack of effective coordination among the contracting parties (0.27). Also, the effects of six demographic variables (gender, age, education, years of service, field of study, type of organization), on all four factors were studied. For example, contractors are more likely to change orders than public sector organizations. The findings of this study can play an effective role in better understanding the factors affecting the cost overruns and then managing them.

The main goal of this research was to assess the criteria pertaining to delays in infrastructure projects of Bushehr Water and Sewerage Company. Assessments were conducted by library studies, interviews, and questionnaires. The relating factors were provided to the statistical population in the form of a questionnaire. Subsequently, using the fuzzy TOPSIS method, the most effective factors were calculated and then the factors were introduced by degree of effectiveness. The statistical population of this research was divided into three categories with different responsibilities, characteristics, and perspectives as follows: Consulting engineers, Contracting companies, and Employer. Purposeful and available sampling method was used to determine the sample size and 30 persons were considered as the statistical sample. In this study, the factors influencing water and sewage project delays were identified in four categories of factors caused by financial issues, resources and materials, manpower management, and the knowledge and experience of the contractor, as well as 28 sub-criteria. Ranking factors effective in Bushehr water and sewage project delays indicated that the most important ones of these factors by importance respectively are: Failure to pay the contractor's claims on time; Inefficient manpower management and poor quality of work performed by the contractor; Lack of pricing by contractors to win the tender; Weak history or low number of contractor's technical and executive personnel; and Poor work planning due to inexperienced contractor.

The formation of the short column phenomenon in reinforced concrete structures has caused design engineers to study the behaviour of such structures. One of the conditions that lead to the formation of a short column is the placement of the structure in a steep position. In this paper, two 8- and 16-story structures were modelled once on a flat surface and again on a sloping site, and their sections were designed using equivalent static analysis. Then, using nonlinear time history analysis, the behaviour of these structures in the plastic region was compared. Structures were modelled in Sap2000v20 software and SeismoSignal.v2018 software was used to scale the accelerometers used in nonlinear time history analysis. Examining the results, it was observed that the formation of short column phenomenon in reinforced concrete structures with special bending frame system has a negative effect on the seismic response of structures; It increases the displacement of the floors, increases the drift of the structure and also creates a mechanism (or the formation of plastic joints). For example, based on the results obtained from 8 and 16 storey structures with and without short columns, it was observed that the average drift of 8 and 16 storey structures with short columns was 19% and 7.1% in the X direction more than the structure, respectively. It has no short columns and also in the Y direction, the average drift of 8 and 16 storey structures with short columns is 7% and 12.8% more than the structure without short columns, respectively.

Non-ductile reinforced concrete frames are commonly found in older buildings in many parts of the world. These structures designed for gravity loads, have limited lateral strength and ductility, are prone to excessive one-way lateral movement and soft-story mechanism. This paper focuses on the retrofit of an existing reinforced concrete frame, using steel X-braces by indirect internal connection method. The main purpose is the analytical study of general behavior and response of large scale vulnerable frames. An experimental study was used to validate the numerical modeling performed in ABAQUS. Next the base samples were retrofitted with X-braces and four proposed indirect internal connection methods. Furthermore, in a separate parametric studies, the effect steel frame profile type, connection type and use of high strength grout in the boundary zones between steel and reinforced concrete frames were investigated. The results indicated that the stiffness and bearing capacity of the reinforced concrete frame by using steel X-braces increases up to 3.7 and 2.8 times, respectively. It also reduces the final displacement and drift by 50%. Moreover, bracing acts like the first defense system against lateral loads, such as structural fuse with its yield, increases the amount of energy dissipation. It also removes the plastic hinges by reducing the ultimate displacement and stress of lateral load in the panel zone.

Population growth, space limitation, economic and social factors are some of the reasons that led to the construction of tall buildings. However, the invention of light weight and durable materials has made tall buildings with low damping and high vibration period and sensitive to wind forces. Therefore, the study and analysis of tall buildings under wind forces seem necessary. The purpose of the present research work is to provide the necessary solutions for performance based design of a tall building having elliptic plan shape against the wind. In the present study, a tall elliptical building is exposed to wind interaction. Moreover, wind modeling and building specifications are performed in ANSYS.17 software. To simulate the atmospheric boundary layer in the software as a virtual wind tunnel, two parameters of the mean wind speed and turbulence includes length and intensity, are required. The results of software analysis were presented as a time history of longitudinal and transverse acceleration at three different heights of the building for four various mean wind speeds in short afterbody orientation for perpendicular to wind direction and 72 m/s in wind direction, then the standard deviation of acceleration was calculated and placed in standard curves of the regulation and interpreted. The effect of different factors on the performance of tall buildings against the wind is a type of response (alongwind or acrosswind), mean wind speed, orientation of the building, and the height of the desired point from the ground. Results show that the acrosswind response of tall buildings to wind does not follow a specific law and is a function of the mean wind speed, height of the building, and the alongwind and acrosswind response of the building ,i.e, displacement and accelerations .