JOURNAL OF STRUCTURAL AND CONSTRUCTION ENGINEERING
Year:2022 | Volume: | Issue: |Papers Count:12

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.

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 descriptiveexploratory 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.

Project completion on predicted time is one of its success indicators. Delays may be defined as increased time or prolonged completion time of the project. In various projects, delays often result in late completion of the project, increased cost, and stoppage of project, reduced production, increased claims, and termination of contract. 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 short columns in concrete structures has been a common practice that has led design engineers to study the behavior of structures when dealing with it. One of the conditions that lead to the formation of a short column is the placement of the structure in a sloping position. Its sections are designed using static-equivalent analysis and then 8 and 16 story structures without short columns are assumed to be on a flat surface so that the responses of structures with and without short columns are compared. Then, using nonlinear time history analysis, the behavior of structures in the plastic region is compared. Structures were modeled in Sap2000v20 software and SeismoSignal. v2018 software was used to scale the accelerometers required for nonlinear time history analysis. According to the results of the software, it was observed that the formation of short columns in concrete structures with a special bending frame system causes a negative effect on the seismic response of the structure, so that it increases the displacement of floors, drifts the structure and also creates a mechanism of plastic joints.

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 Xbraces 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 tall buildings 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, 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 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.