فهرست مطالب حامد شکری

Investment in the construction industry can only cause economic growth and achieve economic results when capital injection and housing production are targeted and ultimately lead to housing consumption; because if the imported funds are not directed to the building sector, the final price of housing will increase and will make real consumers less able to buy. Therefore, the entry of liquidity into the construction industry requires formulation of strategy and policy in order to increase the growth rate of housing. Also, risk management and knowing its key components lead to reducing construction costs and creating a more appropriate price in the construction industry. The aim of the current research is to know the dimensions and components of risk management in Iran's construction industry with a fuzzy Delphi approach with interpretive structural modeling and DEMATEL technique.

The current research method is exploratory and the goal is to answer the research questions. In terms of the type of research, it is practical because its results are used for risk management in Iran's construction industry. The method of the current research is mixed (qualitative-quantitative). In the qualitative dimension, using the fuzzy Delphi method, it has identified the dimensions and components of risk management in the construction industry in Iran. In the quantitative dimension, by using interpretative structural modeling technique and DEMATEL, by using surveys of experts and university professors, it has been done to stratify and examine the intensity of relationships between dimensions.

The results show that at the lowest level of the model (level three), the risk dimension of political factors is placed, which acts as the cornerstone of the model and to achieve risk management in projects. Iran's construction should start from this factor. Also, the results of examining the intensity of relationships between dimensions with Dimetal show that the social risk dimension is the most effective dimension, has the highest numerical value based on the row sum (D), and thus, with the most influential dimension among the investigated dimensions of risk management in Iran's construction industry has been identified. Also, according to (D-R), the lowest value, the risk dimension of laws and regulations, is the most effective dimension of risk management in Iran's construction industry.

Originality/Value:

 The current research is new in terms of the subject area, i.e. in the field of the construction industry of Iran, and in terms of the location area, i.e. companies active in the field of the construction industry of New Tehran. The research gap that creates the space for innovation in the current research, according to the perspective of soft operations research, which is a tool for creating complex and new problems, is the use of Interpretive Structural Modeling (ISM) and DEMATEL. Less research has been done on leveling and examining the intensity of impact and effectiveness of the components of risks in the construction industry.

 The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a river reach. Although most of flow in nature are unsteady, the quasi-steady flow condition was considered to be simple in this study and the water surface profile along the river reach with irregular cross sections was calculated by standard step-by-step method. In order to calculate suspended sediment load under non-equilibrium condition, the advection-diffusion equation with source term was numerically solved. In the present sediment model, ten discretization methods, five relations for calculating capacity of suspended sediment load, eight relations for diffusion coefficients and eight relations to calculate particle fall velocity were used and their effects on suspended sediment distribution along 18480 m of Gharasoo river were investigated.

 The HEC-RAS model output was used to calibrate the present hydraulic model. The models were run with the conditions as same as Manning roughness coefficient and river geometry conditions. The results showed that the calculated water surface profile along the river reach by two models are completely overlapped each other. In other words, the present model has a very good accuracy to predict the water surface profile in the river reach. As most commercial 1-D models (same as HEC-RAS) only consider the equilibrium condition  for sediment  transport and the bed or total load sediment, comparing the results of present sediment model with them seems not to be reasonable. Therefore, to validate the present suspended sediment model and finding the best method of discretization, an especial shape concentration hydrograph was introduced to the present model as input hydrograph and the model was run when the source term has been deleted deliberately.  The volume below the input concentration hydrograph and calculated hydrographs in different cross sections was compared to each other. Comparing the hydrographs showed that the maximum error in calculating the volume of concentration hydrograph with the input hydrograph was 0.029% implying that the model satisfies the conservation laws as well as reliable programing. Among ten discretization methods, the best method for discretization of the advection-diffusion equation was Van Leer's method with the least error compared to other methods. After validating the model, effect of five relations for calculating capacity of suspended sediment load was investigated. The results showed that using the Wife equation estimated the amount of suspended sediment higher than other equations. The Toffaletti equation also estimated suspended sediment load lower than other equation. Among eight particle fall velocity formulas, Stokes relationship estimated the fall velocity larger than other equations. Hence, the Stokes equation application decreases the possibility of suspending the sediment particles. However, employing Van Rijn and Zanke relationships resulted in a greater suspended sediment load distribution along the river reach. Among eight relationships for diffusion coefficients, Elder and the Kashifipour - Falconer equations exhibited the lowest and the highest amount of diffusion in the concentration hydrograph, respectively. Furthermore, the calculated suspended sediment concentration under non-equilibrium conditions was 11.7 % higher than that under equilibrium conditions along the river reach.

 Most 1-D numerical models only simulate the bed and total loads sediment transport under equilibrium condition while sediments are transported under non-equilibrium conditions in nature. Sediment transport under non- equilibrium conditions may be greater or lower than the equilibrium condition known as the capacity of sediment transport. In this research, a numerical model was developed to simulate the suspended sediment transport in a river reach under non-equilibrium conditions. The amount of suspended sediment concentration was calculated for each sediment grain size. The results showed that the distribution of suspended load along the river reach is not significantly sensitive to the fall velocity relations while the type of sediment transport equation affected the suspended sediment transport concentration. The concentration of suspended sediments for non-equilibrium conditions was also 11.7% higher than the concentration of sediments in equilibrium condition.