نشریه مهندسی عمران فردوسی
سال سی و سوم شماره 2 (تابستان 1399)

Bridges are known as one of the most important communicational hydraulic structures. This is particularly so important in bridge piers exposed to river currents.The flow contact with bridge piers causes erosion around them and would result in damage. Therefore, controlling the erosion around the piers is one of the most important objects in the bridge safety. Many different experimental models have been prepared so far to investigate the flow pattern and local scour around this structure. Regardless of the cost and time of the experiments, problems resulting from changes in scale are also available. Nowadays, the Hydrodynamic behavior of the fluid is more extensively investigated by using the more efficient codes of computational fluid dynamic (CFD). The Flow3D software is used for this regard. This study focuses on the simulation of flow around the different bridge piers and studied the flow pattern and bed erosion around them. In this regard, the assumption of incompressible fluid is used and the sharp free surface is modeled by Volume of Fluid (VOF). Considering the sensitivity of numerical models to the number of cells in the computational domain, verifying the number of cells has been done by comparing the velocity profiles. Three different turbulence models also are investigated, and the free surface profiles, flow pattern around the pier and the Strouhal number are compared. Finally, the flow simulation is done by LES turbulence model. For investigation the two key factors causing local scouring, flow separation and downward flow in upstream of the pier, th1 10 models is selected. The countermeasures that considered in this regard include berm, cross-section and middle slot. The results show that the effect of flow separation control in reducing the bed erosion is much more than controlling the downward flow. Also the results revealed that in most cases using one countermeasure may be acts more better than situations different countermeasures was applied. In using lenticular cross-section, the scouring depth weas decreased up to 58% and with using the combined round-nosed rectangular cross-section, berm, and slot, the scouring depth showed decreasing up to 50%. Also, it was concluded that controlling the flow separation from the pier in boundary layer and the vortex shedding affect the bed erosion much more than the downward flow in pier upstream.

The HSE technique is used for evaluating the health, safety and enviromental risks. This is a systematic method which is utilized for protection of capital, manpower and environmental towards the risks of unpredictable events in construction projects. In this paper, HSE method is utilized for evaluating construction projects in Mashhad. For this purpose, health, safety and environmental risks are identified. Then a performance function is proposed based on assumed risks. Weight of identified factors and evaluation the efficiency of proposed function are performed by SWOT matrix and Monte Carlo simulaton technique, respectively. To do this, by prapering, distribution and purchasing health, safety and environment checklists between HSE experts, project managers and supervisors of workshops, their comments are recieved. By running SWOT matrix method and Monte Carlo simulation, health, safety and environmental risks of Mashhad construction projects are classified based on proposed function. Results show that the highest and the lowest risks in construction projects in Mashhad are caused by welding safety related processes and the risks of HSE planning, respectively.

One way to stability analysis of tunnel is to examine the convergence and radius of the plastic zone around it. On the other hand, uncertainties in the design parameters lead to the evaluation of the safety of structures using probabilistic and reliability methods. In this research was presented a methodology for stability analysis of two tunnels (under different conditions), by Hock-Brown and Mohr-Coulomb theory using robust reliability methods including: first order method (FORM), second order method (SORM) and Monte Carlo simulation in new RT and @Risk software. After probabilistic modeling in these two software, the results of the analysis show that the second order reliability method is more accurate than the first order method in more complex limit state functions. Also, at high values ​​of failure probability, first order and Monte Carlo simulation methods provide more realistic outputs and at low values ​​of failure probability, Monte Carlo simulation method is not recommended.In addition, the tunnel without pressure has a high probability of failure (24%), so that providing a support with 0.12 MPa pressure is efficient.

Soil as a substrate of land and the foundation of civil structures is of particular importance in the development of urban areas. Some soils are classified as problematic soils due to their low mechanical resistance or high sensitivity to moisture changes, such as the Chalus coastal sand. Soil stabilization with suitable materials is one of the methods of soil improvement for problematic soils. The effect of calcium carbonate (i.e., lime) and nano-calcium carbonate (i.e., nano-lime) on the mechanical properties of the Chalus coastal sand is evaluated in this study. For this purpose, after sampling the soil from the coasts of Chalus city and conducting basic geotechnical experiments, the mixtures were prepared with different percentages of lime and nano-lime and compaction and strength tests were performed on the mixtures. The results showed that lime and nano-lime improved the mechanical properties of the soil material. However, the effect of nano-lime on the mechanical properties of Chalus sand is more significant compared to lime-sand mixtures. In addition, the increase in the lime and nano-lime content in soil mixtures resulted in an increase in the internal friction angle and cohesion.

The purpose of this study was to investigate the behavior of high flow in bending with Erodible Bed, This paper presents a series of experiments in which saline gravity currents flowed through a sinuous channel model. This flume contains three successive bends with three different relative curvature radiuses:40, 80 and cm,8.5 m length, 20cm width and 70cm height. The results show, in condition of a constant discharge, increasing the concentration of the inlet current, the flow velocity of the body flow increases on a mobile bed. The rate of increase in velocity depends on changes in the form of the bed the flow rate of the body will be reduced to about 19%. The velocity of the forehead has increased in the conditions of the mobile bed by forming the form of the bed. So decrease shear stress and omit the bed form cause increasing the velocity of the forehead decrease about 6%.

Telescopic Self-Centering braces are one of the very successful examples of Self-Centering braces which perform well in seismic loading. In this study, a new example of Telescopic Self-Centering brace is introduced,which has superior features over other telescopic braces.These include: high axial load capacity, use of shorter cables in brace construction, simplicity of construction, use of separate cables for compressive and traction modes, less fatigue in cyclic loads and, allowing for more dynamic loading cycles. In this paper, a sample was designed with an axial force capacity of 300kN. Modeling of behavior (DT-SCED) was accurately expressed using numerical relationships. nonlinear incremental stiffness analysis method was also used to calculate the hysteresis brace behavior. The cyclic load test was applied to this brace and the result showed complete Self-Centering behavior.Then, a sample building with the double telescoping Self-Centering Energy-Dissipative Brace (DT-SCED) was subjected Single direction pushover analyses and the results are compared with the sample buildings with theSelf-Centering Energy-Dissipative Bracing (SCED) and the Telescoping Self-Centering Energy-Dissipative Bracing(T-SCED).The results of the analysis and comparing with other samples confirm the seismic superiority of performance of the DT-SCED brace over other samples.