International Journal of Civil Engineering
Volume:14 Issue: 1, 2016

Steel–concrete hybrid systems are used in buildings, in which a steel structure has been placed on a concrete structure to make a lighter structure and have a faster construction. Dynamic analysis of hybrid structures is usually a complex procedure due to various dynamic characteristics of each part, i.e., stiffness, mass and especially damping. Dynamic response of hybrid structures has some complications. One of the reasons is the different stiffness of the two parts of structure and another reason is non-uniform distribution of materials and their different features such as damping in main modes of vibration. The available software is not able to calculate damping matrices and analyze these structures because the damping matrix of these irregular structures is non-classical. Also an equivalent damping should be devoted to the whole structure and using the available software. In the hybrid structures, one or more transitional storeys are used for better transition of lateral and gravity forces. In this study, an equation has been proposed to determine the equivalent uniform damping ratio for hybrid steel–concrete buildings with transitional storey(s). In the proposed method, the hybrid structure containing concrete, steel and transitional storeys appropriately substituted with 3-DOF structure. A wide range of eigenfrequency and mass ratios is examined for each ratio pair, and given the characteristics of the primary system, the complete 3-DOF structure can be formed. Equivalent uniform damping ratio is derived by means of a semi-empirical error minimization procedure. The multiple nonlinear regressions are used for determination of equations of modal damping ratios of hybrid buildings.

Stilling basins dissipate energy to form hydraulic jumps and rotational flows. Hydraulic jump and rotational current phenomenon produce pressure fluctuation at the bottom of stilling basins. In the present study, pressure fluctuations and their locations have been studied in a physical model of Namrod Dam. Results showed that fluctuations in presence of jump in the basin are high and, therefore, the fluctuation factors are, respectively, high. In positive pressure coefficient (CP), it is evident that when a jump is present, the turbulence and disturbance factors increase and, therefore, the pressure fluctuations go up, respectively. In negative pressure coefficients (CP−), as is expected from positive pressure coefficients, the maximum pressure fluctuations occurred at Q/Qmax = 0.47 with regard to forming a complete hydraulic jump at this discharge. Regarding available empirical equations, the thickness of slab for different hydraulic conditions was calculated and compared in one-dimensional (1D) and two-dimensional (2D) conditions. By analyzing collected data, it was observed that, results of 1D were underestimated in comparison to 2D calculations. Concrete slab thickness could be observed that fluctuations have significant effect on thicknesses. However, such calculations can provide designers with general ideas on how to better understand the conditions.

The cavitation erosion induced by high-speed flow is very prominent in tunnel with high head and large discharge. Air entrainment is an effective technology to solve this problem. In this study, numerical simulation and physical model were applied to the comparative study of air–water flows in curve-connective tunnel including ogee segment, steep segment and anti-arc segment, where three aerators were set up for protecting the bottom-floor and sidewall. The flow pattern, aeration cavity, air concentration and pressure distribution were obtained and the calculated results agree with the Experimental data. The hydraulic characteristic and aeration effect of the flows in a curve-connective tunnel are analyzed specific to the bottom aerator and the whole cross-section aerator, respectively. When the bottom aerators were only set up, the flows appeared the black water triangle zone near sidewalls in curve-connective segment. The air concentration was observably improved on sidewalls downstream of the ogee section while the added lateral aeration facility on bottom aerator. Thus, the black water triangle zone disappeared so that the floor and sidewalls were protected so well. These results indicated that the whole cross-section aerator not only weaken the backwater in bottom aeration cavity and then increase the length of the bottom cavity but also benefit the protection of sidewalls.

This paper addresses the ambient vibration-based finite element model updating of long span reinforced concrete highway bridges. The procedure includes ambient vibration tests under operational conditions, finite element modeling using special software and finite element model updating using some uncertain parameters such as section properties, damage, boundary conditions and material properties. The structural carrier system of the bridge consists of two main parts: arch and beam compartments. In this paper, the beam compartment is investigated. Three-dimensional finite element model of the beam compartment of the bridge is constituted using SAP2000 to determine the dynamic characteristics. Operational modal analysis (OMA) is performed for experimental measurements. Enhanced frequency domain decomposition (EFDD) method is used to extract dynamic characteristics. Analytical and experimentally identified dynamic characteristics are compared with another and finite element model of the beam compartment of the bridge is updated by changing some uncertain parameters such as section properties, damage, boundary conditions and material properties to reduce the differences between the results. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies reduce in average from 46.7 to 2.39 % by model updating. In addition, a good conformity is found between mode shapes after model updating.

Due to the existence of the nonlinear relationship between storage and discharge in Muskingum model, the model parameters and outflow cannot be directly determined. The traditional routing procedure has been widely applied in model calibration and flood routing. However, most previous studies only focused on the accuracy of parameter estimation which adopt the traditional routing procedure, ignored the correctness and effectiveness of routing procedure itself. In this study, three routing schemes of traditional routing procedure are evaluated by simulation experiment and the results demonstrate that the routing scheme 1 is the best, and scheme 3 is followed, the worst one is scheme 2. But the scheme 1 and 3 yield parameters estimates and the corresponding outflow hydrographs may violate the routing equations in terms of residuals. The scheme 2 is legitimate; however, the accuracy is not high enough. As an alternative, a new routing procedure based on iterative method is proposed for parameter estimation and flood routing of the nonlinear Muskingum models. The proposed routing procedure is applied to model calibration and flood routing for three examples involving single-peak, multi-peak, and non-smooth hydrographs. The results indicate that the proposed routing procedure can not only satisfy the routing equations for all time stages in the routing process, but also be superior to scheme 2. Therefore, it can be confidently applied to parameter estimation and flood routing for the nonlinear Muskingum models.

Construction industry projects impose some unsought constraints on employers to manage and define new projects including investment risk, performance variation and diversity of the project. Annually, a significant part of the governmental budget is being spent to execute water and wastewater projects in Iran. However, further projects are on demand to develop the country. The aim of this study is to develop the courses of action to attract private partnership into the projects defined and executed in the Water Sector of the Iranian Ministry of Energy. To determine the criteria and implementing the proposed strategies, SWOT (strength, weakness, opportunity, threat) method was used as a powerful tool for understanding the context of the organization. To understand the importance of the criteria, we weighted them; then the extracted strategies from SWOT matrix (ANP method) were prioritized and divided into short- and long-term range in terms of the performance and capabilities. According to the results, SO strategies have more weight than the other strategies. Therefore, regarding the nature of strategies, the opportunities should be completely used through reinforcing the strengths and short- and long-term period planning.