International Journal of Civil Engineering
Volume:15 Issue: 1, 2017

In this paper, self-consolidating concrete (SCC) mixtures are considered for airfield concrete pavements. A series of rheological, mechanical, transport and frost action durability tests were conducted on the prepared SCC mixtures with and without chemical air-entraining agents (AEA). Mineral admixtures including slag, fly ash, silica fume and metakaolin were included in SCC mixtures. The results showed that application of mineral admixture led to significant improvements on the performance of airfield concrete pavement mixtures. Moreover, the performance of mixtures against frost action upgraded when AEA included in companion with the mineral admixtures.

A robust periodic train-scheduling problem under perturbation is discussed in this paper. The intention is to develop a robustness index and to propose a mathematical model which is robust against perturbations. Some practical assumptions as well as the acceleration and deceleration times along with periodic scheduling in addition to a practical new robustness index are considered. The aim is to obtain timetables with minimum traveling time that are robust against minor perturbations, while the unnecessary stops are minimized. In general, the spread of delays in the railway system is called delay propagation. We show that in addition to this phenomenon, there exists a more complicated case in periodic type of scheduling that is the fact of delay propagation from one period to the next. In fact, if the delays of a period are not absorbed by the next one, the size of delays may converge to infinity. We name this as delay intensification. Furthermore, we develop a hybrid heuristic algorithm which is able to find near-optimal schedules in a limited amount of time and can absorb perturbations. To validate the algorithm, a new lower bound is introduced.

This paper compares the hydraulics and 3D flow features of the ordinary rectangular and trapezoidal plan view piano key weirs (PKWs) using two phase RANS numerical simulations. The main aim is to investigate effects of the inlet key area and angle of the side walls on discharge capacity of the PKW, while keeping the developing length of the crest intact. The numerical model has been used to carry out a sensitivity analysis for geometrical parameters and hydrodynamics of the rectangular and trapezoidal weirs (TPKWs) have been compared for wide range of the water head on the weir. Results show that the trapezoidal weir has higher efficiency than the ordinary rectangular PKW. This is partly related to the inlet key flow conditions. The trapezoidal geometry increases the inlet flow area resulting in reduction of the velocity along the key axis. Consequently, flow is distributed more uniformly over the side crests. The gradual transition of the inlet key limits the development of the recirculation zones along the side walls, and it also limits the formation of the critical section along the inlet key. These phenomena result in increase of the effective weir length and thus discharge capacity increases in trapezoidal weir compared with rectangular one. Discretization of the discharge along the crest of the tested weirs clearly confirms these findings.

To fully explain hydropower unit operational problems, an optimal multi-objective dynamic scheduling model is presented which seeks to improve the efficiency of reservation regulation management. To reflect the actual hydropower engineering project environment, fuzzy random uncertainty and an integrated consideration of the natural resource constraints, such as load balance, system power balance, generation limits, turbine capacity, water head, discharge capacities, reservoir storage volumes, and water spillages, were included in the model. The aim of this research was to concurrently minimize discharges and maximize economic benefit. Subsequently, a new hybrid dynamic programming-based multi-start multi-objective simulated annealing algorithm was developed to solve the hydro unit operational problem. The proposed model and intelligent algorithm were then applied to the X Hydraulic and Hydropower Station in China. The computational unit commitment schedule results demonstrated the practicality and efficiency of this optimization method.

A least squares based meshfree method is used in the numerical simulation of a turbulent flow. The proposed approach is integral free, vectorized and enjoys sparse positive definite matrices. Here, the standard k–ε model is employed to model the turbulent flow. A matrix formulation is illustrated that simply can be extended for other turbulence models. Three bench mark problems are solved and results are compared with the literature.

This paper proposes an efficient method for allocating a number of blood centers to a set of hospitals to minimize the total distance between the hospitals and the blood centers, based on the concept of graph partitioning (p-median methodology) and metaheuristic optimization algorithms. For this purpose, a weighted graph is first constructed for the network denoted by G0. A coarsening process is then performed to match the edges in n stages. Then, the enhanced colliding bodies (ECBO) algorithm is applied to the coarsened model to decompose it into p subdomains by using a p-median methodology. In the present problem, p is the number of blood centers to be allocated for the hospitals. The results indicate that the proposed algorithm performs quite satisfactory from both computational time and optimality points of view.

A nonlinear finite element algorithm is proposed to analyze the reinforced concrete (RC) columns subjected to cyclic biaxial bending moment and axial loading. In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of the columns. In the proposed numerical simulation, the column is discretized into two macro-elements located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into fixed rectangular finite elements. The basic equilibrium is justified over a critical hypothetical cross section assuming the kinematics Navier’s hypothesis with an average curvature. The method used qualifies as a “strain plane control process” that requires the resolution of a quasi-static simultaneous equation system using a triple iteration process over the strains in each section. To reach equilibrium, three main strain parameters (the strains in the extreme compressive point, the strains in the extreme tensile point and the strains in another corner of the section) are used as the three main variables. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns. The application of the components effects combination method is also compared with the proposed simultaneous direct method. The results obtained show the necessity of applying SDM for the post-elastic phase, which occurs frequently during earthquake loading.

Steel bridges play an important role in the transportation system of many countries. To ensure that bridges are structurally sound, engineers monitor their performance, which is known as structural health monitoring. Historical evidence indicates that bridge damage is pervasive and that the service life of bridges is decreasing. To manage safety and costs, engineers must be able to accurately predict the service life of bridges. A statistical method to predict service life for steel bridges is presented, which can assist bridge engineers, bridge owners, and state officials in the objective assessment of deteriorated bridges for retrofit or replacement. Timely repair and retrofit of bridges increase their safety levels and decrease costs. A nonparametric statistical approach based on the bootstrap method for stress analysis for fatigue life prediction of steel bridge components is proposed. The bootstrap provides a simple approach for the reproduction of the extremely complex probability distribution of measured strain data. It is completely automated numerical method which requires no theoretical calculations and it is not based on the asymptotic results. The service life index is introduced which quantifies the fatigue life of steel bridges under daily traffic loads. A regression model is developed for the prediction of remaining service life of steel bridges using a service life function. The predicted remaining service life derived from the function can contribute to effective management of steel bridges.

The drawer bracing system (DBS) is a ductile bracing system that is developed to enhance the seismic performance of braced frames. The system is composed of three parallel plates that are attached together via transfer plates at right angle. Seismic energy is dissipated through the formation of flexural plastic hinges at the two ends of the transfer plates. The parallel plates must have adequate strength and stiffness to prevent global buckling and to remain elastic while transferring forces to transfer plates. Height, width, thickness, and the number of the transfer plates may be varied to achieve the desired strength and stiffness of the system. In contrast to common bracing systems, the main advantage of a DBS is the conversion of the axial forces to flexural moments in the dissipating elements. In this paper, the nonlinear shear response of the DBS is predicted via closed-form formulas for calculation of strength, stiffness, and post-yield behavior of the system. These formulations are based on both experimental observations and theoretical analysis. The calculated force–displacement backbone curve is verified to be a very good approximation for predicting the nonlinear shear response of the system.

Based on the methodology of “Understanding by Design”, UbD, the course “Design of Hydraulic Structures” was developed and implemented. A series of learning experiences, with emphasis on hydraulics and hydrology, for civil engineering undergraduate students is presented that encourages the development of high technical and scientific competence, communication skills oral and in written, the ability for teamwork and the capability to learn. The experiences were designed, using the above methodology, based on learning that is desired. Once taught the course, the results obtained were compared based on the planned framework (expectations), the characterization of the student population, the course products as well as the activities, according to the students, considered relevant in the learning process.