Application of Suspension Bridges Stiffened by Prestressed Concrete Slabs in China

Four suspension bridges stiffened by prestressed concrete slabs were designed and constructed on highways in southwestern mountainous areas of China. These bridges are the first applications of its kind in China. This paper discusses the site condition, adaptability, and design and construction features of these bridges. These bridges have single suspension spans between 278 and 388?m and deck width between 14.4 and 15.0?m. The longitudinal distance between hangers is only 5?m, which is relatively small for this bridge type, and there are only two lanes. The dual direction prestressed concrete slabs are 0.6?m deep, and its wind blocking area is relatively small. Dynamic analysis and wind tunnel tests verify that the wind resistance requirements are easily satisfied.     

Low sidelobe arrays of parallel dipoles with finite reflector

The effects of a finitely sized reflecting plane on the radiation patterns and on the input impedances of linear low sidelobe arrays of parallel dipoles are analysed. The differences between arrays with a finite reflector and those with an infinite one are studied and the design criteria are discussed.<>     

Freeze-proof method and test verification of a cold region tunnel employing electric heat tracing

In recent decades, numerous tunnels have been built in the cold region of China. However, frost damage occurs frequently inside the tunnels; this damage threatens the stability of the tunnels. In order to prevent frost damage, a method employing electric heat tracing (EHT) was presented in this study. Moreover, the EHT-based freeze-proof system layout and installation procedures were also introduced. The tunnel liner EHT system is composed of four parts: heating cable, insulation layer, protective layer and fire protection layer. This EHT system was adopted in the Dongnanli highway tunnel (located in northeastern China) to verify its applicability. In-situ test results indicated that the temperature behind the liner begins to heat up after one hour of electrifying the system; next, the temperature becomes positive and remains stable after three hours of electrifying the system. The operation of the heating system is quite stable, and the insulation effect is significant. Through the assessments of the heating efficiency that is required to reach the target temperature and a constant temperature heating effect, it is suggested that the combination of thermal insulation and electric heat tracing is feasible and effective in preventing frost damage in tunnels. The research results provide references for the design and construction of frost prevention systems in tunnels in cold regions.     

A hybrid differential evolution approach based on surrogate modelling for scheduling bottleneck stages

Surrogate modelling based optimization has attracted much attention due to its ability of solving expensive-to-evaluate optimization problems, and a large majority of successful applications from various fields have been reported in literature. However, little effort has been devoted to solve scheduling problems through surrogate modelling, since evaluation for a given complete schedule of these complex problems is computationally cheap in most cases. In this paper, we develop a hybrid approach for solving the bottleneck stage scheduling problem (BSP) using the surrogate modelling technique. In our approach, we firstly transform the original problem into an expensive-to-evaluate optimization problem by cutting the original schedule into two partial schedules using decomposition, then a surrogate model is introduced to, quickly but crudely, evaluate a given partial schedule. Based on the surrogate model, we propose a differential evolution (DE) algorithm for solving BSPs in which a novel mechanism is developed to efficiently utilize the advantage of the surrogate model to enhance the performance of DE. Also, an improved adaptive proximity-based method is introduced to balance the exploration and exploitation during the evolutionary process of DE. Considering that data for training the surrogate model is generated at different iteration of DE, we adopt an incremental extreme learning machine as the surrogate model to reduce the computational cost while preserving good generalization performance. Extensive computational experiments demonstrate that significant improvements have been obtained by the proposed surrogate-modelling based approach.     

Cause investigation and verification of lining cracking of bifurcation tunnel at Huizhou Pumped Storage Power Station

A wide range of cracking happens in concrete lining at the crown of the lower adit and high-pressure bifurcation in the water-filled test of bifurcation tunnel at Huizhou Pumped Storage Power Station. Then a field investigation is undertaken to explore the main reason of such prominent lining cracking. Through investigating several possible inducing factors, it is found that mass defects exist in the concrete lining in constructing bifurcation tunnel, and insufficient thickness of concrete lining is probably the main factor causing lining cracks. In order to verify if this conclusion is reasonable, comparative analysis through numerical simulation is utilized to assess the influence of different concrete thicknesses on tunnel stability for the lower adit and high-pressure bifurcation. And then the fracturing process of concrete lining with the increase of internal water pressure during the water-filled test is simulated. The results reveal that the displacements and tensile strains in the lining crown are significantly bigger than other parts of tunnel, with deficiency in concrete thickness considered. It is also concluded that whether the cavities exist or not in the crown, rather than the cavity thickness, is the main factor influencing the values and distributions of the tensile strains and displacements for tunnel lining. Besides, the distribution of tensile-strain-concentrated zones is approximately in good agreement with the in-situ fractured status of concrete lining. Finally, a conclusion can be drawn that deficiency in concrete thickness in the crown is the primary triggering factor for lining cracking.     

Dynamic Demand of Bridge Structure Subjected to Vessel Impact Using Simplified Interaction Model

Assessing the dynamic demand using general-purpose finite-element codes is not only low in efficiency, but also unaccepted in practical application due to the complicated nonlinear dynamical behaviors of vessel-bridge collision. In this paper, an alternative simplified interaction model is presented to evaluate the dynamic demand of bridge structure under vessel impact efficiently. In this method, ship motion is regarded as the motion of single degree of freedom, and ship-bow is modeled by a nonlinear spring element (only compression) connected to bridge structure. A quasi-static method is employed to obtain the nonlinear static relationships between impact forces and crush depths of ship-bow, and the effect of the height of pile cap is discussed. Based on two different approaches, the influence of strain-rate effect on impact force is taken into account to obtain the corresponding dynamic crush curves, which are developed for the proposed interaction model. Results show that the dynamic responses of bridge structures using the simplified interaction models are in good agreement with the general-purpose collision analyses, while the former computation efficiency is improved obviously.     

The CMAS corrosion behavior of high-entropy (Y0.2Dy0.2Er0.2Tm0.2Yb0.2)4Hf3O12 hafnate material prepared by ultrafast high-temperature sintering (UHS)

High-temperature molten calcium-magnesium-alumina-silicate (CMAS) corrosion has become a fatal factor for the failure of aero-engine thermal barrier coatings. In this study, a promising entropy-stabilized (Y_0.2Dy_0.2Er_0.2Tm_0.2Yb_0.2)₄Hf₃O₁₂ (5YH) hafnate was prepared by the emerging ultrafast high-temperature sintering (UHS), and its corrosion and wetting behavior of molten CMAS were investigated. For the corrosion mechanism, the precipitation of the high-entropy apatite phase promotes the formation of the HfO₂ phase, and it can improve the density and stability of the slow-growing reaction layer, hindering the further penetration of molten CMAS. At 1300 ℃, a reaction layer with a three-layered morphology is generated, resulting from the decreased viscosity of the molten CMAS. Moreover, computational analysis shows that molten CMAS on the 5YH surface has a larger contact angle (17°) than traditional YSZ (13°), and the spreading area is about 90 % of traditional YSZ, which benefits for its good CMAS corrosion resistance.     

Planar dipole arrays with equal element input impedances

Planar antenna arrays of unequal dipoles in which all the input impedances of the elements are the same are proposed to simplify the matching networks or to improve the matching condition for broadside arrays. A method to design this type of array is described. The array produces a given radiation pattern. The elements are of different lengths and different radii     

Electromagnetic imaging of two-dimensional perfectly conducting cylinders with transverse electric scattered field

Electromagnetic imaging of two-dimensional perfectly conducting cylinders using measured transverse electric scattered field is studied in this paper. The contours of cylinders are denoted by local shape functions /spl rho//sub i/=F/sub i/(/spl theta//sub i/) in local polar coordinates which are then approximated by closed cubic B-splines instead of trigonometric series. By using the boundary condition of vanishing tangential electric field on surfaces of perfectly conducting cylinders, a set of electric field integral equations governing the scattering problem is derived. The scattering problem is solved by a point-matching method with pulse basis and Dirac delta testing functions. The inverse problem is reformulated as an optimization problem and solved by a real-coded genetic algorithm with closed cubic B-splines local shape function. Numerical examples show good agreement between the true profiles and the reconstructed results.     

Construction of non-repeating frequency-hopping sequences with no-hit zone

Based on finite field GF(p/sup m/), a new construction of frequency-hopping (FH) sequences with no-hit zone for quasi-synchronous FH code-division multiple-access systems to eliminate multiple-access interference is presented. These new FH patterns are non-repeating and possess ideal Hamming autocorrelation.