Abstract:The present paper firstly introduces a fundamental concept for a novel structure, i.e., the composite concrete structure. Taking the mechanical properties of various types of concretes into consideration, concrete in structures could be combined in different levels (material, component and structure) according to this new concept. Through optimization design, the safety, serviceability and durability of concrete structures could be significantly improved, and the sustainability of concrete structures could be achieved consequently. Based on the proposed new concept, case studies were carried out, including composite concrete beams, columns, slabs and frame structures. Finally, the scientific problems and future development of composite concrete structures, including interface design method, 3D-printing construction technique and the sustainability evaluation, are suggested and analyzed. Recommendations for future investigations are also put forward.

Abstract:A test of three concrete beams with 500MPa high-strength stirrups under indirect load was performed to analyze the structural behaviors, the development of the diagonal cracks and failure modes under direct and indirect load. Numerical models were established with ABAQUS to study the effect of shear span ratio and stirrup ratio on the shearing capacity of the tested beams. The results show that the shearing capacity of high-strength concrete beams under direct load can be precisely predicted with the ’Code for design of concrete structures’. Moreover, the shearing capacity of the beams under indirect load decreases compared with the beams under direct load due to the variation of the shear span ratio and the stirrup ratio. The detailing requirements of additional transverse reinforcement as the code puts can effectively compensate the shearing capacity reduction of the high-strength stirrups beam under indirect load.

Abstract:An experimental study was carried out to investigate the mechanical properties of domestic high strength steel Q550 at elevated temperatures. Steady-state tests were conducted on specimens at high temperatures ranged from 20 ℃ to 800 ℃. The experimental phenomena, mechanical properties and stress-strain curves at different temperatures were obtained. The tests results were compared with the reduction factors determined by current standards and by other researchers. The results showed that, the surface and fracture of the specimens at different temperatures were significantly different. When the temperature of specimen was higher than 300 ℃, the elastic modulus, yield strength and ultimate strength decreased with the increase of temperature, the linear elasticity and strain-hardening stage of the stress-strain curves shortened, and the descending stage tended to be gentle. The high temperature had little influence on elongation when the temperature was below 450 ℃. The current parameter models of high temperature mechanical properties were not applicable for Q550 steel. In order to obtain the mathematical models for mechanical properties of Q550, polynomial model and high temperature material model proposed by National Institute of Standards and Technology were employed.

Abstract:Plastic-forming based on plat-patterning is applicable to ETFE cushions owing to good plasticity property of ETFE foils. Two right angled trapezoidal ETFE cushion models are designed and manufactured. Cushion forming and cyclic inflating-deflating tests of the two ETFE cushion models are carried out by employing a pressure control system. Vertical displacements on the lower surface are measured by laser displacement transducer. The results indicate that rise-to-span ratios of the two cushions are respectively 1/9.4 and 1/10.3 under the condition that the maximum internal pressure of plastic-forming is 2kPa. In addition, the ETFE foils are strengthen during the forming process the. A multi-linear elastic-plastic model with isotropic hardening in ANSYS is employed in numerical analyses of the forming and cyclic inflating-deflating processes, and the results are compared with the experimental data.

Abstract:The geopolymer, consists of carbide slag (CS) and metakaolin (MK), was used to solidify and stabilize the Cu₂₊ contaminated soils. A series of toxic characteristic leaching procedure (TCLP) tests were conducted on the solidified soils and then the optimal contents of CS and MK were selected for this geopolymer. The results obtained from laboratory experiments show that the pH of leaching solution increases and the Cu₂₊ concentration decreases with the increases in CS content, while the Cu₂₊concentration does not continue to reduce when the CS content is more than 9%. As MK content increases, the pH of leaching solution decreases slightly, but the Cu₂₊concentration firstly decreases and then increases. Based on the results, the optimal contents of CS and MK were selected for this geopolymer to be 10% and 5%, respectively.

Abstract:At present, the available wind observation data for estimation of directional extreme wind speeds is lacking, especially the data of tropical cyclones. Up to the present, there is still no method can provide directional extreme wind speed estimates in mixed climates. In this paper, the samples of extreme wind speeds in typhoon climate and normal climate are separately obtained using the Monte Carlo method. For the typhoon climate, the samples of extreme wind speeds are simulated by the typhoon wind field model established by Yan Meng. For the normal climate, the samples of extreme wind speeds are simulated by the distribution function fitted from the wind observation data. Then, a new method of estimating the directional extreme wind speeds is proposed. The results of estimated extreme wind speeds are presented and discussed using Shanghai as an example. The results demonstrate the distribution of extreme wind speeds in those two kinds of climates and the reasonable transition between these climates. The strong correlation among the extreme wind speeds in different directions is also shown in the mixed climate.

Abstract:3D finite element model was used to analyze the contact state between dowel bar and cement concrete pavement. Based on the equivalent principle of bending stiffness, the dowel bar and concrete surface layer system were simplified to double-layer beam structure. The calculation results show that the double-layer beam structure on elastic foundation can describe the deflection effect of concrete pavement well. In addition the relative displacement, rotation angle and the stress of the double-layer beam are different from the 3D finite element solution, which can be eliminated by modifying the vertical reaction modulus between the double-layer beams. Furthermore, the regression formulas of the relative displacement, rotation angle and the resultant force of extrusion stress were summarized. The formulas of the shear stiffness and bending stiffness of the dowel bar joint were given, and it was pointed out that the ability of the dowel bar to transfer bending moment was negligible. Finally, the load transfer problem of double-layer beam joints under the concentrated loads at the beam end was calculated and analyzed, which shows that the existence of base can increase the joint deflection ratio and reduce the shear force transmitted by the joint, when the joint shear stiffness is constant.

Abstract:As an important safety measurement for longitudinal steep slope, truck escape ramps are widely used in China. Limited to complex terrain of mountainous highway, truck escape ramps will be inevitably built in the horizontal curve. In this paper, UC-win Road 9.0 driving simulation was selected to study the departure angle and approach length of the truck escape ramps locating in the right-turning circular curve. Four indexes, adjusting time, minimum turning radius, steering wheel angle amplitude and frequency, were selected and analyzed by regression analysis using the data of 16 drivers entering the truck escape ramps. Then the quantitative model of each index with the circular curve radius and the departure angle was established. Through the second order clustering method, the setting range of the departure angle and approach length was narrowed. Finally, considering the lateral stability of errant vehicle, the design parameters of truck escape ramps were determined. It was recommended to set truck escape ramps at the main line with radius no less than 1000m, and the departure angle was 0°-5° while the approach length was 6s design speed travelling length. With the restricted condition, the truck escape ramps could be set at the horizontal curve radius of 600m-1000m, and the departure angle was 0°-5° while the approach length was 9s design speed travelling distance. The departure angle was 5 °-10 ° and the approach length was 12s design speed travelling distance.

Abstract:Based on the traffic data and crash data collected on G15, this paper studied short-term traffic flow risk prediction model on freeways with high proportion of trucks and high proportion of truck crashes. The overall traffic flow parameters, the truck traffic flow parameters and the comprehensive parameters were selected as the risk characteristic variables. The support vector machine was adopted for the modeling and genetic algorithm was used to optimize the parameters. Classification models of different time periods, different risk characteristics variables were got and compared. The results show that the model using the data within 5 to 10 minutes before the accident performs the best. When considering truck factors,the overall prediction accuracy improves 7.1% , the crash rate prediction accuracy improves 6.6% and the false alarm rate is 7.7% lower. Finally, the different importance of characteristic variables was obtained through mean impact value. The results show that truck factors have larger effects on the prediction model. The model in this research can be used to developSearly warningSsystem of traffic security and provide theoretical basis of truck safety management on freeways.

Abstract:To transport passengers as soon as possible, a coordinated adjustment method for preceding trains of the delayed train was developed for urban rail transit system. Based on the interaction between train capacity and passenger demand, operational constraints and the adjustment time constraints, an integer programming model was established to minimize total passenger travel time with considering the in-vehicle and on -platform passengers. A combined dynamic programming algorithm of time selection of multiple trains at multiple stations was designed to solve this model. The numerical results show that the proposed model and algorithm are effective and the method yields the minimal passenger travel time than the other methods.

Abstract:As the problem of fastener screw bolt fracture and affect the operation safety in some subway lines, field experiments were carried out to obtain the relationship between the torque and axial force of screw. Based on the measured data and considering the irregular spatial shape of spring washer, non-uniformity of the contact stress, and nonlinear contact between different parts, etc, fine finite element model of fastener screw was established. The mechanical characteristics of each component of the screw with single and double spring washers were analyzed respectively. The results show that compared with the single washer, the axial force of screw with double washers increases less under train load and the possibility of damage is greatly reduced because of the shear deformation in the compression state. The special shape of spring washer causes stress concentration in the combining site of nut and washer, partial load on nut, it is an important reason that the crack are easy to be generated and expanded in the combining site of nut and washer. These analysis results coincide with the actual situation.

Abstract:The operation complexity, station complexity and line complexity measurement of production line was brought out on the basis of considering uneven load, station block and rhythm disorder caused by uncertain factors. Multi-objective optimization model was established aimed to maximize balance rate, minimize complexity equilibrium index and minimize line complexity. Method was devised to figure out the optimal division of operations. Balancing algorithm was devised to calculate an instance for verifying the effectiveness of the optimization model and the validity of the method. The research achievement shows that this method can balance the unevenness of complexity among the stations and can reduce the line complexity with the assurance of maximizing balance rate. It can reduce the possibility of balance failure caused by accumulating of uncertain factors and can improve the robustness of production line.

Abstract:Aimed at the problem that the output pressure of newly developed rotary direct drive electrohydraulic pressure control servo valve (RDDPV) was oscillating, the mathematical model and block diagram of RDDPV were established, and the stability criteria was obtained. In RDDPV, the electrical feedback of motor rotational angle and output pressure are used instead of traditional mechanical or hydraulic feedback. When the spool valve near the middle position between inlet and outlet port, steady state flow forces provides the positive feedback on spool motion, leads to a negative stiffness of mechanical and hydraulic parts, and the stability of RDDPV is poor. In order to improve the stability of RDDPV, the electrical feedback stiffness of the servo valve was improved by increasing the electrical feedback coefficient of motor rotational angle. Numerical simulation and experiment results shown that the stability of RDDPV can be effectively improved by increasing the electrical feedback coefficient of motor rotational angle.

Abstract:In this paper, we developed a functional and robust microfluidic perfusion-based 2-D cell culture system for mammalian cells (Hela) with long term monitoring. This device is capable of providing a closed environment for cell growth and manipulation without the need of an incubator. A 9-chamber poly(dimethylsiloxane) (PDMS) flow system with multi-layer Quake-valve control was merged with a microheater fabricated on an Aurum/Chromium (Au/Cr) wafer. By employing valve control and bypass, each chamber works independently, either feeding cells with desired density into the chamber or chasing cells out of it. The novel network microheater enable to provide a local temperature at 37°C with uniform temperature distribution for cells living in each chamber. Results show that cells growth characteristics and morphology in each chamber with different seeding density are comparable to those with conventional tissue cultural vessels.

Abstract:The collision simulation between a city tram and an automobile at the level crossing is carried out based on the multi-body dynamics. The research results indicate that when the city tram is impacted laterally by an automobile with a speed of 20 km?h-1, the maximum derailment coefficient of the city tram is 1.63, exceeding the limit (1.2) defined in the standard GB5599-1985. That means the collided city tram has a high risk to derail. Besides that, the dynamic response and the derailment risk of the collided city tram are affected seriously by the collision boundary conditions. When the first or the last vehicle of the city tram is collided by the automobile, the lateral impact load can be transmitted to the adjacent vehicle by only one side, which results in a high derailment coefficient. With the increased impact mass and speed of the automobile, the impact force is obviously increased. As a result, the derailment coefficient of the city tram is also gradually increased. As the distance between the impact point and the mass center of the car body increases, the collided city tram is endured not only the lateral impact force but also the yam moment. Due to this reason, the collided city tram has a high risk of derailment. Besides that, when the friction coefficient decreases due to bad weather, the braking distance of city tram and automobile increases, so that the collision accident is more likely to occur. On the other hand, the reduced friction coefficient decreases the wheel-rail forces against the lateral motion of wheel sets. As a result, the collided city tram is more likely to derail.

Abstract:To improve grinding quality and enhance vehicle dynamic performance, this paper presents an inverse design method for determination of rail grinding profiles. This method aims at optimizing rolling radii difference after grinding. It uses designed wheel-rail contact distribution as boundary conditions. With the designed rolling radii difference and contact distribution, a numerical algorithm is deduced to find the grinding profiles. Computer simulation results prove the validity of the proposed algorithm. This method not only can solve both sides design problem, but also can solve single side design problem. By designing different rolling radii difference and contact distribution, it could satisfy different grinding requirements.

Abstract:The multifactor version of Copula models is useful in fitting the complex correlation structure among the base portfolio of CDOs. However, plain Monte Carlo simulation is quite incapable of accurately measuring rare but significant loss events. We provide a fast numerical inversion of conditional Laplace transform in multifactor models.The method is capable of estimating loss probability P(L>y) and expected loss E[L∧y].Numerical examples illustrate the efficiency of the method, especially when handling rare events.

Abstract:With the uncertainty of vessel arrival time and marketing demand, a disruption management based method is developed for resources allocation problem at import/export container terminals in periodic environment. Considering the existed periodic template, a dynamic decision framework based on 2-stage approximation is proposed, including the fixed decisions to be executed in the 1st stage and adjustable pre-decisions in the 2nd stage. For reducing the fluctuation in execution process, the objective is set to minimize the weighted deviation in both temporal and spatial aspects. A double nested tabu search is provided to illustrate the effectiveness and efficiency of the proposed model and algorithms. Results indicate that 2-stage decision framework can better cope with the impact of disruption events comparing with traditional methods.