Advanced Materials Research Vols. 446-449

Abstract: The effects of wood fiber and polypropylene fiber on the mechanical performance, drying shrinkage and moisture loss of sulphoaluminate cement (SAC) mortar were studied. The experimental results show that wood fiber and polypropylene fiber can both improve the flexural strength of the mortar and reduce drying shrinkage ratio and moisture loss at different ages. Polypropylene fiber can also improve the late compressive strength of the mortar. Adding 0.3% mass fraction of wood fiber, the drying shrinkage ratio and moisture loss of the motar reach minimum values. The drying shrinkage ratio reduces to 0.029% at 28d. Moisture loss reduces to 0.4%. Adding 0.5% mass fraction of polypropylene fiber, the drying shrinkage ratio and moisture loss of the motar also reach minimum values. The drying shrinkage ratio reduces to 0.03% at 28d and moisture loss reduces to 0.39%.

Abstract: A typical case of integral all-welded panel joints on Shanghai Minpu Second Bridge is discussed in this paper. The prediction of welding residual stresses at joints is achieved by thermal elasto finite element analysis, and the research reveals that a proper scheme of multi-layer welding craft will reduce welding distortions and residual stresses through mutual offset. The welding distortions at upper and lower chord joints (Type I) and those of the overall structural model are predicted with the distribution of residual stresses obtained. The research aims to provide a theoretical basis for the control of welding distortion, the optimization of welding craft and the constitution of optimal assembly welding craft.

Abstract: Considering the uncertainties in structural capacities and seismic motions, a probabilistic-based seismic risk analysis approach for bridges is proposed in this paper. In this approach, the Total Probability Theory (TPT) is used to divide seismic risk analysis into three main steps: seismic hazard analysis; structure damage analysis; and failure probability analysis. The parameters of seismic risk analysis are assumed to be an independent and discrete Markov process, resulting in rigorous and consistent seismic risk functions for calculating the annual average probability of exceeding a designated limit state of structure under a specific level of seismic intensity. A case study of seismic risk analysis was performed on a three-span continuous rigid-frame bridge. The results show that the approach presented in the paper is applicable for the seismic risk analysis of bridge structures, and is an effective tool to assess the performance of bridge structures under earthquake actions.

Abstract: Techniques of lifting large segments of steel box girder by floating crane is used in construction of Chongqi Bridge. Considering the hydrological environment on the site, characteristics of steel box girders and performance parameters of floating crane, the selection of floating crane is carried out. To ensure hoisting work achieve function and safety, a new type of lifting device named Self-balance lifting device is designed, and the lifting-points design is optimized to make the reaction of all lifting-points of large segments equal. In the erection process of large segments, the security risk control is analyzed to ensure the steel box girders and lifting equipments safety.

Abstract: Abstract: Variable cross-section components are widely used in engineering practice. It is clear that reliability-based optimization design of variable cross-section component is important for engineering design. This variable section widget for reliability and the perturbation design, we propose a perturbation method of the reliability design about the variable cross-section components. We may rapidly obtain the variable cross-section component's reliability information accurately, in basic random variable probability characteristic certain situation. We propose a method with practicality for the relevant reliability design.

Abstract: Composite beam using asymmetric H-shaped steel is one of the constructional structures developed in the advanced countries in Europe since early 1990s. The purpose of this study on composite beams where H-shaped steel is partially laid in concrete slabs was to find how to design fire protection and improve fire-resistance to make deep deck plates provide the beams with advantages upon a fire and to improve stiffness in structural aspect. Only lower flange which is directly exposed to a fire was included in fire-resistance design in order to decide optimal fire- protection design condition and test was conducted for spray-coating and paint-coating. In the fire resistance test, web thickness and lower flange thickness were varied to derive the optimum condition for improving fire-resistance performance. It was observed from the test that 90-minute-protection employed to lower flange provided fire resistance for 3 hours. It was also observed that the basic shape resisted fire for 89 minutes, while web reinforcement and lower flange reinforcement provided fire-resistance for 112 and 157 minutes, respectively. The result showed that lower flange reinforcement is the most effective way to improve fire-resistance.

Abstract: Stay-cable is infinite dimensional nonlinear dynamical system with a very complex vibration types and mechanism which are not described reasonably yet. In order to better control its dynamic behavior, it is necessary to study complex dynamic behavior carefully. Fistly, partial differential equation of the cable motion is established based on the parabolic initial configuration and is simplified into n Duffing-equations by using Galerkin method. Secondly, the chaos behaviors of the first order Duffing-equation under periodic excitation are studied by taking advantage of Melnikov method. At last , parameters may lead to chaotic motion of a true cable in laboratory are calculated and the methods of chaos control are discussed briefly. The study shows that: 1. First order vibration of cable under periodic excitation has much more complex behaviors than the freedom vibration; 2. The Melnikov method can be very effective and convenient for the analysis of chaotic motion of cable.

Abstract: When the cold wave comes, there are worse effects on thin-walled concrete structure than its on mass concrete structure during construction. In the view of this problem, the 3-D FEM is adopted to simulate the thermal field and stresses field of thin-walled concrete launder during construction when it is struck by cold wave. The simulation results show that shrinkage stress in the surface and inner of thin-walled concrete structure will appear and bring a lot of difficulties for temperature control and crack prevention. In order to reduce the impact degree of cold wave strike, some effective measures should be taken, including enhancing the level of external heat preservation and prolonging the form removal time and so on. This research is of practical reference value for the construction of the concrete structure which is built in the area where cold wave easily occurs.

Abstract: Based on the anti-seismic research achievements of tired arch bridge at home and abroad, taking River City Bridge in Jilin as an example, a finite element model is established for dynamic performance analysis by general finite element software midas civil. Natural vibration characteristics of tied arch bridge are calculated as a basis for further dynamic calculation. Firstly, choose appropriate seismic waves according to the geological data. Then perform the dynamic response analysis of this bridge under different loading cases. Dynamic responses of this bridge under longitudinal and transverse seismic waves are studied respectively, and the influence of vertical seismic wave is also considered. It is shown that the influence on seismic response of vertical seismic waves is very obvious. The vertical seismic waves should be considered while doing seismic design of tied arch bridges.

Abstract: Through conducting load test on reinforced concrete piles of the bridge in Kunlun Pass Basin, the research is mainly about pile foundation bearing capacity on permafrost regions. The paper expounds the fundamental of pile vertical load test and the loading method. Through analyzing the test data, what can be concluded is that it can be close to actual working condition of piles when pile load test is conducted on permafrost regions. Meanwhile, reference data is provided for future bridge projects in the application of pile on permafrost regions.