Applied Mechanics and Materials Vols. 638-640

Abstract: By using the explicit nonlinear dynamic analysis program of LS-DYNA, three-dimension finite element model of rock breaking by disc cutter of tunnel boring machine is established, in which elastic material is adopted to describe the elastic behavior of cutter ring and Holmguist Johnson Concrete (HJC) model is adopted to describe the brittle behavior of rock. With the finite element method, the process of rock breaking by disc cutter is simulated, and then the movement characteristics, forces of disc cutter and rock fragmentation mechanism are analyzed. The results indicate that the numerical technique can contribute to gaining an understanding of rock breaking mechanism by disc cutter and improving the design of disc cutter parameters.

Abstract: Hydraulic fracturing is a method which combines a natural action with a factitious means to alter rock structure. In order to control the extending direction of fracture in the process of hydraulic fracturing, directional hydraulic fracturing is necessary. According to fracture initiation and extension mechanism, taking fully into account the flow-stress-damage coupling effect, simulating with numerical way and analyzing a law of the roof under the dynamic failure process on a working face with a hard and stable roof in 2 cases, the one is the non-directional directional hydraulic fracturing, and the other one is wedge groove directional hydraulic fracturing by RFPA^2D-Flow. Based on analyzing the distribution law of the primary stress field on roof surrounding rock, we reveal the control mechanism and behavior law of directed by wedge groove directional fracturing. The study results shows that: First, under the coupling effect from the high hydraulic pressure and crustal stress, failure of roof is not simply a shearing failure, but a compound stress effect from tensile and compress failure which tension contributes more. Second, the directional fracturing by wedge-groove guides to the main fracture progressing into directional expansion, relying on man-made weak plane, it also makes the roof directional hierarchically, timely and fractionated carving come true.

Abstract: Aiming at the face roadway 22109 of Cuncaota coal mine, using FLAC^3D numerical simulation software, 19 of 5 groups about bolt and anchor combined support schemes were analysed and compared, and the reasonable scheme of φ18×2000mm thread steel bolt and φ17.8×6500mm anchor cable combined support was obtained. Support result of this scheme was analysed with FLAC^3D software, the result show that this scheme can support the roadway effectively. Practical application show that this scheme can achieve the security, economical and effective support result, and can be used in this type of roadway.

Abstract: To control the stability of deep well broken surrounding rock, single-hole sonic method is used to test the loose circle of-1180 east-rock main roadway and its damage range. The study indicates the loose circle is about 1.8 ~ 2.2 m, which is typical large loose circle. And its button is slightly larger than two sides’, right side slightly larger than left. The roadway rock has some engineering features of soft rock. The broken and expand deformation of loose circle does large, difficult to support. Combined support is usually used in this rock condition.

Abstract: This paper presents a method to optimize the composite fore-fulcrum form traveler which makes the traveler more reasonable and economical, and the method can be conveniently used by designers while designing form travelers for single-plane cable-stayed bridges using cantilever cast-in place construction method. After a general theoretical description (theory and process) of the optimization model, an engineering case is optimized using this method. And the method is proved feasible by analyzing the primary and optimized travelers in Midas Civil and comparing their properties.

Abstract: To study aerodynamic interference of twin-deck sections under vortex-induced vibration (VIV), a series of wind tunnel tests are implemented. Horizontal interval ratio (D/B) is taken into consideration a factor influencing VIV behavior, and the results are compared with single section. Surface pressure distribution of the twin sections are acquired by synchronous pressure measurements when the sections are under vertical and torsional VIV. Proper orthogonal decomposition (POD) is employed to reconstruct the randomly fluctuating wind pressure field. It identifies the vertical and torsional vibration frequency of model and energy proportion of eigenmodes. VIV behavior of twin-deck sections is different from single section, and it changes with different D/B. In general, the position, where D/B=1, is unfavorable to VIV behavior of twin-deck sections. The aerodynamic interference does not always amplify or restrain the amplitude of VIV. Several lower modes can reconstruct fluctuating pressure field to the accuracy meeting the requirement of engineering.

Abstract: In this paper, passenger and freight bi-purpose railway tied arch bridge is studied. Dynamic simulation train model is built on multibody system dynamics approach, and dynamic bridge model is built by using the finite element method.Coupled vibration response analysis of the tied arch bridge based on co-simulation technology of ANASYS and SIMPACK between multibody system dynamics and finite element is made. By calculating, analyses and assess are made of the bridge when trains are moving at different speeds. Results provide theoretical support and refer to the same type of bridge design.

Abstract: With the bridge member resistance deterioration and traffic volume increasing on the bridge, bridge reliability considering time-variant factors has become an important problem. This paper presents a method to estimate the bridge safety performance based on time-dependent model of resistance decreasing and load change. Power form functions are used to fit the resistance degradation models in three environmental conditions, and time-dependent model of load increasing is built in accordance with traffic observation results somewhere. The results show that normal distribution probability model can be used to fit dead load time-varying model. In analysis, the most disadvantageous load combination effect is mainly considered, live load time-varying function approximately follows extreme type I distribution model. Finally the proposed approach combined with Monte Carlo method is used to assess the time-varying reliability index and the safe serving time of one prestressed concrete bridge in use.

Abstract: Down-deflection of long-span prestressed concrete (PC) continuous rigid-frame bridges in highway is more serious than in railway. Deflection comparison of highway bridges and railway bridges can provide a reference for the deflection control of highway bridges. Differences of highway and railway design codes about deflection were firstly analyzed. Then, the whole construction processes of a highway bridge and a similar span railway bridge were simulated by Midas/Civil. Both the stress state and long-term deformation were compared. The results show that stress states of the railway bridge will reduce the down-deflection. Finally, for highway bridges, we propose the compressive stress at upper edge of pier-top section should be slightly larger than that at lower edge during the layout of prestressed tendons.

Abstract: This paper simulates the practical engineering, using plexiglass to make a three-span continuous wide curved box girder model by the geometry scale ratio 1:30. With the model load test, measured the strain and deflection of the control cross-sections, got the distribution about the stress and deflection of the wide curved continuous box girder; And we proposed the “uniformity coefficient” to express the uneven force of the curved bridge. Compared the finite element analysis results and experimental data, the results show both are in good agreement.