In view of the frequent occurrence of burst and leakage accidents of crossing river oil and gas pipelines, it is important to analyze the mechanical characteristics of the oil and gas pipelines and their safety prevention and control measures. Based on the vibration failure criteria, this paper determines the maximum safety dangling length of the pipe. The ABAQUS software is used to determine the dynamic stress during the level suspended period of the oil pipeline which is in the bottom of the river and it is shown that the length of the single span suspended pipe shall not be greater than 0.65 of the suspended section, and during the process of the load application, the vibration failure happens first, followed by the yield failure. According to the maximum length of the suspended pipeline, the steel structure support method is used to deal with the safety issues due to a too long pipeline span length.
In order to understand the uniaxial mechanical performance of the deep soft rock under the frozen condition, the undisturbed pelitic sandstone from northeast of China is taken for test. The uniaxial compressive strength test and the uniaxial creep experiment for the artificial frozen pelitic sandstone are performed by using the self-developed artificial soil test instrument of WDT-100 type, and the stress-strain curve of the mud-sandstone, the uniaxial compressive strength at different temperatures, and the creep duration curve are obtained. The uniaxial compressive strength test shows that the stress-strain curve has an obvious yield point, and shows hardening phenomenon. The uniaxial creep experiment shows that the creep duration curve has nonlinear characteristics, the isochronous stress-strain curves are deviated to the strain axis, and the uniaxial compression creep modulus decreases with time, then tends to be stable over time. Finally the empirical formula is obtained by using a genetic algorithm to optimize model parameters. Compared with the results of test, the agreement is good.
Millions of asteroids are in various shapes, which show unique dynamical phenomena, including their own revolutions and the vicinal surrounding objects. This paper reviews the recent development of studies of asteroids. Significant effects on the long-term evolution of asteroids' attitude and orbit are introduced, i.e., the Yarkovsky effect and the YORP effect. Modeling methods of their irregular gravitational fields are presented as well as naturally periodic orbits in complex universal curves. Some basic problems and potential research directions are suggested.
The failure of some critical bearing members in building structures caused by accidental loads such as explosion and impact could trigger a devastating progressive collapse of the global structures. This paper reviews the experimental and theoretical research results on the progressive collapse of building structures, and the resistance mechanisms during the collapse as well as the their contributions to the collapse resistance. The current design and assessment methods are discussed. Finally, the prospective research directions on the structural collapse are highlighted.
The welding residual stress is the main cause of the stress corrosion cracking. The accurate determination of the residual stress distribution in the soldering seam of the structure is the key step to assess the structure integrity. In this paper, two penetration prototypes of the control rod drive mechanism (CRDM) are manufactured using the same processing technique and design method of the real CRDM penetration product, and the blind-hole method is selected to test the welding residual stress of the two J-shaped welds, in order to explore the residual stress distribution of J-shaped welds in the penetrations of the control rod drive mechanism in the reactor pressure vessel closure head. Experimental analysis has determined the residual stress distribution of J-shaped welds of CRDM penetrations in the reactor pressure vessel closure head, which can provide the necessary reference for the study of the structure integrity of reactor pressure vessels.
Kerosene supply through apron network is one of the major methods for civil aviation kerosene supply. In practical engineering, vertical pipes in apron network maybe deformed or even broken due to slippage of concrete pavement. In this work, for sake of studying the mechanism for vertical pipes deformation and damage, FEM analysis has been performed on apron vertical pipes with different norms and tee types, in which P-y curves has been applied to simulate interaction between pipe and soil. Parameters for P-y curves have been determined through indoor physical model tests. The results show that the section with high stress besides tee in the bottom came out as result of backfill soil. And the stress distribution on the vertical pipes is related to the backfill layer distribution and slippage of concrete pavement. At last, through analysis of certain field case, failure point is ascertained, which is in accordance with test result.
The different mechanical properties in mortar and in aggregates may lead to stress concentrations in concrete. However, as the distribution of aggregates is very complicated, a numerical analysis of concrete on micromechanical scales will involve a large computation and the difficulty of element meshing. Therefore, analytical solutions for the stress concentration factor caused by the existence of aggregates are derived in this paper based on a 2D model. Then, together with the superposition method, analytical solutions are used for the stress analysis in concrete of homogeneous media to approximate the real case, which makes the problem much easier. Analytical results are compared with those obtained by the FEM method for concretes with one aggregate and four aggregates, respectively, which verifies the accuracy of the method given in this paper.
Based on the Mohr-Coulomb failure criterion, this paper proposes a calculation method of the ultimate bearing capacity for the beam end concrete under the constraint of prestressed reinforcement, by which the theoretical value of the ultimate bearing capacity is obtained. The result is compared with that obtained by the finite element software ABAQUS. It is shown that the theoretical formula derived based on the failure criterion of Mohr-Coulomb gives a result consistent with the numerical one, which verifies the correctness of the theoretical formula. The theoretical formula shows that the prestress can improve the stress state of the beam end concrete, and the ultimate bearing capacity of the beam end.
To improve the structural seismic property, ductile and energy-dissipated connections represented by the reduced beam section connections gradually replace the ordinary connections. Therefore, in this paper, the beam's ultimate load under unidirectional and proportional loading is analyzed to judge the location of the plastic hinge, and the results are compared with those of the ordinary beam. It is shown that the ultimate load decreases more significantly when the beam is longer. A suitable reduced parameter should be chosen when the beam is short, to avoid the plastic hinge being formed at the end of the beam.The results can serve as the plastic design basis for the reduced beam and expand ultimate load content in structural mechanics.
The shrinkage and the creep of concrete will lead to a stress redistribution in new-old composite concrete beams. The nonlinear differential equation for the composite beam is derived in terms of the deflection. By solving the differential equation, the displacement shape function, the stiffness shape function and the equivalent nodal load shape function are introduced. Finally, the improved element stiffness matrix and the equivalent nodal loads with the combination of the new concrete beams, the old concrete beam and the Goodman elastic intermediate layer, are obtained, which may serve as an effective way to calculate the internal force of the concrete under the influence of shrinkage and creep. An example is given to verify the analysis.
In order to analyze the restrained torsion of a thick-walled open-section short member, the warpings and the stress distributions of a T-shaped short member and an L-shaped short member due to restrained torsion are determined by employing a unified analytical beam model and a finite nodal-line method. The computational results of examples show that:a thick-walled open-section short member has a torsional (bending) center that does not coincide with its cross-section centroid; when the torque or horizontal loadings do not pass through the torsional center, the member will have a coupling deformation consisting of bending and torsional deformations, and its cross section will undergo an uneven warping, and the warping normal stress and the torsional shear stress on the cross section will have nonlinear distributions.