Yuanlin Zhu

Elastic visco-plastic analysis for earthquake response of tunnels in cold regions

Abstract In this paper, in order to determine the initial stresses of tunnels in cold regions before earthquake occurs, a mathematical mechanical model and the governing differential equations of the coupled problem of temperature, seepage and stress fields, with phase change, are first derived from the theory of heat transfer, the theory of seepage and frozen soil mechanics. Then, the finite element formulae of this problem are obtained from Galerkins method. Secondly, the visco-plastic constitutive equations of frozen soil for dynamic computation are given. Finally, an illustrative example is provided. The example shows that the effect of seepage field and stress field on the frozen depth of cold region tunnels is large and the influence of frost-heaving force on the stresses of the tunnel lining is very large. This example also indicates that the influence of initial stresses of tunnels in cold regions on the time stress response of tunnels to earthquake is large. So the effects of these factors on the tunnel lining should be taken into account in cold regions engineering design.

Analysis of thin-walled composite box beam under torsional load without external restraint

A procedure for analyzing the mechanical behavior of laminated thin-walled composite box beam under torsional load without external restraint is presented. The method is based on the theory of composite laminated plates and is deduced by means of the free torsion theory of thin-walled beams, which makes the procedure simple and practical. In the present theory, the stresses are considered distributing unequally along the wall thickness and various coupling effects are taken into account. The calculation formulas of torsional angle and stress given by this method are concise and easy to use. The present analysis results indicate that by reason of coupling effects, in general, the free torsion of composite box beams may not exist definitely, so a concept of torsion without external restraint is suggested. Finally, the examples are given and their numerical results are analyzed and discussed. The values of torsional angle, ply stresses (including their variation with the off-axis ply angle) obtained by this paper are compared with those obtained by model test or finite element method (FEM).

Experimental studies on salt expansion for coarse grain soil under constant temperature

Abstract In order to discuss and analyze the processes of salt expansion that affect the stability of engineering building, the salt expansion experiments of coarse grain saline soil with Na2SO4 are developed. The salt expansion of coarse grain soil with and without salt concentration layer is designed to compare their difference in laboratory. The results show that the coarse grain soil with salt concentration layer produced abrupt destroyed salt expansion if there is suitable water content. However, coarse grain saline soil without salt concentration layer was not able to produce the larger salt expansion that destroys engineering construction.

Geometrical non-linear analysis of a simply-supported cross V-shaped folded plate roof

Abstract In this paper, the equation of the middle surface of a simply-supported cross V-shaped folded plate roof is established by means of the inclined coordinate system and generalized functions—sign function and step function. Then, the non-linear analysis for this simply-supported roof subjected to uniform load and point load is given by using the non-linear theory of shallow shell and the non-linear Galerkins method. Finally, an illustrative example of this roof is presented. This example indicates that the largest stress of this roof is much less then that of the four pitch roof of same dimensions. Therefore, a lot of construction material could be saved by using this proposed roof.

In situ determination of mechanical properties of frozen soils with the pressuremeter

Abstract An in situ test was conducted to investigate the short-term mechanical behavior of frozen soils along the Qinghai–Tibet Highway, in China, using the pressuremeter. This paper uses the plane elasticity theory and the radial expansion equation of cylindrical hole in infinite elastic medium provided by Lame to interpret the test data. The initial horizontal pressure, the critical plastic load and the limit pressure are reduced from the pressuremeter testing curves, and then, the pressuremeter modulus and the shear modulus are worked out. This paper also analyses the relationships between the mechanical parameters and the soil temperature and the water contents, respectively, and gives out the approximate formula. At the same time, some inevitable problems encountered during the operating of test are discussed.

Experimental study on settlement of model piles in frozen soil under dynamic loading

Test results show that the settlement process of model piles is mainly the rheological process of fmzen soil under shear loading. The settlement rate of model piles increases with increasing temperature of frozen soil, decreasing royghness of pile surface and increasing rigidity of pile foundation. As the water content of frozen soil reaches its saturation value, the settlemerrt rate is the least. When the level of loading is higher, the settlement rate under dynamic loading is less than that under static loading. With the level of loading lowering, the effect between dynamic and static loading on the settlement rate becomes close gradually. Under the present test conditions, the settlement rate of model piles is independent of the frequency of dynamic loads.

Nonlinear analysis for the coupled problem of temperature and seepage fields in cold regions tunnels

The govrrning differential equations of the coupled problem of temperature and seepage fields with phase change are first derived from the theory of heat transfer and the theory of seepage. The finite element formulae of this problem are obtained from Galerkin’ s method. And considering the seepage influence, an illustrative example of the temperature field in a cold-region tunnel is provided. The example shows that the influence of seepage on the frozen depth of the tunnel is very great, and thus the effect of the seepage factor should be taken into account in the engineering design

Fractal approximation of the stress-strain curve of frozen soil

A method to approach the stress-strain curve of frozen soil is presented based on the fact that the stressstrain curve of frozen soil has fractal property. First, a linear hyperbolic iterated function system (LHJB) in which the perpendicular contraction factors are regarded as parameters is established using fractal geometry theories. Secondly, a method to calculate the best point which makes the attractor of the LHIFS an optimal approximation of the stress-strain curve of frozen soil is presented. Then, a method for calculating the fractal dimension of the stress-strain curve of frozen soil is obtained. Finally, a simple example is provided. The method presented in this paper provides a new method for simulating the stress-strain curve and calculating its fractal dimension of geomaterials that have the fractal feature by using computer

Geometrically nonlinear analysis of a simply-supported hip-truncated combined parabolical cylinder roof

In this paper, the equation of the middle surface of a simply-supported hip-truncated combined parabolical cylinder roof is established by means of the local inclined coordinate system and step function. Then, the nonlinear analysis for this simply-supported roof subjected to uniform load and point loads is given by using the nonlinear theory of shallow shell and the nonlinear Galerkin method. Finally, an illustrative example of this roof is presented. This example indicates that the largest stress of this roof is much less than that of the hip-truncated four pitch roof of same dimensions.