Proposed Strength Criterion Research Articles

Relating shear strength of unsaturated soils with capillary water retention curve

This paper proposes a new water retention model for unsaturated soils, which takes into account capillary condensation of adsorbed water. In the proposed water retention model, the degree of saturation of a soil is separated into that based on capillary water and that based on adsorbed water. Through the analysis of a partially saturated two-cylinder system, a new shear strength criterion for unsaturated soils is proposed, in which only the degree of saturation based on capillary water contributes to the variation of shear strength with suction. The proposed shear strength criterion is justified against thermodynamic principles. The proposed strength criterion is compared against existing criteria in the literature, which shows that it provides a much improved prediction of the experimental data, for a wide range of suction values.

Strength criterion for rocks subjected to cyclic stress and temperature variations

The strength of rocks subjected to cyclic stress and temperature variations must be determined to ensure the stability of caverns for underground compressed air energy storage. This paper proposes a strength criterion for rocks subjected to cyclic stress and temperature variations; the proposed criterion is based on the least energy dissipation principle and the rock damage induced by cyclic stress and temperature effects. The cyclic uniaxial stress-temperature tests and uniaxial compression tests after cycling are conducted to validate preliminarily the proposed criterion. The applicability of the proposed strength criterion and the influence of damage factor selection are discussed. The proposed strength criterion has a clear physical meaning and only involves four parameters to be determined. The predicted rock strengths are in good agreement with the laboratory test results, confirming the applicability of the proposed criterion. The proposed strength criterion can degenerate into certain existing criteria. Moreover, the damage factor is suggested to be calculated with the use of the peak secant modulus when the proposed strength criterion is applied.

A new strength criterion for structured soils

Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soils in many aspects, especially in their strength properties. Thus, the influence of soil structure (bonding and fabric) on the mechanical properties of structured soils cannot be correctly described. By analyzing the breakage mechanism of natural soils, the structured soils can be conceptualized as binary medium materials consisting of bonded blocks and weakened bands. On this basis, a new strength criterion is proposed for structured soils. The expressions of the strength criterion on both meridian and deviator planes are given to describe the strength properties of structured soils on these planes. The proposed strength criterion is compared with available test data under conventional and true triaxial stress conditions in the literature. It is observed that the proposed strength criterion agrees well with the test data.

Modeling and behaviours of rockfill materials in three-dimensional stress space

A bounding surface model incorporating a unified nonlinear strength criterion is proposed. The proposed bounding surface model contains 9 model parameters, which can be determined from the conventional triaxial tests. The bounding surface model can reproduce such behaviours as the strain hardening, the post-peak strain softening, and the volumetric strain contraction and expansion. Based on the comparisons between the predictions and the test results, the proposed strength criterion and model can well reproduce the experimental results of the strength and stress-strain behaviours of rockfill material in three-dimensional stress space. The strength behaviour of rockfill material is summarized as: (a) the failure stress ratio decreases with the initial confining pressure on the meridian plane; (b) the failure deviatoric stress decreases with the Lode angle from 0° to 60° on the deviatoric plane. The stress ratio decreases with increasing one of such factors as the initial void ratio, the intermediate principal stress ratio and the minor principal stress at the same strain when the other factors are given.

DISCUSSION ON RESEARCH ACTIVITY PUBLISHED AS “FAILURE CRITERION OF BLOCK SHEAR STRENGTH OF TIMBER PARALLEL TO THE GRAIN”

Experimental and analytical achievements on the block shear strength of wood in the above paper are discussed about the following items: 1) The proposed failure criterion seems inadequate, because the compressive stress does not act on both sides of the failure section. 2) The elastic modulus for FE analysis seems inadequate, because the Young's modulus in the transverse direction is too small. 3) The proposed equation for bearing deformation seems inadequate, because it is contradictory to the proposed strength criterion. 4) The test specimens seem improperly arranged, because the directions of the grain are inclined or curved to the bearing force.

Cyclic performance of steel beam-column moment joints

The performance of ten seismic beam-to-column moment connection specimens using bolted web-welded flanges (BWWF) detail is critically assessed. Key parameters include: beam flange to entire section plastic modulus ratio, Z F Z , supplemental web bolts, supplemental web welds and column panel zone strength. It was found that the cyclic plastic rotational capacities of the BWWF connections ranged between 0.009 and 0.018 rad, and did not indicate apparent relationships with respect to the beam section modulus ratios. The ultimate beam flange flexural strength, Z F F u , well predicted the ultimate moment capacities of BWWF connections. Using the proposed strength criterion, the supplemental web welds, but not the supplemental web bolts, significantly enhance the strength, ductility and energy absorbing capacity of the BWWF connections.

A compressive strength criterion for anisotropic rock materials

This paper proposes a general compressive strength criterion for anisotropic rock materials under multiaxial states of stress. The proposed criterion is a generalization of the Von Mises' criterion for yielding of ductile metals, which has also been used previously as a strength criterion for brittle fracture in the spirit of both being limits of linear elastic behavior. The presently proposed criterion takes into consideration the effects of the confining pressure, the various stress components, and the material anisotropy on rock material failure in a multiaxial stress state. To verify the applicability of the proposed criterion, it has been used to construct the failure envelopes for several types of rock materials. Consequently, the constructed failure envelopes and the corresponding experimental results have been compared. In all cases, a close agreement with the experimental results has been achieved. This result demonstrates the versatility and applicability of the proposed strength criterion in representing the compressive strength behavior of anisotropic rock materials under complex multiaxial states of stress. Key words: strength, rock materials, anisotropy.