Mechanical Characteristics and Failure Mechanism of Siltstone with Different Joint Thickness

The mechanics of rock mass is significantly affected by joints, but many existing studies of jointed rocks make simplifications that do not consider the joint thickness. To further study the influence of joint thickness on rock mechanics (mechanical properties, failure mechanism, damage model, etc.), we fabricated jointed siltstone specimens with different joint thickness (5, 10, 15, and 20 mm) and the specimens were subjected to uniaxial compression tests. The effects of joint thickness on the uniaxial compression strength (UCS), the strain at UCS, the elastic modulus, and the stress-strain curves were thus analyzed. For the stress-strain curve, with rising joint thickness, the upper concave in the initial compression stage intensified, the slope of the stress-strain in the elastic stage decreased, and the sudden stress drop after peak strength became more obvious. Both the peak compression strength and the elastic modulus gradually decreased with rising joint thickness, but a positive correlation was found between the strain at UCS and the joint thickness.

The effect of material type and joint thickness on wall behavior in conventional masonry walls

Masonry walls are systems that are typically preferred in conventional structures. The complex structure of masonry walls makes it harder to determine wall behavior; however, wall behavior is affected by the types of material used in conventional walls and the way in which joints interact with masonry units. The aim of this study is to investigate the effect of joint thickness and material factors on wall performance. To accomplish this, materials used in historical and conventional structures are preferred. This study involved hollow bricks, clay bricks, NHL 3.5, and CEM 32.5. Three different joint thicknesses were used to set up 12 different combinations. Damage estimation of the wall was carried out by moving a live load under a constant vertical load. Different materials of different joint thicknesses and mechanical properties were studied for their effects on the wall. The results indicated that a joint thickness of 20 mm preferred in wall production was more convenient. The strength of walls produced from durable material was found to be higher.

Experimental research on stress-dependent permeability and porosity of rock-like materials with different thicknesses of smooth hidden joints

In this paper, a method is proposed to prepare rock-like materials with different thicknesses of hidden joints. Then, permeability and porosity of the self-prepared jointed specimens under different pore pressures during confining pressure loading and unloading are measured. The experimental results indicate that the gas permeability of the jointed specimens gradually decreases with the rise of pore pressure due to the existence of Klinkenberg effect, and Klinkenberg effect gradually decreases with the rise of hidden joint thickness. As the main seepage channels, hidden joints govern the seepage characteristics, and due to the existence of hidden joints, the intrinsic permeability is improved significantly. Besides, due to the existence of hidden joints, the intrinsic permeability and porosity are more sensitive to confining pressure loading than that of the intact specimen, and the sensitivity increases with the rise of hidden joint thickness. During confining pressure loading, there is a permanent deformation of the hidden joints and pores in the specimens, which results in both the intrinsic permeability and porosity being always lower than those in the loading process. Meanwhile, the permanent deformation rises with the increases of hidden joint thickness, which leads to the increases of gap of intrinsic permeability and porosity under loading and unloading processes. Additionally, after comparison of the fitting results, the sub-cubic law can reflect the relationship between flow rate and the thickness of non-persistent joints better than the cubic law.

Transient Thermo-Mechanical Analysis of Steel Ladle Refractory Linings Using Mechanical Homogenization Approach

Mortarless refractory masonry structures are widely used in the steel industry for the linings of many high-temperature industrial applications including steel ladles. The design and optimization of these components require accurate numerical models that consider the presence of joints, as well as joint closure and opening due to cyclic heating and cooling. The present work reports on the formulation, numerical implementation, validation, and application of homogenized numerical models for the simulation of refractory masonry structures with dry joints. The validated constitutive model has been used to simulate a steel ladle and analyze its transient thermomechanical behavior during a typical thermal cycle of a steel ladle. A 3D solution domain and enhanced thermal and mechanical boundary conditions have been used. Parametric studies to investigate the impact of joint thickness on the thermomechanical response of the ladle have been carried out. The results clearly demonstrate that the thermomechanical behavior of mortarless masonry is orthotropic and nonlinear due to the gradual closure and reopening of the joints with the increase and decrease in temperature. In addition, resulting thermal stresses increase with the increase in temperature and decrease with the increase in joint thickness.

Comparing the Accuracy of Radiography and Sonography in Detection of Knee Osteoarthritis: A Diagnostic Study

BACKGROUND: Knee osteoarthritis (OA) is the most common degenerative disorder occurring in elderly people. Radiography and sonography are convenient techniques to detect diverse pathological features of knee OA. BACKGROUND: Knee osteoarthritis (OA) is the most common degenerative disorder occurring in older people. Radiography and sonography are convenient techniques to detect diverse pathological features of knee OA. AIM: The aim of the present study was to evaluate the diagnostic efficacy of radiography and sonography in the detection of diverse features of knee OA. METHODS: In a prospective cross-sectional diagnostic accuracy study, 50 consecutive patients with suspected knee OA (40 women and 10 men, mean age 41.2 ± 6.1 years), referred to the rheumatology clinic of the Shohada Hospital of Khorramabad. All obtained magnetic resonance imaging (MRI), radiographic and sonography images were evaluated by two radiologists and rheumatologist with sufficient expertise in degenerative knee disorders. MRI has been considered as a gold standard test in evaluating other tests. The sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV) and accuracy with 95% confidence intervals of radiography and sonography in the diagnosis of knee OA were calculated. RESULTS: Prevalence of the marginal osteophyte, geode and decreased joint thickness were significantly higher in patients with age > 40 years compared to ≤ 40 years (P ˂ 0.05). The incidence of diverse features of knee OA was not significantly different in terms of the patient’s gender, except for decreased joint space. The specificity of radiography was higher than its sensitivity. CONCLUSION: Our study showed that both radiography and sonography are useful imaging modalities, especially to diagnosis the positive cases of knee OA. The specificity of radiography is higher than to its sensitivity for all pathological features of knee OA. The sensitivity of sonography to detect some features of knee OA such as decreased joint thickness is considerably higher than radiography.