Search Results (4)

The roof slab, as a critical component for partitioning the vertical space within RC frame structures, can effectively mitigate the propagation of shock waves and reduce damage levels in adjacent rooms. This study employed finite element (FE) modeling to investigate the vertical propagation of blast waves and roof ejection velocity in RC frames. The model’s reliability was verified by reconstructing internal explosion tests on RC frames and close-in explosion tests on masonry walls. On this basis, two typical single-room RC frame structures that are vertically adjacent were designed, and numerical simulations of the internal explosion were conducted under four explosive equivalents and four venting coefficients. The propagation of shock waves, load characteristics in the vertically adjacent room, and the dynamic response of roof slabs were examined. The results show that shock waves propagated to the vertically adjacent room decreased by approximately two orders of magnitude for peak overpressure and one order of magnitude for impulse due to the obstruction of shock waves by roof slabs, respectively, compared to the source explosion room. For larger venting coefficients, abundant energy was released through the venting openings, making it difficult to form a quasi-static pressure with a long duration inside the source explosion room. In addition to the shock wave, the explosive ejection of roof slabs in the explosion source room will further exacerbate the damage to the vertically adjacent room. Peak overpressure and impulse propagated to the vertically adjacent room were reduced significantly by the increase in the venting coefficient, resulting in an attenuation of structural damage. Finally, empirical models incorporating the venting coefficient were established to characterize the attenuation coefficients of power parameters, demonstrating the predictive capability for peak overpressure, impulse, and roof ejection velocity in both the explosion source room and the vertically adjacent room. Full article

During the gob-side entry driving of the Jurassic coal seam in Western China, ejection disasters occur under the influence of roof drainage, which rarely appear in the eastern mining area. To address this problem, a method combining theoretical analysis, numerical simulation, and field monitoring was used to study the disaster induced by head-on ejection during speedy driving under the influence of roof drainage in the context of gob-side entry driving of the 2202 auxiliary haulage roadway in a mine. A calculation model for the critical energy conditions for disasters induced by head-on ejection was established. The relationships between the driving velocity and the dynamic and static loads on the driving face and the disasters induced by ejection were clarified under the influence of roof drainage. The results indicate that the energy threshold for ejection-induced disaster is 12.23 kJ, and the elastic energy of the driving face induced only by static load fails to reach the energy threshold. When the driving velocity exceeds 5 m/d, microseismic activity in front of the driving face increases in a stepwise manner, and the influence of dynamic load intensifies. The superposition of accumulated elastic energy induced by static load and the energy transmitted by microearthquake to the driving face exceeds the energy threshold, resulting in the risk of ejection-induced disaster. Based on this, measures such as microseismic monitoring in front of the driving face, advanced pulverized coal monitoring, driving speed adjustment, and advanced pressure relief of large-diameter boreholes are adopted to ensure safe driving. Full article

Roof structures are suffering serious threats caused by unbalanced snow distribution, especially long-span spatial structures, such as gable roofs. The formation of unbalanced snowdrifts on the gable roof is affected by the meteorological condition and the drifting snow. This study was conducted to explore the snowdrift characteristics on gable roofs under different snowfall conditions based on a new Eulerian–Eulerian multiphase approach. To consider the diffusive process of snow in different states, the governing equations of air and snow phases were modified separately according to the actual transport process. Additional terms based on the deposition/erosion process were inserted into the governing equations to consider the processes of snow particles being trapped or ejected by snow surface. The feasibility of the new model for the snowdrift was validated by comparing with a field observation. Then, the snowdrifts characteristics on typical gable roofs were investigated under different wind velocity and snowfall intensity conditions. The formation mechanism of snowdrifts and the influence of meteorological conditions on snowdrifts were clarified by analysis. The results show that the uneven distribution of snow on the gable roof becomes more significant with the increase in wind velocity. Furthermore, the distribution of snow on the roof tends to be more even in the case of heavier snowfall. Full article

Objective: Cardiac involvement is a predictor of poor prognosis in patients with systemic sclerosis (SSc); therefore, preclinical diagnosis of heart involvement is crucial. Two-dimensional speckle tracking echocardiography (2D-STE), a method for evaluating the myocardial strain, could be helpful for the early diagnosis of cardiac mechanical function abnormalities. In this study, the simultaneous evaluation of all cardiac chambers was studied in patients with SSc, compared with normal individuals. Methods: The results of transthoracic echocardiography (TTE) and 2D-STE of 37 patients with SSc and 37 healthy individuals and the longitudinal strain (LS) of all chambers was precisely evaluated. The collected data were analyzed using SPSS version 16, and independent-sample t test and Chi-square test were used for comparison between the groups. Results: The mean ± SD of the participants’ age was 45.7 ± 11.54 (range of 17 to 68) years; most of them were women (75.7%). TTE showed higher left atrial (LA) volume (p < 0.001), right atrial (RA) area (p = 0.007), the severity of ventricular dysfunction (p < 0.05) and inferior vena cava diameter (p = 0.005), compared with the control group. Spectral and tissue Doppler echocardiography showed higher systolic pulmonary arterial pressure (sPAP) and mitral A wave velocity, and lower E/A ratio, E’ velocity of left ventricular (LV) septal and lateral wall in the case group (p < 0.05). Color Doppler echocardiography showed a higher frequency of valvular regurgitation in the case group (p < 0.05). The results of 2D-STE showed lower LA roof LS (p < 0.001), LA average LS (p = 0.015), LA global LS (p = 0.028), and LA ejection fraction (LAEF) (p = 0.001), lower mean RA left wall (p = 0.048) and EF (p < 0.001), and higher RV global LS in the case group (p = 0.025). Conclusions: Simultaneous evaluation of all cardiac chambers by 2D-STE provides valuable information about the myocardial involvement in patients with SSc. Therefore, it is suggested to use this method for the early diagnosis of cardiac involvement in such patients. Full article