The mechanical behavior of recycled coarse aggregates self‐compacting concrete‐filled steel tubular columns (RCA ‐ SCCFST) under eccentric compression is investigated in this study. Nine specimens with different eccentricities (
e) and column length‐to‐diameter ratios (
L/D) are designed and tested, including six long columns (
L/D > 4) and three short columns (
L/D ≤ 4). Test results indicate that the long columns under eccentric compression exhibit overall flexural buckling failure, while the short columns under eccentric compression experience drum‐like bending failures. The ultimate bearing capacity of specimens decreases as eccentricity or column length‐to‐diameter ratio increases. The increase of column length‐to‐diameter ratio or eccentricity would accelerate the stiffness degradation. The ultimate longitudinal and circumference strains decrease as the eccentricity or column length‐to‐diameter ratio increases. The application of existing concrete filled steel tube (CFST) design specifications, such as American specification (AISC360‐16‐2016), Chinese code (GB50936‐2014) and Japanese code (AIJ‐1997) for the RCA ‐ SCCFST long columns are evaluated. AISC360‐16‐2016 and AIJ‐1997 are a little conservative. GB50936‐2014 is comparative accurate. Considering the influence of replacement ratio of RCA, a modified formula for predicting the ultimate bearing capacity of RCA ‐SCCFST long columns is presented in this study. The theoretical values estimated by the modified formula are in good agreement with test data.
Is Long COVID-19 under-diagnosed? The definition of this new condition has received many contributions, and it is still under development as a great variety of symptoms have been associated to it. This study explores the possibility that there are non-diagnosed cases among individuals who have been infected by SARS-CoV-2 and have not been vaccinated. The long-term symptoms identified among a sample 255 individuals have been associated to Long COVID-19 by recent literature. The study relates these symptoms to risk factors and health-related quality of life (HRQoL) negative impacts. The individuals were screened 1 year after discharge to explore its potential relation to Long COVID-19. Patients diagnosed with COVID-19 and discharged from designated hospitals in a Chinese province between January and April 2020 were included in this study. They received computed tomography (CT) scans one month after discharge. One year after discharge, patients were invited to physical examination and interviewed with questionnaire on health-related quality of life (HRQoL) and post-COVID-19 symptoms. Tobit regression and Logistic regression were applied to evaluate the risk factors for health utility value and pain/discomfort and anxiety/depression. One year after discharge, 39.61% patients complained of several of the symptoms associated to Long COVID-19. More than half had abnormal chest CT. Previous studies focused on the post-COVID-19 symptoms and chest CT findings of patients, but few studies have assessed the COVID-19-associated risk factors for health-related quality of life.
Polyacrylamide (PAM) was prepared by a new method of inverse microemulsion polymerization, with (NH4)2S2O8-Na2SO3 as initiator and liquid paraffin/Span80-Op10/AM-H2O-NaAc as polymerization system in this paper. The effects of initiator dosage, emulsifier dosage, monomer concentration, oil–water ratio, and temperature on molecular weight, electrical conductivity, particle size distribution, and monomer conversion were studied as well. The results indicate that that the more stable Polyacrylamide (PAM) polymer was prepared under the conditions of initiator dosage of 0.4~0.5%, emulsifier dosage of 55~60%, temperature of 40~45 °C, hydrophile–lipophile balance (HLB) value of 8.0~8.2, and NaAc concentration of 3%.
Tropospheric delay is one of the important errors in positioning and timing. Lots of researches have been done, and many tropospheric correction models have been proposed. The precision of the models change with the location and meteorological conditions of the user. Significant improvements will been made within the precision of positioning and timing on researching tropospheric correction models. In this paper, the effects of different factors on the precision of tropospheric correction models are analyzed, and their proportions in the measurement uncertainty are elaborated. Based on the two years ZTD (zenith tropospheric delay) of BJFS station, the effects of meteorological parameters on the zenith delay correction are analyzed, and the precision of various models are compared. The result shows that the precision of models are the highest by using direct meteorological measurements, and the precision of ENGONS and UNB3 follow, and the models using reference atmospheric information get poor precision.
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