Development of an optimum pre-founded column system for top-down construction

In this work, circular concrete-filled steel tubular (CCFT) columns, rather than the more popular H-shaped columns, were suggested as pre-founded columns for top-down construction. In addition, a novel shear connection system with headed stud shear connectors between the CCFT columns and the flat slabs was developed. It was noted that a CCFT column with a design compressive strength similar to that of an H-shaped column without consideration of length effects can be easily installed, even into a smaller borehole. Furthermore, compared to the H-shaped column, less steel is required for the CCFT column. It was shown that the amount of steel needed can be reduced by decreasing the wall thicknesses or diameters of the CCFT column depending on the exposed length of the column during excavation. The fillet-welded joint of the developed shear connector system was also tested before its in-situ application. The test results revealed that the joint possessed sufficient shear and deformation capacities. The CCFT column with the developed shear connection system was ultimately applied to an actual top-down construction process. The good constructability of the CCFT column system and reductions in construction costs and time were confirmed

Nondestructive evaluation of concrete using wideband microwave techniques

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995.Includes bibliographical references (leaves 190-193).by Hong Chul.Ph.D

Effect of Steel Plates on Estimation of the Compressive Strength of Concrete via Ultrasonic Testing

The presence of embedded steel affects the estimates obtained for the compressive strength of concrete during ultrasonic testing, as it increases the ultrasonic wave velocity. Thus, if the presence of steel in concrete is inevitable, then a correction factor is required for an accurate estimation of the concrete strength. While previous studies focused on the effect of steel reinforcing bars on the speed of ultrasonic waves in concrete, this work expands on the significance of embedded steel from steel bars to include steel plates. The wave velocity was measured for varying dimensions of embedded steel plates from 15 mm to 150 mm using 54-kHz ultrasonic testing equipment. Through experiments, the effect of steel plates on the ultrasonic testing of concrete was quantified to derive proper correction factors. It was found that the thickness, depth, and height of the steel plates significantly affected the test results. These findings can be applied to ultrasonic testing to estimate the compressive strength of concrete consisting of a significant volume of steel, such as in steel-reinforced concrete structures

The antipyretic efficacy and safety of propacetamol compared with dexibuprofen in febrile children: a multicenter, randomized, double-blind, comparative, phase 3 clinical trial

Abstract Background We aimed to compare the antipyretic efficacy, safety, and tolerability between oral dexibuprofen and intravenous propacetamol in children with upper respiratory tract infection (URTI) presenting with fever. Methods Patients aging from 6 months to 14 years admitted for URTI with axillary body temperature ≥ 38.0 °C were enrolled and randomized into the study or control group. Patients in the study group were intravenously infused with propacetamol and subsequently oral placebo medication was administered. Patients in the control group were intravenously infused with 100 mL of 0.9% sodium chloride solution without propacetamol and then oral dexibuprofen was administered. We checked the body temperature of all patients at 0.5 h (hr), 1 h, 1.5 h, 2 h, 3 h, 4 h, and 6 h after oral placebo or dexibuprofen had been applied. Results A total of 263 patients (125 in the study group) were finally enrolled. The body temperatures of patients in the study group were significantly lower until 2 h after administration (37.73 ± 0.58 vs 38.36 ± 0.69 °C (p < 0.001), 37.37 ± 0.53 vs 37.88 ± 0.69 °C (p < 0.001), 37.27 ± 0.60 vs 37.62 ± 0.66 °C (p < 0.001), 37.25 ± 0.62 vs 37.40 ± 0.60 °C (p = 0.0452), at 0.5 h, 1 h, 1.5 h, and 2 h, respectively). The two groups showed no significant differences in terms of the range of body temperature decrease, the Area Under the Curve of body temperature change for antipyretic administration-and-time relationship, the maximum value of body temperature decrease during the 6 h test period, the number of patients whose body temperature normalized (< 37.0 °C), the mean time when first normalization of body temperature, and the development of adverse events including gastrointestinal problem, elevated liver enzyme, and thrombocytopenia. Conclusions Intravenous propacetamol may be a safe and effective choice for pediatric URTI patients presenting with fever who are not able to take oral medications or need faster fever control. Trial registration CRIS KCT0002888. Date of registration: July 31st, 2013