The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were ...The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed into the samples, layer by layer, by applying a drill-mounted mortar mixing device. For each amount of fiber content, 4 rings were cast, and of the plain concrete control samples, 5 rings were cast. After removing the outer steel casting, strain gages were installed on the exposed outer concrete surface. Strain values were continuously logged, and crack developments and crack widths were measured daily. Sufficient data with statistically high significance were obtained to indicate that: A synthetic fiber content of 3 kg/m3 did not decrease crack-widths as compared to the non-fiber concrete samples. Synthetic fiber contents of 5 kg/m3 and higher, did reduce crack widths on par with hooked-end steel fibers in the amounts of 25 kg/m3 and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with regards to crack width reduction, yielding 33% narrower cracks, than hooked-end steel fibers, at equal weight-contents, with aspect ratio 45.展开更多
Laminar airflow(LAF)is essential for maintaining a sterile environment in operating rooms,but its rapid unidirectional flow decay leads to low airflow efficiency and increases energy consumption.The objective of this ...Laminar airflow(LAF)is essential for maintaining a sterile environment in operating rooms,but its rapid unidirectional flow decay leads to low airflow efficiency and increases energy consumption.The objective of this study is to investigate the energy-saving and air quality benefits of using a low-turbulence air curtain around laminar airflow,which is referred to as protective laminar airflow(PLAF).Numerical simulations were used to model airflow and particle transport,and a series of experiments were conducted in a real operating room at St.Olavs Hospital,Norway,to validate the simulation results.The findings indicate that when the unidirectional airflow supply velocity is maintained at 0.25 m/s,combined with an air curtain that has the width of 2 cm and the velocity of 1.5 m/s,the PLAF system outperforms the conventional LAF system operating at a unidirectional airflow supply velocity of 0.30 m/s.This configuration results in a 17.3%energy saving,showing the potential of this airflow distribution strategy to enhance both cleanliness and energy efficiency.展开更多
文摘The object of this research effort was, upon request for evidence from a building contractor, to compare the influence of various amounts and types of fibers on crack widths, using a steel ring mold. Comparisons were made between synthetic fibers (polyolefin) of 48 mm length, hooked-end steel fibers of diameters 0.6 mm and 1.05 mm, both of 50 mm length. 10-liter samples were extracted from concrete ready-mix truck batches at delivery sites, whereupon fibers were mixed into the samples, layer by layer, by applying a drill-mounted mortar mixing device. For each amount of fiber content, 4 rings were cast, and of the plain concrete control samples, 5 rings were cast. After removing the outer steel casting, strain gages were installed on the exposed outer concrete surface. Strain values were continuously logged, and crack developments and crack widths were measured daily. Sufficient data with statistically high significance were obtained to indicate that: A synthetic fiber content of 3 kg/m3 did not decrease crack-widths as compared to the non-fiber concrete samples. Synthetic fiber contents of 5 kg/m3 and higher, did reduce crack widths on par with hooked-end steel fibers in the amounts of 25 kg/m3 and above. Hooked-end steel fibers of aspect ratio 80 are more efficient with regards to crack width reduction, yielding 33% narrower cracks, than hooked-end steel fibers, at equal weight-contents, with aspect ratio 45.
基金the China Scholarship Council for the financial support to Yang Bi(CSC student ID:202009210006).
文摘Laminar airflow(LAF)is essential for maintaining a sterile environment in operating rooms,but its rapid unidirectional flow decay leads to low airflow efficiency and increases energy consumption.The objective of this study is to investigate the energy-saving and air quality benefits of using a low-turbulence air curtain around laminar airflow,which is referred to as protective laminar airflow(PLAF).Numerical simulations were used to model airflow and particle transport,and a series of experiments were conducted in a real operating room at St.Olavs Hospital,Norway,to validate the simulation results.The findings indicate that when the unidirectional airflow supply velocity is maintained at 0.25 m/s,combined with an air curtain that has the width of 2 cm and the velocity of 1.5 m/s,the PLAF system outperforms the conventional LAF system operating at a unidirectional airflow supply velocity of 0.30 m/s.This configuration results in a 17.3%energy saving,showing the potential of this airflow distribution strategy to enhance both cleanliness and energy efficiency.
