The post buckling strength of web plate of I section plate girders is considered to resist the shear force in many other countries code for design of steel structures,while it has not been considered in the Chinese ...The post buckling strength of web plate of I section plate girders is considered to resist the shear force in many other countries code for design of steel structures,while it has not been considered in the Chinese code GB J17-88.For the code revising,some important conclusions have been drawn through the theoretical analysis and experimental research of the post buckling strength of web plate of I section plate girders.展开更多
To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with di...To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.展开更多
This study covers optimization of I-sectional flange beams. Scope of this study is limited to medium weight flange beams of Table 1 of IS 808:1983 but it can be further extended for the other sections of this code. Be...This study covers optimization of I-sectional flange beams. Scope of this study is limited to medium weight flange beams of Table 1 of IS 808:1983 but it can be further extended for the other sections of this code. Best possible geometric shape of the cross-section is found for maximum performance of the beam with minimum material consumption. All possible loading conditions are considered in the study for which a beam in flexure undergoes in its life. ANSYS software program is used for the analysis and optimizing the sections. It is found that sections MB 125, MB 300 and MB 400 of Table 1 of IS 808 are not the optimum sections but other alternative of these cross-sections is available which within the same material consumption performs better than these sections of IS code.展开更多
Background: In Cameroon, the prevalence of HIV in pregnant women was 7.8% in 2012, and they were 8500 HIV positive newborns in 2013. Option B+ is the first highly active antiretroviral therapy (HAART) preventive proto...Background: In Cameroon, the prevalence of HIV in pregnant women was 7.8% in 2012, and they were 8500 HIV positive newborns in 2013. Option B+ is the first highly active antiretroviral therapy (HAART) preventive protocol. The objective was to evaluate the rate of HIV transmission on children born from mothers who were on Option B+ during pregnancy, in three university teaching hospitals of the University of Yaoundé I. Methods: It was a retrospective, cross-sectional study over a period of four years (2013-2017). We included HIV positive mothers not on previous antiretroviral treatment and who received a single tablet daily of combined tenofovir (300 mg) + Lamivudine (300 mg) + Efavirenz (600 mg) started at any time during pregnancy. Newborn received nevirapine syrup according to WHO option B+ protocol. Results: 179 women were included. The average age was 33.5 ± 2.92 years, all ages were represented. Blood donation was the most frequent HIV positive screening opportunity, voluntary testing rate was 29% (29/179), and adherence rate was 98.9%. Few male partners were involved (58/179). Premature deliveries and low birth weight were rare (5/179;10/179)), the indication of mode of delivery was strictly obstetrical, newborn feeding choice didn’t affect the transmission outcome, and the mother to child transmission rate was 2.2% (4/179). Conclusion: Option B+ could achieve the lowest mother to child transmission ever in Cameroon and should be generalized in high endemicity low resources settings.展开更多
文摘The post buckling strength of web plate of I section plate girders is considered to resist the shear force in many other countries code for design of steel structures,while it has not been considered in the Chinese code GB J17-88.For the code revising,some important conclusions have been drawn through the theoretical analysis and experimental research of the post buckling strength of web plate of I section plate girders.
基金the National Natural Science Foundation of China under Grant No.51478244
文摘To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.
文摘This study covers optimization of I-sectional flange beams. Scope of this study is limited to medium weight flange beams of Table 1 of IS 808:1983 but it can be further extended for the other sections of this code. Best possible geometric shape of the cross-section is found for maximum performance of the beam with minimum material consumption. All possible loading conditions are considered in the study for which a beam in flexure undergoes in its life. ANSYS software program is used for the analysis and optimizing the sections. It is found that sections MB 125, MB 300 and MB 400 of Table 1 of IS 808 are not the optimum sections but other alternative of these cross-sections is available which within the same material consumption performs better than these sections of IS code.
文摘Background: In Cameroon, the prevalence of HIV in pregnant women was 7.8% in 2012, and they were 8500 HIV positive newborns in 2013. Option B+ is the first highly active antiretroviral therapy (HAART) preventive protocol. The objective was to evaluate the rate of HIV transmission on children born from mothers who were on Option B+ during pregnancy, in three university teaching hospitals of the University of Yaoundé I. Methods: It was a retrospective, cross-sectional study over a period of four years (2013-2017). We included HIV positive mothers not on previous antiretroviral treatment and who received a single tablet daily of combined tenofovir (300 mg) + Lamivudine (300 mg) + Efavirenz (600 mg) started at any time during pregnancy. Newborn received nevirapine syrup according to WHO option B+ protocol. Results: 179 women were included. The average age was 33.5 ± 2.92 years, all ages were represented. Blood donation was the most frequent HIV positive screening opportunity, voluntary testing rate was 29% (29/179), and adherence rate was 98.9%. Few male partners were involved (58/179). Premature deliveries and low birth weight were rare (5/179;10/179)), the indication of mode of delivery was strictly obstetrical, newborn feeding choice didn’t affect the transmission outcome, and the mother to child transmission rate was 2.2% (4/179). Conclusion: Option B+ could achieve the lowest mother to child transmission ever in Cameroon and should be generalized in high endemicity low resources settings.
