The Türkiye earthquake sequence on February 6, 2023, was featured by the closely located earthquake doublet of M_(W)7.8 and M_(W)7.5. The consequent strong ground motions are supposed to be able to impose high de...The Türkiye earthquake sequence on February 6, 2023, was featured by the closely located earthquake doublet of M_(W)7.8 and M_(W)7.5. The consequent strong ground motions are supposed to be able to impose high demands on the ultra-low-cycle fatigue performance of metallic dampers in buildings, including the widely used buckling restrained braces. This study evaluates the cumulative plastic deformation(CPD) demands on bucklingrestrained braces(BRBs) in multi-story buildings imposed by the strong ground motions in the 2023 Türkiye earthquake doublet. Thirty-two records of the highest peak ground accelerations were selected from the strong motion database. Among them, eight captured the ground motions during both events, and the rest only captured the shaking of either of the events. The CPD demands on the BRBs in reinforced concrete frames with various fundamental periods, brace-to-frame stiffness ratios, and BRB ductility ratio are calculated by nonlinear time history analyses and are summarized in the form of enveloped spectra of CPD ratios at constant ductility. The results show that the CPD demands on BRBs increase with smaller brace-toframe stiffness ratios and larger BRB ductility ratios. The enveloped CPD demands are several hundreds of times the nominal yield deformation of the BRB, which are much higher than the CPD demands for the calibration tests of BRBs stipulated by AISC 341 in the US.展开更多
To enhance the reliability of aluminum alloy welding quality,this study investigates the effects of gas pulse parameters on the arc characteristics and weld quality in pulsed plasma gas variable polarity plasma arc we...To enhance the reliability of aluminum alloy welding quality,this study investigates the effects of gas pulse parameters on the arc characteristics and weld quality in pulsed plasma gas variable polarity plasma arc welding(PPG-VPPAW)of 5051 aluminum alloy.Results showed that increasing the gas duty cycle enhanced arc pressure fluctuation but reduced average arc pressure.When the duty cycle exceeded 1/2,excessive pressure fluctuations destabilized the weld pool.Arc voltage fluctuations also intensified with larger duty cycles,reducing arc heat input and stability.Severe variations in arc divergence and high-temperature area were observed at duty cycles above 1/2,leading to poor heat transfer.Weld morphology confirmed these findings:duty cycles of 1/5 and 2/5 produced uniform surfaces with dense fish-scale ripples,while 3/5 and 4/5 introduced defects such as humping and undercut.Mechanical testing showed that conventional variable polarity plasma arc welding(VPPAW)joints reached 262 MPa tensile strength and 18.3%elongation,corresponding to 79.8%and 85.1%of base metal values.At a duty cycle of 2/5,the tensile strength increased to 297 MPa and the elongation to 21.5%,representing the best overall performance.Variations in the gas pulse frequency did not significantly affect the average arc pressure or arc voltage.However,as the gas pulse frequency decreased,the fluctuation frequency of the arc pressure and arc voltage also decreased,while the fluctuation amplitude of the arc voltage increased.At 8 Hz,the tensile strength and elongation increased by 13.4%and 17.5%,respectively,compared with lower frequencies(4 and 2.6 Hz).展开更多
基金supported by the Natural Science Foundation of China [grant number 52122811]。
文摘The Türkiye earthquake sequence on February 6, 2023, was featured by the closely located earthquake doublet of M_(W)7.8 and M_(W)7.5. The consequent strong ground motions are supposed to be able to impose high demands on the ultra-low-cycle fatigue performance of metallic dampers in buildings, including the widely used buckling restrained braces. This study evaluates the cumulative plastic deformation(CPD) demands on bucklingrestrained braces(BRBs) in multi-story buildings imposed by the strong ground motions in the 2023 Türkiye earthquake doublet. Thirty-two records of the highest peak ground accelerations were selected from the strong motion database. Among them, eight captured the ground motions during both events, and the rest only captured the shaking of either of the events. The CPD demands on the BRBs in reinforced concrete frames with various fundamental periods, brace-to-frame stiffness ratios, and BRB ductility ratio are calculated by nonlinear time history analyses and are summarized in the form of enveloped spectra of CPD ratios at constant ductility. The results show that the CPD demands on BRBs increase with smaller brace-toframe stiffness ratios and larger BRB ductility ratios. The enveloped CPD demands are several hundreds of times the nominal yield deformation of the BRB, which are much higher than the CPD demands for the calibration tests of BRBs stipulated by AISC 341 in the US.
基金supported by the National Natural Science Foundation of China(Grant No.52275302 and 52322508)the R&D Program of Beijing Municipal Education Commission(Grant No.KZ20231000519)。
文摘To enhance the reliability of aluminum alloy welding quality,this study investigates the effects of gas pulse parameters on the arc characteristics and weld quality in pulsed plasma gas variable polarity plasma arc welding(PPG-VPPAW)of 5051 aluminum alloy.Results showed that increasing the gas duty cycle enhanced arc pressure fluctuation but reduced average arc pressure.When the duty cycle exceeded 1/2,excessive pressure fluctuations destabilized the weld pool.Arc voltage fluctuations also intensified with larger duty cycles,reducing arc heat input and stability.Severe variations in arc divergence and high-temperature area were observed at duty cycles above 1/2,leading to poor heat transfer.Weld morphology confirmed these findings:duty cycles of 1/5 and 2/5 produced uniform surfaces with dense fish-scale ripples,while 3/5 and 4/5 introduced defects such as humping and undercut.Mechanical testing showed that conventional variable polarity plasma arc welding(VPPAW)joints reached 262 MPa tensile strength and 18.3%elongation,corresponding to 79.8%and 85.1%of base metal values.At a duty cycle of 2/5,the tensile strength increased to 297 MPa and the elongation to 21.5%,representing the best overall performance.Variations in the gas pulse frequency did not significantly affect the average arc pressure or arc voltage.However,as the gas pulse frequency decreased,the fluctuation frequency of the arc pressure and arc voltage also decreased,while the fluctuation amplitude of the arc voltage increased.At 8 Hz,the tensile strength and elongation increased by 13.4%and 17.5%,respectively,compared with lower frequencies(4 and 2.6 Hz).
