Ten full-scale steel beam-to-column moment connections used in moment-resisting frames （MRFs） were tested to study the failure process, failure mode, strength and plastic rotation capacity. The specimens include one...Ten full-scale steel beam-to-column moment connections used in moment-resisting frames （MRFs） were tested to study the failure process, failure mode, strength and plastic rotation capacity. The specimens include one traditional welded flange-bolted web connection, one traditional fully welded connection, four beam flange strengthened connections, three beam flange weakened connections, and one through-diaphragm connection. The test results show that the connections with flange cover plates or with partly cut beam flanges satisfy the beam plastic rotation demand for ductile MRFs. From the measured stress profiles along the beam flange and beam web depth, the mechanics of brittle fracture at the end of the beam is discussed. Design recommendations for steel beam-to-column moment connections are proposed.展开更多
Despite the inherently advantages of the box column, finding the best option for the I beam to the box column connection is the main challenge in using the box column as a structural member for special moment frames. ...Despite the inherently advantages of the box column, finding the best option for the I beam to the box column connection is the main challenge in using the box column as a structural member for special moment frames. In this paper, the seismic performance of urtreinforced connection, weakened connection and strengthened connection was evaluated through a comprehensive experimental program. The seismic comparisons were fabricated by assessing the strength, ductility and energy dissipation in each configuration. Three full scale tests with several connections were carried out. All the specimens were subjected to cyclic loading and prior to failure by forming a plastic hinge in the beam, all the connections managed to reach an inelastic rotation of more than 6.0% rad. The experimental and analytical results showed that the seismic performance of the strengthened connection with flange and shear plates turned out to be the most effective in the beam to the box column connection. Moreover, the normalized stress distribution of the continuity plates revealed that the possibility of the weld fracture in unreinforced connection is more than other specimens.展开更多
Most reinforced concrete(RC)frame structures did not achieve the "strong column-weak beam" failure mode in recent big earthquakes, resulting in a large number of casualties and significant property loss. To ...Most reinforced concrete(RC)frame structures did not achieve the "strong column-weak beam" failure mode in recent big earthquakes, resulting in a large number of casualties and significant property loss. To deal with this serious problem, a new column-beam relative factor was proposed to characterize the relative yield situation of column ends and beam ends. By limiting the column-beam relative factor, RC frame structures could achieve the "strong column-weak beam" failure mode under the excitation of strong ground motions. The limit values of column-beam relative factor were calculated, analyzed and verified by using structural simulation models for corner columns in the bottom story of structures, which are destroyed most seriously in earthquakes. The results show that the limit values should be analyzed under bi-directional ground motion and with different axial compression ratios of columns. The peak ground acceleration(PGA)of ground motions has no significant effect on the limit values, while the type of strong ground motions has a significant effect on the limit values.展开更多
Methylcyanopolyynes (CH3-[C≡C]n-CN) are a particular kind of linear molecular wires, where the first three oligomers have been detected in the interstellar medium, particularly in CW Leonis (IRC + 10216), as well as ...Methylcyanopolyynes (CH3-[C≡C]n-CN) are a particular kind of linear molecular wires, where the first three oligomers have been detected in the interstellar medium, particularly in CW Leonis (IRC + 10216), as well as in the envelopes of carbon-rich stars in a similar way to the unsubstituted cyanopolyynes. Based on the projected natural distribution in cold clouds under LTE, we have determined the radial column density of new expected methylcyanopolyynes to be present in CW Leonis (IRC + 10216). By following, we have made use of the inner molecular resistances of the internal charge transfer process presenting in these oligomeric species in order to determine the reactivity trends between them. Therefore, geometrical parameters and dipole moments determinations for these methylcyanopolyynes involving the n = 1 to 14 molecular species were obtained from Ab initio molecular orbital calculations by means of a GAUSSIAN Program, using a restricted Hartree-Fock approach and 6-311G* basis set. Our results present a similar behavior observed in cyanopolyynes, where this series reaches a saturation level at the 14th oligomer with a maximum dipole moment of 8.21 ± 0.01 (Debyes). Thus, this molecular wire model permits us to comprehend how these methylcyanopolyynes reach a maximum length in such chemical environment, in agreement to the astronomical observations and cosmological chemical models. The following CH3C9N and CH3C11N oligomers in CW Leonis should be expected near to 3.52 × 1010 [cm2] and 1.82 × 1010 [cm2], respectively.展开更多
文摘Ten full-scale steel beam-to-column moment connections used in moment-resisting frames （MRFs） were tested to study the failure process, failure mode, strength and plastic rotation capacity. The specimens include one traditional welded flange-bolted web connection, one traditional fully welded connection, four beam flange strengthened connections, three beam flange weakened connections, and one through-diaphragm connection. The test results show that the connections with flange cover plates or with partly cut beam flanges satisfy the beam plastic rotation demand for ductile MRFs. From the measured stress profiles along the beam flange and beam web depth, the mechanics of brittle fracture at the end of the beam is discussed. Design recommendations for steel beam-to-column moment connections are proposed.
文摘Despite the inherently advantages of the box column, finding the best option for the I beam to the box column connection is the main challenge in using the box column as a structural member for special moment frames. In this paper, the seismic performance of urtreinforced connection, weakened connection and strengthened connection was evaluated through a comprehensive experimental program. The seismic comparisons were fabricated by assessing the strength, ductility and energy dissipation in each configuration. Three full scale tests with several connections were carried out. All the specimens were subjected to cyclic loading and prior to failure by forming a plastic hinge in the beam, all the connections managed to reach an inelastic rotation of more than 6.0% rad. The experimental and analytical results showed that the seismic performance of the strengthened connection with flange and shear plates turned out to be the most effective in the beam to the box column connection. Moreover, the normalized stress distribution of the continuity plates revealed that the possibility of the weld fracture in unreinforced connection is more than other specimens.
基金Supported by the National Natural Science Foundation of China(No.51525803)the Scientific and Technological Development Plans of Tianjin Construction System(No.2013-35)+1 种基金International Science&Technology Cooperation Program of China(No.2012DFA70810)the Basic Science Research Foundation of IEM,CEA(No.2013B07)
文摘Most reinforced concrete(RC)frame structures did not achieve the "strong column-weak beam" failure mode in recent big earthquakes, resulting in a large number of casualties and significant property loss. To deal with this serious problem, a new column-beam relative factor was proposed to characterize the relative yield situation of column ends and beam ends. By limiting the column-beam relative factor, RC frame structures could achieve the "strong column-weak beam" failure mode under the excitation of strong ground motions. The limit values of column-beam relative factor were calculated, analyzed and verified by using structural simulation models for corner columns in the bottom story of structures, which are destroyed most seriously in earthquakes. The results show that the limit values should be analyzed under bi-directional ground motion and with different axial compression ratios of columns. The peak ground acceleration(PGA)of ground motions has no significant effect on the limit values, while the type of strong ground motions has a significant effect on the limit values.
文摘Methylcyanopolyynes (CH3-[C≡C]n-CN) are a particular kind of linear molecular wires, where the first three oligomers have been detected in the interstellar medium, particularly in CW Leonis (IRC + 10216), as well as in the envelopes of carbon-rich stars in a similar way to the unsubstituted cyanopolyynes. Based on the projected natural distribution in cold clouds under LTE, we have determined the radial column density of new expected methylcyanopolyynes to be present in CW Leonis (IRC + 10216). By following, we have made use of the inner molecular resistances of the internal charge transfer process presenting in these oligomeric species in order to determine the reactivity trends between them. Therefore, geometrical parameters and dipole moments determinations for these methylcyanopolyynes involving the n = 1 to 14 molecular species were obtained from Ab initio molecular orbital calculations by means of a GAUSSIAN Program, using a restricted Hartree-Fock approach and 6-311G* basis set. Our results present a similar behavior observed in cyanopolyynes, where this series reaches a saturation level at the 14th oligomer with a maximum dipole moment of 8.21 ± 0.01 (Debyes). Thus, this molecular wire model permits us to comprehend how these methylcyanopolyynes reach a maximum length in such chemical environment, in agreement to the astronomical observations and cosmological chemical models. The following CH3C9N and CH3C11N oligomers in CW Leonis should be expected near to 3.52 × 1010 [cm2] and 1.82 × 1010 [cm2], respectively.
