Experimental research and numerical analysis were applied to study the ultimate load capacity(ULC) and reinforcement of circular-hollow-section N-joint.Four specimens were tested under static load.The ULC of each spec...Experimental research and numerical analysis were applied to study the ultimate load capacity(ULC) and reinforcement of circular-hollow-section N-joint.Four specimens were tested under static load.The ULC of each specimen was obtained and the detailed failure conditions were discussed.Based on the results, both welding a plate on the chord member and filling concrete in the chord member are effective to reinforce the N-joint, but it is suggested that these two methods should not be applied simultaneously.Moreover, considering the four important influence factors of ULC of the joints, the ratio of chord diameter to chord thickness, the ratio of diagonal member diameter to chord member diameter, the axial load on the chord member and the gap size between the two brace members, a new prediction formula of ULC of N-joint was put forward based on numerical analysis results.The new formula was proved to be more accurate than the current Chinese design code in a wide range.展开更多
Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadwa...Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.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
The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desi...The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desired directions or at several frequencies. Numerical results of these procedures are presented. The theoretical predictions are confirmed with an experiment. The proposed synthesis procedure is completely general and can be applied to arbitrarily shaped conducting bodies.展开更多
For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so ...For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.展开更多
为研究分析实施轨道交通预约进站机制对乘客出行效率的影响,通过对乘客乘坐轨道交通全过程进行仿真推演,选取北京轨道交通早高峰时段预约进站试点沙河站所在线路——昌平线作为研究对象,通过获取自动售检票(automatic fare collection, ...为研究分析实施轨道交通预约进站机制对乘客出行效率的影响,通过对乘客乘坐轨道交通全过程进行仿真推演,选取北京轨道交通早高峰时段预约进站试点沙河站所在线路——昌平线作为研究对象,通过获取自动售检票(automatic fare collection, AFC)刷卡数据和列车运行方案对其进行实例分析。结果表明,相较于常规排队进站方式,预约进站机制可有效减少乘客的站外排队时间,并且随着预约人数占所有进站乘客数比例的增加,乘客站外等待时间减少效果更加显著;同时可提高相应列车的区间满载率,这是由于将部分在站外等待的乘客调整至其他时段进站,提高了列车资源利用率,在一定程度上分散乘客需求,但前提是部分乘客的出行习惯将被改变。仿真结果可为各大城市轨道交通车站实施更大规模的预约进站机制提供理论支持。展开更多
基金Supported by National Natural Science Foundation of China (No.50608054)
文摘Experimental research and numerical analysis were applied to study the ultimate load capacity(ULC) and reinforcement of circular-hollow-section N-joint.Four specimens were tested under static load.The ULC of each specimen was obtained and the detailed failure conditions were discussed.Based on the results, both welding a plate on the chord member and filling concrete in the chord member are effective to reinforce the N-joint, but it is suggested that these two methods should not be applied simultaneously.Moreover, considering the four important influence factors of ULC of the joints, the ratio of chord diameter to chord thickness, the ratio of diagonal member diameter to chord member diameter, the axial load on the chord member and the gap size between the two brace members, a new prediction formula of ULC of N-joint was put forward based on numerical analysis results.The new formula was proved to be more accurate than the current Chinese design code in a wide range.
基金provided by the National Natural Science Foundation of China (Nos. 51274204 and 51134025)National Key Basic Research Program (No. 2010CB732002)The Ministry of Education Program for New Century Excellent Talents to Support Project of China (No. NCET-12-0965)
文摘Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.
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The reduction of TE-scattering by a conducting cylinder with multiple surface impedance loads is investigated. Synthesis procedures are developed to find the optimal loading which result in zero scattering in the desired directions or at several frequencies. Numerical results of these procedures are presented. The theoretical predictions are confirmed with an experiment. The proposed synthesis procedure is completely general and can be applied to arbitrarily shaped conducting bodies.
文摘For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.
文摘为研究分析实施轨道交通预约进站机制对乘客出行效率的影响,通过对乘客乘坐轨道交通全过程进行仿真推演,选取北京轨道交通早高峰时段预约进站试点沙河站所在线路——昌平线作为研究对象,通过获取自动售检票(automatic fare collection, AFC)刷卡数据和列车运行方案对其进行实例分析。结果表明,相较于常规排队进站方式,预约进站机制可有效减少乘客的站外排队时间,并且随着预约人数占所有进站乘客数比例的增加,乘客站外等待时间减少效果更加显著;同时可提高相应列车的区间满载率,这是由于将部分在站外等待的乘客调整至其他时段进站,提高了列车资源利用率,在一定程度上分散乘客需求,但前提是部分乘客的出行习惯将被改变。仿真结果可为各大城市轨道交通车站实施更大规模的预约进站机制提供理论支持。
