2023 Vol. 38, No. 2

Performance Analysis of Complex Cast Steel Joint in the Steel Roof of Hangzhou West Railway Station
XING Zunsheng, YE Dongchen, ZHANG Zhihao, JIA Shangrui
2023, 38(2): 1-7. doi: 10.13206/j.gjgS22120101
The steel roof of Hangzhou West Railway Station is a complex spatial structure system which is the combination of grid and truss. Thus, there are many multi-pole intersection connection problems in this structure, which could be solved by the cast steel joints. Due to the large number of intersecting members and complex forces of the such joint, the analysis is difficult. In this paper, the complex cast steel joint in the steel roof of Hangzhou West Railway Station was analyzed by finite element and tested to determine the safety and reliability of the design of the cast steel joint.When the finite element analysis method was adopted, the joint was discussed under the design load and the limit load respectively, and the design load was taken as the most unfavorable load case of the joint, and the limit load was 3 times the design load. The finite element analysis results indicated that under the design load, the stress level of the joint was lower than the yield strength of the material. The maximum stress was 179.088 MPa, and the equivalent plastic strain was 0. Under the limit load, the stress in some parts of the joint exceeded the yield strength of the material, but the overall load-displacement curves were still linear. Since then, experimental studies had been carried out on the cast steel joint. A full-scale test study was carried out on this joint, and the maximum test load is 1.3 times the design load. When loading, the load force was divided into 26 levels from 0 to maximum. From the beginning to the end of the test, no obvious deformation of the cast steel joint was observed. Moreover, the data collected by each strain gauge showed that the maximum strain of the cast steel joint was 1 036×10-6. This paper compared the test results with the finite element calculation results, and the degree of agreement was good, which showed the accuracy of the finite element calculation results. And the joint was in a fully elastic state under the design load, and the partial plasticity did not affect the overall mechanical performance of the joint. Therefore, it could be judged that the joint is safe and reliable, which could provide a reference for the design of cast steel joint in related projects in the future.
Study on Direct Analysis and Design Method of Space Truss Structure with Steel Pipes
WANG Jun, QING Qiang, GONG Jinghai
2023, 38(2): 8-17. doi: 10.13206/j.gjgS22101701
At present, many steel structure design standards at home and abroad recommend the direct analysis method as the preferred method for steel structure analysis and design. The simulation method of the rear member and the implementation details of the cross-section fiber division method are not described in detail. The displacement-based beam-column element is used to comprehensively consider the geometric nonlinearity, material nonlinearity, the overall initial defect of the circular steel tube space truss structure, the initial defect of the circular steel tube member and other factors that have an important influence on the structural stability and bearing capacity, and the nonlinear analysis of the structure is carried out. Based on the analysis and full stress optimization design, the direct analysis and design process of the circular steel tube space truss structure is proposed. Taking a main truss in an actual project of a three-center truss structure as an example, the structural orientations of different member equal fractions, different initial geometric defect application directions of different members, and different fiber division numbers of circular steel tube sections are compared. The maximum deformation of z-direction, the stress, the axial force and the bending moment of the member are studied. The influence of these three factors on the results of the direct analysis of the circular steel tube space truss structure is studied. By comparing the calculation results with the traditional first-order elastic analysis method, the applicability of the proposed direct analysis and design method of the circular steel tube space truss structure in engineering practice is verified. The results show that: under the combined working conditions of 1.3D+1.5L and 0.9D+1.5W, the calculated truss deformation and the stress of the members increase gradually with the increase of the equal fraction of the members; With the increase of the rotation angle of the maximum bending direction of the member around the biaxial direction of the member, the maximum z-direction deformation of the structure obtained by direct analysis and calculation, the stress of the member and the biaxial bending moment all show a decreasing trend, and the biaxial bending moment of the member is greatly affected with a change rate exceeding 80%; because the wall thickness of the round steel pipe is much smaller than the circumference, the change of the structural calculation results is very limited when the radial equal fraction increases from 2 to 4, and the change rates of deformation and stress are both less than 0.1%. Under the combined condition of 0.9D+1.5W, the maximum z-direction deformation of the structure when the hoop equal fraction is 32 is 15.9% different from that when the hoop equal fraction is 4, indicating that the number of section divisions has a nonnegligible effect on the structural stiffness; for the members with small slenderness in the circular steel tube space truss structure, the stress calculated by the direct analysis and design method and the traditional first-order elastic analysis method are relatively close, and the difference between the stress results under the two working conditions is less than 3%. For slender members, the difference between the calculation results of the two calculation methods is obvious, and the difference can reach 25.5%.
Static Behavior Analysis of Hinged Six-Bar Tetrahedral Spherical Lattice Shell
ZHANG Shuailiang, XU Zhen, LI Xudong
2023, 38(2): 18-22. doi: 10.13206/j.gjgS22111403
In order to simplify joint form of semi rigid and semi hinged six-bar tetrahedral spherical lattice shell, this paper presents two new types of hinged six-bar tetrahedral spherical lattice shell with a circular ring projection surface. The new shell configuration was simple because of comparatively fewer members and high evacuation ratio than double-layer spherical lattice shell structure. Six-bar tetrahedral spherical lattice shell has advantages of both single-layer and double-layer spherical lattice shell structure. Static and linear and nonlinear stability analyses of shell with two new types of hinged six-bar tetrahedral spherical lattice shell were carried out. Through the linear eigenvalue buckling analysis, stability analysis considering load asymmetry distribution and geometrical initial defects, the results show that the six-barred tetrahedral spherical reticulated shell structure with the lower chord support of the upper chord arranged along the span direction and the upper chord support of the lower chord arranged along the span direction are good in integral rigidity, mechanical property, stability. The hinged six-bar tetrahedral spherical lattice shell with bolted spherical joints is beneficial to standardized design, industrial production and assembly construction, which meets the characteristics of green architecture industry.
Study on Refined Numerical Simulation Method of Mechanical Behavior of Prefabricated Bailey Beam
ZHAO Qiu, CAI Wei, CHEN Peng, YU Ao, LIN Yongxin
2023, 38(2): 23-31. doi: 10.13206/j.gjgS22111601
In order to solve the disadvantages of modeling difficulty and high calculation cost in the finite element analysis of the Bailey beam solid model, a bar system model for the assembled Bailey beam is proposed based on the verified Bailey beam solid finite element model using the finite element analysis software ANSYS, and the modeling details of the solid model and bar system model are briefly described. It is also compared with the Bailey beam test in the Multi-purpose Manual for Prefabricated Highway Steel Bridges to verify the accuracy of the Bailey beam solid model and the member system model in the linear state. This paper carries out nonlinear buckling analysis, compares the differences between the two models in nonlinear state, and obtains the correct finite element model of the bar system through modification, and uses the modified bar system model to replace the solid model to study the ultimate bearing capacity under different conditions. The influence of initial geometric defects on the mechanical properties of Bailey beams is explored, and the selection reference of geometric defects for checking the ultimate bearing capacity of Bailey beams is proposed. The results show that the displacement value of the solid model under the same load in the linear stage is slightly larger than that of the rod model, and the maximum displacement difference in the midspan is 4%, but the displacement values of the rod model and the solid model at each measuring point are close to the test results, and the error range is less than 2%. The internal forces of the bar model and the solid model are basically consistent, and the maximum error of the average equivalent stress of the section is 2.78%; in the nonlinear stage, the instability modes obtained by the two models under different lateral bracing spacing are highly consistent, and the difference of ultimate bearing capacity is within 2.4%. The load-displacement curve is basically consistent, the failure mode is basically consistent, and the load-displacement curve of the member system model is in good agreement with the test curve. It is proved that the member model can replace the solid model for the ultimate bearing capacity analysis. The lateral support spacing of Bailey beams plays a decisive role in the failure mode of the structure. When the lateral spacing of Bailey beams is greater than or equal to 7.5 m, the overall buckling of the structure occurs. When the lateral support spacing is less than 5 m, the Bailey beam will be local buckling. The buckling mode is that the top chord of the mid-span element is subjected to out-of-plane bending failure, and obvious local buckling deformation occurs, and the Mises stress of the largest part of bending deformation reaches yield. When the Bailey beam is globally unstable, the overall geometric defect has a great impact on the bearing capacity of the structure, and when the structure is locally unstable, it is necessary to pay special attention to the local geometric defect of the structure. The stable bearing capacity is sensitive to the amplitude of the overall defect, while the in-plane local defect has little impact on the stable bearing capacity of the bailey beam, and the out-of-plane local geometric defect has a significant impact on the stable bearing capacity of the bailey beam. When considering the initial geometric defect with the out-of-plane initial bending amplitude of 1/1 000, the out-of-plane local defect of the chord, vertical bar and diagonal bar reduces the stable bearing capacity by 6.1%, 1.3% and 1.2% respectively, while the in-plane defect only reduces it by 1.0% 1.0% and 0.5%. Therefore, special attention should be paid to the out-of-plane deformation of the chord when selecting the bailey sheet.
Study on the Influence of Chloride Ion Corrosion on Wind-Induced Vibration Response of Transmission Towers in Coastal Area
LI Lixiao, RONG Xiangxi, LI Qiang, GU Jundeng, LIU Shizeng, ZHOU Haijun
2023, 38(2): 32-40. doi: 10.13206/j.gjgS22082204
Transmission tower structures in coastal areas suffer from the long-term erosion of the corrosive atmosphere, and the effective bearing area of its components is reduced due to corrosion, and the mechanical properties are gradually reduced. The service safety and durability of transmission tower structure are seriously threatened under the coupling action of long-term environmental corrosion and coastal wind. In order to accurately characterize the mechanism of long-term chloride ion erosion on the wind-induced dynamic response of the coastal transmission tower structure system, this study first uses the laboratory to conduct accelerated salt spray corrosion tests on the transmission tower angles, the corrosion duration is set to 0 h, 800 h, 1 600 h and 2 400 h respectively. Then, tensile specimens were made of corroded angle steel and mechanical properties were tested by MTS testing machine to explore the influence of corrosion on the cross section loss rate and mechanical properties degradation of angle steel, and to build a regression model of corrosion duration(cross section loss rate) and mechanical properties parameters of angle steel. Finally, the constitutive model of corroded angle steel was described based on the modified secondary flow tracing model, and the finite element analysis software Sap2000 was used to establish the finite element analysis model of transmission tower structure considering the influence of corrosion. Wind-induced vibration response of transmission tower line structure system was analyzed to explore the influence mechanism of coastal chloride ion erosion. The results show that: with the increase of chloride ion erosion time, the mechanical properties of angle steel showed a gradual decline trend. When the corrosion time was 800 h, the ultimate strength and yield strength degradation rate were 4.00% and 3.01%, respectively, the elongation and elastic modulus of angle steel decrease by 5.33% and 7.02%, respectively. When the corrosion time reached 2 400 h, the degradation rates of both reached 16.49% and 15.22%, respectively, compared with the non-corrosion condition. After 2 400 h of corrosion, the decreasing amplitudes reach 9.74% and 14.33%, respectively. Through the dynamic analysis of transmission tower structure, it is found that with the accumulation of corrosion, the natural vibration frequency of transmission tower structure decreases gradually. When the corrosion is as long as 2 400 h, the first-order natural vibration frequency of the transmission tower structure decreases by 4.08% compared to non-corrosion condition, and the corrosion has a more significant effect on the high-order frequency of transmission tower structure. Corresponding to the three corrosion conditions(corrosion time is 800 h, 1 600 h and 2 400 h), the wind vibration displacement response of the transmission tower structure and the stress of the tower rod show a gradual increasing trend. When the corrosion time reaches 2 400 hours, the maximum displacement of the tower top reaches 0.466 m, which increases by 9.8% compared with the non-corrosion condition. The maximum increase of rod stress is 5.1%. The yield strength ratios of the maximum stress under the same wind load and the corresponding corrosion time under the four conditions are 0.52, 0.55, 0.58 and 0.60, respectively.
Design Discussion
Relation of Period and Buckling Factor: Limiting Second-Order Effect Through Period
TONG Genshu
2023, 38(2): 41-43. doi: 10.13206/j.gjgS22092815
The similarity and difference of the stiffness equations for buckling and period eigenvalue analysis of structural systems are presented. The buckling factor is related to the period of the for different structural systems. Because there are a lower limit required by codes for the buckling factor of a real structure, the upper limit of the period is thus determined through the relation of period and buckling factor. The period is related to the square root of the total height multiplied by a factor, this equation changes slightly for different structural systems.
Hot Spot Analysis of Steel Structures
ZOU Anyu
2023, 38(2): 44-46.