2022 Vol. 37, No. 1

Mechanism, Research Advances and Prospect of Steel for Cryogenic Service
Xiaofeng Yang, Huiyong Ban, Hong Chen, Yunbing Luo
2022, 37(1): 1-8. doi: 10.13206/j.gjgS21111001
The low-temperature brittle fracture of steel is a major challenge in steel structure engineering, which threatens the safety of structures in low-temperature environments. Cryogenic steel is widely used in various liquid gas storage tanks, pipelines and equipment serving in low-temperature environments because of its good low-temperature toughness and low toughness-brittle transition temperature. For better understanding its performance characteristics, brittleness mechanism and product development of the cryogenic steel, a review of research progress available in the literature is conducted herein. First, the concept and regulations of cryogenic steel were introduced in this paper. Then, four main theories about toughness-brittle transition were summarized, namely classical mechanics theory, lattice dislocation theory, energy theory and statistical theory. Based on the lattice dislocation theory, the micro mechanism of the change in steel properties at low temperatures was explained in detail, the main influencing factors of toughness-brittle transition, and the toughening mechanism and measures of steel at low temperatures were analysed, and the main ideas of research and development of the cryogenic steel were clarified. Finally, the current general classification and product series of cryogenic steel were introduced herein. At present, the research and development of the cryogenic steel are mainly focused on Ni-containing cryogenic steel and high-manganese austenitic cryogenic steel. The chemical composition content and performance requirements of different content Ni-containing cryogenic steel in domestic and foreign standards were compared, and the types of cryogenic steel commonly used in the field of containers in China were summarized. Combined with the Antarctic Projects, an idea was put forward for the use of cryogenic steel in building structures in China to further promote the application of cryogenic steel materials and structures.
Simplified Calculation Model and Dynamic Characteristics Analysis of Modular Prefabricated Steel Frame Structure
Xiaojie Liang, Yan Wang, Guangxing Zhou
2022, 37(1): 9-20. doi: 10.13206/j.gjgS21052002
Modular building, as the most prefabricated building structure system, has become a hot research topic in the construction industrialization with its significant advantages such as high degree of assembly, fast construction speed, less environmental interference, controllable module quality, excellent sound insulation, fire prevention, and thermal insulation performance, removable reuse, green environmental protection and so on. China has made some achievements in the research and application of modular buildings, but mostly of which focuses on the modular joints and components, which lacks the research on the overall performance of multi-storey or high-rise modular structures under wind, earthquake and other load conditions. Therefore, the design and analysis of the whole structure of modular prefabricated steel frame with plate-inner sleeve joints was carried out to study the seismic performance of the structure under earthquake.
In order to facilitate the overall structural modeling and analysis, the simplified calculation models of the joints were studied according to the structural forms and force transfer characteristics of the joints between modules, and the simplified calculation models of the modular plate-inner sleeve joints were proposed and compared with the corresponding solid model for rationality verification; MIDAS/Gen 2020 was used to establish the calculation model of modular steel frame structure to carry out the response spectrum analysis, and the calculation results were compared with the current national standard limits; the structural dynamic response of modular steel frame under earthquake was studied, and the seismic performance of the structure was analyzed by elastic and elastic-plastic time-history to discuss the yield mechanism and development of plastic hinges.
The results show that:1) The stress distribution and failure modes of the simplified models are the same as those of the solid models, the failure modes of the two models are modular beam yielding and plastic hinges failure at the end of beam, and the load-displacement curves of that are similar. There is little difference in the stiffness in elastic stage, and the initial stiffness of the simplified model is about 0.84~0.91 times that of the solid model. Under the same load, the displacement and deformation of the simplified model are larger; after entering the elastic-plastic stage, the yield load and ultimate bearing capacity of the solid model are greater than those of the simplified model, which verifies that the simplified calculation model is reasonable and safe. 2) The relevant mechanical performance indexes of the modular steel frame structure obtained by response spectrum analysis, such as periodic mode, vertex displacement, story drift ratio and stress ratio meet the requirements of seismic design, and the steel consumption of the structure is 84.02 kg/m2, which is reasonable within the range of steel consumption. Therefore, the design of the whole structure is reasonable. 3) Through the elastic-plastic analysis, it is found that most of the structural components are still in the linear elastic stage under rare earthquakes, and only a few components reach yield.The plastic hinges are mainly concentrated at the end of the module beam, and the module beam yields before the module column, which indicates that the modular structure belongs to the system of "strong column and weak beam", and has good seismic performance under rare earthquake.
Progressive Collapse Resistance Analysis and Research on Cable Dome Structural System with Suspended Bucket Screen of Desheng Sports Center in Shunde
Lianfei Zhang, Tong Ou, Xuebing Liu, Zhengrong Jiang
2022, 37(1): 21-30. doi: 10.13206/j.gjgS21073002
The Geiger type and Levy type composite cable dome structure system is adopted in Shunde Desheng Sports Center Gymnasium. The plane projection is ellipse. The clear span of the cable dome in the long axis direction is 124 m, and the clear span of the cable dome in the short axis direction is 105 m, which is the largest cable dome structure with closed metal roof in China. In order to investigate the mechanical properties of cable dome structure with bucket screen after local cable(bar) breaking or relaxation, the progressive collapse analysis of cable(bar) after breaking or relaxation was carried out by using the finite element nonlinear dynamic analysis method. This paper expounded the collapse failure criterion of cable dome structure from the component level and structural system level, and finally determined the collapse failure criterion of structural system level based on the deformation standard and the development mechanism of plastic hinge of residual components after failure. Firstly, it took the failure of the key components of the third ring cable and related inclined cables and braces with large stress as an example, the nonlinear dynamic continuous collapse analysis of the calculation model with or without heavy-duty bucket screen was carried out, and the mechanical properties of the collapse process under the two working conditions were compared. Secondly, the nonlinear dynamic cable breaking analysis of single cable(bar) or multiple cables(bars) at different positions was carried out on the basis of heavy-duty bucket screen, and the mechanical effects of key components at different parts in the structural system were compared. Finally, based on the calculation model with heavy bucket screen, the cable force relaxation analysis of different parts was carried out to investigate the mechanical response of cable members in different degrees of relaxation.
The calculation results show that the combined cable dome structure of Geiger type and Levy type has good resistance to continuous collapse, and the suspended bucket screen, as a centralized suspension mass, has a certain impact on the dynamic response of the structure after cable breaking. By considering the cable breaking analysis at different positions, it is found that the ring cable has the greatest impact on the structure, and the structure still has good resistance to continuous collapse after cable breaking. In order to improve the progressive collapse ability of ring cable in practical engineering design, the design idea of double cable or four cable can be adopted in actual engineering. The structural safety reserve of the structure under accidental load also can be improved.
Finite Element Analysis of Double-Through Plate Joint
Junming Jiang, Hongliang Liu, Qiaosheng Chen
2022, 37(1): 31-38. doi: 10.13206/j.gjgS21060801
The common single plate shear joint is to weld a shear connecting steel plate directly on the surface of the steel pipe. This kind of joint connection often causes the stress concentration around the weld, and weld cracking is also a common failure mode of this kind of joint. To realize the fabricated shear connection between concrete-filled steel tubular column and steel box beam, a double-through plate joint was studied. In the joint, two shear connecting plates were parallel placed in the reserved slots on the two opposite walls of the steel tubular column, respectively. The part of the two through plates in the steel pipe was anchored by the filled concrete, and the plate's part outside the steel pipe was respectively close to the two webs of the steel box beam, which were connected with the beam webs by high-strength bolts. In this way, for the fabricated connection, there is no welding operation on the construction site, and the installation is simple and easy to operate. The finite element model of the joint was established, and the joint test results verified the effectiveness of the model. On this basis, the finite element method was used to optimize the design of the original test joint. Through detailed parameter analysis, the effects of initial gap between beam and column, thickness of through plate, bolt specification, bolt hole layout and other parameters on the joint performance such as stress distribution, deformation characteristics, bearing capacity, ductility and failure mode were studied.
The results show that compared with elliptical bolt holes and through core bolts, circular bolt holes and blind hole bolts are more conducive to improve the bearing capacity and ductility of the joint. With the increase of the initial gap between the end of the beam and the surface of the steel pipe, the through plate can full give play to its plastic deformation ability, and the rotation ability of the joint will be enhanced. However, when the gap is too large, the lower part of the plate is prone to buckling, which can lead to joint failure. Increasing the thickness of the plate can enhance the stability of the plate and improve the bearing capacity of the joint, but the thickness of the plate does not affect the angle of the end of the beam when it is extruded to the surface of the steel pipe. The influence of bolt specification on the overall bearing capacity and ductility of the joint is very small, but its influence on the failure mode of the joint is very obvious. When the bolt diameter is small, it is easy to shear failure. In terms of bolt layout, the excessive horizontal distance between the two bolt holes can not significantly improve the stress distribution. With the increase of the edge distance, the yield region of the plate is fully expanded, the plastic deformation ability of the through plate is enhanced, and ductility of the joint is significantly enhanced. It is suggested to use the layout of five or four holes in double or three rows instead of single row of bolt holes.
Bearing Capacity Adjustment Coefficient of Tension Angle Members Connected with One Bolt in Single Shear
Longyu Yang, Rui Zhang
2022, 37(1): 39-45. doi: 10.13206/j.gjgs21053001
The end distance Ld and edge distance Lz of bolt holes affect the bearing capacity of single angle steel members connected by a single bolt and the size of gusset plates at both ends in the transmission tower. Reducing Ld can reduce the geometric size of the connection area, reduce or cancel the gusset plate, and increasing Ld can improve the tensile bearing capacity of members. At present, the bolt Ld and Lz in DL/T 5442-2020 are fixed values. In order to study the tensile bearing capacity of such members, the material property test and tensile test of single bolt connection of angle steel of ∟56, ∟80, ∟90 and ∟110 specifications were carried out. The angle steel is made of Q235 B, and the diameters of high-strength bolt are 16 mm and 24 mm. Displacement meters were set to measure the member deformation and hole elongation. After the specimen was loaded, the bolt hole had plastic deformation and longitudinal elongation. When the ultimate tension was reached, both sides of the pressure hole wall and the middle of the end surface of the corresponding angle steel were torn. The finite element model of connecting plate, angle steel and bolt was established according to the test piece parameters, and the grid size near the contact surface of each component was less than 2 mm.
The calculation resuls show that the distribution of high stress areas are identical for specimens and FEA models, and the average error of ultimate tension foce between the two is 5.8%, and the load-hole elongation curves are consistent with the test results. Four groups of one bolt connected angle models(Ld=(0.8~3.7)d0) are built for further study with yield strength fy=235 MPa and elastic modulus E=2.06×105 MPa:∟40×3, 1 M12, ∟40×3, 1 M16, ∟50×4, 1 M16, ∟63×5, 1 M20.
The results show that the diameter of the bolt hole is larger than that of the bolt, resulting in the stress concentration on the compression hole wall during the single shear connection. When the total elongation of the specimen is small, plastic deformation has occurred in some areas, and then the specimen loses its initial stiffness, and the bolt hole continues to elongate. When the reference end distance is adopted, the bearing capacity Nrt of the specimen is about 95% of the DL/T 5486-2020 bearing capacity Ncode, and the tensile bearing capacity Nt of the four groups of specimens is about 75% of the ultimate tensile force Nu. There is a certain margin in DL/T 5486-2020. The length of the linear section of the load-hole elongation curve, the position of stiffness change and the bearing capacity of the specimen are jointly affected by Ld and Lz. Taking Ld/Lz=1.5 as the boundary, there are mainly two failure modes:when it is less than the critical value, the specimen has end shear and tear failure; after exceeding the critical value, it gradually turns into the net section failure of steel angle, and the continuous increase of Ld has little effect on the bearing capacity. At present, M16 bolts are used for ∟40 angle steel in China. When M12 bolts are used, Ld/d0 can be reduced to obtain a higher upper limit of bearing capacity. EC 3, ASCE and other specifications consider the influence of Ld and Lz on tensile bearing capacity. The values of material strength and other parameters are mainly for local steel, and the formula form is complex. Combined with the actual situation of steel in China and the calculation framework of transmission tower, the calculation method including bearing capacity adjustment coefficient is given according to the test and model results. Considering the different effects of Ld and Lz, the same calculation formula is used for members with different bolt diameters and steel angle leg widths, which is suitable for the calculation of tensile bearing capacity of hot-rolled steel angle members connected by single bolt and single shear within the range of Ld=(1.0~3.0)d0.
Construction Technology
Simulated Analysis on Optimum Scheduling of Outrigger-Brace Connection for Super High-Rise Structure
Jun Wu
2022, 37(1): 46-52. doi: 10.13206/j.gjgS21062901
Super high-rise structure is a hot research issue of large-scale complex structure. Many of its structural systems adopt the hybrid structure system composed of steel structure outer frame tube and reinforced concrete core tube, and are equipped with outrigger truss. Due to the different materials of steel structure outer frame tube and concrete core tube, the vertical deformation during construction is also different. Premature connection of outrigger truss will produce large initial deformation and initial internal force in the truss, and too delayed connection may lead to incomplete structural stiffness and structural safety problems under extreme load conditions.
In this paper, the 33-34 storey truss and 51-52 storey truss in the South Tower of Yinchuan Lvdi Center were taken as the research objects, and the numerical simulation is carried out by using ANSYS software. In five cases, the effects of different connection time on the internal force and deformation of outrigger truss structure were compared. Through the numerical simulation results, the axial force, stress and deformation curves of the most unfavorable member in five cases were obtained. The analysis results show, the later the connection time is, the smaller the axial force, stress and deformation of truss members are. According to the axial force curves of the outrigger truss, it can be obtained that in the five cases, the maximum axial forces of members No.1, No.2 and No.3 are 340 kN, 1 830 kN and 870 kN, respectively. Under case 4, the maximum axial forces are 90 kN, 400 kN and 120 kN respectively, which are reduced by 73.5%, 78.1% and 86.2%. According to the deformation curve of outrigger truss, the maximum deformations of members No.1, No.2 and No.3 are 9.73 mm, 9.82 mm and 9.98 mm in five cases. Under case 4, the maximum deformations are 3.26 mm, 3.43 mm and 3.27 mm respectively, which is reduced by 66.4%, 65.0% and 67.2%.
During the construction of the south tower of the twin towers of Yinchuan Lvdi Center, considering the long period of structural shrinkage and creep, it is difficult to form greater lateral stiffness without the connection of the inner and outer tubes with the outrigger truss for a long time. At the same time, considering the construction period and the ability to resist disaster loads, select the case 4 where the truss response is relatively small, that is, the extended truss is connected after the completion of the outer frame tube construction section. During the connection and closure of the upper and lower outrigger trusses, the on-site outrigger truss construction monitoring system was deployed. The data analysis shows that the strain variation of the outrigger truss is in good agreement with the numerical simulation results, which verifies the reliability of the connection timing optimization algorithm proposed in this paper.
Hot Spot Analysis of Steel Structures
2022, 37(1): 53-53.