2022 Vol. 37, No. 12

Experimental Investigation of a Fan-Shaped Assembled Joint for Curved Lattice Shells
XU Jianshe, WU Jin, LU Jin, ZHANG Qian
2022, 37(12): 1-9. doi: 10.13206/j.gjgS22081402
A new fan-shaped assembled joint for curved lattice shell structure is proposed, which is mainly composed of three parts: fan-shaped component, central rib plates and high-strength bolts. Different from the traditional welded joints, the main sections of this joint are prefabricated by the factory and assembled on site using high-strength bolts, which not only reduces the welding work but also avoids overhead welding, and reduces the construction difficulty and risk. In addition, the joint is connected without cover plates, fully reflecting its semi-rigid characteristics, and also facilitating later maintenance. The static comparison experiment between the assembled joint and the welded joint was conducted for exploring mechanical characteristics of the joint. A total of six full-scale joint specimens were tested with the type and loading condition as test variables. The strain distribution, load-displacement curve, moment-rotation curve and failure mode of the key parts were analyzed, and the weak parts and the influence of bias pressure were obtained. The evolution process of mechanical characteristics under uniaxial compression and bending was analyzed by finite element method and compared with the experimental results. Through the experiment and finite element analysis, the following conclusions can be drawn: under uniaxial compression, the fan-shaped assembled joint shows the same mechanical performance as the welded joint, the force is reliable, the deformation is small, and the axial stiffness is very close during the whole process of loading. Under the eccentric compression, the axial stiffness of the fan-shaped assembled joint decreases significantly, indicating the influence of the compression-bending combination on the joint should be considered in the practical engineering application. In the bending test, the failure process of the fan-shaped assembled joint experiences three stages: 1) the elastic stage(<81.5 kN·m), in which the joint shows good bending performance; 2) the elastic-plastic stage(81.5-142.6 kN·m), in which the bending stiffness decreases markedly, and the rotation increases gradually owing to bolt slippage and deformation of the bolt hole wall; and 3) the plastic failure stage(>143 kN·m), in which the bolt is brittle and the specimen fails, indicating that the key to improving the bending stiffness of the fan-shaped assembled joint is improving the shear strength of the bolt. The final failure mode, stress distribution, and bending moment-rotation curve of the finite element analysis are in good agreement with those of the experiments.
Section Optimization of Elastic-Plastic Buckling of Cold-Formed Thin-Walled Lipped Channel Steel Column Based on Machine Learning
QUAN Song, HUANG Lihua
2022, 37(12): 10-17. doi: 10.13206/j.gjgS22032502
There are many factors that affect the elastic-plastic buckling capacity of cold-formed thin-wall steel lipped channel members. However, the relationship between section form and bearing capacity cannot be accurately expressed analytically. In order to optimize the section form and improve the buckling capacity of channel steel, the gene expression programming(GEP) algorithm and the particle swarm optimization(PSO) algorithm were combined to optimize section form. Through calling ABAQUS by Python programming, the finite element calculation of 15 test components in the literature was carried out in batches. The accuracy of the numerical solution was verified by comparing with the experimental values. A group of components were selected as samples to carry out anti-buckling section optimization. A total of 97 ensembles of sample data including different section sizes and corresponding buckling loads were generated by the batch finite element calculation. The gene expression programming algorithm was used to fit the dataset, and the surrogate model of the objective function of cross-section optimization was constructed. The particle swarm optimization algorithm was used to obtain the optimal section size corresponding to the maximum elastoplastic buckling capacity of cold-formed thin-walled lipped channel steel. Compared with the original specimen, the buckling capacity is increased by 30.4% after section optimization. The results show that the combination of finite element, machine learning and traditional optimization methods can be adopted to effectively optimize the section form of thin-walled channel column.
3D Laser Scanning Technology Research for Erection Line-Shape Monitoring of Long-Span Steel Truss Arch Bridge
AN Luming, ZHAO Jian, REN Yanlong, SHI Linze, CHENG Bin
2022, 37(12): 18-23. doi: 10.13206/j.gjgS22051001
The rapid development of bridge construction level leads to the increasing demand for bridge construction volume and construction risk dynamic assessment. Line-shape monitoring is crucial in the erection process of large steel truss arch bridge, which can ensure that bridge line-shapes accurately extend. Guangzhou Mingzhuwan Bridge is a six-span continuous steel truss structure with full cantilever construction method in the erection process. The erection working conditions account for a large proportion when the cantilever length is more than 200 m, and most of the rods are splice with high-strength bolts outside the joints in terms of the freedom of adjustment of the rods is large, so that the erection alignment is difficult to control under the influence of wind, temperature and other natural factors. The 3D laser scanning technology can obtain the coordinate information of massive structure surface through fast scanning, realizing the rapid real-time monitoring of multiple key points in the structure. The research has monitored the erection line-shapes of the main arch and girder of Mingzhuwan Bridge by using 3D laser scanning technology. Three key erection conditions of main arch girder erection, main arch closure and main girder closure were monitored through reasonable arrangement of scanner monitoring positions, and several structural scans were carried out mainly around the cantilever of main girder and around the tower crane. In the monitoring process, the rear intersection method was used to obtain the coordinates of scanner erection position and then calculated the coordinate information of the point cloud of the monitoring target. Moreover, the point cloud processing software Cyclone was used to realize the overall model splicing of the main bridge point cloud through noise elimination and point cloud association, and then multiple linear monitoring indicators were extracted for analysis by combining the point cloud data processing technology. At the same time, the same point coordinates were obtained by the total station for verification. The results show that the average difference of the relative distance between the cantilevers of the main arch and girder is 19 mm for the 3D laser scanning and total station measurement methods, which is within the relative point position measurement error between adjacent points allowed by Technical Specifications for Construction of Highway Bridge and Culverts(JTG/T F50—2011), indicating that the linear monitoring method based on 3D laser scanning can meet the engineering application requirements. The verticality index between the tower crane joints is generally within ±3‰, thus the bottom of the tower crane does not reach the ultimate bending moment without structural failure. However, when the main arch or girder is large cantilever, the upper structure of the tower crane has a large vertical deviation, and it is still necessary to strengthen monitoring during the erection of the main bridge. The monitoring line-shapes of the main arch and girder are basically consistent with the theoretical line-shapes, and the mean values of transverse and elevation deviation indexes are 2.9 mm and 16.6 mm, which are in line with the deviation threshold of the longitudinal axis and height difference of steel arch bridges in JTG/T F50—2011. Moreover, the cantilever rods on both sides of the main arch and girder constantly approach the theoretical value during the erection process, indicating that the erection alignment of the main bridge well control and meeting closure needs.
Application of 3D Laser Scanning Technology in Large-Scale Soccer Field Engineering
NI Ming, LUO Huijian, GUAN Lei, WU Debao, XU Siwei
2022, 37(12): 24-30. doi: 10.13206/j.gjgS22071601
In recent years, with the rapid development of science and technology, engineering survey technology is also constantly innovation, from the original theodolite, total station to GPS and now the 3D laser scanning technology, for the construction industry has made an important contribution to the leap-forward development. The application of 3D laser scanning technology in engineering has solved the problems of low measuring efficiency and large construction deviation caused by backward technology or equipment. The roof steel truss and cable-membrane structure used in the Kunshan Football Stadium project is faced with a series of construction problems, such as complex shape, long span, difficult assembly, high machining precision and complex construction technology. In order to solve the project construction problems, in this paper, the difficulties of field assembling precision control, precise positioning control of hoisting, deformation control of steel truss, forming quality control of K-type concrete column and shape control of membrane structure in the process of construction of football field are fully studied. The advantages of 3D laser scanning technology were made full use to solve the above difficulties: 1) in the field assembly of steel structure, because the components are large, the supporting frame should be used in the field assembly. In order to control the assembly precision, the 3D laser scanner is used to scan all the components in the field, the scanned point cloud data are compared with the BIM model by software analysis, and the assembly deviation is corrected in time to ensure the accuracy of the whole structure. Considering that the roof steel truss is affected by load and its end is deflected, it needs to be pre-arched and installed, and then it needs to be unloaded by stages, and the shape of the roof steel truss at each stage is monitored in time by means of the 3D laser scanning technology, by comparing the simulation data to control the construction process to ensure the safety of the structure. 2) The concrete structure of K-type column is a complex structure with a height of 43.9 m and a C-type steel column with an inclined angle of 55.57°. To ensure the accuracy of the 3D positioning of the K-type column, it is necessary to use 3D laser scanning technology for 3D scanning, and compared with BIM model data, to correct the structural deviation in time. 3) The membrane unit of this project has a large span. After the installation, the self-weight of the membrane will produce the problem of down deflection, and the middle part will appear a relatively smooth area, which will affect the overall shape of the membrane, and even will appear the phenomenon of water accumulation. For this problem, it is necessary to set the highest point coordinates in the 3D model to control the tensile stress of the membrane to ensure the design value of the tensile stress. In the field, each element membrane is scanned by 3D laser scanning technology, and the collected point cloud data is analyzed to ensure that the point position is controlled within the allowable range to ensure the installation accuracy.
Construction Technology
Research and Application of Long-Span Orthogonal Inclined Space Tube Truss Structure to Improve Construction Accuracy Control
WANG Zhixing, ZHENG Ligang, HAN Juhu, WANG Jin
2022, 37(12): 31-36. doi: 10.13206/j.gjgS22041801
The roof structure of the middle group project of Xiaohe International Convention and Exhibition Center is the most complex part. It belongs to the discontinuous long-span orthogonal inclined space tube truss structure. It is divided into three parts: four corner roofs, glass roof of cross traffic corridor and central dome, the projected area of the corner top steel truss is 6 575 square meters, the span is 63 m, and the maximum span of the corner top oblique truss is 88.7 m, and a four-sided unequal height shape, the entire truss node is complex. There are various forms of steel pipe truss(single-curved arc, hyperbolic arc), variable diameter, welded ball, box-shaped cantilever, etc. The high-altitude workload is heavy, the construction period is short, and the professional cross-operation is frequent. In order to effectively reduce the construction difficulty and safety risks, and ensure the construction quality and progress, a combination of "floor(ground) assembly, block-by-block overall cumulative improvement + local floor in-situ direct bulk loading" is adopted for installation. In order to realize the control of the construction accuracy of the long-span orthogonally inclined space tube truss structure, the pre-camber setting before ground assembly was firstly studied, and the SAP 2000 software was used to simulate and analyze the staggered lifting, closing and unloading of the partitions, and calculate the lifting process accurately. At the same time, the nonlinear finite element simulation software simufact welding was used to analyze the welding deformation of each truss, and the pre-camber was considered by improving the deformation and welding deformation data; secondly, the virtual pre-assembly was realized by using 3D laser scanning technology during the ground assembly process; finally, in the lifting process, real-time control of the lifting synchronization was carried out to realize the research on the assembly welding from the ground and the control accuracy of the lifting process, which promoted the construction accuracy of the roof structure to reach the millimeter level, and avoided the rework of construction operations effectively and ensured that the entire roof space tube truss structure met the design requirements of the original state of the building.
Key Technology of Cross Steel Truss Construction of Supercomputer Cloud Roof
YANG Guosong, ZOU Huanmiao, CUI Qiang
2022, 37(12): 37-44. doi: 10.13206/j.gjgS22032301
The structure of the Xiongan Supercomputer cloud project is novel in shape, and the spatial relationship is complex. The floor under the roof is split-level, so it is difficult to choose the installation plan and support layout. Therefore, it is necessary to choose a reasonable support unloading sequence to ensure the safety of the structure unloading. The roof steel structure adopted the diagonal cross grid truss structure system, and the truss strings were inclined to each other. The west side of the grid truss extended down in an arc to the sealing beam, and then the roof load was transferred to the lower frame through the curved curved torsion V-shaped support of the variable section. The east side of the grid truss connected with the three-dimensional arch truss, and a small number of round steel pipe strings were arranged in the span to form the long-span spatial structure. The deep design technology was used to optimize the joint design of the long-span structure, so that the bending and twisting V-shaped support processing could meet the demands of the structural force transmission and architectural modeling. According to the structural system and layout characteristics of the project, through the horizontal comparative analysis of the support system, construction difficulty, safety management difficulty, schedule and construction cost of the three schemes, such as lifting scheme, sliding scheme and hoisting scheme, the optimal segmented in-situ hoisting scheme was selected. The east stereoscopic arch truss divided the arch truss into the upper and lower trusses reasonably according to the structure. The next trusses set the support for sectional installation and positioning. At the same time, the next trusses provided the fulcrum to support the previous trusses, which solved the construction problem that the arch trusses are high in height and heavy in weight and difficult to install. The long-span oblique grid truss was divided into reasonable segments, and the multi-span portal support system adopts tower crane to install the roof cross grid truss in segments, and adopted cross stabilizer rod to temporarily fix the structure during the installation process, which solved the construction problem of stability outside the plane during the single piece installation of grid truss and ensures the installation accuracy of the truss structure. The installation sequence of multiple tower cranes advancing from the corner of the roof structure to the core area not only solved the problem that each step of installation can form a temporary stable system to ensure construction safety, but also improved the construction progress through simultaneous installation of multiple cranes, providing a reference for the installation of other long-span truss structures. MIDAS/Gen, a finite element analysis software, was used to calculate the influence of temperature stress on the unloading of long-span cross grid structure. The unloading simulation analysis and comparison of long-span cross truss with different combinations of temperature stress and unloading direction were carried out under multiple working conditions, and the stress-strain nephogram of the maximum stress and maximum deformation of the structure were analyzed. The simulation calculation showed that, the role of temperature stress should be considered in the unloading of multi-fulminated long-span cross truss, and the unloading sequence should be taken from the mid-span support with large deformation. The structural temperature during unloading should be close to that during the installation, so as to reduce the stress caused by the change of structural construction temperature and ensure the safety of structure construction.
Design Discussion
Distortional Buckling of Framed Beams: Stiffener or Fly Bracing?
TONG Genshu
2022, 37(12): 45-47. doi: 10.13206/j.gjgS22101206
The concepts ”independent bracing” and “ relative bracing” were explained, fly bracing between bottom flanges of orthogonal framed beams was a type of relative bracing whose functions were played only when the other beam had surplus stiffness and capacity. This paper suggests using stiffener to prevent distorsional buckling of frame beams on the place of 1.5 times the beam height away from the column, and the condition that no stiffener is needed is provided.
Hot Spot Analysis of Steel Structures
ZOU Anyu
2022, 37(12): 48-48.
Total Contents of Steel Construction(Chinese & English) in 2022
2022, 37(12): 49-52.