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Research on the Main Structure of the Central Detector of Jiangmen Underground Neutrino Observatory (JUNO)
Gaoming Zhang, Feng Liu, Tao Song, Jihong Qian
2020, 35(9): 1-9.   doi: 10.13206/j.gjgS20072001
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Abstract:
The Central Detector of Jiangmen Underground Neutrino Observatory (JUNO) is a further exploration of neutrino after Daya Bay neutrino experiment. It will measure and rank the mass of three kinds of neutrino. The central detector is the core component of JUNO, which is used to capture the neutrino produced by nuclear reactor or other ways. The overall shape of the central detector is spherical, which is divided into inner layer structure and outer layer structure. The inner layer structure is a PMT shell with a diameter of 35. 4 m (inner diameter), which is used to hold 20 000 tons of liquid scintillation for capturing neutrinos; the outer structure is not only used as the support carrier of PMT (photomultiplier tube), but also provides support for the inner PMMA's sphere; the whole central detector structure is through the column supported at the bottom of the pool.
After the comparison and selection of multiple schemes, the center detector selects the single-layer steel reticulated shell as its main structure scheme. It is composed of a single-layer reticulated shell and an internal PMMA's sphere which are formed by the warp and weft braiding of the outer steel members (bolt connection between the components). The PMMA's sphere is connected with the outer shell through a strut, and the lower part of the shell is connected with the pool bottom through the column. The materials used in the central detector must be low background (low radioactivity), such as PMMA's sphere and stainless steel. All materials in contact with liquid flash and pure water shall meet the compatibility requirements. Therefore, s31608 stainless steel, PMMA's sphere and A4-70 stainless steel bolts are used as the main material forms of the structure. The section form of H-beam is selected, and the buoyancy of structural members is considered by reducing the weight of water from that of stainless steel. In this paper, in order to accurately calculate the force on the PMMA's sphere, the gravity of the PMMA's sphere, the pressure on the inner surface and the pressure on the outer surface are separately considered in the form of load calculation, so as to consider the influence of the thickness of the PMMA's sphere on the buoyancy. The internal and external liquid level difference refers to the height of liquid flash liquid level in the upper chimney higher than the external pure water level. This liquid level difference will add a constant uniform pressure on the inner wall of the PMMA's sphere, partially offset the internal and external pressure difference of some spheres, and improve the force of strut, but has little effect on the total buoyancy. In the scheme calculation stage, two calculation models are considered, one is the calculation model of single-layer reticulated shell without considering the effect of PMMA's sphere; the other is the overall calculation model of single-layer reticulated shell considering the interaction with PMMA's sphere.
The main structure of the detector in JUNO is designed to support the inner PMMA's sphere with a single-layer steel shell, and the inner and outer glass is filled with non-uniform density liquid, which makes the structural stress more complex, especially the simmulating and loading of buoyancy. In addition, due to the brittleness and low reliability of PMMA, the safety margin of structural design is required to be very high, mainly to control the internal force of strut, glass stress and stability of single-layer reticulated shell. Through a large number of program calculations, the detector structure is optimized based on the control index from the aspects of steel consumption, strut number, strut internal force, lattice shell internal force and plexiglass stress. The static performance, stability, seismic analysis, nodal finite element analysis, single point failure and tolerance analysis of the optimized structure are carried out, and the performance of the detector structure is improved from various aspects Detailed analysis shows that the calculation indexes meet the requirements.
Numerical Simulation Investigation on Wind-Resistance Performance of the Metal Roof Aluminum Sheet
Yande Lai, Shixiang Zhang, Qingxiang Li, Ruoqiang Feng
2020, 35(9): 10-16.   doi: 10.13206/j.gjgS20071303
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Abstract:
Continuous welded stainless steel metal roofing system is a new type of metal roofing maintenance system. Because of its easy processing, light weight and high strength, it has been widely used in various large public buildings such as stadiums, terminal buildings, and railway stations in recent years. The problems involved in continuous welding of stainless steel metal roofing systems are comprehensive and complex. This has also led to our country's lack of relevant construction and management specifications for metal roofing systems, which is not conducive to the promotion and application of this type of roofing. Based on the above problems, this article carried out related research on the continuous welding of stainless steel metal roof system.
Firstly, the metal roof structure is introduced. Through the analysis of the structure of the continuous welding stainless steel metal roof system, its advantages are summarized:good integrity and sealing, excellent durability, and low maintenance cost. Based on the finite element analysis software MIDAS Fea, a numerical simulation analysis model of metal roof aluminum panels is established to simulate the failure process of the roof system under wind load, and the wind resistance performance of the continuous welded stainless steel metal roof system is studied and analyzed. A uniform load of 8. 0 kN/m22 along the positive direction of the z-axis is applied to the aluminum plate of the metal roof, and the deformation and force of the aluminum plate are analyzed.
The analysis results show that the middle position of the triangular plate has the largest displacement, and the direction is mainly along the positive z-axis; compared with the middle position plate, the edge plate has a larger displacement due to poor restraint; for the edge position plate and the middle position plate, when the load reaches 6. 4 kN/m2, increase the same load, the displacement increment becomes larger, that is, the load-displacement curve shows a nonlinear growth, and the aluminum plate produces nonlinear deformation. Under the uniform load of 8. 0 kN/m2, the stress at the grooves of the adjacent triangular aluminum plates is relatively large, and it will enter the shaping stage first; in the triangular aluminum plates, the stress at the corner points is the most concentrated, so the stress increases faster, and the stress is the largest; the connecting plate at the groove is connected to the substructure by bolts. During the load transfer process, the vertical load on the roof triangular plate is transmitted to the bolts through the connecting plate. Because the bolt connection is weak, stress is likely to occur the phenomenon of concentration, which will lead to structural damage. Corresponding strengthening measures should be taken when necessary.
Through the modal analysis of the structure, the first 5 modes and periods are obtained. The wind pressure time history analysis is performed on the roof panel, and the maximum displacement and stress response corresponding to each measuring point are obtained. On this basis, combined with the failure mode of the metal roof aluminum panel under the action of wind suction, several suggestions for improving the roof wind resistance ultimate bearing capacity are put forward.
In-Plane Elastic-Plastic Stability Design of Pin-Ended Circular Spoke Arches
Chao Dou, Le Cheng, Xingping Han, Yangze Zhu
2020, 35(9): 17-25.   doi: 10.13206/j.gjgS20040501
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Abstract:
Due to the pulling effect of cables to the arch rib, the stability problem of spoke arches is more complex than that of steel arches, which is influenced by arch rib slenderness ratio, rise-to-span ratio, cable disk height, cable number, cable area and the prestressing in cables. At present, the studies on spoke arches are limited to the qualitative analysis of elastic stability, while the elasto-plastic stability and design method are lacking. By using finite element analyses, the paper dealt with the in-plane elasto-plastic buckling performance of pin-ended circular spoke arches under full-span and half-span uniformly distributed loading, and proposed the optimized parameter ranges for design and the calculation formulas for the ultimate buckling strength. Firstly, the inerative method of applying intial strain was aclopted, the prestressing in spoke arches was applied by stretching the two cables connected to the arch ends, and the effects of prestressing on the inner forces, deformation and ultimate buckling strength were investigated. Next, the influence of a single parameter on the buckling strength was analyzed individually, including the slenderness ratio, rise-to-span ratio, cable number and cable area ratio. According to the load-carrying efficiency, the optimized range of the parameters was suggested. Then the response surface method was used to create 30 representative examples of spoke arches, and the buckling strength ratios to the corresponding pure steel arches were obtained. With 4 key parameters namely the rise-to-span ratio, slenderness ratio, arch-to-cable area ratio and the number of cables, the fitting equations for in-plane buckling strength of spoke arches were established and the accuracy and applicability were verified. The results showed that:1) The presence of prestressing had little effect on the ultimate load-carrying capacity of the spoke arch. In actual engineering, the spoke arch could be designed without prestressing, or the prestressing could be applied according to the requirement of the arch thrust adjustment. 2) In design, the optimal value range of cable disk height was 1/2 of the sagittal height, number of cable was 8~20, arch-to-cable area ratio was 10~30, rise-to-span ratio was 0. 20~0. 50, which covered the common application range. 3) From the results of the response surface method, the influence of the rise-span ratio on the buckling strength was the most significant, followed by the slenderness ratio, while the influence of the arch cable area ratio and the number of cables was relatively small. 4) The proposed equations for the in-plane elasto-plastic buckling strength of spoke arches had the accuracy within 5%, the simplified formula was conservative, most of the errors were within 15%, and it was suitable for different steel strength, which could be used to safely predict the buckling strength of spoke arches in practical design.
Performance Comparison of Structural Steels in Chinese and American Standards
Yaohua Wu
2020, 35(9): 26-43.   doi: 10.13206/j.gjgS20052508
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Abstract:
The differences and similarities in the performance and test methods of steel products commonly used in Chinese standards (GB) and American Society for Testing and Materials (ASTM) standards, GB Q235-Q460 steel in, ASTM A36(M), ASTM A572(M) steel, structural steel with atmospheric corrosion resistance and cast steel in chemical composition, yield strength, tensile strength, impact toughness, elongation after fracture and cold bending performance were compared and summarized in detail.
The analysis results show that Chinese steel standards have more detailed provisions on the chemical composition, and the welding performance is better. The yield strength of common used carbon steel and highstrength low-alloy steel decreases with the increase of the thickness of the steel plate, but the corresponding mechanical properties of the steel in ASTM will remain the same. The tensile strength of GB Q235 and Q235GJ steel is more than 6% lower than that of ASTM A36 steel. The mechanical properties of GB Q355 steel whose thickness is no more than 40 mm and GB Q345GJ steel whose thickness is no more than 50 mm are higher than those of ASTM A572GR50 steel. The mechanical properties of GB Q390 steel with thickness of no more than 40 mm and GB Q390GJ steel with thickness of no more than 100 mm are not lower than those of ASTM A572GR55 steel. The mechanical properties of GB Q420, Q420GJ, Q460 and Q460GJ steels are not lower than those of ASTM A572GR60 and ASTM A572GR65 steels respectively. The atmospheric corrosion resistance indexes of weathering steel of Chinese and American standards are both greater than 6. 0, but the chemical composition is different. The number of grades for GB weathering steel is more; the strength coverage is larger; and the mechanical properties of GB weathering steel with thickness of no more than 40 mm are not lower than those of the corresponding grade of ASTM steel. The GB cast steel has more steel grades and the coverage of strength grade is larger. The mechanical properties of cast steel specimens are different in shape and thickness, and the ASTM specimens are thicker.
The Key Technology for Factory-Production of Large-Span Steel-Concrete Box Girder
Yicheng Li
2020, 35(9): 44-51.   doi: 10.13206/j.gjgS20031601
Abstract(0) PDF (16177KB)(0)
Abstract:
The new steel-coarse aggregate active powder concrete composite box girder deck panel has the advantages of high compressive strength, high tensile strength and high elastic modulus. Under the premise of performance, without changing the excellent mechanics of the steel-concrete composite structure, compared with the traditional steel-concrete composite box girder, the new steel-coarse aggregate active powder concrete composite box girder deck panel can effectively reduce the structural size of the bridge deck, achieve the advantages of reducing the self-weight of the composite girder and improving the long-span spanning capacity. Although the new steel-concrete composite box girder has many advantages, but it still has problems likes the high accuracy of the prefabrication bridge deck panel, low strength of the large opening segment, high degree of difficulty for control the geometric, high accuracy of overlap the bridge deck panel with the steel box girder, high requirements of matching the segments and trial assembly linear control, and it is difficulty to control the secondary deformation of the rebar position and structural geometric of grouting the wet joints. The existing construction technology cannot meet the construction quality and precision control goals. Therefore, this technology is aimed at this new type of steel-concrete composite box girder of the Fifth Nanjing Yangtze River Bridge. The manufacturer CRBBG has research and breakthrough the technology barrier and formed a complete set of technological innovations, mainly including:1) Developed a highprecision precast technology for concrete bridge deck panel, which controls the manufacturing accuracy of embedded parts accordance with control the reference line, the application of large-scale high-precision combined formwork and the standardized prefabrication process of the intelligent production line, achieved the precise control of positioning of the rebars and embedded steel members of the new steel-coarse aggregate active powder concrete bridge deck panel and the overall structure external dimensions. 2) Developed a highprecision trial assembly technology of steel-concrete composite box girder. This technology carried out the continuous trial assembly without allowance of camber design, achieved the precision control referred to the survey and control network, matching constraint positioning technology, and high-precision combined technology of prefabricated bridge deck panel to achieve the precision control purpose of trial assembly for the new type of steel-concrete box girders. 3) Developed the longitudinal wet joint construction precision control technology, which through carried out the rigid support restoration system, adjustable combined wet joint bottom formwork, high-precision rebars positioning formwork and intelligent wet joint construction production system, achieved the high-precision control for positioning of rebars in wet joint and overall structure dimension of steel-concrete box girder. At present, the technical achievements have been successfully used in the factory manufacturing of steel-concrete composite box girder of the main span of the Fifth Nanjing Yangtze River Bridge. Referred to the acceptable factory inspection and verification on construction site, the new steel-concrete composite box girder manufacturing accuracy control goals have been achieved to ensure the successful installation and erection of the bridge.
2020, 35(9): 52-53.  
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