2021 Vol. 36, No. 11

Display Method:
Differentiation Analysis of Vertial Stiffnees and Cable Force Sensitivity of Double-Layer Cable Net and Beam String Structure
Ou Tong, Lin Quanpan, Jiang Zhengrong, Shi Kairong
2021, 36(11): 1-7. doi: 10.13206/j.gjgS20062901
Due to the introduction of cable element, the mechanical performance of long-span flexible and semi-rigid structures is significantly improved, so that more structures meeting the requirements of architectural innovation can be realized. In recent years, the above two kinds of structures are widely used in large stadiums and gymnasiums. Scholars at home and abroad have done a lot of theoretical research on them, and the research results have been well used in practical engineering. Due to the difference of the dependence of flexible and semi-rigid structures on cable elements, there are great differences in the vertical stiffness and the sensitivity of cable forces between the two structures, which makes large effects on the actual design and construction.In order to explore the above problems, large-span spoke double-layer cable net and radial beam string structures with the same size were established by using the general finite element software ANSYS, and the corresponding contrast parameters were set for the vertical stiffness and cable force sensitivity, including the equivalent vertical stiffness coefficient G, the cable force sensitivity value TS1 and the cable force sensitivity relative value TS2. Comparative analysis was carried out to guide the design of similar projects.The results showed that: in the process of increasing the external load, the vertical stiffness of the cable net structure had the phenomenon of mutation and slow enhancement. Through tracking and recording the internal force of the circumferential cable (structural cable), it was found that the internal force of the circumferential cable gradually decreased from positive value to 0 (relaxation) at the point of stiffness mutation, which indicated that the relaxation of the circumferential cable led to the mutation of the vertical stiffness of the structure. According to the data analysis, compared with the initial stiffness of the load, the final stiffness of the cable net structure increased by about 3.2%, which could be ignored in the actual analysis because of the small increase. The vertical stiffness of beam string structure was basically unchanged and there was no sudden change of stiffness. When the span was small, the equivalent vertical stiffness G of cable net structure and beam string structure was close. With the increase of span, the equivalent vertical stiffness G of both structures decreased, but the decline rate of cable net structure was much faster than that of beam string structure. Under the same plane layout, the cable force sensitivity TS1 and the relative value TS2 of the cable net structure were greater than that of the beam string structure, which indicated that the cable net structure was less sensitive to the cable force, while the overall stiffness of the beam string structure had been formed in the case of small cable force due to the existence of upper rigid members, which made the structure more sensitive to the cable force. In the process of increasing prestress or reducing span, the sensitivity of cable net and beam string structure to cable force decreased. After comparing the cable force sensitivity value TS1 of cable net and beam string structure, it was found that the TS1 ratio of the two structures was stable between 2.43 and 2.55, which could provide reference for similar projects.
Analysis of Mechanical Performance of Steel Frames Composed of Non-Compact Members
Tang Qiang, Liu Qiang, Wang Liankun, Yang Huixian, Guo Yu, Yan Ziqiang, Wang Jicong
2021, 36(11): 8-13. doi: 10.13206/j.gjgS20092302
To analyze the influence of the strength-weakness axis, the width-thickness ratio, the high span ratio, and the axial compression ratio on initial stiffness bearing capacity of flexible frame structure under low cyclic reciprocating load, the quasi-static test study of a single-span and double-layer steel frame was carried out, and the test results were obtained. Based on the test results, a nonlinear finite element model was established. The specific content: 1)Study the effect of the axial compression ratio of 0.1, 0.2, 0.3, 0.4 on the peak displacement, peak load, initial stiffness, and deformation capacity of the structure. 2)Study the structural performance, by changing the height of the structure layer and the span. 3)Study the effect of the width-to-thickness ratio to structural performance by changing the width-to-thickness ratio of the web and the flange. 4)Study the influence of the strength-weakness axis of the column on the members.Specific conclusions: 1)With the axial compression ratio increasing, the bearing capacity, deformation capacity, and initial stiffness were all reduced. 2)The bearing capacity, initial stiffness, and height-span ratio of the structure were inversely related, and the deformation capacity increased with the increase of the height-span ratio. 3)The width-to-thickness ratio increased the load-bearing capacity and the initial stiffness. 4)The change in the direction of the strong and weak axis had a greater impact on the overall performance of the structure. When the steel column changed from the strong axis to the weak axis, the bearing capacity decreased by 40%, the initial stiffness dropped by 65%.
Analysis on the Hysteretic Behavior of Special Truss Moment Frame Connections
Pang Lin, Sun Guohua, Dong Jiaying, Liao Qianwen
2021, 36(11): 14-21. doi: 10.13206/j.gjgS20081102
The brittle failure of traditional beam-to-column connections in moment resisting steel frame was found in the investigation reports of Northridge earthquake (1994) and Kobe earthquake (1995), which led to the poor ductility and deformation capacity of moment resisting steel frame. Therefore, the behavior of beam-to-column connections became a key factor that affected the seismic behavior of moment resisting steel frame. To adapt to the characteristics of large-span public buildings (such as hospitals, shopping malls, stadiums, etc.), the Special Truss Moment Frame (STMF) was attempted to use in some large public building. The STMF structure had the large lateral stiffness, high lateral bearing capacity, and great energy dissipation capacity, which had a wide application prospects. However, the beam-to-column connection between steel column and truss beam was easy to break, especially at the joint weld of chord and steel column, which led to the poor overall ductility and deformation ability of STMF structure. At present, the relative researches on the STMF connections were still small, which was not conducive to the engineering application of STMF structure. In order to clarify the hysteretic behavior of STMF connection, the side beam-to-column STMF connection was selected as the research object. The mechanical characteristics of STMF connection was analyzed through the finite element method, and the effects of the main relative design parameters on its hysteretic behavior were systematically evaluated that could provide reference for its engineering application.Firstly, the BASE specimen of STMF connection was designed in this study, and the three dimensional geometry models were established and meshed by CAD and HyperMesh program, respectively. The ABAQUS program was adopted to build the micro finite element model and to conduct the cyclic analysis. Secondly, the three series STMF connections were designed on the basis of BASE specimen, and the main design parameters, such as chord section, truss height, and end diagonal web member section, on its hysteretic behavior, moment resisting capacity, deformation capacity, yielding mode, and Mises stress distribution, were considered.The analytical results showed that the Mises stress was considerably high at the bottom chord member in STMF connection. The bottom chord member of end segment occurred the overall and local buckling at the nonlinear stage. With the increase of chord section, the moment resisting bearing capacity, and initial rotation stiffness of STMF connection took on the increasing tendency, but had the slight influence on the hysteretic loop shape. With the increase of truss height, the moment resisting bearing capacity and initial rotation stiffness, and energy dissipation also exhibited the increasing tendency except that the energy dissipation had a slight influence, but had the little effect on the failure mode. Under the consideration of non-weaken inclined end web member, the section of inclined end web member did not produce any obvious effect on the hysteretic behavior of STMF connections.
Orthoronal Experimental Study on the Effect of Heat Treatment on the Properties of G20Cr2Ni4A Steel
Dong Fuyuan, Meng Zhaojing, Zhang Mingxu
2021, 36(11): 22-27. doi: 10.13206/j.gjgS20032601
G20Cr2Ni4A steel belongs to CrNi system high quality alloy carburized carbon steel and Cr and Ni content is high. The hardenability of G20Cr2Ni4A is good and its carburized surface has quite high hardness, wear resistance and contact fatigue strength, while its core also retains good toughness, which has excellent comprehensive mechanical properties.Because of the temperature range between critical point Ac1 and Ac3 of G20Cr2Ni4A steel is narrow and Ac3 is 785 ℃, a lower quenching temperature can be selected to ensure surface and core hardness and reduce gear distortion.G20Cr2Ni4A can improve the impact toughness of the material and the comprehensive mechanical properties of the core of the component by heating quenching and tempering.The impact toughness of G20Cr2Ni4A steel after tempering at different temperatures was studied. It was found that the impact toughness was the highest when the tempering temperature was about 200 ℃.The 200 ℃ tempering temperature was selected. G20Cr2Ni4A steel was conducted heat treatment, through the orthogonal test of two factors and three levels, and the effects of quenching temperature and tempering time on the metallographic structure, residual austenite content, hardness and impact properties were observed.Orthogonal test adopted quenching temperature of 800, 850, 900 ℃ and tempering time of 1, 3, 5 h to heat G20Cr2Ni4A, and then measureed its hardness, impact energy and residual austenite content respectively. Through orthogonal test analysis and comparison with the original sample, the corresponding experimental conclusions was drawn: quenching heating temperature and tempering time had significant effects on mechanical properties of G20Cr2Ni4A steel.With the quenching heating temperature increased, the hardness, impact energy and residual austenite volume increased first and then decreaseed slowly; with the extension of tempering time, hardness, impact energy and residual austenite volume all decreased first and then increased.The hardness increased with the increase of residual austenite content, and the impact toughness had an approximate linear relationship with the residual austenite volume.After quenching at 850 ℃ and tempering at 200 ℃ for 1 h, the residual austenite content of G20Cr2Ni4A steel was 2.97%. The experimental steel had the best comprehensive mechanical properties with 45.1 hardness and 25.0 J impact energy.
Discussion on the Detailed Design of the Composite Beam Bridge Structure in China
Liu Zhiguo, Li Junping, Che Ping, Zhang Haifeng
2021, 36(11): 28-33. doi: 10.13206/j.gjgS20062702
In recent years, although China's highway steel structure bridge construction has made great achievements, but as a result of steel bridge professional characteristics of strong, high technology, combined with the collaborative design and manufacturing unit is poorer, designers often ignore the technology of steel bridge manufacture, so in the process of steel bridge manufacture, presents the design and manufacture of the disconnect between phenomenon, in order to improve design staff awareness of steel bridge structure detail processing, combining with our country more than combination bridge of steel bridge construction details for more detailed instructions. The disjunction between the design and manufacturing of steel bridge is mainly reflected in: 1) Some steel plates or sections cannot be purchased due to the influence of rolling capacity, market supply and supply quantity of the steel mill; 2) In the design of steel bridge, the thickness of webs or cover plates in the manufacturing segment should be unified to reduce the waste of manufacturing resources; 3) The composite beam members should be welded in the factory, and the installation segment interface should be connected by high-strength bolts. In the structural design, the screw space of bolts and the bridge installation relationship should be considered. In order to prevent the occurrence of slurry leakage, the thickness of the rubber strip should not be too small; The transverse slope design is realized by adjusting the height of the longitudinal beam. The upper cover plate can be set in a horizontal state, and the transverse slope changes can be realized through the compressibility of the rubber strip. 4)The composite beam steel plate beam manufacturing alignment should be "dead load +1/2 live load" reverse arch superposition bridge longitudinal slope generated vertical alignment, and should consider the impact of erection construction conditions on the bridge alignment; In order to realize the standardized manufacturing, the curve vector height of steel plate beam manufacturing segment is small, so it is appropriate to adopt the scheme of "replacing the curve with the straight curve". The precision relationship between steel structure members and concrete prefabricated parts should be considered in the design of composite beam anti-collision guardrail. 5)The steel bridge should be reasonably set up welding joints according to the need to minimize the damage caused by excessive welding, for the partial penetration fillet weld with penetration requirements should make clear requirements. 6)The weathering steel bridge design needs to pay attention to the details of the bridge deck waterproof, beam body ventilation, support protection and so on, at the same time according to the environment of the bridge to determine the coating or coating free use. 7)The conventional span bridge has the characteristics of long line and complex linear shape, so the design mode of "general drawing + special drawing" can be adopted. In order to ensure the accuracy of bridge linear shape and connection relation of components in the transformation process of construction detail drawing, it is crucial to select a reasonable detail drawing transformation mode. The detail treatment of steel structure bridge described in this paper has a strong guiding significance for improving the disjunction between the design and manufacture of steel structure bridge and enhancing the level of detail treatment of steel structure bridge designers in China, and also provides reference for the design and manufacture of similar steel structure bridge.
Finite Element Analysis of Transition Piece of Built Foundation and New Wind Turbine Tower
Peng Wenbing
2021, 36(11): 34-39. doi: 10.13206/j.gjgS21031102
Under the background of rush to install in 2019 and 2020, incidents such as contract breaches and equipment not being delivered on schedule occured from time to time. This paper takes the wind farm in East China as an example, most of the foundation has been poured, but the wind turbine manufacturer cannot deliver the tower and equipment as scheduled, and the owner is forced to choose another wind turbine manufacturer. However, the tower of the new wind turbine manufacturer does not match the interface of the established foundation. The interface of the built tower is larger than the interface of the foundation and cannot be installed directly. The Transition joints between the foundation and the tower has become one of the most important design links. This paper takes a wind turbine tower with a height of 141 m for a 2.4 MW wind turbine as an example. Based on the ABAQUS finite element analysis software, the mechanical performance of the transition joint between the established wind turbine foundation and the replacement tower was analyzed, including extreme conditions and fatigue conditions. The analysis results showed that the total plastic strain is less than 1.0% when the wall thickness of the transition joint steel tube changes within the range of 37-45 mm under the extreme conditions; during the service period of the tower, the cumulative value of the damage at the weld toe of the butt weld between the steel tube and the lower flange is relatively large, and the fatigue conditions control the design. When the wall thickness of the transition joint steel tube changes within the range of 37-45 mm, cumulative fatigue damage of dangerous point decreases while the thickness increase. The cumulative fatigue damage exceeds 1.0 with the thickness 39 mm, and equals 0.66 with the thickness 45 mm. For the safety consideration, the final thickness will be 45 mm. With the transition piece, the bending stiffness of the foundation is 81 GN·m/rad, that can fulfil the minimum 30 GN·m/rad requirements of the wind turbine manufacturer. The wind turbine manufacturer can run safely.
Research on the Optimal Design of the Flexible Suspension Bridge Suspender Based on the Failure Safety
Huang Jiaxin, Li Rui, Kong Dan, Liu Kun, He Jia
2021, 36(11): 40-47. doi: 10.13206/j.gjgS20080302
Flexible suspension bridge refers to a suspension bridge without stiffening beams or with a small stiffening beam height. Because of its simple bridge deck structure, low steel consumption, convenient bridge deck erection and maintenance, beautiful bridge shape, and low cost, it has the characteristics of being suitable for the complex topography of the southwest mountainous area in my country. Most of the load in the flexible suspension bridge is borne by the cables. Although a certain safety factor is considered in the design, with the passage of time, under the action of the vehicle load, the bridge deck will undergo S-shaped deformation as the shape of the suspension cable changes. It is not conducive to driving safety. At the same time, the boom will be damaged due to uncertain factors such as overload and fatigue, posing a threat to the safe operation of the suspension bridge. In addition, the harsh natural environment in the mountainous area causes the fatigue life of the flexible suspension bridge to become increasingly apparent. In recent years, there have been frequent incidents of bridge collapse due to suspender breaks in our country, and the consequences cannot be ignored. Therefore, it is necessary to optimize the design of the boom of the flexible suspension bridge to ensure the safety and efficiency of the bridge.Based on the engineering example of Chelige Bridge, the paper studied the optimization design plan of damage safety the boom, and calculated the internal force of the original bridge suspension rod and the optimized boom the based on the stress difference with the aid of finite element software, and analyzed whether it could achieve the life difference. The main contents include: 1)through theoretical analysis and calculation analysis, a single boom optimization plan composed of internal and external parts proposed to replace the traditional parallel double boom, and the "damaged safety boom system" of stress difference and strength difference was evaluated. 2)A design method to achieve damage safety by changing the stress amplitude was introduced, and compared with ordinary single boom. 3)Used the full dynamic simulation method to simulate the sudden breaking of the boom, and explored the influence of the stiffness of the elastic block on the breakage of the safety boom. 4)By changing the area ratio of the inner and outer parts of the boom and the stiffness of the elastic block, the optimization effect of the safety boom with poor service life was explored.The results showed that: The optimization design plan of damage safety of the boom could not achieve a significant difference in life. On the basis of the above, a plan to add rubber pads under the safety beam was proposed, the stress amplitude was adjusted to achieve the purpose of damage safety optimization design, and the optimization effect was verified through static and dynamic analysis; finally, the section parameters and the stiffness of the rubber pads were adjusted to explore the force characteristics of the damaged safety boom. It was found that the adjustment of the section parameters had smaller effect on the force of the boom, and the change of the stiffness of the rubber pad had a significant impact on the stress amplitude of the boom.
Discussion on Overall Stability Capacity Analysis of Long-Span Single-Layer Special-Shaped Shell
Wang Lijun
2021, 36(11): 48-49. doi: 10.13206/j.gjgS21110201
The deflection span ratio of long-span is the same as the storey displacement angle of multi-storey and high-rise buildings, which has always been an important index of design control. The structural design of the protective building project of Zhoukoudian Site (Peking Man Cave) is comprehensively and carefully introduced from the perspective of structural stability in Overall Stability Capacity Analysis of Long-Span Single-Layer Special-Shaped Shell. Based on the limit value of deflection span ratio and seismic stability of reticulated shells, it further discussed the project in order to attract the attention and participation of colleagues in the industry.
2021, 36(11): 50-50.