2022 Vol. 37, No. 2

Study on Pure Flexural Buckling Behavior of Web of Castellated Composite Beams with Regular Hexagonal Hole
Lianguang Jia, Jiahui Du, Ran Bi, Wenting Ji, Chen Chen
2022, 37(2): 1-12. doi: 10.13206/j.gjgS21061602
Castellated components have been widely used in high-rise buildings and long-span structures in recent years because of their advantages such as high bearing capacity, great bending stiffness and convenient crossing pipelines. For the castellated component, the local buckling of the web is one of its main failure modes, and the buckling will cause a rapid increase of the local deformation of the web until the work is terminated, which may result in the overall instability of the components and the structural chain reaction. In the traditional steel structure design, the local buckling of the web is avoided by limiting the height to thickness ratio of the web. In the castellated component, the inter-hole pier and its bridge are likely to have local buckling problems, which is more complicated than the solid member. At present, most of the researches on the local stability of castellated beam members are carried out around pure steel castellated beams, and there are few studies on castellated beams considering concrete slabs. Therefore, it is necessary to study the pure flexural buckling of castellated composite beams.
On the basis of the two pure steel castellated beams, two simply supported castellated composite beams were designed and fabricated. The static test of these two castellated steel beam-concrete composite beams was carried out at the four points. By observing the location of buckling on the steel beam and shape of the cracks in the concrete slab, the web buckling performance, bearing capacity and hole angle strain were analyzed, and compared with the pure steel castellated beams, in order to study the effect of the stiffening rib between the floor and web on the failure pattern, stress distribution and bearing capacity of castellated steel beam specimens. The finite element software ABAQUS was used to establish the model to carry on the numerical simulation, by comparision between the test result and the finite element simulation result, the model result is consistent with the test result.Based on the experimental model, the influence of height to thickness ratio and the opening ratio on the pure flexural buckling and the ultimate bearing capacity of castellated composite beams was analyzed.
It shows that pure castellated beams buckle at the upper flange and the corresponding bridge plate, and the composite beams buckle at the pier plate and bridge slab. Concrete slab can effectively improve the yield load and ultimate load of composite beams, improve the ductility of specimens, and avoid the occurrence of local buckling. Setting stiffeners between the webs of composite beams can reduce the stress concentration at the corner of the holes and avoid buckling of the pier plates between the holes. There are two buckling modes of the composite beams, both of which are the semi-wavy out-of-plane instability of the piers between holes. The difference lies in the out-of-plane displacement distribution.The displacement of the first buckling mode centrosymmetric distributes with respect to the middle of the beam span and the displacement of the second buckling mode centrosymmetric distributes with respect to the middle of the beam span.The height to thickness ratio is a decisive factor affecting the failure mode and pure flexural buckling of composite beams. When the height to thickness ratio is less than 80, strength failure occurs. When the height to thickness ratio is greater than 80, buckling failure occurs. Reducing height to thickness ratio of web can effectively improve the buckling resistance of specimens and increase the buckling resistance of specimens. Opening ratio is an important factor affecting the failure mode and pure flexural buckling of composite beams. Increasing the opening ratio within a certain range can increase the buckling load of specimens.
Theoritical Study of Flexural-Torsional Buckling of Biaxial Symmetric Dumbbell-Shaped CFST Arches Based on Plate-Beam Theory
Wenfu Zhang, Feng Ma, Kaijie Zhu, Bin Huang
2022, 37(2): 13-21. doi: 10.13206/j.gjgS21090401
The existing theoretical formulas are only applicable to single-material components, and the existing stability theory cannot be used to solve components composed of different materials. Therefore, Professor Wenfu Zhang independently proposed a new engineering theory that can solve the combined torsion and flexural-torsional buckling of thin-walled members in 2014. The theory mainly adopts three basic assumptions:rigid periphery assumption, plate deformation assumption, beam deformation assumption. Different from the traditional Vlasov theory, the longitudinal displacement, linear and nonlinear strain, and strain energy in the plate-beam theory can be derived from the mature Kirchhoff thin plate theory and Euler beam theory. It can not only solve the problem of warpage that cannot consider the influence of different materials of steel and concrete, but also avoid the controversy caused by the arbitrariness of assuming the warpage function.
For the convenience of description, two sets of coordinate systems are introduced in the plate-beam theory, namely the global coordinate system xyz and the local coordinate system nsz. These two sets of coordimate systems are similar to the Vlasov coordinates, and both satisty the right-handed spiral rule.The origin of the global coordinate system coincides with the centroid of the section, and the x and y axes are the main axes of the section, respectively. Unlike Vlasov curvilinear coordinate system, the local coordinate system nsz is a rectangular coordinate system. The origin coincides with the centroid of each plate, the s-axis coincides with the mid-plane of the plate, and the n-axis coincides with the normal to the mid-plane of the plate. Turning from the n-axis to the s-axis conforms to the right-hand screw rule, and the thumb should be aligned with the positive z-axis.
Based on the plate-beam theory, the cross-sectional properties of the biaxially symmetric dumbbell-shaped CFST section are deduced, and the displacement field and strain field for bending-torsional buckling are established according to related assumptions, and the total strain energy and total initial stress potential energy are derived. Furthermore, the bending stiffness, warping stiffness and free torsion stiffness of the biaxially symmetric dumbbell-shaped concrete-filled steel tube section are obtained, and the correctness of the theoretical formula is verified through calculation examples and finite element analysis.
Research on Partition-Multi-Objective Equivalent Static Wind Load Method for Roof Structure
Yun Li, Xianlong Zhang, Yang Liu, Jiawu Zhang, Ruoqiang Feng
2022, 37(2): 22-29. doi: 10.13206/j.gjgS21022803
The roof structure has the characteristics of light weight, large span and low stiffness, which makes it sensitive to wind load. In this kind of structural design, wind load often plays a major control role. In addition, there are many members in structural joints, and many target responses are concerned. Consequently, the traditional single-objective equivalent method is difficult to achieve the equivalent of multiple responses.
In view of the uncertainty of the control points and the equivalent static wind load of the roof structure, a partition-multi-objective method is proposed in this paper. The partition is based on the roof structure shape and the average wind pressure coefficient of the measuring point. A small amount of partition fluctuating wind pressure is used as the basic vector of the load distribution. When the equivalent static wind load is calculated using the multi-objective equivalence theory, the equivalence of the target response can be ensured. However, the distribution of the equivalent static wind load may be unreasonable, and the static wind pressure in the local area may be far beyond the actual situation. Therefore, in order to ensure the reasonableness of the partition equivalent static wind pressure distribution, the weighting factor is introduced to determine the distribution of equivalent static wind loads by solving the minimum of constraint equation. In this paper, the wind vibration response calculated by the time-history method is assumed as the accurate value, which is compared with the vibration response calculated by the partition-multi-objective method to verify the calculation accuracy. Finally, taking the practical engineering of roof structure as an example, the equivalent response accuracy and applicability of the proposed method are analyzed.
Conclusionsare drawn as following:1) For the multi-objective equivalent static wind load of the actual roof structure, the multi-objective equivalent method without constraint conditions has the highest equivalent response accuracy and the lowest overall error. However, this method facing the problems of unreasonable extreme wind pressure, the wind pressure changes violently and intensively, which is not applicable to practical engineering. Therefore, constraint conditions should be introduced for the multi-objective equivalent equation. 2) After the constraint conditions are set for the multi-objective equivalent equation, the overall equivalent response accuracy is slightly lower than that of the unconstrained multi-objective method, but the errors are acceptable. The maximum equivalent wind pressure is effectively constrained, and the wind pressure changes gently. In the weighted constraint multi-objective method that setting the critical equivalent objective, the equivalent response of the critical objective is in good agreement with the wind vibration response, and the distribution pattern of equivalent wind pressure can be further improved. 3) In practical application, the distribution coefficient can be used to constrain the partition fluctuating wind pressure. Generally, the peak factor is taken as the constraint range of the distribution coefficient, or the constraint range can be appropriately extended to ensure the equivalent response accuracy. The results show that the basic vector of this method can well describe the wind field characteristics of the roof. In addition, the equivalent static wind load distribution obtained by this method is reasonable, and the change of wind pressure in the partition is uniform and continuous. In conclusion, the equivalent response is high, and it is convenient for engineering application.
Research on Global Stability Design Method of Steel-Concrete Composite Beams of Negative Moment Region
Shan Wang, Yi Zhang, Long Hao
2022, 37(2): 30-36. doi: 10.13206/j.gjgS21012701
Steel-concrete composite beams are widely used in medium and small span bridges because of their reasonable acceptance, light lifting weight and convenient in construction, but they have lateral instability in the negative moment region. For the global stability design in the negative moment region, each code gives the calculation method according to the elastic foundation beam theory or inverted U-frame theory, but the results of different codes are different. How to select a method with good accuracy and relatively simple to assist the design that has become an urgent problem to be solved.
Using MATLAB numerical calculation method, this paper analyzed the parameter sensitivity of span, web height thickness ratio and reinforcement ratio of concrete slab of the global stability calculation method of composite beams in Eurocode 4, Code for Design of Steel and Concrete Composite Bridges(GB 50917-2013) and Standard for Design of Steel Structures(GB 50017-2017), and analyzed the influence of parameter changes of the stability reduction coefficient of composite beams. Based on ABAQUS nonlinear finite element analysis method, the arc-length method was used to simulate the global stability of composite beams. The differences were compared between the elastic-plastic critical buckling moment calculated by the three code and the finite element analysis under the changes of span and web height thickness ratio.
Through a large number of data analysis, it is found that:increasing the reinforcement ratio of concrete slab will slightly reduce the stability reduction coefficient, on the one hand, the increase in longitudinal reinforcement ratio will improve the stiffness of steel beams, on the other hand, it will lead to the upward movement towards neutral axis and increase of compression region. In both cases, the adverse effect of upward movement towards neutral axis is slightly greater than the beneficial effect of increasing section stiffness. On the whole, improving the reinforcement ratio of concrete slabs has no obvious effect on the stability of negative moment region; the height thickness ratio has a great influence on the stability of composite beams. With the increase of height thickness ratio, the stability reduction coefficient decreases obviously; the upper flange of the composite beam is restrained and the lateral displacement is limited, when the span increases to a certain extent, the instability mode changes from one half wave to two halves wave. Therefore, when the span is small, the stability in the negative moment region decreases with the increase of the span. When the span increases to a certain value, the increase in the span has little impact on the stability in the negative moment region. The results show that the elastic-plastic critical moments calculated by the three design methods are less than the simulated values, and there is a certain safety margin; the calculation results of the Eurocode 4 is closer and more conservative than the finite element simulation results, Code for Design of Steel and Concrete Composite Bridges is simple and can also ensure a certain degree of safety, Standard for Design of Steel Structures is closer to the finite element simulation results, and the safety reserve is relatively low than the other two code.
Structural Design Regarding Long-Span Outdoor Corridors of Langfang Airport Economic Center
Xusong Wang, Jiantao Liu, Chunguang Wang
2022, 37(2): 37-45. doi: 10.13206/j.gjgS21060701
In order to satisfy both architectural and structural needs and to avoid disadvantages of single form, complexity and high cost, the long-span outdoor corridors of Langfang Airport Economic Center project innovatively adopted the curved-shape truss with fixed condition. In view of the stress distribution, the overall stability of the truss, the local stability of the joints and the seismic performance of the structure, YJK 2.0.3 was adopted for comprehensive calculation considering dead, live and temperature loads; SAUSAGE 2020 was adopted for stability analysis based on direct analysis method with initial imperfection according to first linear buckling model, considering geometric and material non-linearity together with non-uniform distribution of live loads, within which truss with or without concrete slab were both accounted.YJK 2.0.3 was adopted for earthquake static analysis; SAUSAGE 2020 was adopted for dynamic time history analysis subjected to severe earthquake records, from which structural deformation, plastic damage and weak components were found out. ANSYS R19.2 was adopted for finite element static analysis towards the most heavily loaded joint using solid element and considering geometric and material non-linearity.
Following statements were concluded. Changing shape of the truss is closely associated with bending moment diagram of the truss and stress ratio of steel components is within control. Effects of concrete slab on global stability are obvious. Due to enhancing effects from slab, critical buckling mode changes from lateral deformation of upper layer of truss to bi-axial deformation for column. Comprehensive index, stress ratio and reinforcement ratio from seismic design was satisfied. There is no vulnerable spot and plastic damage under severe earthquake was limited. Peak stress around joint is less than steel yielding strength and area with stress concentration reduced rapidly. There was certain amount of sufficiency in joint capacity, and local stability can satisfy code limit. Enhancing measures were adopted in construction drawings according to previous analysis results.
Construction Technology
Key Installation Technology of New Sidesway-Resisting Modularized Low-Position Jacking Steel Platform Scaffold System in Tianjin Goldin 117 Building
Xinying Ai, Dihua Yu, Jian Ye, Yongchang Li, Beinuo Chen, Yong Lu
2022, 37(2): 46-52. doi: 10.13206/j.gjgS21072202
The construction of the core tube of Tianjin Goldin 117 Building has many construction difficulties, such as large volume(the maximum single-layer area is 1 072 m2), high structural height(the construction height of the structure is 596.2 m), many changes in storey height(a total of more than 20 storey heights), many changes in wall segmentation, thickness and elevation(the thickness of the external wall is reduced from 1 400 mm to 300 mm), and many stiffness column components.
In order to ensure the progress and quality of engineering construction, the project team integrated a variety of formwork forms at home and abroad, and finally selected the anti-lateral modular low-position jacking steel platform scaffold system for core tube construction, and studied its design principle and composition, installation and construction process and operation points. The research results include:1) The formwork system consists of five parts:steel platform system, support and jacking system, hanging frame and retaining system, formwork system and anti-lateral device. Each part needs to meet the safety and quick requirements of super high-rise construction and its strength and stiffness. 2) In order to adapt to the change of layer height, the formwork system is equipped with the stereotyped formwork according to the standard layer height. The vertical position of the formwork can be adjusted by itself when the formwork frame system is fixed, and the formwork at the end of the core tube needs to be adjusted according to the structure. When the layer height changes greatly, the support column is adjusted by adding non-standard sections. The hydraulic cylinder with large stroke meets the lifting height requirements of different layer heights. 3) In order to facilitate the hoisting of steel members in the core tube, steel plate and rigid column hoisting holes are left on the steel platform, and the horizontal slideway is set up for the steel plate that cannot be in place at one time and slide horizontally to the installation site. The height of the column meets the requirements of the maximum hoisting section. 4) According to the overall construction deployment of the project, after the core tube construction of four layers of sandwich structure, the tower crane is first installed, and then the top die is inserted after the installation of the tower crane is completed. It is planned to install and debug for 30 days. 5) The overall process of jacking formwork installation is as follows:measurement setting-out → hoisting of lower box girder → hoisting of hydraulic cylinder → hoisting of upper box girder → hoisting of supporting column → installation of steel platform truss → installation of hanger and enclosure system → installation of formwork system → installation of lateral resistant device. 6) The installation method of prefabricated steel truss platform truss is "ground assembly, aerial assembly", that is, the platform truss is pre-assembled into short pieces in the manufacturer, transported to the site, and then assembled into pieces on the ground, and then hoisted to the aerial assembly and bolted. The internal and external hangers are assembled into units on the ground, and then hoisted in pieces or blocks.
The application practice of Tianjin Goldin 117 Building has proved that the top formwork system has the unique advantages of supporting column height, carrying out the vertical flow construction of the whole process of steel plate shear wall at the same time, and resisting wind-induced lateral displacement. It has reached the construction speed of 5 days/floor, created good economic and social benefits, and has broad application prospects.
Hot Spot Analysis of Steel Structures
2022, 37(2): 53-53.