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Steel Construction Published the List of Highly Influential Articles of 2020
2021 Vol. 36, No. 2
Abstract
PDF (29538KB)Stainless steel structure has good mechanical properties and excellent corrosion resistances, which is one of the best choices of the structural schemes for important infrastructures in highly corrosive environments. Related researches on stainless steel structures began from 1960s, and have grew rapidly in the past 20 years as the more and more attentions have been taken to the durability and the safety of structures. Currently, researches on stainless steel structures mainly focused on the material properties and the performance of cold-formed members, while the researches on the behavior of the stainless steel welded members were rare. Besides, the material characteristic of stainless steel has not been fully incorporated into the design method. This study would report an experimental study on the lateral-torsional buckling of duplex stainless steel welded I-section flexural members, and modify the related design formula to include the material properties characteristic of duplex stainless steel.
Firstly, a four-point bending test rig with the strong constraints at the loading points was proposed for the lateral-torsional buckling test in this study. In this test rig, to clarify the boundary conditions and reduce the possible redundant constraints from the test rig applied to the test specimen, the lateral constraints were configured at the same location as that of the loading points, which was different from the traditional test rig that following the concept to release the constraints at the loading points. A series tests were then conducted for seven flexural members to obtained full set of test data, including the initial geometric imperfection, the material properties, and the failure mode and capacity. The test data was compared with the predictions of Eurocode and Chinese code. Finite element models of the welded stainless steel flexural members were established and verified by test data, and then parametric analysis were carried out. Based on the results of parametric analysis, the design formulas for the lateral-torsional buckling were modified considering the strain hardening characteristic of stainless steel.
All the specimens showed the lateral-torsional buckling except the S-DI-150-3000, which had the local-global interaction buckling. Comparisons between the test data and the predicted values of the Eurocode and the Chinese code showed that the predicted values of the two design codes were both conservative. The mean ratios of the test values over the predicted values were 1. 23 and 1. 18, respectively. The finite element model can accurately predict the bearing capacity. The mean ratio of the test values over the bearing capacity obtained by finite element analysis was 1. 06. Based on the analysis results and the characteristic of stainless steel, a two-stage formula was established. When the slenderness was not less than 0. 54, the modified Perry formula was used to express the relationship between the slenderness and the reduction factor. When the slenderness was less than 0. 54, a linear relationship between the slenderness and the reduction factor was approximately employed. To make full use of the characteristic of considering strain hardening after yielding, the reduction factor was allowed to be greater than 1. 0 with the maximum value of the ratio of the tensile stress over the nominal yield stress. Comparisons of the test data and the predictions of the proposed formulas showed that the proposed formula can accurately predict the bearing capacity. The mean ratio of the test values over the predicted values was 1. 00, with a low scatter of 0. 11.
“Strong column and weak beam” is the current international mainstream seismic design concept of engineering structures. The investigation of existing earthquake disasters have shown that due to the complexity of earthquake action mechanism and the lack of understanding of the ultimate earthquake resistance of engineering structures, frame structures after strong earthquakes will not only appear “strong column and weak beam” damage caused by beam hinges, but also “strong beam and weak column” damage caused by the overall collapse, column hinges and local floor collapse.
In order to reasonably understand the various failure forms, the author first subdivided the traditional concept of plastic hinge into “compression hinge” and “tension hinge”, and pointed out that “tension hinge” is likely to cause the overall loss of the structure; then taking the steel-concrete composite frame structure as the object, the refined finite element seismic calculation model of composite frame structure based on solid element and shell element was established and used to carry out the ultimate seismic resistance of composite structure, and preliminarily discussed the effects of various horizontal seismic wave conditions on the displacement, stress, axial compression ratio and other time history responses of composite frame structure, as well as the distribution mechanism of plastic energy dissipation, the formation mode of plastic hinge and failure mechanism of frame beam column were preliminarily discussed.
The analysis results show that: 1) The tie bars stiffened column end reduce the slip between the steel tube and the concrete, thus increase the stiffness of the column and the frame, reduce the strain level of the steel tube and concrete, and increase the stress level of the steel beam. Under the action of seismic waves with intensity of 620 cm/s2 and above, the “strong column” construction of the column end tie bars can significantly reduce the maximum inter story displacement angle of the composite frame structure. The column end tie bars yield when the horizontal seismic wave is close to the ultimate strength, and the frame beam end longitudinal reinforcement of concrete slab is generally not easy to yield; 2) The “strong beam and weak column” composite frame is shown as “constrained beam” and “energy dissipating column”, at this time, the frame beams strongly restrain the frame column, and the frame mainly consumes energy from the frame column. The beam ends only form “compression hinges”, at this time, the energy dissipation capacity of the frame depends on the frame columns. The “strong column and weak beam” composite frame appears as “energy dissipating beams” and “load-bearing columns”, at this point, the frame beam is weakly constrained to the frame column, the frame is based on the energy consumption of the frame beams so that the beam ends form a “compression hinge”. When the energy consumption of the beam ends reaches the limit, a “tension hinge” is formed, which causes the frame column slenderness ratio to increase, and then leads to accelerated failure of the frame, which is not conducive to the use of frame columns energy dissipation potential; 3) The “strong column” construction of the tie bars stiffened column end technology will improve the stiffness, plastic energy dissipation, and anti-collapse ability of the composite structure, in particular, the seismic capability of the 6-storey frame with energy dissipation column.
With the increase of the higher steel residential buildings, the traditional cold-formed steel wall is not suitable for the high-rise and mid-rise buildings. For this reason, a novel cold-formed steel wall was developed. In order to newly study the superiority of the steel skin composite wall to the traditional cold-formed thin-walled steel structure composite wall in lateral resistance, the new cold-formed thin-wall steel structure composite steel skin shear wall of gypsum board + steel sheathing. The research on seismic performance was carried out. The two monolithic composite wall specimens were horizontally monotonously loaded without vertical force, and the characteristic parameters such as the failure characteristics, bearing capacity, displacement, shear strength and lateral rigidity of the specimen were obtained. Using ABAQUS to conduct numerical simulation research on the composite wall under horizontal monotonic loading, and numerical results were compared to the test results.
The results show that increasing the thickness of studs can significantly enhance the bearing capacity, stiffness and ductility of the shear wall. The failure types of the wall are brittle failure and ductile failure. Brittle failure is caused by buckling of wall side columns under compression. Ductile failure occurs at the joint of wall panel and tapping screws, and the failure process consumes more energy. The ratio of the stud thickness to the total thickness of the sheathing plays a controlling role in the failure mode of the composite walls. In the design, the stud thickness should be guaranteed, and the thickness of the steel sheathing should be rationally designed to make the wall ductile. In addition, the finite element numerical simulation results are in good agreement with the test results which shows the method used in this paper can effectively predict the mechanical performance of the composite wall.
Curved steel pylon of cable-stayed bridge has the characteristics of complex cable shape, large overall slenderness ratio, and the overall structure is composed of thin-walled members. Its stability has become the key control factor of structural design. In order to research the stability of the curved steel pylon under the main vertical loads such as dead weight, dead load of the bridge superstructure from the cable system and vehicle load, further clarify the element type selection, instability mode and stress characteristics, a curved steel pylon cable-stayed bridge with a span of ( 200+ 200) m is taken as the research object, and the ANSYS general finite element software is used to establish a spatial beam element model and a spatial shell element model for the steel pylon. The model is numerically calculated and analyzed for its stability to obtain the instability mode and instability critical load in the elastic state, as well as the ultimate bearing capacity, the stress distribution, structural deformation in the ultimate bearing capacity state after considering the influence of nonlinear factors. In the spatial beam element model, Beam 4 element is used to simulate the main girder of the cable-stayed bridge as a fishbone model, Link 10 element is used to simulate the cable and the initial tension is applied, and Beam 188 element is used to simulate the pylon. In the spatial shell element model, the main beam and cable are simulated in the same way as the beam element model, and Shell 143 element is used to simulate the pylon according to the actual structure. The material nonlinear simulation of Q345 steel used in the pylon adopts the MKIN model, and the first-order buckling mode obtained in the first type of stability analysis is taken as the shape of the initial geometric defect of the structure.
Through calculating:1) The first type stability safety factor of the pylon calculated using the beam element model is 94. 51, and the second type stability safety factor, which considering the effects of double nonlinearity and structural initial defects, is 19. 89. The first type of stable instability mode of the pylon calculated by the spatial shell element model is firstly shown as local out-of-plane buckling of the wall plate, the corresponding stability safety factor is 25. 15, and the stability safety factor is 61. 42 in case of overall instability; 2) The second type of stability has a minimum safety factor of 12. 90, and the instability mode is local instability. The stress and elastic strain concentration areas of the outer wall and stiffeners of the pylon are mainly located in the middle of the cable. The stress and elastic strain concentration area of the stiffeners, middle webs and diaphragm inside the pylon is mainly located at the diaphragm at the cable, and the plastic strain inside the pylon is mainly concentrated in the cable anchorage area of the diaphragm. The two types of instability modes of the steel pylon calculated by the shell element model are local buckling, and the corresponding buckling load characteristic value is much smaller than that of the overall instability. It is necessary to pay attention to the stress and deformation of key parts such as the wall plate and the inner anchorage zone of the pylon when making stability and safety judgment.
The sightseeing tower, with its high structural height and slender shape, greatly improves tourists’ visual experience, but it also brings great challenges to structural design. By analyzing a complex high - rise sightseeing tower project, the characteristics and difficulties are introduced in terms of steel structure design of sightseeing tower. The total height of the sightseeing tower is 204. 4 m, which mainly includes four parts: podium, tower body, tower and amusement equipment at the top of the tower. Its functions include shopping malls, property service, revolving restaurants, sightseeing platforms and amusement facilities. The main structure of the steel tower adopts the form of steel structure cylinder, and the cylinder body is composed of concrete filled steel tube columns and steel bracings. The plane of the cylinder body is octagonal, and eight concrete-filled steel tubular columns and cross-story X-shaped braces are vertically arranged along the octagonal periphery as the main lateral force resistance system.
On the basis of introducing the overall structural system and functional distribution, the paper expounds the structural design scheme in combination with the characteristics and difficulties of each part of the structure. The height-width ratio of the main tower structure of the sightseeing tower is large, the tower has a large diameter and a high position, which enlarges the adverse effect of large height-width ratio. According to this characteristic, four outrigger trusses were arranged at the bottom of the tower body, and the elevation of the connection between the outrigger trusses and the steel column was determined through comparative analysis, which effectively reduced the adverse effect of large height-width ratio of the main tower structure; For the stiffness weakening caused by large openings in the floor, horizontal steel braces were arranged in the floor, and a long truss resisting horizontal force was formed together with floor steel beams; The bottom layer of the tower was set as the transfer truss layer to realize the large cantilever of the tower, and the cantilever truss members were all made of H-shaped steel; In order to effectively anchor the space shuttle amusement equipment at the top of the sightseeing tower, a transfer truss was arranged at the bottom of the space shuttle support to directly transfer the load to the concrete-filled steel tubular column of the tower; Special steel beams were arranged to support the revolving restaurant equipment, and the structural height difference caused by the height of rotating equipment was solved by adopting the methods of variable truss height and variable cross-section height beams respectively.
Using finite element software, modal analysis, wind load and earthquake action analysis, structural deformation and stress analysis were carried out on the sightseeing tower structure, and fine finite element analysis was conducted on the key joints in the structure, such as the connections between the outrigger trusses and the podium. The analysis results show that the performance indexes such as vibration mode and period of the structure, lateral deformation of the structure under wind load and earthquake, vertical deformation of the structure and the bearing capacity of members all meet the requirements of the code; Cast steel joints were completely in the elastic range and meet the design requirements; Wind load is the control load in the structural design of the sightseeing tower, and the earthquake action has little influence.
