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Flexural-Torsional Buckling of Concrete-Filled Multicellular Steel Tube Walls
TONG Ji, TONG Gen-shu
2022, 37(11): 1-23.   doi: 10.13206/j.gjgS22070401
Abstract(3) PDF (17628KB)(0)
Concrete-filled multicellular steel tube walls(CFT-walls) are a newly-developed lateral-force-resisting member in China, it begins with a cold-formed rectangular box, and then added by a series of cold-formed lipped wide-flange U-section in a direction to form a multicellular steel tube wall, concrete is filled-in-situ to form a multicellular CFT-wall.The current equation used in the design of CFT-walls for flexural-torsional buckling is from steel box column, detailed study is lack. This paper presents a study on the flexural-torsional buckling of CFT-walls under axial force and in-plane bending moment, the main works are as follows:1)As the first step of the development, plastic interactive relations are derived for the axial force and bending moments about the strong axis and about the weak axis respectively. When the CFT-walls are degenerated into a sandwich cross-section with two face steel plates and a concrete mid-layer, explicit expressions are obtained for these two interactive relations. Based on these expressions, fitting curves with good accuracy are provided for them. 2)For the general cases of axial force and biaxial bending moments, exact analysis is carried out for the state of spatial plastic hinges and an approximate interactive equation for biaxial bending under a given axial force is also proposed. The effect of bi-moment is incorporated into the proposed equation. 3)Based on the codified column strength reduction factor, the equivalent initial out-of-plane deflections are obtained by taking the buckling strength of the column about the weak axis as a plastic hinge state under the axial force and the amplified bending moment due to the second order effect and initial deflection, this equivalent initial deflection includes the effect of residual stress, initial deflection and the additional deflection increment due to plasticity development. 4)Second-order analysis is carried out for the walls with initial deflection and initial twisting, after introducing a specific relation between the initial deflection and initial twisting, simple expressions are obtained for the lateral displacement, twisting angle, lateral bending moments and bi-moments. 5)Flexural-torsional buckling of CFT-walls under pure bending is also studied, it is found that as the slenderness for flexural buckling about the weak axis is 1.6, the slenderness for flexural-torsional buckling of the CFT-walls under pure bending is less than 0.5, and the buckling capacity is very close to the plastic bending moment. 6)Introducing the equivalent initial deflection and initial twisting into the second-order bending moment about the weak axis and into the bi-moment, together with the second-order in-plane bending moment, they are substituted into the spatial interactive equation of the axial force and biaxial bending moments, an interactive equation for flexural-torsional buckling of walls is derived. But this is an upper bound solution of the interactive equation because the process of elastic-plastic development has not been included. To achieve the load-carrying capacity of the CFT-walls in reasonable safety, the second-order in-plane bending moment, and further the out-of-plane bending moments and bi-moment must be amplified to consider the elastic-plastic development. A series of curves are provided to show the interaction curves, the curves are close to the interactive relation of strength when the slenderness is small, and the curves are higher when the slenderness is increased. The curves are close to the interactive relation for elastic flexural-torsional buckling when the flexural-torsional slenderness is about 2.5. Based on the observation of the derived curves, 3 sets of formulas with different simplicity are proposed, and may be applied on individual preference for simplicity.
Research on the Influence of Residual Stress on the Stability of BS700 High Strength Steel Welding Box Section Columns Fabricated By Channel Sections
GAO Lei, WANG Jing-wen, BAI Lin-yue, LIU Hu
2022, 37(11): 24-30.   doi: 10.13206/j.gjgS22072601
Abstract(0) PDF (3982KB)(0)
High-strength steel has been used in more and more projects because it can reduce the amount of structural steel and resource consumption, but the research on the stability of high-strength steel members is still relatively lacking, and residual stress is an important factor affecting the stability of members. BS700 high-strength steel(nominal yield strength is 700 MPa) has no section steel, so the steel plate is first cold-formed into a channel-shaped section member, and then butt-welded to form a box-shaped section member. However, the welding will generate residual stress in the section of the member, and the research on the influence of welding residual stress on the stability of BS700 high-strength steel box section columns fabricated by welding channel sections is still a lack of relevant information. This paper studies this problem by means of experimental and numerical analysis methods, in order to understand the effect of residual stress on BS700 high-strength steel box section columns fabricated by welding channel sections impact on stability. The mechanical property parameters of BS700 high-strength steel material were obtained through material tensile test. With the help of tensile test, the stress release coefficient when the member that opened was obtained. The blind hole method was used to test the residual stress of the middle section of the BS700 high-strength steel box section columns fabricated by welding channel sections, and the residual stress value of the relevant points on the section was obtained. Combined with the existing research results, the residual stress distribution model of BS700 channel-butt-welded box-section members was proposed. With the help of the finite element analysis software ANSYS and its APDL programmable language, a nonlinear buckling analysis model that can introduce geometric defects and residual stress was written. The model was used for nonlinear buckling analysis of 68 components with and without residual stress. The 68 components simulated the conditions with slenderness ratios of 15, 20, 30, 40, 50, 60, 70, 80, 90, 100 and the cross-section width-thickness ratios are 10, 15, 20, 25, 30, 35, 40, and 50, respectively. The effect of residual stress on the stability of BS700 high-strength steel box section columns fabricated by welding channel sections under different width-thickness ratios and different slenderness ratios was studied. Through the research, it is found that there is residual tensile stress at the weld and corner, and residual compressive stress at the rest. The maximum residual tensile stress level at the weld is about 0.76 times the yield strength, and the maximum residual compressive stress at the middle of the web is about 0.14 times the yield strength. On the basis of the existing research, a polyline residual stress distribution model is proposed, which is in good agreement with the experimental results; the residual stress has an influence on the stability coefficient of members under different width-to-thickness ratio conditions, and the overall trend is with the width-to-thickness ratio. Increase, the influence of residual stress gradually decreases, mainly due to the phenomenon of local elastic buckling of the member under the condition of large width-to-thickness ratio; the effect is relatively small when it is small or large. When the slenderness ratio is between 20 and 70, the residual stress has a great influence on the stability coefficient of the member. By comparing the critical slenderness ratio when the plate is partially buckled, it is found that the two overlap. In the stability design, the members in the range of medium slenderness ratio are relatively sensitive to residual stress, so this influencing factor should be paid attention to in the process of component stability design.
Finite Element Analysis of Cable Saddle’s Mechanical Performance Considering the Influence of Cast Steel Material Inhomogeneity
ZHONG Chang-jun, SHEN Rui-li, WANG Hui
2022, 37(11): 31-38.   doi: 10.13206/j.gjgS20092001
Abstract(0) PDF (8594KB)(0)
To study the influence of cast steel material non-uniformity on the mechanical performance of cable saddle, based on probability theory and finite element numerical simulation technology, a random simulation program of PYTHON material was compiled on the ABAQUS platform, and a random finite element model considering the cast steel material non-uniformity was established. The complex stress and plastic distribution of cable saddle under three-way load were discussed in depth, and the influence of cast steel material non-uniformity on the ultimate bearing capacity of cable saddle was analyzed. The results show that the reduction of grid size will lead to the increase of randomness of bearing capacity, but has little influence on the determination of bearing capacity. The randomness of steel casting materials will lead to uneven stress distribution of steel castings, and local areas will enter the plastic state under the design load. The non-uniformity of material yield strength has a great influence on the bearing capacity of the structure, while the non-uniformity of elastic modulus has a small influence on it. The material inhomogeneity of the steel casting has no obvious influence on the static mechanical behavior of the cable saddle, but it will reduce the bearing capacity of the structure slightly and make the structure appear greater deformation in the limit state.
Discussion on Shape Coefficient in Wind-Induced Fatigue Analysis of Rectangle High-Rise Steel Structures
2022, 37(11): 39-45.   doi: 10.13206/j.gjgS22051701
Abstract(0) PDF (6800KB)(0)
Welded beam-to-column connections in high-rise buildings may be subjected to fatigue failure under wind. At present, the analysis method of wind-induced fatigue is to replace wind pressure coefficients on different parts of the structural surface with the shape coefficient as a whole to average the distribution of wind pressure coefficients, and then to calculate the wind pressure and to conduct fatigue analysis in combination with the quasi steady assumption. However, the distribution of wind pressure on the surface of high-rise structures is complex, and the distribution of stress at key connections may be affected by this average treatment. Moreover, the specified shape coefficient in "Load Code for the Design of Building Structures(GB 50009-2012)" is mainly for displacement-based wind vibration calculation. Whether it can meet the calculation need of wind induced fatigue based on local stress has not been studied or verified by relevant literature so far, so it is necessary to verify the accuracy of calculating wind induced fatigue of structures using shape coefficient.A rectangular-plane high-rise steel frame supporting structure located in the wind disaster prone area was selected. First, considering the spatial correlation, the fluctuating wind speed time history at the representative beam-to-column connection of the structure was simulated by using the harmonic superposition method. The simulated wind speed time history was converted into a power spectral density curve through inverse Fourier transform, and was compared with the target spectrum. Then a numerical wind tunnel calculation model with 1:300 scale ratio of the structure was established in the CFD software FLUENT. The wind pressure coefficient distribution on the structure surface was calculated using Reynolds average simulation(RANS), and was compared with the wind tunnel test data of similar structure models in the wind tunnel test database of Tokyo Polytechnic University, Japan; Finally, the multi-scale finite element model of the structure was established using the finite element software ANSYS, and the wind pressure time history is calculated based on the wind pressure coefficient and the shape coefficient respectively, combined with the quasi steady assumption. The wind pressure time history is transformed into the wind load time history of each beam-to-column connection and finally applied to the multi-scale finite element model. The fatigue assessment of the structural welded beam-to-column connections is carried out using the equivalent structural stress method.The analysis results based on wind pressure coefficient are compared with those based on shape coefficient. The results show that the power spectrum of fluctuating wind speed time history simulated by harmonic superposition method is in good agreement with the target spectrum in most frequency bands; The wind pressure coefficient results on the structural surfaces are close to the wind tunnel test results of Tokyo Polytechnic University with the same change trend. Therefore, in general, the numerical wind tunnel simulation results of the wind pressure coefficient of this structure are reasonable; The wind-induced fatigue calculation results based on the shape coefficient are close to those based on the wind pressure coefficient of different parts of the structural surface, which can meet engineering demands and are safer; The specified value of shape coefficient in Load Code for the Design of Building Structures GB 50009-2012 can be well applied to the calculation of wind-induced fatigue of welded joints of rectangular plane high-rise steel structures.
Formulae for Bearing Stress in Web of Crane Beam Under Wheel Load
TONG Gen-shu
2022, 37(11): 46-48.   doi: 10.13206/j.gjgS22093001
Abstract(0) PDF (798KB)(0)
Equation for bearing stress in web of crane beam under wheel load has been varied several times in the Chinese code for design of steel structures, and they were different from the counterparts in the codes of European, Russian and the United States. This paper introduces a closed form solution whose numerical results are in good agreement with Finite Element analysis. Formulae for the equivalent bearing length of two types of rails are presented.
ZHANG Li-jun, ZOU An-yu
2022, 37(11): 49-50.  
Abstract(0) PDF (537KB)(0)