2022 Vol. 37, No. 10

Flexural-Torsional Buckling Capacity of Beam-Columns with H-Section
ZHOU Jia, TONG Gen-shu
2022, 37(10): 1-23. doi: 10.13206/j.gjgS22041701
A theoretical study is carried out for the flexural-torsional buckling capacity of beam-columns with H-section. The main works and developments are as follows: 1)Comparisons are carried out between the formulae used in the codes of GB 50017—2017, AISC LRFD 2016, Eurocode 3 part 1-1 and the formulae derived in the flexural-torsional theory, possible improvements are pointed out. 2)Second-order analysis is carried out for the beam-columns 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. 3)Plastic interactive relations are obtained for the axial force and bending moments about the strong axis and about the weak axis respectively. Fitting curves with good accuracy are provided for interaction equations of axial force-bending moments about the strong axis and about the weak axis. 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. 4)Based on the well-accepted and 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. 5)Introducing this equivalent initial deflection 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, the interactive equation of beam-column is derived for flexural-torsional buckling. But this is an upper bound solution of the interactive equation because the process of elastic-plastic development has not been included. After amplifying the second order in-plane bending moment, and further amplifying the out-of-plane bending moments and bi-moment to consider the elastic-plastic development, the obtained equation is applicable. 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 close to the interactive relation for elastic flexural-torsional buckling when the slenderness is large. Comparison shows that the current formula in GB 50017-2017 is on the safe side. The paper proposes also a new formula based on the observation of the derived curves, and lying between the strength interaction curves and the elastic buckling interaction curves.
Comparative Study on Structural Performance of Box-Type Hollow Roof and Traditional Roof
ZHAO Yu-ran, ZHENG Teng-teng, ZHAO Cai-qi, YUAN Liang-jian
2022, 37(10): 24-31. doi: 10.13206/j.gjgS22052901
In this paper, a new type of spatial structure-aluminum honeycomb plate box-type hollow roof structure is proposed. It is a pentahedral or hexahedral box-type hollow roof structure composed of lightweight and high strength aluminum honeycomb plates spliced by special connectors. It not only has the characteristics of tension structure of light weight and high strength, but also absorbs the advantages of high strength and high stiffness of rigid structure. In order to explore the advantages of the structural performance of the box-type hollow roof compared with the traditional roof, based on the bearing capacity test of the aluminum alloy honeycomb plate box-type hollow roof, the mechanical properties of the box-type hollow roof were studied. Two finite element analysis models, the complete coordination model and the coupling model, were established by ANSYS software, and the effectiveness of the finite element analysis model was verified. The mechanical properties of three-dimensional grid single-layer reticulated shell, orthogonal pyramid double-layer reticulated shell, pentahedral box type hollow roof without bottom plate and hexahedral box-type hollow roof with bottom plate were analyzed, and its economy was analyzed. The results show that the aluminum alloy honeycomb plate box-type hollow roof has good connection performance and high spatial overall stiffness. The ultimate bearing capacity is as high as 11 times of the self-weight of the structure, and the stable bearing capacity is about 3.6 times of the self-weight. The deformation of the structure during buckling is minimal, and the deflection-span ratio is only 1/800. The coupled model is suitable for the finite element analysis of box-type hollow roof structure. It is consistent with the test in the elastic stage, and its ultimate bearing capacity is only 15% higher than the test value. It can be used as the design value of structural bearing capacity after considering the safety factor. In terms of static performance of reticulated shell structure, the mid-span deflection value and component stress ratio of box-type hollow roof structure with bottom plate are the smallest among the four, showing high bearing capacity and deformation resistance. In the case of similar mid-span deflection values, the component stress ratio of latticed shell with bar system structure is generally greater than that of plate system structure, and the spatial force transmission of plate system structure is more reasonable. In terms of the economy of the reticulated shell structure, for the same size of the reticulated shell, the box-type hollow reticulated shell without bottom plate has the smallest structural weight, while the three-dimensional grid type single layer reticulated shell has the largest building space. With the increase of the shell plane size, the average weight of the structure decreases, and the difference in the building space is also increasing. On the premise of satisfying the mechanical performance of the structure, considering the building space and structural weight, the box-type hollow structure can obtain relatively good economy. In terms of the dynamic performance of reticulated shell structure, the frequency of plate structure is generally higher than that of bar structure under the same conditions. The plate structure has the characteristics of light weight and high strength, and its mass and stiffness distribution are more reasonable than that of bar structure. The mechanical properties and economic indexes of box-type hollow roof are excellent, but they have their own applicable span range. The box-type hollow structure without bottom plate is suitable for reticulated shells with span less than 20 m, and the box-type hollow structure with bottom plate is suitable for reticulated shells with span of 20-30 m because of its greater stiffness.
Load Bearing Capacity and Economic Analysis of Cold-Formed Stiffened High-Strength Steel Beams
WANG Wei-yong, WANG Zi-qi, TAN Xing-kui, PANG Shi-yun, HUANG Dan, HUANG Yong-dong
2022, 37(10): 32-42. doi: 10.13206/j.gjgS22033101
With the progress of steel-making technology, high-strength steel is gradually applied in the construction field. Compared with ordinary steel, high-strength steel has the advantages of saving steel, reducing section size, reducing structural weight, and improving seismic performance. Local buckling is easy to occur for wide and thick plates under pressure, which reduces the bearing capacity of the members. The setting of stiffening ribs can change the mechanical properties and buckling behavior of the original plate, improve the comprehensive rigidity of the stiffened plate, and the cold-formed stiffening has the advantages of easy production and low processing costs. In order to investigate the load bearing capacity and economy of high-strength steel beams with cold-formed semi-circular stiffeners, the bending analysis model of H-shaped and box-section steel beams with flange and web stiffening was established after verifying the accuracy of the finite element model by comparing the test results of H-shaped steel beams clamped at both ends and loaded at a single point in the mid-span. Four H-section steel beams with different section sizes were selected to investigate the influence of flange stiffening on the strength and stable bearing capacity of steel beams. Three section types, namely, H-section, upper flange stiffening, and both upper and lower flanges stiffening, were simulated by numerical simulation, and the bending strength bearing capacity of steel beams with different section types was compared. By changing the thickness of upper and lower flanges, the thickness of flanges was obtained when the ultimate bearing capacity of steel beams with grade Q355 H-section was the same. The corresponding proportion of steel quantity reduction under different sizes was obtained. The cross-sections of steel beams with stiffened ribs in H-shaped and box-shaped webs were optimized by increasing the thickness of the flanges while keeping the steel consumption of the cross-section unchanged, and comparing the flexural strength load capacity of the stiffened cross-section of Q355 grade webs with that of the unstiffened H-shaped cross-section steel beams for different optimized cross-section sizes.By optimizing the section size, when the same load bearing capacity was obtained, the amount of steel used in the stiffened high-strength Q690 steel beam was less than that of Q355 steel beam. The results show that the upper flange of H-shaped steel beam stiffened outward has higher flexural strength bearing capacity than that stiffened inward, and the flange stiffened will significantly reduce the overall instability bearing capacity; the flexural strength bearing capacity of flange stiffened Q690 steel beam with the same cross-sectional area is more than twice that of Q355 steel beam, and the steel consumption of flange stiffened Q690 steel beam with the same strength bearing capacity is about half that of Q355 steel beam; the thickness of the web is reduced and a stiffener is added to ensure that the flange thickness is increased under the condition of constant steel consumption, and the strength failure bearing capacity of the steel beam is higher; H-shaped Q690 steel beam adopts optimized section, which saves about 40% of steel consumption under the condition of ensuring that the bearing capacity is equal to that of Q355 steel beam; the box Q690 steel beam adopts optimized section, and the steel consumption can be saved by about 30% under the condition of ensuring that the bearing capacity is equal to that of Q355 steel beam.
Construction Technology
Common Installation Methods and New Ideas of Long-Span Spatial Grid Structures
ZHANG Zai-chen, JIA Xin-juan, HU Chen-xi, MO Hai-zhao
2022, 37(10): 43-49. doi: 10.13206/j.gjgS21100901
Spatial grid structure is widely used in large-scale public construction projects in recent years, such as terminal buildings, convention and exhibition centers and gymnasiums, etc. With the growing emergence of new structural form, on-site installation is also facing great challenges. Through combing the typical cases of spatial grid structure in recent years and analyzing the advantages and disadvantages of several common installation methods, it is found that the existing installation methods have certain limitations in practical application. So it is urgent to carry out in-depth research on the new installation technology. Guangzhou football field is built in accordance with international FIFA standards with 100 000 seats. It is a rare sports and cultural complex project in China that combines stadium and business and has a basement under the center of the field. The project design inspiration comes from “twin lotus flowers on one stalk”, take its “bud and tightly embrace” beautiful form, unique shape. The highest point elevation of the steel canopy structure is 88.6 m, and the maximum cantilever length is about 91 m. Three layers of diamond petal shaped blocks are arranged from top to bottom and the petal shape of each layer is composed of 12 units. The length of a single member is 40~64 m, forming a giant ribbed space folded plate grid structure. After the preliminary analysis of the existing methods of high-altitude in-situ installation and cumulative sliding installation, it was found that there were many problems, such as large amount of measures, many cross operations and difficult quality control. Referring to the idea of bridge vertical rotation installation, a negative angle vertical installation method of spatial grid structure was proposed. The core steps were as follows: low position assembly-vertical turning in place-nesting and closing-synchronous and graded unloading. Then the key points such as vertical rotation interface and unit division, vertical rotation system design and hinge structure were analyzed. From this, MIDAS/Gen software was used to carry out construction simulation calculation of deformation and force in key working conditions of vertical rotation process, and compared with the results of design conditions, so as to verify the operability of vertical rotation installation method. The results showed that the simulated deformation values of steel canopy after unloading were basically consistent with the design values. Compared with conventional installation methods, vertical rotating installation technology had certain advantages in safety, quality, quaitity of temporary measures and schedule control, and had a wide application prospect and practical value in the installation of large-span spatial grid structures.
Design Discussion
Rigidity of Steel-Concrete Composite Beams
TONG Gen-shu
2022, 37(10): 50-52. doi: 10.13206/j.gjgS22092204
The equivalent bending rigidity of steel-concrete composite beam was derived, it was found that the rigidity was composed of two parts: one is the bending rigidities of the slab and the steel section about their own centroid axes, the other was the truss stiffness whose upper chord was the slab and lower chord was the steel section and the studs were the web members, and a simple calculated formula was proposed. The deflection due to the shear strain of the steel web and the interfacial shear-slip stiffness of the stud are also presented.
Hot Spot Analysis of Steel Structures
ZOU An-yu
2022, 37(10): 53-53.