Academic Journal of Science and Technology 
ISSN: 2771-3032 | Vol. 11, No. 3, 2024 

 

124 

Review	of	Research	Progress	on	Bearing	Capacity	of	
Steel	Pipe	Joints	
Shuo Xu, Wenyong Li 

School of Civil Engineering, Central South University of Forestry and Technology, Changsha, Hunan 410004, China 

 

Abstract: This paper summarizes the research progress of rectangular steel pipe or round steel pipe joints in recent years. This 
paper makes a comprehensive analysis from round steel pipe, square steel pipe and square steel tube. Through experimental 
study and finite element model analysis, the effects of the geometric parameters such as the main branch diameter (side length) 
β, the main section diameter (side length) and the branch wall thickness γ, and the τ on the ultimate bearing capacity and the 
seismic performance of the node are discussed. The study shows that the reasonable diameter, wall thickness and pipe length of 
the main and branch pipes can significantly improve the ultimate bearing capacity and seismic capacity of the steel pipe node. 

Keywords: Steel Pipe Node; Ultimate Bearing Capacity; Seismic Performance; Finite Element Analysis. 
 

1. Introduction  
In recent years, with the rapid development of urbanization 

in China, high-rise buildings can be seen almost everywhere, 
and the number of large-span buildings and super high-rise 
buildings, which are generally landmarks, has gradually 
increased, such as the Bird's Nest in Beijing, the Green Space 
Center in Wuhan, and the Zhuhai-Hong Kong-Macao Bridge. 
In this environment, more and more buildings use steel tube 
structure, such as: gymnasium, airport, station, warehouse, 
etc., so the steel tube structure has also been greatly developed. 
Round steel tube and square steel tube are the most common 
forms of steel tube structure. Round steel pipe is a kind of 
steel with open ends, hollow and concentric circular section. 
Compared with other types of steel, round steel pipe has the 
characteristics of closed section, arbitrary symmetry of 
section, large stiffness, beautiful appearance and so on. In 
addition, the cross section of the round steel pipe is 
symmetrical, and the moment of inertia of the cross section of 
each axis is the same, so the round steel pipe has good 
compression and torsion resistance. Square steel pipe usually 
refers to the steel with open ends, hollow and square section. 
Compared with other types of steel, the square steel pipe has 
the characteristics of light weight and good economy when 
the bending and torsional strength are the same. In addition, 
the square steel pipe also has many other advantages: (1) it 
has most of the advantages of round steel pipe, such as 
symmetrical section, beautiful appearance, etc.; (2) the form 
is simpler, the construction is more convenient, and more 
choices can be provided when the building is arranged; and 
(3) the form is diversified, the appearance and the inner wall 
are smooth and flat, and various requirements of people on 
the appearance can be greatly met. Because of these 
characteristics of steel pipe, steel pipe structure also has the 
characteristics of strong space, good integrity, large stiffness, 
light weight, beautiful, simple and so on. As the connection 
component in the steel tube structure, the steel tube joint bears 
the load in the plane and out of the plane, the destruction of 
the joint will generally lead to the overall destruction of the 
building structure, and the performance of the structure is 
directly related to the overall safety of the structure, so the 
steel tube joint occupies an extremely important position in 
the design of the steel tube structure. There are many joint 

forms of steel tube structure, such as X type, K type, Y type, 
T type, N type and so on. In practical engineering, the most 
commonly used forms of steel pipe joints are the main round 
and branch round steel pipe joints whose branch pipes and 
main pipes are composed of round steel pipes and the main 
square and branch square steel pipe joints whose branch pipes 
and main pipes are composed of square steel pipes. However, 
there are some special advantages for the joint of square steel 
tube and circular steel tube with square steel tube in the main 
pipe and circular steel tube in the branch pipe. (1) Compared 
with the main round steel pipe node, the main square round 
steel pipe node can be welded with the main pipe only by 
cutting the branch pipe simply, while the round steel pipe 
node can be welded with the main pipe only by cutting the 
branch pipe complicatedly under the same condition, so the 
square round steel pipe node is simpler and more economical 
than the round steel pipe node; (2) Compared with RHS joints, 
RHS joints have lower stress concentration level [2]. In 
addition, because there are no additional stiffening parts in the 
main square and support round steel pipe joints, it also has the 
advantages of convenient connection and less steel 
consumption. 

2. Research Status at Home and 
Abroad 

The research on the static behavior of traditional tubular 
joints can be summarized into two aspects: bearing capacity 
and stiffness. Because of the extensive application of steel 
pipe truss in practical engineering, and in these structures, the 
branch pipe connected with the tubular joint is mainly 
subjected to axial force, the earliest research on the static 
performance of T-shaped, K-shaped and other simple plane 
tubular joints is mostly carried out. Later, in order to meet the 
needs of architectural performance, structural stress, 
manufacturing and construction technology, there are more 
and more studies on joint deformation performance, 
hysteretic performance, fatigue performance, reinforced joint 
performance, fracture resistance performance and complex 
spatial tubular joints, including joint failure mechanism, joint 
flexibility, weld bearing capacity, stress and strain, energy 
dissipation and so on. 



 

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2.1. Research Status of Tubular Joints 
The research history of tubular joints is relatively long in 

all kinds of cross section tubular joints, the accumulated 
research data is more, and the research results are more 
mature. It is reported that the earliest research on plane 
circular steel tubular joints was the ultimate strength test of 
steel tubular joints carried out by the former West Germany 
in 1948. In the 1950s, the United States began to study the 
tubular joints of circular steel tubes. Since the 1960s, the 
research on tubular joints has been carried out in many 
countries. From the late 1960s to the early 1970s, the design 
codes of some countries and regions began to incorporate the 
design of circular tubular joints, and during this period, the 
application of circular tubular structures in building structures 
began to increase slowly. In the 1990s, the research and 
application of tubular structures and their joints became more 
and more extensive and in-depth. In 1984, Kurobane [3] 
considered that it was unreasonable to calculate the ultimate 
bearing capacity of joints by pure theoretical methods, and by 
using regression method, the experimental results of 73 X-
shaped tubular joints, 50 T-shaped tubular joints and 398 K-
shaped tubular joints were arranged, and the formula for 
calculating the strength of tubular planar joints was proposed. 
The formula can cover the calculation of the bearing capacity 
of circular tubular joints with the diameter of the main pipe 
ranging from 60 mm to 510 mm and the yield point of steel 
ranging from 270 MPa to 500 MPa, and has become the basis 
for the formulation of design guidelines by the Architectural 
Society of Japan and the International Committee for 
Research and Development of Tubular Structures. Lee and 
Wilmshurs [4] carried out numerical simulation on multi-
plane hollow circular tubular K-joints in 1994. Through the 
analysis and study of the results, the ultimate strength 
calculation formula of multi-plane hollow circular tubular K-
joints was given. In 1996, Lee and Wilmshurst [5] established 
a finite element model for spatial KK-shaped joints 
considering geometric and material nonlinearity, and obtained 
the ultimate bearing capacity of the joints, which laid the 
foundation for the study of the bearing capacity of spatial 
joints at that time. In 1998, Kang et al. [6] carried out 
experimental research and theoretical analysis on the bearing 
capacity of spatial TT-shaped circular tubular joints with 
compression on the chord. The test results showed that the 
axial compression on the chord significantly reduced the 
ultimate bearing capacity of the joints, but the finite element 
analysis underestimated the reduction of the bearing capacity 
of the joints caused by the axial compression on the chord. In 
1999, Dexter and Lee [7-8] carried out finite element 
simulation and loading test on hollow circular tubular K-
joints, and gave the parametric equation of static strength of 
hollow circular tubular K-joints. In 2001, Chen Yiyi et al. [9] 
carried out an experimental study on four X-type joints with 
different types of hollow circular tubular joints, and found 
that there are two main reasons for the failure of X-type joints 
with hollow circular tubular joints: (1) the plastic deformation 
of the main pipe is too large; (2) the tensile weld cracks, and 
for different types of joints, their failure modes are completely 
different. In 2003, Chen Yiyi et al. [10] took K-type, XK-type 
and TK-type hollow circular tubular joints as experimental 
research objects, carried out static loading on them, and took 
the corresponding load when the displacement of the joint 
reached 0.005 times of the diameter of the main pipe as the 
ultimate load of the joint. By analyzing the test results, it was 
found that in K-type, XK-type, When the two tubes in the K-

plane of the tubular TK joints are the main loaded tubes, the 
spatial effect should be considered. In addition, the modified 
formula of the bearing capacity of the tubular TK joints is 
given. In 2006, Gho et al. [12-14] carried out parametric 
analysis on 1296 fully overlapped N-shaped circular tubular 
joints, and conducted in-depth research on the failure mode 
and failure mechanism of the joints. In 2008, the scholar 
proposed a parametric formula for the bearing capacity of the 
above types of joints, and pointed out that the constraints at 
the end of the joints and the stress of the chord would not 
significantly affect the bearing capacity of the joints. In 2006, 
Tong Lewei and Chen Zhuo [15] carried out a static 
experimental study on a spatial KTT-shaped tubular 
overlapped joint with all branches welded along the perimeter 
of the intersection line of the joint and a spatial KTT-shaped 
tubular overlapped joint with the overlapped branches 
partially welded along the perimeter of the intersection line. 
The failure modes, load-deformation curves, strain and stress 
distributions, and ultimate strength of the two joints were 
compared and analyzed. The results show that the difference 
of welding methods has little effect on the ultimate strength 
of the joints, but leads to the inconsistency of the failure 
modes of the joints. In 2010, Chen Yu et al. [16] carried out 
finite element analysis on the overlapped hollow circular tube 
KT-type joint, studied the whole process of deformation and 
failure of the specimen and the final failure mode of the 
specimen, and derived a parameter formula to calculate the 
ultimate bearing capacity of the overlapped hollow circular 
tube KT-type joint. In 2017, Lan et al. [17] carried out 
experimental tests on high-strength steel hollow circular 
tubular X-joints, and compared the experimental results with 
the design strength calculated in the current CIDECT code 
and EN 1993-1-8 code. It is found that the CIDECT 
specification is more accurate than the EN 1993-1-8 
specification in the design of high strength steel hollow 
circular tubular X-joints. In 2019, Hu Xibing, Liu Xueyao et 
al. [18] used finite element numerical simulation to study the 
mechanical properties of high-strength steel N-type lap joints, 
analyzed the influence of failure mode, geometric parameters 
and chord axial force on the ultimate bearing capacity of 
joints, and compared the simulation results with the current 
code, and proposed a formula for the correction factor of the 
bearing capacity of joints. In 2020, Qian et al. [19] carried out 
static loading experimental study and finite element analysis 
on the hollow circular tube X-shaped joint with larger wall 
thickness as the research object, and proposed the calculation 
formula for the ultimate bearing capacity of the thick-walled 
hollow circular tube X-shaped joint through the analysis of 
the test results and finite element parameters. In 2020, Shang 
Renjie et al. [20] carried out finite element analysis on the 
axial force of the branch pipe of the T-shaped tubular joint of 
the circular steel tube, and concluded that when the branch 
pipe of the tubular joint is subjected to axial force, the 
relationship between the local deformation of the joint and the 
axial force of the branch pipe is linear at the initial stage, and 
the overall analysis of the structure can be considered as linear 
elasticity. 

2.2. Research Status of Square Tubular Joint 
The production and application of square steel pipe is later 

than that of round steel pipe. Square steel pipe began to appear 
in Britain in the 1950s. However, as a structural member, the 
square steel tube also has its own unique advantages: as far as 
the mechanical performance of the section is concerned, it 



 

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basically has all the advantages of the circular tube, because 
only the end face of the connecting rod needs to be cut flat, 
the processing and manufacturing of the connection node 
between the square steel tube sections is much easier than that 
of the circular tube node. Of course, although it is easy to 
manufacture, the load transfer is very complex because of the 
uneven stiffness distribution in the corner and middle area of 
the joint section, and the uneven degree of stress distribution 
in the joint section is more than that in the circular tube 
section. Similarly, domestic and foreign scholars have carried 
out a large number of theoretical and experimental studies on 
square tubular joints, and have achieved very fruitful results, 
which have been widely used in engineering practice. In 1982, 
Packer et al. [21] conducted an experimental study on hollow 
square K-joints, established a plastic model for them, and 
derived a parameter equation for calculating the ultimate 
bearing capacity. The accuracy of the parameter equation was 
verified by comparison. In 2000, Zhao [22] took the cold-
formed hollow square T-joint as the research object and 
carried out the loading test on it. The results showed that the 
β value had a greater impact on the ultimate displacement of 
the joint, and proposed the calculation formula of the ultimate 
bearing capacity of the joint under two failure modes. In 2004, 
Wu Zhenyu and Zhang Yaochun [23] established a nonlinear 
finite element analysis model for T-shaped RHS joints with 
equal section widths of main and branch tubes, and 
investigated the failure modes of the joints under different 
geometric parameters and different compression levels of the 
main tube axis, as well as the influence of the above factors 
on the static performance of such joints. At the same time, the 
formulas for calculating the bearing capacity of RHS T-joints 
with the same section width of main and brace in Chinese 
Code for Design of Steel Structures (2003 edition) are 
compared with the formulas in foreign codes or design 
guidelines and the results of nonlinear finite element analysis. 
The results show that the formulas in Chinese code are 
reasonable and feasible In 2008, Wu Zhenyu et al. [24] 
conducted an experimental study on the hysteretic behavior 
of hollow square T-joints, and obtained the failure mode and 
hysteretic curve of the joints. It was found that the failure of 
the joints was due to the excessive deformation of the 
compression joints of the branch pipes under reciprocating 
loads, and the cracks at the welds of the tension joints. In 2009, 
Moazed et al. [25] carried out finite element analysis on thin-
walled hollow square T-joints subjected to in-plane bending. 
The analysis results showed the maximum stress position of 
the joint, and the calculation formula of bending stiffness was 
given according to the finite element analysis results. In 2009, 
Shao Yongbo et al. [26] carried out finite element numerical 
simulation and dynamic test on the square T-joint with 
thickened main pipe wall, and found that the hysteretic 
performance of the joint with thickened main pipe wall is 
better than that of the ordinary joint. In 2017, Lv Yuxia and 
Shao Yongbo [27] also studied hollow square tube T-joints 
under high temperature, and carried out experimental research 
and finite element analysis. In 2017, Chen Hengchao et al. [28] 
applied cyclic loading to four hollow square tube T-joints with 
inner diaphragms to study their seismic performance. In order 
to compare, two ordinary square tube T-joints were designed. 
Through comparison, it was found that the addition of inner 
diaphragms could significantly increase the ultimate bearing 
capacity of the joints, and the seismic performance of the 
joints could also be improved. In 2017, Xia et al. [29] carried 
out numerical simulation and experimental research in order 

to study the axial hysteretic behavior of square T-joints 
reinforced by double-layer plates, discussed the hysteretic 
curve, skeleton curve, energy dissipation capacity, ductility, 
strength and hysteretic mechanism of the joints, and analyzed 
the influence of double-layer plate reinforcement on the 
hysteretic behavior of the joints. It is found that the double-
layer plate reinforcement can effectively prevent the 
occurrence of cracks, ensure the integrity of the tube, and 
improve the strength of the joint, but the energy dissipation 
capacity and ductility of the joint will be somewhat reduced. 
It is also shown that the ratio of the width of the branch pipe 
to the chord pipe and the ratio of the width of the double-layer 
plate to the chord pipe are the key parameters affecting the 
load transfer mechanism and failure mode of the joint. In 
2018, Chen Yadong et al. [30] applied axial pressure and 
cyclic load to the branch pipe of hollow square T-joint with β 
value of 0.4 and 0.8, and analyzed the influence of β value on 
the hollow square T-joint. The results showed that the square 
T-joint with β value of 0.4 and 0.8 was buckling failure of the 
main pipe under axial pressure, while it was tearing failure of 
the joint under cyclic load. 

2.3. Research Status of Square and Round 
Steel Tube Joints 

The square and round steel pipe node is a general term for 
the node with the main pipe being square pipe or rectangular 
pipe and the branch pipe being round pipe (referred to as 
"square main pipe and round branch pipe node") and the node 
with the main pipe being round pipe and the branch pipe being 
square pipe or rectangular pipe (referred to as "round main 
pipe and square branch pipe node"). In the traditional steel 
tube truss structure, the main tube and branch tube are usually 
designed as the same type of section, that is, both of them are 
circular tubes or rectangular (square) tubes. For the various 
forms of joints, scholars at home and abroad have carried out 
a lot of research, and formed a more systematic calculation 
method of bearing capacity. However, there are few 
researches on the joints with square chord and circular branch 
and the joints with square chord and square branch. 

In 2001, Liu Jianping et al. [31-33] carried out finite 
element analysis of K, T and Y-shaped circular steel pipe 
joints by using ANSYS software, investigated the mechanical 
properties of the joints, obtained the failure forms, ultimate 
bearing capacity and plastic development of the joints, deeply 
analyzed the law of influence of geometric parameters on the 
mechanical properties of the joints, and proposed the 
reinforcement method of the joints on this basis.  However, 
the research is based on finite element analysis, and no 
experimental research has been carried out.   

In 2003, Mashiri and Zhao[34] conducted in-plane static 
bending tests on T-shaped joints of thin-walled hollow and 
square steel pipes. The results showed that the joint failure 
was due to the buckling of the main pipe surface. After large 
deformation, the main pipe cracked, causing these joints to 
reach peak load, and a joint yield line model was 
established.  Based on the plastic mechanism analysis of yield 
line theory, a formula for calculating the ultimate strength of 
T-shaped joints of hollow and square steel pipes is derived. It 
is also shown that there is a good agreement between the 
predicted ultimate strength and the experimental ultimate 
strength.   

In 2004, Wan Haiying et al. [35] used Nastran to conduct 
elastoplastic large-deflection numerical simulation analysis 
of Y-shaped circular intersecting pipe joints, understand the 



 

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displacement change and stress distribution of intersecting 
joints at each loading stage and the development of plastic 
zone during the whole loading process, and investigate the 
failure forms of intersecting joints.  The relative theory of 
orthogonal experimental design is introduced to 
quantitatively analyze the Y-shaped square and square 
intersecting joints, and the variation law of ultimate bearing 
capacity and geometric parameters is obtained.  The research 
on the node mainly focuses on the parameter analysis and 
does not compare with the calculation result of the standard 
formula.   

In 2010, Chen Yu and Tang Jumei [36] carried out finite 
element numerical simulation with K-shaped joints of hollow 
circular steel pipe. The results showed that the ultimate load 
of hollow circular steel pipe K-shaped joints was greatly 
influenced by γ value and τ value, while the β value was 
relatively small. The parametric equation for calculating the 
ultimate load of the joints was also fitted, and its rationality 
and accuracy were verified. 

In 2011, Chen Yu and Tang Jumei [37] conducted 
experimental research and finite element analysis on K-
shaped joints of hollow and square steel pipes. The research 
showed that increasing the wall thickness of branch pipes 
could change the failure mode of joints. The bearing capacity 
calculation formulas of circular and square K-shaped joints in 
current norms were not applicable to K-shaped joints of 
circular and square steel pipes, and the experimental results 
were greater than the calculated values of the formulas. 

In 2011, Deng et al. [38] carried out finite element 
simulation on KT shaped joints of circular steel pipes. Based 
on the analysis of experimental data, a formula was given to 
calculate the bearing capacity. 

In 2012, Shu Xingping [39] used finite element software to 
verify the failure mode, deformation process and bearing 
capacity of 8 N-shaped main square branch circular lap steel 
pipe joints and 2 gap steel pipe joints, analyzed the influence 
of geometric parameters on the ultimate bearing capacity, and 
concluded that the inner concealed part was not welded and 
had little influence on the bearing capacity of joints under 
pressure from the lap branch pipe.  At the same time, multiple 
linear regression method is applied to fit the revised 
calculation formula of the bearing capacity in the code. In 
particular, it is pointed out that the calculation formula of the 
bearing capacity of the joint of the N-shaped square branch 
pipe in the current code at home and abroad is not applicable 
to the local buckling failure mode of the main pipe.  Moreover, 
the formula does not take into account the influence of factors 
such as whether the inner concealed part is welded or not, the 
nature of the branch pipe axial force and the main shaft force, 
etc., so it needs to be improved. 

In 2013, Tong et al. [40] took T-shaped joints of hollow and 
square steel pipes as the research object, conducted tests and 
finite element simulation, and analyzed the stress distribution 
of joints at the weld.  

In 2015, Wang Wei et al. [41] conducted an experimental 
study on the axial tensile properties and strength of X-shaped 
joints of hollow and circular steel pipes with 5 non-rigid 
connections and 3 rigid connections, and proposed a formula 
for predicting weld strength according to the effective length, 
which also proved that the formula met the reliability 
requirements of the AIC-LRFD method. The study mainly 
focused on the tension of joint welds.  No studies were carried 
out under tube pressure. 

In 2016, Yang Wenwei et al. [42] numerically analyzed the 

influence of geometric parameters such as lap rate OV, 
diameter-width ratio β of main square branch, thickness ratio 
τ of main branch, width-thickness ratio γ of main branch and 
Angle θ of main branch on the ultimate bearing capacity of 
such joints, and obtained the influence law of each parameter 
on the bearing capacity of joints. 

In 2017, Guo Teng [43] for the first time studied and 
analyzed the hysteretic performance, ductility, stiffness and 
energy dissipation capacity of the joint reinforced by circular 
K-type main pipe grouting concrete with main square 
support.  Secondly, the mechanical properties of K-type 
square joints under two different strengthening modes of the 
main pipe wall with casing and the main pipe with concrete 
grouting are compared by variable parameters, and the 
ultimate bearing capacity of the joint is the best strengthening 
measure. 

In 2018, Yuan Zhishen [44] studied the ultimate bearing 
capacity of the N-shaped main square branch circular lap joint 
under the influence of the main shaft force, established a finite 
element model based on the test, calculated the parameters of 
the influence of the main shaft force on the joint, and 
compared the calculation results with the current standard 
formula.  The suggested formula of the influence parameter 
of the main axial force on the bearing capacity of the N-
shaped main square branch circular lap joint is presented. 

In 2021, Yuan Zhishen and Gan Yu et al. [45] studied the 
relationship between the static properties of the gap joints of 
N-shaped main square-supported round steel pipes and the 
mechanical properties of the lap joints, conducted a 
comparative test between the gap joints of N-shaped circular 
steel pipes and the lap joints, and found that the bearing 
capacity of the gap joints was lower than that of the lap joints 
of the same diameter.  The linear regression method is used to 
fit the modified calculation formula of bearing capacity in the 
present line specification. 

In 2021, Li Xueting et al. [46] conducted an ultra-low cycle 
fatigue test on X-shaped square steel pipe, studied the failure 
mode of joints, analyzed the strain distribution law at joints, 
and obtained the fatigue life of joints. They found that joints 
with stiffeners in the main pipe had poor deformation ability 
and showed the characteristics of tensile fracture failure. 

Packer[47] first proposed in his doctoral thesis in 1978 
that:  Since the ratio of section circumference and area of 
square and round pipes with the same side length and 
diameter is π/4 when the wall thickness is thin, when 
calculating the bearing capacity of round branch pipe joints 
of square pipes, the size of round branch pipe can be 
multiplied by π/4 to convert into equivalent square pipe size, 
and then the bearing capacity calculation formula of square 
pipe joints can be substituted.  However, when this concept is 
applied to the semi-empirical design formula in national 
norms, it is not the size of the round pipe multiplied by PI /4 
to convert the equivalent square pipe size into the bearing 
capacity of the joint of the square pipe, but directly assume 
that the side length of the square pipe is the diameter of the 
round pipe.  The bearing capacity of square branch pipe joints 
is obtained by substituting the bearing capacity formula and 
multiplying by π/4.  Moreover, there is no comparison of test 
data in a large number of specifications and design guidelines 
that adopt this "branch conversion method" [48]. 

3. Conclusion and Prospect 
To sum up, in recent years, domestic and foreign scholars 

have carried out a large number of experimental studies and 



 

128 

theoretical analyses on the mechanical properties of tubular 
joints, but the studies mainly focus on joints where the main 
and branch pipes are both round or rectangular, and mainly 
focus on finite element parameter analysis, and their 
mechanical properties and experimental studies are scarce. 

Compared with the research of circular pipe joints and 
rectangular pipe joints, the research of main square-supported 
round steel pipe intersecting joints at home and abroad is not 
sufficient. Especially in the joint bearing capacity calculation, 
the bearing capacity calculation formula of the joint 
intersecting the main square-supported round steel pipe 
directly uses the simple geometric relationship between the 
thin-walled round pipe and the thin-walled square pipe, and 
locally modiifies the bearing capacity calculation formula of 
the rectangular pipe joint, but the formula has not been 
verified by enough tests. From the existing research results, 
the joint bearing capacity calculated in this way is sometimes 
too conservative, and sometimes too unsafe. On the one hand, 
the advantages of the intersecting joints of the main square 
supported round steel pipe cannot be fully utilized, on the 
other hand, the safety and reliability of the design cannot be 
fully guaranteed, so the popularization and application of the 
main square supported round steel pipe structure is limited. 

Therefore, it is an urgent problem to study the branch 
transformation method of the main square and branch circle 
intersecting joints, and it is also an important topic to further 
improve the current design specification. 

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