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members adopted circular hollow sections (CHS) orwelded rectangular hollow sections (RHS). One sideof this megatruss is supported on two columns, andthe other side is supported on the transfer trusswhich transfers the load to the bottom columns. Thespan between the supports is 91.3m, and the cantile-ver spans from each support are 26.91m and 17.41m,respectively. The maximum height of the truss is

12.4m.A Vierendeel truss is a type of truss without di-agonals, in which shear forces are resisted by thevertical web members and chords, acting as an mo-ment-resisting frame. It may have diagonals in some

bays in some designs, but may also be designed torely totally on the verticals. The CHS roof truss ofChongqing Jiangbei International Airport Terminal(Fig. 2) is an example of this type of tubular struc-tures.

The same construction can be done with spatialsystem.

No. 3 Terminal of Beijing Capital InternationalAirport (Fig. 3) is a project matching with the Bei-

jing 2008 Olympic Games. The roof structure of theproject belongs to a slightly bending hyperboloidalvacuum triangle pyramid type space truss. Thelength from south to north is 958m, the width fromeast to west is 775m, and the elevation of the highesttop reaches 42m. The space truss owns over 12,600tubular joints and over 50,000 components with dif-ferent sizes, including about 4,300 bolted spherical

joints and over 8,300 welded hollow spherical joints.

Solid steel pin nodes were adopted in the supports.

Figure 1. Shanghai F1 International Circuit.

Figure 2. Chongqing Jiangbei International Airport Terminal.

CHS space trusses are commonly used as themain structural system in super high steel TV towersin China, such as the 336m high Heilongjiang Dra-gon Tower (Fig. 4a). It is the highest steel tower inAsia and the 2nd highest in the world. Besides, inthe recent years, space tubular trusses are beingwidely used in high electricity transmission towersin China. By the end of 2007, approximately one

hundred high electricity transmission towers havebeen built in China, 50 percent of which are spacetubular trusses. Figure 4b gives a typical example ofhigh electricity transmission tower with 215m high.The maximum tube diameter at the tower footreaches 1,580mm.

The main reasons of adopting CHS members inhigh steel towers are: (1) wind load is the dominatedload for high towers and the wind pressure coeffi-cient for CHS is lower than any other types of crosssections; and (2) axial compression force is the dom-inated force in the main structural members. CHS is

central symmetric and has the same radius of gyra-tion about any axis of the cross section.

2.2 Frame-type tubular structuresFrame-type tubular structures can be divided intotwo subclasses, i.e. high-rise moment resisting tubu-lar frames and space frame tubular structures.

Figure 3. No.3B Terminal of Beijing Capital International

Airport

(a) (b)

Figure 4. Space tubular truss towers, (a) Heilongjiang DragonTower and (b) Yamen electricity transmission tower.

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High-rise moment resisting tubular frames are de-fined as rigid frames adopting continuous tubularcolumns or concrete filled tubular (CFT) columns asmain bearing elements. Guangzhou New TV Toweris a high-rise tubular frames under construction inChina (Fig. 5). It consists of a main tower of 454mheight and an antenna mast of 156m, totaling 610min height. After completion of the project, it will be

the highest tower around the world. The toweradopts 24 oblique straight cone-shaped steel pipecolumns filled with concrete, 46 ring tubular beamsand 24 oblique tubular supporting. The sections ofcone-shaped steel pipe are 2,00050~1,20030,the steel material includes Q345GJC and Q460GJC.The consumption of the steel for the project totalsabout 50,000 tons.

West Tower of Guangzhou Twin Towers (Fig. 6)is also a representative moment resisting tubularframe. The project covers an area of 449,000m2.There are 103 floors on the ground for the main

tower with 432m height. The tube-in-tube structuralsystem was adopted. The outer tube is composed ofoblique grid CHS columns and the inner tube is aconcrete core tube. The plane size is a centrosym-metric equilateral triangle with round-corners. CHStube ranges from 1,80055~70020.

Figure 5. Guangzhou New TV Tower.

Figure 6. West Tower of Guangzhou Twin Towers.

Compared with high-rise moment-resistingframes, space frames are another class of frame-typetubular structures. They usually have irregular con-figuration and demonstrate a frame behavior withsignificant spatial load transferring mechanism. Na-tional Stadium is the main stadium of Beijing 2008Olympic Games (Fig. 7), adopting frame-type struc-ture formed by 48 huge tubular trusses. The stadium

has a plane projection size of 323.3m 296.4m,maximum elevation of 68.5m and minimum eleva-

tion of 42.8m. The structure is composed of bend-ing-torsion members and straight members withwelded box section. The maximum size of the boxsections of frames is 1,200mm, and the maximumthickness is 110mm. Most materials are Q345D andQ345GJD-Z25, and the material with higheststrength is Q460E-Z35. The column base uses GS20Mn5V casting steel joints.

Polyhedron space frame structure with EFTEcladding is adopted in the National Swimming Cen-

ter Water Cube. In which, rectangular hollow sec-tions are used as chords, circular hollow sections areused as web members and welded hollow balls areused as joints. Although the form of the new struc-ture is like space truss, the member behavior is en-tirely different from the truss members which mainly

bearing axial force. The joints of the polyhedronspace frame are rigidly connected and the membersare space frame elements. Element forces contain

bending moment, axial force, shear force and tor-sional moment. The moment stress is larger than the

axial stress.

Figure 7. National Stadium (nicknamed Birds Nest).

Figure 8. National Swimming Centre (nicknamed Water Cube).



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2.3 Lattice shell tubular structuresLike space trusses, lattice shell structures are three-dimensional skeletal structures. They are now themost widely used tubular structures for long-span

buildings in China.The main building of the National Grand Theater

consists of an exterior shell, within which are a2,416-seat opera house, a 2,017-seat concert hall, a

1,040-seat theater, a lobby and other supporting fa-cilities. The exterior is a shell in the shape of a halfellipsoid with a long east-west axis of 212.20 metersand a short south-north axis of 143.64 meters. It is46.285 meters tall, and it reaches to a maximum un-derground depth of 32.50 meters. Most of the shell iscovered by titanium panels, and it is broken in themiddle by a curtain of glass that opens graduallyfrom top to bottom.

Guangzhou Opera will be a landmark architecturein Guangzhou City of China. It adopts Double-

Gravel-based irregular geometric configuration,covering an area of 42,000m2. The periphery of thebuilding adopts three-dimensional grids folded plateand single layer reticulated shell structures. Allmembers of this structure are thin-walled box girder.Rigid joints made of cast steel are used where planesintersect. The highest weight of the single joint is 37tons and the longest one is 12m. The consumption ofsteel totals 10,000 tons, including 1,200 tons of steelcasting.

Figure 9. National Grand Theater (nicknamed Big Egg).

Figure 10. Guangzhou Opera.

3 RECENT ADVANCES IN THE RESEARCHOF TUBULAR JOINTS IN CHINA

One important difference of tubular structures fromother steel structures lies in the design of tube-to-tube connections. Connections between hollow sec-tion members are usually configured by welding onemember directly to the surface of the other, where

possible, without any exposed stiffening or reinforc-ing element. Conventional design procedures appli-cable to welded plate-to-plate connections can not beapplied to the design of these connections. With thevigorous application of tubular structures in practicalengineering in China, fruitful research of both theo-retical and practical significance has been carried outon tubular joints. Some of these are described below.

3.1 Non-rigid behavior of tubular joints and inter-action with global performance of tubular

structuresIn engineering practice, tubular joints are usually as-sumed pinned or rigid. Recent research showed thattubular joints may exhibit non-rigid behavior underaxial or bending loads (Fig. 11). It may have signifi-cant influence on the behavior of Vierendeel trussand single-layer lattice shell structures.

Recent investigations on non-rigid behavior oftubular joints include experimental investigations onCHS X- and KK-joints under in-plane bending orout-of-plane bending loads on the brace (Chen &

Wang 2003, Wang et al. 2007). Test results showedthat the joints primarily failed by excessivedeformation and punching shear cracking at the weldtoe. It is found that the stiffness ratio of theconnection to the brace member is a critical factor toclassify this joint to be rigid or semi-rigid.Parametric formulae for predicting tubular jointrigidities are proposed, which are based on numeri-

Compression Tension

In-plane bending Out-of-plane bending

Figure 11. Non-rigid deformation under axial or bending loads.



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cal investigations through systematic variation of themain geometric parameters (Wang & Chen 2005).By considering the deformation patterns of respec-tive parts of Vierendeel lattice girders, the boundary

between rigid and semirigid tubular connection isbuilt in terms of joint bending rigidity. In order toinclude characteristics of joint rigidity in the globalstructural analysis, a type of semirigid element

which can effectively reflect the interaction of twobraces in K joints is introduced and validated. Thenumerical example of a Warren lattice girder withdifferent joint models shows the great effect of tubu-lar joint rigidities on the internal forces, deformationand secondary stresses (Wang & Chen 2005). A fur-ther study is in process on a new classification sys-tem of tubular joints based on the global perform-ance of CHS lattice shell structures.

3.2 Seismic behavior of tubular jointsMany large-span tubular truss applications now existin regions of high seismic risk in China. Unlikecommon beam-column connections in moment re-sisting frames, unstiffened tubular joints sometimeshave lower capacity than adjacent tubular members.In order that the inelastic seismic performance oftruss structures can be evaluated properly, it is nec-essary to study the hysteretic behavior of tubular

joints.A series of cyclic loading tests of CHS T-, K-,

and KK-joints were performed to understand the

seismic properties of these joints (Wang & Chen2007, Chen & Zhao 2007) (Fig. 12). Some of thenew findings were as follows: (1) Monotonic load-deformation curves can cover the skeleton of thehysteretic curves for the joints having the same ge-ometry, but the ductility will deteriorate under cyclicloading. (2) Both member failure mechanism in theform of brace yielding and joint failure mechanismin the form of chord wall plasticity demonstrategood energy dissipation capacity, if weld crackingcan be prevented or delayed. For proper design ofweld, stress distribution around intersection weldsshould be further studied, and seismic design criteriaof tubular joints should be established pertain tostructural deformability.

Figure 12. Cyclic loading test of a multiplanar CHS KK-joint.

3.3 Behavior of inner-stiffened tubular jointsAlong with the development of large-span spatialstructures, inner-stiffened tubular joints are moreand more applied to engineering projects of China. Ithelps to improve both strength and rigidity of the

joint, as well as to keep its original appearance.A number of experimental and analytical investi-

gations into inner-stiffened tubular joints are found

in recent years, including CHS joints with multiplebraces (Tong et al. 2007), RHS T-joints (Yan et al.2007), and CHS brace to RHS chord joints (Cao &Yao 2008).

The present study proposed some basic designguidelines for the ring stiffeners in the complicatedCHS joints with multiple brace members. A set offormulae used to predicting ultimate strength of in-ner-stiffened CHS-RHS T- and K-joints were alsorecommended.

3.4 Behavior of tubular joints with curved chordsIn tubular structures of China, welded trusses withcurved circular hollow sections have been increas-ingly used in order to meet the needs of more attrac-tive architectural appearance. It confronts structuralengineers with the question that how to check thestrength of tubular joints with curved chord mem-

bers.Nine static tests on CHS joints with curved and

straight chord members were carried out (Tong et al.2006) (Fig. 13). Behavior in failure modes, load-

deformation curves and stress distributions is com-pared between joints with curved and straight chordmembers. Test results show that the curved circularchord members do not exert more significant influ-ence upon the behavior of joints. Both the experi-mental and numerical results indicated that thestrength of the joints with curved chords at a widerange of curvature radiuses used in practical engi-neering can be checked like the joints with straightchords based on the current design specifications.

3.5 Behavior of overlapped tubular K-jointsFor partially overlapped CHS K-joints (Fig. 14), it is

Figure 13. A CHS joint with curved chord under loading.



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Figure 14. Configuration of overlapped CHS K-joint.

a common practice to mount the CHS members onan assembly rig and tack welds them in fabricationworkshops. Final welding is then carried out in a fol-lowing separated operation. This sequence makes it

impossible to weld the hidden toe of overlapped K-joints. In tubular structures, this type of joints iswidely used. It is thus necessary to investigate what

parameters and how they affect the behavior of over-lapped CHS K-joints with unwelded hidden seam.

In total twelve specimens of uniplanar overlappedCHS K-joints were tested under axial loading (Zhaoet al. 2006). The study concentrated on the effect ofvarying the joint geometry, the loading hierarchy aswell as the presence or absence of the hidden weldon the behavior of the joints. Results show that the

welding situation of the hidden seam has some effecton the stress distribution and failure mechanism, butthe static ultimate capacity of the overlapped CHSK-joints is not affected significantly given that thethrough brace is under compression. When the

brace-to-chord thickness ratio is smaller, the localfailure is the main failure mechanism observed.

3.6 Fatigue behavior of tubular jointsWelded trusses composed of the brace memberswith CHS and the chord members with concretefilled CHS (CFCHS) have come into increasing usein large span highway arch bridges in China. It isworth while to pay attention to the fatigue problemof this new kind of welded joints under repeatedloads.

Stress concentration factors (SCF) of CHS-to-CFCHS T- and K-joints subjected to axial loadingand in-plane bending were experimentally studied

by Tong et al. (2007, 2007, 2008) (Fig. 15). Fatigueassessment of the welded CFCHS joints can be per-formed based on one of three approaches, namely

classification method, hot spot stress method andfracture mechanics method. The last one is the ad-vanced approach in which the parameter of dominat-ing fatigue crack propagation, stress intensity factor(SIF), needs to be determined first. Gu et al. (2008)

crack

through brace footprintlapbrace footprint

chord

2

t

dd

t

t

p

21

1

dchord

-q

1 2

d

lapbrace throughbrace

hidden seam

Ov%=(-q/p) 100%

= d /di

= t /ti

=d/2t

Figure 15. Fatigue crack propagation of CFCHS T-joints.

proposed a simplified fracture mechanics model, andsuccessfully predicted stress intensity factors (SIF)of this joint with semi-elliptical surface cracks underaxial brace loading through the FE methodology.

3.7 Behavior of tubular flange jointsSteel poles are more and more used in transmissionline systems especially in urban areas of China in re-cent years. Bolted flange joints subjected to axialforces and bending moments are one most commontype of connection of steel poles.

Experimental study were performed on 3 flangejoints with stiffened ribs of steel transmission polesfor Baihuadong transmission lines being constructedin Guangdong province in China (Deng, Huang &Jin 2008) (Fig. 16). The tubes are made of Q420Bsteel. The biggest diameter of the tube is 2,100mm.

It is found that the flange plates have enoughstrength and prying force does not exist in the flange

plates connected to the tensile zone of the tube. Anew rotational axis for calculating bolt force is rec-ommended for large-scale flange joints, and maxi-mal bolt force will be increased by 17.3% comparedwith the conventional calculating method. This can

be used as a reliable reference in engineering prac-tice.

4

CODE DEVELOPMENT OF TUBULARSTRUCTURES IN CHINA

The aim of all realistic research projects should be to

Figure 16. Test set-up of a tubular flange joint.



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provide new or improved design criteria. Indeed,many researchers consider the acceptance of their

proposals into the codes to be the highest form ofpeer recognition and achievement.

The first edition of design provisions for steel tu-bular structures in China was published as a sectionof Code for Design of Steel Structures (MCC 1988)in 1988. The second edition (MCC 2003) was re-

vised and published in 2003. Extensive research onsteel tubular structures has been carried out all overthe world in the last 5 years. There is a need to builda special design specification for tubular structuresin China. This section summarizes the ChineseTechnical Specification for Structures with SteelHollow Sections (CECS 2008), recently completed

by the China Association for Engineering Construc-tion Standardization (CECS).

The new Chinese specification contains 9 sec-tions and one annex. The first two sections cover thescope, symbols, terms and definitions. Section 3

gives the requirements for steel tube materials, con-nection materials, and infilled concrete materials.Section 4 prescribes the basic design principle, ma-terial strength value, service limit state design indi-ces and some detail requirements for steel tubularstructures. The design procedures and the resistanceformulae of tubular members and joints are outlinedin the following Section 5, 6 and 7. Section 8 givesthe information about the calculating method of pre-dicting the fatigue strength of tubular joints. In thelast section 9, some detailed recommendations of fa-

brication, assembly and erection aspects of tubularstructures are presented.

5 CONCLUSIONSThe aim of this paper was to provide information re-garding the state of the art of research, design andapplications of tubular structures in China.There aresome issues that are awaiting intensive future study,including a new classification system of tubular

joints based on the global structural performance,seismic design criteria of tubular joints and welds,and resistance formulae of overlapped tubular joints.

It should be pointed out that because many inten-sive studies have been conducted, studies dealingwith beam-to-column connections in concrete filledtubular frame are excluded from this review for thesake of brevity.

ACKNOWLEDGEMENTS

The reported work is supported by Natural ScienceFoundation of China (50578117).

REFERENCES

Cao, G.F. & Yao, N.L. 2008. Load-Carrying Capacity Study onT- and K-Shaped Inner-Stiffened CHS-RHS Joints. Proc.12

thIntern. Symp. on Tubular Structures, Shanghai, China.

China Association for Engineering Construction Standardiza-tion 2008. Technical Specification for Structures with SteelHollow Sections. CECSXX: 2008, to be published, ChinaAssociation for Engineering Construction Standardization,Beijing, China.

Chen, Y.Y. & Wang, W. 2003. Flexural behavior and resis-tance of uni-planar KK and X tubular joints. Steel & Com-posite Structures, Vol.3, No.2: 123-140.

Chen, Y.Y. & Zhao, X.Z. 2007. Experimental study on hyster-etic behavior of CHS overlap K-joints and Gap KK-joints.Proceedings of the 5th International Conference on Ad-vances in Steel Structures, Singapore, Vol.2: 207-217.

Deng, H.Z., Huang, Y. & Jin, X.H. 2008. Experimental Re-search on large-scale flange joints of steel transmissionpole. Proc. 12th Intern. Symp. on Tubular Structures,Shanghai, China.

Fan, Z., Fan, X.W., Peng, Y., Wang, Z. & Sun, H.L. 2008. De-sign and research of welded thin-wall box components for

the national stadium. Proc. 12th

Intern. Symp. on TubularStructures, Shanghai, China.

Gu, M., Tong, L.W., Zhao, X.L. & Lin, X.G. 2008. Stressintensity factors of surface cracks in welded T-jointsbetween CHS brace and concrete-filled CHS chord. Proc.12

thIntern. Symp. on Tubular Structures, Shanghai, China.

Ministry of Construction of China 1988. Code for design ofsteel structures. GB17-88, Ministry of Construction ofChina, Beijing, China.

Ministry of Construction of China 2003. Code for design ofsteel structures. GB50017-2003, Ministry of Constructionof China, Beijing, China.

Tong, L.W., Wang, B., Chen, Y.Y. & Chen, Z. 2006. Study oneffect of curved chords on behavior of welded circularhollow section joints. Proc. 11th Intern. Symp. on TubularStructures, Quebec, Canada: 153-160.

Tong, L.W., Sun, C.Q., Chen, Y.Y., Zhao, X.L., Shen, B. &Liu, C.B. 2008. Experimental comparison in hot spot stressbetween CFCHS and CHS K-joints with gap. Proc. 12thIntern.Symp. on Tubular Structures, Shanghai, China.

Wang, W. & Chen, Y.Y. 2007. Hysteretic behavior of tubularjoints under cyclic loading.Journal of Constructional SteelResearch, Vol. 63, No. 10: 1384-1395.

Tong, L.W., Sun, J.D., Zhou, L.Y., Chen Y.Y. & Gu M. 2007.Behavior of circular hollow section joints with multiplebrace members and internal stiffeners. Proceedings of the5th International Conference on Advances in Steel Struc-

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Tong, L.W., Wang, K., Shi W.Z. & Chen Y.Y. 2007. Experi-mental study on stress concentration factors of concrete filled Circular hollow Section T-joints under axial loading.Proceedings of Eighth Pacific Structural Steel Conference,Wairakei, New Zealand: 153-158.

Wang, W. & Chen, Y.Y. 2005. Modeling & classification oftubular joint rigidity and its effect on the global response ofCHS lattice girders. Structural Engineering and Mechanics,Vol. 21, No.6: 677-698.

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Yan, S., Wang, W. & Chen, Y.Y. 2007. Study on the static be-havior of vierendeel truss joints reinforced with internalstiffeners under in-plane bending. Proceedings of the Sec-ond International Conference on Advances in ExperimentalStructural Engineering, Shanghai, China, Vol.1: 117-122.

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