cidect 5bj-3_02

CIDECT PROJECT 5BJ

The Strength of Multiplanar KK-joints of Square Hollow Sections

Final Report No. 5BJ-3/02

D.K. Liu J. Wardenier

Faculty of Civil Engineering and Geosciences

Delft University of Technology Delft

The Netherlands

CIDECT REPORT 5BJ-3/02 1

TABLE OF CONTENST 1. EXECUTIVE SUMMARY 2. RESEARCH PROGRAMME 3. MAJOR ASPECTS COVERED IN THE ATTACHMENTS 4. RECOMMENDATIONS 5. REFERENCES

ATTACHMENT 1: Effect of boundary conditions and chord preload on the strength of RHS uniplanar gap K-joints ATTACHMENT 2: Effect of boundary conditions and chord preload on the strength of RHS multiplanar gap KK-joints ATTACHMENT 3: Effect of axial reaction force in chord members on the strength of RHS uniplanar gap K-joints ATTACHMENT 4: The strength of multiplanar gap KK-joints of rectangular hollow sections under axial loading ATTACHMENT 5: Multiplanar influence on the strength of RHS multiplanar gap KK-joints ATTACHMENT 6: The strength of multiplanar overlap KK-joints of rectangular hollow sections under axial loading ATTACHMENT 7: The strength of multiplanar overlap KK-joints (Ov = 100%) of rectangular hollow sections under axial loading


1. EXECUTIVE SUMMARY This is the Final report for the CIDECT research project “The Strength of Multiplanar KK-Joints of Rectangular Hollow Sections” Compared to connections between CHS in the past years less attention has been devoted to multiplanar connections between RHS. Because of a lack of sufficient experimental and numerical evidence there is not sufficient information available for such connections. A correction factor of 0.9 has been recommended by CIDECT (Packer et al, 1992) to apply to the uniplanar connection resistance. This factor is similar to that used for circular hollow section KK-joints. To address this deficiency, an ECSC and CIDECT funded research program was carried out to investigate the effect of the multiplanar interactions on the static strength of RHS KK-joints. It is noted (O’Connor, 1993, 1995 and Yeomans, 1993) that for all specimens in this investigation the chord is supported at the chord ends and a tension force is applied to the chord to prevent failure by yielding of the chord. Before this research some indications for the multiplanar effect of KK gap joints were given within the CIDECT programs 5W and 5W/2, however the parameter range was limited and a deformation limit was not defined. In program 5BG, all influencing parameters have been investigated for XX- and TT- joints. The results provide a good basis for design rules for XX- and TT- joints. Furthermore, a deformation limit of 3% has been defined. Logically, the next step is thus to provide the required information for KK- joints. This project sponsored by CIDECT concerns a numerical analysis of the static strength of multiplanar KK-joints in square hollow sections. The objective of this project is to provide sufficient data to define design recommendations for multiplanar KK-joints in square hollow sections. The work carried out during this CIDECT research project 5BJ has been summarized in five reports [1, 2, 3, 4, 5] and six conference publications. Five of these conference publications have been published and one has been submitted for review. This final report consists of the publications and a summary of the work of the last report [5] on 100% overlap joints, which summarise the work done within the CIDECT research project 5BJ. The publications are given in this final report as attachments: From this work the following conclusions can be drawn. • The strength of multiplanar gap KK-joints (chord face failure) can be based on the strength of

the counterpart uniplanar gap K-joints provide that the larger chord force is taken into account for the chord face for the chord force reduction function.

• In case of shear failure of the chord the larger shear force caused by the loading from two planes as well as the large chord force has to be taken into account in the strength interaction formulae. This can be done by considering the forces in one plane and assuming that half of the chord cross section is effective for the resistance.


• The strength of multiplanar overlap KK-joints (Ov = 50% and Ov = 100%) is the same as that for uniplanar overlap K-joints if the strength of the joints is governed by the brace effective width criterion. However, this study has also shown that for uniplanar overlap K-joints with a large 2γ ratio and for multiplanar overlap KK-joints with medium to large 2γ ratios another failure mode i.e. chord face failure by yielding or buckling may occur, which is not yet covered by the CIDECT Design Recommendations. If this failure mode is governing the existing recommendation may not be safe. It is proposed therefore to investigate this failure mode in a new CIDECT programme.


2. RESEARCH PROGRAMME Table 1. Research programme of the numerical parameter study for gap K- and KK-joints

β θi 0.4 0.6 0.8 30° b b b 45° b b b

2γ = 15

60° b b b 30° b b b 45° b b b

2γ = 25

60° b b b 30° b ----- -----

45° b ----- ----- 2γ = 30

60° b ----- -----

30° * b b 45° * b b

2γ = 35

60° * b b * : The validity condition of bi/bo ≥ 0.1 + 0.01(bo/to) is not met : The validity condition of 0.55 ≤ e/bo ≤ 0.25 is not met

Table 2. Research programme of the numerical parameter study for overlap K- and KK-joints

2γ = 15 2γ = 25 2γ = 35

Uniplanar Joint

Multiplanar joint

Uniplanar Joint

Multiplanar joint

Uniplanar Joint

Multiplanar joint

β = 0.4 b b b b b b β = 0.6 b b b b b b β = 0.8 b b b b b b


3. MAJOR ASPECTS COVERED IN THE ATTACHMENTS The various aspects of the CIDECT project 5BJ are covered in the attached papers from which the parameters considered are summarized in table 3. Table 3 Summary parameters considered in the publications

Attachment No. Joint type Boundary

conditions Preload

Nopβ 2γ θ Gap Overlap

1 Uniplanar UBC1 to UBC6 listed in Figure 1A

zero tension 0.6

15 25 35

45° yes ----

2 Multiplanar UBC1 to UBC6 listed in Figure 1A

zero tension compression

0.6 15 45° yes ----

3 Uniplanar All boundary conditions listed in Figure 1B

zero tension compression

0.6 15 25 35

45° yes ----

4 Uniplanar Multiplanar

UBC3 listed in Figure 1A

zero compression

0.4 0.6 0.8

15 25 30 35

45° yes ----



zero compression

0.4 0.6 0.8

15 25 30 35

30° 45° 60°

yes ----



zero 0.4 0.6 0.8

15 25 35

45° ---- 50%



zero 0.4 15 25 35

45° ---- 100%

UBC3UBC1 UBC2

F

F1F1

F2 F1F2

F1

UBC4F1

UBC5 F1

UBC6

igure 1A Boundary conditions considered in attachment 1, 2, 4, 5, 6 and 7


1N NN N 1N1N

F ADsI Iuw C(

(

(

ADsI Itg C(

UBC2

Nop

2UBC1

Nop

1 2

UBC2-S1N 2N

UBC1-S1N 2N

UBC3-T

Nop

UBC3-C

Nop

UBC3-T-S1N

UBC3-C-S1N

igure 1B Boundary conditions considered in attachment 3

TTACHMENT 1: .K. Liu, Y. Yu, J. Wardenier, 1998 “Effect of boundary conditions and chord preload on the

trength of RHS uniplanar gap K-joints”, Tubular Structures VIII, Proceedings of Eight nternational Symposium on Tubular Structures. Singapore. n this paper the effect of boundary conditions and a chord tensile preload on the strength of RHS niplanar gap K-joint has been investigated for one particular joint geometry with different chord idth to thickness ratios. Five different boundary conditions are considered.

onclusions are as follows: a) For the particular joints investigated (∃ = 0.6; 2γ = 15, 25 and 35; 2 = 45o and e = 0), boundary

conditions have a considerable effect on the joint strength. The effect varies with the chord width to thickness ratio, and the effect is highly dependent on the chord axial load.

b) The numerically determined joint strengths at a deformation limit of 3%bo for the joints for which the chords are in tension are more in agreement with the predicted CIDECT design capacities than those for which the chords are in compression.

c) For this particular joint geometry investigated the ultimate joint load capacity is dependent upon the ultimate deformation criterion used, particularly for the joint with high chord width to chord thickness ratio.

TTACHMENT 2: .K. Liu, Y. Yu, J. Wardenier, 1998 “Effect of boundary conditions and chord preload on the

trength of RHS multiplanar gap KK-joints”, Tubular Structures VIII, Proceedings of Eight nternational Symposium on Tubular Structures. Singapore.

n this paper the effect of boundary conditions and the chord loading (tension or compression) on he strength of RHS multiplanar gap KK-joint has been investigated for one particular joint eometry with five different boundary conditions.

onclusions are as follows: a) For the particular joint ( ∃= 0.6; 2 = 45o; 2( = 15 and e = 0), the effect of boundary conditions

on the joint strength is highly dependent on the chord forces.


(b) For this particular joint, the ratio between the strength of the multiplanar joints and that of the uniplanar joints varies between 0.85 to 1.0 depending on the chord force.

(c) The current study shows that the effect of the chord force No on the joint strength appears to be very significant and might even be higher for joints with higher chord width to thickness ratio (2(). It is noted that for the multiplanar KK-joint the chord force No in fact is a combination of the forces for the two planes of the joint.

ATTACHMENT 3: D.K. Liu, J. Wardenier, 1998 “Effect of axial reaction force in chord members on the strength of RHS uniplanar gap K-joints”, Proceedings of Fifth Pacific Structural Steel Conference. Seoul, Korea. In this paper the effect of axial tensile or compressive forces in the chord members on the strength of RHS uniplanar gap K-joint has been investigated in more details. Eight different boundary conditions are considered in the study. Conclusions are as follows: (a) For the particular joint geometry investigated (∃= 0.6; 2γ = 15, 25 and 35; 2= 45o and e = 0),

the axial force in the chord has a considerable effect on the joint strength not only for compressive but also for tensile forces. The effect varies with the chord width to thickness ratio.

(b) The numerical results show that the function f(n) adopted in the CIDECT Recommendations to account for the effect of the axial force in chord members does not accurately describe the reduction in strength, particularly for the joints with a high chord width to chord thickness ratio 2(.

(c) The effect of different boundary conditions i.e. boundary condition UBC1 and UBC3-C, UBC2 and UBC3-T can be neglected if the governing chord forces are the same.

(d) Boundary conditions UBC3-C-S and UBC3-T-S give an unrealistic high capacity for the joint. ATTACHMENT 4: D.K. Liu, J. Wardenier, 2001 “Multiplanar influence on the strength of RHS multiplanar gap KK-joints”, Tubular Structures IX, Proceedings of Ninth International Symposium on Tubular Structures. Germany. The strength of multiplanar gap KK-joints in square hollow sections (RHS) and their counterpart uniplanar gap K-joints are studied in more detail (variation of β) in order to determine the multiplanar effect. This study concerns the joints with a geometry of ∃ = 0.4, 0.6 and 0.8; 2γ = 15, 25, 30 and 35). The acute angle between the brace and the chord considered in the study is 2 = 45o. Conclusions are as follows: (a) Since the CIDECT design recommendations are based on the ultimate strength of experiments

the strengths are higher than the numerically determined strengths for multiplanar gap KK-joints with a large 2γ and low β ratio where the numerical determined strength is limited by the chord face indentation of 3%bo.


(b) It is shown that with the exception of chord shear failure the strength of multiplanar gap KK-joints can be based on the strength of the counterpart uniplanar gap K-joints however considering the actual chord member force. No further multiplanar correction is necessary for gap joints if chord face failure is the governing failure mode.

ATTACHMENT 5: D.K. Liu, J. Wardenier, 2001 “The strength of multiplanar gap KK-joints of rectangular hollow sections under axial loading”, Proceedings of The 11th International Offshore and Polar Engineering Conference. Norway.

The strength of multiplanar gap KK-joints in square hollow sections (RHS) and their counterpart uniplanar gap K-joints are studied in more detail (variation of θ) in order to determine the multiplanar effect. This study concerns the particular joint with a geometry of ∃ = 0.4, 0.6 and 0.8; 2γ = 15, 25, 30 and 35). The acute angle between the brace and the chord considered in the study is 2 = 30o, 45o, 60o. Based on this study the relationship between the strength of multiplanar gap KK-joints and uniplanar gap K-joints has been determined. Further comparisons are made with existing design recommendations. Conclusions are the same as mentioned in attachment 4 for the joint with 2 = 45o: ATTACHMENT 6: D.K. Liu, J. Wardenier, 2002 “The strength of multiplanar overlap KK-joints of rectangular hollow sections under axial loading”, Proceedings of The 12th International Offshore and Polar Engineering Conference. Japan. This paper deals with RHS multiplanar overlap KK-joint with θ = 45° and Ov = 50%. In this FE study a basic overlap KK-joint with θ = 45° has been considered. The nominal values of the width to chord thickness ratio i.e. 2γ are 15, 25 and 35. The nominal brace to chord width ratio β ranges from 0.4 to 0.8. Conclusions are as follows: (a) It is shown that the strength of multiplanar overlap KK-joints can be based on the strength of

the counterpart uniplanar overlap K-joints if the failure mode of the joints is governed by the brace effective width. In this case no further multiplanar correction is necessary.

(b) A failure mode observed in the numerical analysis for overlap joints, which is not yet covered in the current recommendations e.g. in the CIDECT Design Guide, is chord face yielding / plastic buckling. This may result in unsafe designs.

(c) To get inside into the problem, a further detailed study is required in an extended programme.


ATTACHMENT 7: D.K. Liu, J. Wardenier, 2002 “The strength of multiplanar overlap KK-joints (Ov = 100%) of rectangular hollow sections under axial loading”. CIDECT Report 5BJ-3a/02, Faculty of Civil Engineering and Geosciences, Delft University of Technology. Delft, The Netherlands. In this report the results for multiplanar KK joints (θ = 45°; β = 0.4 and Ov = 100%) are published. Load-indentation relationships, modes of failure and the ultimate loads of the joints are reported in the report. Comparisons are made with existing design recommendations. Conclusions are as follows: (a) The observations are that no multiplanar correction has to be included in case failure is

governed by the brace effective width. (b) The chord face yielding / plastic buckling failure mode observed in the numerical analysis is

not yet covered in the current design recommendations. This failure mode is observed particularly for uniplanar overlap K-joints with a large γ ratio(2γ = 35) and multiplanar overlap KK-joints with medium to large γ ratio. To get inside into the problem, a further detailed study is required. It is also not yet clear if this failure mode can occur for joints with a lower γ ratio with high chord preloads

(c) As already indicated for 50% overlap joints [Attachment 6] chord failure of overlap K- and KK-joints requires further consideration in an extended programme.


4. RECOMMENDATIONS 4.1 Multiplanar gap KK-joints

• Chord face plastification No further multiplanar correction is necessary and the strength can be based on that of the uniplanar joints provided that the actual chord force of the multiplanar joints is taken into account for the chord load reduction function.

• Chord shear and chord axial force interaction The same strength interaction formula can be used as for uniplanar joints. However, it should be born in mind that half of the chord cross section is available for resisting the forces from each plane.

4.2 Multiplanar overlap KK-joints with with Ov = 50% and Ov = 100%

• Failure based on brace effective width criterion The numerical results show that for small γ (2γ = 15) the strength of multiplanar overlap KK-joints is governed by the brace effective width criterion which is similar as for the counterpart uniplanar overlap K-joints. No further multiplanar correction is necessary.

• Chord face failure For the multiplanar overlap joints with medium to large 2�ratios a chord yielding / plastic

buckling failure mode have been observed in the numerical analysis which is not yet covered in the current design recommendations. To better understand this problem, a further detailed study is required.


5. REFERENCES Reports 1. Liu, D.K. and Wardenier, J. (1999). “Multiplanar KK-joints of square hollow sections”,

CIDECT Report 5BJ-6/99, Interim Report. Faculty of Civil Engineering and Geosciences, Delft University of Technology. Delft, The Netherlands.

2. Liu, D.K. Liu Wardenier, J. (2000) "Multipanar KK-joints of square hollow sections",


3. Liu, D.K. Liu Wardenier, J. (2001) "Multipanar overlap KK-joint of square hollow sections",


4. Liu, D.K. Liu Wardenier, J. (2001) "Multipanar KK-joint of square hollow sections", CIDECT

Report 5BJ-5/00, Interim Report. Faculty of Civil Engineering and Geosciences, Delft University of Technology. Delft, The Netherlands.

5. Liu, D.K. Liu Wardenier, J. (2002) "Multipanar KK-joint of square hollow sections (Ov =

100%)", CIDECT Report 5BJ-3a/02, Interim Report. Faculty of Civil Engineering and Geosciences, Delft University of Technology. Delft, The Netherlands.

Publications 6. D.K. Liu, Y. Yu, J. Wardenier, 1998 “Effect of boundary conditions and chord preload on the

strength of RHS uniplanar gap K-joints”, Tubular Structures VIII, Proceedings of the Eight International Symposium on Tubular Structures. Singapore. Publisher: A.A. Balkema.

7. D.K. Liu, Y. Yu, J. Wardenier, 1998 “Effect of boundary conditions and chord preload on the

strength of RHS multiplanar gap KK-joints”, Tubular Structures VIII, Proceedings of the Eight International Symposium on Tubular Structures. Singapore. Publisher: A.A. Balkema.

8. D.K. Liu, J. Wardenier, 1998 “Effect of axial reaction force in chord members on the strength

of RHS uniplanar gap K-joints”, Proceedings of the Fifth Pacific Structural Steel Conference. Seoul, Korea. Publisher: Techno-Press.

9. D.K. Liu, J. Wardenier, 2001 “Multiplanar influence on the strength of RHS multiplanar gap

KK-joints”, Tubular Structures IX, Proceedings of the Ninth International Symposium on Tubular Structures. Germany. Publisher: A.A. Balkema.

10. D.K. Liu, J. Wardenier, 2001 “The strength of multiplanar gap KK-joints of rectangular

hollow sections under axial loading”, Proceedings of the 11th International Offshore and Polar Engineering Conference. Norway. Publisher: ISOPE.


11. D.K. Liu, J. Wardenier, 2002 “The strength of multiplanar overlap KK-joints of rectangular hollow sections under axial loading”, To be presented at the 12th International Offshore and Polar Engineering Conference. Japan. Publisher: ISOPE.


ATTACHMENTS


ATTACHMENT 1: Title: Effect of boundary conditions and chord preload on the strength of RHS uniplanar

gap K-joints Authors: D.K. Liu, Y. Yu, J. Wardenier Status: Published in proceeding of the Eight International Symposium on Tubular

Structures. 1998, Singapore. Publisher: A.A. Balkema

CIDECT REPORT 5BJ-3/02

16


17


18


19


20


21


22


ATTACHMENT 2: Title: Effect of boundary conditions and chord preload on the strength of RHS uniplanar

gap KK-joints Authors: D.K. Liu, Y. Yu, J. Wardenier Status: Published in the proceedings of the Eight International Symposium on Tubular Structures. 1998, Singapore. Publisher: A.A. Balkema


24


26


27


28


29


30


31


ATTACHMENT 3: Title: Effect of Axial Reaction Force in Chord Members on the Strength of RHS

Uniplanar gap K-Joints

Authors: D.K. Liu, J. Wardenier Status: Published in the proceedings of the Fifth Pacific Structural Steel Conference. 1998, Seoul, Korea. Publisher: Techno-Press.


33


34


35


36


37


38


ATTACHMENT 4: Title: Multiplanar influence on the strength of RHS multiplanar gap KK-joints

Authors: D.K. Liu, J. Wardenier Status: Published in the proceedings of the Ninth International Symposium on Tubular Structures. 2001, Germany. Publisher: A.A. Balkema


40


41


42


43


44


45


46


47


48


49


ATTACHMENT 5: Title: The Strength of Multiplanar Gap KK-Joints of Rectangular Hollow Sections

Under Axial Loading

Authors: D.K. Liu, J. Wardenier Status: Published in the proceedings of the 11th International Offshore and Polar Engineering Conference. 2001, Norway. Publisher: ISOPE.


52


53


54


55


56


57


58


ATTACHMENT 6: Title: The strength of multiplanar overlap KK-joints of rectangular hollow sections

under axial loading

Authors: D.K. Liu, J. Wardenier Status: To be presented at the 12th International Offshore and Polar Engineering Conference. 2002, Japan. Publisher: ISOPE.


61


62


64


65


66


ATTACHMENT 7: Title: The strength of multiplanar overlap KK-joints (Ov = 100%) of rectangular hollow

sections under axial loading CIDECT Report 5BJ-3a/02, Interim Report. Faculty of Civil Engineering and Geosciences, Delft University of Technology. Delft, The Netherlands.

Authors: D.K. Liu, J. Wardenier Status: CIDECT Report 5BJ-3a/02, Interim Report. Faculty of Civil Engineering and

Geosciences, Delft University of Technology. Delft, The Netherlands.

cidect 5bj-3_02

Documents

kk joints

tt joints

multiplanar connections

multiplanar influence

multiplanar interactions

cidect project

strength of rhs uniplanar

rectangular hollow sections