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EUROSTEEL 2008, 3-5 September 2008, Graz, Austria

THE INFLUENCE OF STRUCTURAL DETAILS ON THE

DISSIPATIVE BEHAVIOUR OF BEAM-TO-COLUMN JOINTS

Fabio Iannone, Vincenzo Piluso, Gianvittorio Rizzano

University of Salerno, Faculty of Civil Engineering, Salerno, Italy

INTRODUCTION

The knowledge of the cyclic behaviour of beam-to-column joints has a paramount importance for the seismic

design of moment-resisting steel frames, especially when the dissipation of seismic input energy has to occur

in the joint components. In particular, beam-to-column bolted joints are widely used in practical design for

their simplicity and their ability to provide a variety of structural solutions. In recent years different structural

details have been tested aiming to investigate both to the whole joint behaviour and to basic joint

components.

In order to verify the possibility to develop a component approach to predict the cyclic response of bolted

beam-to-column joints, new experimental tests have been carried out on full scale beam-to-column joints.

Aiming to verify the correct identification of the main dissipative joint components, the experimental test

results are herein presented in terms of both the total cyclic response of the joint and the cyclic response of

each joint component.

1 DESIGN OF DISSIPATIVE JOINTS

Within the experimental program, still in progress, four cyclic tests have been carried out on external steel

beam-to-column bolted joints designed in order to obtain the same bending strength, but varying the weakest

dissipative joint component, representing the dissipative component.

The following tests have been performed:

• Partial strength extended end plate connection having the column web panel in shear as weakest

component [EEP-CYC01];• Partial strength extended end plate connection having the end plate in bending as weakest component

[EEP-CYC02];

• Full strength extended end plate connection with reduced beam section (dog-bone) [EEP-DB-CYC03];

• T-Stub connection [TS-CYC04].

The specimens have been composed with an HEB200 column (steel grade S355), an IPE270 beam (steel

grade S275), end plates with steel grade S275 and bolts M20 and M24 (class 10.9).

With reference to the EEP-CYC01 joint (Fig. 1), the ultimate moment corresponding to the shear resistance

of the column web is computed as:

≅= t

vcwcu

spu h A f

M 3

,

, 140kN ⋅ m (1)

were Avc is the shear area of the column, ht is the lever arm and f u,wc is ultimate stress of the column web.

The “equivalent T-stub” for the end-plate in bending of EEP-CYC01 joint has been designed by imposing

type-1 dissipative mechanism, according to Eurocode 3, characterized by the formation of plastic hinges at

the bolt axis and at the flange-to-end plate connection and by imposing a 20% overstrength with respect to

the shear panel resistance:

≅⋅

⋅

= t epu

epeff

Tstubu h f m

t b M ,

2

, 1.2 M u,sp (2)

were beff is effective width of the equivalent T-stub assumed equal to width of the end-plate; t ep is the

thickness of the end-plate; m is the distance between the plastic hinges.

Regarding the joint ductility, an ultimate rotation mainly given by the contribution of the shear panel

deformation and of the end-plate deformation, equal to 0.06 rad has been imposed as design condition:

≅+

⋅

⋅= spu

t ep ht

mC ,

2

2γ ϑ 0.06 (3)



were C is a constant depending on material mechanical properties [1] and assumed equal to 0.195, γ u,sp is the

shear deformation, computed by means of the model of Krawinkler et al [2, 3], corresponding to the ultimate

moment given by Eq. (1).

The EEP-CYC02 joint (Fig. 2) has been designed imposing as weakest component the equivalent T-stub

corresponding to the end-plate in bending. Its design flexural resistance is approximately equal to M u,sp of

EEP-CYC01 joint. In order to maximize the energy dissipation of this joint component, the shear panel has

been strengthened by means of continuity plates and supplementary web plates.

The joint EEP-DB-CYC03 (Fig. 3) was designed by weakening the beam flanges (RBS) so that the plastic

moment achieved at the center of the reduced section zone is equal to:

≅⋅⋅= E y DB pl DB p f W M ,,,

15.1 120 kN ⋅ m (4)

were 1.15 is an amplification factor accounting for strain-hardening [4]; W pl,DB is the plastic section modulus

at minimum section of RBS and f y,E is the expected yield stress of the beam assessed with a coefficient of

overstrength equal to 1.2 with respect to the nominal resistance. Thus, the maximum moment expected at the

face of the column is, according to design, M c ≅ 140kN ⋅ m. The geometry of the reduced section zone has

been designed following the procedure set out in “Steel Tips” [4]. In addition, in order to concentrate the

energy dissipation mainly in the reduced section zone of the beam, the shear panel has been strengthened

with continuity plates and supplementary web plates. In addition, the thickness of the end-plate was designed

aiming to avoid its engage in plastic range.

Finally, the last joint, TS-CYC04 (Fig. 4), has been designed by imposing the following values of strengthand ductility of T-stub elements:

≅⋅

⋅

= t epu

epeff

Tstubu h f m

t b M ,

2

, 140 kN ⋅ m (5) ≅

⋅

⋅=

t ep ht

mC

2

2

ϑ 0.08 (6)

Also in this case the shear panel has been strengthened as in previous joints.

In each of these four cases, the welds between the beam and the end-plate and the welds of supplementary

web plates have been designed as full penetration welds.

HE200B

IPE270

3290

32

4 5

9 3

1 6 7

9 3

4 5

154

4 4 3

t = 20 mm

bolt M20 (10.9)

ep

170

2 0 0

4 4 3

Fig. 1. EEP-CYC01

3094

30

4 0

1 3 4

1 2 6

1 3 4

4 0

4 7 4

154

17025

12025

2 0 0

HE200B

IPE270

bolt M20 (10.9)

t = 20 mmep

t = 10 mmwp

5 3

t = 10 mmcp

4 0 0

Fig. 2. EEP-CYC02

2 EXPERIMENTAL ANALYSIS

2.1 Test setupThe tests have been executed at the structural engineering laboratory of the University of Salerno. Fig. 5

shows the complete scheme of experimental tests. Two hydraulic actuators MTS (model 243) have been used

for the application of the axial load in the column and for the control of the imposed displacement history at

the top of the cantilever beam. Two hinges bolted to a base steel beam anchored to the strong floor allow to

obtain a structural scheme representing the behaviour of external joints as shown in Fig. 5. Finally, an

horizontal frame has been adopted to prevent the lateral buckling of the beam.

In particular, the bottom horizontal actuator (capacity: 1000 kN) has been governed under strength control

applying a costant axial compression in the column equal to 650 kN. The upper actuator (capacity: 250 kN)

has been hooked to the free end of the beam to apply, under displacement control, cyclic displacements. The

amplitude and the number of cycles have been planned according to AISC code for cyclic tests on beam-to-

column joint [5]. Such code proposes displacement history depicted in Fig. 6 . in terms of interstorey drift

angle.

During the tests many parameters have been monitored and acquired: displacements and loads of both the

actuators and the displacements of the different joint components. To this scope 3 position sensors and 6

LVDTs located in different points of the joint, as shown in Fig. 7 , have been adopted.



70 180

2 2

2 2

3 5

9 3

1 6 7

9 3

3 5

4 2 3

3594

35

164

HE200B

IPE270

bolt M24 (10.9)

t = 25 mmept = 10 mmwp

t = 10 mmcp

4 0 0

RBS

17025

12025

2 0 0

5 3

R 1 9 5

Fig. 3. EEP-DB-CYC03

2 5 7

1 7 7

4 0

2 5 7 8 1

8 1

4 0

4 0

4 0 5

4 2

7 5

3 0

1 3 5

3 0

73 60 60 6040

29317025

12025

2 0 0

25

HE200B

IPE270

bolt M20 (10.9)

t = 10 mm

t = 10 mmcp

4 0 0

wp

t = 25 mmep

3094

30

154

Fig. 4. TS-CYC04

HE200B

IPE270

Hydraulic Actuator

Concrete floorSleigh base

Left hinge

Right hinge

Vertical frame

Horizontal frame

JOINT

IPE270L=170cm

L=200cm

max load: 250 kNmax disp.: 500mm+/-

+/-

Hydraulic Actuatormax load: 1000 kNmax disp.: 125mm+/-

+/-

Fig. 5. Experimental test setup

Fig. 6. Displacement history (AISC)

LVDT 1

Load / Displacement

Actuator 1000 kN

Load / Displacement

Actuator 250 kN Transd. 3

Transd. 1 Transd. 2

LVDT 2

LVDT 3 e 4 LVDT 5 e 6

Trasducer

LVDT

2700

1 5 5 7

Fig. 7. Location of measuring devices

2.2 Geometrical and mechanical properties of the tested joints

In Table 1, the main geometrical properties of tested specimens are given. In particular, reference to the

notation of Fig. 8 is made.

With reference to the mechanical properties of steel, tensile coupon tests have been carried out providing the

following values:

y,ep = 290 N/mm2

u,ep = 493.7 N/mm2 (*)

ε h / ε y = 11.3

ε u / ε y = 589

E = 207288 N/mm2

E / E h = 86.5

E / E u = 632.8

f y,wc = 430 N/mm2

f u,wc = 523 N/mm2

f y,fc = 382.5 N/mm2

f u,fc = 522 N/mm2

(*) True stress



Table 1. Measured properties of tested joints (mm)

Joint Bolt Bolt

preloadingStiffening bep , hep , tep

e1 , e 2 ,

p1 , p 2 , p 3 HE200B IPE270

EEP

CYC01

8 M20

(10.9)550 N⋅m nothing

153.6

441.0

20.1

30.5, 42.2,

92.6, 94.2, 168.1

hc = 201

bc = 201

t w = 9.2

t f

= 15.3

hb = 268

bb = 134

t w = 6.6

t f

= 10.9

EEP

CYC02

8 M20

(10.9)550 N⋅m

continuity plates

+

supplementary

web plates

156.7

474.4

20.7

31.2, 40.5,

94.3, 133.6, 126.2

hc = 198

bc = 198

t w = 9.2

t f = 15.5

hb = 271

bb = 131

t w = 6.8

t f = 10.7

EEP

DB

CYC03

8 M24

(10.9)800 N⋅m

continuity plates

+

supplementary

web plates

161.0

427.0

25.3

36.0, 33.0,

89.0, 99.0, 163.0

hc = 198

bc = 198

t w = 9.2

t f = 15.5

h RBS = 271

b RBS = 88.8

t w = 6.8

t f = 10.7

TS

CYC04

8 M20

(10.9)550 N⋅m

continuity plates

+

supplementary

web plates

154.0

2×257.0

25.0

30.0, 40.0,

94.0, 177.0

hc = 198

bc = 198

t w = 9.2

t f = 15.5

hb = 271

bb = 131

t w = 6.8

t f = 10.7

2.3 Experimental results

The moment-rotation curves of the four joints are shown in Figs. 9, 10, 11

and 12, while in Fig. 13 the corresponding monotonic envelopes are

compared. It is possible to observe that the four joints exhibit similar

strength as desired, but significant differences occur regarding rotational

capacity and width and stability of hysteresis loops. In particular, the

dissipative behaviour of EEP-CYC01 joint is mainly due to the

contributions of the shear panel and of the equivalent t-stub (Figs. 14 and

16 ), while the column web in compression and tension (Fig. 18) provider a

minor contribution. In case of EEP-CYC02 and TS-CYC04 joints, the

dissipative behaviour is essentially due to the equivalent t-stubs only(comparision among the Figs. 15 and 17 ) which are also responsible of

some pinching.

Hysteretic Curve M-θ EEP-CYC 01

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0,100 -0,075 -0,050 -0,025 0,000 0,025 0,050 0,075 0,100

Joint Rotation [rad]

M o m e n t [ k N · m m ]

Nodal M-rot

Envelope

Mmax = 181479 kN·mm

Mmin = -200894 kN·mm

Fig. 9. Moment-rotation of EEP-CYC01

Hysteretic Curve M-θ EEP-CYC 02

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0,100 -0,075 -0,050 -0,025 0,000 0,025 0,050 0,075 0,100



Nodal M-rot

Envelope



Fig. 10. Moment-rotation of EEP-CYC02

Hysteretic Curve M-θ EEP-DB-CYC 03

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0,100 -0,075 -0,050 -0,025 0,000 0,025 0,050 0,075 0,100



Nodal M-rot

Envelope



Fig. 11. Moment-rotation of EEP-DB-CYC03

Hysteretic Curve M-θ TS-CYC 04

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0,100 -0,075 -0,050 -0,025 0,000 0,025 0,050 0,075 0,100



Nodal M-rot

Envelope



Fig. 12. Moment-rotation of TS-CYC04

tep bep

h e p

p1

e1 e1

e 2

e 2

p 2

p 2

p 3

Fig. 8. Bolts and end-plate



The contribution of the column web in compression-

tension is negligible for last three joints (Fig. 19). In

EEP-DB-CYC03 joint, as expected, the plastic

rotation supply has entirely offered by the weakened

zone of the beam in bending, being negligible the

contribution of all the other components. Regarding

the failure modes, the brittle fracture of welds

between the beam flanges and the end-plate caused

sudden collapse of EEP-CYC01 joint at about 0.07

rad (Fig. 9). Conversely, failure made of EEP-CYC02

was due to low-cycle fatigue of the end-plate leading

to complete fracture of the heat affected zone at the

welded connection to the flanges of the beam, with a

quick degrade of strength at about 0.04 rad.

Monotonic envelopes

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0,100 -0,075 -0,050 -0,025 0,000 0,025 0,050 0,075 0,100



Envelope EEP-CYC1

Envelope EEP-CYC2

Envelope EEP-DB-CYC3

Envelope TS-CYC4

Fig. 13. Moment-rotation envelopes

In case of EEP-DB-CYC03 joint, the degrade of strength is due to local buckling of beam flanges. Finally,

the collapse of TS-CYC04 joint was due to the fracture of the T-stub flanges resulting from low-cycle

fatigue. The measured displacements deal with both the overall behaviour of the joints and their components,

so that it is possible to outline the contribution of each component to the joint energy dissipation. During

EEP-CYC01 test the formation of yield lines at 45° inside the panel zone has been observed since the earlycycles, while the plastic engagement of the end-plate has been evident only in an advanced phase of the test.

Fig. 20 shows that dissipation is mainly located in the shear panel. However, the contribution due to the

equivalent T-stubs is not negligible. Conversely, the column web in compression-tension is not significantly

engaged. It is important to underline that Fig. 20 points out that the external work developed in the

experimental test can be obtained as the sum of the energy dissipated by each joint component. Analogous

considerations are possible for tests EEP-CYC02 and TS-CYC04 where only the plastic engagement of the

T-stubs has been observed (Figs. 21 and 23). Finally, in EPP-DB-CYC03 test the concentration of plastic

deformations in the weakend portion of beam occurs. The dissipated energy is almost completely due to the

dog-bone while the energy dissipated by the other joint components is not significant (Fig. 22).

4 CONCLUSIONS

On the base of the experimental results obtained in the present work, the possibility to extend the component

approach to predict the cyclic behaviour of beam-to-column joints appears feasible, because experimental

evidence shows that the total energy dissipated by beam-to-column joints can be obtained as the sum of the

energies dissipated by each component, provided that the joint components are properly identified and

modelled.

Hysteretic Curve M-γ EEP-CYC 01

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

-0 ,0 5 - 0,0 4 -0 ,0 3 - 0,0 2 - 0,0 1 0 ,0 0 0 ,0 1 0,0 2 0 ,0 3 0 ,0 4 0 ,0 5

γ [rad]

M o m e n t [ k N · m ]

Shear Panel

Fig. 14. Shear panel of EEP-CYC01

Hysteretic Curve M-γ EEP-CYC 02

-250000

-200000

-150000

-100000

-50000

0

50000

100000

150000

200000

250000

- 0 ,0 05 - 0, 00 4 - 0,0 03 - 0, 00 2 - 0, 00 1 0 ,0 00 0 ,0 01 0 ,0 02 0 ,0 03 0 ,0 04 0 ,0 05

γ [rad]

M

o m e n t [ k N x m m ]

Shear Panel

Fig. 15. Shear panel of EEP-CYC02

Hysteretic Curve F-δ EEP-CYC 01

-800

-600

-400

-200

0

200

400

600

800

-1 0 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 16

Displacement [mm]

F o r c e [ k N ]

T-Stub Sx

Fig. 16. Left equivalent T-stub of EEP-CYC01

Hysteretic Curve F-δ EEP-CYC02

-800

-600

-400

-200

0

200

400

600

800

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Displacement [mm]

F o r c e [ k N ]

T-Stub Sx

Fig. 17. Left equivalent T-stub of EEP-CYC02



Hysteretic Curve F-δ EEP-CYC 01

-800

-600

-400

-200

0

200

400

600

800

-4 -3 -2 -1 0 1 2 3 4

Displacement [mm]

F o r c e [ k N ]

Panel T-C Sx

Fig. 18. Column web of EEP-CYC01

Hysteretic Curve F-δ EEP-DB-CYC03

-1000

-800

-600

-400

-200

0

200

400

600

800

-4 -3 -2 -1 0 1 2 3 4

Displacement [mm]

F o r c e [ k N ]

Panel T-C Sx

Fig. 19. Column web of EEP-DB-CYC03

Energy dissipation EEP-CYC 01

0

50000

100000

150000

200000

250000

20 25 30 35 40

n° cycles

E

n e r g y [ k N · m m ]

Node

Shear Panel

T-Stub EP Sx

T-Stub EP Dx

PAN Sx

PAN Dx

SUM Comp.

Fig. 20. Energy dissipation of EEP-CYC01

Energy dissipation EEP-CYC 02

0

10000

20000

30000

40000

50000

60000

20 25 30 35

n° cycles

E

n e r g y [ k N · m m ]

Node

Shear Panel

T-Stub EP Sx

T-Stub EP Dx

PAN Sx

PAN Dx

SUM Comp.

Fig. 21. Energy dissipation of EEP-CYC02

Energy dissipation EEP-DB-CYC 03

0

50000

100000

150000

200000

250000

20 25 30 35 40

n° cycles

E n e r g y

[ k N · m m ]

Node

Shear Panel

T-Stub EP Sx

T-Stub EP Dx

PAN Sx

PAN Dx

SUM Comp.

Fig. 22. Energy dissipation of EEP-DB-CYC03

Energy dissipation TS-CYC 04

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

20 25 30 35 40

n° cycles

E n e r g y

[ k N · m m ]

Node

Shear Panel

T-Stub EP Sx

T-Stub EP Dx

PAN Sx

PAN Dx

SUM Comp.

Fig. 23. Energy dissipation of TS-CYC04

REFERENCES

[1] C. Faella, V. Piluso, G Rizzano (2000): “Structural Steel Semirigid Connections”, CRC Press, Florida,

ISBN 0-8493-7433-2.

[2] H. Krawinkler, V.V. Bertero, E.P. Popov (1971): “Inelastic Behaviour of Steel Beam-to-ColumnSubassemblages”, Report UCB/EERC-71/7 , Earthquake Engineering Recent Center, Univ. of

California, Berkley.

[3] H. Krawinkler, V.V. bertero, E.P. Popov (1973): “Further Studies on Seismic Behaviour of Steel

Beam-Column Subassemblages”, Report UCB/EERC-73/27 , Earthquake Engineering Recent Center,

Univ. of California, Berkley.

[4] K. S. Moore, J. O. Malley, M. D. Engelhardt, (1999): “Design of Reduced Beam Section (RBS)

Moment Frame Connections”, Steel TIPS, August, Structural Steel Educational Council

[5] AISC (2202):”Seismic Provisions for Structural Steel Buildings”, ANSI/AISC 341-02, American

Institute of Steel Construction

the influence of structural details on the dissipative beh…

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