THE EFFECTS OF BEHAVIOUR OF A BEAM-TO … a moment connection ... Turkish Code for Design and Construction of Steel ... The primary distortion of the steel beam-to-column steel connections

4th International Conference on Earthquake Engineering and Seismology

11-13 October 2017 – ANADOLU UNIVERSITY – Eskisehir/TURKEY

THE EFFECTS OF BEHAVIOUR OF A BEAM-TO-COLUMN CONNECTION

WITH LIMITED STIFFNESS AND STRENGTH ON SEISMIC BEHAVIOUR

OF A STEEL BUILDING

Adem Karasu1

and Cüneyt Vatansever2

1 Res. Ass. Adem Karasu, Civil Engineering Department, Istanbul Technical University, Sarıyer

2 Assist. Prof. Dr. Cüneyt Vatansever, Civil Engineering Department, Istanbul Technical University, Sarıyer

Email: [email protected]

ABSTRACT:

In seismically active regions such as Turkey, nonlinear behavior of a structure is very important and is governed

by the behavior of beams, columns and their connections constituting the seismic force resisting system of the

structure. Of these members, beam to column connections can play a considerably important role even if they have

a capability of limited stiffness and flexural strength. Structural steel connections are mainly classified as a pinned

or a moment connection whose stiffness and strength do not exist or are required to define it. However, some

beam-to-column connections having limited stiffness and strength, which are called semi-rigid connections such

as header end plate connection, can be characterized by moment-rotation relationship. So the article presents the

contribution of moment-rotation behavior of typical bolted semi-rigid connections on improvement of seismic

behavior of the steel buildings. This also provides a good understanding of the nonlinear response of the steel

buildings including semi-rigid beam to column connections. In this study, a four story steel building was selected

and designed under load combinations with seismic loads. All structural members are proportioned according to

Turkish Code for Design and Construction of Steel Structures 2016 by using SAP 2000 software. The four-

parameter power model is used for modelling of moment-rotation relationship (M-θ) of header end plate

connection. Nonlinear time history analyses were performed in OpeenSEES framework. Analyses results have

been evaluated in terms of inter-story drifts, additional strength and energy dissipation. It is observed that inter-

story drifts decreased, and an additional strength was provided together with the more energy dissipation.

KEYWORDS: Header Plates, Semi-Rigid Connections, Nonlinear Time History Analysis

1. INTRODUCTION

Due to brittle failure of welded connections of steel frames, there is increasing interest in bolted connections

(Çıtıpıtıoğlu & Haj-Ali, 2002). Bolted end plate steel connections consist of plate, bolts and welds. Because of the

large variety of connection configurations, stress concentrations, frictional and contact forces between components

these connections are classified semi-rigid connections (Baei, Ghassemieh, & Goudarzi, 2012). In designing a

steel framework, it is customary to represent the actual connection behavior by rigid moment connection or flexible

pinned connection. So, most of the design engineers assume that the behavior of the connections is perfectly rigid

or pinned. However, this theory leads to an inaccurate prediction of the frame behavior. Because perfectly rigidity

and complete flexibility are idealized forms of connection behavior and cannot be reached in practical connections.

The AISC design code, referred to as the Load and Resistance Factor Design (LRFD) designates two types of

constructions in its provisions which are fully restrained (FR) and partially restrained (PR)(Abdalla & Chen, 1995).

Therefore, if partially restrained construction is used, the flexibility on the behavior must be taken into account in

the design procedures.



Figure 1. Rotational deformation of connection

The primary distortion of the steel beam-to-column steel connections is their rotational deformation, θr, caused by

the in plane bending moment, M, (Fig.1)(Abdalla & Chen, 1995). Header plate connections consist of an end plate

whose length is smaller than the beam depth and connectors. Flexible end plate (header plate) is welded to beam

web and bolted to column flange. The importance of header plate connections in the context of overall structural

behavior lies in their rotational stiffnesses. Actually, they are assumed to be pinned flexible connections during

the design procedures although they have pronounced rotational stiffnesses. The goal of this paper is to investigate

the nonlinear response of 4-story building including header plate beam-to-column connections and to show the

effectiveness of these connections on limiting the inter-story drifts. Behavior of the header plate connections is

represented by moment-rotation curve.

Moment-rotation (M-θ) characteristics of bolted connections are indicative for the connection stiffness, strength

and ductility which reflect the connection behavior (En, Avant-projet, En, & Modifications, 2010). In determining

the behavior, geometric variables such as plate thickness, bolt diameter, bolt gauge, etc. are governing. In this

study, the connection stiffness and strength is initially calculated accurately with the component method

considering these variables.

2. DESIGN OF THE MODEL BUILDING

Four-story steel building whose lateral force resisting system consists of high ductile moment frames (special

moment frames) has been considered to show the effectiveness of the stiffness and the strength of the header plate

beam-to-column connections. Plan and 3D view of the building are shown in Fig.2 and Fig.3, respectively. Model

building was designed for modified version of the example building which was included in Turkish Earthquake

Code 2007 (TEC-07) Structural and Seismic Design Guide-Code Application Examples (Aydınoğlu, Celep, Özer,

& Sucuoğlu, 2009). The building has four and three bays in x- and y- directions, respectively. Moment frames in

axes 1 and 4 and A thru E constitute the lateral load carrying systems of the building in x- and y-directions,

respectively. The bay length is 6 m for both directions and the height of each story is 3m. The columns are pinned

for the weak axis and fixed for the strong axis to the foundation. The floor slab system consists of the secondary

beams and reinforced concrete on steel deck which carries the gravity load to columns and acts as a diaphragm.

Composite action neither between slab and beams nor between slab and steel deck is considered. At first, the

building has been designed assuming the header plate connections act as pins. In the design, TEC-07 and Turkish

Code for Design and Construction of Steel Structures 2016 (TCDCSS-16) have been followed. The seismic region

is I and corresponding effective ground acceleration coefficient A0 is equal to 0.40. Local site class is taken as Z2.

Direct analysis method was used to obtain the required strengths including second order effects for the structural

members. For this, 3D structural model of the building has been developed and all analyses have been performed

by using SAP2000. In member sizing, strong column weak beam principle is applied scrupulously. Accordingly,

the columns are chosen to be HE320M. IPE 450 and IPE 270 are used for the girders and secondary beams,

respectively. All members were produced with S235 steel with a specified minimum yield stress Fy=235 N/mm2

and minimum tensile strength Fu=360 N/mm2. Fundamental periods of the building are obtained as T1x=0.979s,

T1y=0.885s. To verify the 2D OpenSEES model, the period corresponding to the next mode in x-direction was also

.

𝜃𝑅

𝑀



acquired, T2x =0.268s. The total equivalent base shear Vt was computed as 603.47 kN and 653.69 kN for the x-

and y-direction, respectively. The analytical model is shown in Fig.3.

Figure 2. Plan view of the structure

Figure 3. 3D Analytical model (SAP 2000)

Fig. 4 shows the dimensions and elements of the typical header plate connection with its details. Thickness of the

end plate is 15 mm and it is welded to beam web with fillet welds and bolted to column with M24-10.9 high-

strength bolts (yield stress = 900 MPa and ultimate stress = 1000 MPa).

IPE 450 IPE 450

C D E

IPE 450 IPE 450

IPE 450 IPE 450

IPE 450 IPE 450

HE320MHE320MHE320M

Semi-rigid

connection

momentconnection

6000 6000 6000SEMI-RIGID

rotSpring

IPE 450

IPE 450

IPE 450

HE320MHE320MHE320M

HE320MHE320MHE320M

HE320MHE320MHE320M

12

34

A B C D E

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

SB

MF IPE450 MF IPE450

MF

IP

E4

50

MF

IP

E4

50

MF

IP

E4

50

MF

IP

E4

50

SEMI-RIGID IPE450 SEMI-RIGID IPE450

pinned

connection

moment

connection

y

x

60

00

60

00

60

00

6000 6000 6000 6000

2000



Figure 4. Details of the header plate connections

The prediction of the beam-column connection behavior can be carried out by means of the component method

which is specified in Eurocode 3 (EC3) (En et al., 2010). Provided that the elementary components governing the

joint behavior are properly identified, the component method can be used. It is not easy to recognize that the

prediction of the overall joint behavior involves the following eight components, such as column web panel in

shear, column web in compression, column flange in bending, end plate in bending, bolts in tension, column web

in tension, beam flange and web in compression, beam web in tension. While the first six components govern the

flexural resistance and rotational resistance, the last two components have to be considered in the evaluation of

the flexural resistance only (Ciro Faella, Vincenzo Piluso, 1999). In this study, prediction of T-stub failure modes

on the end plate connections was applied emphasizing interaction between the bolts and end plate. Based on the

component method, initial stiffness and flexural resistance of the header plate connection were calculated as

18178.86 kNm/rad and as 56.45 kNm, respectively.

It is very important to establish a simple model for estimating the nonlinear moment rotation relationship (M-θ)

of the semi-rigid connections to rationally perform structural analysis. In the present study four parameter model

is used to investigate the moment rotation relationship since the model reflects the strain hardening connection

stiffness. This model is proposed by Richard and Abbott (Kishi, Komuro, & Chen, 2004). The connection moment

in this model is represented as follows:

ki kp r

kp rn 1/nr

0

(R -R )θM= +R θ

θ(1+( ) )

θ

(1)

where Rki = initial connection stiffness and M0=reference connection moment obtained based on the provision of

EC3, Rkp = strain hardening connection stiffness, θ0=reference relative rotation and it is equal to M0/( Rki- Rkp) and

n is shape factor. The shape factor n was assumed 1.7 for the header plate connection type. The connection moment

values are obtained according to the rotation values varying from 0.00 rad to 0.08 rad with the interval of 0.0001

rad. Fig. 5 shows the moment-rotation behavior of the header plate connection in one direction. The curve is

implemented so as to create a cyclic behavior in the analysis. For this, symmetric behavior for both negative and

positive moments is adopted.

HE

320M

IPE 4507

51

50

75

125 62.562.5

15x250 - 300 IPE 450

15

HE320M

bolts

M24-10.9



Figure 5. Moment-Rotation relationship

2.1. Selection and scaling of earthquake accelerograms

Due to increasing interest in structural behavior under earthquake loads of the structure and developments in

computational facilities, nonlinear time-history analysis is becoming more remarkable in seismic analysis of

structures. However, selection of acceleration time histories to represent the design spectrum is critical issue. The

best fitted ground motion time histories are selected and classified taking into account the earthquake magnitude,

focal mechanism and site conditions (Fahjan, 2008).

The criteria given in TEC-07 are considered during the selecting ground motion data ( Turkish Earthquake Code,

2007) ;

The duration of the strong motion part shall neither be shorter than 5 times the fundamental period of the

building nor 15 seconds.

Mean spectral acceleration of generated ground motions for zero periods shall not be less than Ao g and

the mean spectral accelerations of artificially generated acceleration records for 5% damping ratio shall

not be less than 90% of the elastic spectral accelerations, Sae(T), in the period range between 0.2T1 and

2T1 with respect to dominant natural period, T1, of the building in the earthquake direction considered.

The ground motions that meet the above requirements are tabulated in Table 1 for the local site class Z2. The

damping ratio is taken as 5% for the target spectrum curve (Durgun, Vatansever, Girgin, & Orakdogen, 2013).

3. ANALYSIS ESSENTIALS

For the nonlinear dynamic analysis of the moment frame that represents the one direction behavior of the 3D

structural system, OpenSEES (Open System for Earthquake Engineering Simulation) software was used. For the

representation of the building for x-direction, the frame in axis-1 has been considered. First, fundamental periods

of the building, T1x=0.969 s and T2x=0.285 s, were obtained and compared with those from the 3D model. Based

on the comparison, 2D OpenSEES model shown in Fig. 6 is found to be acceptable to represent the behavior of

the 3D building model in x-direction only.

In order to show the contribution of the beam-to-column connections with header plates on the system behavior,

two analytical models have been developed; one having header plate connections’ model defined in Fig. 5 and the

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

10

20

30

40

50

60

70

80Moment Rotation Curve

rotation (rad)

Mom

ent

(kN

m)



other with the header plate connections acting as pinned as assumed in practical engineering. In both models all

beams and columns are modeled using ‘nonlinearBeamColumn’ element from the element library of OpenSEES

software. Beam-to-column connections with the header plates are modeled with ‘rotSpring’ element, which is a

typical definition for a rotational spring. The behavior of pinned connections to the columns is simulated using

‘uniaxialMaterialElastic’ with very small stiffness and strength. However, ‘uniaxialMaterial Hysteretic’ was used

for modelling of the actual behavior of the beam-to-column connections with header plates under the reverse

dynamic loading (Vatansever & Yardimci, 2011) (Mazzoni, McKenna, Scott, & Fenves, 2007). In this modeling,

the moment-rotation curve employed in the rotational spring is idealized with three linear lines defined by three

points, except at the origin, for each direction.

Table 1. Duration and scale factors of the records

Earthquake Duration(s) Scaling factor(α) Peak

acceleration(g)

Imperial

Valley-06 37.815 1.831 0.402

Imperial

Valley-06 38.955 1.064 0.375

Superstition

Hills-02 22.29 1.384 0.416

Northridge

-01 39.98 1.449 0.446

Imperial

Valley-06 28.35 1.558 0.577

Kocaeli 29.995 1.598 0.351

Chalfant

Valley-02 39.975 2.141 0.375

Figure 6. 2D OpenSEES model of the Moment Frame

IPE 450 IPE 450

SEMI-RIGID

rotSpring

A B C D E

IPE 450 IPE 450

IPE 450 IPE 450

IPE 450 IPE 450

HE320MHE320MHE320MHE320M

Semi-rigid

connection

moment

connection

z

x

30

00

30

00

30

00

30

00

6000 6000 6000 6000SEMI-RIGID

rotSpring

IPE 450

IPE 450

IPE 450

IPE 450

IPE 450

IPE 450




HE320M

HE320M

HE320M



The following assumptions were made for the nonlinear dynamic analysis;

The moment frame in Axis 1 was considered for 2D OpenSEES model.

Probable torsional effects induced by the rotation about global z-direction were ignored.

The beam-to-column connections except flexible connections were modeled as a rigid connection.

The supports were fixed to the foundation.

Story masses consisted of full dead loads and thirty percent of the live loads.

The buildings subjected to dead loads, live loads (G+0.3Q) and earthquake loads (E) during the nonlinear

time history analysis.

Rayleigh damping ratio was taken to be %2 in the analysis.

4. ANALYSIS RESULTS AND COMPARISON

Two analytical models were analyzed under seven ground motion histories. Mean of seven ground motion analyses

results is used for the performance evaluation of the models. Fig. 7 shows the inter-story drift ratios. In this figure,

the ratios were computed as the mean of seven maximum values for each story. According to the figure, inter-

story drift ratios obtained from the model including header plate connection behavior were found to be lower than

those from the other model. Pushover curves, shown in Fig. 8, were also obtained for each model to indicate the

contribution of the header plate connections to the overall strength. As can be seen from the figure, taking the

actual behavior of the header plate connection into account provides an additional strength. Base shear increases

by 10% thanks to the actual behavior of the header plate connections. Furthermore, as the actual behavior of the

header plate connections provide additional plastifications they also help to increase the energy dissipation.

Figure 7. Comparison of inter-story drift ratio (avg.)

Figure 8. Pushover curve of the 2D models

0 0.004 0.008 0.012 0.0140

1

2

3

4

inter-story drift ratio

Sto

ry N

um

ber

pin assumption

actual behavior

0 100 200 300 400 500 600 7000

500

1000

1500

Displacement (mm)

Base s

hear

forc

e (

kN

)

Base shear force-Displacement curve

pin assumption

actual behavior



5. CONCLUSION

The goal of the paper is to present to show the effectiveness of the actual behavior of the header plate connections

on limiting the inter-story drifts. For this purpose, nonlinear time history analyses were performed.

Analyses results show that when the actual behavior of the header plate connections defined by the moment-

rotation relationship is utilized inter-story drifts can be limited and an additional strength can be provided for the

system together with an increase in energy dissipation. Finally, considering this connection behavior in the

analyses can also provide an economic solution for the structural systems.

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Structures, 56(4), 553–564. https://doi.org/10.1016/0045-7949(94)00558-K

Aydınoğlu, N., Celep, Z., Özer, E., & Sucuoğlu, H. (2009). Structural and Seismic Design Manuel-Code

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Durgun, Y., Vatansever, C., Girgin, K., & Orakdogen, E. (2013). The Seismic Performance Evaluation of An

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Sciences, 19(6), 266–274. https://doi.org/10.5505/pajes.2013.22932

En, P. N. F., Avant-projet, K., En, N. F., & Modifications, C. A. (2010). European Standard. Management.

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Documents

THE EFFECTS OF BEHAVIOUR OF A BEAM-TO … a moment connection ... Turkish Code for Design and Construction of Steel ... The primary distortion of the steel beam-to-column steel connections