IOP Conference Series: Materials

Science and Engineering

PAPER • OPEN ACCESS You may also like

- Structural performance of concentrically
Seismic performance of eccentrically braced and eccentrically braced frame
J Tanijaya
frames - Influence NiO on the structure, elastic
properties and buildup factor of BaO-CdO-
borosilicate glasses
To cite this article: Rinu G David and N Sarif 2020 IOP Conf. Ser.: Mater. Sci. Eng. 989 012021 M I Sayyed, M A Abdo, H Elhosiny Ali et
al.

- Study the correlation of natural frequency

and damage index of 2D steel EBF-vertical
shear link
View the article online for updates and enhancements. Sarah F Nugroho, M Orientilize and B O B
Sentosa

This content was downloaded from IP address 158.140.164.83 on 07/09/2024 at 15:04

ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

Seismic performance of eccentrically braced frames

Rinu G David1,2 and Sarif N1

1
Department of Civil Engineering, TKM College of Engineering, Kollam, Kerala,
India.
2
Email: rinugdavid@gmail.com
Abstract. The main objective of this research is to assess the seismic performance of
Eccentrically Braced Frames of different configurations. Modelled Eccentrically Braced
Frames subjected to both linear and nonlinear analysis in SAP 2000. The linear analysis gives
an insight to mode shapes and mass participation ratios. The nonlinear analysis includes the
pushover analysis, which provides information about the collapse mechanisms and
performance points. This study also extended to compare the performance of Eccentrically
braced frames with the performance of Special Moment Resisting Frames that helps to
understand the structural efficiency of both systems. This study concludes that all selected
configurations of Eccentrically braced frames undergo small roof displacement that is well
below the target drift whereas SMRF frames will show large displacement. 2D braced EBFs
shows a better post yielding behaviour and is more ductile compared to other frame systems.
Shear links in the EBF frames increase the stiffness of the frame which in turn results in high
base shear demand. Post yielding behaviour of EBF frames can be improved by proper
detailing of beam-column joints and link connections which confirms that performance of EBF
frames is superior to SMRF frames in seismic areas.

1. Introduction
In the present era, the occurrence of earthquakes is quite often compared to ancient times. This
increases the challenge in the construction industry to design the seismic-resistant structures which
should reduce the human casualty, without much compromising the performance of the building. This
resulted in the development of different types of lateral force resisting frames. In high seismic hazard
areas, steel structures face the problem of Lateral stability. Eccentrically Braced Frame (EBF) is a
combination of concentrically braced frame and moment-resisting frame which brings high elastic
stiffness and high inelastic responses to the system [1, 2]. EBFs are one of the systems which resist the
lateral load usually adopted in high seismic areas. Eccentrically braced systems have a ‘structural fuse’
which is the link element that dissipates energy through yielding. AISC Seismic Provisions for
Structural Steel Buildings (1997) changed the link-to-column connections design requirements of EBF
after the Northridge Earthquake. Currently, the AISC Seismic Provisions suggest the designer to either
use a connection after the qualification testing or use a short shear link with reinforcement which
exclude the inelastic action in the link-to-column connection. However, data available for the cyclic
loading performance of EBF link-to-column connections, including connections with reinforcement
are limited.
The present research work mainly focusing to understand the more realistic the behaviour of the
EBF structures by the nonlinear static pushover analysis. This study also compares the performance of
different Eccentrically Braced Frames with Special Moment Resisting Frames and thereby assess the
efficacy of the EBF as a lateral force resisting structure. This study is limited to single bay nine-storey
bare frame having horizontal shear yielding links.

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Published under licence by IOP Publishing Ltd 1
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

2. Special moment resisting frames (SMRF) and Eccentrically braced frames (EBF)
In high seismic areas, Steel Moment Resisting Frames is preferred because of its high capacity of
ductility, speed and ease of their construction. Lateral loads acting on this structural system is resisted
by structural frame members and rigid joints. The lateral stiffness and strength of the whole structure
depends on the strength of the frame and bending rigidity. Comparing to braced systems, moment
frames requires members of larger size to keep the deflection in the lateral direction within the code
limits, which may increase the cost of construction. The inherent flexibility of moment resisting
frames may also induce non-structural damages under the earthquake excitation. After the occurrence
of 1994Northridge earthquake, it is seen that the performance of the special moment resisting frames
is not up to the satisfactory level, because the high ductility property of the system is challenged by the
brittle failure of beam-column connections [3]. Minimum inelastic rotation capacity of 0.03 radian is
required for Beam-to-column connections in SMRFs as per AISC. Proper placing of semi-rigid
connections along with the rigid connection could improve the performance of moment frames.
The unique characteristic of an EBF is that one end of the brace is joined to another brace or a
column through a beam section called a link. Brace force is transmitted either through the shear and
bending action of the link of an eccentric brace. Lateral stiffness of an EBF frame varies by the ratio
of the length of the link to that of the beam. As the length of the link decreases, it makes the frame
stiffer, thereby approaching the stiffness equivalent to a Concentrically Braced Frame. Long links
make the frame more flexible thereby reduces the stiffness equivalent to that of a moment frame. The
foremost function of the link is to provide a weak section in the frame so that its plastic deformation
capacity can be utilised and thereby dissipates more energy due to earthquakes. Ductility and energy
dissipation capacity of EBFs is explained, by evaluating the behaviour of EBF frames in cyclic load
[4]. Well-designed EBF prevents buckling of braces and also link can withstand large deformations
without loss in strength, and make stable hysteretic loops analogous to SMRF.
Short links yields in shear whereas the long links will form plastic moment hinges at the ends. An
intermediate link shows significant amounts of both shear and moment yielding occur. Several shear
link specimens are failed by fracturing the link web before achieving the required inelastic rotation
levels [5] and finds that AISC 2002 loading protocol is inadequate. The revised loading protocol AISC
2002 for shear links achieves the inelastic rotations and thereby avoids the premature failure.
Increasing the link beam length leads to a reduction in the stiffness of the structure whereas the
ductility increases [6]. Premature failure of specimens is observed in the experimental investigation of
link-to-column connections in eccentrically braced frames [7]. The inelastic behaviour of six
Eccentrically Braced Frames under Non-Linear Range is studied in 2014 [8]. The V-braced frame is
more economical whereas Eccentric Inverted-V frame shows a better performance. Stiffness, ultimate
capacity, and inelastic member deformation requirements of an active beam links in Eccentrically
Braced Frames were compared [9]. The behaviour of long links in eccentrically braced frames is
analysed in 1989 [10]. Long links attached to columns is not usually preferred in EBFs. The present
study aims to assess the performance of different configurations of Eccentrically Braced Frames in
seismic areas. This study also aims to compare the seismic performance of Eccentrically Braced
Frames and Special Moment Resisting Frames.

3. Methodology and Numerical modelling of frames

3.1 General
From the past researches, a suitable methodology is adopted to analyse the performance of the frames
in the seismic environment as shown in Figure 1. The numerical modelling is done with the help of
SAP 2000.The effective time period, roof displacement, performance points, lateral stiffness, post
yielding behaviour, the formation of the hinge mechanism is discussed from the results of the analysed
model. Link damage is stated in terms of post-yield and inelastic deformation limits.

2
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

Figure 1. Methodology.
3.2 Pushover method
This nonlinear static procedure can be used to find the maximum displacement of the structure. By
using the capacity spectrum method, the intersection point of the capacity (pushover) curve and a
reduced response spectrum can be found out (ATC40 Vol. 1). In this method, the global force-
displacement capacity of the structure can be plotted and is used to compare the response spectra
representations of the earthquake demands. In this analysis, the structure is loaded in a specific
predefined pattern and is boosted until the target displacement or before the collapse. SAP2000 have
the ability to carry out nonlinear static pushover analysis for both two and three-dimensional
structures as described in ATC-40 and FEMA-273 documents.
3.3 Hinge details
The inelastic behaviour of SMRF is obtained by the introduction of plastic hinges which estimates the
additional capacity of the frames beyond the elastic limit. In this research, auto hinges are used for
beam and column elements. From Tables in ASCE 41-13, moment M3 hinges are assigned at the beam
endings and for columns, P-M2 hinges are provided at both ends. Nonlinear behaviour of EBF is
captured by modelling the plastic hinges in the link member using the nonlinear modelling parameters
as recommended by ASCE41-13 (ASCE, 2014). A deformation-controlled shear (V2) hinge is
provided at the middle of the link where shear is expected to be maximum. All other elements are
designed as elastic elements as they are expected to behave linearly. A default kinematics hysteresis
model is considered in the study.
3.4 Modelling and Designing of frames
SAP2000 version 20 is the platform used for numerical modelling and analyses of EBFs. Both
material nonlinearity and geometric nonlinearity such as P-Delta effects are considered for this study.
Fixed base restraints are provided in all cases.

(a) SMRF (b) EBF 1 (c) EBF 2 (d)EBF 3 (e) EBF

4
Figure 2. Different configurations selected for the study.

3
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

The 9 storey 2D building SMRF and EBF designed as per ASCE provisions. Grade of steel used
for the frame is A992 steel G50. The single bay 9storey 2D frame has a bay width of 9.15m, with a
storey height of 3.96m. The soft storey of the frame have a height of 5.49m. The 2D frame is designed
and is checked in SAP 2000. The designed frame section details are shown in Table 1 and Table 2. In
this study, four different configurations of EBF frames are selected namely, Split V- Braced EBF, V-
Braced EBF, D Braced EBF, 2D Braced EBF represented as EBF 1, EBF2, EBF3, EBF4 respectively.

Table 1. Section details of EBF frames.

Storey Beam size Column size Brace size Link
size
1 W 150X24 W 250X131 HSS 335.6X335.6X12.7 W 150X24
2 W 150X22.5 W 250X131 HSS 406.4X406.4X12.7 W 150X22.5
3 W 150X22.5 W 250X115 HSS 406.4X406.4X12.7 W 150X22.5
4 W 150X18 W 250X101 HSS 406.4X406.4X12.7 W 150X18
5 W 150X18 W 250X89 HSS 406.4X406.4X12.7 W 150X18
6 W 150X13.5 W 250X80 HSS 406.4X406.4X12.7 W 150X13.5
7 W 150X13.5 W 250X73 HSS 406.4X406.4X12.7 W 150X13.5
8 W 150X13 W 250X67 HSS 406.4X406.4X12.7 W 150X13
9 W 150X13 W 250X58 HSS 406.4X406.4X12.7 W 150X13

Table 2. Section details of SMRF.

Storey Beam Size Column Size
1 W 150X24 W 250X131
2 W 150X22.5 W 250X131
3 W 150X22.5 W 250X115
4 W 150X18 W 250X101
5 W 150X18 W 250X89
6 W 150X13.5 W 250X80
7 W 150X13.5 W 250X73
8 W 150X13 W 250X67
9 W 150X13 W 250X58

Table 3. Link length of different configurations.

Link Length
Story EBF 1 EBF 2 EBF 3 EBF 4
1 1.22 0.61 1.08 0.61
2 0.61 0.60 1.08 0.61
3 0.61 0.60 1.08 0.61
4 0.91 0.50 1.08 0.46
5 0.91 0.50 1.08 0.46
6 1.22 0.61 1.08 0.61
7 1.22 0.61 1.08 0.61
8 1.83 0.91 1.08 0.99
9 1.83 0.91 1.08 1.83

4
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

4. Results and discussions

4.1 Linear analysis
During earthquake shaking, building oscillates which induces inertia force in the building. During
earthquake shaking, inertia force is induced in the building due to its oscillation. The magnitude of
induced inertia force, its intensity and duration of oscillation depends on the dynamic features of a
building. Dynamic characteristics of building includes modes of oscillation and damping. For steel
buildings, the damping ratio is commonly adopted as 2%. The modal analysis gives a mathematical
description of structures about its dynamic behaviour. The time period and frequency of different
structural systems are shown in Table 4.

Table 4. Time period and frequency of different configurations.

Structural Systems SMRF EBF 1 EBF 2 EBF 3 EBF 4
Mode1
Time Period 1.995 0.306 0.292 0.359 0.358
Frequency 0.501 3.268 3.425 2.788 2.795
Mode 2
Time Period 0.611 0.133 0.102 0.133 0.158
Frequency 1.636 7.529 9.84 7.499 6.332
Mode 3
Time Period 0.276 0.085 0.072 0.083 0.115
Frequency 3.62 11.790 13.825 11.988 8.719

From Table 4, it is clear that EBF has large stiffness as compared to a SMRF which owing to large
time period to SMRF frames. SMRF undergoes large oscillations and takes more time to come back to
its mean position. Introduction of braces in the structure improves the stiffness of the structure and
reduced the time period. Among the four configurations, EBF 2 has shown the maximum stiffness and
reduced the time period to 0.292seconds. EBF 2 is 85% stiffer than SMRF so that it can attract large
forces into it. Mass participation of EBF frames in higher modes is negligibly small as compared to
SMRF. Thus, lower modes are dominating the overall response of the structure in EBF systems.
Introducing braces in EBF improves the in-plane stiffness in the vertical plane and increases the
torsional stiffness of the building.

4.2 Pushover analysis

Earthquake-resistant design controls the type of damage and sequence of its occurrence in various
structural elements of a building. In this design, some structural damage is allowed for normal
buildings, but it prevents the collapse condition during a strong earthquake shaking. The nonlinear
analysis makes it possible to understand the whole failure mechanism of the building. In this study,
pushover analysis is used to study the nonlinear behaviour of the structure. The whole deformability of
the building is assessed from the Pushover Analysis. The ideal lateral load-deformation curve of a
building in pushover analysis reveals the linear, nonlinear and plastic behaviour under the monotonic
lateral displacement loading.
Five different types of bare frames with the same cross-sections are analysed for the study and the
undergo pushover analysis. The graph showing the variation of base shear with displacement is shown
in Figure 3. EBF 4 is showing the maximum lateral strength and more ductile compared to other
systems whereas EBF 2 is the stiffest configuration. EBF 2 frame has two links at a floor level which
is connected to fixed support using braces. Additional support increases the redundancy of the
structure and makes the structure stiffer. SMRF frames show poor resistance to lateral load and are
more flexible compared to other systems. When the demand curve goes through the capacity curve of
the structure makes the performance point.

5
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

800
700

BASE SHEAR (kN)

600
500 SMRF
400 EBF 1
300 EBF 2
200
EBF 3
100
EBF 4
0
0 0.05 0.1 0.15 0.2 0.25
DISPLACEMENT (m)

Figure 3. Graph showing variation of base shear with displacement for different structural systems.

Table 5. Performance points of different configurations.

Parameters SMRF EBF 1 EBF 2 EBF 3 EBF 4

Performance 16.223 218.967 213.75 191.572 186.494

Point, V (K N)
Roof Storey 0.3 0.033 0.029 0.038 0.044
Displacement
(M)
Effective Time 1.599 0.257 0.245 0.305 0.309
Period (S)
Table 5 illustrates the performance point of all five frames and is compared. EBF1attracts a large
amount of lateral force compared to other frames. SMRF frames have larger roof displacement and
base shear demand of magnitude 16.223k N. EBF2 frame reduces the roof storey displacement to 90%
as compared to SMRF frames. SMRF resist lateral loads by using both beams and columns. The axial
forces, bending moment and shear force generated in them will handle these forces. Braces and links
in EBF frames diminish the overall lateral displacement, bending moment and shear force demands on
beams and columns. Thus, EBF frames are able to resist more lateral loads as compared to SMRF and
dissipate energy through shear deformations (shear link).

4.3 Post yeild mechanisms

Due to reversed cyclic loading, inelastic material steel will enter in to a stage beyond yield and
eventually hysteresis will take place. EBF frames enter into the inelastic range after the yielding is
much earlier than SMRF frames. EBF frames designed by the capacity design principles. Here links
beam is the weak element which shows the inelastic response. In all the configurations of EBF, it is
seen that nonlinear hinges are formed only in the link elements which are assigned with shear hinges
and all other elements are in the elastic range. This behaviour of frames validates the capacity design
principles. Figure 4 shows the collapse mechanisms of different frames. Uniformity in forming the
hinges is not achieved in these frames. In EBF 3 formation of hinges is concentrated only on the first
floor whereas in EBF 1 and 2 shows the formation of more hinges in two stories. Among all the four
EBF frames, EBF 4 shows a better formation of hinges. Non-uniformity in the formation of hinges is
due to the presence of the soft storey. The soft storey is subjected to large forces and is stressed more
compared to other storeys resulting in the damage to be concentrated in the soft storey and it results in
a collapse of link elements.

6
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

(a) EBF 1 (b) EBF 2 (c) EBF 3 (d) EBF

4
Figure 4. Collapse mechanisms of EBF frames.

From the analysis, the EBF 4 frame shows that up to a roof displacement of 0.02, the frame is in
the collapse prevention stage. Table 6 shows the maximum roof displacement permitted to each frame
before the collapse. EBF 4 frame shows the maximum displacement of 0.129 m before collapse
confines that it is more ductile compared to other frames.
Table 6. Maximum displacement of different configurations.
Frames Maximum
Displacement
(m)
EBF 1 0.101
EBF 3 0.094
EBF 4 0.129
5. Conclusions
Seismicity of the world is increasing day by day. This creates a new challenge in the construction
industry to create more earthquake-resistant infrastructures having desired performance and
economically viable structures. In this study, seismic performance of different configurations of EBF
is analysed and is compared with the performance of SMRF. The main criteria selected for the study
are target drift and post yield mechanisms. The frames under study are subjected to both linear and
nonlinear analysis. Major observations and conclusions arrived from the study are:
1. Mass participation ratios of EBF frames are much more in lower modes than SMRF. Therefore,
the lower modes predominate the overall response of the structure.
2. Modal analysis suggest EBF 2 is stiffer than all other frames, having a natural time period of
0.292 seconds.
3. Pushover analysis gives the performance point of various frames. Introduction of braces and
links in EBFs makes the frame stiffer and reduces the displacement. EBF 2 reduces displacement to
90% as compared to SMRF whereas it enhances the demand of the structure to a magnitude of 213.75
k N.
4. SMRF show a maximum displacement of 300mm whereas EBF frames shows a maximum
displacement of 44mm which is below the target displacement of 93mm.
5. Link beams dissipate energy through shear deformations which reduce the demand on beams and
columns.
6. Post yield mechanisms of EBF 4 shows a better formation of hinges as compared to other EBF
frames

7
ERTSE 2020 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 989 (2020) 012021 doi:10.1088/1757-899X/989/1/012021

7. Non uniformity in the formation of hinges is due to the presence of the soft storey. This can be
improved by proper detailing of beam column joints and link connections.
8. EBF 4 allows a displacement of 0.129m before the collapse and is exhibiting more ductile
behaviour.
9. Among all these frames, EBF 4 can be selected as the better configuration, whose displacement
values are below the target drift, enough lateral strength, better post yielding mechanisms and is more
ductile compared to other frames.
10. Stiffness of the structure can be improved by EBF frames results in minimum displacement as
compared to SMRFs.

6. References
[1] Fujimoto M, Aoyagi T, Ukai K, Wada A and Saito K 1972 Structural characteristics of
eccentric K-Braced frames Transctions AIJ 195 39-49
[2] Tanabashi R, Naneta K and Ishida T 1974 On the rigidity and ductility of steel bracing
assemblage In Proceedings of the 5th World Conference of Earthquake Engineering
1 834-40
[3] Bruneau M, Uang C M and Whittaker A S 1998 Ductile design of steel structures
(NewYork: McGraw-Hill)
[4] Popov E P, Kasai K and Engelhardt M D 1987 Advances in Design of Eccentrically Braced
Frames Earthquake Spectra 3 43-55
[5] Okazaki T, Arce G, Ryu H C and Engelhardt M D 2005 Experimental study of local buckling,
overstrength, and Fracture of links in eccentrically braced frames Journal of Structural
Engineering 131(10) 1526-38
[6] Naji A and Zadeh M K 2019 Progressive collapse analysis of steel braced frames Pract.
Period. Struct. Des. Constr. 24 1-9
[7] Okazaki T, Engelhardt M D, Drolias A, Schell E, Hong J K and Uang C M 2008 Experimental
investigation of link-to-column connections in eccentrically braced frames Journal of
Constructional Steel Research 65 1401-12
[8] Tande S N and Sankpal A A 2014 Study of inelastic behavior of eccentrically braced frames
under non-linear range IJLTET 4 273-86
[9] Hjelmstad K D and Popov E P 1983 Seismic Behaviour of Active Beam Links in Eccentrically
Braced Frames Report no. UCB/EERC-83/15. Berkeley (CA): Earthquake Engineering
Research Institute
[10] Engelhardt M D and Popov E P 1989 Behaviour of long links in eccentrically braced frames
Report no. UCB/EERC-89/01. Berkeley (CA): Earthquake Engineering Research Institute