Seismic Assesment of Different Types of Eccentrically Braced Frames

IJIRST –International Journal for Innovative Research in Science & Technology| Volume 3 | Issue 04 | September 2016 ISSN (online): 2349-6010

All rights reserved by www.ijirst.org 123

Seismic Performance Assessment of Different

Types of Eccentric Braced Systems

Sreeshma. K. K Nincy Jose

M. Tech. Student Assistant Professor

Department of Civil Engineering Department of Civil Engineering

FISAT, Kerala, India- 683577 FISAT, Kerala, India- 683577

Abstract

Steel structures are exhibit ductile behaviour when subjected to transient lateral loading, caused by wind or earthquake action.

Steel bracings are lateral load resisting system used in seismic region. In eccentrically braced frames, a distance is either created

between the two ends of the bracing members, or between the bracing member and the column, or between the bracing member

and the beam. The created distance is called link. The main function of the link is to provide a weak section in the frame which

provides plastic deformation capacity and the energy released by the earthquake. EBF configuration is similar to traditional

braced frames with the exception that at least one end of each brace must be eccentrically connected to the frame. The energy

dissipation is achieved through the yielding of a beam segment called the link, while the other frame members, including outer

beam segments, braces, and columns, should remain essentially elastic. Present study deals with eccentrically braced frames with

short link. Assess the performance of different types of eccentrically braced frames by performing seismic analysis over the

structure. The variation of performance with change in link length, height of the building was also considered in this study.

Keywords: Eccentrically Braced Frames, Plastic Deformation, Seismic Analysis

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I. INTRODUCTION

Steel structures are widespread; they exhibit ductile behavior when subjected to lateral loading, caused by wind or earthquake

action. There are three main types of frames in steel structures, Moment frames, truss moment frames, and braced frames. Braced

frames are of two types-concentrically braced frames (CBF) and eccentrically braced frames (EBF). The concentric bracings

increase the lateral stiffness of the frame and they usually decrease the lateral drift. However, increase in the stiffness may attract

a larger inertia force induced due to earthquake. Further, while the bracings decrease the shear forces and bending moments

in columns and they increase the axial compression in the columns to which they are connected. Eccentrically braced frames

(EBFs) are relatively a new lateral force resisting system developed to resist seismic events in a suitable manner. Eccentric

bracings minimize the lateral stiffness of the system and improve the energy dissipation capacity. The energy dissipation is

achieved through the yielding of a beam segment called the link and the other frame members, including outer beam segments,

braces, and columns, should stay essentially elastic. The main function of link is to provide a weak section in the frame which

provides plastic deformation capacity and dissipate the energy released by the earthquake. EBF systems with shear yielding links

are stable and exhibit more ductility than in the case of EBF systems with flexural yielding links, since internal shear force is

constant along the length of the link. This present study concentrated on eccentrically braced frames with shear links. The

performance of different types eccentrically braced frames is evaluated and it compared with concentric and normal steel

building. Linear static, linear dynamic and non- linear static analysis were performed over the structure and its performance are

evaluated based on storey displacement, storey drift, time period, ductility and energy dissipation. It is also evaluate the frame

performance with two different heights and with different shear link lengths by conducting same seismic analysis.

II. LITERATURE REVIEW

Significant researches were carried out on seismic behaviour of eccentrically braced frames and a few published works on

seismic response steel framed structures are reviewed in this section. Muthumani K studied the seismic performance of steel

moment resisting frames with eccentric braces. It has been observed that the performances of building 6 storeys, 9 storey and 15

storey with eccentric configuration has minimum displacement. SandaKoboevic et al studied the global seismic response of 3-

and 8-story eccentrically braced frames (EBFs), designed for western and eastern North American locations. Different models

did not consistently predict either the magnitude of maximum deformation or their location over the height of structure, and large

record-to-record variations were observed when examining 84th percentile results. M. A. Musmar investigated the effect of link

on eccentrically braced frames. The study incorporated applying lateral loading to several types of eccentrically loaded frames.

All eccentric frames in this study exhibit lateral stiffness close to that of concentrically braced frames and demonstrate ductility

similar to that of the Moment Frame hence EBFs are efficient laterally stiff framing systems with significant energy dissipation

capability to accommodate large seismic and wind forces.

Seismic Performance Assessment of Different Types of Eccentric Braced Systems (IJIRST/ Volume 3 / Issue 04/ 023)


III. MODELING IN ETAB

Modeling and analysis of the tank is performed in ETAB 2015. Two group of models were modeled in ETAB 2015.One group

consist of 6 number of 6 storey models and another group consist of 6 number of 10 storey models. Each group consist of four

types of steel eccentric braced frames such as inverted- v braced frame, diagonally braced frame, Chevron braced frame(V

braced frames), Zipper type frame, one concentrically-x braced frame and one normal moment resisting frame. Concentric x

configuration was chosen because various studies show that among different types of concentric configuration concentric x

configuration show better performance. The geometric details and the section details of the building are provided in table. 1 and

2 respectively. Table – 1

Geometric Details of the building

Type of building Steel

Plan area of building 24x18

No bays in X direction 5

No bays in Y direction 3

Number of stories 10 and 6

Bay width 6m

Total height 30m(10 storey),18m(6 storey)

Storey height 3m

Table - 2

Section Properties

Column ISWB350

Beam and links ISHB350

Bracing ISB 91.5X91.5X5.4,ISNB250H

Fig. 1: ETAB model of MRF and V-type EBF

Fig. 2: ETAB model of inverted V-type EBF and Diagonal EBF

IV. LOADS CONSIDERED IN THE STUDY

The loads applied on building consist of dead load, live load, wind load and earthquake load .It is assumed that building is

situated in Kerala that means in moderate seismic region and is a commercial steel building. So loads are considered from



conditions corresponding IS: 875-1987 and IS: 1893(Part 1)-2002.The gravity loads such as super dead load, live load applied on

structures are 2 KN/m2 ,3 KN/m2 respectively and dead loads acting on a structure will calculate the software itself.

V. ANALYSIS RESULTS

Static Analysis

The top storey displacement and structural weight are taken as parameter from this analysis. Top storey displacement and structural weight of

CBF, EBF and MRF are studied and compared. Also the top storey displacement and structural weight of four different types of EBF such as v-

type, inverted v type, d-type and z type also studied and compared. The results obtained for 10 storey models are given below in figure

3,4,5,6.The results for 6 storey also same as that of 10 storey.

Fig. 3: Storey displacement for CBF,EBF,MRF(10 storey)

Fig. 4: Storey displacement for four types of EBF (10 storey)

Comparison of the structural weight of 10 storied and 6 storied CBF, EBF and MRF are shown in below table 3.It is observed

that structural weight of EBF is in between CBF and MRF. The structural weight of V-TYPE is higher than other configuration. Table – 3

Structural weight (kN) TYPE 10 storey 6 storey

MRF 10545.3 6381.7

V-type EBF 10830.25 6581

Inverted V-type EBF 10814 6574

D-type EBF 10758 6528

Z-type EBF 10828 6580

CBF 11018 6714

Response Spectrum Analysis

The results of response spectrum analysis are shown in following graph. The storey displacement, storey drifts and time period

were taken as parameter for this analysis.

Fig. 5: Storey displacement for CBF, EBF, MRF (10 storey)



Fig. 6: Storey displacement for four types of EBF (6 storey)

Fig. 7: Time period for CBF, EBF, MRF

Push Over Analysis

The results of pushover analysis are shown in the following table. The hinge formation at the final step of push is also depicted.

The push is provided in the x-direction. The ductility and energy dissipation of building can be calculated from the push over

curves. The area under pushover curves gives the energy dissipated by the building. The area under push over curve is high

means the building have high energy dissipation capacity during earthquake. Table – 4

Ductility and energy dissipation for 10 storey

Model Ductility Energy Dissipation (Kn-M)

MRF 8.03 4846

V- TYPE EBF 2.35 2269

IV-TYPE EBF 2.19 2187.6

Z-TYPE EBF 4.06 2554.5

D-TYPE EBF 2.16 2383.5

CBF 1.27 1807

Table - 5

Ductility and energy dissipation for 10 storey

Model Ductility Energy Dissipation (Kn-M)

MRF 7 2735

V- TYPE EBF 2.54 1142

IV-TYPE EBF 2.1 1091

Z-TYPE EBF 4.94 1579

D-TYPE EBF 2.5 1207.5

CBF 1.52 773.5

VI. CONCLUSIONS

The three dimensional analysis done in ETABS 2015 provided approving results in the form of acceptable control of parameters.

The results showed that MRF have the lowest lateral strength and lateral stiffness and high deformation capacity. Building

braced either eccentrically or concentrically the lateral load resisting capacity of the building improved. The performance of EBF

is in between CBF and MRF. The displacement, drift, structural weight, time period, energy dissipation, ductility all shows that

EBF is improvement over both CBF and MRF and also there is no variation in performance of EBF with the height. The

decrease in time period of the building can be used as means to evaluate the behavior of the building during a seismic event. The

decrease in time period of the building is due to increase in building stiffness that is facilitated by providing either CBF or EBF.

But EBF shows less time period than CBF. Push over curves gives good result about energy dissipation and ductility. The energy

dissipation will vary with height, building with 10 storey have high energy dissipation than 6 storey. The displacement, drift,

ductility, energy dissipation, time period are maximum for Z-type as compared to other three types, Z-type showed the better

performance, so it is the best configuration.



REFERENCES

[1] Xue Ming Han, P.Eng., P.E, “Eccentrically braced frame design for moderate seismic regions”, The 14 th World Conference on Earthquake Engineering

October 12-17, 2008, Beijing, China

[2] M. A. Musmar“,Effect of link on eccentrically braced frames”, Journal of Engineering Sciences, Assiut University, January 2012 [3] SandaKoboevic, Jonathan Rozon, and Robert Tremblay, “SeismicPerformance of Low-to-Moderate Height Eccentrically Braced Steel Frames Designed for

North American Seismic Conditions”, American Society of Civil Engineer2012.

[4] ArdeshirDaneshmand,BehrokhHosseiniHashemi,“Performance of intermediate and long links in eccentrically braced frames”, Journal of Constructional Steel Research 70 (2012) 167–176, sciencedirect

[5] Boaco, P.P. Rossi, “Seismic behavior of eccentrically braced frames”, Engineering Structures 31 (2009) 664674, science direct. [6] M. N. Chimeh& P. Homami, “Efficiency of bracing systems for seismic rehabilitation of steel structures”,15 WCEE 2012

[7] GülYiğitsoy,CemTopkaya, “Stability of beam in eccentrically braced frame”, Journal of Constructional Steel Research 96 (2014) 14–25

[8] M. Naghipour, N. Javadi, A. “Investigation of RBS Connection Ductility in Eccentrically Braced Frame,Procedia Engineering 14 (2011) [9] Mazen Ali Musmar, “Effect of link dimension on D type eccentric steel frames”,American Journal of Engineering and Applied Science ,2013

[10] Ramya A, Muthumani K, Nafeez Ahmed L, “Performance of eccentrically braced frames under the action of lateral load”,IJRET:

Seismic Assesment of Different Types of Eccentrically Braced Frames

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