Behavior of Shear Link of WF Section with Diagonal Web Stiffener of Eccentrically Braced Frame (EBF) of Steel Structure

Transcription

1 ITB J. Eng. Sci. Vol. 42, No. 2, 21, Behavior of Shear Link of WF Section with Diagonal We Stiffener of Eccentrically Brace Frame (EBF) of Steel Structure Yurisman, Bamang Buiono, Muslinang Moestopo & Mae Suarjana Civil Engineering Department, Institute of Technology Banung. Astract. This paper presents results of numerical an experimental stuy of shear link ehavior, utilizing iagonal stiffener on we of steel profile to increase shear link performance in an eccentric race frame (EBF) of a steel structure system. The specimen is to examine the ehavior of shear link y using iagonal stiffener on we part uner static monotonic an cyclic loa. The cyclic loaing pattern conucte in the experiment is ajuste accoring to AISC loaing stanars 25. Analysis was carrie out using non-linear finite element metho using MSC/NASTRAN software. Link was moele as CQUAD shell element. Along the ounary of the loaing area the noal are constraint to prouce only one irection loaing. The length of the link in this analysis is 4mm of the steel profile of WF 2.1. Important parameters consiere to effect significantly to the performance of shear link have een analyze, namely flange an we thicknesses, thickness an length of we stiffener, thickness of iagonal stiffener an geometric of iagonal stiffener. The ehavior of shear link with iagonal we stiffener was compare with the ehavior of stanar link esigne ase on AISC 25 criteria. Analysis results show that iagonal we stiffener is capale to increase shear link performance in terms of stiffness, strength an energy issipation in supporting lateral loa. However, ifferences in isplacement uctility s etween shear links with iagonal stiffener an shear links ase on AISC stanars have not shown to e significant. Analysis results also show thickness of iagonal stiffener an geometric moel of stiffener to have a significant influence on the performance of shear links. To perform valiation of the numerical stuy, the research is followe y experimental work conucte in Structural Mechanic Laoratory Center for Inustrial Engineering ITB. The Structures an Mechanics La rotary PAU-ITB. The experiments were carrie out using three test specimens with moel an imension ientical to the moel in the numerical stuy. Experimental testing apparently has shown results of the same ehavior as preicte in the numerical stuy. However, when it is compare to the shape of the hysterical curve, a slight ifference is apparent. This is ue to the influence of stiffness of olt joints an the supports which is ifficult to moel precisely in the numerical stuies. Keywors: cyclic loaing; iagonal we stiffener; uctility; energy issipation; monotonic loaing; shear link; stiffness; strength. Receive June 22 n, 21, Accepte for pulication July 12 th, 21.

2 14 Yurisman, et al. 1 Introuction Inonesia is locate in a tectonic area with high occurrences of earthquakes. This has resulte in many efforts to reuce risk create y this situation. Most fatalities ue to earthquakes are cause y uiling collapse. To prevent such risks, esigns of earthquake resistant uilings are ase on a prevention concept where in the case of a major earthquake, uilings may experience amages, an however people insie the uiling must remain unharme. Base on Inonesia s National Stanar (SNI) for earthquake resistant uilings is esigne y allowing the uctility concept. Base on this concept, in the event of a major earthquake, certain elements of a structure may unergo plastification. This plastification is a mechanism to issipate earthquake energy on the structure, preventing the structure to collapse. To allow this, elements nee to e esigne to experience a staile inelastic eformation uring a major earthquake. A steel structure is regare as an earthquake resistant structure with a remarkale performance. This is ue to unique characteristics of steel. By relying on the uctility an high strength characteristics, steel is suitale to e applie in areas with high seismic activity. Uner the steel structure s category, there are three systems which are resistant to earthquakes, (1) Moment Resisting Frame (MRF); (2) Concentrically Brace Frame (CBF); an (3) Eccentrically Brace Frame (EBF). MRF has superiority in energy issipation aility to achieve require uctility, however this structure lacks of strength an stiffness resulting the requirement of a larger surface area an an expensive oule plate panel zone to fulfill rift requirements. CBF efficiently fulfills eformation limits through its framework action; however the staility in the mechanism of energy issipation is limite [1]. The limitation of oth structures has resulte in the evelopment of a new structure system name Eccentrically Brace Frame (EBF) structures. The ifference in the three steel structural systems is shown in Figure 1. P Figure 1 Behavior Differences in Three Steel Structure s System [2]. Δ

3 Behavior of Shear Link of WF Section 15 2 The Ojective of Research The article presente in this paper is part of a Doctor s stuent research conucte in Civil Engineering Department of Institute of Technology Banung (ITB) ivision of structural engineering. The specimen of the stuy is to otain an EBF structure with maximum performance through increasing performance of link elements. To achieve the specimen, this stuy is aims to: 1) Unerstan mechanism of earthquake energy issipation in eccentric race frame steel framework structure. 2) Determine parameters which significantly affect link element ehavior in eccentric race frame, 3) examine each parameter in resulting an improvement of performance link, 4) examine the usage of iagonally place we stiffeners on link element increasing link performance in EBF. 3 Literature Stuy 3.1 General Overview of Eccentric Brace Frame (EBF) Structure System Eccentric race frame (EBF) structure system is a evelopment from the two previous lateral force resistant systems, which are MRF an CBF. MRF has superiority as it is very uctile an it capale of for large energy issipation capacity, ut low in stiffness, while CBF has high stiffness ut a small energy issipation capacity. Therefore EBF was evelope to perfect oth MRF an CBF systems. Figure 2 illustrates forms of EBF system which are generally applie [3]. EBF system joins each avantage from oth structure systems, an ecrease the weakness. The EBF characteristics are: 1) has a high elastic stiffness; 2) has a stale inelastic response uner lateral cyclic loaing; 3) has a high uctility an energy issipation aility. In EBF, asorance of earthquake energy is carrie out through a mechanism of plastic joint formation on link elements. Link elements are part of the eam which is assigne to issipate energy in the event of a large earthquake. Plastic hinges occurring on link elements can e in a form of shear or flexural yieling. The type of yieling is epenent on link length.

4 16 Yurisman, et al. a a c c c a a a a c c c c a a c c c a a c c a = link = eam segment outsie of link c = iagonal race = column Figure 2 Eccentrically Brace Frame Configurations [3]. 3.2 Link Element Characteristic in EBF System Link is an element insie EBF system which ehaves as a short (eep) eam an on oth sies apply shear forces with opposite irections along with the corresponing flexures (see Figure 3). Plastification occurring on link element is cause y oth forces aove; therefore link element ehavior in overall can e classifie into two types namely; 1) Moment (flexural) link an 2) Shear link. Link is classifie as shear link if yieling is cause primarily y shear, an is classifie as moment link if the yieling is cause y flexural moment. M M V V Figure 3 Shear Forces on Link Element [4-5].

5 Behavior of Shear Link of WF Section 17 Deformation after yieling occurre of a link eam is cause y either shear yieling or flexural yieling or comination of oth. By applying a simple analytical moel, it can e etermine the exact limit etween flexural an shear mechanisms. This limit can e escrie y using a shear span which simultaneously yiels in oth flexure an shear conition [6]. P t f a f Figure 4 Shear Span an Surface of A Simple Cantilever Beam [7-8]. Shear span is a comparison etween moment with shear on a point or spacing etween point M= (inflection point) with a maximum moment point with no increase in loa etween oth points. Shear span in its simplest form is escrie as a cantilever eam loae on its en, as seen in Figure 4. Behavior of link in EBF system uring mechanism situation is escrie with the same concept, which is a simple shear span as in Figure 4. A alance strength ratio is achieve when shear span experiences oth flexural an shear yieling simultaneously. M a = (1) V Where a = length of cantilever eam shear span, M = moment working on eam, V = shear force working on eam. Meanwhile length of cantilever in alance plastic conition can e translate in the formula: a M p = (2) Vp where: M. p = Z x Fy, V p =,6. Fy.. t w a = Comparison of alance strength ratio

6 18 Yurisman, et al. Mp = plastic moment, Vp = plastic shear force, Zx = surface moulus x axis irection, = height of eam surface profile WF, t w = thickness of we profile WF, Fy = yiel stress. The cantilever eam will yiel cause y shear if the cantilever s length is less than a an will yiel cause y flexure if the length of cantilever excees a. From the perspective criteria, link esign is consiere as a confine eam on oth ens, alance link length can e given in the formula: M Vp e = 2a = 2 p (3) where: e = alance link length. Base on the yiel mechanism occurring in link eams, link is ivie into two namely moment link an shear links epening on flexural an shear yiels mechanism. However, there is no apparent limit etween shear link an moment link. To ientify a link yiels cause y moment or shear, experiments are require. Pure shear occur uring link length (e) maximum 8 % from shear span length in equilirium (e ); thus e 8% e =, 8.2a = 1,6Mp/Vp. While pure flexural conition is consiere to occur when e excees 5Mp/Vp Behavior of eam link etween oth conitions is illustrate y applying strength ratio Mp/Vp as follows: 1) pure shear link if: e < 1,6Mp/Vp, 2) ominant shear link if 1,6Mp/Vp < e < 2,6Mp/Vp, 3) flexural ominate link if: 2,6Mp/Vp < e < 5,Mp/Vp, 4) pure flexural link if: e > 5Mp/Vp. 3.3 Effects of We Stiffener towars Shear Link Performance Due to the high uctility eman on short links, the flange area of the link surface (WF profile) might experience uckling phenomena; therefore it is require to install we stiffeners. If these we stiffeners are not installe, a large premature torsional uckling may occur on the we which in turn might cause lateral torsional uckling on the link. Figure 6 shows shear link WF profile with a spacing to we stiffener as far as a where a is we stiffener spacing. Experiments conucte y Ghoarah [9] on short links has shown links with we stiffeners result in igger shear aility, along with wier an more staile hysteric loops. Other researchers such as Kasai an Popov [1,12] have etermine a few simple requirements regaring we stiffener spacing with a maximum inelastic rotational angle (γ p ) to the eginning of we torsional uckling, which are as follows :

7 Behavior of Shear Link of WF Section 19 a = 29t w /5 then γ p = ±. 9 ra. a = 38t w /5 then γ p = ±.6 ra. a = 29t w /5 then γ p = ±.3 ra. a = we stiffener spacing, = eam height, t w = we thickness. f t w a a a a Figure 5 Shear Link with Spacing of Intermeiate We stiffener a [11]. The current coe of practice of we stiffener spacing is liste in AISC 25, intermeiate we stiffener for shear links cannot e less than (3t w /5) an the thickness of we stiffener cannot e less than t w or 1 mm. 4 Metho of Research This research was conucte with two methos, namely, (1) numerical stuy an (2) experimental stuy. Numerical stuy is aime to examine ehavior of shear link uner cyclic an monotonic loa, also to etermine parameters which influence significantly uner the performance of shear link. Numerical stuy was conucte with non linear finite element using MSC/NASTRAN software where link is moele using element of Shell CQUAD4. Element moels, up until shear links WF profile were mae. These were fixe on oth ens, where one en was given 1 DOF in irection of the Z axis, which can e seen in Figure 6. The loa given to test specimen was in the form of static monotonic an cyclic loa uner isplacement control. Parameters analyze in this numerical stuy were: flange thickness, we thickness, we stiffener thickness, spacing of we stiffener, also thickness an geometric moel of iagonal we stiffener. Next an experimental stuy was conucte to perform a valiation towars results of numerical stuy.

8 V1 C1 V1 C1 Z X Y Y Z X V1 L1 C1 V1 C1 Y Z X Z X Y 11 Yurisman, et al. A B C D Figure 6 Finite element moel of shear link with various type of stiffner [4,5,7,8]. Experimental stuy was conucte in Structural Mechanic Laoratory Center for Inustrial Engineering ITB. In this stuy, three test specimens were create in the form of shear link with an without iagonal we stiffeners. Shape an imension of the three test specimens were ajuste with element moels until ones analyze in numerical stuy. The test specimens was create from profile WF 2.1.5,5.8 (as in numerical stuy profile), the thickness of we stiffener was 1 mm, while the thickness of iagonal we stiffener were mae in two variations, 8 mm an 4 mm as seen in Figure 7. After creating test specimens, loaing frames an the software were then prepare along with tools to perform testing. Each test specimen is place on support of test specimen an connecte to the actuator with joint plates 4 mm thick, connection of joint plates to actuator is using 27 mm olts.

9 Behavior of Shear Link of WF Section 111 (a) () Figure 7 The form of specimens of shear link with an without iagonal we stiffener. Loaing pattern given on test specimens is ase on loa patterns in AISC 25. Applie loa are cyclic loas with isplacement control. Figure 9 shows a graph of loa pattern applie on the test specimen. Loaing frame LVDT Specimen Actuator for applie of loa to specimen Support of specimen Figure 8 Set up of equipment an specimen of shear link.

10 112 Yurisman, et al. 4 Typical Quasi-static Cyclic Loaing (AISC 25) 3 2 isplacement (mm) loaing cycle Figure 9 Quasi-static cyclic loaing pattern were sujecte to the specimens accoring with AISC Numeric Stuy Results Results of numerical stuy have shown parameters which significantly affect the performance of shear link. These parameters are: thickness of iagonal stiffener an the geometric moel of the stiffener. A few parameters such as spacing an thickness of we stiffener, has no significant effect on link performance. Other parameters, such as thickness of flange an thickness of we, is kept constant in this analysis ecause these parameters cannot e moifie in the fiel ue to the applie WF profile which is efault from the factory. Therefore this research analysis topic is focuse on iagonal stiffener an vertical stiffener where those parameters coul e moifie easily to increase performance of shear link. 5.1 Effect of We stiffener on Shear Link Performance AISC 25 regulate intermeiate we stiffener spacing for shear link to not e less than (3t w /5) an the thickness to not e less than t w or 1 mm. This research applies a spacing of stiffener to e 1 mm an thickness of stiffener 1 mm. To examine effect of spacing an thickness to the performance of shear link, oservation of three stiffener s spacing variation as much as 2 mm (2 spacings); mm (3 spacing s) an 1 mm (4 spacing s) was conucte. Thickness of stiffener was one in three variations: 4 mm, 6 mm, an 1 mm.

11 Behavior of Shear Link of WF Section 113 Loa-Displacement Curve of Shear Link with Various Stiffener Spacing (1 mm, 133 mm, 2 mm) loa (N) 15 = 1 mm = 133 mm = 2 mm isplacement (mm) Figure 1 Link Performance with ifference vertical we stiffener spacing. 3 Loa-Displacement Curve of Shear Link with Various the Thickness of Verical We Stiffener loa (N) t = 6 mm t = 8 mm t = 1 mm isplacement (mm) Figure 11 Link Performance with ifference vertical we stiffener thickness.

12 114 Yurisman, et al. Results of non linear finite element analysis are presente in the form of loa vs. isplacement curves. Loa vs. isplacement curve in Figure 1 shows effects of we stiffener spacing on performance of shear link. The nonlinear analysis shows that the spacing of stiffener oes not have a significant effect, ue to the vertical stiffener attache on IWF we profile which only elays local uckling occurring on the we. Generally encountere IWF profile in the market has a compact surface characteristic resulting in minimizing the effect of local uckling occurring on the section. The same applies to stiffener spacing; variation of stiffener thickness also oes not have a significant effect on the performance of shear link. Plot on Figure 11 illustrates the effect of stiffener thickness on the performance of shear link. 5.2 Increase of Shear Link Performance through Installation on Diagonal Stiffener Base on the previous analysis, there is no significant effect on the variety of stiffener thickness an spacing of we stiffener to the performance of shear link, although regulations regaring stiffener thickness an spacing of we stiffener have een regulate in AISC 25 [3] an from previous researches. Moel Tale 1 Moels of Shear Links for Cyclic Analysis. Sketch The thickness of Vertical Plate (mm) The thickness of Diagonal Plate (mm) DV8 (spec.i) 1 8. WS3 (spec.ii) 1 DV42 (spec.iii) In this analysis, an innovation to increase performance of shear link through the installation of iagonal we stiffener on we area was attempte. The hypothesis the research is y installing a iagonal stiffener, a change in surface properties may occur. These changes inclue increase of inertia moment an

13 Behavior of Shear Link of WF Section 115 shear surface. The installation is also preicte to prevent local uckling on link element. Although there is yet a coe or previous research results which regulate the esign of iagonal stiffener on link, numerical an experimental stuies to further etermine shear link ehavior with iagonal stiffener on the we area was conucte. Tale 1 shows a sketch moel of the analyze specimens with cyclic loaing. Base on the results of initial stuies which have een performe numerically, it was foun an inication that the installation of iagonal racing on the we profile of WF on the link element can increase link capacity of lateral force resistance, an improve the aility of shear link in the energy issipation. Inicators aility shear links in the energy issipation is expresse in the form of hysteretic curve Force vs. Displacement relationship otaine from the quasistatic loaing (cyclic) as shown in Figure loa (N) isplacement (mm) WS3 DV42 DV8 Figure 12 Comparison of shear link hysteretic curve with thickness variation of iagonal racing an shear link uner AISC-25 stanars. 6 Experimental Stuy Results Experimental tests conucte on three specimens of each link namely link without iagonal stiffener, iagonal stiffener link with 4.2 mm thick an a link

14 116 Yurisman, et al. with a iagonal stiffener of 8 mm. All specimens were steel profile of WF 2.1.5, 5.8 an 4 mm in length. The first specimen (Specimen I) is capale to withstan large lateral force at failure. This is ecause the influence of the iagonal stiffener increasing the stiffness an the strength of the specimens. However, thicker iagonal stiffener can inhiit plastification of the we leaing to rittle failure mechanism. The amount of the maximum loa that can e resiste for specimen 1 is N in compression an N in tension whilst the value of the corresponing maximum isplacement of the specimen is mm in tension an 1.94 mm in compression. Specimen II is the stanar shear link complying with the AISC 25 is capale to withstan the lateral force of N in compression an N in tension, whilst the value of the corresponing maximum isplacement of specimens is mm in compression an mm in tension. The failure mechanism, however, is more uctile compare to the first Specimen. Specimen III is a shear link with iagonal stiffener of 4.2 mm thick, unerwent plastification on the flange, we an iagonal stiffener efore collapse. Because the thicknesses of the iagonal stiffeners are relatively thin with lower yiel stress, uckling has occurre in the iagonal stiffener efore the collapse of the specimen. Maximum loa that can e retaine y the specimen is N in compression an N in tension, whilst the corresponing maximum isplacement is mm in compression an 18.4 mm in tension. The failure mechanism is close to Specimen with comparale uctility. Figure 13 Cracks in the flange of the Specimen I in the top of the wele joints, no uckling occurre in the iagonal stiffener uring collapse.

15 Behavior of Shear Link of WF Section 117 All of the specimens have the same failure moes starting with the occurrence of cracks on the flange aroun the joint at the supporte area. High stresses concentration ue to thick wele joints in these positions causes the vicinity ecomes rittle an it is prone to crack or fracture. This phenomenon accelerates the collapse of the specimen an the cracking (fracture) of the specimen. However, this ehavior is ifficult to moel in numerical stuies. Figures 13 to 15 show cracks that occurre in the thir Specimen at failure. Figure 14 Fracture in the flange of the Specimen II at the top of the wele joints at the time of collapse. Figure 15 Fracture in the flange on the thir specimen in the top of the wele joints at the time of the collapse.

16 118 Yurisman, et al. Peraningan Respons Tiga Bena Uji Dalam Menahan Bean Siklik Hingga Mengalami Keruntuhan loa (N) isplacement (mm) spec 1 spec 2 spec 3 Figure 16 Hysteretic curves of three specimens. Response of Three specimens of shear links uner cyclic loaing (rotation.3 raian) loa (N) isplacement (mm) thickness of stiffner 4 mm no stiffner thickness of stiffner 8 mm Figure 17 Response of specimens uner stale conition (rotation of.3 raiant).

17 Behavior of Shear Link of WF Section 119 The comparisons among the hysteretic curves of Specimens are showe in Figure 16. The curves show that the link with the iagonal stiffener has the aility to withstan greater lateral force, ut less inelastic eformation. To achieve the aility to the link with optimal performance, the thickness an material properties of iagonal stiffener must e esign in such a way as to not impee the plasticity process of the we. The Figure also shows that the shear link with a thinner thickness of the stiffener has fatter hysteretic curve inicating a etter performance espite the lateral force is slightly lower. Hysteretic curves in Figure 16 cannot e use irectly to compare the performance of iniviual specimens ecause failure occurs at ifferent loa. In orer to compare the performance of the samples iniviually stale conition shoul e chosen rather than at failure. Stale conition in this case is efine as a conition wherey the three specimens were alreay experiencing inelastic eformation without collapse of any parts of the specimens or stale inelastic conition. In this test a stale inelastic conition occurs when the rotation is.3 raians or isplacement of 12. mm as shown in Figure Cyclic Analysis towars Performance of Shear Link Specimens Cyclic analyses of the three specimens were conucte to compare the shear link performance of the three specimens for strength, stiffness, energy issipation, an uctility ase on the results of oth experimental work an numerical moel. Strength is efine as the maximum lateral force (shear force) that can e retaine y the specimens in each stage of loaing (loa step). Loa vs. isplacement curve in Figures 18 an 19 show the comparison of the strength of three specimens from the results of experimental tests an numerical stuies. Loa vs. isplacement curves in the figure shows that Specimen I (shear link with iagonal racing of 8 mm thick) otaine the highest strength in a lateral withstaning tension an compression compare to Specimens II an III. Stiffness is efine as secant stiffness is the ratio etween the maximum lateral force an isplacement at each stage of loaing (loa step). Similar to the analysis of strength, the secant stiffness for the three moels of the specimens were oserve in the tension an compression. Figure 2 shows the relationship etween the stiffness vs. isplacement of the experimental tests. Specimen I has the highest secant stiffness, espite it is more rittle compare to Specimens II an III. In numerical stuies, the earlier failure phenomenon cannot e picke up moele with computer software use. The results of numerical stuies

18 12 Yurisman, et al. shown in Figure 21 are in a goo agreement with the experimental work that the use of the iagonal stiffener improves the stiffness of the shear link loa (N) spec.1(dv8) spec. 2 (WS3) spec. 3 (DV42) isplacement (mm) (a) loa (N) spec.1 (DV8) spec. 2 (WS3) spec. 3 (DV42) isplacement (mm) () Figure 18 Comparison of shear strength of three moel specimens of shear link, the experimental results in tension (a) an the compression ().

19 Behavior of Shear Link of WF Section force (N) spec.2 (WS3) spec.3 (DV42) spec.1 (DV8) ispalcement (mm) (a) 5 45 force (N) spec.2 (WS3) spec.3 (DV42) spec.1 (DV8) isplacement (mm) () Figure 19 Comparison of shear strength of three moel specimens of shear link, the results of numerical stuies on the conition of tension (a) an the compression ().

20 122 Yurisman, et al stiffness (N/mm) spec.1 (DV8) spec.2 (WS3) spec.3 (DV42) isplacement (mm) (a) 12 1 spec.1 (DV8) spec.2 (WS3) spec.3 (DV42) stiffness (N/mm) isplacement (mm) () Figure 2 Comparison of secant stiffness of the specimens of experimental work in tension (a) an compression ().

21 Behavior of Shear Link of WF Section 123 stiffness (N/mm) WS3 DV42 DV isplacement (mm) (a) 12 WS3 DV42 DV8 stiffness (N) isplacement (mm) () Figure 21 Comparison of secant stiffness of three numerical moel of specimens in tension (a) an compression ().

22 124 Yurisman, et al spec.2 (WS3) spec.1 (DV8) spec.3 (DV42) energy of issipation (N.mm) isplacement (mm) (a) 35,, 3,, energy of issipation (N.mm) 25,, 2,, 15,, 1,, 5,, ,, isplacement (mm) spec.2 (WS3) spec.1 (DV8) spec.3 (DV42) () Figure 22 Comparative performances of three specimens in the issipation of energy of the experimental test results (a) an the results of numerical stuies ().

23 Behavior of Shear Link of WF Section 125 In this stuy, the amount of energy issipation in the specimen of the shear link is expresse y the area uner cyclic hysteretic curves in terms of the force vs. isplacement relationship. Calculate the area of hysteretic curve analysis is conucte using the incremental metho where the curve is ivie into small triangle. The amount of energy issipation is the result of a cumulative sum of the total hysteretic curve generate in each stage of loaing. Cumulative energy issipation curve vs. isplacement in the Figure 22a shows the amount of energy issipation capacity of shear links ue to cyclic loaing. From the experimental results showe that the shear link with iagonal stiffener 4.2 mm has the highest energy issipation (Specimen III), while the link with 8 mm thick iagonal stiffener (Specimen I) in the early stages of loaing is capale to achieve the highest energy issipation among the three specimens, however, this specimen collapse in the early stage of loaing. The failure is ecause of fracture occurre on the flange in the support. The curve in Figure 22 is the result of numerical stuy. The curve inicates that the shear link with iagonal stiffener 8 mm (Specimen I) has the est performance in terms of energy issipation. As shown in Figure 22, the numerical result is slightly ifferent with the experimental tests for Specimen I. This is ecause of the phenomenon of crack (fracture) occurre on the flange is ifficult to moel in the numerical stuies. Displacement uctility is efine as the ratio of the maximum isplacement to the isplacement at initial yiel. Tale 2 shows the values of yiel isplacement (y), ultimate isplacement (u) an the uctility of the experimental results. Information otaine from Tale 2 that the Specimen III (shear link with 4.2 mm thick stiffeners) has the highest uctility, an Specimen II (shear link AISC stanars) is lower whilst the Specimen I is the lowest uctility. Tale 2 Comparison of Displacement Ductility of the Specimens (Experimental Test Results). Specimen DV8 (spec.i) WS3 (spec.ii) DV42 (spec.iii) Yieling Failure y (mm) Py (N) u (mm) Pu (N) Ductility , , , , ,84-16,58-457, Tale 3 presents the value of yiel, ultimate isplacement an uctility resulting from numerical stuies. Base on these results it was foun that Specimen II

24 126 Yurisman, et al. (AISC stanar shear link) has the highest uctility compare to the two other specimens an Specimens I (shear link with iagonal stiffener 8 mm) ha the lowest uctility. Tale 3 Comparison of Displacement Ductility of the Specimens (Numerical Analysis Results). Specimen DV8 (spec.i) WS3 (spec.ii) DV42 (spec.iii) Yieling Failure P y (N) y (mm) P u (N) u (mm) Ductility 215, , , , , , Analysis of uctility parameters shows that it is ifficult to compare etween numerical an experimental results, especially in terms of etermining the value of yiel isplacement. In the numerical stuies the yiel isplacement is etermine using the value of initial yiel strain which occurre at one noal point on the moel in the vicinity of the support. The etermination of initial yiel in the experimental work is etermine from the initial yiel strain of the strain gage close to the support, although this strain gage is not locate exactly in the same position at the noal point in the numerical moel. However, oth results of the numerical stuies an the experimental tests show very similar results that the shear link with thinner iagonal stiffener achieves higher isplacement uctility. 8 Conclusion Base on the results of numerical an experimental stuies on the ehavioral of shear link profile of WF steel representing Eccentrically Brace Frame system (EBF), several conclusions can e rawn as follows: a) The results of numerical stuies show that the installation of iagonal stiffeners with a certain thickness on the we of WF profiles can improve the link performance in terms of strength, stiffness, isplacement uctility, an energy issipation. The vertical stiffener only improves the staility of the link ut not the strength, stiffness, isplacement uctility an energy issipation of the shear link. ) The experimental results showe that all three specimens have the same failure moe where the failure occurre in specimen are always initiate

25 Behavior of Shear Link of WF Section 127 y the occurrence of cracks in the flange of WF profile close to the support. c) Experimental tests of the three specimens showe that iagonal stiffener is significantly influence the shear link performance. The initial failure along the wel of the flange of the profile at the vicinity of the support was oserve with in-elastic strain even though this in-elastic strain still elow the ultimate strain. ) Comparison of the performance of each specimen carrie out at.3 raians of in-elastic rotation where the three specimens were consiere in-elastically stale efore failure. e) The est performance of the shear link in terms of strength, stiffness, isplacement uctility an the cyclic energy issipation is Specimen III with the thinness iagonal stiffener (4.2 mm) followe y Specimens II with no iagonal stiffener (AISC Stanar) an Specimen I with 8, mm thick iagonal stiffener. Acknowlegements The Author an the co-authors woul like to express their gratitute an appreciation to The Research an Community Services Agency of ITB (LPPM ITB) which has fune this program through Structural Engineering Division of ITB uner Research program 29, contract no 77.A/K1.1/KP/29 also Grant of Doctor Program of ITB No.418/K1.12/KU/29. References [1] Popov, E.P., Recent Research on Eccentrically Brace Frames, Journal of Engineering Structures, 5(1), pp. 3-9, [2] Moestopo, M. & Aulia, M., Link Performance with Bolt Connection of EBF (In Inonesian), Association of Inonesian Structural Engineer Seminar, August, Jakarta, 26. [3] American Institute of Steel Construction, Seismic Provision for Structural Steel Builings, AISC, Inc., 25. [4] Yurisman, Buiono, B., Mustopo, M. & Suarjana, M., Numerical Analysis of the Shear Link Using Diagonal We Stiffener of EBF Uner Cyclic Loaing (In Inonesian), Journal Teknik Sipil ITB,17(1), April 21. [5] Yurisman, Buiono, B., Mustopo, M. & Suarjana, M., Parametric Stuy of the Shear Link of WF Profile Using Diagonal We Stiffener of EBF Uner Cyclic Loaing (In Inonesian), National Conference of Post Grauate Program of Civil Engineering, Banung, May 26, 21 [6] Englekirk, R., Steel Structures: Controlling Behavior through Design, John Wiley an Son, Inc., 1994.

26 128 Yurisman, et al. [7] Yurisman, Buiono, B., Mustopo, M. & Suarjana, M., The Behaviour of Shear Link with Diagonal Stiffener of EBF System (In Inonesian), National Seminar on the Recent Development of the Usage of Steel Material in the Worl of Construction Inustry, University of Parahyangan, Civil Engineering Faculty, Banung, Inonesia, 29. [8] Yurisman, Buiono, B., Mustopo, M. & Suarjana, M., The Improvement of the Shear Link Using Diagonal We Stiffener of EBF Uner Cyclic Loaing (In Inonesian), Seminar an Exhiition of Inonesian Structural Engineer Association, Jakarta, August 8-9, 29. [9] Goarah A. & Ramaan.T., Seismic Analysis of Links of Various Lengths in Eccentrically Brace Frames, Can. Journal of Civ. Eng., , [1] Engelhart, M.D. & Popov, E.P., Behavior of Long Links in Eccentrically Brace Frame. Report No. UCB/EERC-89/1. Berkeley: Earthquake Engineering Research Centre. University of California, [11] Kasai K. & Popov, E.P., General Behavior of WF Steel Shear Link Beams, Journal of the Structural Division. Feruary, 112(2), ASCE, [12] Bruneau, M., Uang, C.M. & Whittaker, A., Ductile Design of Steel Structures, McGraw-Hill, 1998.