Dynamic analysis of fiber-reinforced elastomeric isolation structures

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1 Joural of Mechacal Scece ad Techology 3 (9) 3~4 Joural of Mechacal Scece ad Techology DOI.7/s6-8-4-y Dyamc aalyss of fber-reforced elastomerc solato structures Gyug Ju ag ad Beom Soo ag * School of Mechacal Egeerg Pusa Natoal Uversty Busa orea Dept. of Aerospace Egeerg Pusa Natoal Uversty Busa orea (Mauscrpt Receved Jauary 8 8; Revsed December 6 8; Accepted December 8 8) Abstract Ths paper presets a aalyss of sesmcally solated buldgs usg fber-reforced elastomerc structures that are subject to exctatos caused by earthquakes. I aalyzg the vbratos the buldgs are modeled by lumped mass systems. The fudametal equatos of moto are derved for base solated structures ad the hysteretc ad olear-elastc characterstcs are cluded the umercal calculatos. The earthquake waves used as the exctato forces are those that have bee recorded durg strog earthquake motos order to exame the dyamc stablty of buldg structures. The sesmc (olear) resposes of the buldg are compared for each restorg force type ad as a result t s show that the buldg s motos are ot so large from a sesmc desg stadpot. Isolatg structures are show to reduce the resposes suffcetly allowg the buldg s motos to be cotrolled to wth a practcal rage. By creasg the accelerato of the earthquake the yeldg forces the cocrete ad steel frames ca be determed whch shows the advatages of performg olear dyamc aalyss such applcatos. eywords: Fber-reforced elastomerc solator (FREI); Steel reforced elastomerc solator (SREI); Earthquake; Base solato; Vbrato of buldg Itroducto Recetly worldwde earthquake duced damage coutres such as Ira Japa Ida Southeast Asa ad North Amerca has bee creasg ad the damage low-rse housg propertes of -3 floors s especally huge. For example followg the cdets Turkey Greece Tawa etc. durg 999 low-rse housg buldgs suffered casualtes of more tha 9%. To avod these damages base solato methods have bee proposed for a log tme. The ma dea of base solato s to shft the fudametal frequecy of a buldg structure away from the domat frequeces foud typcal earthquake-duced groud motos. I addto the am addg the solato systems s to provde eergy dsspato mechasms so Ths paper was recommeded for publcato revsed form by Assocate Edtor Dae-Eu m * Correspodg author. Tel.: Fax.: E-mal address: bskag@pusa.ac.kr SME & Sprger 9 that the acceleratos trasmtted to the buldg superstructure are reduced. Thus base solato systems are desged to essetally decouple the structure from the groud durg earthquake exctato. Curret sesmc solato systems of buldg structures are usually of two types: steel-reforced multlayer elastomerc systems ad mechasms employg sldg beargs. The rubber beargs form has bee used extesvely Japa ad South Amerca. The early developmet of sesmc solato systems usg beargs ca be backdated to the late 96s New Zealad but the cocept was cosdered to be very mpractcal by most structural egeers those days. Nowadays t has become a major strategy for desgg earthquake-resstat buldgs to protect huma lves Uted States Europe ad Japa [-3]. Rubber has bee used as the base beargs the past three decades followg the developmets of elly [4] 976. At preset owg to the tremedous cost of mplemetg base solato techques applca-

2 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 33 tos ca oly be see structures wth crtcal or expesve cotets. I order to apply sesmc solato for commo buldgs ad publc housg the cost ad weght of the solators eed to be drastcally reduced. The ma reaso for the hgh cost of the solators s the process used preparg the steel plates ad bodg them to the rubber layers. Also the hgh weght of the solators s due to the same steel plates. elly [5] suggested that both the weght ad cost of buldg solators ca be reduced by substtutg the steel reforcg plates wth fber reforcemet of hgh elastc stffess. Moo et al. [6] desged ad maufactured fber-reforced multlayer elastomerc solators usg dfferet kds of fbers such as carbo glass ylo ad polyester. From these studes t was cocluded that the performace of carbo fberreforced solators was eve superor to that of the steel-reforced solators vew of vertcal stffess ad that they were able to provde effectve dampg. ag et al. [7] vestgated carbo fber-reforced solator specmes wth ad wthout hole ad lead plugs. The result of ths study was that the hole ad lead plugs fber -reforced elastomerc solators have lttle effect o mprovg the effectve stffess ad the resultg dampg. Although prevous studes have addressed ad resolved mportat aspects there s a eed for assessg the key characterstcs fluecg the dyamc resposes of structures wth fber-reforced elastomerc solators. I partcular t s mportat to exame the dyamc resposes of buldgs agast strog earthquakes whe fber-reforced elastomerc solato systems have bee added to them. Cosequetly t s also ecessary to explore specfc features of the fbers as reforcemet of the solator structure. I ths paper the dyamc characterstcs of buldg structures wth fber-reforced elastomerc solators uder earthquake exctato are examed. After troducg the desg procedures of fberreforced elastomerc solators the umercal models ad dyamc resposes eeded ths vestgatos are descrbed.. The maufacturg of elastomerc solator ad expermets The steel-reforced ad fber-reforced elastomerc solators have bee fabrcated to compare ther respectve performaces. As the stffess of carbo fber s hgher tha that of steel t has bee wdely used fber-reforced elastomerc.. Modellg of steel-reforced elastomerc solators The steel-reforced elastomerc solator s composed of layers of rubber ad steel plates. The plates protect from lateral bulgg of the rubber layers yet allow the rubber layers to udergo shear deformato. The horzotal ad the vertcal stffess values are the key performaces; the horzotal stffess ( H ) ad vertcal stffess ( V ) of a elastomerc solator are gve as follows: H V GA = tr () EA c = t () r where G s elastc coeffcet of rubber; A s the crosssecto area of the solator; t r s the total thckess of the rubber layers; E c s the cdetal compresso stffess uder specfc vertcal loads the steelreforced solator. The value of E c for a sgle rubber layer s cotrolled by ts shape factor (S) defed as Eq. (3) whch s a dmesoless measure of the aspect rato of the sgle layer of the elastomerc solator: S = loaded area forced free area. (3) The shape factor (S) of a crcular pad wth radus R ad thckess t s S = R / t. The model of steelreforced elastomerc solators s show Fg... Modellg of fber-reforced elastomerc solator The modellg ad desg cocept for realzg fber-reforced elastomerc solators reles o elmatg the steel reforcg plates ad replacg them wth fber reforcemet of hgh elastc stffess so that the weght ad cost of the solators ca be reduced. Fg. shows the model of fber-reforced elastomerc solators. The vertcal stffess of a solator s the same as Eq. () but the effectve compresso stffess s gve by that show Eq. (3) [8] 6+ ν ( ν ) G Ec = 6 GS ( α R ) α = (4) 4( + ν) Eftt f

3 34 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 where G s the elastc coeffcet of rubber; ν s Posso s rato; t s the thckess of the rubber layer; E f s the elastc coeffcet of reforcemet; t f s the thckess of the reforcemet; ad S s the shape factor. I the case of rgd reforcemet the compresso stffess s E c =6GS. Therefore wth flexble reforcemet the compresso stffess decreases ad accordgly the vertcal stffess also decreases..3 Comparso of ylo FREI ad SREI Some fber-reforced elastomerc solator specmes have bee desged ad fabrcated to compare the characterstcs of solators accordg to ther reforcg fbers. The dmesos of the specmes are show Table. I ths secto ylo s used as the reforcg fber. For the sake of comparso steelreforced elastomerc solator specmes ad fberreforced elastomerc solators wth ylo were fabrcated ad the deformatos uder vertcal load were compared as show Fg. 3(a). Uder equal vertcal loadg the deformato of ylo FREI s hgher tha that of SREI whch dcates that the vertcal loadg capacty of ylo FREI s lower tha that of SREI. Fg. 3(b) shows the comparso of the horzotal stffess of SREI ad FREI. The tests were carred out usg a forcg sgal at a frequecy of.hz o each specme; each test volved the applcato of a force cosstg of four full se wave cycles. The appled vertcal load o the top ad bottom plates was 3kgf. The rubber layer s thckess was 6.mm ad maxmum deformato allowed the tests was 5% of ths rubber thckess. The expermetal tests the fabrcated specmes were carred out wth a bearg test mache whch s capable of subjectg a sgle bearg to vertcal ad horzotal loadgs smultaeously ad s able to develop the maxmum axal load of 3tof o the bearg as show Fg. 4. The effectve horzotal stffess eff correspodg to each loadg cycle was computed from the secat le measured from peak-to-peak each loop. eff F = D max max F D m m (5) Here F max ad F m are the maxmum postve ad egatve shear forces respectvely ad the subscrpts max ad m represet the maxmum postve ad Flage Rubber layer Steel reforcg plate Ed plate Fg.. Model of a steel-reforced elastomerc solator (SREI). Rubber layer Fber Fg.. Model of a fber-reforced elastomerc solator (FREI). Lateral force(tof) Vertcal load(tof) SREI FREI Deflecto(mm) (a) Comparso of vertcal tests 3 - SREI FREI Dsplacemet(mm) (b) Comparso of horzotal tests Fg. 3. Comparsos of ylo FREI ad SREI.

4 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 35 Table. Dmesos of steel- ad fber-reforced elastomerc solator beargs. Dmeso SREI 74.5Φ 43 Φ 8T FREI 74.5Φ 43 Φ 8T Reforcemet Isolator secto Ed plate T 9EA 5T EA.5T 75EA 5T EA Ier rubber layer 3T EA.55T 76EA Total thckess of rubber 6T.75T Table. Test results comparg ylo- ad steel-reforced structures. Reforce met Nylo Fber Vertcal test Vertcal stffess (kgf/mm) Ta(γ ) Horzotal test Effectve stffess (kgf/mm) Equvalet Dampg(β ) (%) Steel egatve shear dsplacemets respectvely. The equvalet vscous dampg was computed by measurg the eergy dsspated each cycle (EDC) whch s composed of the area that s eclosed by the hysteress loop. The formula to compute β eq s gve as follows [9]: β = EDC π eff D D max (6) where eff s obtaed from Eq. (5) ad D s the average of the postve ad egatve maxmum dsplacemets. eff ad β of SREI uder 5% shear deformato are 6.kgf/mm ad 6.9% respectvely. eff ad β of FREI uder 5% shear deformato are 8.6kgf/mm ad.6% respectvely. The test results show that the vertcal stffess of ylo FREI s lower tha that of SREI ad the dampg of ylo FREI s two tmes hgher tha that of SREI. The vertcal ad horzotal test results are show Table..4 Comparso of carbo FREI ad SREI I the prevous secto t was show that the vertcal stffess of ylo-reforced elastomerc solators were lower tha those of the SREI oes; ths results from the fact that the tesoal stffess of ylo s lower tha that of steel. The teso stffess of the ylo ca be stregtheed by usg hgh carbo fber ad the sesmc characterstcs of the ew solator have bee vestgated. The horzotal ad vertcal loadg tests were carred out o both carbo FREI ad SREI samples ad Fg. 5 shows that the vertcal stffess of carbo FREI ad SREI uder varyg vertcal loads from 9(tof) to 37(tof) were 3857(kgf/mm) ad 73(kgf/mm) respectvely. The test results dcate that the vertcal load of carbo FREI s three tmes hgher tha that of SREI. The horzotal ad vertcal test results are show Table 3 ad the horzotal test results (see Fg. 6) of Carbo FREI ad SREI show that the effectve horzotal stffess ad dampg of FREI are 33(kgf/mm) ad 5.85% respectvely; the effectve horzotal stffess ad dampg of SREI are 35(kgf/mm) ad 6.% respectvely. These results dcate that the effectve dampg of carbo FREI s over two-tmes hgher tha that of SREI. The vertcal test results shows that vertcal stffess of carbo FREI s threetmes hgher tha that of SREI. Because the rubber layers betwee the fbers are th there s lttle bulgg of the rubber ad also the teso stffess of carbo s hgher tha that of steel plate. It s kow that the effectve dampg of carbo FREI s.5 tmes hgher tha that of SREI whch meas that more earthquake eergy ca be absorbed usg FREI structures..5 Result aalyss ad dyamc aalyss codto The comparatve vestgato test results of ylo FREI carbo FREI ad SREI are summarzed Table 4. The results show that for ylo-reforced structures both the vertcal ad horzotal stffess s decreased ad case of carbo reforcemet the stffess s also creased compared wth SREI. Usg these test results the dyamc aalyss was determed the vertcal ad horzotal drectos. However because the horzotal respose s the most domat our results focus o the horzotal aalyss. Eqs. () ad () mply that the horzotal stffess ad the vertcal stffess are depedet of the rubber materal s property G. Our dyamc aalyss was carred out uder varyg reforcemet stffess codtos.

5 36 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 3. Theoretcal backgroud of dyamc aalyss 3. Goverg equato of moto The buldg structure model wth fber-reforced elastomerc solator as show Fg. 7 cossts of a buldg superstructure ad a base solato structure. The buldg superstructure has a olear recoverg force ad the base solato mechasm was modeled as a elasto-plastc model wth sprg plus damper characterstcs. The shear force of elastoplastc models agast exctatos caused by earthquakes betwee the th ad - th floor s Q = (x -x - ) + y Q t ad has a dampg coeffcet s C where deotes the elastc stffess of the th floor; x ad y represet the coordates. Note that C was assged as a costat dampg coeffcet. The goverg equvalet equato for the th floor ca be obtaed as follows: mx && + C( x& x& ) + C ( x& + x& + ) + ( x& x& ) + + ( x& x& + ) + Q Q = my && ( = 3 L N). y y + (7) The goverg moto equato show Eq. (7) ca be expressed matrx form as. { } + { } + { } + { } = { } && & y && (8) M x C x x H Q ME y where { } { } x = [ x L x L x ] Τ yq = [ yq L yq L yq] Τ Τ E = [ L L ] m+ m H = M = m m CCC ++ C + + C CC C= = C + C C + C C. Table 3. Test results comparg carbo- ad steel-reforcemets. Reforcemet Vertcal test Vertcal stffess Ta(γ ) (kgf/mm) Horzotal test Effectve stffess (kgf/mm) Equvalet Dampg(β ) (%) Carbo Fber Steel Table 4. Carbo- ad ylo-reforced elastomerc solato structures. Fg. 4. Test mache operato. Vertcal load(tof) SREI FREI Deflecto(mm) Fg. 5. Comparso of the vertcal stffess of SREI ad FREI. Nylo/steel Carbo/steel Vertcal test Vertcal stffess.5 3 Horzotal test Lateral force(tof) Effectve stffess.9.9 Dampg 8 64 SREI FREI Dsplacemet(mm) Fg. 6. The hysteress effect due to the solators.

6 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 37 m C m + C m C + C + m m C m m m C C Q x Q Hgh Dampg Rubber Bearg & y& Fg. 7. Elasto-plastc model of a buldg ad solator. 3. Numercal aalyss of the sesmc respose The umercal methods used studyg sesmcally solated structures wll be brefly explaed together wth the equatos of motos that eed to be hadled. Whe deformato velocty ad accelerato are depedet varables after expadg the goverg moto equato a Taylor s seres t ca be expressed as follows: 3 τ τ da τ um + = u + τv m m+ am+ = u + τv m m+ a t 6 dt t= f τ da vm + = v + τa ( ) m m+ = v + τa t m dt t= f ( ) (9) where t' ad t'' are pots of tme betwee the terval(t m t m+ ) whch ca be expressed by usg superposto of the values of at both eds a m a m+ at ( ) = ( β ) a + β at ( ) = ( µ ) a + µ a m m m+ m+. () Q Q y (a) k y Ths scheme s the Newmark-β method. I case t s β =/6 accelerato vares learly the secto. The value of μ was used as.5. Wth ths method the dsplacemet vector the velocty ad the accelerato were expressed as follows: Q y k y { } { &} τ {&&} x = D x = V / x = A/ τ. () k x (b) Fg. 8. Aalyss model: (a) Arragemet of FREI; (b) D- trlear model. From the relato of Eqs. (9) ad () the followg equatos are obtaed: Dm+ = Dm + Vm + [( β ) Am + βam+ ] () Vm+ = Vm + ( Am + Am+ ). (3) From Eq. (8) the followg equato ca be obtaed: MAm + / τ + CVm + / τ + m + Dm+ + HQ y m+ = ME && y m+. (4) Fg. 9. El-Cetro (NS) earthquake wave forces. Substtutg Eqs. () ad (3) to Eq. (4) we ca obta:

7 38 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 ( β) + ( C/ τ + m + ) Vm+ m + Dm+ HyQm + = ME && y m+ ( M / τ + C/ τ+ βm + ) Am + + [ C/ τ+ m + ] Am. (5) I ths paper the hysteress characterstcs betwee the terval ( tm t m + ) were assumed to be costat for coveece performg the calculatos. From Eq. (5) the accelerato at the (m+) step ca be calculated ad from Eqs. () ad (3) the dsplacemet ad velocty ca be calculated. From calculated dsplacemet at the (m+) step the hysteress characterstcs ca be obtaed wthout repeatg the calculato of the results reflected the ext step. Therefore hgher precso calculated results ca be obtaed by shorteg the tme terval betwee the steps. 4. Dyamc aalyss of buldgs wth fberreforced elastomerc solator 4. Modelg of buldg structure wth fber-reforced elastomerc solator A dyamc aalyss was performed of buldg base solated structures wth solators whch are located o prcpal frames of low storey buldg as show Fg. 8(a). The recovery force of the buldg superstructure s show Table 5. The buldg superstructure was assumed to have a D-trlear recovery characterstc as show Fg. 8(b). The dampg coeffcet of the buldg ad that of the solator are. ad.5 respectvely. The yeld pots of the the D-trlear Q y Q y relatos are selected to allow comparsos wth the characterstcs of the D-trlear values arsg due to the El-Cetro (NS) earthquake wave. 4. Aalyss put data The sesmc respose of a mult-storey basesolated buldg s vestgated uder realstc earthquake groud motos. The earthquake motos selected for the study are the NS compoet of 94 El- Cetro earthquake wave (Fg. 9). The peak groud accelerato (PGA) of the El-Cetro earthquake moto s 439 gal(whch s a ut of accelerato used extesvely the scece of gravmetry ad s defed as cetmeter per secod squared ( cm/s²)). Fg. shows the accelerato respose spectrum caused due to the earthquake whch dcates that there are hgh accelerato compoets wth secod ad low accelerato compoets above.5 secod. The propagato of the earthquake wave was assumed to be the logtudal drecto ad the aalyss was carred out for 3 secods. The domat frequecy of the earthquake s motos s Hz. 4.3 Aalyss results Fg. shows the accelerato resposes of each storey of the buldg solated by fber-reforced elastomerc solators subjected to the El-Cetro 94 earthquake s motos. The fgure dcates that the Fg.. Buldg accelerato respose spectrum. Table 5. Desg parameters of a buldg superstructure. No. Weght (tof) Hgh (m) Qy Qy y/k (tof/cm) (tof) (tof) y/k Isolator Fg.. Tme hstory respose of accelerato (f f ad 3f from bottom graph respectvely).

8 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 39 vbrato perod wth solator becomes log ad the ter-storey deflecto decreases whch mples that the fber-reforced elastomerc solator s qute effectve for protectg buldgs uder earthquake exctato. To vestgate the dyamc behavor of basesolated buldg structures wth fber-reforced elastomerc solators vestgatos accordg to the vertcal ad horzotal stffess of the solator the mode shape resposes the ter-storey absolute accelerato resposes ad the shear force resposes have bee carred out. Also order to exame the dyamc resposes accordg to accelerato magtude the accelerato of the El-Cetro (NS) wave was used from half- to two-tmes magtude of peak groud accelerato of the El-Cetro s data (amely 439gal). The mode shape s plotted Fg. where t s observed that the secod ad thrd order modes are comparatvely lower wth 5% of the frst order mode. The fgure dcates that the frst mode s clearly domat ad the buldg superstructure moves wthout torso. Fg. 3 shows that the absolute accelerato resposes of f f ad 3f are almost the same wth varyg solator stffess. The aalyss wth low stffess mples that the dyamc aalyss for low stffess solators such as ylo FREI ad also hgh stffess oes dcate the case of carbo FREI. It s observed that low stffess cases the absolute accelerato respose s comparatvely low. The ter-storey shear forces are compared for varyg solator stffess ad the results are show Fg. 4. The fgure dcates that the shear forces are hgh at lower storeys whch meas that the possblty of collapse s hgh for comparatvely low storeys. Also t s observed that at low stffess values the shear force s low. Fg. 5 shows the absolute accelerato respose for varous acceleratos ad t s observed that the absolute accelerato creases whe hgh magtude acceleratos are appled. 7 ( -3) F ( -) F ( -) F Shear force(tof) Fg.. Mode shape Shear modulus (kgf/ cm ) Absolute accelerato(gal) base f f 3f Fg. 4. Shear force respose of each storey. Absolute accelerato(gal) gal 39 gal 439 gal 47 gal 658 gal 768 gal 878 gal Shear modulus (kgf/ cm ) Fg. 3. Absolute tme respose Shear modulus (kgf/ cm ) Fg. 5. Resposes due to varous magtudes of earthquake.

9 4 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 5. Coclusos The aalytcal sesmc respose of mult-storey buldgs solated by fber-reforced elastomerc solators s vestgated uder strog earthquake codtos. The recorded earthquake wave El-Cetro (NS) s used to vestgate the varato of the top floor accelerato ad bearg dsplacemet of a solated buldg. The respose of the solated buldg structure s plotted uder dfferet magtudes of earthquakes. From the results obtaed certa treds ad coclusos may be draw. As the frequecy of the buldg structure creases accordgly the terstorey deformato decreases. FREI wth low stffess fber such as ylo shows low accelerato resposes but o the other had wth hgh stffess such as obtaed usg carbo fber shows hgh accelerato resposes. The moto of the buldg superstructure wth solator s smoother tha that wthout a solator. The value of the accelerato resposes creases accordace wth the magtude of the earthquake put. Parametrc studes dcate that both ter-storey deformatos ad floor acceleratos crease wth the stregth of the earthquake. I order to esure low accelerato resposes comparatvely hgh dampg solators are suggested as potetal practcal protectos mechasms of buldg agast strog earthquakes. The results reported here could provde a better uderstadg to develop more advaced fber - reforced elastomerc solators. Moreover t s beleved that ths study ca be utlzed to provde the dyamc propertes of fber-reforced elastomerc solators. Ackowledgmet Ths work has bee supported by the orea Scece ad Egeerg Foudato (OSEF) NRL Program grat fuded by the orea Govermet (MEST) (No. RA-8--7-). Also the last author would lke to ackowledge the partal support by grats--ad for the Natoal Core Research Ceter program from MOST/OSEF (No. R ). Refereces [] J. M. elly Sesmc solato of cvl buldgs the USA Progress Structural Egeerg ad Materals (3) (998) [] A. Martell ad M. For Sesmc solato of cvl buldgs Europe Progress Structural Egeerg ad Materals (3) (998) [3] T. Fujta Sesmc solato of cvl buldgs Japa Progress Structural Egeerg ad Materals (3) (998) [4] J. M. elly Earthquake-resstat desg wth rubber Secod Ed. Sprger Lodo U.. (997). [5] J. M. elly Aalyss of fber-reforced elastomerc solators. J. Sesmol. Earthquake Eg. () (999) [6] B. Y. Moo G. J. ag B. S. ag ad J. M. elly Desg ad maufacturg of fber reforced elastomerc solator for sesmc solato J. Mater. Process. Techol 3/3 () [7] B. S. ag G. J. ag ad B. Y. Moo Hole ad lead plug effect o fber reforced elastomerc solator for sesmc solato J. Mater. Process. Techol. 4 (3) [8] J. M. elly Aalyss for fber-reforced elastomerc solators. Aual Report to Egeerg Research Ceter for Net-Shape ad De Maufacturg Pusa Natoal Uversty orea. (). [9] B. Y. Moo G. J. ag B. S. ag ad. S. m Desg ad expermetal aalyss of fber reforced elastomerc solator Trasactos of the SME A. 6 () () 6-33.

10 G. J. ag ad B. S. ag / Joural of Mechacal Scece ad Techology 3 (9) 3~4 4 Gyug-Ju ag receved a B.S. M.S. ad Ph.D degrees Aerospace Egeerg from Pusa Natoal Uver-sty orea ad 5 respectvely. Dr. ag s research terests are the area of sesmc bearg desg base solato cold forgg ad steel structure. Beom-Soo ag receved a B.S. degree Mechacal Egeerg from Pusa Natoal Uversty Busa orea 98. He the wet o to receve hs M.S. degree Aerospace Egeerg from AIST (orea Advaced Isttute of Scece ad Techology) Seoul orea 983 ad Ph.D. degree Mechacal Egeerg from Uversty of Calfora at Berkeley 99. Dr. ag s curretly a Professor at Departmet of Aero-space Egeerg at Pusa Natoal Uversty. He s curretly servg as the Drector of ILIC (Idustral Laso Iovato Cluster). Dr. ag s re-search terests clude flexble formg umaed system desg mult-stage deep drawg ad cold forgg.