Seismic Control of Steel Structures with Shape Memory Alloys

Transcription

1 Sesmc Control of Steel Structures wth Shape Memory Alloys S.M.R. Mortazav 1, M. Ghassemeh *2, and S. A. Motahar 2 1 Shahd Rajaee Teacher Tranng Unversty, Tehran, Iran 2 School of Cvl Engneerng, Unversty of Tehran, Tehran, Iran mortazav@srttu.edu, *mghassem@ut.ac.r, ardavan_motahar@yahoo.com Abstract Shape Memory Alloys (SMA s are able to reach very large recoverable strans. They have found ther means nto many nventve applcatons ncludng sesmc structural control. Due to ther recenterng capablty as well as dampng capacty, SMA materals are favorable for use n earthquake applcatons. The man dea of ths research s the smultaneous use of SMA elements n dfferent phases and steel elements s structural systems, n order to utlze each favorable characterstcs. Dampng capacty of Martenste phase of the SMA wll leave resdual strans n structure whch s n contrast wth the recenterng characterstc of Austente phase of the SMA. Therefore an attentve arrangement wll be requred n order to get the best structural performance. In ths artcle an ntatve was taken for arrangng dfferent states of SMA materals n structures as bracng elements n order to reach the best feasble performance. Keywords Sesmc; Shape Memory Alloy; Dampng; Steel Structure; Recenterng Introducton Structural Protectve Systems can be generally dvded nto three classes of passve energy dsspaton, actve or sem actve control systems and base solaton system [Soong and Dargush (1997]. Passve devces reduce earthquake damages to structures n the course of reducng the structure demand by dsspatng the nput energy of the exctaton and let the real structure members to wthstand less severe actons. Today several types of passve energy dsspaton devces has been mplemented and used. However the ncreasng demand for better and more relable performances requres the development of new devces wth better behavours and fewer lmtatons. Some of the lmtatons nvolved wth current passve devces are mantenance for flud vscous dampers, durablty for rubber based devces and complexty of nstallaton and the need for replacement after severe earthquakes for those based on steel yeldng or lead extruson and dependence upon temperature for polymer based devces [Dolce and Marnetto (2000]. One alternatve of usng current passve energy dsspaton devces are Shape Memory Alloyed based components. Shape memory alloys, one of the new and smart materals, nowadays have shown to be an nterestng materal for use n sesmc applcatons because of ther pecular propertes. Although Soong and Dargush (1997 have placed Smart Materals n the category of sem actve devces, Shape Memory Alloys or SMAs have been mostly regarded as passve devces n the lterature [Dolce and Marnetto (2000 and Aken, Nms, Whttaker and Kelly (1993]. Shape Memory Alloys (mostly used as NT are capable of undergong large strans up to 8% wthout any resdual stran, whle dsspatng consderable amounts of energy. Ths feature named superelastcty (or pseudoelastcty besdes ther very hgh fatgue and corroson resstance are features whch are of great nterest for sesmc applcatons. The frst work n the applcaton of SMAs n sesmc applcaton goes back to the work of Graesser and Cozzarell (1991 who evaluated the use of NT SMAs as sesmc dampers. They studed the effect of loadng frequency and hstory on the energy dsspaton characterstcs of NT wres. There have been many expermental works on the applcablty of SMA based devces n structures [DesRoches, McCormc and Delemont (2004, Dolce and Cardone, (2001a, Dolce and Cardone (2001b, and Dolce, Cardone, and Marnetto (2000]; but the analytcal studes usng SMA devces n a modeled structure are very lmted [Baratta and Corb (2002, Bruno and Valente (2002, DesRoches and Delemont (2002, DesRoches, Leon Hess and Ocel (2000, DesRoches and Smth (2004, and Wlde, Gardon and Fujno (2000]. Bratta and Corb (2002 nvestgated the 28

2 Internatonal Journal of Automaton and Control Engneerng Volume 2 Issue 1, February nfluence of SMA tendons elements as dagonal elements of a smple portal. Bruno and Valente (2002 performed a comparatve nvestgaton of tradtonal earthquake resstng members wth SMA based resstng members. The results of ths study showed that the SMA solaton system can reduce the structure response much more than any other devce. DesRoches and Delemont (2002, DesRoches, Leon Hess and Ocel (2000, and fnally DesRoches and Smth (2004 showed that SMA wre restraners can sgnfcantly reduce the relatve dsplacements of brdge pers specally n near feld ground motons. Wlde, Gardon and Fujno (2000 proposed a smart solaton system whch combnes a lamnated rubber bearng wth a devce made of SMA bars. Black, Aken and Krumme (2006 conducted tests on large dameter SMAs. Usng steel and SMA fasteners, Abolmaal, Treadway and Aswath (2006 compared the energy dsspaton of bolted T stub connectons. Czadersk, Hahnebach and Motavall (2006 conducted experments on a renforced concrete beam equpped wth SMA materal and compared t wth conventonal beam. Also, L, L and Zhang (2007 expermentally studed the behavor of concrete beams wth SMA renforcements. Rahman, Akanda and Hossan (2008 numercally nvestgated the effect of cross sectonal geometry on the bendng of a beam and also bucklng of a column made of SMA. Motahar and Ghassemeh (2006 developed a multlnear consttutve model to capture the behavors of SMA. Motahar, Ghassemeh and Abolmaal (2007 also ntroduced a specal SMA damper to have both recenterng and energy dsspatng characterstcs smultaneously. In recent studes on SMA materals, Ozbulut and Hurlebaus (2011 nvestgated the effectveness of SMA/rubberbased solaton systems for protectng brdges. Johnson, Padgett and Maragaks (2008 determned the effects of SMA restraner cables on the sesmc performance of multple frame concrete box grder brdge. Kar, Ghassemeh and Abolmaal (2011, for the new desgn as well as retrofttng purposes, nvestgated the mplementaton of the combnaton of bucklng restraned braces and shape memory braces n structures. Ghassemeh, Mostafazadeh and Saberdel Sadeh (2012 and Ghassemeh, Bahaar, Ghodratan and Nojoum (2012 mplemented both pseudoelastc and shape memory effect propertes of Ntnol shape memory alloy for sesmc control of concrete shear wall structure. Fnally Ghassemeh, Ghodratan, Bahaar and Nojoum (2013 utlzed superelastc propertes of Ntnol shape memory alloy for sesmc enhancement of coupled concrete shear walls. The man dea n ths paper whch s the use of dfferent states of SMAs s based on some conclusons of DesRoches, McCormc and Delemont (2004 and Dolce, Cardone and Marnetto (2000 n ther expermental studes. These remarks havenʹt yet been used n any analytcal model. Therefore, the goal of ths paper s to show the applcablty of ths dea for use n real structural analyses. For ths reason, n order to compare between dfferent structural systems, the dea of Structural Damage ndces has been mplemented. Shape Memory Alloys SMAs have two crystallographc phases, one parent phase called Austente wth hgh symmetry and one product phase wth lower symmetry called Martenste. Austente phase s stable at hgher temperatures and lower stresses; whle Martenste s stable at lower temperatures and hgher stresses. The unque behavor of these materals s due to the phase transformaton between these two phases. If the ambent temperature s above Austnte fnsh temperature, the specmen s n Austente phase and the large stran nduced by stress can be completely recovered by removal of stress (Superelastcty and f the Temperature s below Martenste fnsh temperature, t s n Martenste Phase and a large resdual stran wll reman on the specmen after unloadng whch s also recoverable by means of heatng above Austnte fnsh temperature (Memory effect. (a FIG. 1 SMA BEHAVIOR a SUPERELASTICITY IN AUSTENITE PHASE b MEMORY EFFECT IN MARTENSITE PHASE Desgn and the Incluson of the SMA Damper The man objectve of usng SMA Damper has set to (b 29

3 be full recenterng and good energy dsspaton. Addtonal objectves are functonal smplcty, no need for mantenance, lmted encumbrance and compatble costs [Dolce, Cardone and Marnetto (2000]. Accordng to ntensve experments conducted by DesRoches, McCormc and Delemont (2004 and Dolce, Cardone and Marnetto (2000, the best shape and stress mode of SMAs for achevng these goals are Austente wres n tenson and Martenste bars n bendng. The mechancal behavor of these two phases for sesmc applcatons can be categorzed as follow: a Austente wres n tenson wth rather low energy dsspaton capacty, n range of nterest for sesmc applcatons, zero resdual stran at the end of the acton, and consderable fatgue resstance; b Martenste bars n bendng wth good energy dsspaton capacty, large resdual strans after removng the external force, thermally recoverable, very hgh fatgue resstance and ndependence from temperature and on stran rate. As noted n the prevous secton Austente phase shows full recenterng capablty but canʹt dsspate large amounts of energy especally at hgh rate exctatons. On the other hand, Martenste has a large dsspaton capablty whle remanng resdual strans on the structure. These two objectves seem to be conflctng. But wth proper mplementaton of both states and use of prestressng, an deal soluton can be acheved [Dolce, Cardone and Marnetto (2000]. The dealzed behavor of both recenterng components and dsspatng components are shown n Fg. 2. The rgd stffness at the begnnng of recenterng component s obtaned va prestress of the Austente wres. As noted above, Austente wres should always be n tenson state and therefore specal mechansms of studs and tubes are needed n the devce [Dolce, Cardone and Marnetto (2000]. Modellng of SMA Damper (SD In general, consttutve modellng of shape memory materals under dfferent loadng condtons s a complcated problem and there s a large amount of lterature regardng ths case. Addng the complexty, lmted applcablty and unrelablty of these models to the complexty of the ntroduced damper, there couldnʹt be any possble and ratonal measure to analytcally model ths damper. The proper and more relable method s to use expermental results and calbrate t nto the numercal model. An example of such approach can be found n DesRoches and Delemont (2002. Accordng to Dolce, Cardone and Marnetto (2000 an approxmate smplfed mult lnear consttutve model for the proposed Specal SMA damper s gven n FIG. 3. Force (KN Force (KN Stran (% (a Stran (% (b FIG. 2 RECENTERING AND DISSIPATION ENERGY COMPONENTS AND THE COMBINATION OF THE TWO FIG. 3 FORCE STRAIN RELATION OF SMA a EXPERIMENTAL RESULTS [DOLCE, CARDONE AND MARNETTO (2000] (b MATERIAL MODEL 30

4 Internatonal Journal of Automaton and Control Engneerng Volume 2 Issue 1, February Selected Structure For brevty, only one common three two bay braced steel structure, s selected for performng analyses. Ths Structure s shown n Fg. 4. Ths structure s once braced wth common steel braces as shown n Fg. 4(a and the other tme wth specal SMA Damper as n Fg. 4(b. The two structure systems are subjected to El Centro ground acceleraton scaled to peak ground acceleratons of 0.3g, 0.6g and 0.9g. Nonlnear tme hstory analyses were performed on the two structures and the results are compared. In order to compare between the behavours of two structures, t s mportant to resort to approprate ndcators of total structural damage. by Park and Ang, and Wen (1987 whch s mostly used n practce s appled. In ths method, the damage of any component s derved as a lnear combnaton of the effect of excessve deformaton and a contrbuton due to the repeated load cycles,.e. u D u max ultmate F y u ultmate de h n whch umax s the maxmum response, β s a parameter dependng on type of structural system, uultmate s the ultmate lmt correspondng to monotonc loadng, Fy s the yeld strength and deh s the ncremental dsspated hysteretc energy. The damage of each s then computed as: D m 1 D, E m j1 E j (1 (2 where m s the number of plastc hnges of. The total damage of the frame s then calculated as: n ( E D frame ( ( D, n 1 ( E j1 j (3 where n s the number of stores. The damage level classfcaton as proposed by Park and Ang, and Wen (1987 s appled; as follows: D < 0.1 (No Damage 0.1 <D < 0.25 (Mnor Damage 0.25 < D < 0.4 (Moderate Damage (a 0.4 <D < 0.1 (Severe Damage D >1.0 (Total Damage (4 The damage of SMA dampers s taken to be zero n ts workng lmts because of ts very hgh fatgue resstance. Ths character of the SMA seems to be one of the most nterestng features of ths materal n decreasng the damage of the total buldng snce t does not leave any damage to the structure even after long duraton actons. Results (b FIG. 4 THREE STOREY STRUCTURES a WITH STEEL BRACES, b 3 WITH SPECIAL SMA DAMPER In our Study, the damage ndex defnton proposed The results obtaned are presented n Table 1. Detaled results ncludng each component and dsspated energes, roof dsplacements and element behavors are also llustrated n Fgs. 5 8 for the case of 0.9g peak ground acceleraton. As shown n Table 1, the use of SMA can remarkably decrease the damage of the structure due to ts specal characterstcs. 31

5 TABLE 1 DAMAGE INDICES FOR STRUCTURES SUBJECTED TO EL CENTRO GROUND ACCELERATIONS WITH DIFFERENT PGAS Earthquake PGA Steel Braced System D.I. Lmt of Damage SMA Braced System D.I. Lmt of Damage Moderate 0.07 None Severe 0.11 Mnor Severe 0.18 Mnor In Fg. 5, the damage ndces of each ndvdual component and of each are shown for both systems. In SMA system n addton to the elmnaton of damage of braces, the damage to the columns of the braced bay s also dmnshed, because the steel bracng system s stffer (due to the low stffness of SMA Dampers and gans more forces and transfers the forces to the columns. At the other hand, the SMA bracng system s softer and dsspates the energy va ts especal behavor nstead and let the other parts of the structure to wthstand less forces and actons. In Fg. 6 the dsspated energy of each element and each are shown n unts of Kgf.Cm 2. As been ndcated, the reason that dsspated energes are less n SMA System s that all members experence much less actons and the SMA bracng start dsspatng energy at much lower force, so the magntude of hysteretc dsspated energes are less n ths system. In Fg. 7 the top dsplacement tme hstores of two systems are shown. Snce the steel system s stffer t experences lower deformatons and the damage to non structural systems s less n steel bracng structure. Ths s the cost we should pay nstead of gettng the beneft of decreasng the structural damage n SMA bracng system. As llustrated n the fgure, unlke the steel braced system, the structure s deformng n dfferent modes wth dfferent frequences. Ths s because of the rapd changes of stffness of the SMA damper whch forces the hgher modes to be excted. In Fg. 8, axal force dsplacement responses for 1st bracngs are shown for two systems. (a Steel Braced System (b SMA Braced System FIG. 5 COMPONENT DAMAGE INDICES FOR BOTH SYSTEMS FIG. 7 TIME HISTORY OF THE SYSTEM (TOP DISPLACEMENT FIG. 6 DISSIPATED ENERGIES FOR BOTH SYSTEMS (UNIT: Kgf.Cm 2 (a Steel Bracng System 32

6 Internatonal Journal of Automaton and Control Engneerng Volume 2 Issue 1, February (b SMA bracng System FIG. 8 RESPONSES OF 1ST STOREY BRACES (FORCE DISPLACEMENT Conclusons As presented n ths paper, utlzng the ntroduced specal shape memory damper the structural damage of a typcal frame can be notceably reduced. However, t s very essental to note that partcular concern must be compensated n desgn of such a frame. The desgn should be proportonal n a way that the SMA dampers are the man energy absorber of the system and ther unque behavor s fully utlzed. Furthermore, snce the stffness of the damper s much lower than the common steel braces, care should be pad also to the damage of nonstructural components of the structure and keep the deformatons of the structure to acceptable lmts. Fnally, the last thng to consder s that SMA damper changes ts stffness very rapdly and ths may cause the hgher modes of the structure to be excted n the event of sesmc actons. Therefore t s shown that shape memory alloys can be successfully used for control of structures subjected to sesmc forces due to ther unque characterstcs. REFERENCES Abolmaal, A., Treadway, J., and Aswath, P., Hysteress behavor of t stub wth superelastc shape memory fasteners, Journal of Constructonal Steel Research, 8(62, 2006, Aken, I.D., Nms, D.K., Whttaker, A.S. and Kelly, J.M., ʺTestng of Passve Energy Dsspaton Systemsʺ, Earthquake Spectra, 9, No. 3, 1993, Baratta, A., and Corb, O., ʺOn the dynamc behavor of elastc plastc structures equpped wth pseudoelastc SMA Renforcementsʺ Computatonal Materals Scence, 25, 2002, Black, C., Aken, L., and Krumme, R., Expermental testng of large dameter shape memory alloys Proceedng of shape memory and superelastc technologes conference, May 7 11, Bruno, S., and Valente, C., ʺComparatve Response Analyss of Conventonal and nnovatve sesmc protecton strategesʺ, Earthquake Engneerng and Structural Dynamcs, 31, 2002, Czadersk, C., Hahnebach, B. and Motavall, M., RC beam wth varable stffness and strength, Constructon and Buldng Materals, 20, 2006, DesRoches, R., and Delemont, M., Sesmc retroft of smply supported brdges usng shape memory alloys Engneerng Structures, 24, 2002, DesRoches, R., Leon R., Hess, G. and Ocel. J., ʺSesmc desgn and retroft usng shape memory alloysʺ, Proceedngs of the Chna U.S. Mllennum Symposum of Earthquake Engneerng: Earthquake Engneerng Fronters n the New Mllennum, DesRoches, R., McCormc, J., and Delemont, M., ʺCyclc Propertes of Superelastc Shape Memory Alloy Wres and Barsʺ, Journal of Structural Engneerng, 130, No. 1, 2004, DesRoches, R., and Smth, B., ʺShape Memory alloys n sesmc resstant desgn and retroft: a crtcal revew of the state of the art, potental and lmtatonsʺ, Journal of Earthquake Engneerng, 8(3, 2004, Dolce, M., and Cardone, D., ʺMechancal behavor of Shape Memory alloys for sesmc applcatons 1. Martenste and Austente NT bars subjected to torsonʺ, Internatonal Journal of Mechancal Scences, 43, 2001, Dolce, M., and Cardone, D., ʺMechancal behavor of Shape Memory alloys for sesmc applcatons 2. Austente NT wres subjected to tensonʺ, Internatonal Journal of Mechancal Scences, 43, 2001, Dolce, M., Cardone, D. and Marnetto, R., ʺImplementaton and Testng of Passve control devces based on shape memory alloysʺ, Earthquake Engneerng and Structural Dynamcs, 29, 2000,

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