Evaluation of the behavior factor of portal structures according to Moroccan seismic code RPS2000

Transcription

1 Intrnational Journal of Enginring sarch and Dvlopmnt -ISSN: 78-7X, p-issn: 78-8X, Volum 9, Issu (Novmbr ), PP. 7- Evaluation of th bhavior factor of portal structurs according to Moroccan sismic cod Said Louhibi, Elbachir El Kihl, Mimoun Chourak Mohammd Prmir Univrsity, Ecol National ds Scincs Appliqués, E.N.S.A - BP 9 Quartir Alquods complx univrsitair, Oujda Morocco Mohammd Prmir Univrsity, Ecol National ds Scincs Appliqués, E.N.S.A - BP 9 Quartir Alquods complx univrsitair, Oujda Morocco Départmnt d Bioologi, Chimi, Géologi, Faculté Pluridisciplinair Nador Morocco Abstract:- Th bhavior factor K rcommndd by th Moroccan sismic cod () is th main subjct of this work to valuat th lastic forc and its us in th procdur for sismic dsign of portal structurs. In fact, th currnt formulation of th bhavior factor k undr totally nglcts th rsistanc, th rdundancy as wll as th scond-ordr dynamic P- ffct of th portal structurs; this ld us to procd to th comparison of th bhavior factor K with othr univrsal formulations. This work has thrfor for goal to improv th scurity rsrv of portal systms for diffrnt cass of sits. Th rsults clarly show that th bhavior factor as prsntd in is far to b abl to guarant th rquird scurity. Our suggstion is to introduc th bhavior factor K in a nw format ( K = C. S. ) to provid a bttr stimation of th shar forc and thrfor a bttr arthquak-rsistant protction. Kywords:- bhavior factor, ductility, portal structur, rlativ displacmnt, rsistanc,, sismic prformanc. I. INTODUCTION Th first sismic rgulations in Morocco ar AGADI standards appard in 9 aftr th arthquak of Agadir (Dcr No of --9). In April, a nw rgulation "" [] prsntd and approvd by Dcr No. 77 ( Fbruary ), stablishing th National Committ for Earthquak Enginring (CNGP). This gulation lays down th ruls for th calculation and dsign of structurs to nhanc th holding of buildings to arthquaks. It also lays down th tchnical rquirmnts of civil nginring and architctural dsign ncssary to nsur buildings optimal rsistanc to shock intnsitis. II. THE MOOCCAN SEISMIC CODE -VESION [] Objctivs of th rviw: Aftr svn yars of application of th, th Ministry of Habitat and Spatial Planning has initiatd a partnrship framwork with th Moroccan Univrsity Mohammd V, th updating of this rgulation. This updating has th main objctiv of: Accompany th dynamic volution of th arthquak nginring; Excd th problms of application dtctd on th application of with th profssionals of th Building and Public Works; Updat th tchnical contnt of th : nw sismic maps of Morocco and nw sismic paramtrs. dfin a nw classification of buildings according to thir importanc and thir functions. Th main changs introducd by th nw PS hav bn dfind following an approach of xtndd consultation with institutional and profssionals partnrs of th Ministry and this, among othr things, by th launching of a survy in 8 among profssionals in th housing and Construction (Architcts, Consultants, Proprty Dvloprs and Contractors ). This survy was primarily dsignd to assss th opinion of profssionals concrning th and to dtct th difficultis ncountrd in its application. III. PESENTATION OF THE BEHAVIO FACTO ACCODING TO THE CODE AND -VESION In Morocco, th procdur of lastic analysis of structurs is th main practic of sismic dsign. It taks into account th nonlinar rspons of a Parasismic systm through th rspons modification factors, 7

2 K Evaluation of th bhavior factor of portal structurs according to Moroccan also calld bhavior factor K. This factor is usd to rduc th sharing forc ( V ) calculatd from th lastic analysis using a rspons spctrum with % damping. Th quivalnt latral sismic forc rprsnting lastic rspons of V according to [] is calculatd using th following formula: W () and V S D I W.... (-VESION ) () V A. S. D. I. K K A : th acclration cofficint of sismic zons in Morocco : spd cofficint S : th sit cofficint basd on soil proprtis D : th dynamic amplification factor givn by th dynamic spctrum of amplification I : th cofficint of importanc or priority basd on Building Class K : th bhavior factor W : th load takn by wight of th structur Th bhavior factor K has not changd in th two vrsions of th and th -vrsion, th valus of K according to th (Tabl I) includs only th dsird lvl of ductility and slctd typ of bracing rgardlss of th priod of th sit and also nglcts th rsistanc, th rdundancy of th structur and th scond-ordr dynamic P- ffct. Tabl I: Bhavior factor K (PS ) according to th lvl of ductility [ND: lvl of ductility (low); ND : lvl of ductility (avrag); ND: lvl of ductility (larg)] Typ of bracing ND ND ND Concrt frams. This formulation thus adoptd is far from bing prfct, contrary to th diffrnt formulations of this factor in th intrnational sismic cods, dspit its mpirical charactr. To tak into account of th priod of th sit, w xprssd th valus of bhavior factor in portal bracing systm for diffrnt lvls of ductility for priods ranging from to sconds (Fig. ).... Priod T (scond) ND ND ND Fig.: Distribution of th bhavior cofficint K according to for th portal bracing systm Fig. shows that thr is no influnc of th priod of th sit on th valus of th bhavior factor for a portal systm that taks constant valus and only th lvl of ductility influncs th valus of th bhavior factor. IV. METHODS AND BIBLIOGAPHIC SYNTHESIS OF THE EDUCTION FACTO IN THE UNIVESAL SEISMIC CODES Th structural bhavior factor, th quivalnt of th bhavior cofficint K of th sismic cod, rprsnts th minimum rduction cofficint of th corrsponding calculation strngth to a spcific lvl of ductility in ordr to nsur an inlastic bhavior. = Vlastic/Vcalcul () Th bhavior factor K undr th taks xact valus dpnding on th lvl of ductility and th slctd typ of bracing. Whil in its univrsal formulation, th bhavior factor dpnds on th ductility factor 8

3 Evaluation of th bhavior factor of portal structurs according to Moroccan that has bn th subjct of svral formulations basd on statistical studis that wr abl to giv mor accurat valus of this factor. A. Ductility factor μ is a masur of th ovrall nonlinar rspons of a bracing systm according to th charactristics of th structur (ductility, damping and vibration priod of ground motion). Th formulation of ductility cofficint is vry complx. It must tak into account th soil-structur intraction, imprfction rlatd to th gomtry of th structur and its dgradation ovr tim. All ths shortcomings hav ld th majority of sismic cods to adopt mpiric formulations of th bhavior factor. Th sismic cods NEHP [] "National Earthquak Hazards duction Program" (997), ATC [] "Applid Tchnology Council" (99), SEAOC [] "Structural Enginrs Association of California" (999) as wll as UBC cod [] "Uniform Building Cod" (98) also obyd to mpirical formulation of th bhavior factor; this maks thir rliability on th prformanc of th sismic rspons unknown. In our work w focusd on th valuation of bhavior factor for th diffrnt formulations compard to most currntly usd, of which w cit as follow: Nwmark and Hall [7] proposd for th bhavior factor th following xprssions: = for T. s =.s T. s (Equal acclrations) () (Equal nrgy) () T s (Equal displacmnt) () = Krawinklr and Nassar [8] valuatd rlationships of slop of th bilinar systm by considring a damping of %. = c c a T b c(t, ) = a ; b. for = T a T 9 basd on th natural priod, and th scond Whr th paramtrs a and b wr obtaind from th rgrssion analysis, and is th hardning paramtr. Miranda and Brtro [9] hav stablishd xprssions of a unifid shap and asy to us, obtaind from rcordings of ground motion as follows: - = (7) = xp.(n ( T).) T - T T ock sit : Cofficint charactrizing th natur of soil and its charactristic priod Factor proposd by Pristly [], taks in account th spcific charactristic priod in th sit and is xprssd by th rlation: T (8) = -. T g Which assums qual displacmnt whn T. Tg and qual acclrations whn T. Borzi and Elnashai [] found that th bhavior cofficint is th sam for th whol structur. It allows th limitation of constraints and thir transformation in movmnts. For this it must not rduc th dmand for rsistanc and thus hav a bhavior factor qual to to rmain in th lastic spctra. Th Algrian sismic cod PA99 [] introducd a quality factor Q to considr th ffct of irrgular gomtric structurs, whr th sismic forc calculation is quantifid as follows: A.D.Q V () V =. W =.. Q Th ratio '/Q' rfrs to th cofficint charactrizing th structural bhavior. cnt studis conductd by Mouzzoun t al. [] basd on th xamination of ight rinforcd concrt structurs dimnsiond according to th sismic cod by push ovr analysis using th softwar Structural Analysis Program (SAP), showd th influnc of svral paramtrs on th valu of th bhavior factor K, i.., th numbr of Portal Frams, typ of soil and fundamntal priod of th structur. Th rgulation ATC [] proposs a nw formulation basd on xprimntal rsarch in thr indpndnt cofficints of th bhavior factor. It is givn as: ()

4 Evaluation of th bhavior factor of portal structurs according to Moroccan factor. =. S. (9) Whr is th factor of structural rdundancy, is th ductility factor and is th rsistanc S B. Strngth rduction factors S Th sismic ffort Vcalcul providd by th majority of th arthquak-rsistant cods gnrally xcds th dmand of th structur rsistanc V which allows th structur to support a larg capacity of rsultant fforts. Th rport V for a structural systm dpnds on th sismic zon and th fundamntal priod. VCALCUL Svral studis for diffrnt portal structurs hav bn mad to calculat th cofficint S. Som diffrnt S valus obtaind by som authors and sismic cods ar as follow:. [],.7 (N.E.H..P Cod []),. (N.Z.S Cod []),.7 for T =. and.7 for T. []. Th significant diffrncs btwn S valus (ranging from. to.7) may hav unfortunat consquncs for its profssional us, thrfor a nd for furthr studis to bttr control and hav rational valus that can b adoptd by sismic cods. C. dundancy Cofficint It is known that whn an lmnt of th structur suffrs damag, th ntir D structur is mobilizd to rdistribut and rsist fforts; and this is rlatd to th ffct of hyprstatic systm and altrnativ paths of load rdistribution. Howvr, th cod dos not considr th rdundancy factor whil th structural rdundancy is strongly rcommndd in arthquak-rsistant cods. To ndow structurs with adquat rdundancy, Whittakr t al. [7] rcommnd for an auto-stabl structur four portal lins in ach dirction as minimum rqustd ( =). D. Factor taking into account th dynamic P- ffct Th scond-ordr dynamic P- ffct is dtrmind by th stability indx θ in th. Han t al () considrd th dynamic P- ffct into sismic dsign procdurs: = Ao{-EXP(-BoT) with Ao =,99u +, and Bo =,9u -,8 () grssion analysis ncompassing arthquak rcords (rock or stiff soil condition), 7 natural priods (. sc to sc with. sc intrval), 9 stability cofficints ( to. with. intrval), and ductility ratios ( to ) allowd th introduction of Th modification factor C with th following xprssion: C F(, ) ( ).( ). whr µ. / θ () '. C(,, T ) () E. Introduction of th bhavior factor in Prformanc Basd Sismic Dsign In ordr to proprly stimat th sismic ffort in Prformanc Basd Sismic Dsign of, th Introduction of th bhavior factor (K) in its ovrall shap bcoms a ncssity [8]: K = C. S. () This formulation will allow us to bttr assss th sismic ffort and thrfor would b suitabl for incorporation into sismic dsign procdurs. In this cas, for a prliminary dsign, th limits of ductility ratio dmand and its rlativ displacmnt vary with th structural systm and th lvl of slctd prformanc (lif safty, nar collaps, collaps); in addition, thir tolrabl maximum rqusts must ncssarily b spcifid. V. ESULTS AND DISCUSSIONS W wantd as illustration for rocky sit ( ) in figur to compar th valus of factor K according to th PS with diffrnt lvl of ductility (ND, ND, and ND), Algrian sismic cod PA99 [], and th aformntiond authors (Nwmark and Hall [7]; Krawinklr and Nassar [8]; Miranda and Brtro [9]; Pristly []).

5 ND ND Brtro (99) Pristly (997) ND PA99 Nwmark (98) Krawinklr (99) Coff (K) ND ND Brtro (99) Pristly (997) ND PA99 Nwmark (98) Krawinklr (99) Coff. (K) ND Nwmark (98) ND Brtro (99) Krawinklr (99) ND PA99 Pristly (997) Coff. (K) Evaluation of th bhavior factor of portal structurs according to Moroccan Fig Variation of K according to th priod T for µ = (rocky sit). K: Bhavior factor Figur show that dos not join diffrnt univrsal cods in th formulation of bhavior factor. Th valu takn for lvls of ductility ND and ND is significantly undrstimatd and thrfor th sismic ffort will in turn undrstimatd. Th Graphs in Figur (a, b, c, and d) show th volution of bhavior factor K according to th basd on th priods rlatd to diffrnt sits and compard th diffrnt univrsal formulations of th rduction cofficint.... Fig a Variation in bhavior factor for T =. s..7. Fig b Variation in bhavior factor for T = s... Fig c Variation in bhavior factor for T =.s

6 K ND ND Brtro (99) Pristly (997) ND PA99 Nwmark (98) Krawinklr (99) Coff (K) Evaluation of th bhavior factor of portal structurs according to Moroccan Fig d Variation in bhavior factor for T = s Fig Variation in bhavior factor for diffrnt priods ( to s). Th bhavior factor K according to th is in good agrmnt with th valus of th majority of univrsal sismic cods and th aformntiond authors for a ductility lvl ND, whil it is for a ductility lvl ND, whil it is significantly lowr for th ductility lvls ND and ND. W apply this corrction for ductility dmand, and if th scond-ordr dynamic P- ffct ar nglctd (. ) following thn C taks th valu of.8, which rsults in an incras of almost 7% ovr th bas shar buildings. Hnc th important influnc of th dynamic P- ffct into sismic dsign procdurs µ = Ao{-EXP(-BoT) 'µ = C.µ for θ =. 'µ = C.µ for θ =. Priod T (scond) Fig Effct of Stability Cofficint (θ) on th bhavior Factor (K) for (µ = ) In our xampl (fig. ) w tak μ = portal structur Auto stabl highly ductil for two stability cofficints θ =. and θ =.. For short and intrmdiat priods (fig ), thr is a significant rgrssion of bhavior factor/ cofficint for diffrnt stability cofficints; ths lad us to th conclusion as follows: - Thr is a strong rlationship btwn th variabls θ and μ with th factor C, which affcts its rol in rduction factor. - As long as th stability cofficint incrass, th modification factor bcoms smallr, which lads to an undrstimation of th latral forcs. VI. CONCLUSIONS AND PESPECTIVES Th formulation of th bhavior factor including ductility dmand, th strngth rduction and scondordr dynamic P- ffct, allows a bttr stimation of th modifying factor of th sismic ffort. This study highlights th following points: Th bhavior factor K in dos not tak into account th soil typ and th fundamntal priod of th structur []. Th bhavior factor K of th taks constant valus dpnding on th lvl of ductility and bracing systm chosn rgardlss of th priod that ld to an undrstimation of latral sismic forc V spcially for short and intrmdiat priods.

7 Evaluation of th bhavior factor of portal structurs according to Moroccan Th bhavior factor K according to th is in good agrmnt with th valus of th majority of univrsal sismic cods and aformntiond authors for a ductility lvl ND, whil it is significantly lowr for th ductility lvls ND and ND. Th nglcts th rsistanc, structural rdundancy and th scond-ordr dynamic P- ffct, this lads to an undrstimation of about 7% of th shar forc at th bas. Introducing th bhavior factor K in its ovrall shap will allow bttr stimating th sismic ffort and nsuring an additional rsrv of rsistanc to th structurs studid. Th main purpos of this work is to rviw th dsign procdur stablishd by to th frstanding concrt portal. Howvr, this work is far from bing sufficint to improv th rliability of th valus attributd to th bhavior factor K for diffrnt structural systms, by charactrizing th intrdpndnc of factors of ductility, strngth and rdundancy. Ductility and rsistanc factors should b valuatd for ach typ of structural systm and for ach sismic zon using th standard dfinitions of ductility and rsistanc. EFEENCES []. ( Févrir ) èglmnt d construction parasismiqu applicabl aux bâtimnts fixant ls règls parasismiqus t instituant l Comité national du géni parasismiqu (B.O. n 988 du mars ), Décrt n --77 du 9 hija []. -vrsion : []. FEMA. NEHP (997) commndd provisions (National Earthquak Hazards duction Program) for sismic rgulations for nw buildings and othr structurs, Fdral Emrgncy Managmnt Agncy port, FEMA, Washington, D.C. []. ATC (99) Structural spons Modification Factors, ATC-9 port, Applid Tchnology Council, dwood City, California []. SEAOC (999) commndd Latral Forc quirmnts and Commntary, Structural Enginrs Association of California, San Francisco, CA. []. UBC-8 (98) Uniform Building Cod, Earthquak gulations, Intrnational Confrnc of Building Officials, Whittir, California [7]. Nwmark NM, Hall WJ (98) Earthquak spctra and dsign. EEI Monograph Sris. Earthquak Enginring sarch Institut, Oakland, California [8]. Krawinklr H, Nassar AA (99) Sismic dsign basd on ductility and cumulativ damag dmand and capacitis, in Nonlinar Sismic Analysis and Dsign of inforcd Concrt Buildings, (d. Fajfar, P. and Krawinkl, H.), Elsvir Applid Scinc, Nw York [9]. Miranda E, Brtro VV (99) Evaluation of strngth rduction factor for arthquak-rsistanc dsign. Earthquak Spctra :7 79 []. Pristly MJN (997) Displacmnt-Basd Sismic Assssmnt of inforcd Concrt Buildings. Journal of Earthquak Enginring :7-9 []. Borzi B, Elnashai AS () find forc rduction factors for sismic dsign, Enginring Structurs :- []. PA99 () èglmnt Parasismiqu Algérin, Documnt tchniqu réglmntair D.T.. - B.C..8, Cntr national ds rchrchs appliqués n géni-parasismiqu []. Mouzzoun M, Moustachi O, Talb A () Evaluation du factur d comportmnt pour l calcul parasismiqu ds bâtimnts n béton armé (Assssmnt of th bhaviour factor for sismic dsign of rinforcd concrt buildings). J. Matr. Environ. Sci. ():- []. Uang CM, Maarouf A (99) Sismic Displacmnt Amplification Factor in Uniform Building Cod. SEAONC sarch Bulltin Board, BB9-, pp. B-B, and Displacmnt Amplification Factor for Sismic Dsign Provisions, Proc. Structurs Congrss, ASCE, vol.,irvin, CA, pp - []. Nw Zaland Standard NZS (99) Cod of Practic for Gnral Structural Dsign, Standards Association of Nw Zaland []. Kappos AJ (999) Evaluation of Bhaviour Factors on th Basis of Ductility and Ovrstrngth Studis. Enginring Structurs :8-8 [7]. Whittakr A, Hart G, ojahn C (999) Sismic spons Modification Factors. J. Struct. Eng. ():8 [8]. Djbbar N, Djbbar A, Chair A, Athmani A (9) Evaluation du factur d comportmnt prconis par l cod PA99. SBEIDCO -st Intrnational Confrnc on sustainabl Built Environmnt Infrastructurs in Dvloping Countris ENSET Oran (Algria)