OPTIMUM DESIGN OF BRIDGE SYSTEM SUBJECTED TO DEVASTATING EARTHQUAKE CONSIDERING PERFORMANCE AT ULTIMATE STATE

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1 OTIMUM DESIGN OF BRIDGE SYSTEM SUBJECTED TO DEVASTATING EARTHQUAKE CONSIDERING ERFORMANCE AT ULTIMATE STATE Kzuiro Tniw, Kent Tnk Associte rofessor,, Deprtment of Civil nd Environmentl Eng., Fukui University of Tecnology, Gkuen 3-6-, Fukui , Jpn E-mil: Telepone: Cief Exminer, Codi Co. Ltd., ootemci -8-4, Nk-ku, Hirosim , Jpn E-mil: Telepone: Abstrct: In tis study, rtionl nd efficient optiml seismic design metod for bridge system subjected to devstting ertqukes considering performnce t ultimte stte is proposed. Te bridge system consists of superstructure, rubber berings, RC piers nd cst-in-plce concrete pile foundtion. In te proposed optimum design metod, te optimum solutions for te eigts of rubber berings, cross-sectionl dimensions nd mount of steel reinforcements for RC piers nd te detil of concrete pile foundtion re determined for severl llowble ductile fctors of RC piers considering te constrints on te reltive orizontl displcements of rubber berings to te bot bridge nd trnsverse directions, te ductile fctor of RC piers, nd te constrint on te cst-in-plce concrete pile foundtion. From te prcticl design te eigts of rubber berings cn tke continuous vlues, but te oter vribles must be selected from discrete vrible sets. Terefore, te construction cost minimiztion problem cn be expressed s mixed discrete-continuous problem. Tis problem is trnsformed into convex pproximtion problem wit te estimtion formule by using te experimentl design, nd te dynmic beviors nd tose sensitivities re clculted nlyticlly by using te estimtion formule witout nlyzing te structures. Te optimum design problem is solved by clssicl brnc nd bound metod wit dul lgoritm. In te numericl design exmples, it is empsized tt te optimum solutions cn be obtined efficiently by using te experimentl design. It is lso demonstrted tt te reductions of te eigts of rubber berings nd cross-sectionl dimensions of RC piers cn be observed by incresing te llowble ductility fctor. Keywords: Bridge system, Optimiztion, Seismic design, Design of experiments, erformnce t ultimte stte. Introduction After te Hyogoken Nnbu Ertquke in 995, te seismic design code for igwy bridges, JSHB [], s been revised in order to ensure sufficient ultimte dynmic cpcities in te bridge systems for lrge displcements cused by devstting ertqukes. Recently, te performnce-bsed design metod s been introduced for te seismic design t ultimte stte in te JSHB. According to te JSHB, te bridge members re not llowed to yield for te frequent ertqukes (Level), nd te bridge members must ve te sufficient ultimte dynmic cpcities to be ble to repir tose rpidly fter te excittions due to devstting ertqukes (Level). Tis tsk ccompnies wit tremendous complexity in te process of design of te bridge system. In generl, Level design is criticl for determintions of member sizes for lrge scle bridge systems. Terefore, te estblisment of rtionl nd efficient optiml seismic design metod, wic cn determine te optimum member sizes considering performnce t ultimte stte in te Level design process, s been wited expectntly in te prcticl design. From tis point of view, one of utors proposed n optiml seismic design metod using te design of experiments nd suboptimiztion tecnique [,3]. In tis reserc works, utors mde effort to introduce severl reltions between construction cost nd design vribles to mke te optimiztion problem simple. Te design vribles for bridge members re delt wit s continuous vribles nd te optimum solutions considering te displcement constrints for bridge direction re determined. In tis study, n rtionl nd efficient optiml performnce-bsed seismic design metod for bridge system subjected to devstting ertqukes is proposed. In te design of bridge system, te Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00

2 dimensions of superstructure re ssumed to be given, nd te eigts of rubber berings, cross-sectionl dimensions nd mount of steel reinforcements for RC piers, nd numbers of piles nd te dimeters of piles in te cst-in-plce concrete pile foundtion re tken into ccount s design vribles. Te dynmic nonliner beviors of te bridge system re nlyzed precisely by using te generl purpose nonliner nlysis softwre (TDA-III) wit te ccelertion specified in te JSHB. Te reltive orizontl displcements between superstructure nd piers to te bot bridge nd trnsverse directions re delt wit s design constrints for te rubber berings. Te ductile fctor, wic is given by te rtio of worng curvture to te yield curvture, is delt wit s te design constrints for te RC piers so s to ensure te performnce specified t te ultimte stte. Furtermore, te constrint on te cst-in-plce concrete pile foundtion is lso delt wit to ensure te sufficient ultimte dynmic cpcity in te RC pile foundtion. However, te constrint on te RC pile foundtion is not treted in te optimiztion process to simplify te optimiztion lgoritm. After determintion of optimum solution te constrint on te RC pile foundtion is exmined, nd te RC pile foundtion is replced wit te lrger one so s to stisfy te constrint. From te prcticl design te eigts of rubber berings cn tke continuous vlues, but te oter vribles must be selected from discrete vrible sets. Terefore, te construction cost minimiztion problem cn be expressed s mixed discrete-continuous problem, nd it is solved by clssicl brnc nd bound metod [4] wit dul lgoritm nd convex pproximtion [5,6] in tis study. Te sensitivities of te design constrints need in te optimiztion process nd we encounter te difficulty to obtin tose in utilizing te generl purpose nonliner nlysis softwre. To overcome tis problem te design of experiments is pplied successfully in order to clculte te dynmic beviors nd tose sensitivities in te optimiztion process. In te design of experiments, te estimtion formule for dynmic beviors re introduced in te expression of qudrtic functions of te design vribles. Te dynmic beviors nd tose sensitivities re clculted nlyticlly by using te estimtion formule witout nlyzing te structures. After te determintion of optimum solution te design constrints wit te estimtion formule re exmined by re-nlyzing te bridge system using TDA-III. In cse tt te design constrints violte te llowble limits, te estimtion formule for dynmic beviors re improved nd te minimum cost design problem is re-solved. Tis optimiztion process is iterted until te reltive errors between te estimted design constrins nd te exct ones stisfy te llowble limits. Te proposed optiml design metod is pplied to five-spn continuous steel girder bridge system, nd te optiml solutions t vrious llowble ductility fctors of RC pier re compred. In te numericl results, it is demonstrted tt te reductions of te eigts of rubber berings nd cross-sectionl dimensions cn be observed by incresing te llowble ductility fctor. It is lso empsized tt te optimum solutions cn be obtined efficiently t few itertions of improvements of te estimtion formule for dynmic beviors. Te ccurcy of te estimtion formule is excellent H H H H B/ oint of ppliction to te force of inerti of superstructure 00 B 6000-B/ H A 3 4 A Fig. Five-spn continuous steel girder bridge system () Front view (b) Side view Fig. Front nd side views of piers nd RC pile foundtion Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00

3 M H My H H-H 5 Mc Kd H 5 φ y φ C 0 6 φ C 3 φ y 9 φ B Fig.3 Cross section of pier witin 7 percent of reltive errors between te exct beviors nd estimted ones.. OTIMUM DESIGN FORMULATION AND OTIMIZATION ALGORITHM. Design Model In tis study, te five-spn continuous steel girder bridge system sown in Fig. is considered in wic te superstructure is supported by six rubber berings, RC piers nd te cst-in-plce concrete pile foundtion. Te front nd side views of pier nd RC pile foundtion re described in Fig.. Te lengts of piles re 5m nd five types of soil conditions in strtum re considered to clculte spring constnts. Te reinforcements in te cross section of piers re rrnged in two lyers for te bridge direction nd one lyer for te trnsverse direction, nd te intervl of ec reinforcement re fixed t 5mm s sown in Fig.3. Following n enlrgement of cross section te numbers of reinforcements increse so s to keep te intervls of reinforcements. Te stiffness of RC pier is tken into ccount s te triliner rigidity reduction type model (Tked model) sown in Fig.4. Te nonliner beviors of te bridge system for te bot bridge nd trnsverse directions subjected to devstting ertqukes re nlyzed precisely by using TDA-III in wic te Type II stndrd strong ccelertion wve motion model t te Type II soil ground specified in te JSHB is pplied. In te time-istory response nlysis te spring constnts of rubber berings, pile foundtions nd superstructure re elstic, nd bot te superstructure nd butment re ssumed s rigid body. Te piers re divided into 50 segments in order to clculte te nonliner dynmic beviors ccurtely.. Optimum Design Formultion In te design of te bridge system, te dimension of superstructure is ssumed to be given nd widts of rectngulr rubber berings re ssumed to be 70cm nd 80cm t butment nd piers, respectively. Te design vribles for rubber berings re te eigts of tose t butment nd piers, B nd B. For te cst-in-plce concrete pile foundtions te numbers of piles nd dimeters of piles re intensively summrized s te properties of orizontl nd rottion spring constnts. In tis study te orizontl spring constnts of RC pile foundtion, K, wic cn be commonly used for te time-istory response nlysis to te bot bridge nd trnsverse directions, re considered s te design vribles. Te widts to te bridge nd trnsverse directions nd te mount of steel reinforcements in cross section, H, B nd A s, re tken into ccount s te design vribles for RC piers. Te bridge system sown in Fig. is symmetricl to te centerline nd te totl number of design vribles is six of B, B, K, H, A, B S. B-B B B Fig.4 Triliner rigidity ysteresis model for RC pier (Tked model) Engineers ve to design te bridge system wic ve sufficient ultimte dynmic cpcities for lrge displcements cused by devstting ertqukes. Terefore, te reltive orizontl displcements between superstructure nd piers to te bot bridge nd trnsverse directions re delt wit s te design Mc φ, Μ: Crcng curvture nd moment -My c φ, Μ: Initil yieldcurvture nd moment y c y M C + M y φmx kd = φ + φ φ c y y 0.4 Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 3

4 Tble roperties of tree types of RC piles Dimeter φ Number of piles Widt of footing B Widt of footing H Heigt of footing Construction cost(0 3 yen) K(kN/m) K θ (knm/rd) (bridge direction) K θ (knm/rd) (trnsverse direction) weigt(kn).0m 9 7.0m 7.0m.5m 3, m 9 8.4m 8.4m.5m 6, m 7.0m 9.5m.5m 7, constrints, g, g, gt, gt, for te sfety of te rubber berings. Furtermore, te ductile fctors re lso delt wit s te design constrints for te RC piers, g μ, so s to ensure te performnce specified t te ultimte stte. In te design of RC pile foundtion, for te cse tt te orizontl ultimte dynmic bering cpcity for te RC pier is not enoug lrge for te orizontl force clculted using te specified design seismic coefficient, RC pile foundtion is not llowed to yield wen te equivlent lods corresponding to te orizontl ultimte dynmic bering cpcity for te RC pier re pplied to te RC pile foundtion. For te cse tt te orizontl ultimte dynmic bering cpcity for te RC pier is sufficient, RC pile foundtion is llowed to yield up to te ductile fctor 4.0. Tis constrint is quite complex to del wit in te optimiztion process. Furtermore, we need to consider tt te design vrible for RC pile foundtion is dependent on te design vribles for RC piers. To simplify te optimum design problem, terefore, it is ssumed tt te design vrible for RC pile foundtion is independent, nd te constrint on te RC pile foundtion is not delt wit in te optimiztion process. After te determintion of optimum solution te constrint on te RC pile foundtion is exmined. Te totl construction cost minimiztion problem, wic is expressed s te summtion of bering construction cost, COST B ( B,B ),pier construction cost, COST F ( K ), nd pier construction cost, COST ( H, B ), cn be formulted s find B, B, K, H, B wic minimize COST ( B, B, K, H, B ) = COST B ( B, B ) + COSTF ( K ) + COST ( H, B ) () subject to g δ δ 0 (), g δ δ 0 (3), g δ δ 0 (4) = = t = t gt = δ t δ 0 (5), g μ = μ μ 0 (6), were δ nd δ re te llowble reltive orizontl displcements of berings t butment nd piers, wic re given s te products of te eigts of berings B, B multiplied by.5. μ is te ductile fctor of pier, wic is given by te rtio of worng curvture to te yield curvture for te bridge direction. In te optimum design problem B nd B cn tke continuous vlues, but te oters must be selected from list of discrete vlues. In tis study, K, H nd B re selected from te following discrete sets in wic tree types of pile foundtions summrized in Tble re considered to clculte K. { 657( kn / m), 76477, 9500} K H { 000( mm), 00, 00, 300, 400, 500, 600, 700, 800, 900,3000} A S { 98.6( mm ), 86.5, 387., 506.7, 64.4, 794., 956.6, 40} B { 3000( mm), 3500, 4000, 4500, 5000, 5500, 6000, 6500} Terefore, te construction cost minimiztion problem cn be expressed s mixed discrete-continuous problem. Severl types of optimiztion tecniques ve been developed, nd Hung nd Aror [4] investigted te efficiency nd relibility of tose for discrete nd mixed discrete-continuous problems. Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 4

5 Replcement of pile foundtion Fig.5 Mcro-flow of te proposed optimum design metod In tis study te optimiztion problem is solved by te clssicl brnc nd bound metod wit dul lgoritm nd convex pproximtion [5,6] for te reson tt te pproc is efficient nd relible for mixed discrete-continuous problem witout ny prmeters..3 Optimiztion Algoritm In tis optimiztion process, in generl, number of nonliner seismic response nlyses nd sensitivity nlyses re necessry to determine te optiml solutions. To void tese complexity nd difficulties nd mke te optimum design process tremendously efficient, te design of experiments [7] is pplied to introduce te estimtion formule for te dynmic beviors. Te dynmic beviors nd tose sensitivities re clculted by using te estimtion formule witout nlyzing te structure. In te design of experiments, ccording to te ortogonl rry tble L ( ) [7] given in Tble, te tree levels for ll design vribles re ssumed nd te twenty seven runs of nonliner seismic response nlyses re crried out in usge of TDA-III for te bot bridge nd trnsverse directions, respectively. Te first six fctors mong tirty fctors in Tble re ssigned to te design vribles B, B, K, H, B, respectively. Assuming tt te intended vrible for te kt fctor is x k nd te men vlue of tree levels ( xˆ, i =, L,3) for te kt fctor is x k, te generl form of estimtion formul is introduced in te expression of qudrtic functions of te design vribles given s eqs.(7)-(0). y = b m m 0 + bkzk + bk Mk Mk3zk + Mkzk ) k= k= (, (7) i i i were M ( ˆ ˆ ˆ = zk + zk + + zkn) ( k =, L, m), (8) n zˆ ˆ = x xk ( i =, L, n) ( k =, L, m) (9), zk = xk xk, (0) m nd n re respectively te number of fctors, i.e. te number of design vribles (= 6), nd te number of levels for ec fctor (= 3). Te estimtion vlues of b 0, b k nd b k in eq.(7) re given s n b ˆ 0 = T i rs, n b ˆ kl = WT ( l =,) rs () were = n S k W, () i= Initil tree levels Clcultion of eigenvlue Nonliner time-istory response nlysis Estimtion formule of dynmic beviors by te experimentl design Formultion of optimum design problem Optimiztion by te brnc nd bound metod NO NO Convergence? YES Clcultion of eigenvlue Nonliner time-istory response nlysis NO Accurte? YES Stisfy te pile foundtion constrints? YES stop k i= Improvement of tree levels Tble Ortogonl rry tble L ( 3 3 ) No No. No. No No No No No No No No No No No No No No No No No No No No No No No No No Fctor:, Fctor: B, Fctor3: K, Fctor4: H, Fctor5: A, Fctor6: B B r is te number of runs wit te level xˆ (= 9). T is te summtion of results by te design of experiments wit te level of xˆ. W is te vlue of function of coefficient f k ( z k ) in eq.(7) wit respect to b k nd b k were zk = zˆ, nmely, W = zˆ nd W = M M zˆ + M z. Fctor ˆ k k3 k i= 7 S Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 5

6 After te determintion of optimum solutions te design constrints wit te estimtion formule re exmined by re-nlyzing te bridge system. In cse tt te design constrints violte te llowble limit, te tree levels for ll design vribles nd estimtion formule for dynmic beviors re improved nd te minimum cost design problem is re-solved. Tis optimiztion process is iterted until te reltive errors between te estimted design constrins nd te exct ones stisfy te llowble limit. After te determintion of optimum solution te constrint on te RC pile foundtion is exmined. In te cse tt te constrint is violted te RC pile foundtion is replced wit te lrger one nd te bridge system is re-optimized. Te mcro-flow of te proposed optimiztion lgoritm is depicted in Fig.5. Levels Itertion Itertion Tble 3 Improvements of tree levels in te optimiztion process B (cm) (spring constnt(kn/m)) B (cm) (spring constnt(kn/m)) spring constnt of pile K (kn/m) K θ (knm/rd) K θ (knm/rd) H (mm) A s(mm ) B (mm) 6.0(533) 4.0(857) (7500).0(6667) (047) 0.0(3000) (3065) 8.0(40000) (4500) 9.0(35556) (047) 0.0(3000) Allowble ductile fctors B (spring constnt) B B Tble 4 Optimum solutions for μ =.0, 3.0 nd 4.0 μ (spring constnt) K (φ, n).0 4.8cm (773kN/m).8cm (8366kN/m) (φ=.m, n=9) 700mm cm (8035kN/m) 8.0cm (40000kN/m) (φ=.m, n=9) 800mm 8.37cm (957kN/m) 8.0cm (40000kN/m) 657 (φ=.0m, n=9) 700mm As 40mm 387.mm 387.mm H 4000mm 4500mm 3000mm δ / δ δ / δ δ t / δ δ t / δ μ / μ yield of pile foundtion D.exp. *.000 D.exp. *.000 D.exp. * 0.99 Anl ** 0.97 Anl **.0 Anl **.03 D.exp. * 0.9 D.exp. * D.exp. * 0.43 Anl ** Anl ** 0.60 Anl ** D.exp. * D.exp. * D.exp. *.000 Anl ** Anl **.0 Anl ** D.exp. * D.exp. * D.exp. * Anl ** Anl **.038 Anl ** 0.83 D.exp. *.000 D.exp. * D.exp. * 0.97 Anl **.0 Anl **.000 Anl **.008 Bridge dir: μfr=.5 Trnsverse dir:μfr=.6 Bridge dir: not yield Trnsverse dir:μfr=.6 not yield Totl cost (0 3 yen) D.exp.* : Fesibility of design constrints wit te estimtion formule by te design of experiments Anl** : Fesibility of design constrints using exct beviors by nlysis Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 6

7 3. DESIGN EXAMLES Te proposed optiml design metod is pplied to te five-spn continuous steel girder bridge system sown in Fig. nd te optiml solutions for severl llowble ductile fctors μ re compred. Te unit cost of rubber is s 45yen/cm 3. Te construction costs of pile re ssumed s 6500yen/m 3 for te dimeter.0m nd 73800yen/m 3 for te dimeter.m. Te construction costs of footing nd form for pile foundtion re ssumed s 33500yen/m 3 nd 8000yen/m. Te construction costs of concrete, form nd reinforcement for piers re ssumed s 8500yen/m 3, 8000yen/m nd 0000yen/tf, respectively. Following te flow-crt in Fig.5 te optimiztion processes for μ =. 0, 3.0 nd 4.0 re initited wit te levels of itertion sown in Tble 3. In te optimiztion process, te lower nd upper limits for discrete design vribles re set t te djcent discrete vlues of te minimum nd mximum vlues of te tree levels to limit improvements of design vribles. Te optimum solution for μ =. 0 cn be obtined quite efficiently witout ny improvements of te tree levels for ll design vribles. Te optimum solutions for μ = 3. 0 nd 4.0 determined by te lower limits set s te move limits. After ten, te tree levels re improved to te vlues of itertion in Tble 3 referring to te optimum solutions wit te previous tree levels. Te optimum solutions for μ = 3. 0 nd 4.0 cn be obtined efficiently t tis stge witout dditionl improvements of te tree levels. Te optimum solutions for μ =.0, 3.0 nd 4.0 re summrized in Tble 4. Te orizontl spring constnts of pile foundtions for ll cses re determined by te lower limit wic indictes te lowest cost. Ten, te RC pile foundtions for μ =. 0 nd 3.0 re replced wit te lrger one so s to stisfy te constrint on te RC pile foundtion. In cse of μ =. 0 te lrgest dimensions of cross section, H nd B, nd reinforcement in te piers A S re required in order to stisfy te llowble ductile fctor. By incresing te eigts of rubber berings B nd B, nmely reducing te vlues of spring constnt, te period of bridge system is mde longer nd te effect from superstructure is minimized. As te result te totl construction cost is minimized. In cse of μ = 3. 0 B, B nd A S re remrkbly reduced compred wit tose in cse of μ =. 0, nd B nd A S re determined by te lower limits. Te totl cost is reduced to 8 percent of tt in cse of μ =. 0. In cse of μ = 4. 0 B, K, AS nd H re determined by te lower limits. Te totl cost is reduced to 7 percent of tt in cse of μ =. 0. As clerly seen from te vlues of fesibility of design constrints using exct beviors by nlysis in Tble4, bot te constrints on reltive orizontl displcements t butment to te bridge direction g nd ductile fctors g μ re ctive for ll cses simultneously. Te displcements t butment nd piers to te trnsverse direction g t re lso ctive for μ = Te displcements t piers to te bridge direction g re inctive for ll cses. Te ccurcy of te estimtion formule is excellent witin 7 percent of reltive errors. Te exct constrints re enoug fesible witin 3.8 percent of violtion for ll cses. 4. CONCLUSIONS Te following conclusions cn be drwn from tis study: ) Te proposed optiml design metod cn determine te eigts of rubber berings, cross-sectionl dimensions nd mount of steel reinforcements for RC piers, nd numbers nd dimeters of piles rigorously nd efficiently. Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 7

8 ) By pplying te design of experiments, te estimtion formule for te ductile fctor in piers nd te mximum orizontl displcements to te bridge nd trnsverse directions cn be introduced ccurtely wit smll number of nonliner seismic response nlyses. Te ccurcy of te estimtion formule is excellent witin 7 percent of reltive errors between te exct beviors nd estimted ones. 3) A few itertions of improvements for tree levels re required to obtin te optimum solutions in te proposed design metod. 4) In te cse tt te llowble ductile fctor is set t smll vlue, te eigts of rubber berings increse in order to mke te period of bridge system longer, nd te effect from superstructure is minimized. As incresing te vlue of llowble ductile fctor te eigts of rubber berings re reduced nd te dimension of cross section nd reinforcement in te piers re lso reduced. 5) In te proposed design process, te constrint on te RC pile foundtion is not delt wit in te optimiztion process nd, ten, te RC pile foundtion is replced wit te lrger one so s to stisfy te constrint on te RC pile foundtion. Tis design process cn simplify te optimiztion lgoritm gretly. 6) Te constrints on reltive orizontl displcements t butment to te bridge direction g nd ductile fctors g μ re ctive t te optimum solutions simultneously. Acknowledgements rt of tis work s been supported by FUT Reserc romotion Fund. References. Jpn Rod Assocition, Specifiction for Higwy bridges, rt V seismic design, Tokyo, Mruzen (in Jpnese), 00.. Okubo,S., Tnk,K., Wtnbe,T., Yositke,R., Optuml design metod for seismic-isoltion bridge systems subject to uge ertqukes, Journls of JSCE., No.703/I-59, pp.67-8 (in Jpnese), Okubo,S., Tnk,K., Kdot,K., Minimum cost design metod for seismic-isoltion bridge systems considering initil construction cost nd repir cost cused by uge ertquke, Journls of JSCE., No.70/I-60, pp.9-08 (in Jpnese), Hung,M., Aror,J.S., Optiml design wit discrete vribles: some numericl exmples, Int. J. Num. Met. Eng., 40, pp.65-88, Fleury,C. nd Bribnt,V., Structurl optimiztion: A new dul metod using mixed vribles, Int. J. Num. Met. Eng., 3, pp , Tniw,K. nd Okubo,S.: Optiml syntesis metod for trnsmission tower truss structures subjected to sttic nd seismic lods, Int. J. Struct. Multidisc. Optim. Vol.6, pp , Tguci,G., System of Experimentl Design, New York, UNIUB/Krss Interntionl ublictions, Volume &, 987. Interntionl Conference on Sustinble Built Environment (ICSBE-00) Kndy, 3-4 December 00 8