STUDIES FOR PREVENTING THE IMPACT OF CLIMATE CHANGES UPON BUILT ENVIRONMENT

Transcription

1 BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Pulict de Universitte Tehnică Gheorghe Aschi din Işi Tomul LXI (LXV), Fsc. 2, 2015 Secţi CONSTRUCŢII. ARHITECTURĂ STUDIES FOR PREVENTING THE IMPACT OF CLIMATE CHANGES UPON BUILT ENVIRONMENT BY ELENA AXINTE 1, ELENA-CARMEN TELEMAN 1, GEORGETA BĂETU 1,*, RADU-AUREL PESCARU 1 nd RADU SILION 2 Gheorghe Aschi Technicl University of Işi 1 Fculty of Civil Engineering nd Building Services, 2 Fculty of Automtic Control nd Computer Engineering Received: My 29, 2015 Accepted for puliction: June 12, 2015 Astrct. Current climte chnges correlted with development of urn res on lrge scles, often exposing the communities to unnticipted consequences cused y extreme mnifesttions of nturl phenomen produced y intensifiction of wind ction. These climte chllenges hve prompted n increse of studies regrding the effects of rndom wind ction on construction nd the uilt environment. The pper summrizes some of the experiments performed in turulent oundry lyer wind tunnel, in prllel with numericl simultion techniques, developed ltely with the purpose of refining the process of modelling t reduced scle in lortory nd lso of dvncing on the nlyticl directions of study of the wind flow in oundry tmospheric lyer. These studies helped to enrich the informtion from stndrds, regrding the fluctuting pressure distriutions on the surfce of tll uildings or other importnt structures with typicl geometry, the movement of the ir flow t the ground level with notle consequences for outdoor ctivities, the uneven snowdrift on rooftops nd lso on the trffic infrstructure during the winter deposits resulting in more ccurte nd relistic design lods from snow. Key words: wind ction; oundry lyer wind tunnel; numericl simultions; snow ction; pedestrin comfort. * Corresponding uthor: e-mil: get_vsies@yhoo.com

2 62 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion 1. Introduction High-rise structures re sensitive to wind ction nd recent scientific dvnces contriute to improvement of the design process. Two reltive new directions of engineering emerged from the comintion of mthemtics, sttistics, meteorology, physics nd uilding engineering: uilding erodynmics, domin of studying the modifictions of the wind flow field y the presence of the uilt environment tht induce consequences upon the humn comfort nd wind structurl engineering, domin relted with the sfety design to wind dynmic ction. Ltely mssive preoccuptions were directed towrds integrtion of the wind ction in producing the green energy; the design of the individul solr collectors or of solr frms otined y grouping these individul elements reveled new directions of study. The erodynmics of environment is one of the most ctive fields of study t interntionl level; the frmework of different governmentl progrms comprise exhustive nlyses underlying the entire policy of regionl development nd the policy in the field of uildings nd sptil plnning. One of the most significnt cses of studies on the impct of wind ction tht fundmentlly chnged the trditionl concepts ws developed in U.S.A. nd Cnd (Boundry Lyer Wind Tunnel Lortory, South Ontrio University, Cnd). After disstrous collpses of importnt ridges in USA nd UK erly in the yers of 1900 due to wind extreme ction, highlighting the impct of wind forces induced on tll uildings is quite relevnt cse of the XX century studies. In Europe, lrge urn res hve mster plns vlidted nd developed sed on erodynmic testing environment (e.g. the environmentl wind tunnel C.S.T.B. in Frnce). A relevnt exmple in the field is the involvement von Krmn Institute from Brussels to city development, in ccordnce with the requirements of the criteri of urn comfort. Accordingly, the whole Europen Community susequently dhered to the principles nd recommendtions developed, so fr stndrd nlysis of the impct of wind is required s n importnt condition for grnting certifictes of construction nd environmentl permits. Insufficient knowledge of ll spects tht define the ction of wind on uildings led to the production of numerous ccidents (Fig.1), requiring the need to develop nd deepen the erodynmics nd the wind engineering. At the Fculty of Civil Engineering from Isi, is working the Lortory of Building Aerodynmics tht hs over 40 yers reserch ctivity, dedicted to the vst effects wind ction on the uilt environment. Settled in 1969 from the inititive of prof.univ.dr.eng. h.c. Adrin Rdu, the lortory is intended for experimenttion on physicl models nd is equipped with turulent oundry lyer wind tunnel used to simulte the mechnicl effects of wind lods on

3 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, uildings nd uilding elements, the moving of ir flow to ground level with importnt consequences on outdoor ctivities, the dispersion of pollutnts under wind ction, optimiztion of the urn rchitecturl detils for reducing het loss from uildings nd nturl ventiltion of uildings, snow lods uneven deposits on rooftops nd on rods nd high wys, etc. The lortory is equipped Fig. 1 Dmges produce y wind: Tkom Nrrows ridge ( Roof from Colentin, Bucureşti ( with wind tunnel for very smll scles of modelling (SECO 1) (Fig. 2 ) nd n tmospheric oundry lyer wind tunnel for lrger scles (SECO-2) hving 1.40m x1.40 m cross-section (Fig. 2 ), nd 10 m length, stisfying wide rnge of tests (Axinte, 1988; Pescru, 2000; Axinte & Pescru., 2000). Fig. 2 Lortory of uildings erodynmics: SECO1 tunnel, SECO 2 tunnel. The development of methods used for the investigtion the wind effect in B.L.W.T. y reproducing t smll scle the uilt re nd the possiility of otining the specific turulent oundry lyer conditions from specific

4 64 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion environment ws importnt ecuse of the most dvntgeous ility to put in evidence y wind tunnel experiments the sensitivity to wind ction of the prototypes. Becuse oth wind tunnel nd experiments t nturl scle require significnt time nd finncil resources, new direction emerged from erodynmics nd wind engineering tht llows the numericl simultion of the wind effects, sed on computtionl fluid dynmics (CFD). The numericl simultion is n mivlent method of supplying the physicl modelling if the simultion conditions re cler nd verifiction nd visuliztion of the generl spects of ir flow surrounding the structures situted on the ground nd immersed in the oundry lyer. 2. Experimenttions Concerning the Wind Effects on the Built Environment Full scle oservtions nd mesurements, correlted with the physicl modelling technique of turulent ir flow in the uilding re, reveled different mnifesttions of wind ction, sometimes with unexpected unfvourle effects. The ssessment of wind lods required for the strength structure design of uildings nd their light envelopes (wlls nd roofs), re sed on the pressure coefficients tht reproduce the wind pressure field. The pressures vlues otined s result of the mesurements on rigid models in wind tunnel llow the evlution of wind lods for oth long term, men effect, used for the structurl design nd the short term gust effects, importnt in the design of the non-structurl elements sensitive to wind ction Assessment of the Pressure Field on the Surfce of the Buildings In urn res, shrp edged uildings, so clled luff odies, from erodynmic point of view, hve the cpcity to model the ir flow due to shpe nd size (Fig. 3 ); the wind speed incresed genertes turulence occurring in strong eddies on the in wind uilding fce nd t the corners. Behind the uildings the wind flow in wke produces strong vortices whose dimensions re scled y the speed of the flow nd the in plne shpe of uildings; regrdless of these dimensions, it is common fct tht on encountering luff ody the ir flow diverges, the deflected stremlines eing shped y the speed of the flow, the dimensions of the uilding nd the turulence of the site. The pttern of the ir flow, in plne or in spce, is directly relted to the configurtion of the uildings nd theirs neighouring res. In the cse of multi-storey uildings with 16 to 30 levels (Telemn, 2000), the unfvourle effects mnifest regrdless the position of the uilding in prticulr site. Wke is present in the rer flow nd the shrp edges model the divergence of the wind lines of flow, which generte corner sher nd delt wing vortices cused y the interfce etween the in wind positive pressures

5 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, nd the sher lyers generted on the surfces prllel to wind flow, resulting in negtive pressures. Locl incresed speeds nd turulence re lwys expected in these prticulr res on the surfce of the uildings. Fig. 3 The complexity of fluctuting ir flow round tll uildings: Chnging the direction of ir flow due to the uilding geometry, The model of the uilding equipped for wind tunnel mesurements. Some studies crried out in the Lortory of Building Aerodynmics imed to ssess wind pressures required for the design of multi-storied uildings nd their fçdes nd their gol consisted in otining the vlues of fluctuting pressure coefficients tht customize the intensity of pressure field. The clssic nd most relile mesurement equipment nd dt processing of the lortory, llowed the cquisition of instntneous velocities nd pressures nd the possiility of determining the dynmic chrcteristics of the turulent flow in the wind tunnel (Fig. 4). According to the results otined, the internl pressure depends on the ction of externl pressure on the whole uilding, s well s the importnce nd the loction of the openings (windows nd doors) provided on the envelope. For these situtions, studies were performed in order to put in evidence the prticulr effects tht occur in the cse of light fcdes of multi-storey uildings, sensitive to wind fluctutions. An exmple of evlution of the wind effects upon the roof of prticulr structure sensile to wind ction refers to the study of construction plced on Ctlin hill (out 400 feet) situted closely to Isi, in the Cucuteni re, the hitt of the well-known Neolithic culture. Hving shpe of prolic hyperoloid shpe, sustined y tensioned gles this structure is

6 66 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion most prticulrly sensitive to wind dynmic ctions. Due to strong glloping with lrge mplitudes nd periodic phenomenon of vortex detchment, the roof cover memrne, mde of hevy pnels egn to deteriorte grdully, finlly reching the collpse (Fig. 5). Fig. 4 Signls recorded/processed sed on dt cquisition in wind tunnel, Energy spectrum of fluctuting pressure. Fig. 5 The dmged construction nd rigid model reduced to 1/100 scle. As result of the mesurements mde on rigid model scled 1/100 s well s the model of the construction nd the Ctlin hill, on the 1/400 scle, the men nd pek pressure (suction) were determined y lgeric summrizing the externl nd internl effect of wind ction on the envelope. An importnt experimentl progrm of study in the Lortory of Building Aerodynmics imed to ssess the ehviour of lrge roof to the ction of wind nd snow (Fig. 6 nd 11) (Telemn et l., 2012; Telemn et l., 2011).

7 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, Fig. 6 The model of the uilding with lrge-spn roof nd the neighouring re; the model of the uilding equipped for pressure mesurements nd pressure tues connected to the scnner. The irregulr shpe nd wide dimensions of the structure nd of the cupol tht covers it, s well s the prticulr t site position of the uilding in the surroundings, mde impossile the clssifiction of the uilding in the stndrd situtions given y design codes specific to climte ctions. The experimentl study ws conducted in two stges, the gols eing to determine the drg coefficient of verge nd pek pressure on roof surfce nd the evlution of snow drifted deposits in lizzrd conditions nd erosion of the deposited snow lyer, respectively (Telemn et l., 2011). Considering severl directions of wind ction, smll-scle reproduction of the uilding nd the djcent uilt re, the ccurte reproduction of detils tht lter the irflow t full scle, s well s the lrge numer of tps where pressure mesurements were mde, hve led to lrge mount of informtion needed to ssess the effect of wind nd snow on dome roof Evlution of Wind Pressures on Solr Pnels Plced on the Roofs of the Building Mny experimentl nd numericl studies were crried out ll over the world with purpose to ssess the effect of wind ction on solr pnels, single or displyed in consecutive rows, prticulrly motivted y the lck of dequte recommendtion tht the design codes would give for such cses of design to wind ction. Cr prking spces re potentil sites for solr pnels s well s uilding roofs. A complex progrm hs een developed in the lortory (Axinte, 1988), sed on physicl modelling nd numericl simultion (Văsieş, 2012), hving s

8 68 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion oject the solr pnels plced on the flt roofs of uildings (Fig. 7) or open cr prking (Fig. 8). The mesurement of locl pressure vlues on the solr pnels surfces without perturing the ir flow round them, ws possile y using new method for verging the pressure pneumticlly (Rdu et l., 1986; Rdu & Axinte, 1989). Fig. 7 Altered pttern of the ir flow on the roof terrce of the uilding due to the presence of solr pnels rows; The physicl model used in experiments. c d e f Fig. 8 Study of the ir flow in the field of the solr pnels rry plced on the top of prking plce: Model of the prking plce free of ny occupncy; Model of the prking plce occupied y crs; c, d, e Pressure contours on the pnels in the situted nlysed otined y simultion in ANSYS CFX; f Vrition of the pressure coefficients resulted from vrition of the wind direction nd the position of the pnel in the rry.

9 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, Anlysis on Smll Scle Models in Wind Tunnel of the Pedestrin Comfort in Urn Ares Our city centres with importnt monumentl historicl uildings hve lwys represented our cultures nd civiliztion, true centres of touristic ttrction. A sustinle development must hve severl gols in ttention; ccordingly, esides rehilittion of these uilt environments tht worth eing preserved, the humn comfort in urn context must lso e considered. The interction etween the urn texture nd the wind flow confined in nrrow spces proves to ecome criticl in specific situtions; the wind ursts t the ground level incresing in turulence with the sptil dimensions of the ostcles nd the density of the uilt environment, humn ctivities re ffected sometimes in the cutest level. The following two methods re conceived for the investigtion of the pedestrin comfort in lortory. ) The powder method This is known s clssic method of visuliztion of the movement of ir currents t the ground level. It consists in plcing the models tht form the uilt re on smooth plte in glss or plstic ord nd covering it with thin uniform lyer of mixture of white powder nd voltile sustnce; the ir flow drives the mixture forming the strem lines, the res of stgntion nd the shpe of the eddies tht wipe out the white fluid solution from the floor (Fig. 9). When drying, the imge gives qulittive, eloquent informtion out the exposed or sheltered res, the res of formtion of the sttionry vortex, the flow lines nd in prticulr, the snow gglomertions (Pescru, 2000; Axinte & Pescru, 2000;), eing similr to the rdiogrphy of the ir flow etween the ostcles implnted in the urn texture. Fig. 9 Visuliztion of ir currents using powder method.

10 70 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion ) The pwns method An originl method ws developed in the Lortory of Building Aerodynmics of the Civil Engineering Fculty in Isi tht llows determining the wind discomfort in the uilt environment y using luminium pwns, rryed t guged distnces throughout the re of interest round the uilt ostcle (Pescru et l., 2000). The method consists in slow growth of ir speed, in the wind tunnel, until the first pwns re flling (Fig. 10). Fig. 10 The model t scle representing tower uilding nd the iso-comfort mp of wind speeds drwn y using the pwns method. The ir speed is mrked nd the entire procedure is repet, incresing grdully the ir velocity. Compring the speed of flling the pwns on the ground level without ostcles (V), in the sence of the uilding with the speed of flling of the pwns plced in the rry contining the uilding (V 1... V n ) k i coefficient is otined, representing the degree of discomfort to wind speed, t pedestrin level, for different points of loction of pwns. The dt re used for drwing mps mrking the pedestrin res of similr degree of pedestrin discomfort cused y wind. The method is useful for optimizing the detils of the systemtic circultion in the proximity res of lrge uildings Agglomertion of Snow Due to Wind Action Simultion of deposits snow in the conditions of generting lizzrds involves understnding the phenomen tht occur during snowfll ccompnied y n increse of wind speed nd lso the choice of n optiml mteril tht simultes the snow fll in order to reproduce the rel trjectory of snowflkes

11 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, crried y wind. The mount of deposited snow, s well s the snow gglomertions or the sheltered res, depend on the wind speed nd turulence. c Fig. 11 Snow gglomertions on wide spn roof hving geometry tht fvours the snow deposits: model of the uilding nd the surroundings plced in the SECO2 wind tunnel, snow drift formtion during snow storms, c eroded res of the snow deposit under wind ction. According to Iversen (Iversen, 1979), the physicl scle model of wind trnsporttion hs to reproduce the slttion phenomenon, which is predominnt in the first few centimetres ove the snow lyer. Modelling the snow-scle in wind tunnel is quite difficult due to the complexity of snow fll phenomenon extremely sensitive to severl fctors mong which the ir temperture, ground temperture, durtion of the event, wind flow field nd other chrcteristics of the studied res. To evlute the snow deposits nd highlighting the drifting phenomenon, two methods hve een used in lortory during multiple simultions tht re sed on the erosion nd deposition of mteril tht simultes the snow prticles. Two grnulr mterils were used to simulte the snow, wood swdust nd glss micro eds. Using oth methods, quntittive mesurements of deposited respectively eroded snow lyer hve een mde for roof with lrge dimensions (Telemn et l., 2011), (Fig. 11). By reproducing the phenomenon of snow flls during wind storms on the roof terrce equipped with solr pnels, the snow drifted res were

12 72 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion nlysed (Axinte et l., 2012) (Figs. 12 nd 13); systemtic studies were lso developed for modelling t smll scle the efficiency of the snow fences tht protect the rods from snow drifting (Florescu, 2001) (Fig. 13). Fig. 12 Simultion of the snow gglomertion during storming wether on terrce provided with solr collectors plced in prllel rows: formtion of the snow drift; incresed mounts of the snow deposit due to the presence of the solr pnels. Fig. 13 Physicl model of the snow drift on rods using glss eds. 3. Conclusions The experimentl studies developed in wind tunnel provide us relevnt informtion upon the effects of wind flow round the uildings plced in urn res. They help y enlrging the necessry dt for the design of wide rnge of uildings nd other structures, drw the ttention upon unexpected effects of wind turulence in uilt environment nd increse the ccurcy of the nlyticl modelling vi numericl methods. They re now powerful instrument of simultion of the complex impct of the field of speeds nd pressures on the

13 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 2, volumetric shpe generted y the presence of the uilt structures in the tmospheric oundry lyer. The dvntges of studying on scled models in wind tunnel re importnt: optimizing the structurl design, reducing the excesses in the design due to uncertinties, qusi-exhustive ssessment of the wind effects upon the environment nd the possiility of modelling wide rnge of other connected phenomen (pollution, therml effects of incresing the urn density, etc). The future reserch directions in the oundry lyer wind tunnel hve in view importnt fundmentl spects, like: ccurcy of the physicl in order to mtch lrger numer of similrity, vlidtion of the results otined, clirtion of the methods dopted for mesurements through sttisticl nlyses of the sets of dt, ppliction of severl types of numericl simultions in order to otin ccurcy nd control the complex mechnisms of modelling the wind flow. REFERENCES Axinte E., Modelre fizică intercţiunii vânt-structură pentru proiectre cpttorelor solre. Ph.D. Diss., Gheorghe Aschi Techn. Univ., Jssy, Axinte E., Pescru R.A., Studiul cţiunii vântului în tunel erodinmic. Edit. Cermi, Işi, Axinte E., Telemn E.C., Văsieş G., Roşc E.-V., (2012). Extreme Actions of Snow Drift Cused y Wind on Built Environment in the Context of Glol Climtic Chnges. 12th Internt.l GeoConf. SGEM 2012, SGEM Conf. Proc., , Florescu E.C., Modelre prmetrilor climtici in vedere otimizrii elementelor geometrice le profilului trnsversl l drumului in regiuni cu ierni spre, Ph.D.Diss., Gheorghe Aschi Techn. Univ., Işi, Iversen J.D., Drifting-Snow Similitude Trnsport Rte nd Roughness Modeling. J. of Glciology, 26, 94, (1979). Pescru R., Contriuţii l studiul cţiunii vântului în tunel erodynmic. Ph.D.Diss., Gheorghe Aschi Techn. Univ., Işi, Pescru R., Văsieş G., Akileh H.A.A., Rdu A., Numericl Simultion Approch to Estimte the Ground Level Wind Action Ner Prismtic Building. Proc. of the 10th Intent. Symp. Comput.l Civil Engng., New Computtionl Concepts in Civil Engineering, Işi, Români, , Rdu A., Axinte E., Teohri C., Stedy Wind Pressures on Solr Collectors on Roofed Buildings. J. of Wind Engng.. Industril Aerodynmics, 23, (1986). Rdu A., Axinte E., Wind Forces on Structures Supporting Solr Collectors. J. of Wind Engng.. Industril Aerodynmics, 32, (1989). Telemn E.C., Contriuţii privind lcătuire şi clculul clădirilor ultietjte cu structură metlică. Ph.D.Diss., Gheorghe Aschi Techn. Univ., Işi, 2000.

14 74 Elen Axinte, Elen-Crmen Telemn, Georget Băetu, Rdu-Aurel Pescru nd Rdu Silion Telemn C-E, Axinte E., Silion R, Avrm C., Văsieş G., Study in Boundry Lyer Wind Tunnel of the Wind nd Snow Actions Upon Wide Spn Domed Roof. Contrct 2055P/2010 CCTT POLYTECH, eneficiry S.C. BUILD CORP S.R.L Işi, Telemn E.C., Axinte E., Văsieş G., Roşc V., Study on Snow Drift on Domed Roof in Atmospheric Boundry Lyer Wind Tunnel. Proc. of Internt. Sci. Conf. DEDUCON Sustinle Developmentin Civil Engng., Işi, 1, C449-C464, Telemn E. C., Axinte E., Văsieş G., Roşc V., Wind Extreme Dynmic Effects on Wide Spn Domed Roofs. 12th Internt. GeoConf. SGEM 2012, SGEM Conf. Proc., , Văsieş G., Contriuţii l studiul cţiunii vântului în contextul dezvoltării durile. Ph.D.Diss., Gheorghe Aschi Techn. Univ., Işi, PREOCUPĂRI ÎN PREVENIREA CONSECINŢELOR IMPACTULUI SCHIMBĂRILOR CLIMATICE ASUPRA MEDIULUI CONSTRUIT (Rezumt) Modificările climtice ctule corelte cu dezvoltre rpidă zonelor urne, expun comunităţile l consecinţe dese nenticipte, cuzte de mnifestările extreme le fenomenelor nturle produse de intensificre cţiunii vântului. Aceste provocări climtice u determint intensificre studiilor privind efectele cţiunii letore vântului supr construcţiilor şi mediului construit. În lucrre se prezintă sintetic unele dintre experimentele relízte în tunel erodinmic cu strt limită turulent, complette in ultimii ni cu simulre numerică. Aceste studii u contriuit l completre informţiilor din normtive referitore l distriuţii de presiuni fluctunte pe suprfţ clădirilor înlte su cu forme tipice, deplsre curenţilor de er l nivelul terenului cu consecinţe importnte supr ctivităţilor în er lier, glomerre zăpezii cu consecinţe supr încărcărilor pe coperişuri şi circulţiei pe căile de comunicţie pe timp de irnă etc.