Evaluation of floor systems for multi-storey buildings

Transcription

1 Evlution of floor systems for multi-storey buildings Sigrist, Christophe 1, Gerber, Christophe 2, Weber, Heinz 3, Brunner, Rolnd 4 ABSTRACT Selected specilists from the timber industry hve defined reserch needs nd future strtegies to further improve the use of timber s competitive building mteril. The rnge of trditionl building mterils is lrge, their vilbility, price nd performnce re rted good to very good. In the lst yers mny new building products with excellent nd relible chrcteristics ppered on the mrket. The vilble products seem to be well documented; systemtic presenttion of the most importnt products together with their field of ppliction nd n extensive set of chrcteristics is still required. For the developer, the designer nd even for the future owner it is wdys extremely difficult to quickly find fesible nd ecomicl solution for given ppliction. Experts hve clerly indicted tht in future the degree of prefbriction must be incresed, stndrd detils (in terms of bsic solutions) hve to be creted without imposing on the liberty of design nd the choice of mteril. The stndrd solutions must comply with lrge rnge of conditions to fulfil requirements with respect to building physics, coustics, fire resistnce, lod bering nd others. Two lrge reserch project hve been strted mid lst yer on this topic. The first project dels with Investigtions on mteril nd systems in light timber floors nd ttempts to bring some systemtic into the wide rnge of mterils, systems, connection detils nd fields of ppliction for timber floors. The nlysis of the existing floor systems proposed by different leding builders nd mnufctures nd the feedbck from interviewed users should led to new results. The second project trets the Systemtistion of timber constructions in view of coustic behviour nd is strted simultneously. The systemtic comprison of different floor systems in terms of mterils nd connections used from the first project is further nlysed with prticulr emphsis on coustics. If required in situ mesurements will be crried out to better understnd the difference between prticulr solutions. In terms of stndrdistion floor systems re of prticulr interest. In mny buildings problems with respect to service limit stte re ted. Existing floor systems proposed by different leding builders nd mnufctures re compred nd nlysed nd should led to selection of reduced number of high performnce timber floors, which re t the time simple nd fesible. INTRODUCTION Timber is recognised s being n dequte building mteril. A lrge rnge of building components however currently over floods the mrket nd it is getting more nd more difficult to correctly select the mterils. Architects, engineers nd suppliers of building components hve recognised the need of certin stndrdistion t different levels in order to improve the mrket presence of timber in the building industry. To build with timber still mens more time for the development of detil solutions nd for plnning in generl. It is lso recognised tht existing detil solutions nd vilble solutions for entire prts of the building s floor, wll or roof systems often don t comply simultneously with requirements for sttics, fire regultions, coustic nd dynmic behviour. Too much effort is put by individul mnufctures into developing new nd often similr solutions for one nd the sme ppliction. Avilble systems re t well defined nd possible differences from one mnufcturer to the other re t evident. The dvntges, disdvntges nd limits of different systems re unkwn to n-specilists. 1 nd 3 Professor, Dept. of Engineering, Swiss School of Engineering for the Wood Industry (SWOOD), Solothurnstrsse 102, 2504 Biel-Bienne, Switzerlnd 2 nd 4 Reserch engineer, Dept. of Reserch nd Development, Swiss School of Engineering for the Wood Industry (SWOOD), Solothurnstrsse 102, 2504 Biel-Bienne, Switzerlnd

2 The expecttions from the customers with respect to qulity, durbility nd finish of homes in Switzerlnd re considerble. From discussions with experts in different fields it is understood tht fr too high stndrd is demnded for timber constructions in comprison with other building mterils, nd certin perfectionism is observed. The future of timber buildings is thought to offer even more performnce for tody s prices. The required qulity however hs to be redefined bsed on the present sitution nd resonble nd chievble stndrd hs to be defined. Sensitive res to strt systemtistion of construction nd detil proposls re in prticulr wll nd floor systems, which re treted here. The deciding fctor t only for prticulr solution, but whether to build in timber or t, is finlly the cost of the entire building. In forming common pltform within the timber building industry, good bsis to effectively solve some bsic problems is given, collbortion with respect to development, optimistion, rtionlistion nd production is possible. A systemtic nlysis nd the evlution of existing proposls re required for strt in order to identify the most competitive system. In next step the constructive requirements hve to be defined in order to llow for the definition of pproprite detil solutions. A systemtistion of prts of the construction nd lso of detil solutions will give the possibility of industril mnufcturing of components. The industril (pre)fbriction will of course hve n impct on the price sitution. The difficulty of such stndrdistion is to t limit the liberty of design nd cretivity, nd to t restrict the competition nd mrket. The stndrdistion hs still to llow for individul products. Finlly good documenttion of the bsic, stndrd solutions, together with simple spn tbles s plnning tool hs to be provided. The development of mtrix or expert system would be n lterntive possibility to simplify the comprison nd selection of pproprite solutions to problem. The development of systems nd the industril production of such systems sk for specil kw-how nd infrstructure. If the developed system cn respect prticulr desires of the owner, nd the rchitect to express his own lnguge, the system is ble to survive on the hrd mrket. The flexibility of the design could go s fr s providing time dependent, dptble structure. It hs been stted tht prefbriction nd the production of systems t only re the trend, but the future of timber construction t lest in the housing sector. It ppers to be evident tht good systems with pproprite detil solutions, nd geometry which llow most vilble clddings to be fixed, give mny dvntges. The free choice of mterils, the dptbility of the systems to the needs nd freedom in design hve to be gurnteed when developing such systems. Next to the reduction of cost nd shorter erection times, better qulity of the construction is chieved due to off site construction in controlled environment. Efforts re undertken tody to crete lbel of qulity for some selected timber homes of rewned mnufcturers. The existence of good nd proofed systems would enhnce the mening of such lbel nd simplify the control nd the ssurnce of the qulity. RESEARCH AND DEVELOPMENT In Mi 1999 substntil reserch project hs been grnted with the im to compre nd to systemticlly document existing building systems nd detil solutions. The systems re to be nlysed with respect to sttic, coustic nd ecomic prmeters. A finl publiction is plned to provide rchitects nd engineers with the required tool for plnning nd decision-mking. To best hndle the tsk strong industry involvement is plned. The reserch progrm hs been ccepted by COST Switzerlnd nd directly reltes to COST E5 (Timber Frme Building Systems), Europen project. A considerble mount of work hs been crried out lredy. Severl publictions tret with the stte of the rt in timber construction in Switzerlnd in generl [1], the comprison of existing floor systems - subdivided into light nd hevy, trditionl nd modern solutions [2, 6] in prticulr. A workshop hs been held in Switzerlnd with representtives of the timber industry nd min reserch nd competence centres. The gol ws to nlyse the current sitution in Switzerlnd nd to compre the reserch needs defined by working group of COST E5 with Swiss requirements. The conclusions [2] mentioned in the introduction issued from these discussions. Furthermore short-term scientific missions (STSM) hve been relised with the support of COST to different Europen countries for contcts, kw-how trnsfer nd for the coordintion of future ctivities [4, 5]. The STSM hve clerly shown tht in other countries different solutions re present. This is primrily due to industry hbits nd secondrily to different ttitudes of the customers nd the mrket. In view of the work to be ccomplished in future, investigtions on lightweight floor systems hve been crried out [3] to determine the procedure for systemtic pproch considering I bems only, nd their clssifiction into limited

3 number of groups. The reserch on the min topics hs been strted lst summer. The generl progrm nd first results from the different ctivities re presented in the following chpters. CURRENT FLOOR SYSTEMS Sitution Until mid lst century floor systems were relised in timber only, solid timber floors were the chepest solution. Due to the invention of reinforced concrete nd due to poor execution of timber floors nd/or detil solutions they grdully lost importnce. With the ppernce of new engineered mterils certin revivl is ticed, the old problems however re still t solved. The tody s systems my be clssified into mssif, reltively hevy floors eventully in composite ction with concrete top lyers, nd light floors s shown in Figure 1. New prefbriction methods nd consequently interesting prices further increse the use of timber floors gin. Most mterils vilble cn be used for the production of floors. Lrge size pnels nd new, engineered products my yield interesting solutions to be used in floors with reltively long spns nd/or high floor lods. Trditionl floor systems re rmlly composed by liner members supporting superimposed lining. In function of spn nd lod the bems re plced t vrious centres. No trnsverse distribution of lods is chieved for this type of structure, the lod crrying cpcity is limited or lrge cross section the consequence. The trditionl floor system is prone to vibrtions for spns exceeding 5 to 6m. Bords my constitute mssive floors, lrge bem sections, glued lminted timber or specilly produced glued products composed by vrious lyers. If single elements re pre-stressed trnsverslly the lod crrying cpcity is improved in this direction. The mssive floor systems re suitble to be further developed into composite timber-concrete floors with enhnced sttic properties nd improved fire resistnce. Light floor systems re obtined from I bems composed by solid or glued lminted timber nd wood bsed bord products. Alterntively hollow sections cn be formed by solid bords. These bsic elements my be combined to form slb elements, which re suitble to be prefbricted for esy erection. A further development of these systems is the stress skin pnels with open or closed cross sections. The light floor systems rmlly crry the required superimposed lyers to fulfil specific requirement such s sound insultion, therml insultion or others nd re generlly t used in composite ction with concrete. Light floor systems nd in prticulr their systemtistion re further discussed in the next chpter. System Product Trnsversl System Product Trnsversl lod distrib. lod distrib. mssive trd Solid solid glued bords glulm block-pnel ne little little limited fir fir light I-joists hollowsections boxes stress skin open stress skin box ne ne limited limited fir mssive pre-stressed bords logs glulm good good good Figure 1 - Lod crrying floor systems purely relised in timber Sttic behviour

4 The lods nd the lod trnsfer re generlly t problem when designing the floors. Nominl lods for different types of buildings re given by the current stndrds. Design for strength (ULS) nd service (SLS) hve to be crried out. In most cses, s for timber construction liner systems re relised, service conditions rule the design. It hs been ted tht current limittions on deflections ccording to the Swiss code on floors in timber re t sufficient to prevent disturbing vibrtions. More severe restrictions on deflections nd limittions on clculted ccelertions nd nturl frequencies on timber floors re recommended. Isolted bems or limited floor stripes over generlly one or eventully two spns re in principl considered for design. Box systems or ribbed pltes my in most cses be ssumed to liner systems with ll or prt of the sheeting mteril being lod crrying, considering composite ction ( I or T sections) between ribs nd the sheeting mteril. The composite ction hs to be determined in these cses considering the stiffness of the connection between rib nd pnel. In the cse of floor systems with considerble trnsverse stiffness prticipting width bsed on FE-nlysis or full scle tests my be considered for the clcultions. Next to verticl lods modern floor systems my lso be used to trnsfer in plne (horizontl) forces nd therefore ct s brcings for the structure. Specil service conditions Next to sttic service conditions (deflection, vibrtions) specil service conditions with respect to coustics, fire nd therml insultion my hve to be considered. The therml insultion is generlly unproblemtic nd only required if the considered floor lies directly bove the ground (instlltion void) or below n-insulted roof. Specil ttention hs to be given in these cses to condenstion in prticulr nd durbility of the selected solution in generl. Figure 2 shows for selected exmple how specific requirements for sound, therml or other conditions influence the composition of trditionl floor in terms of different, superimposed lyers. Drwing ) indictes floor without specific requirement. By dding different lyers b) nd c) miniml sound or therml insultion is provided. Drwing d) shows the possibility of floor composition with high requirements for sound. It must be ted tht the superimposed lyers don t prticipte to the lod crrying ction. For resons of sound insultion they must even be fully disconnected from the lod crrying structure s presented in Figure 1 nd therefore ct s pure ded lods. Similr solutions cn be developed for other floor systems s well, by simply considering logicl superposition of specific lyers. For this reson the weights of the floor systems re t fully defined nd considerble vritions of the totl weight of prticulr solution my vry considerbly. As mtter of fct when it comes to high requirements in sound insultion, it is necessry to plce hevy lyer within the floor composition to improve the impct sound insultion. This dditionl weight or ded lod my then be responsible for deflection problems. ) c) b) d) Figure 2 - Adpttion of prticulr floor system to specil needs The sound insultion becomes more nd more importnt due to ltered construction hbits. In the pst timber houses provided living spce for one single fmily. As further development semi detched homes were built, requiring specil ttention for the medin wll plying role s fire stop nd lso s insultion ginst ise. In more recent pplictions s in the cse of multi storey timber buildings with severl prtments, horizontl brriers hve to be provided for both conditions. Importnt is the fct tht in these prtments socilly independent fmilies or groups of people re living. Disturbnce from one unit to the other must be voided. PRELIMINARY INVESTIGATIONS ON LIGHT FLOOR SYSTEMS Grouping of light floor systems Light floor systems cn show different lod bering structures (Figure 1). As rule the structurl products re solid wood or trnsformed timber products hving low weight. Associted with certin number of superimposed n-bering lyers, the floor systems show importnt vritions regrding the finl weight of the construction. Indeed ccording to the customer s wishes nd budget, the floor my remin simple nd chep with low sound insultion properties, wheres

5 ther my meet high requirements with respect to coustics nd/or fire resistnce. The superimposed lyers re t considered further here nd the investigtions concentrte on the lyout nd fbriction of the lod crrying systems only. Considering the lod crrying members of light floors it cn be distinguished between liner products (TJI, Nil Web, Msonite, etc.), single or multiple hollow core elements nd stress skin pnels. An dequte method is to be found in view of systemtic grouping of floor systems. A multitude of solutions exists for ech subgroup, more thn 10 products re lredy vilble in Switzerlnd within the fourth group of floor systems s presented in Figure 1. Comprison of light floor systems using I -bems The following criteri form the bsis for comprison between the different floor cores of systems of light weight floors: the structurl system, mterils in use, the mechnicl nd coustic properties, the fire resistnce brought by the system nd the superimposed lyers nd the possibilities nd levels of prefbriction. The lod crrying system is primrily selected ccording to its sttic cpcity (spn, lods, geometry), s it hs to meet the ULS codes requirements. Thus the choice of the structurl mteril cn be mde freely to some extent. The engineers lso hve to tke into considertion the stbilistion of the building. Therefore the floor construction my enble certin slb effect nd the connection between the floor system nd the lod bering wlls hve to be ble to trnsfer stbilistion lods. Further to these sttic requirements the floor systems cn be evluted with respect to mnufcturing nd erection spects. It is importnt to consider the possibilities of pre-fbriction of the different systems nd thus the time needed on site. The mterils in use my represent ther selection criterion in prticulr when environmentlly friendly mterils re demnded. To illustrte the procedure dopted nd the criteri systemticlly pplied to selected systems, n exmple relted to typicl I -joist is shown in the tble below: Tble 1 - Systemtic nlysis of n I-joist Description Mnufcturing Geometry Mteril Sttics vlues Implementtion Generlities I-joist is liner lod bering system I-joist is composed section with I shpe 2 flnges glued with centre web the flnges re cut nd routed to receive the centre web. wterproof dhesive is pplied to the routs, nd the flnges nd centre web re brought together under high speed nd pressure height from 241 to 610mm width from 44 to 133mm length up to 15m flnges re in lminted veneer lumber (LVL) centre web is in oriented strnd bords (OSB) E-modulus of flnges: MP E-modulus of centre web: 6000 MP G-modulus: 1600 MP I-joists under flexure hve to be stbilized to prevent ny lterl buckling web stiffener my be required t support points vrious steel hngers enble numerous connections holes of defined size my be positioned within the centre web low fire resistnce I-joists hve to be stored in verticl nd level position nd protected from the wether By consequently pplying this procedure to ll vilble floor systems nd by extending the investigtions to detil solutions s well, it is hoped to find the right prmeters of comprison in order to reduce the lrge nd unnecessry number of tody s solutions. Stndrdistion nd documenttion The structurl products offered on the mrket must be optimised considering the best rte between the floor properties nd the price in order to mke full use of the product qulities. The gol is the use of the most optiml product (performnce nd cost) with respect to the specific spn nd lods nd with considertion of prticulr spects. The min prmeters of stndrdistion re the berer chrcteristics, the construction detils, the ppliction res nd the ecomicl spects. In order to stndrdise floor systems considering such prmeters, first proposls hve to be elborted. In second step discussions with the concerned mnufcturers hve to be hold in order to chieve certin hrmonistion. To further

6 improve the mrket presence of good systems, the different mnufcturers hve to collborte - which is probbly the most difficult nd delicte point - nd to gree on design vlues. Finlly common documenttion hs to be estblished nd eventully even common reserch nd mrket strtegies hve to be defined. SYSTEMATISATION OF LIGHT FLOOR SYSTEMS Definition of components The objective of the systemtistion is to rpidly get to solution for lrge rnge of design requirements nd to give the cost t the sme time. To chieve this gol the floor system hs been exploded nd ech sequence ws given nme. Figure 3 presents the model. The floor is divided into 8 min components tht cn hve sub sequences. To these 8 components correspond ctlogues tht contin specific informtion such s the cost nd the specific lod to wide rnge of products. The definitive content of the ctlogues hs still to be defined. Flooring, FL Under flooring, UF Edge sup, ES A Floor core, FC B Filling, FG Figure 3 Explosion drwing of floor system Edge inf, EI Acoustic extr, AE Ceiling, CG Decision chrt The decision chrt gives structure to the floor design. The structure llows logicl or step-by-step floor conception. Figure 4 shows the trnsltion from the components of the explosion drwing to the decision chrt. The order of the steps hs been set ccording to sequence reverse to the construction sequence, i.e. from the outer lyer to the lod bering system. At ech step the designer hs to choose, with respect to the strength nd service requirements of the floor, if the component is wnted nd/or needed. In cse it is required, the designer is invited to select the most pproprite mteril from the corresponding ctlogue. Step 1: Ceiling (CG) Step 5: Filling (FL) Step A: Connection A Step 2: Acoustic extr (AE) Step 6: Edge inferior (EI) Step B: Connection B Step 3: Flooring (FL) Step 7: Edge superior (ES) Step S: Support Step 4: Under flooring (UF) Step 8: Floor core (FC) Ech step is importnt to the design s every component plys role on the finl ULS nd/or SLS properties of the floor s well s in the finl cost. The root gol of the project on optimistion of lightweight floors is however focused on the berer prts of the system, i.e. step 8 lone or combintion of steps 6 to 8. In the ltter cse, connections A & B ply key role with respect to the design. The other steps re t relevnt for the design of the berer system of the floor but hve n importnt impct on the coustics nd/or therml properties of decks, thus on the life qulity in the multi-storey buildings. Next steps The design chrt hs been equipped with empty boxes, which hve to be filled in by the designer. The next stge of the project will be to provide the tools or ctlogues tht will help the designer with the conception nd design of the floor system. For this purpose SWOOD will contct key plyers of the timber building ecomy, i.e. plnners, engineers, mnufcturers nd mteril suppliers. To support this gthering of informtion nd optimistion, workshops re plnned.

7 Strt of floor conception Lod summry Cost summry Ceiling Ct CG() live lod: CG: lod: Acoustic extr Ct AE() AE: lod: Flooring Ct FL() FL: lod: Under flooring Ct UF() UF1: Insultion UF1: lod: UF2: Weight UF2: lod: UF3: Insultion UF3: lod: UF4: Pnelling UF4: lod: UF5: Imp. lyer UF5: lod: Filling Ct FG() FG: lod: Edge inf Ct EI() EI: lod: Edge sup Ct ES() ES: lod: Subtotl lod: Floor core Spn, l ULS: SLS: A B Smll Spn l 4.0m + l 4.5m + l 5.0m + + l 6.0m A B Averge spn l = m + l= m + l = m + + l = m A B Lrge spn l 6.0m + l 6.5m + l 7.5m + + l 9.0m Solid joist GLT-bem LVL-joist PSL-bem I-joist Hollow sections Solid profil Glued profil Bords GLT-pnel Block-pnel Bords Logs GLT-bems Ct FC() Ct A() Ct B() Ct S() FC: lod: A: lod: B: lod: S: Totl cost: End of floor conception Figure 4 - Decision chrt for floor design ACOUSTIC ANALYSIS OF LIGHT FLOOR SYSTEMS Definition of the problem Sound insultion is relevnt spect of the qulity of building. The qulity of life in building with insufficient sound insultion is considerbly reduced. In the cse of timber constructions the coustic insultion of timber floors must be treted from the beginning of the plnning stge. The pproprite requirements nd the qulity of selected mesures for prticulr type of structure must be kwn in detil.

8 Plned investigtions Mesurement methods used to determine the coustic behviour of mssive constructions re t pplicble t 1:1 scle to timber systems s the constructions re t homogeneous nd generlly composed by severl lyers. Therefore different wve ptterns re obtined in comprison to homogeneous constructions (concrete) nd thus different sound propgtion. The consequence is to dpt the mesurement method nd to simplify the clcultion models. In view of providing multitude of solutions, the coustic properties re to be nlysed nd presented to the user. The impct on different wys of sound trnsmission of single components or lyers nd their interction nd prticiption to the sound trnsmission hs to be determined for vrious cses. The predominnt prmeters re: linings, screeds, the lod bering system, coustic ceilings nd the support conditions. First ctions in view of the nlysis nd systemtistion of the coustic behviour of timber floors nd the development of pproprite design ids re in preprtion. CONCLUSIONS Too mny mterils nd systems re currently vilble nd it is difficult for rchitects, engineers nd builders to find dequte systems t times. To fcilitte the comprison of systems, the superimposed lyers nd floor cores treted seprtely in this study. It is ssumed tht the sttic behviour of the floor is disconnected from dditionl service lyers. Mnufcturers, distributors nd users of light floor systems hve been interviewed nd much dt hs lredy been collected nd nlysed. In first step it ws necessry to get generl overview of the different products nd floor systems, to gther informtion nd to clssify the mteril with respect to their chrcteristics nd the systems ccording to the type of construction. A grouping of the discussed I-bem systems hs been undertken nd it hs been distinguished between liner systems, hollow boxes, nd stress skin pnels. It hs been ted tht within one group little difference for given ppliction exists between different providers. Due to these little differences in geometry nd concept of the systems it seems evident to stndrdise or t lest hrmonise the systems, the construction detils nd the possible pplictions. To chieve this the producers hve to be brought together in order to discuss such stndrdistion. The gol is evident: cler sitution on the product side, extensive nd precise mteril properties, well defined rules nd limits of ppliction. The collbortion of the brnch in view of joint reserch, documenttion, mrketing nd mrket presence would certinly led to n incresed use of timber floors on the construction mrket. From here resonble rules nd limits of ppliction my be defined. Stndrdised documents nd tbles re plnned iming to provide systemtic overview on the products ccording to their sttic performnces. The documents my provide uniform tbles with prmeters such s joist type, loding per m, spn, nd permissible deflection. The tbles should lso provide informtion bout typicl nd stndrdised floor detils or requirements for overll stbility. Aspects of the building physics nd the house technics will lso be considered. The stndrdistion ims to give n effective tool to the rchitects nd builders. It my llow finding the proper solution to specific sitution without too high time expense. The rchitect, engineer nd builder my find useful help nd to the customer, rnge of solutions my be provided within his finncil possibilities. To conclude, the document should llow the rchitects nd builders to quickly find system ccording to the structurl needs nd the customer desires within the best ecomic yield. REFERENCES 1. Sigrist, C., The potentil of timber in residentil nd public buildings in Switzerlnd, 5 th World Conference on Timber Engineering, Montreux, Switzerlnd, Sigrist C., Reserch needs in the re of multi-storey buildings in Switzerlnd, report COST E5, unpublished, Switzerlnd, Häfeli, M., Häuselmnn, H., Leichte Deckensysteme in Holz, Project 4 th semester, Swiss School of Engineering for the Wood Industry, Brunner R., Scientific short term mission Schllschutz im Holzbu; report Cost E5, Switzerlnd, Gerber Ch., Scientific short term mission Light weight floor systems; report Cost E5, Switzerlnd, 1998

9 6. Sigrist, C., Gerber Ch., Evlution of floor systems for multistorey buildings, Pcific Timber Engineering conference, Rotoru, NZ, 1999