AITC TECHNICAL NOTE 19 GUIDELINES FOR EVALUATION OF HOLES AND NOTCHES IN STRUCTURAL GLUED LAMINATED TIMBER BEAMS (July 2012)

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1 AIT TEHNIAL NOTE 19 GUIDELINES OR EVALUATION O HOLES AND NOTHES IN STRUTURAL GLUED LAINATED TIBER BEAS (Jly 01) AERIAN INSTITUTE O TIBER ONSTRUTION 701 S. Reere Parkway Site 140 entennial, O 8011 Pone ax info@aitc-gllam.org Website: SOPE Tis tecnical note as been eelope to assist engineers, arcitects, biling officials, an oters in ealating te effects of oles an notces in strctral gle laminate timber beams. Tese gielines are applicable to oles tat are to be se to proie access ("open") oles an are not applicable to oles rille for mecanical fasteners or connectors. Tese gielines only apply to ron or rectanglar oles as escribe erein an to te specific notc types escribe erein. Holes an notces in cre or tapere beams are not aresse. INTRODUTION Strctral gle laminate timber (gllam) is typically se in igly stresse engineering applications. Becase gle laminate timbers are se in igly stresse applications, it is ery important to aoi moification of tese members in any manner tat wol aersely affect teir intene strctral performance. Holes an notces rece te section aailable to resist stresses an also proce stress concentrations an tension stresses perpeniclar to grain. As sc, oles, notces, an oter moifications to gllam sol be aoie or limite. Were naoiable, oles an notces sol be place in zones of lesser beam stresses. Generally speaking, oles an notces mst be approe by an engineer qalifie in timber esign. Small orizontal oles witin te prescriptie limitations for orizontal oles incle in tis ocment are permitte witot engineering analysis. Large orizontal oles, ertical oles, an notces always reqire engineering approal. It is recommene tat te en grain srfaces expose by te fabrication of oles an notces be coate wit an en sealer to minimize potential cecking. HOLES Te proceres erein apply to oles fabricate trog gle laminate timbers to accommoate te passage of electrical conit, sprinkler lines, or oter lines, bt not to oles se to transfer loa. Holes for mecanical fasteners an oles tat transfer significant loas to te beam mst be ealate separately. AIT 104 Typical onstrction Details [1] an te Timber onstrction anal [] proie giance on esigning connections. Permissible Horizontal Holes witot Engineering Analysis Drille orizontal oles in niformly loae, simply spporte beams are allowe in te zones NOT ientifie as critical (igre 1) wit te following limitations: 1. Holes mst be a minimm of 4 ole iameters from te top or bottom srface of te beam an a minimm of 8 ole iameters from te en of te beam. Te istance is measre from te ege of te ole to te nearest ege of te beam.. aximm ole size is 1-1/ iameter or a ole iameter eqal to 1/10 te beam ept, wiceer is smaller. 1

2 AIT Tecnical Note aximm Nmber of Holes: Te nmber of oles (not incling oles relate to connections) sall not excee one ole per eac 5 feet lengt of te member (i.e. 4 oles in a 0 foot member). (Tis rle oes not apply to spacing of oles.) 4. Spacing between oles sall be a minimm of 8 ole iameters (base on te largest iameter of any ajacent ole in te member) from any oter ole in te member. Te istance is measre between te nearest eges of ajacent oles. Uniform Loa oment /4 Sear Sear Bearing oment Bearing /4 L/8 L/4 L igre 1. zones in a niformly loae, simply spporte beam Engineering Ealation of Horizontal Holes Large orizontal oles an oles of any size in any of te critical zones mst be approe by an engineer qalifie in timber esign. Te presence of oles reces te section capacity an creates stress concentrations wic mst be consiere. Te effect of te ole mst be ealate wit regar to (1) bening capacity, () sear capacity, an (3) stress concentrations. Te following sections escribe analysis proceres for eac of tese cases, sbject to te following limitations. Limitations on Holes: 1. oncentrate loas at location of oles sol be aoie.. Holes mst be circlar or rectanglar wit rone corners (igre ). 3. Te istance from te nearest ege of te ole to te face of te nearest spport, l a, mst be greater tan or eqal to alf te beam ept, (igre ). 4. Te istance from te nearest ege of te ole to te en of te beam, l, mst be greater tan or eqal to te beam ept, (igre ). 5. Rectanglar oles mst ae a corner rais, r, of 1 in. or more (igre ). It is recommene tat in. iameter or larger oles be rille at te corners of te ole prior to sawing te straigt portions. No oerctting is permitte. 6. Te ole imension measre perpeniclar to te longitinal axis of te beam,, mst be less tan or eqal to alf te beam ept, (igre ). Te imension mst not excee 14 inces. 7. Te istance from te nearest ege of te ole to te top,, or bottom, l, of te beam mst be greater tan or eqal to 15% of te beam ept, (igre ). 8. Were mltiple oles are present, te nearest eges of ajacent oles mst be separate by a istance eqal to or greater tan te largest of (1) 1 inces, () te beam ept,, an (3) for times te ole iameter for ron oles or for times te lengt of te iagonal for rectanglar oles.

3 AIT Tecnical Note r 1 in in a 0.5 = ( + ) = in 0.15 a 0.5 igre. Hole limitations for engineering analysis. Bening apacity Te esign bening capacity of te rece (net) section mst be ealate an compare wit te esign bening moment at te location of te ole. Te following steps are reqire: 1. Te netral axis at te section trog te ole is locate (Eqation 1, igre 3): y = ( ) (1) y igre 3. Location of netral axis. 3

4 AIT Tecnical Note 19. Te moment of inertia of te net section is calclate (Eqation ): 3 3 Inet = b + y + y 1 1 () 3. Te section mols of te net section is calclate (Eqation 3): S net Inet Inet = min, y y (3) 4. Te bening capacity of te section is ealate (Eqation 4): Sear apacity ( or ) S (4) b D t V L net Te net section sear capacity at te ole mst be ealate an compare to te sear force at te ole (Eqation 5): V ( ) b D t r (5) 3 Stress oncentrations A ole in a gllam beam istrbs te normal flow of stresses in te beam. Reslting stress concentrations can case failre of te beam wit cracks originating near te corners of te ole an propagating parallel to te grain. Te following procere is aapte (see commentary) for U.S. esign from a meto propose Aicer an Hofflin [3]. Te ole size,, is efine as te iameter for ron oles or te lengt of te iagonal ( + ) for rectanglar oles. Analysis of Stress oncentrations: 1. Te moment an sear on te section trog te center of te ole are calclate.. Te following conition mst be satisfie (Eqation 6) : 3V b b were: ol in = b r D t ol (6) (7) Tese proceres o not accont for concentrate loas occrring aboe or below te ole. Were concentrate loas occr at a section wit a ole, aitional analysis may be necessary to ealate te localize effects of bening, sear, an tension perpeniclar-to-grain. Analysis of localize bening stresses sol incle consieration of lmber grae placement trog te ept of te gllam beam. Tese proceres also o not accont for potential bckling in te compression flange at te location of a ole. Aitional analysis may be necessary were localize bckling is a possibility. Engineering Ealation of Vertical Holes A ertical ole reces te net wit of te beam at te location of te ole an may significantly rece te beam s bening an sear strengt. Prior to rilling any ertical oles, a qalifie engineer mst be conslte. 4

5 AIT Tecnical Note 19 It is recommene tat rilling ertical oles in gle laminate orizontal beams be aoie weneer possible. Not only is tere a rection in section properties at te ertical ole, tere are also stress concentrations e to te iscontinity of te woo fibers at te ole. Te minimm ege istance from eiter sie of te member to te center of a ertical ole mst be 3 times te iameter of te ole. Te ealation of ertical oles mst also satisfy te following criteria: 1. Te section mols at te ertical ole mst be base on te wit of te member mins 1.5 times te ole iameter (Eqation 8): ( b 1.5 ) Snet, = (8) 6. Te maximm bening moment mst not excee te allowable fiber stress in bening mltiplie by te rece section mols (Eqation 9): ( or ), S (9) b D m t V L net 3. Te sear parallel to grain (orizontal sear) capacity at te section wit te ertical ole mst be base on te net section at te ole (Eqation 10): ( ) b D t r V (10) 3 NOTHES Tese gielines apply to simply spporte, single span, beams an to te ens of mltiple span beams. Notces at center bearings of mltiple span beams are not aresse. Tension ace Notces A ecrease in strengt is case by stress concentrations ince at te corner of te notc as well as a rection of te section aailable to resist te esign stresses. Notces also ince tension perpeniclar to grain stresses tat interact wit te sear parallel to grain forces casing a tenency for te member to split along a line extene from te corner of te notc. Tis type of notc sol be aoie weneer possible. Uner no circmstances sol a simple span gle laminate timber beam be notce on te tension face oter tan at an en bearing. Were a notc on te tension face cannot be aoie (igre 4), te ept of a tension sie notc is limite to a maximm of 1/10 te ept of te member, not to excee 3 inces. Te esign sear reaction at te notc mst be limite by Eqation 11: R be Dtr e 3 (11) 0.9 in. e 1 3 igre 4. En bearing notc etail Drill 1 in. iameter ole t from beam face to ole. 5

6 AIT Tecnical Note 19 A graal tapere notc configration in lie of a sqare cornere notc or mecanical reinforcing at sqare cornere notces may be se to rece te effects of stress concentrations at te reentrant corner of notces. Te notc sol be ct from te face of te beam to a rille ole as sown in igre 4. Te bearing capacity of te woo at te notc sol also be ealate. Tablar esign ales for bearing (compression perpeniclar to grain) for gle laminate timbers are base on te relatiely iger grae bottom lamination(s). Notcing te beam at te spport may reslt in bearing on lower grae material, wic mst be consiere. ompression ace Notces at Ens In some instances, it may be necessary to notc a beam on its compression face at te en of te member. Limitations on sc notces are sown in igre 5. or te conitions sown, te esign sear reaction mst be limite accoring to Eqation 1 or 13, as appropriate: - e RV b - e D t r were: 3 e e e (1) RV be Dtr were: e> e 3 (13) 3 ax. e 3e ax. e /3 in. e e 0.6 in. igre 5. Notc restrictions on compression face at ens ompression ace Notces Away from Ens Occasionally, it is necessary to ct a notc across te wit of te top of a gle laminate timber member to proie for passage of a small iameter plmbing or conit rn. Sc notces are only permitte on te compression sie of cross sections tat are stresse to less tan 50% of te allowable flexral stress. ember stresses mst be ealate base on te rece (net) cross section reslting from te notc. De to remoal of ig grae lmber at te srface, notcing will also case a rection in allowable bening stresses. A preferre meto for proiing reqire passage for pipes, conit, etc. is to mecanically attac aitional (nonstrctral) laminations of ept eqal to or greater tan te esire notc. In tis way te aitional material is notce leaing te original strctral member naffecte. Notces for Hangers antileere inge connections. Te necessity to proie for te fls fit of a cantileer inge connector is a commonly encontere fiel sitation tat reqires te ctting of a notc or ap. or cantileer inge connectors, te notc sol be limite to te tickness of te steel plate. Top mont sale type angers. AIT recommens tat gle laminate members not be appe at top monte angers wen te tickness of te metal is sc tat is oes not interfere wit te installation of te floor 6

7 AIT Tecnical Note 19 or roof seating or ecking. If apping is necessary, te ap sol only be ct in zones of compression stress an sol be limite to te tickness of te metal. In all cases of apping a gle laminate beam to accommoate a metal anger, te esigner mst ceck te member stresses base on te rece (net) section mols reslting from te ap. ADDITIONAL ONSIDERATIONS Pressre-Treate embers If it is necessary to notc or rill a gle laminate timber tat as been pressre impregnate wit a preseratie treatment, all ct srfaces mst receie a fiel treatment of preseratie. One commonly se fiel preseratie treatment is copper naptenate. AWPA 4 [4] contains information an reqirements for fiel treating. Oter Strctral Applications Tis tecnical note aresses te rilling an notcing of gle laminate timber beams. Howeer, similar consierations an limitations sol be applie wit respect to rille oles an notces in any gle laminate timber member sc as colmns, arces, an trss members. Oter Loaing an Spport onitions Non-niform loas. or non-niform loaing conitions, a qalifie engineer mst be conslte for ealation an approal of oles an notces. ontinos an cantileere spans. All oles an notces in gle laminate timber for continos or cantileere spans, sbject to any loaing conitions, mst be ealate an approe by a qalifie engineer. Generally, continos span or cantileer span beams sol not be notce in te top of te member oer te spport were negatie moments exist. Te engineer may coose to esignate critical zones (imensione as appropriate) were fiel rilling is not allowe wit a rawing similar to igre 6 or igre 7. oment /4 Sear Sear Sear Bearing oment Bearing oment Bearing /4 igre 6. zones in a mlti-span beam oment /4 Sear Sear Bearing oment Bearing oment /4 igre 7. zones in a cantileere beam. 7

8 AIT Tecnical Note 19 Holes for ecanical asteners an onnectors or te installation of gle laminate timber, it is often necessary to rill oles in te member to attac connection arware. AIT 104 Typical onstrction Details [1] illstrates an escribes arios connections commonly se. AIT 104 [1] also inicates certain connection etails tat sol be aoie, incling connections wic ince tension perpeniclar to grain stresses an connections tat restrain srinkage. onnection esign is goerne by te National Design Specification for Woo onstrction [5]. Sspene Eqipment Spport Te necessity to proie spport for biling elements sc as for sspene conit, plmbing lines, mecanical nits or ceiling fans is freqently encontere in te fiel. Sc impose loas sol be sspene in sc a manner tat te loa is applie to te top of te member (igre 8) to aoi introcing tension perpeniclar to grain stresses (loa transferre trog orizontal oles rille in beam). a a igre 8. Preferre connection etail for sspening eay loas section a-a or orizontal oles carrying ligt loas sc as small plmbing lines or electrical conit, fasteners sol be positione at least 5% of te ept or 4 laminations, wiceer is greater, away from te tension face of te member. If it is necessary to rill orizontal oles for te spport of eaier loas, sc as plmbing lines, mecanical nits or oter sspene loas, te oles sol be locate aboe te netral axis of te member an at a section stresse to less tan 50% of te esign flexral stress. In all cases, oles wit loas mst be ealate by an engineer. All effects of tese ae loas mst be consiere in te ealation of te member. 8

9 b D L = wit of te beam = loa ration factor = beam stability factor = wet-se factor t V = temperatre factor = olme factor for flexre in gllam beams NOENLATURE ol = olme factor for stress concentrations at oles r e l e b = sear rection factor = ept of te beam = ept of te beam mins te ept of te notc = ept of te beam below te ole = ept of te beam aboe te ole = istance from te face of te spport to te fartest ege of te notc = reference sear esign ale = reference bening esign ale = ole iameter for ron ole = lengt of iagonal for rectanglar ole, = iameter of ertical ole + I net = moment of inertia of net section trog orizontal ole L l a l r R = beam span = istance from te en of te beam to te nearest ege of te ole = istance from te face of te spport to te nearest ege of te ole = esign bening moment at ole = rais of rone corners on rectanglar ole = ertical en reaction force S net = section mols of net section trog orizontal ole S net, = section mols of net section trog ertical ole V = esign sear force at ole = lengt of rectanglar ole = imension of ole measre perpeniclar to member axis AIT Tecnical Note 19 9

10 AIT Tecnical Note 19 OENTARY: STRESS ONENTRATION ANALYSIS or te analysis of stress concentrations e to ron oles in gllam beams, Aicer an Hofflin [3] presente a moel of te form: k f k k t,05,erope mo t, is ol γ were: ft, = tension perpeniclar-to-grain stress e to ltimate applie loas t,05,erope = Eropean caracteristic ale for tension strengt perpeniclar-to-grain (base on a reference olme of 10 liters) γ = material safety factor for Eropean esign k mo = moification factor for ration of loa, serice conitions, etc. k = stress istribtion factor is k = olme factor for tension perpeniclar-to-grain strengt ol Te critical tension perpeniclar-to-grain stress can be escribe as: f 3V 0.6 = b b t, were: V b = sear force at location of ole at ltimate loa leel = bening moment at location of ole at ltimate loa leel = wit of beam = ept of beam = iameter of ole Eropean Design Eqation Te reslting esign criterion (Eropean basis) ten becomes: 3V b b γ t,05,erope mo k k is k ol Te olme factor for tension perpeniclar-to-grain is: k ol ( ) mm = 0.19b Te stress istribtion factor is: 1.8 for / V < 5 kis = 1.9 for / V > for pre moment 10

11 alibration actor AIT Tecnical Note 19 Aicer an Hofflin [3] recommene te se of a calibration factor of 1.15 to increase te resisting stress. omparison of te larger beam ata presente by Daniellson [6] for ron oles to te esign eqation presente erein i not spport te se of te calibration factor, so it as been conseratiely neglecte in tis tecnical note. igre 9 illstrates te comparison of te ata presente by Daniellson [6] to cres eelope base on te proceres in tis note. igre 9. omparison of test reslts from beams wit ron oles wit preictie eqations presente in tis tecnical note. Proceres are conseratie for all points tat plot aboe te cres. H = beam ept, D = ole iameter, T = beam wit, V = sear force at location of ole, A net = net area of cross section. res represent a ratio of /VH =. Points below te cres are captre for /VH ratios matcing test conitions. Rectanglar Holes Aicer an Hofflin [3] i not present proceres for te analysis of beams wit rectanglar oles, oweer, teir procere for ron oles gies reasonable reslts wen applie to rectanglar oles wit te ole size,, efine as te lengt of te iagonal of te rectanglar ole an te olme factor calclate base on te beam wit an te imension of te ole measre perpeniclar to te beam s longitinal axis,. Beam test reslts reporte by Daniellson [6] were compare wit te preictie eqations to erify reasonable fit wit te ata. igre 10 illstrates te comparison of te ata for beams wit rectanglar oles to a esign cre eelope accoring to te proceres presente erein. = + k ol ( ) mm = 0.19b were: = imension of rectanglar ole measre parallel to longitinal irection = imension of rectanglar ole measre perpeniclar to longitinal irection 11

12 AIT Tecnical Note 19 igre10. omparison of test reslts from beams wit rectanglar oles wit preictie eqations presente in tis tecnical note. Proceres are conseratie for all points tat plot aboe te cres. H = beam ept, D = ole iagonal lengt, T = beam wit, V = sear force at location of ole, A net = net area of cross section. re represents a ratio of /VH =. Points below te cre are captre for /VH ratios matcing test conitions. Deriation of U.S. Design Eqations Tere is no allowable esign stress for tension perpeniclar-to-grain in U.S. esign, so te correlate property of sear stress is se in esign. It is necessary, terefore, to relate te Eropean tension perpeniclar-tograin caracteristic ale to te U.S. allowable sear ale. Eropean softwoos consiere in te Erocoe ae similar ensity to lower strengt softwoos in te U.S. represente by te gllam general softwoos (SW) species grop. A ale of 0.5 Pa (7.5 psi) is se as a caracteristic tension perpeniclar-to-grain ale for esign wit Eropean softwoos. Te allowable stress esign (ASD) reference sear ale for te SW species grop is 195 psi. If it is assme tat te SW species grop is similar to te Eropean softwoos a factor can be erie to conert from a Eropean esign basis to a U.S. esign basis. = K K t,05,erope r 1 Pa 0.5 Pa = K ( 195 psi)( 0.7)(.88) 145 psi K = 0.18 = 0.18 K t,05,erope r were: = caracteristic ale in tension perpeniclar-to-grain from Eropean test t,05,erope r = allowable stress sear reference ale se in U.S. esign = sear rection factor specifie in U.S. esign for non-prismatic members 1

13 K = format conersion factor for U.S. LRD esign AIT Tecnical Note 19 Te olme factor for tension perpeniclar-to-grain also reqires nit conersion for U.S. esign: k ol ( ) mm 610. in 1 in = = = 5.0 = b 0.19b b ol Te partial safety factor for Eropean esign, 1 γ, seres te same prpose an as approximately te same magnite as te material safety factor, φ, se in U.S. LRD esign, terefore: γ 1 = φ were: φ = material safety factor for U.S. LRD esign Te Eropean moification factor, k mo, is essentially eqialent to te proct of te U.S. factors for time effect, λ, wet-se, k = λ mo t, an temperatre, t, terefore: were: λ = time effect factor for U.S. LRD esign = wet-se factor for U.S. esign = temperatre factor for U.S. esign In aition, te minor ifferences in t kis base on loa istribtion are neglecte, an it is assme tat k = 1.8 for all loa cases. Sbstitting te relationsips establise aboe into te Eropean esign is eqation yiels te following esign criterion for U.S. LRD esign: 3V 0.6 t,05,eropekmo k iskol b b γ 3V K φλ b b V rkφλ t ol( 1.6) b b ( )( ) r t ol Base on te cosen calibration point between U.S. allowable stress esign (ASD) an U.S. loa an resistance factor esign (LRD), ltimate loas are 1.5 times te serice (allowable) loas. = 1.5 V = 1.5V were: V = bening moment at te location of te ole e to serice loas = sear force at te location of te ole e to serice loas Te format conersion factor for U.S. LRD esign can be expresse as: 13

14 AIT Tecnical Note D 1.5 K = φλ = K φλ D were: φ is te resistance factor for sear K is te format conersion factor se to ajst te ASD reference sear esign ale for se in LRD metoology Terefore, te reslting U.S. ASD esign criterion becomes: 3V rk t ol b b ( ) ( ) ( φλ) ( ) 3 1.5V D rk t ol b b K 3V rd t ol( 1.6) b b ( ) U.S. Design Eqations Te reslting esign eqations for bot ron an rectanglar oles are as follows for U.S. ASD an LRD esign metoologies: or ASD esign: or LRD esign: were: 3V b b r D t ol 3V φλ K b b ol in = b r t ol REERENES 1. AIT Typical onstrction Details. American Institte of Timber onstrction, entennial, O.. AIT Timber onstrction anal. 5 t eition. Jon Wiley an Sons, Inc. Hoboken, NJ. 3. S. Aicer an L. Hofflin New Design oel for Ron Holes in Gllam Beams, Proceeings of te 8 t Worl onference on Timber Engineering (WTE 004), Volme I, pp. 67-7, Jne 14-17, 004, Lati, inlan. ISSN , ISBN AWPA 4-06 Stanar for te are of Preseratie-Treate Woo Procts, American Woo-Protection Association, Birmingam, AL. 5. AW. 01. National Design Specification for Woo onstrction. American Woo oncil, Leesbrg, VA. 6. H. Daniellson Te Strengt of Gllam Beams wit Holes: A Srey of Tests an alclation etos. Diision of Strctral ecanics, Ln Uniersity, Ln, Sween. 14