WOOD CONNECTIONS II Michelle Kam-Biron, S.E. Wood Products Council WoodWorks! Continuing Education Wood Products Council is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non AIA members are available on request. This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. 1
Learning Objectives Basic Theory Design Examples Resources Available Mechanical Connectors Common Fasteners Nails Staples Wood Screws Metal plate connectors Lag screws Bolts Mechanical Connectors Other types: Rivets Split rings Shear plates Wood dowels 2
Mechanical Connectors Codes, Provisions, and Guidance Prescriptive Follows a recipe CBC, ER, NER reports No design values Engineered NDS & NER-272 Design values Accounts for performance of different materials Nominal value End use application Codes, Provisions, and Guidance ICC Reports NER-272 International Staple, Nail and Tool Association ESR-1539 International Staple, Nail and Tool Association ISANTA 3
Codes, Provisions, and Guidance CBC & ICC-ES Codes, Provisions, and Guidance National Design Specification for Wood Construction, 2005 Edition (NDS) Where to Find Specifics The NDS has design provisions Allowable = nominal x adjustment factors Adjustment factors account for a wide range of different end use applications 4
Basic Theory: Engineered Design Nominal Design Values defined by a table in code or NDS. Nominal Design Values based on equations in the NDS Nominal i ldesign Values Vl based on assumed end use conditions Normal Load Duration (10 year) Dry Condition of Use No Sustained exposure to elevated temperatures And others. Basic Theory: Engineered Design For nails, spikes, bolts, lag screws and wood screws Lateral load design values are calculated by yield limit equations Yield Model Withdrawal design capacity calculated from empirical (test based) equations. Split rings, shear plates, dowels, drift pins, and timber rivets etc. Lateral and withdrawal design values from empirically based tables. Connection Behavior Strength Ductility 5
Mechanical Connections Basic Type of Connections Dowel-type fasteners Bolts, Lag Screws, Wood Screws, Nails/Spikes, Drift bolts, and Drift Pins Split Ring and Shear Plate Connectors Timber Rivets Lateral and Withdrawal Loads. NDS DOWEL YIELD EQUATIONS MODE I bearingdominated yield of wood fibers MODE II pivoting of fastener with localized crushing of wood fibers NDS DOWEL YIELD EQUATIONS MODE III fastener yield in bending at one plastic hinge and bearing dominated yield of wood fibers MODE IV fastener yield in bending at two plastic hinges and bearing dominated yield of wood fibers 6
NDS DOWEL YIELD EQUATIONS 4 Modes 6 Equations Single & Double shear Reduction term Rd NDS DOWEL YIELD EQUATIONS NDS DOWEL YIELD EQUATIONS 7
NDS DOWEL YIELD EQUATIONS Fastener Values NER s are now called: ESR ES ICC Evaluation Service Reports Connecting Wood Wood Bearing Strength Sawn wood Glulam OSB Plywood Structural Composite Lumber (SCL) 8
Making Angle to Grain Adjustments Calculate wood bearing strength, F e, at any angle to grain (for fastener dia. > 0.25 ) Hankinson Formula θ Feθ F e F = F F e F e e θ 2 sin θ + F cos 2 e e θ F ell Lateral connection strength, Z, depends on: Crushing (bearing) strength of wood Size of wood pieces Fastener size and strength The Basics Engineered Plus appropriate end use adjustment factors i.e. Wet service, edge distance, end grain, etc. Z Nails Nail capacity tables in 2005 NDS 9
Fastener Interchangeability NER 272 & ESR 1539 Has conversion tables for prescriptive requirements For example, if model code requires 8d commons at 6 oc, then what fastener type and spacing is equivalent Has values for engineered designs for staples and a variety of other power driven fasteners Available from international staple, nail and tool association (ISANTA) www.isanta.org 708 482 8138 Mechanical Connections Nail installation Overdriving reduces performance Mechanical Connections Overdriven nails TT 012A APA Recommendations Prescriptive If < 20% fasteners overdriven by <1/8, then they may be ignored. If > 20% fasteners overdriven by >1/8, then add 1 additional fastener for every 2 overdriven. 10
CAUTION! If the additional nails violate the minimum spacing requirements (3 o.c. for 2 inch lumber for splitting), use staples and ignore the original nails. Mechanical Connections Overdriven nails APA Recommendations Mechanics Based If < 20% fasteners overdriven by <1/8, then they may be ignored. Otherwise, re analyze capacity based on average thickness of panel measured from the bottom of the nail head. (i.e. 5/8 panel with fasteners overdriven by 1/8 = capacity of ½ panel.) Adjust nailing schedule accordingly. The Basics - Engineered Withdrawal Connection Strength Depends On: Depth of penetration Wood density Fastener size and type Plus appropriate end use adjustment factors i.e. wet service, edge distance, end grain, etc. 11
Fastener Penetration Lag screws, wood screws, and nails Fastener Type Full Minimum reduced Per 11.1 Tip Lag Screws 8D 4D Excluded Wood Screws 10D 6D (inc. from 4D) Included Nails & Spikes 10D 6D Included D = Diameter (in) If min. < p < full then Z x p/full per table footnotes. Full Body Diameter Lag Screws Lag Screws All tabulated values All tabulated values in the 2005 NDS are based on D r 12
Lag Screws For calculations using the shank diameter, D DOWEL BEARING STRENGTHS Table 11.3.2 SAWN LUMBER DOWEL BEARING STRENGTHS TABLE 11.3.2B ENGINEERED WOOD PRODUCTS Glulam is a function of the species used. LVL and other SCL see manufacturer. 13
Nominal Design Values Tabulated Values in NDS They must be adjusted to account for actual conditions. Examples for dowel type fasteners: C D = Load duration factor (Only ASD Basic Load Combination) C M = Wet service factor C t = Temperature Factor C g = Group action factor, C = Geometry factor C eg = End grain factor C di = Diaphragm Factor C tn = Toe nail factor K F = Format conversion Factor, Appendix N.3.1 (Only LRFD) Φz =Resistance Factor (Only LRFD) λ = Time effect factor, Appendix N.3.3 (Only LRFD) CD, Load Duration Factor ASD ONLY TABLE 2.3.2 Wood capacity greater for short time loading LOAD DURATION Load Duration Factor - CD Typical Loads Permanent 0.9 Dead Load Ten years 1.0 Floor live load Two months 115 1.15 Snow load Seven days 1.25 Construction load Ten minutes 1.6 Wind/Earthquake Impact (does not apply to connections) 2.0 Vehicles These factors are applied to member capacity 14
CM, Wet Service Factor Design Values Wood seasoned to a moisture content of 19% Continuously dry conditions (most covered structures) CM apply to: Wood unseasoned or partially seasoned or Exposed to wet service use Shall not apply for nails in withdrawal 2005 NDS Provisions Wet Service Factor, C M for connection Z values Saturated 19% MC Bolts Lag screws Wood screws fabrication MC in-service MC Dry C M 1.0 0.7 0.4 Lateral Load 1.0 0.7 1.0 Withdrawl Load (lag & wood screws only) 2005 NDS Provisions Wet Service Factor, C M for connection Z values Saturated 19% MC Bolts Lag screws Wood screws CM = 0.7 if D < ¼ CM = 1.0 if: 1 fastener 2+ fastener Dry C M 0.4 Lateral Load fabrication MC in-service MC Split splice plates Table 10.3.3 footnote 3 15
Ct, Temperature Factor Ct apply to: Sustained exposure to elevated temperatures up to 150 degree Fahrenheit Mechanical Connections Larger fasteners Group action factor, C g NDS tables Equation calculation Does NOT apply to sill plates Unit loads act along the length of the member Loads are not axial Mechanical Connections Figure 10B 16
Calculated Group Action Factor, C g EQ. 10.3-1 Applicable for split ring connectors, shear plates connectors, or dowel-type fasteners with D < 1 in a row. Calculated Group Action Factor, C g 10.3.6 Calculated Group Action Factor, C g Example: Find C g for two rows of 1 diameter bolts spaced 4 apart in a woodto-wood double shear splice connection using 2x12 s for main and side members. 17
Calculated Group Action Factor, C g EQ. 10.3-1 m = 0.808 u = 1.023 R EA = min (E s A s /E m A m, E m A m /E s A s ) = 0.5 C g = 0.669 Tabulated Group Action Factor, C g A s /A m > 1.0, so use A m /A s =0.5 to enter column 1 of the table (footnote 1) Use A m for column 2 m (footnote 1) Read across to column for 10 fasteners in a row Interpolate C g = 0.665 Tabulated Group Action Factor, C g A = sum of gross x- A m = gross x-sectional member, in 2 side members, in 2 area of main s sectional areas of all Table 10.3.6C 18
Geometry Factor, C Bolts Spacing, End, & Edge Distances Parallel and perpendicular to grain Figure 11G Tables 11.5.1A through D When D < ¼ CΔ = 1.0 When D > ¼ If end distance OR spacing < required, then CΔ min. applied to all bolts Local Stress in Fastener Group 10.1.2 Stresses in Members at Connections Local stresses in connections using multiple fasteners shall be checked in accordance with principles i of engineering i mechanics. One method for determining these stresses is provided in Appendix E. Local Stress in Fastener Group Closely spaced fasteners Brittle failure Lower capacity Wood failure mechanism need to be consider in design 19
Local Stress in Fastener Group Properly spaced fasteners Increased ductility Higher capacity Spread out the fasteners! Local Stresses in Fastener Groups Appendix E NDS Expressions Local Stresses in Fastener Groups Appendix E NDS Expressions Group tear-out: 20
Geometry Factor, C Lag Screw - Spacing, End, & Edge Distances 11.1.3.7 Shall not be less than the requirements for bolts Tables 11.5.1A through D plus E. Wood Screw, Nails and Spikes - Spacing, End, & Edge Distances 11147&11156Shallbesufficienttopreventsplittingof 11.1.4.7 11.1.5.6 to splitting of the wood. Drift Bolts and Drift Pins - Spacing, End, & Edge Distances 11.1.6.3 Shall not be less than the requirements for bolts Tables 11.5.1A through D. Geometry Factor, C Split Ring and Plate Connectors - Spacing, End, & Edge Distances Placement of Split Ring and Plate Connectors per 12.3 Geometry Factors, C Table 12.3 Timber Rivet - Spacing, End, & Edge Distances Placement of Timber Rivets per 13.3 Geometry Factors, C Table 13.2.2B Tabulated Values in NDS C d = Penetration Depth Factor Split ring and Shear Plate. See Tables12.2.3 C eg = End grain factor (Not recommended) Dowel type fasteners and Lag Screws Ch. 11.5.2 C st = Metal Side Plate Factor Shear Plate Table 12.2.4 (depends on Species group) Timber Rivets Table 13.2.3 (depends on thickness of metal side plate) Is only applied when rivet capacity controls. C di = Diaphragm Factor Applies to nails or spikes used in diaphragms Lateral design values, Z x C di = 1.1 21
Toe-nail Factor, C tn Nail installation (11.5.4) Correct toe nailing Fig. 11A C tn = 0.67 for withdrawal C tn = 0..83 for lateral "Air Nail" Factor, C air C air = 0.00 Summary of Connection Design Two General Approaches: Prescriptive CBC, NER and ER Engineered NDS and NER-272 Nominal strength calculated Adjusted by for application, end-use adjustment factors 22
Nail Tension Tie Design connection ties between first and second floor. Given: 9-1/2 9 I-joist floor framing 2x6, dry Douglas Fir-Larch studs spaced at 16 o.c. 2400 lbs. tension (overturning wind) Design Example 1 Strap 9-1/2 2x6 Dbl. Studs 3 Design Example 1 Nail Tension Tie Strap = Side member 2 2x6 = Main member Fe=61850 psi Minimum Penetration for full values = 10D = 10x.148 = 1.5 Since penetration = 3.06 > 1.5 OK Note: If 6D < p < 10D then Z = Z x (p/10d) Table 11P Table 11.3.2 Table 11.3.1B Nail Tension Tie Design Example 1 Mode IIIs controls: Table 11.3.1A EQ. 11.3 5 23
Design Example 1 Nail Tension Tie ASD Z = Z x C D x C M C t Z = 0.116 x 160X 1.60 1.0 10x 10 1.0 =.186 n = 2.4 kips/.186 kips = 12.9 nails Use: 14 10d common nails per side, or 2 rows of 7 each. (Note: C D can not be used for Alternative Load Combinations) Design Example 1 Nail Tension Tie LRFD Appendix N Table N1, N2 & N3 Design Example 1 Nail Tension Tie Strap = Side member 2 2x6 = Main member Table 11P Fe=61850 psi Minimum Penetration for full values = 10D = 10x.148 = 1.5 Since penetration = 3.06 > 1.5 OK Note: If 6D < p < 10D then Z = Z x (p/10d) 24
Nail Tension Tie Strap = Side member 2 2x6 = Main member Table 11P Design Example 1 Side Member thickness, ts = 18ga Nail Diameter, D = 0.148 G=0.50 Douglas Fir Larch (Table 11.3.2A) Z = 115 lbs. Design Example 1 Nail Tension Tie 2005 NDS Table 11P notes & Table 10.3.1 Nail Tension Tie Design Example 1 25
Nail Tension Tie Design Example 1 Nail Tension Tie Design Example 1 Design Example 2 Group Fasteners Loaded Parallel to Grain Determine the group action factor for the bolted butt joint shown. 26
Design Example 2 Group Fasteners Loaded Parallel to Grain Solution: An effective area for the 3 x 6 in. member is: A m = 2.5 5.5 = 13.75 in. 2 A s = 2 (1.5 x 5.5) = 16.50 in. 2 for 2-2 x 6 s Per footnote 1 of Table 10.3.6A A s /A m > 1 use A m /A s = 13.75/16.5 = 0.833 and use A m in place of A s Group reduction: Linear interpolation: o C g = 0.87 + (0.93 0.87) ((0.833 0.5)/(1 0.5)) = 0.91 C g = 0.91 Design Example 2 Group Fasteners Loaded Parallel to Grain Design Example 3 Group Fasteners Loaded Perpendicular to Grain Determine the group action factor for the bolted connection shown. 27
Design Example 3 Group Fasteners Loaded Perpendicular to Grain Solution: An effective area for the 4 x 12 in. member is: A m = 2.5 2 x 3.5 = 17.5 in. 2 Where 2.5 x 2 = overall width of fastener group and 3.5 is the thickness of the main member. A s = 2 (2.5 x 7.25) = 36.25 in. 2 for 2-3 x 8 s Per footnote 1 of Table 10.3.6A A s /A m > 1 use A m /A s = 17.5/36.25 = 0.48 (round to 0.5 for simplicity) and use A m in place of A s Group reduction: Linear interpolation: o C g = 0.95 (20 17.5) ((0.95 0.92)/(20 12)) = 0.94 C g = 0.94 Design Example 3 Group Fasteners Loaded Perpendicular to Grain Design Example 4 Bolted Splice Joint Check Determine the size, number, and placement of bolts needed to transfer the 7500 lb. load (dead load plus snow load) through the butt joint shown. Wood is seasoned No. 1 Douglas-fir (MC < 19%), which will remain dry in service (MC < 19%). 28
Design Example 4 Bolted Splice Joint Check Size of member: Assuming a nominal 2 8 is used, 1.2 is the size factor (Table 4a) CC D = 115(S 1.15 (Snow Load dtable 232) 2.3.2) A (required) = P/F t = 7500/(675 1.15 1.2*) = 8.05 in. 2 Try a 2 8 in., A = 10.875 in. 2 for both main member and side plates Bolts: Design Example 4 Bolted Splice Joint Check Try 5/8-in. bolts Z (nominal) = 1310 lb. per bolt (Table 11F) Z (allowable) = Z C D C M Z = 1310 1.15 1.0 = 1506 lb. Number required = 7500/1506 = 4.98 Try 6-5/8 in. bolts, two rows of (3) bolts. Design Example 4 Bolted Splice Joint Check Group reduction: A m = 1.5 7.25 = 10.875 in. 2 A s = 2 10.875 = 21.75 in. 2 Per footnote 1 of Table 10.3.6A A s /A m > 1 use A m /A s = 10.875/21.75 = 0.5 and use A m in place of A s 29
Design Example 4 Bolted Splice Joint Check Group reduction: Linear interpolation: C g = 0.96 (12 10.875) ((0.96 0.92)/(12 )( 5)) = 0.95 Q = 1506 0.95 6 = 8584 lb. > 7500 lb. ok Design Example 5 Multiple-Bolt Tension Connection Determine the adjusted ASD capacity of the multiple-bolt double shear tension connection at the end of the 24F-V4 Douglas-Fir glulam member (24F-1.8E Stress Class): Given: (2) ¼ thick A36 steel side plates 5 1/8 x 12 GLB (6) 1 Φ A307 bolts GLB dry (initial & service) Seismic Tension Load Temperature normal 2 steel pl s (1/4 x6 ) 8 4 4 5 1/8 x 12 glulam T 3 6 3 6 T 1 Φ bolts typ. 1 Φ bolts typ. GIVEN: D = 1.0 in. F yb = 45 ksi t m = 5.125 in. θ m = 0 degrees G m = 0.50 F em = 5600 psi Design Example 5 Multiple-Bolt Tension Connection From table 11I Z = 5720 lbs. t s = 0.25 in F es = 1.5F u =1.5(58000) = 87,000 psi (A36 steel plate) Adjusted ASD connection capacity based on bolt yield limit equations: n = 3 bolts in each row C D = 1.6 (seismic) C M = 1.0 given C t = 1.0 given 30
Design Example 5 Multiple-Bolt Tension Connection Find Group Action Factor C g 10.3.6: EQ. 10.3-1 γ = 270,000(D 1.5 ) load/slip modulus = 270,000(1 1.5 )= 270,000 lb/in. m = 0.0.8601 C g = 0.993 u = 1.011 R EA = min (E s A s /E m A m, E m A m /E s A s ) = 0.8321 Design Example 5 Multiple-Bolt Tension Connection Find Group Action Factor C g 10.3.6: Or using table 10.3.6C A s /A m (3/61.5) = 0.05 C g = 0.993 Design Example 5 Multiple-Bolt Tension Connection Find Group Geometry Action Factor C 11.5.1: Check spacing and edge distance requirements: End distance min = 7D = 7(1 ) = 7 in. < 8 in. OK (for C = 1.0 parallel tension member table 11.5.1B) c.-to-c. spacing between bolts in a row s = 4D OK (for C =10table1151C) 1.0 11.5.1C) s = 4(4 ) = 4 in.< 4 in. OK Spacing between rows = 1.5D (table 11.5.1D) =1.5(1 ) = 1.5 in. < 3 in. OK Edge distance = 1.5D (for lm/d = 5.125/1 = 5.125 < 6 table 11.5.1A) = 1.5(1 ) = 1.5 in. < 1.5 C = 1.0 (since all NDS base dimensions are met or exceeded) 31
Design Example 5 Multiple-Bolt Tension Connection Adj P = N(Z ) = N(Z)(C D C M C t C g C ) = (6)(5720)(1.6)(1.0)(1.0)(0.993)(1.0) = 54,500 lb Design Example 5 Multiple-Bolt Tension Connection Check local stresses: Adjusted ASD capacity based on tension and shear stresses in the glulam member: Since the bolts penetrate the wide face of the 24F-V4 glulam member the shear design value for bending about the strong x-axis. multiply by a reduction factor 0.72 (footnote 4 supplement table 5A). Fv = (0.72)(265psi) = 191 psi F v = Fv(C D C M C t )= 191(1.6)(1.0)(1.0) = 305 psi F t = Ft(C D C M C t )= 1100(1.6)(1.0)(1.0) = 1760 psi Design Example 5 Multiple-Bolt Tension Connection Net section tension for ASD (NDS eq. E.2-1): An = 5.125[12-2(1.0+1/16)] = 50.6 in.2 (Note: 1/16 was added to the bolt to account for drilling oversize holes in accordance with NDS 11.1.2) Z NT = F t (A n ) = 1760(50.6) = 89100 lb > 54,500 lb OK 12 5 1/8 Net section of glulam 12 5 1/8 Portion of net area between rows of bolts Bolt Holes 32
Design Example 5 Multiple-Bolt Tension Connection Row tear-out for ASD (NDS Eqs. E.3-2 and E.3-3): s crit = s = 4.0 in Z RT-1 = Z RT-2 = nfv t s crit = 3(305)(5.125)(4.0) = 18775 lb n row Z RT = Z RT-2 = 18,775 + 18,775 =37,500 lb. < 54,000 lb. i=1 Group tear-out for ASD (NDS Eqs. E.4-1): A group-net = 5.125[3-2(1/2)(1.0+1/16)] = 9.93 in. Z GT = (Z RT-1 )/2 + (Z RT-2 )/2 + F t A group-net Z GT = 18,775.2 + 18,775/2 + 1760(9.93) = 36,300 lb < 54,500 lb The adjusted ASD capacity is 36,000 lb due to group tear-out at the connection RESOURCES Where to get more information WEBSITES American Wood Council www.awc.org APA The Engineered Wood www.apawood.org Canadian Wood Council www.cwc.ca Forest Products Laboratory www.fpl.fs.fed.us Southern Pine Council www.southernpine.com Wood Truss Council of America www.woodtruss.com WoodWorks www.woodworks.org 33
Where to Find Specifics CBC & ICC-ES NDS Where to Find Specifics Where to Find Design Examples NDS Free Download htttp://www.awc.org 34
Where to Find Design Examples NDS Free Download htttp://www.awc.org Where to Find Design Examples Timber Rivet Connections AWC & WWPA FREE DOWNLOAD Notching & Boring Guide http://www2.wwpa.org/techguidepages/literature/tabid /883/Default.aspx Timber Rivet Connections www.awc.org/pdf/timberrivetconnections.pdf Lag Screw Connections www.awc.org/pdf/da1-lagscrew.pdf Dowel Equations for Lateral Loads 2001 NDS www.awc.org/pdf/tr12.pdf Toenail Connections www.awc.org/pdf/da2-toenails.pdf Post Frame Ring Shank Nails Connections www.awc.org/pdf/da4-ringshank.pdf 35
For More Information: APA Forms Go to www.apawood.org and enter the Publications store The following publications expand on the information given in this presentation and can be downloaded for free using subject, title, or form number APA Forms (www.apawood.org) T300 Glulam connection details E830 Screw and plywood connections E825 - Bolt and plywood connections D485 Corrosion resistant fasteners TT-035 Corrosion resistant fasteners TT-036 Glued floors TT-039 Nail withdrawal TT-070 Nail pull through Next... Design software 36
WWPA Lumber Design Suite Beams and Joists Post and Studs Wood to Wood Shear Connections (nails, bolts, wood screws and lag screws) WWPA Free Downloadable http://www2.wwpa.org/techguidepages/designsoftware/tabi d/859/default.aspx AWC Free Online Calculator Single and Double Shear Withdrawal Bolts, nails, lag screws and wood screws. Wood-to-Wood Wood-to-Concrete Wood-to-Steel http://awc.org/calculators/connections/ccstyle.asp www.apacad.org 37
www.wooduniversity.org AWC Free Online Course http://www.awc.org/helpoutreach/ecourses/index.html AWC Free Online Course http://www.awc.org/helpoutreach/ecourses/std104/std104eco ursev11-2007.pdf 38
Take home messages... It s easy to create strong durable wood connections 1. Avoid the use of details which induce tension perpendicular to grain stresses in the wood 2. Allow for dimensional changes in the wood due to potential in-service moisture cycling 3. Minimize exposure of end grain 4. Avoid moisture entrapment in connections 5. Use smaller multiple fastener connections 6. Multiple resource available to assist Quiz: Is the below a code conforming connection? Questions??? WoodWorks! Michelle Kam-Biron, S.E. 805.498.4864 michelle@woodworks.org www.woodworks.org 39