Connection Philosophy. p NDS Chapter-by-chapter description Changes from previous editions Examples. Part 1: Member Design Webinar.

Size: px

Start display at page:

Download "Connection Philosophy. p NDS Chapter-by-chapter description Changes from previous editions Examples. Part 1: Member Design Webinar."

Delilah Wilkins
6 years ago
Views:

1 Outline ASD and LRFD with the 2005 NDS Part 2 Connection Design Presented by: John Buddy Showalter, P.E. Vice President, Technology Transfer Connection philosophy p NDS Chapter-by-chapter description Changes from previous editions Examples Part 1: Member Design Webinar Available at WoodWorks.orgorg Connection Philosophy Notching Tension perpendicular to grain Wood s weak link Avoid if possible Reinforce if not initiators: Notches Hanging loads Eccentricity Problem Solution

2 Hanger to Beam Hanger to Beam Lower half of beam may cause splits not recommended Top bearing option Upper half of beam extended plates move fasteners away from tension side of bending member Split Compression side of the bending member Beam to Concrete Beam to Concrete Notched Beam Bearing may cause splitting not recommended Notched Bearing Wall alternate to beam notch Split

3 Beam to Concrete Beam to Concrete Sloped Beam not fully supported may split exposes end grain not recommended Sloped Beam notched concrete wall alternate to beam notch Split Outline NDS 2005 Chapters Connection philosophy p NDS Chapter-by-chapter description Changes from previous editions Examples Today s focus { General Requirements for Building Design 2 Design Values for Structural Members 3 Design Provisions and Equations 4 Sawn Lumber 5 Structural Glued Laminated Timber 6 Round Timber Poles and Piles 7 Prefabricated Wood I-Joists 8 Structural Composite Lumber { 9 Wood Structural Panels 10 Mechanical Connections 11 Dowel-Type Fasteners 12 Split Ring and Shear Plate Connectors 13 Timber Rivets 14 Shear Walls and Diaphragms 15 Special Loading Conditions 16 Fire Design of Wood Members

4 NDS 2005 Appendices 2005 A Construction and Design Practices B Load Duration C Temperature Effects D Lateral Stability of Beams E Local Stresses in Fastener Groups Important! F Design for Creep and Critical Deflection Applications G Effective Column Length H Lateral Stability of Columns I Yield Limit Equations for Connections J Solution of Hankinson Equation K Typical Dimensions for Split Ring and Shear Plate Connectors L Typical Dimensions for Standard Hex Bolts, Hex Lag Screws, Wood Screws, Common, Box, and Sinker Nails M Manufacturing Tolerances for Rivets and Steel Side Plates for Timber Rivet Connections N Appendix for Load and Resistance Factor Design (LRFD) - Mandatory Chapters Mechanical Connections Chapter 10 mechanical connections Chapter 11 dowel-type connectors (nails, bolts, lag/wood screws) Chapter 12 split rings and shear plates Chapter 13 timber rivets Chapter 10 Mechanical Connections Multiple Fastener Connections When a connection contains two or more fasteners of the same type and similar size, each of which exhibits the same yield mode (see Appendix I), the total adjusted design value for the connection shall be the sum of the adjusted d design values for each individual id fastener. Local stresses in connections using multiple fasteners shall be checked in accordance with principles of engineering mechanics (see ). 1 Chapter 10 Mechanical Connections Stresses in Members at Connections Local stresses in connections using multiple fasteners shall be checked in accordance with principles of engineering mechanics. One method for determining i these stresses is provided in Appendix E.

5 2005 NDS Appendix E Appendix E - Local Stresses in Fastener Groups new topic introduced in 2001 NDS Local Stresses in Fastener Groups Closely spaced fasteners brittle failure lower capacity wood failure mechanisms need to be considered in design Local Stresses in Fastener Groups Properly spaced fasteners increased ductility higher capacity spread out the fasteners! Local Stresses in Fastener Groups Appendix E NDS Expressions Net tension: Z ' NT F A ' t net Row tear-out: Z Z ' RTi ' RT ' n F ts i n row i1 v Z ' RTi min

6 Local Stresses in Fastener Groups Appendix E NDS Expressions Group tear-out Fasteners on Common Splice Plate Good detailing to allow for shrinkage Z ' GT Z ' RT top 2 Z ' RT bottom 2 ' t F A groupnet Note: spacing between outer rows of fasteners paralleling the member on a single splice plate < 5 Local Stresses in Fastener Groups Example Truss Bottom Chord and Splice Design the bottom chord of a sawn lumber commercial/industrial truss to support a tensile force (T) of 20,000 lbs (D+L) Assume a dry moisture service condition, un-incised material and a load duration factor of 1.0. Local Stresses in Fastener Groups Example Truss Bottom Chord and Splice The chord includes connections with two rows of 7/8 bolts (in a 1/16 oversized hole) spaced per NDS Section 11.5 for full design values. Check the local stresses to verify your member size selection.

7 Local Stresses in Fastener Groups Solution Try 4x12 No.1 Hem Fir: T = 24,600 lbs Local Stresses in Fastener Groups Solution Single shear steel splice plate Neglect eccentricity Rows spaced at 1/3 depth within NDS limits Local Stresses in Fastener Groups Solution Using Appendix E provisions: Net Section Tension Net cross section area = (3.5)( ( )) = 32.8 in. 2 Z NT = 625(32.8) = 20,500 lbs > 20,000 lbs OK Local Stresses in Fastener Groups 7D = 7(0.875 ) = Solution Using Appendix E provisions: 3.75 > 1.5D = 1.31 Row Tear-out Capacity From the NDS Supplement 4D = 4(0.875 ) = 3.5 F v = 150psi Critical spacing s critical is lesser of end distance (7D) or fastener spacing (4D) = 4(0.875 ) = /8 + 1/ /8 + 1/16 Z RT = n row n i F v t s critical = (2)(8)(150)(3.5)(3.5) = 29,400 lbs > 20,000 lbs OK

8 Local Stresses in Fastener Groups Local Stresses in Fastener Groups Solution Using Appendix E provisions Group Tear-out tcapacity Assume: uniform row spacing edge distance = 3.75 inches Alternate: maximum spacing between rows Using Appendix E provisions: Group Tear-out tcapacity 5 max Assume: 5 max between rows edge distance = Z GT = Z RT /2 + F t A group-net = (29,400) / (3.5) [ (3.75) - ( )] = 20,850 lbs > 20,000 lbs OK The design is still acceptable. Net section tension controls. Z GT = Z RT /2 + F t A group-net = (29,400) / (3.5) [ (3.125) - ( )] = 27,688 lbs > 20,000 lbs OK The design is still acceptable. Local Stresses in Fastener Groups Alternate: minimum spacing between rows Using Appendix E provisions 4.97 Group Tear-out tcapacity Assume: Spacing between rows 1.5D D = 1.31 inches Z GT = Z RT /2 + F t A group-net = (29,400) / (3.5) [1.31 ( )] = 15,515 lbs < 20,000 lbs NG Chapter 10 Mechanical Connections Adjustment factors C g C C d C eg C st C di C tn The design is unacceptable. Spacing between rows is too tight!

9 Group Action Factor, C g Multiple fastener connections accounts for load distribution within the connection Split rings, shear plates, dowels < 1 tabulated values still in the NDS can calculate C g if outside tabulated range Group Action Factor, C g C g definitions row of fasteners 2 or more split ring or shear plate connector units aligned in the direction of load 2 or more bolts of same diameter loaded in direction of load 2 or more lag screws of same type and size loaded in direction of load Group Action Factor, C g Equation method C g n where: 2 n m (1 m ) n m 1 m 1 m 1 R 1 m EA 2 n 1 R EA R EA EsA the lessor of E A m u u 2 1 s 1 u 1 2 Em A m m s m 1 E A s EmA or E A s s m s Group Action Factor, C g Load / slip modulus, (lb/in.) D = diameter of bolt or lag screw (in.) Bolts, lag screws: wood-to-metal connections Bolts, lag screws: wood-to-wood connections (lb/in) (270,000)(D 1.5 ) (180,000)(D 1.5 ) 2-1/2 split ring & 2-5/8 shear plate 400,000 4 split ring &4 shear plate 500,000000

10 Group Action Factor, C g Equation method Example Find C g for two rows of 1 diameter bolts spaced 4 apart in a wood-to-wood double shear splice connection using 2x12 s for main and side members Group Action Factor, C g Equation method Example Wood Data E m psi A m 1.5in11.25in A m in 2 E s psi A s 21.5 in11.25 in A m 0.5 A s Fastener Data s 4in D 1in n 10 Load / Slip lbf D in lbf in Group Action Factor, C g Tabulated values A m = gross x-sectional area of main member, in 2 A s = sum of gross x-sectional areas of all side members, in 2 Group Action Factor, C g Tabulated Values Example A s /A m >10 1.0, so use A m /A s = 0.5 to enter column 1 of the table also, use A m for column 2 according to Note 1 (A m = in 2 ) read across to column for 10 fasteners in a row interpolate C g = from calculation

11 Group Action Factor, C g Not applicable here - loads acting along the length of the member are unit loads Chapter 10 Mechanical Connections Wet Service Factor, C M Bottom Plate Anchor Bolts and Washers as required Wet Service Factor, C M Wet Service Factor, C M Saturated 19% MC fabrication MC in-service MC Dowel-type connectors bolts drift pins drift bolts lag screws wood screws nails Dry C M * Lateral load (*C M =0.7 for D<1/4 ) Withdrawal load - lag & wood screws only Withdrawal load - nails & spikes Saturated 19% MC Dry C M fabrication MC in-service i MC 0.4 Lateral load (D>1/4 ) C M = 1.0 if: 1 fastener 2+ fasteners split splice plates

12 Fasteners on Common Splice Plate Good detailing to allow for shrinkage Chapter 11 Dowel-type Fasteners ASD and LRFD accommodated through Table Bolts Lag screws Wood screws Nails & spikes Fastener Values Fastener Bending Yield Included in U.S. design literature Fastener Type Bolts Lag Screws Wood Screws Nails & Spikes Split Ring Connectors Shear Plate Connectors DiftB Drift Bolts &DiftPi Drift Pins Metal Plate Connectors Hangers & Framing Anchors Staples Reference NDS or NER NDS or NER NDS or NER NDS or NER NDS NDS NDS NER NER NER National Evaluation Reports (NER) are developed for proprietary products

13 Fastener Bending Yield Test Dowel Bearing Strength Center-Point Bending Test Load Yield Limit Equations Yield Limit Equations 6 Yield Modes Single & double shear Wood-to-wood Wood-to-Steel Wood-to-Concrete I II III IV

14 Yield Limit Equations Nail Types and Designations Nails and nomenclature box nail ring shank nail common nail sinker pneumatic Nail Types and Designations Nail types described in Appendix L Nail Types and Designations Nail capacity tables in 2005 NDS

15 Penetration Depth Factor, C d Changed in 2001 NDS Penetration ti is built-in i to Yield Limit it Equations: m main member dowel bearing length s side member dowel bearing length Tables for lag screws, wood screws, and nails: Based on 8D, 10D, and 10D penetrations, respectively Reduced penetration? Use Table Footnotes FAQ available at awc.org Fastener Penetration Fastener Type Lag Screws Wood Screws Nails & Spikes Minimum 4D 6D 6D NDS The length of dowel bearing shall not include the length of the tapered tip of a fastener for fastener penetration lengths less than 10D. Penetration - Nails P = 6D (NDS ) 6D Penetration Wood Screws P = 6D (NDS ) - includes tip 6D

Penetration Lag Screws P = 4D (NDS 11.1.3.

16 Penetration Lag Screws P = 4D (NDS ) - does not include tip 4D Dowel Diameter Lag Screws Reduced Body Diameter D r used to calculate capacity regardless of shear plane location (NDS ) ne shear plan D r Lateral Capacity Full Body Diameter D r used to calculate capacity if threads are in or near the shear plane (NDS ) use D r Lateral Capacity Lag Screws Why no threads near the shear plane? Because the induced maximum moment can occur in the threads if the shear plane is not located sufficiently i into the shank away from the threads shear plane

17 Lateral Capacity Lag Screws Info on where to locate the shear plane Lateral Capacity Wood Screws Rolled Thread D r used to calc capacity if shear plane is anywhere (NDS ) shear plane Lateral Capacity Wood Screws Cut Thread D r used to calc capacity if shear plane is in or near the threads (NDS ) use D use D r ~ 3D to 4D r sh hear plane Toe nailing Withdrawal C tn = 0.67 Lateral C tn =

18 Chapter 11 Connections Capacity definitions Spacing, End, & Edge Distances Z Z m Z s Z Nail Capacity Calculations Nailed Tension Tie Example: Shear Wall Chord Ties with Nails ASD & LRFD A653 How many nails for this connection? Design connection ties between first and second floor shear wall chords. Walls are 2x6, dry Douglas Fir-Larch studs spaced at 16 oc. The specified wind overturning force is 2.4 kips.

19 Nailed Tension Tie LRFD & ASD Try: ASTM A653 Grade metal strap16 gage x 2.5 wide 2 rows staggered 10d common nails Nailed Tension Tie LRFD & ASD 2005 NDS Table 11P Z = 116 lbs Nailed Tension Tie LRFD & ASD 2005 NDS Table 11P, Table , and Appendix N ADJUSTMENT FACTORS LRFD ASD Time dependent = 1.0 Table N3 C D = 1.6 Wet service C M Temperature C t Group Action C g Geometry C End grain C eg Diaphragm C di Toe nail C tn Penetration 3 > 10D Nailed Tension Tie LRFD & ASD DEMAND Wind Overturning LRFD ASD w = ot W ot w = W ot = (1.6)(2,400) = 2,400 lbs = 3,840 lbs Format conversion K F 216/ 2.16 z = Table N1 Resistance z 0.65 Table N2

20 Nailed Tension Tie LRFD & ASD Nailed Tension Tie LRFD & ASD CAPACITY Safety Limit State LRFD ASD Z = Z z K F (all C factors) Z = Z C D (all C factors) = (116)(0.65)(1.0)(3.32)(1.0) = (116)(1.6)(1.0) = 250 lbs = 186 lbs Nails Needed n = w / Z n = w / Z = (3,840) / (250) = (2,400) / (186) = nails = nails CAPACITY Safety Limit State Demand / Capacity Ratio LRFD ASD w Z W Z 3,840 lbs 4,000 lbs 2,400 lbs 2,976 lbs demandd capacity demandd capacity Nails 13 Nails Nailed Tension Tie LRFD & ASD Why the ASD / LRFD discrepancy? 2005 NDS format conversion does not benefit LRFD in the Wind Only case Real benefits are realized with combined multiple transient loads (ie. wind + snow + live) examine load combination cases and LRFD load factors in addition to relative magnitudes of the loads themselves Connection Calculator AWC.org

21 Chapter 12 Split Rings and Shear Plates Capacity tables - unchanged Chapter 12 Split Rings and Shear Plates Availability Chapter 13 Timber Rivets Capacity tables and details - unchanged Chapter 13 Timber Rivets Many applications

Chapter 13 Timber Rivets Rivets Steel AISI 1035 Rockwell Hardness C32-39 F u = 145 ksi Hot-dipped galvanized Plates

yielding P r parallel to grain Q r perpendicular to grain Wood failure P w parallel to grain Q w perpendicular to

org More comprehensive CEU s available Phones General: (202) 463 2766 Helpdesk: (202) 463 4713 Publications: (800)

22 Chapter 13 Timber Rivets Rivets Steel AISI 1035 Rockwell Hardness C32-39 F u = 145 ksi Hot-dipped galvanized Plates Steel ASTM A36 Hot-dipped galvanized if in wet service Timber Rivets - Design Four strength limit states: Rivet yielding P r parallel to grain Q r perpendicular to grain Wood failure P w parallel to grain Q w perpendicular to grain Plate yielding Enhanced ductility Lowest value governs design QUESTIONS? DES110: Connection Design More comprehensive CEU s available Phones General: (202) Helpdesk: (202) Publications: (800) Publications: publications@awc.org Education: education@awc.org Technical: info@awc.org org Website

The Wood Products Council is a Registered Provider with. . Credit(s) earned on completion of this program will be

Connection Solutions for Wood-frame Structures Presented by: John Buddy Showalter, P.E. Vice President, Technology Transfer The Wood Products Council is a Registered Provider with. Credit(s) earned on