woodworks presentation...flat truss dbl. howe truss (4/12 pitch) dbl. howe truss (6/12 pitch)...
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Woodworks Presentation
Presented by Norman Scheel, P.E., S.E., SECB, F.SEAOC, F.ASCE, LEED AP BD+C, LEED AP HOMES
Disclaimer: This presentation was developed by a third party and is not funded by
WoodWorks or the Softwood Lumber Board.
Woodworks Presentation
Presented by Norman Scheel, P.E., S.E., SECB, F.SEAOC, F.ASCE, LEED AP BD+C, LEED AP HOMES
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“The Wood Products Council” is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.
Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request.
This course is registered with 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.
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Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
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Course Description
This course is intended for engineers and architects who specify metal plated wood trusses for use in commercial and multi-family building projects. Metal plate connected wood trusses (MPCWT) have long been used as a cost effective method to achieve long spans in roof and floor applications. This presentation will cover shared responsibilities between the design professional of record and the truss designer: the proper specification of design loads, including examples of trusses used as diaphragm chords, and shop drawing reviews. Bracing, large cantilevers, over-framing, sectional trusses, and shear transfer scenarios will also be discussed.
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Learning Objectives
1. Review the standard-of-practice for shared responsibility of truss design between the design professional of record, responsible for the building as a whole, and the truss manufacturer and designer providing structural components used in the building.2. Outline critical and useful information to include in building construction documents to improve truss manufacturers ability to deliver high performing components.3. Overview how to read truss shop drawings to verify conformance with the intended specifications.4. Examine different configurations and truss details to demonstrate how metal plate connected wood trusses can meet the needs of a variety of building projects.
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• Design Responsibilities
• Design Loads• Vertical Loads
• Lateral Loads (wind & seismic)• Shear transfer (collectors)
• Chords
• Bracing• Webs
• Chords (T.C. & B.C.)• Overframing• Sectional Trusses• Gable End Bracing
• Shop Drawings• Layouts• Truss Drawings
• Special Uses
• Truss Myths
Course Outline
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Design
Responsibilities
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Design LoadsVertical
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Simple Case
Easy enough
Statically Determinate
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WARNING: Do Not Use Pinned Reactions
FORCE
MOVEMENT
0.85#
2508#
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Add interior bearings, not so simple.
If designed, supports will be at a joint.
Simple Case
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Add interior bearings, not so simple.If not designed, supports may be in the middle of panels or near a joint.
Simple Case
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Preliminary Design
Max. Span = 60’
Min. Depth (in.) = Span (ft.) – 10
Flat Trusses
Examples:
40’ span, min. 30” deep average
50’ span, min. 40” deep average
60’ span, min. 50” deep average
Sloping Flats have heel height over 21”
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Preliminary Design
(Cont.)
Gable Trusses
Min. Slopes:
40’ for 3/12
50’ for 4/12
60’ for 5/12 (cap)
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Estimating Deflections
& Interior Reactions
Treat as Bearing –
Use Moment of Inertia (I) for effective depth for deflection
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Calculation for Moment of Inertia (I)
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Calculation for Moment of Inertia (I) cont.
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Flat Truss
Dbl. Howe (4/12 pitch) Truss
Dbl. Howe (6/12 pitch) Truss
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Deflection vs. Load Graph
0 1.580 0.800 0.410 4166 8333
500 1.180 0.680 0.350
1000 0.780 0.560 0.290
1500 0.390 0.440 0.230
2000 0.070 0.320 0.200
1250
K=STIFFNESS (LBS./IN.)
DBL. HOWE
TRUSS (4/12)
DBL. HOWE
TRUSS (6/12) FLAT TRUSS
DL+LL DEFLECTION (IN.)
LOAD (LBS.)DBL. HOWE
TRUSS (6/12) FLAT TRUSS
DBL. HOWE
TRUSS (4/12)
DEFLECTION VS. LOAD
1.580
1.180
0.780
0.390
0.070
0.800
0.680
0.560
0.440
0.320
0.410
0.350
0.290
0.2300.200
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
0 500 1000 1500 2000
CONCENTRATED LOAD (LBS.)
DE
FL
EC
TIO
N (
LL
+ D
L)
Flat Truss Dbl. Howe Truss (4/12 Pitch) Dbl. Howe Truss (6/12 Pitch)
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For Gable Truss, use same as Flat Truss and use 0.8 overall effective depth
Example:
40’ span, 4/12 pitch
0.8 x depth = 0.8 x 4 x 20 = 64”
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Results are within 10% for Deflections and Reactions. This is OK for Preliminary Design.
Reasons:
• Deflections are small
• Beam Reactions are approximate if Truss is continuous
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CODE
REQUIREMENTS
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Old vs New Code Loading
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1.22.848
-0.48.4815
0.587.5814
1.46.6813
2.06.0812
2.05.0711
1.84.2610
1.53.559
0.82.237
0.41.626
-0.21.215
-0.80.804
DifferenceDead Load Slope
Increase (14PSF)
Live Load Decrease
Slope/12
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2006 IBC
Minimum Roof Live Loads
(Tributary Area Reduction)
2012 IBC
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Design LoadsLateral
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Simple Collector Truss
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Complicated Collector Truss
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Shear Transfer to Center Collector Truss
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BRAIN BREAK
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Truss History
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A TRIBUTE TO CEASER
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Now Back to
Serious Stuff
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Pre-Engineered Gang Nail Trusses
Shear Transfer Perpendicular to Trusses
Blocking Details
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Pre-Engineered Gang Nail TrussesFraming Details
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Bracing
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Shop Drawings
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Truss Myths
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Truss Myths
• The truss company handles everything from the top plate up.
• Beams below trusses provide the infinitely rigid support as modeled in the computer analysis.
• Axial forces in truss members are at the member centerlines.
• The pin/roller modeled in the computer is accurate.
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Truss Myths
• Truss joints are all “pin” connected.
• The engineer who sealed the truss drawings has seen the plans.
• The design professional will incorporate the truss designs into the building design.
• If interior walls touch the bottom chord it will overstress the members.
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Truss Myths
• Collector trusses (shear transfer trusses) at the gable end need to be structural (with web instead of verticals only) if the truss has heels at each end.
• Scissor trusses impose lateral loads on the exterior walls at the heels.
• A level return will support the end of a long overhang.
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BRAIN BREAK
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Special Uses
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Six-Sided Roof
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Horizontal Thrust & Tension Calcs for Octagon
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Horizontal Thrust & Tension Calcs for Octagon
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Arch Walls
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Section Set
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Vaulted Trusses
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Girder-to-Girder
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Compression Ring
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Applications
� Agricultural structures
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Truss Lift
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Truss Test
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Questions?
This concludes The American Institute of Architects Continuing Education Systems Course
Norman Scheel
NSSE
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REFERENCESTRUSS DETAILS
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