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ModernPost-FrameStructuralDesignPractice:AnIntroduction
AnIntroductiontoPost-FrameDiaphragmDesignandIsolatedPost/PierFoundations
HarveyB.Manbeck,PE,PhD
Disclaimer:ThispresentationwasdevelopedbyathirdpartyandisnotfundedbyWoodWorks ortheSoftwoodLumberBoard.
Copyright © 2014 National Frame Building Association
“TheWoodProductsCouncil” isaRegisteredProviderwithTheAmericanInstituteofArchitectsContinuingEducationSystems(AIA/CES),Provider#G516.
Credit(s)earnedoncompletionofthiscoursewillbereportedtoAIACESforAIAmembers.CertificatesofCompletionforbothAIAmembersandnon-AIAmembersareavailableuponrequest.
ThiscourseisregisteredwithAIACES forcontinuingprofessionaleducation.Assuch,itdoesnotincludecontentthatmaybedeemedorconstruedtobeanapprovalorendorsementbytheAIAofanymaterialofconstructionoranymethodormannerofhandling,using,distributing,ordealinginanymaterialorproduct.__________________________________
Questionsrelatedtospecificmaterials,methods,andserviceswillbeaddressedattheconclusionofthispresentation.
CourseDescription
Thissessionisintendedforarchitectsanddesignerswhowanttounderstandbasicstructuraldesignmethodsforanengineeredpost-framebuildingsystem.Withoutdelvingintoengineeringdetailsorcalculationprocedures,itcoverscomponentsofthepost-framebuildingsystem,aswellaskeystructuraldesignconcepts.Twoapproachesarehighlightedinparticular:oneforpost-framesystemswithoutdiaphragmaction,theotherforpost-framesystemswithdiaphragmaction.Proceduresfordesigningisolatedpierfoundationsforpost-framebuildingsarealsodiscussed,asaretechnicalresourcesavailabletodesignprofessionals.
LearningObjectives
1.Identifytheprimarystructuralcomponentsofpost-frame(PF)buildingsystems
2.LearnbasicproceduresforconductingstructuralanalysisofPFsystemswithandwithoutdiaphragmaction
3.Definethedesignapproachforisolatedpost/pierPFfoundations
4. Recognizepost-framedesignresourcesavailabletoarchitectsandengineers
MODERN POST-FRAME STRUCTURAL DESIGN
PRACTICE - AN INTRODUCTION
Copyright © 2014 National Frame Building Association
• Identify the primary structural components of post-frame (PF) building systems
• Learn how to conduct structural design of PF systems without diaphragm action
• Learn how to conduct structural design of PF systems with diaphragm action
• Learn how to design isolated post/pier PF foundations
• Identify post-frame design resources available to architects and engineers
LEARNING OBJECTIVES
• Wood industry’s counterpart to low profile (1 to 2-1/2 story) steel buildings
• Developed in late 1930’s for agricultural sector• Known as “pole building” in the past• PF has evolved to highly engineered wood
building system• PF has expanded to many commercial,
residential & institutional applications
POST-FRAME (PF) BUILDING SYSTEMS
POST-FRAME PICTORIAL
Shallow Post or Pier Foundation
Laminated or Solid-Sawn Wood Columns
Roof Framing: Trusses or Rafters
Wall Girts & Roof Purlins
Typical Sheathing:26 to 29 ga ribbed steel OR
Wood structural panels
PF BUILDING SYSTEM FOUNDATION OPTIONS
10
Isolated Pier Foundation
Continuous RC Foundation Wall
Thickened Edge ofConcrete Slab
• 2-dimensional frame design method – Without diaphragm action
• 3-dimensional diaphragm design method – With diaphragm action
PRIMARY PF DESIGN METHODS
PF SYSTEMS WITHOUT DIAPHRAGM ACTION
Unsheathed walls
Unsheathed walls
PF SYSTEM WITH DIAPHRAGM ACTION
Sheathed Version of This Building
LATERAL LOADS: WITHOUT DIAPHRAGM ACTION
Wind directionWind direction
Typical sway (Δ) of interiorpost frame at design lateral load = 5 to 8 inches
LATERAL LOADS: WITH DIAPHRAGM ACTION
Wind direction
∆1
Typical sway (∆1) of centermostpost-frame at design lateral load =
0.5 to 1.0 inch
ADVANTAGES OF DIAPHRAGM DESIGN
• Smaller sidewall posts• Shallower post or pier embedment depths• Benefits:
– More economical design– Greater structural integrity – More durable post-frame structures
WHEN TO USE 2-D FRAME DESIGN METHOD
• Side or endwalls are open, or not sheathed• PF Building with L:W ≥ ≈ 2.5 to 3:1• Connections and other structural detailing don’t
develop a continuous load path for transfer of in-plane shear forces– Through the roof sheathing– Between the diaphragm and the top of the endwall– Through the endwall or shearwall– Between bottom of the endwall and the endwall
foundation
EMBEDDED POST/PIER FOUNDATIONS
• Common post-soil fixity models for embedded post or pier foundations: – Constrained post or pier– Non-constrained post or pier
POST/PIER EMBEDMENT DESIGNHorizontal
movement permitted Horizontal movement prevented by
floor or mechanical connection
Non-constrained Constrained
dR
EMBEDDED POST/PIER FOUNDATIONS
• Design Methods
-Simplified Method
-Universal Method
POST FOUNDATIONS-Simplified Model: NON-CONSTRAINED CASE
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
VG
MG
Structural Analog for Determining PostGround Surface Shear(VG) and Moment (MG)
• Fixed end at depthw below grade
• w = face width of postbearing againstsoil
POST FOUNDATIONS-Simplified Model:CONSTRAINED CASE
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
Structural Analog for Determining PostGround Surface Shear (VG) and Moment (MG)
VG
MG
•Vertical roller at top edge of slab
• Fixed end at ground line
• Soil is homogeneous throughout the entire embedment depth.• Soil stiffness is either constant (cohesive soils) for all depths
below grade or linearly increases (non-cohesive soils) with depth below grade.
• Width of the below-grade portion of the foundation is constant. This generally means that there are no attached collars or footings that are effective in resisting lateral soil forces.
• Post/pier foundation approximates infinite stiffness (EIpier)
PRIMARY ASSUMPTIONS FOR USING THE SIMPLIFIED MODEL FOR GROUNDLINE SHEAR
(VG) & MOMENT (MG) CALC.
Infinite stiffness criteria:• d < 2{E I /(2AE)} 0.20 (cohesionless soils)
• ORd < 2{E I /(2ES)} 0.25 (cohesive soils)
where * d is depth of embedment;* EI is flexural rigidity of the post/pier * ES is Young’s modulus of the soil * AE is the linear increase in Young’s
modulus of soil with depth below grade
STRUCTURAL ANALOGS FOR VG & MG CALCS: SIMPLIFIED METHOD
Δ
Roof Gravity Loads
Ceiling Gravity Loads
s x q wr s x qlr
s x
q ww
s x
q lw
Δ
R
(a)
(b)
Δ
Roof Gravity Loads
Ceiling Gravity Loads
s x q wr s x qlr
s x
q ww
s x
q lw
Δ
R
(a)
(b)
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
dw
Non-constrained post/pier
w
d
Constrained post/pier
Load Direction
Slab
Rotation Point
Constrained Post/Pier
Non-Constrained Post/Pier
• Used to determine ground surface shear, VG, and moment , MG when required conditions for simplified method not met
• Considers the load-deformation behavior of the soil surrounding the embedded post
• Soil – foundation load deformation behavior evaluated using soil spring models
UNIVERSAL MODEL – POST FOUNDATIONS
UNIVERSAL MODEL: SOIL LOAD -DISPLACEMENT BEHAVIOR
Soil Load(psi)
Soil Deformation(in.)
Ultimate Soil Strength, pu,z
(psi)
Slope = soil stiffness, Es(lb/in)
Elastic-Perfectly Plastic Soil
POST FOUNDATIONS-Universal Model:NON-CONSTRAINED CASE
z
t1
t2
t3
t4
t5
Fult,1
Fult,3a
Fult,2
MU
VU1
2
3
4
5
V
1
2
3a
4
5
3b
dRU
Point of foundation
rotation
dRU
Fult,5
Fult,4
Fult,3b
M
z
t1
t2t2
t3t3
t4t4
t5t5
Fult,1
Fult,3a
Fult,2
MU
VU1
2
3
4
5
V
1
2
3a
4
5
3b
dRU
Point of foundation
rotation
dRU
Fult,5
Fult,4
Fult,3b
M
Linearly Elastic, Perfectly Plastic Springs
(Properties based on Site Soil Properties)
POST FOUNDATIONS-Universal Model:CONSTRAINED CASE
z
Post contacts ground surface
restraint
t1
t2
t3
t4
t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
z
Post contacts ground surface
restraint
t1
t2t2
t3t3
t4t4
t5t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
Linearly Elastic, Perfectly Plastic Springs
(Properties based on Site Soil Properties)
GROUNDLINE VG & MG CALCS: UNIVERSAL MODEL
Δ
Roof Gravity Loads
Ceiling Gravity Loads
s x q wr s x qlr
s x
q ww
s x
q lw
Δ
R
(a)
(b)
Δ
Roof Gravity Loads
Ceiling Gravity Loads
s x q wr s x qlr
s x
q ww
s x
q lw
Δ
R
(a)
(b)
z
Post contacts ground surface
restraint
t1
t2
t3
t4
t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
z
Post contacts ground surface
restraint
t1
t2t2
t3t3
t4t4
t5t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
z
t1
t2
t3
t4
t5
Fult,1
Fult,3a
Fult,2
MU
VU1
2
3
4
5
V
1
2
3a
4
5
3b
dRU
Point of foundation
rotation
dRU
Fult,5
Fult,4
Fult,3b
M
z
t1
t2t2
t3t3
t4t4
t5t5
Fult,1
Fult,3a
Fult,2
MU
VU1
2
3
4
5
V
1
2
3a
4
5
3b
dRU
Point of foundation
rotation
dRU
Fult,5
Fult,4
Fult,3b
M
Constrained Post/Pier Non-Constrained
Post/Pier
DESIGN METHODS: 2-D POST FRAME
s x qwrs x qlr
Wind Direction
W
H1
H2
Post-to-truss connections usually modeled as a pin
The post-to-ground reaction is modeled consistent with post embedment details. (Note that one post foundation may be constrained and the other non-constrained)
Each frame is designed to carry its full tributary lateral and gravity loads
s x qww s x qlw
s x w
ASCE-7 Governing Load Combinations (ASD)• Dead + ¾ snow + ¾ wind (or seismic)
or
0.6 dead + wind (or seismic) – Usually controls post design
• Dead + snow (balanced & unbalanced)– Usually controls roof-framing design
2-D DESIGN ANALYSIS
SIMPLIFIED 2-D PF DESIGN METHOD
Wind direction
V = roof truss vertical reaction
P = ½ (Resultant lateralroof load from truss)
Model post-to-soil interaction appropriately
Then design the postfor the design lateral load combinations
Specify dead & snow loads for the metal-plate connected truss manufacturer
½ (qww+qlw) x sor
Max(qww, qlw) x s
• Incorporates in-plane shear strength and stiffness of the roof and wall sheathing to transfer design lateral loads to the foundation
• Significantly decreases wall-post size and post-foundation embedment depth
• Will use an on-line structural analysis program, DAFI
DIAPHRAGM DESIGN METHOD
• Total number of bays in the building• Design eave loads at each post frame, Pi
• Bare frame stiffness of each post frame, ki
• In-plane shear stiffness of each roof diaphragm panel, chi
DAFI INPUTS
IN-PLANE SHEAR STRENGTH & STIFFNESS
Building width
Endwall
Test panel width, a
Test panel length, b
θ
Roof sheet end joint
Building length = LB
Roof spanTest panel(basic element)
bsp = Slope length (roof diaphragm length)
ap
DIAPHRAGM TEST PANEL Sheathing/cladding
Rafter or truss top chord (strut)
Purlin(chord)
CANTILEVER TEST CONFIGURATION
Direction of corrugations
CladdingPurlin
Truss top chord
P = applied force
b = Test diaphragm length
a = Te
st
diap
hrag
m
widt
h
∆s
DIAPHRAGM TEST RESULTS, IN-PLANE STRENGTH & STIFFNESS
∆P
P
c1 ∆∆1
Diaphragm Test Panel Schematic
C = design in-plane shear stiffness (slope)
UltimateStrength = Pult
Design shear strength = 0.4 Pult
Design unit shear strength = (1/b)0.4 Pult
DIAPHRAGM TEST PANEL
Building width
Endwall
Test panel width, a
Test panel length, b
θ
Roof sheet end joint
Roof spanTest panel(basic element)
bsp = Slope length (roof diaphragm length)
ap
Test panel shear props from sheathing supplier
or from PFBDM
Roof diaphragm shear props deduced from test
panel props
• Shear stiffness of a roof diaphragm panel– test panel stiffness, c– Test panel width, a– Test panel length, b– roof panel width, ap
– roof panel roof slope length bsp
– roof slope Θ
ch = [c (a/b)] (bsp/ap)cos2Θ
DIAPHRAGM DESIGN METHOD –ROOF PANEL STIFFNESS
• In-plane shear strength is a linear function of diaphragm length, bsp
V = [unit shear strength](roof diaphragm length)V = [0.4(Pult/b)](bsp)
DIAPHRAGM DESIGN METHOD-ROOF PANEL STRENGTH
DIAPHRAGM DESIGN METHOD-BARE FRAME STIFFNESS, K
P1
Model soil to post interaction using appropriate structural analog for
constrained or non-constrained pier
Pinned Connection
DIAPHRAGM DESIGN METHODPF diaphragm design
procedures based on:1. compatibility of post-
frame and roof panel eave deformations and
2. Equilibrium of horizontal forces at each eave
P = Design LateralEave Load
• Equilibrium of forces at each PF eave Pi = Pfi + Pri– Pi = design eave load in ith PF– Pfi = portion of the design eave load carried by the ith PF– Pri = portion of the design eave load carried by the roof diaphragm panel
at the ith PF
DIAPHRAGM DESIGN METHOD
• DAFI program calculates– Eave displacement of each post frame– Portion of the design eave load carried by each
post frame– Shear forces carried by each roof diaphragm panel
in the building system– Available at no cost at
www.postframeadvantage.com
DAFI OUTPUTS
DIAPHRAGM DESIGN METHOD
1(ch1) 3(ch3)2(ch2)
Panel/PF structural analog of a 3-bay building
DIAPHRAGM DESIGN – STRUCTURAL ANALOG
1 42 3PF 1
(k1) (k2) (k3) (k4)
Diaphragm Panel
P1 P2 P3 P4
DAFI: UNDEFORMED POSITION
21 3 4
DatumDatum
Node
DAFI: DEFORMED EQUILIBRIUM POSITION
Datum Datum
1 2 3 4
DAFI COMPUTER PROGRAM
Pf4
Pf3
Pf2
Pf1
DAFI COMPUTER PROGRAM
V3
V2
V1
• Can be used for post-frame building systems where:– Stiffness, ki, of the interior post frame elements are
not the same– Stiffness, chi, of the diaphragm panel elements are
not the same– Stiffness, ki of the two endwall post-frames are not
the same• Available at no cost to designers at
www.PostFrameAdvantage.com
DAFI: HIGHLY FLEXIBLE
DAFI: MINI DEMONSTRATION
• 48-ft-wide by 96-ft-long post frame• Post frames 8-ft o.c. • Number of bays —12• Post-frame stiffness (k) — 300 lbs/in.• Endwall stiffness (ke) —10,000 lbs/in.• Roof diaphragm stiffness (C) —12,000 lbs/in.• Horizontal eave load at interior post frame —
800 lbs
DAFI: MINI DEMONSTRATION
Access DAFI by:
• Going to www.postframeadvantage.com
• Clicking onto “DAFI” icon
• Running “DAFI” when prompted
NOTE: Recommend you use Explorer or Firefox browser
DAFI: MINI DEMONSTRATION
DAFI: MINI DEMONSTRATION
DAFI: MINI DEMONSTRATION
DAFI: MINI DEMONSTRATION
• Post-embedment details must resist– Downward acting gravity loads – Shear forces and moments from lateral loadings– Uplift post loads
– ANSI/ASAE EP486.2, Shallow post and pier foundation design
POST/PIER EMBEDMENT DESIGN
Two Design Approaches
• Simplified Method
• Universal Method
POST/PIER LATERAL RESISTANCE (VU & MU) & EMBEDMENT DEPTH
CALCS.
• Homogeneous soil throughout the entire embedment depth
• Constant (cohesive) or linearly increasing (non-cohesive) soil stiffness for all depths below grade
• Width of the below-grade portion of the foundation is constant
NOTE: Infinite rigidity of post/pier foundation not required for simplified method Vu & Mu calcs
SHALLOW POST & PIER FOUNDATION DESIGN
Simplified Method Requirements for Vu & Mu Calcs
POST/PIEREMBEDMENTDESIGN:LATERALLOADS-SIMPLIFIED METHOD
MGVG
P
d
y
z
Ground surface
P
Post or pier with width b
R
Soil with a fixed modulus of horizontal subgrade reaction kC
Restraint
Soil forces
3d bKP γ
MGVG
P
d
y
z
Ground surface
P
Post or pier with width b
R
Soil with a fixed modulus of horizontal subgrade reaction kC
Restraint
Soil forces
3d bKP γ
MUVU
PU
d
y
z
Ground surface
PU
Post or pier with width b and depthd < 4b
R
Cohesive soil with an undrained shear strength SU3 b SU +
1.5 d SU
Restraint
3 b SUMUVU
PU
d
y
zz
Ground surface
PU
Post or pier with width b and depthd < 4b
R
Cohesive soil with an undrained shear strength SU3 b SU +
1.5 d SU
Restraint
3 b SUMUVU
PU
d
y
z
Ground surface
PU
Post or pier with width b
R
Cohesive soil with an undrained shear strength SU
4 b
9 b SU
Restraint
3 b SUMUVU
PU
d
y
zz
Ground surface
PU
Post or pier with width b
R
Cohesive soil with an undrained shear strength SU
4 b
9 b SU
Restraint
3 b SU
Case1Cohesionless Soil
ConstrainedatGroundline
Case2CohesiveSoil
(a)d≤4b (b)d>4b
Mu
Vu
2d/3
R
POST/PIEREMBEDMENTDESIGN:LATERALLOADS-SIMPLIFIEDMETHODConstrainedatGroundSurface – DesignCriteria
CASE1: (Cohesionless Soil)
Mu =d3bKpγ ≥DesignUltimateMomentCapacity(MG*fL)
Mu =ultimategroundlinemomentcapacityd=embedmentdepthb=foundationwidthbearingagainstsoilγ =soildensityKp =passivepressurecoefficient(1+sinϕ)/(1 – sinϕ)
MG =CalculatedgroundsurfacepostmomentfL =ASDfactorofsafety
POST/PIEREMBEDMENTDESIGN:LATERALLOADS-SIMPLIFIEDMETHODConstrainedatGroundSurface – DesignEquation
CASE2: (CohesiveSoil)
(a) d≤4b
Mu =d3bSu[3/2+d/(2b)]≥MG(fL)
(b) d>4b
Mu =bSu(4.5d2 – 16b2)≥MG(fL)
whereSu =Soilundrained shearstrength(soilcohesion)
POST/PIEREMBEDMENTDESIGN:LATERALLOADS-SIMPLIFIEDMETHOD
MUVU
PU
d
Ground surface
PU
Post or pier with width b
y
z
3d bKP γCohesionless soil with density ρ and friction angle φ
dRU
3dRU bKP γ
Point of rotation
MUVU
PU
d
Ground surface
PU
Post or pier with width b
y
z
y
z
3d bKP γCohesionless soil with density ρ and friction angle φ
dRU
3dRU bKP γ
Point of rotation
d
dRU
y
z
Ground surface
PU
9 b SU
3 b SU +1.5 dRU SU
PU
MU
VU
3 b SU
Point of rotation
Post/pier with width b and dRU < 4b
Cohesive soil with undrained shear strength SU
d
dRU
y
z
Ground surface
PU
9 b SU
3 b SU +1.5 dRU SU
PU
MU
VU
3 b SU
Point of rotation
Post/pier with width b and dRU < 4b
Cohesive soil with undrained shear strength SU
d
dRU
y
z
Ground surface
PU
4 b
9 b SU
9 b SU
PU
MU
VU
3 b SU
Point of rotation
Post/pier with width b and dRU > 4b
Cohesive soil with undrained shear strength SU
d
dRU
y
z
Ground surface
PU
4 b
9 b SU
9 b SU
PU
MU
VU
3 b SU
Point of rotation
Post/pier with width b and dRU > 4b
Cohesive soil with undrained shear strength SU
Point of rotation
Post/pier with width b and dRU > 4b
Cohesive soil with undrained shear strength SU
Non-ConstrainedatGroundSurface
Case1Cohesionless Soil
Case2CohesiveSoil
(a)dRu ≤4band (b)dRu >4bandd≤4b d>4b
See ANSI/ASAE EP486.2 or PFBDMfor Design Equations
Constrained at ground surface – Spring Model
POST/PIER EMBEDMENT LATERAL LOADS- UNIVERSAL METHOD
z
Post contacts ground surface
restraint
t1
t2
t3
t4
t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
z
Post contacts ground surface
restraint
t1
t2t2
t3t3
t4t4
t5t5
1 Fult,1
Fult,5
Fult,3
Fult,4
Fult,2
MU
VU
2
3
4
5
Foundation moment andshear capacity from basicmechanics
POST/PIER EMBEDMENT LATERAL LOADS- UNIVERSAL METHOD
Non-constrained at ground surface – Design Criteria
Foundation moment andshear capacity from basicmechanics
Design Articles in Frame Building News
• Bohnhoff, David. 2014. Modeling Soil Behavior with Simple Springs, Part 1: Spring Placement and Properties. Pages 49 to 54. April.
• Bohnhoff, David. 2014. Modeling Soil Behavior with Simple Springs, Part 2: Determining the Ultimate Lateral Capacity of a Post/Pier Foundation. Pages 50 to 55. June.
POST/PIER EMBEDMENT LATERAL LOADS- UNIVERSAL METHOD
TYPICAL POST AND PIER UPLIFT ANCHORS
Foundation depth, dF
Preservative-treatedwood post
Uplift anchor (preservative-treated wood
blocking)
Unattached footing
Post embedment
depth, d
Ground surface
Foundation depth, dF
Preservative-treatedwood post
Uplift anchor (preservative-treated wood
blocking)
Unattached footing
Post embedment
depth, d
Ground surface
Vapor retarder
Concrete slab
Vapor retarder in cold climates
Edge and under slab insulation
Exterior wall cladding
Air infiltration/water barrierInterior wall boardInterior girt
Isolated footing
Uplift anchor(concrete collar cast-in-place over footing and around post)
Steel reinforcing bar inserted through post (holds anchor to post)
Splash plank
Preservative-treated wood post
Wall insulation
Grade line
Vapor retarder
Concrete slab
Vapor retarder in cold climates
Edge and under slab insulation
Exterior wall cladding
Air infiltration/water barrierInterior wall boardInterior girt
Isolated footing
Uplift anchor(concrete collar cast-in-place over footing and around post)
Steel reinforcing bar inserted through post (holds anchor to post)
Splash plank
Preservative-treated wood post
Wall insulation
Grade line
POST/PIER EMBEDMENT DESIGN: UPLIFT RESISTANCE
Mass of soil in shaded zone resists post withdrawal due
to uplift forces
Post must be mechanically
attached to the collar or wood
cleat Mass of attached collar or wood cleat
Bu
Governing Design Equations
Weight of attached collar/footing +
Weight of soil above attached collar/footing
≥ Design uplift load of post frame
POST/PIER FOUNDATION EMBEDMENT – UPLIFT LOADS
Ultimate uplift resistance of soil above circular anchorage systems
Cohesive Soils: U = γdu(Bu
2π/4-Ap) + FcSuBu2π/4
du = post embedment depthγ = soil densityBu = anchor diameterAp = post cross sectional areaFc = breakout factor for soil uplift (1.2du/Bu)Su = undrained soil shear strength
POST/PIER FOUNDATION EMBEDMENT – UPLIFT LOADS
U-value equations provided in ASAE/ANSI EP 486.2 and PFBDM for additional cases
• Cohesive soils – rectangular uplift anchors• Cohesionless soils – circular uplift anchors • Cohesionless soils – rectangular uplift anchors
POST/PIER FOUNDATION EMBEDMENT – UPLIFT LOADS
POST/PIER FOUNDATION DESIGN:UPLIFT DESIGN
• Design Equations for Uplift Resistance of Embedded Posts with Uplift Anchors
1. Post Frame Building Design Manual (2014 ed.) (www.nfba.org or
www.postframeadvantage.com)2. ANSI/ASAE EP486.2, Shallow Post & Pier
Foundation Design (www.asabe.org)
POST-FRAME TECHNICAL RESOURCES
• ANSI/ASAE (ASABE) EP 484– Diaphragm design procedures
• ANSI/ASAE (ASABE) EP 486.2– Shallow post & pier
foundation design• ANSI/ASAE (ASABE) EP 559
– Requirements and bending properties for mechanically laminated columns
– asabe.org or nfba.org
POST-FRAME TECHNICAL RESOURCES
POST-FRAME TECHNICAL RESOURCES
Provides structural design procedures, commentary & design examples for post-frame building systems
OTHER PF TECHNICAL RESOURCES•Post Frame Construction Guide•Post Frame Construction Tolerance Guidelines
OTHER PF TECHNICAL RESOURCES
DAFI
www.postframeadvantage.comor
www.nfba.org
MORE STRUCTURAL DESIGN DETAILS?
Additional 1-Hour Structural Design Sessions in NFBA’s On-Line University Course, “Engineering Design of PFBS”
Session 4: Simplified Method for Shallow Post and Pier Foundation Design
Session 5: Universal Method for Shallow Post and Pier Foundation Design
Session 6: Diaphragm Design of Post Frame Using DAFI - Engineering Details
Session 7: Alternative Post Frame Diaphragm Design Methods – Engineering Details
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HarveyManbeckNationalFrameBuildingAssociation(NFBA)[email protected]