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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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