82
Please add relevant logo here Modern Post-Frame Structural Design Practice: An Introduction An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board. Copyright © 2014 National Frame Building Association

Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

  • Upload
    others

  • View
    4

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

Pleaseaddrelevantlogohere

ModernPost-FrameStructuralDesignPractice:AnIntroduction

AnIntroductiontoPost-FrameDiaphragmDesignandIsolatedPost/PierFoundations

HarveyB.Manbeck,PE,PhD

Disclaimer:ThispresentationwasdevelopedbyathirdpartyandisnotfundedbyWoodWorks ortheSoftwoodLumberBoard.

Copyright © 2014 National Frame Building Association

Page 2: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

“TheWoodProductsCouncil” isaRegisteredProviderwithTheAmericanInstituteofArchitectsContinuingEducationSystems(AIA/CES),Provider#G516.

Credit(s)earnedoncompletionofthiscoursewillbereportedtoAIACESforAIAmembers.CertificatesofCompletionforbothAIAmembersandnon-AIAmembersareavailableuponrequest.

ThiscourseisregisteredwithAIACES forcontinuingprofessionaleducation.Assuch,itdoesnotincludecontentthatmaybedeemedorconstruedtobeanapprovalorendorsementbytheAIAofanymaterialofconstructionoranymethodormannerofhandling,using,distributing,ordealinginanymaterialorproduct.__________________________________

Questionsrelatedtospecificmaterials,methods,andserviceswillbeaddressedattheconclusionofthispresentation.

Page 3: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

CourseDescription

Thissessionisintendedforarchitectsanddesignerswhowanttounderstandbasicstructuraldesignmethodsforanengineeredpost-framebuildingsystem.Withoutdelvingintoengineeringdetailsorcalculationprocedures,itcoverscomponentsofthepost-framebuildingsystem,aswellaskeystructuraldesignconcepts.Twoapproachesarehighlightedinparticular:oneforpost-framesystemswithoutdiaphragmaction,theotherforpost-framesystemswithdiaphragmaction.Proceduresfordesigningisolatedpierfoundationsforpost-framebuildingsarealsodiscussed,asaretechnicalresourcesavailabletodesignprofessionals.

Page 4: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

LearningObjectives

1.Identifytheprimarystructuralcomponentsofpost-frame(PF)buildingsystems

2.LearnbasicproceduresforconductingstructuralanalysisofPFsystemswithandwithoutdiaphragmaction

3.Definethedesignapproachforisolatedpost/pierPFfoundations

4. Recognizepost-framedesignresourcesavailabletoarchitectsandengineers

Page 5: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

MODERN POST-FRAME STRUCTURAL DESIGN

PRACTICE - AN INTRODUCTION

Copyright © 2014 National Frame Building Association

Page 6: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 7: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 8: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 9: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

PF BUILDING SYSTEM FOUNDATION OPTIONS

10

Isolated Pier Foundation

Continuous RC Foundation Wall

Thickened Edge ofConcrete Slab

Page 10: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 2-dimensional frame design method – Without diaphragm action

• 3-dimensional diaphragm design method – With diaphragm action

PRIMARY PF DESIGN METHODS

Page 11: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

PF SYSTEMS WITHOUT DIAPHRAGM ACTION

Unsheathed walls

Unsheathed walls

Page 12: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

PF SYSTEM WITH DIAPHRAGM ACTION

Sheathed Version of This Building

Page 13: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

LATERAL LOADS: WITHOUT DIAPHRAGM ACTION

Wind directionWind direction

Typical sway (Δ) of interiorpost frame at design lateral load = 5 to 8 inches

Page 14: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

LATERAL LOADS: WITH DIAPHRAGM ACTION

Wind direction

∆1

Typical sway (∆1) of centermostpost-frame at design lateral load =

0.5 to 1.0 inch

Page 15: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 16: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 17: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

EMBEDDED POST/PIER FOUNDATIONS

• Common post-soil fixity models for embedded post or pier foundations: – Constrained post or pier– Non-constrained post or pier

Page 18: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

POST/PIER EMBEDMENT DESIGNHorizontal

movement permitted Horizontal movement prevented by

floor or mechanical connection

Non-constrained Constrained

dR

Page 19: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

EMBEDDED POST/PIER FOUNDATIONS

• Design Methods

-Simplified Method

-Universal Method

Page 20: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 21: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 22: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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.

Page 23: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 24: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 25: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 26: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 27: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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)

Page 28: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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)

Page 29: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 30: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 31: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 32: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 33: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 34: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 35: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 36: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DIAPHRAGM TEST PANEL Sheathing/cladding

Rafter or truss top chord (strut)

Purlin(chord)

Page 37: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 38: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 39: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 40: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 41: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 42: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 43: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 44: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 45: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 46: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DIAPHRAGM DESIGN METHOD

Page 47: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 48: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: UNDEFORMED POSITION

21 3 4

DatumDatum

Node

Page 49: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: DEFORMED EQUILIBRIUM POSITION

Datum Datum

1 2 3 4

Page 50: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI COMPUTER PROGRAM

Pf4

Pf3

Pf2

Pf1

Page 51: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI COMPUTER PROGRAM

V3

V2

V1

Page 52: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 53: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 54: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 55: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: MINI DEMONSTRATION

Page 56: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: MINI DEMONSTRATION

Page 57: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: MINI DEMONSTRATION

Page 58: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

DAFI: MINI DEMONSTRATION

Page 59: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 60: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

Two Design Approaches

• Simplified Method

• Universal Method

POST/PIER LATERAL RESISTANCE (VU & MU) & EMBEDMENT DEPTH

CALCS.

Page 61: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 62: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 63: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 64: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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)

Page 65: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 66: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 67: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

POST/PIER EMBEDMENT LATERAL LOADS- UNIVERSAL METHOD

Non-constrained at ground surface – Design Criteria

Foundation moment andshear capacity from basicmechanics

Page 68: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 69: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 70: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 71: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 72: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 73: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 74: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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)

Page 75: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

POST-FRAME TECHNICAL RESOURCES

Page 76: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

• 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

Page 77: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

POST-FRAME TECHNICAL RESOURCES

Provides structural design procedures, commentary & design examples for post-frame building systems

Page 78: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

OTHER PF TECHNICAL RESOURCES•Post Frame Construction Guide•Post Frame Construction Tolerance Guidelines

Page 79: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

OTHER PF TECHNICAL RESOURCES

DAFI

www.postframeadvantage.comor

www.nfba.org

Page 80: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

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

Page 81: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

WWW.POSTFRAMEADVANTAGE.COM

WWW.NFBA.ORG

National Frame Building Association8735 Higgins Road

Suite 300Chicago, IL 60631

MORE PF DESIGN GUIDANCE?

Page 82: Modern Post-Frame Structural Design Practice: An Introduction€¦ · An Introduction to Post-Frame Diaphragm Design and Isolated Post/Pier Foundations Harvey B. Manbeck, PE, PhD

Questions?ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse

HarveyManbeckNationalFrameBuildingAssociation(NFBA)[email protected]