An#Introduc+on#to#Structural#Design#of#Post#Frame#Building#Systems#
Presented(on(October(23,(2014(by:(Harvey(B.(Manbeck,((PhD,(PE(( (Consultant(to(NFBA(( (Professor(Emeritus,(Engineering(( (Penn(State(University(
The(Wood(Products(Council(is(a(Registered(Provider(with(The(American(InsRtute(of(Architects(ConRnuing(EducaRon(Systems((AIA/CES),(Provider(#G516.((!Credit(s)(earned(on(compleRon(of(this(course(will(be(reported(to(AIA(CES(for(AIA(members.(CerRficates(of(CompleRon(for(both(AIA(members(and(non\AIA(members(are(available(upon(request.(((
This(course(is(registered(with(AIA(CES(for(conRnuing(professional(educaRon.(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(construcRon(or(any(method(or(manner(of(handling,(using,(distribuRng,(or(dealing(in(any(material(or(product.(___________________________________________
QuesRons(related(to(specific(materials,(methods,(and(services(will(be(addressed(at(the(conclusion(of(this(presentaRon.((
(
Course#Descrip+on#
((((This(program(begins(with(a(brief(descripRon(of(post\frame(building(systems(followed(by(an(overview(of(key(concepts(for(their(structural(design.(InformaRon(is(presented(from(a(conceptual(standpoint(as(opposed(to(an(equaRon(and(computaRonal(standpoint.(Two(design(methods(are(addressed:(one(for(post\frame(systems(without(diaphragm(acRon,(the(other(for(post\frame(systems(with(diaphragm(acRon.((The(majority(of(the(program(is(focused(on(the(la`er.(The(presentaRon(shows(how(a(simple,(yet(powerful(and(readily(available(program,(DAFI,(determines(the(proporRon(of((design(lateral(loads(carried(to(ground(by(the(individual(post\frames(and(that(carried(to(ground(by(roof(diaphragms(&(shear(walls.(The(program(then(shows(how(isolated(post(foundaRons(are(designed(to(resist(lateral(and(uplib(forces.(Technical(resources(available(to(design(professionals(are(also(discussed.((
This!presenta,on!was!developed!by!a!third!party!and!is!not!funded!by!WoodWorks!or!the!so8wood!lumber!check;off.#
Learning#Objec+ves#
1.(((IdenRfy(the(primary(structural(components(of(post\frame(((((((((((PF)(building(systems(
2.(((Learn(how(to(conduct(structural(design(of(PF(systems(without((
(((((((diaphragm((acRon((3. Learn(how(to(conduct(structural(design(of(post\frame(
building(systems(with(diaphragm(acRon(4. Learn(how(to(design(isolated(post/pier(post(frame(
foundaRons(5. IdenRfy(post\frame(design(resources(available(to(architects(
and(engineers(
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 industrys counterpart to low profile (1 to 2-1/2 story) steel buildings
Developed in late 1930s 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
TYPICAL PF BUILDING SYSTEM
Laminated or Solid-Sawn
Wood Columns
Roof Framing Trusses or
Rafters
Roof Purlins Typ. 2x4s
on edge or flat
Sheathing: 26 to 29 ga Ribbed Steel OR OSB or Plywood
Wall Girts Typ. 2x4 or 2x6
flat
PF BUILDING SYSTEM FOUNDATION OPTIONS
9
Isolated Pier Foundation
Continuous RC Foundation Wall
Thickened Edge of Concrete 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 direction Wind direction
Typical sway () of interior post frame at design lateral load = 5 to 8 inches
LATERAL LOADS: WITH DIAPHRAGM ACTION
Wind direction
1
Typical sway (1) of centermost post-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
FULL-SCALE PF BUILDING TESTS
40 ft W x 80 ft L x 16 ft H
16 ft
5 ft
Hydraulic cylinder
Load cell
29 ga ribbed steel sheathing
DIAPHRAGM VS NO DIAPHRAGM ACTION
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 dont
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 DESIGN Horizontal
movement permitted Horizontal movement prevented by
floor or mechanical connection
Non-constrained Constrained
d0
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 Post Ground Surface Shear (VG) and Moment (MG)
Fixed end at depth w below grade w = face width of post bearing against soil
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 Post Ground 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.
PRIMARY ASSUMPTIONS FOR THE SIMPLIFIED MODEL
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
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
MUVU
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
MUVU
2
3
4
5
DESIGN METHODS: 2-D POST FRAME
s x qwr s 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 + snow + wind (or seismic)
or 0.6 dead + wind (or seismic)
Usually controls post design Dea
