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PCI 6thEdition
Fabrication Design
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Presentation Outline
Planning Discussion
Stripping Process Design and Analysis
Prestress / Post Tension Effects
Handling Devices Stripping Stress Examples
Storage Discussion
Transportation Discussion
Erection Discussion
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Introduction
Te loads and forces on precast and prestressed
concrete members during production!
transportation or erection "ill fre#uently re#uire a
separate analysis $oncrete strengts are lo"er
Support points and orientation are usually
different from members in teir final position
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Pre-Planning Piece Size
Te most economical piece si%e for a pro&ect isusually te largest! considering te follo"ingfactors'
Stability and stresses on te element duringandling
Transportation si%e and "eigt regulations ande#uipment restrictions
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Pre-Planning Piece Size
Available crane capacity at bot te plant andte pro&ect site(
Position of te crane must be considered! since
capacity is a function of reac Storage space! truc) turning radius! and oter
site restrictions
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Planning and Setup
*nce a piece as been fabricated! it is necessary to remove itfrom te mold "itout being damaged(
Positive drafts or brea)a"ay forms sould be used to allo" amember to lift a"ay from te casting bed "itout becoming
"edged "itin te form Ade#uate draft also serves to reduce trapped air bubbles(
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Planning and Setup
+ifting points must be located to )eep member stresses "itin limits andto ensure proper alignment of te piece as it is being lifted
,embers "it unsymmetrical geometry or pro&ecting sections mayre#uire supplemental lifting points and auxiliary lifting lines to acieveeven support during andling
-$ome.alongs or -cain.falls are fre#uently used for tese auxiliarylines
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Planning and Setup
0en te member as areas of small crosssection or large cantilevers! it may be necessaryto add a structural steel -strongbac) to te piece
to provide added strengt
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Planning and Setup
,embers tat re#uire a secondary process prior tosipment! suc as sandblasting or attacment ofaunces! may need to be rotated at te productionfacility( 1n tese cases! it may be necessary to cast in
extra lifting devices to facilitate tese maneuvers
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Planning and Setup
0en developing member sapes! te designersould consider te extra costs associated "itspecial rigging or forming! and pieces re#uiringmultiple andling
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Stripping: General
*rientation of members during storage! sipping and final in.place position iscritical in determining stripping re#uirements
Tey can be ori%ontal! vertical or some angle in bet"een
Te number and location of lifting devices are cosen to )eep stresses "itin teallo"able limits! "ic depends on "eter te -no crac)ing or -controlledcrac)ing criteria is to be used
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Stripping: General
1t is desirable to use te same lifting devices forbot stripping and erection2 o"ever! additionaldevices may be re#uired to rotate te member toits final position
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Stripping: General
Panels tat are strippedby rotating about oneedge "it lifting devices
at te opposite edge "illdevelop moments asso"n
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Stripping: General
0en panels are stripped tis "ay! care
sould be ta)en to prevent spalling of
te edge along "ic te rotationoccurs
A compressible material or sand bed
"ill elp protect tis edge
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Stripping: General
,embers tat arestripped flat fromte mold "ill
develop temoments so"n
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Stripping: General
1n some plants!tilt tables orturning rigs areused to reduce
strippingstresses
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Stripping: General
Since te section modulus "it respect to tetop and bottom faces may not be te same! tedesigner must select te controlling designlimitation'
Tensile stresses on bot faces to be less tan tat "ic"ould cause crac)ing
Tensile stress on one face to be less tan tat "ic "ouldcause crac)ing! "it controlled crac)ing permitted on teunexposed face
$ontrolled crac)ing permitted on bot faces
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Stripping: General
1f only one of te faces is exposed to
vie"! te exposed face "ill generally
control te stripping metod
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Rigging Configurations
Stresses and forces occurring duringandling are also influenced by te type
of rigging used to oo) up to te
member
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Rigging Configurations
+ift line forces for a t"o.point lift using
inclined lines are so"n
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Rigging Configurations
0en te sling angle is small! te components offorce parallel to te longitudinal axis of temember may generate a significant moment dueto secondary effects
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Rigging Configurations
0ile tis effect can and sould be accountedfor! it is not recommended tat it be allo"ed todominate design moments
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Rigging Configurations
$onsideration sould begiven to using spreaderbeams! t"o cranes oroter mecanisms toincrease te sling angle
Any suc special andlingre#uired by te design
sould be clearly so"non dra"ings
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Rigging Configurations
3sing a spreader beam can also eliminate te use ofrolling bloc)s
4ote tat te spreader beam must be sufficientlystiffer tan te concrete panel to limit panel
deflections and crac)ing +ifting oo) locations! oo) eigts! and slinglengts are critical to ensure even lifting of temember
For analysis! te panel acts as a continuous beam
over multiple supports
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Stripping Design
To account for te forces on te member
caused by form suction and impact! it is
common practice to apply a multiplier to temember "eigt and treat te resulting force
as an e#uivalent static service load(
Te multipliers cannot be #uantitatively
derived! so tey are based on experience
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Stripping Design
P$1 provides a table of typical values
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Factor of Safety
0en designing for stripping and andling! tefollo"ing safety factors are recommended'
5 3se embedded inserts and erection devices "it a
pullout strengt at least e#ual to four 678 times te
calculated load on te device(5 For members designed -"itout crac)ing! te
modulus of rupture 6,*98 ! is divided by a safety
factor of :(;(
7.5
1.5= 5
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Stress Limits & Crack Control
Stress limits for prestressed members during
production are discussed in Section 7(
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Stress Limits & Crack Control
,embers "ic are exposed to vie" "ill generally bedesigned for te -no discernible crac)ing criteria 6seeE#( 7(.?
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Benefits of Prestressing
Panels can be prestressed! using eiter
pretensioning or post.tensioning(
Design is based on $apter :> of A$1 =:>.
?
restricted to less tan ! must be
follo"ed(5
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Benefits of Prestressing
1t is recommended tat te average stress due toprestressing! after losses! be "itin a range of :?? psi
Te prestressing force sould be concentric "it teeffective cross section in order to minimi%e camber!
altoug some manufacturers prefer to ave a sligtin"ard bo" in te in.place position to counteracttermal bo"
1t sould be noted tat concentrically prestressedmembers do not camber! ence te form adesion
may be larger tan "it members tat do camber
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Strand Recomendation
1n order to minimi%e te possibility of splittingcrac)s in tin pretensioned members! testrand diameter sould not exceed tatso"n in te table belo"
Additional ligt transverse reinforcement maybe re#uired to control longitudinal crac)ing
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Strand Recommendations
0en "all panels are post.tensioned! care must beta)en to ensure proper transfer of force at te
ancorage and protection of ancors and tendons
against corrosion
Straigt strands or bars may be used! or! to reduce
te number of ancors! te metod so"n may be
used
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Strand Recommendation
1t sould be noted tat if an unbonded tendon
is cut! te prestress is lost( Tis can
sometimes appen if an unplanned openingis cut in at a later date
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Handling Devices
Since lifting devices are sub&ect to dynamicloads! ductility of te material is a re#uirement
Deformed reinforcing bars sould not be used
as te deformations result in stressconcentrations from te sac)le pin
Also! reinforcing bars may be ard grade orre.rolled rail steel "it little ductility and lo"
impact strengt at cold temperatures
i i
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Handling Devices
Strain ardening from bending may causeembrittlement
Smoot bars of a )no"n steel grade may be
used if ade#uate embedment or mecanicalancorage is provided
Te diameter must be suc tat locali%edfailure "ill not occur by bearing on te
sac)le pin
Ai f C bl L
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Aircraft Cable Loops
For smaller precast members! aircraft cable can beused for stripping and erection purposes
Aircraft cable comes in several si%es "it differentcapacities
Te flexible cable is easier to andle and "ill not leaverust stains on precast concrete
Ai f C bl L
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Aircraft Cable Loops
For some small precast members suc as coping! teflexible loops can be cast in ends of members andtuc)ed bac) in te &oints after erection
Aircraft cable loops sould not be used as multipleloops in a single location! as even pull on multiple
cables in a single oo) is extremely difficult to acieve 3ser sould ensure tat te cable is clean and tat
eac leg of te loop is embedded a minimum of 7> in(
P i S d L
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Prestressing Strand Loops
Prestressing strand! bot ne" andused! may be used for lifting loops
Te capacity of a lifting loop
embedded in concrete is dependentupon te strengt of te strand! lengtof embedment! te condition of testrand! te diameter of te loop! and
te strengt of te concrete
P t i St d L
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Prestressing Strand Loops
As a result of observations of lift loop beaviorduring te past fe" years! it is important tatcertain procedures be follo"ed to preventbot strand slippage and strand failure
Precast producers tests and/or experienceoffer te best guidelines for te load capacityto use
A safety factor of 7 against slippage orbrea)age sould be used
St d L R d ti
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Strand Loops Recommendations
1n lieu of test data! te recommendationslisted belo" sould be considered "en usingstrand as lifting loops(
5 ,inimum embedment for eac leg of te loopsould be
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Strand Loops Recommendations
$ontinued'5 Te diameter of te oo) or fitting around
"ic te strand lifting eye "ill be placedsould be at least four times te diameterof te strand being used
5 Do not use eavily corroded strand orstrand of un)no"n si%e and strengt(
St d L R d ti
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Strand Loops Recommendations
1n te absence of test or experience! it isrecommended tat te safe load on a
single :/< in( diameter )ips
Te safe "or)ing load of multiple loops
may be conservatively obtained by
multiplying te safe load for one loop by:(B for double loops and
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Strand Loops Recommendations
To avoid overstress in one loop "enusing multiple loops! care sould beta)en in te fabrication to ensure tat
all strands are bent te same Tin "all conduit over te strands in
te region of te bend as been usedto reduce te potential for overstress
Strand Loops Recommendations
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Strand Loops Recommendations
0en using double or tripleloops! te embedded endsmay need to be spreadapart for concrete
consolidation aroundembedded ends "itoutvoids being formed bybundled strand
Th d d I t
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Threaded Inserts
Treaded inserts can ave 4$
64ational $ourse8 or coil treads Ancorage is provided by loop! strut
or reinforcing bar
1nserts must be placed accurately
because teir safe "or)ing loaddecreases sarply if tey are notperpendicular to te bearing surface!or if tey are not in a straigt line"it te applied force
Th d d I t
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Threaded Inserts
Embedment of inserts close to an edge "ill greatlyreduce te effective area of te resisting concretesear cone and tus reduce te tension safe "or)ingload of te embedded insert
0en properly designed for bot insert and concretecapacities! treaded inserts ave many advantages
Ho"ever! correct usage is sometimes difficult toinspect during andling operations
Threaded Inserts
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Threaded Inserts
1n order to ensure tat an embedded insert acts
primarily in tension! a s"ivel plate as indicated in
sould be used
1t is extremely
important tat
sufficient treads
be engaged to
develop testrengt of te bolt
Threaded Inserts
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Threaded Inserts
For straigt tension loads only! eye bolts or "irerope loops provide a fast metod for andlingprecast members(
Do not use eiter device if sear loading conditions
exist(
Proprietary Devices
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Proprietary Devices
A variety of castings
or stoc) steel
devices! macined
to acceptspeciali%ed lifting
assemblies are used
in te precast
industry
Proprietary Devices
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Proprietary Devices
Tese proprietary devices are usually recessed 6using a -poc)et former8to provide access to te lifting unit( Te recess allo"s one panel to beplaced against anoter "itout cutting off te lifting device! and alsoelps prevent spalling around te device
+onger devices are used for edge lifting or deep precast concretemembers
Sallo" devices are available for tin precast concrete members(
Proprietary Devices
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Proprietary Devices
Te longer devices
usually engage a
reinforcing bar to
provide greater pulloutcapacity! and often ave
oles for te bar to pass
troug as so"n to te
left
Proprietary Devices
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Proprietary Devices
Tese units ave a rated capacity as
ig as
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Proprietary Devices
9einforcing bars are re#uired in t"o directions over te base to fully develop te lifting unit! as
so"n in Figure belo"
Tese inserts are
rated up to > tons
Proprietary Devices
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Proprietary Devices
Some lifting eyes do not s"ivel! so rotation may bea concern
1n all cases manufacturer recommendations
sould be rigorously follo"ed "en using any oftese devices
Wall Panel Example
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Wall Panel Example
Tis example and oters in $apter ; illustrate teuse of many of te recommendations in tis capter
Tey are intended to be illustrative and general only
Eac manufacturer "ill ave its o"n preferredmetods of andling
Wall Panel Example
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Wall Panel Example
Given:
A flat panel used as a loadbearing "all on a t"o.storystructure! as so"n on next slide
Section properties 6nominal dimensions are used fordesign8'
Solid panel Panel "it openingsA = C? in? in.?< suggests te total deformation yt! at any time can be estimated as'
yt
=
1 + ( )
Storage
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amplification due to creep and srin)age as afunction of @6reinforcement ratio for non.prestressedcompressionreinforcement!
As/bt8
Transportation
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Te metod used for transport can affect testructural design because of si%e and "eigtlimitations and te dynamic
Except for long prestressed dec) members! mostproducts are transported on eiter flatbed or lo".
boy trailers Trailers deform during auling Si%e and "eigt limitations vary from one state to
state
+oads are furter restricted on secondary roads Te common payload for standard trailers
"itout special permits is
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+o".boy trailers permit te eigt to be increased to about :? to :< ft(
Ho"ever tey ave a ave a sorter bed lengt(
Tis eigt may re#uire special routing to avoid lo" overpasses and overead "ires
Transportation
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Erection is simplified "en members are transported in te same orientation tey "ill ave in testructure
For example! single.story "all panels can be transported on A.frames "it te panels uprigt
A.frames also provide good lateral support and te desired t"o points of vertical support
Transportation
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+onger units can be transportedon teir sides to ta)e advantage
of te increased stiffness
compared "it flat sipment
Transportation
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1n all cases! te panel support locations sould be consistent "it te panel design
Panels "it large openings sometimes re#uire strongbac)s! braces or ties to )eepstresses "itin te design values
Transportation
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For members not symmetrical "it respect to te bending axis! te follo"ingexpressions can be used for determining te location of supports to give e#ualtensile stresses for positive and negative bending moments
Transportation
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For one end cantileveredK
0ereyb distance from te bending axis to te bottom fiber
yt distance from te bending axis to te top fiber
x =1
21 +
1 +
?
???
?
???
Transportation
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For t"o ends cantileveredK
0ereyb distance from te bending axis to te bottom fiber
yt distance from te bending axis to te top fiber
x =1
2 1 + 1 +
?
?
??
?
?
??
Erection
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Precast concrete members fre#uently must bereoriented from te position used to transportto its final construction position
Te analysis for tis -tripping 6rotating8
operation is similar to tat used during oterandling stages
1n capter ; in te P$1 andboo)! maximummoments for several commonly used tripping
tecni#ues are illustrated
Tripping Design Guide
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Erection
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0en using t"o crane lines! te center of
gravity must be bet"een tem in order toprevent a sudden sifting of te load "ile itis being rotated
To ensure tat tis is avoided! te stabilitycondition so"n must be met'
e >
2 2 2
2
Erection
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Te capacities of lifting devices must be cec)edfor te forces imposed during te trippingoperation! since te directions vary
0en rotating a panel "it t"o crane lines! te
pic) points sould be located to prevent te panelfrom an uncontrolled roll on te roller bloc)s canbe done by sligtly offsetting te pic) pointlocations to sift te "eigt to"ard te uppercrane line lift points! or by using cain drags on
te rolling bloc)
Erecting Wall Panels Example
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Given'Te "all panels "itopenings used onprevious examples
Problem'
Determine appropriateprocedures for erectingte "all panels "itopenings! panel "ill besipped flat
Erecting Wall Panels Example
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Assumptions +imit stresses to 6?(=;7 )si8(
$rane as main and auxiliary lines(
A telescoping man lift is available on site(
Solution:
Try tree.point rotation up using stripping inserts androlling bloc)' To simplify! conservatively use solid panel6no openings8 to determine moments(
5 f !
Erecting Wall Panels Example
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" = 1.0/
=
35.17( ) 1( )35.17
2
#
$%&
'(
35.17 0.604 +0.292
2#$%
&'(
= 23.4
1 = 2 = 11.7
Erecting Wall Panels Example
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1n Hori%ontal Position
Terefore! = point pic) not ade#uate
)* = 35.17( ) 1( ) 23.4 = 11.8
MMA+ = 69.6 = 835.2
=1.2(835.2 )
635= 1.58 > 0.354
Erecting Wall Panels Example
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no"ing from te stripping analysistat a four.point pic) can be used!te configurations so"n ere maybe used
Ho"ever! tis rigging may become
unstable at some point duringtripping! i(e(! continued rotation"itout tension in +ine A
Terefore! te lo"er end of tepanel must stay "itin inces of teground to maintain control(
Erecting Wall Panels Example
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Jecause te previous configuration
re#uires six rolling bloc)s and can be
cumbersome! te metod so"n on tefollo"ing slide may be an alternative
Erecting Wall Panels Example
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Erection Bracing Introduction
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Tis section deals "it te temporary bracing "icmay be necessary to maintain structural stability of aprecast structure during construction
0en possible! te final connections sould be used
to provide at least part of te erection bracing! butadditional bracing apparatus is sometimes re#uiredto resist all of te temporary loads
Erection Bracing Introduction
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Tese temporary loads may include "ind! seismic!eccentric dead loads including construction loads!unbalanced conditions due to erection se#uenceand incomplete connections Due to te lo"
probability of design loads occurring duringerection! engineering &udgment sould be used toestablis a reasonable design load
Erection Bracing Responsibilities
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Proper planning of te construction process is essential forefficient and safe erection
Se#uence of erection must be establised early! and teeffects accounted for in te bracing analysis and tepreparation of sop dra"ings
Te responsibility for te erection of precast concrete mayvary as follo"s'5 6see also A$1 =:>.?< Section :?(=8
Erection Bracing Responsibilities
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Te precast concrete manufacturer supplies teproduct erected! eiter "it is o"n forces! or by anindependent erector
Te manufacturer is responsible only for supplying teproduct! F(*(J( plant or &obsite
Erection is done eiter by te general contractor or byan independent erector under a separate agreement
Erection Bracing Responsibilities
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Te products are purcased by an independent erector "o
as a contract to furnis te complete precast concretepac)age(
9esponsibility for stability during erection must be clearlyunderstood(
Design for erection conditions must be in accordance "it all
local! state and federal regulations( 1t is desirable tat tisdesign be directed or approved by a Professional Engineer
Erection Bracing Responsibilities
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1t is desirable tat tis design be directed or approved by aProfessional Engineer
Erection dra"ings define te procedure
on o" to assemble te components into te final structure
Te erection dra"ings sould also address te stability of
te structure during construction and include temporaryconnections
Erection Bracing Responsibilities
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0en necessary! special dra"ings may be re#uiredto include soring! guying! bracing and specificerection se#uences
1t is desirable tat tis design be directed or
approved by a Professional Engineer Erection dra"ings define te procedure
on o" to assemble te components into te finalstructure
Erection Bracing Responsibilities
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Te erection dra"ings sould also address te stability of te structureduring construction and include temporary connections
0en necessary! special dra"ings may be re#uired to include soring!guying! bracing and specific erection se#uences
Erection Bracing Responsibilities
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For large and/or complex pro&ects! a pre.&ob conference prior tote preparation of erection dra"ings may be "arranted! in orderto discuss erection metods and to coordinate "it oter trades
Handling Equipment
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Te type of &obsite andling e#uipmentselected may influence te erection se#uence!and ence affect te temporary bracingre#uirements
Several types of erection e#uipment areavailable! including truc).mounted and cra"lermobile cranes! ydraulic cranes! to"er cranes!monorail systems! derric)s and oters
Te PCI Recommended Practice for Erectionof Precast Concrete provides more informationon te uses of eac(
Surveying and Layout
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Jefore products are sipped to te &obsite! a field cec) of te pro&ect is recommended to ensure tat priorconstruction is suitable to accept te precast units
Tis cec) sould include location! line and grade of bearing surfaces! notces! bloc)outs! ancor bolts!cast.in ard"are! and dimensional deviations
Site conditions suc as access ramps! overead electrical lines! truc) access! etc(! sould also be cec)ed
Surveying and Layout
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Any discrepancies bet"een actual conditions and tose so"n on dra"ings sould be addressed before erection isstarted
Surveys sould be re#uired before! during and after erection'5 Jefore! so tat te starting point is clearly establised and any potential difficulties "it te support structure are determined early(
5 During! to maintain alignment(
5After! to ensure tat te products ave been erected "itin tolerances(
Loads on Structure
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Te publication Design Loads on Structures During Construction 6SE1/AS$E =B.?
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$olumns "it eccentric loads from oter framing
members produce sides"ay "ic means tecolumns lean out of plumb
A similar condition can exist "encladding panels are erected on oneside of a multistory structure
Temporary Loading Examples
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3nbalanced loads due to partially complete
erection may result in beam rotation
Te erection dra"ings sould address tese
$onditions
Temporary Loading Examples
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Some solutions are'5 1nstall "ood "edges
bet"een flange of teeand top of beam
5 3se connection tocolumns tat preventrotation
5 Erect tees on botsides of beam
5 Prop tees to levelbelo"
Temporary Loading Examples
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9otations and deflections of framing members may
be caused by cladding panels( Tis may result inalignment problems and re#uire connections tatallo" for alignment ad&ustment after all panels areerected
Temporary Loading Examples
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1f construction e#uipment suc as concrete buggies! man.lifts! etc(! areto be used! information suc as "eel loads and spacing sould beconveyed to te designer of te precast members and te designer ofte erection bracing
Factors of Safety
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Suggested safety factors are so"n
Jracing inserts cast into precast members =
9eusable ard"are ;+ifting inserts 7
Bracing Equipment and Materials
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For most one.story andt"o.story ig
components tat re#uire
bracing! steel pipe
braces similar to toseso"n are used
Bracing Equipment and Materials
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Proper ancoring of te braces to te precastmembers and deadmen must be considered
0en te pipe braces are in tension! tere maybe significant sear and tension loads applied
to te deadmen Properly designed deadmen are a re#uirement
for safe bracing
$able guys "it turnbuc)les are normally used
for taller structures
Bracing Equipment and Materials
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Since "ire rope used in cable guys can resist onlytension! tey are usually used in combination "itoter cable guys in an opposite direction
$ompression struts! "ic may be te precastconcrete components! are needed to complete
truss action of te bracing system A number of "ire rope types are available
4ote tat capacity of tese systems is oftengoverned by te turnbuc)le capacity
General Considerations
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$areful planning of te erection se#uence is important
Tis plan is usually developed by a coordinated effortinvolving te general contractor! precast erector!precaster production and sipping departments and astructural engineer
A properly planned erection se#uence can reducebracing re#uirements
For example! "it "all panel systems a corner can firstbe erected so tat immediate stability can be acieved
General Considerations
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Similar considerations for sear "all structures canalso reduce bracing re#uirements
All parties sould be made a"are of te necessity ofclosely follo"ing erection "it te "elded diapragmconnections
Tis includes te diapragm to sear "all connections
General Considerations
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1n order for precast erection to flo" smootly'
5 Te site access and preparation must be ready
5 Te to.be.erected products must be ready
5 Precast sipping must be planned
5 Te erection e#uipment must be ready
5 Jracing e#uipment and deadmen must be ready
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Questions?