PCI 6th Edition

1
PCI 6th Edition

• Fabrication Design

2
Presentation Outline

• Planning Discussion
• Stripping Process Design and Analysis
• Prestress / Post Tension Effects
• Handling Devices
• Stripping Stress Examples
• Storage Discussion
• Transportation Discussion
• Erection Discussion

3
Introduction

• The loads and forces on precast and prestressed
  concrete members during production,
  transportation or erection will frequently
  require a separate analysis
• Concrete strengths are lower
• Support points and orientation are usually
  different from members in their final position

4
Pre-Planning Piece Size

• The most economical piece size for a project is
  usually the largest, considering the following
  factors
• Stability and stresses on the element during
  handling
• Transportation size and weight regulations and
  equipment restrictions

5
Pre-Planning Piece Size

• Available crane capacity at both the plant and
  the project site.
• Position of the crane must be considered, since
  capacity is a function of reach
• Storage space, truck turning radius, and other
  site restrictions

6
Planning and Setup

• Once a piece has been fabricated, it is necessary
  to remove it from the mold without being damaged.
• Positive drafts or breakaway forms should be used
  to allow a member to lift away from the casting
  bed without becoming wedged within the form
• Adequate draft also serves to reduce trapped air
  bubbles.

7
Planning and Setup

• Lifting points must be located to keep member
  stresses within limits and to ensure proper
  alignment of the piece as it is being lifted
• Members with unsymmetrical geometry or projecting
  sections may require supplemental lifting points
  and auxiliary lifting lines to achieve even
  support during handling
• Come-alongs or chain-falls are frequently
  used for these auxiliary lines

8
Planning and Setup

• When the member has areas of small cross section
  or large cantilevers, it may be necessary to add
  a structural steel strongback to the piece to
  provide added strength

9
Planning and Setup

• Members that require a secondary process prior to
  shipment, such as sandblasting or attachment of
  haunches, may need to be rotated at the
  production facility. In these cases, it may be
  necessary to cast in extra lifting devices to
  facilitate these maneuvers

10
Planning and Setup

• When developing member shapes, the designer
  should consider the extra costs associated with
  special rigging or forming, and pieces requiring
  multiple handling

11
Stripping General

• Orientation of members during storage, shipping
  and final in-place position is critical in
  determining stripping requirements
• They can be horizontal, vertical or some angle in
  between
• The number and location of lifting devices are
  chosen to keep stresses within the allowable
  limits, which depends on whether the no
  cracking or controlled cracking criteria is to
  be used

12
Stripping General

• It is desirable to use the same lifting devices
  for both stripping and erection however,
  additional devices may be required to rotate the
  member to its final position

13
Stripping General

• Panels that are stripped by rotating about one
  edge with lifting devices at the opposite edge
  will develop moments as shown

14
Stripping General

• When panels are stripped this way, care should be
  taken to prevent spalling of the edge along which
  the rotation occurs
• A compressible material or sand bed will help
  protect this edge

15
Stripping General

• Members that are stripped flat from the mold will
  develop the moments shown

16
Stripping General

• In some plants, tilt tables or turning rigs are
  used to reduce stripping stresses

17
Stripping General

• Since the section modulus with respect to the top
  and bottom faces may not be the same, the
  designer must select the controlling design
  limitation
• Tensile stresses on both faces to be less than
  that which would cause cracking
• Tensile stress on one face to be less than that
  which would cause cracking, with controlled
  cracking permitted on the unexposed face
• Controlled cracking permitted on both faces

18
Stripping General

• If only one of the faces is exposed to view, the
  exposed face will generally control the stripping
  method

19
Rigging Configurations

• Stresses and forces occurring during handling are
  also influenced by the type of rigging used to
  hook up to the member

20
Rigging Configurations

• Lift line forces for a two-point lift using
  inclined lines are shown

21
Rigging Configurations

• When the sling angle is small, the components of
  force parallel to the longitudinal axis of the
  member may generate a significant moment due to
  secondary effects

22
Rigging Configurations

• While this effect can and should be accounted
  for, it is not recommended that it be allowed to
  dominate design moments

23
Rigging Configurations

• Consideration should be given to using spreader
  beams, two cranes or other mechanisms to increase
  the sling angle
• Any such special handling required by the design
  should be clearly shown on drawings

24
Rigging Configurations

• Using a spreader beam can also eliminate the use
  of rolling blocks
• Note that the spreader beam must be sufficiently
  stiffer than the concrete panel to limit panel
  deflections and cracking
• Lifting hook locations, hook heights, and sling
  lengths are critical to ensure even lifting of
  the member
• For analysis, the panel acts as a continuous beam
  over multiple supports

25
Stripping Design

• To account for the forces on the member caused by
  form suction and impact, it is common practice to
  apply a multiplier to the member weight and treat
  the resulting force as an equivalent static
  service load.
• The multipliers cannot be quantitatively derived,
  so they are based on experience

26
Stripping Design

• PCI provides a table of typical values

27
Factor of Safety

• When designing for stripping and handling, the
  following safety factors are recommended
• Use embedded inserts and erection devices with a
  pullout strength at least equal to four (4) times
  the calculated load on the device.
• For members designed without cracking, the
  modulus of rupture (MOR) , is divided by a safety
  factor of 1.5.

28
Stress Limits Crack Control

• Stress limits for prestressed members during
  production are discussed in Section 4.2.2.2 of
  the the PCI Handbook
• ACI 318-02 does not restrict stresses on
  non-prestressed members, but does specify minimum
  reinforcement spacing, as discussed in Section
  4.2.2.1. (PCI chapter 4 member design)

29
Stress Limits Crack Control

• Members which are exposed to view will generally
  be designed for the no discernible cracking
  criteria (see Eq. 4.2.2.2), which limits the
  stress to .
• In the case of stripping stresses, f'ci should be
  substituted for f'c
• Whether or not the members are exposed to view,
  the strength design and crack control
  requirements of ACI 318-02, as discussed in
  Chapter 4 of this Handbook, must be followed.

30
Benefits of Prestressing

• Panels can be prestressed, using either
  pretensioning or post-tensioning.
• Design is based on Chapter 18 of ACI 318-02, as
  described in Chapter 4 of this Handbook. Further,
  tensile stresses should be restricted to less
  than , must be followed.

31
Benefits of Prestressing

• It is recommended that the average stress due to
  prestressing, after losses, be within a range of
  125 to 800 psi
• The prestressing force should be concentric with
  the effective cross section in order to minimize
  camber, although some manufacturers prefer to
  have a slight inward bow in the in-place position
  to counteract thermal bow
• It should be noted that concentrically
  prestressed members do not camber, hence the form
  adhesion may be larger than with members that do
  camber

32
Strand Recomendation

• In order to minimize the possibility of splitting
  cracks in thin pretensioned members, the strand
  diameter should not exceed that shown in the
  table below
• Additional light transverse reinforcement may be
  required to control longitudinal cracking

33
Strand Recommendations

• When wall panels are post-tensioned, care must be
  taken to ensure proper transfer of force at the
  anchorage and protection of anchors and tendons
  against corrosion
• Straight strands or bars may be used, or, to
  reduce the number of anchors, the method shown
  may be used

34
Strand Recommendation

• It should be noted that if an unbonded tendon is
  cut, the prestress is lost. This can sometimes
  happen if an unplanned opening is cut in at a
  later date

35
Handling Devices

• Since lifting devices are subject to dynamic
  loads, ductility of the material is a requirement
• Deformed reinforcing bars should not be used as
  the deformations result in stress concentrations
  from the shackle pin
• Also, reinforcing bars may be hard grade or
  re-rolled rail steel with little ductility and
  low impact strength at cold temperatures

36
Handling Devices

• Strain hardening from bending may cause
  embrittlement
• Smooth bars of a known steel grade may be used if
  adequate embedment or mechanical anchorage is
  provided
• The diameter must be such that localized failure
  will not occur by bearing on the shackle pin

37
Aircraft Cable Loops

• For smaller precast members, aircraft cable can
  be used for stripping and erection purposes
• Aircraft cable comes in several sizes with
  different capacities
• The flexible cable is easier to handle and will
  not leave rust stains on precast concrete

38
Aircraft Cable Loops

• For some small precast members such as coping,
  the flexible loops can be cast in ends of members
  and tucked back in the joints after erection
• Aircraft cable loops should not be used as
  multiple loops in a single location, as even pull
  on multiple cables in a single hook is extremely
  difficult to achieve
• User should ensure that the cable is clean and
  that each leg of the loop is embedded a minimum
  of 48 in.

39
Prestressing Strand Loops

• Prestressing strand, both new and used, may be
  used for lifting loops
• The capacity of a lifting loop embedded in
  concrete is dependent upon the strength of the
  strand, length of embedment, the condition of the
  strand, the diameter of the loop, and the
  strength of the concrete

40
Prestressing Strand Loops

• As a result of observations of lift loop behavior
  during the past few years, it is important that
  certain procedures be followed to prevent both
  strand slippage and strand failure
• Precast producers tests and/or experience offer
  the best guidelines for the load capacity to use
• A safety factor of 4 against slippage or breakage
  should be used

41
Strand Loops Recommendations

• In lieu of test data, the recommendations listed
  below should be considered when using strand as
  lifting loops.
• Minimum embedment for each leg of the loop should
  be 24 in.
• The strand surface must be free of contaminants,
  such as form oil, grease, mud, or loose rust,
  which could reduce the bond of the strand to the
  concrete

42
Strand Loops Recommendations

• Continued
• The diameter of the hook or fitting around which
  the strand lifting eye will be placed should be
  at least four times the diameter of the strand
  being used
• Do not use heavily corroded strand or strand of
  unknown size and strength.

43
Strand Loops Recommendations

• In the absence of test or experience, it is
  recommended that the safe load on a single 1/2
  in. diameter 270 ksi strand loop satisfying the
  above recommendations not exceed 8 kips
• The safe working load of multiple loops may be
  conservatively obtained by multiplying the safe
  load for one loop by 1.7 for double loops and 2.2
  for triple loops

44
Strand Loops Recommendations

• To avoid overstress in one loop when using
  multiple loops, care should be taken in the
  fabrication to ensure that all strands are bent
  the same
• Thin wall conduit over the strands in the region
  of the bend has been used to reduce the potential
  for overstress

45
Strand Loops Recommendations

• When using double or triple loops, the embedded
  ends may need to be spread apart for concrete
  consolidation around embedded ends without voids
  being formed by bundled strand

46
Threaded Inserts

• Threaded inserts can have NC (National Course) or
  coil threads
• Anchorage is provided by loop, strut or
  reinforcing bar
• Inserts must be placed accurately because their
  safe working load decreases sharply if they are
  not perpendicular to the bearing surface, or if
  they are not in a straight line with the applied
  force

47
Threaded Inserts

• Embedment of inserts close to an edge will
  greatly reduce the effective area of the
  resisting concrete shear cone and thus reduce the
  tension safe working load of the embedded insert
• When properly designed for both insert and
  concrete capacities, threaded inserts have many
  advantages
• However, correct usage is sometimes difficult to
  inspect during handling operations

48
Threaded Inserts

• In order to ensure that an embedded insert acts
  primarily in tension, a swivel plate as indicated
  in should be used

• It is extremely important that sufficient threads
  be engaged to develop the strength of the bolt

49
Threaded Inserts

• For straight tension loads only, eye bolts or
  wire rope loops provide a fast method for
  handling precast members.
• Do not use either device if shear loading
  conditions exist.

50
Proprietary Devices

• A variety of castings or stock steel devices,
  machined to accept specialized lifting assemblies
  are used in the precast industry

51
Proprietary Devices

• These proprietary devices are usually recessed
  (using a pocket former) to provide access to
  the lifting unit. The recess allows one panel to
  be placed against another without cutting off the
  lifting device, and also helps prevent spalling
  around the device
• Longer devices are used for edge lifting or deep
  precast concrete members
• Shallow devices are available for thin precast
  concrete members.

52
Proprietary Devices

• The longer devices usually engage a reinforcing
  bar to provide greater pullout capacity, and
  often have holes for the bar to pass through as
  shown to the left

53
Proprietary Devices

• These units have a rated capacity as high as 22
  tons, with reductions for thin panels or close
  edge distances
• Supplemental reinforcement may be required to
  achieve these values
• Shallow units usually have a spread foot or base
  to increase pullout capacity

54
Proprietary Devices

• Reinforcing bars are required in two directions
  over the base to fully develop the lifting unit,
  as shown in Figure below
• These inserts are
• rated up to 8 tons

55
Proprietary Devices

• Some lifting eyes do not swivel, so rotation may
  be a concern
• In all cases manufacturer recommendations should
  be rigorously followed when using any of these
  devices

56
Wall Panel Example

• This example and others in Chapter 5 illustrate
  the use of many of the recommendations in this
  chapter
• They are intended to be illustrative and general
  only
• Each manufacturer will have its own preferred
  methods of handling

57
Wall Panel Example

• Given
• A flat panel used as a loadbearing wall on a
  two-story structure, as shown on next slide
• Section properties (nominal dimensions are used
  for design)
• Solid panel Panel with
  openings
• A 960 in2 A 480 in2
• Sb St 1280 in3 Sb St 640 in3
• Ix 5120 in4 Ix 2560 4 in4
• Unit weight _at_ 150 pcf 100 psf 0.100 ksf
• Total weight 35.2 kips (solid panel)
• 29.2 kips (panel w/
  openings)

58
Wall Panel Example
59
Wall Panel Example

• Stripping method
• Inside crane height prevents panel from being
  turned on edge directly in mold, therefore, strip
  flat
• Handling multipliers
• Exposed flat surface has a smooth form finish
  with false joints. Side rails are removable. Use
  multiplier of 1.4

60
Wall Panel Example

• f'ci at stripping 3000 psi
• Allowable tensile stresses at stripping and
  lifting
• Problem
• Check critical stresses involved with stripping.
  Limit stresses to 0.274 ksi.
• Compare Simple Solution to Mechanics Solution

61
Solution Steps

• Step 1 Determine section properties
• Step 2 Select number of pick points and
  determine maximum stress
• Step 3 Determine stress from mechanic
  approach
• Step 4 Check panel with opening
• Step 5 Check rolling block solution
• Step 6 Check transverse bending
• Step 7 Check secondary effects

62
Step 1 Determine Section Properties

• Solid panel dimensions
• a 10 ft, b 35.2 ft, a/2 5 ft 60 in.
• S for resisting section (half of panel width)

63
Step 2 4-point pick

• Figure 5.36.1.1(a) (page 5-5)

64
Step 2 Check Stresses

• 4 Point Stresses
• Not Good try 8 point pick

65
Step 2 8 Point Pick

• Figure 5.3.1.1(b) (Page 5-5)

66
Step 2 Check Stresses

• 8 Point Stresses

67
Step 3 Mechanics of Materials
68
Step 4 Panel With Openings
69
Step 5 Rolling Blocks

• If using a rolling block for handling as shown
  below, the panel cannot be analyzed with the
  previous method
• Each leg of continuous cable over a rolling block
  must carries equal load

70
Step 5 Rolling Block
71
Step 6 Transverse Bending

• Consider lower portion of panel with openings
• Note that Figure Without the concrete in the area
  of the opening, the weight is reduced and
  unevenly distributed. Also, the resisting section
  is limited to a width of 4.7 ft.

72
Step 6 Transverse Bending

• Section through lifters
• From continuous beam analysis, load carried by
  bottom two anchors is 7.2 kips, therefore

73
Step 7 Secondary Effects

• Check added moment due to sling angle
• Using recessed proprietary lifting anchor
• e 3.5 in

74
Step 7 Secondary Effects

• Resisting Section
• Therefore Section is OK

75
Prestressed Wall Example

• Given
• Same wallpanel as previousexample

76
Prestressed Wall Example

• Problem
• Determine required number of 1/2 in diameter,
  270 ksi strands pulled to 28.9 kips to prevent
  cracking in window panel. Assume 10 loss of
  prestress.
• From previous example, tensile stress is 0.431
  ksi. The desired level of tensile stress is
  or 0.274 ksi

77
Solution Steps

• Step 1 Determine additional compressive
  Required
• Step 2 Determine the number of strands
  required based on stress
• Step 3 Calculate the number of strands

78
Step 1 Additional Compressive

• Compressive stress required
• 0.431 0.274 0.157 ksi

79
Step 2 Of Strands Based On Stress

• From previous the max moment/stress occurs at
  lifting points (-M). This results in tensile
  stresses on the top face.

80
Step 3 Number of Strands

• 0.060(no. of strands) 0.019(no. of strands)
  0.157 ksi
• No. of strands 3.8
• Add four strands to panel (two on each side of
  opening)

81
Storage

• Wherever possible, a member should be stored on
  points of support located at or near those used
  for stripping and handling
• Where points other than those used for stripping
  or handling are used for storage, the storage
  condition must be checked

82
Storage

• If support is provided at more than two points,
  and the design is based on more than two
  supports, precautions must be taken so that the
  element does not bridge over one of the supports
  due to differential support settlement

83
Storage

• Warpage in storage may be caused by
• temperature or shrinkage differential between
  surfaces
• creep
• storage conditions
• Warpage can only be minimized by providing
• Where feasible, the member should be oriented in
  the yard so that the sun does not overheat one
  side

84
Storage

• By superposition, the total instantaneous
  deflection, ymax , at the maximum point can be
  estimated by

Ic , Ib moment of inertia of uncracked section
in the respective directions for 1 in. width of
panel
85
Storage

• This instantaneous deflection should be modified
  by a factor to account for the time dependent
  effects of creep and shrinkage
• ACI 318-02 suggests the total deformation yt, at
  any time can be estimated as

86
Storage

• ? amplification due to creep and shrinkage as a
  function of '? (reinforcement ratio for
  non-prestressed compressionreinforcement,As/b?t)
  

87
Transportation

• The method used for transport can affect the
  structural design because of size and weight
  limitations and the dynamic
• Except for long prestressed deck members, most
  products are transported on either flatbed or
  low-boy trailers
• Trailers deform during hauling
• Size and weight limitations vary from one state
  to state
• Loads are further restricted on secondary roads
• The common payload for standard trailers without
  special permits is 20 tons.

88
Transportation

• Low-boy trailers permit the height to be
  increased to about 10 to 12 ft.
• However they have a have a shorter bed length.
• This height may require special routing to avoid
  low overpasses and overhead wires

89
Transportation

• Erection is simplified when members are
  transported in the same orientation they will
  have in the structure
• For example, single-story wall panels can be
  transported on A-frames with the panels upright
• A-frames also provide good lateral support and
  the desired two points of vertical support

90
Transportation

• Longer units can be transported on their sides to
  take advantage of the increased stiffness
  compared with flat shipment

91
Transportation

• In all cases, the panel support locations should
  be consistent with the panel design
• Panels with large openings sometimes require
  strongbacks, braces or ties to keep stresses
  within the design values

92
Transportation

• For members not symmetrical with respect to the
  bending axis, the following expressions can be
  used for determining the location of supports to
  give equal tensile stresses for positive and
  negative bending moments

93
Transportation

• For one end cantilevered
• Where
• yb distance from the bending axis to the
  bottom fiber
• yt distance from the bending axis to the top
  fiber

94
Transportation

• For two ends cantilevered
• Where
• yb distance from the bending axis to the
  bottom fiber
• yt distance from the bending axis to the top
  fiber

95
Erection

• Precast concrete members frequently must be
  reoriented from the position used to transport to
  its final construction position
• The analysis for this tripping (rotating)
  operation is similar to that used during other
  handling stages
• In chapter 5 in the PCI handbook, maximum moments
  for several commonly used tripping techniques are
  illustrated

96
Tripping Design Guide
97
Erection

• When using two crane lines, the center of gravity
  must be between them in order to prevent a sudden
  shifting of the load while it is being rotated
• To ensure that this is avoided, the stability
  condition shown must be met

98
Erection

• The capacities of lifting devices must be checked
  for the forces imposed during the tripping
  operation, since the directions vary
• When rotating a panel with two crane lines, the
  pick points should be located to prevent the
  panel from an uncontrolled roll on the roller
  blocks can be done by slightly offsetting the
  pick point locations to shift the weight toward
  the upper crane line lift points, or by using
  chain drags on the rolling block

99
Erecting Wall Panels Example

• Given
• The wall panels with openings used on previous
  examples
• Problem
• Determine appropriate procedures for erecting
  the wall panels with openings, panel will be
  shipped flat

100
Erecting Wall Panels Example

• Assumptions
• Limit stresses to (0.354 ksi).
• Crane has main and auxiliary lines.
• A telescoping man lift is available on site.
• Solution
• Try three-point rotation up using stripping
  inserts and rolling block To simplify,
  conservatively use solid panel (no openings) to
  determine moments.

101
Erecting Wall Panels Example
102
Erecting Wall Panels Example

• In Horizontal Position
• Therefore, 3 point pick not adequate

103
Erecting Wall Panels Example

• Knowing from the stripping analysis that a
  four-point pick can be used, the configurations
  shown here may be used
• However, this rigging may become unstable at some
  point during tripping, i.e., continued rotation
  without tension in Line A
• Therefore, the lower end of the panel must stay
  within inches of the ground to maintain control.

104
Erecting Wall Panels Example

• Because the previous configuration requires six
  rolling blocks and can be cumbersome, the method
  shown on the following slide may be an
  alternative

105
Erecting Wall Panels Example
106
Erection Bracing Introduction

• This section deals with the temporary bracing
  which may be necessary to maintain structural
  stability of a precast structure during
  construction
• When possible, the final connections should be
  used to provide at least part of the erection
  bracing, but additional bracing apparatus is
  sometimes required to resist all of the temporary
  loads

107
Erection Bracing Introduction

• These temporary loads may include wind, seismic,
  eccentric dead loads including construction
  loads, unbalanced conditions due to erection
  sequence and incomplete connections Due to the
  low probability of design loads occurring during
  erection, engineering judgment should be used to
  establish a reasonable design load

108
Erection Bracing Responsibilities

• Proper planning of the construction process is
  essential for efficient and safe erection
• Sequence of erection must be established early,
  and the effects accounted for in the bracing
  analysis and the preparation of shop drawings
• The responsibility for the erection of precast
  concrete may vary as follows
• (see also ACI 318-02 Section 10.3)

109
Erection Bracing Responsibilities

• The precast concrete manufacturer supplies the
  product erected, either with his own forces, or
  by an independent erector
• The manufacturer is responsible only for
  supplying the product, F.O.B. plant or jobsite
• Erection is done either by the general contractor
  or by an independent erector under a separate
  agreement

110
Erection Bracing Responsibilities

• The products are purchased by an independent
  erector who has a contract to furnish the
  complete precast concrete package.
• Responsibility for stability during erection must
  be clearly understood.
• Design for erection conditions must be in
  accordance with all local, state and federal
  regulations. It is desirable that this design be
  directed or approved by a Professional Engineer

111
Erection Bracing Responsibilities

• It is desirable that this design be directed or
  approved by a Professional Engineer
• Erection drawings define the procedure
• on how to assemble the components into the final
  structure
• The erection drawings should also address the
  stability of the structure during construction
  and include temporary connections

112
Erection Bracing Responsibilities

• When necessary, special drawings may be required
  to include shoring, guying, bracing and specific
  erection sequences
• It is desirable that this design be directed or
  approved by a Professional Engineer
• Erection drawings define the procedure
• on how to assemble the components into the final
  structure

113
Erection Bracing Responsibilities

• The erection drawings should also address the
  stability of the structure during construction
  and include temporary connections
• When necessary, special drawings may be required
  to include shoring, guying, bracing and specific
  erection sequences

114
Erection Bracing Responsibilities

• For large and/or complex projects, a pre-job
  conference prior to the preparation of erection
  drawings may be warranted, in order to discuss
  erection methods and to coordinate with other
  trades

115
Handling Equipment

• The type of jobsite handling equipment selected
  may influence the erection sequence, and hence
  affect the temporary bracing requirements
• Several types of erection equipment are
  available, including truck-mounted and crawler
  mobile cranes, hydraulic cranes, tower cranes,
  monorail systems, derricks and others
• The PCI Recommended Practice for Erection of
  Precast Concrete provides more information on the
  uses of each.

116
Surveying and Layout

• Before products are shipped to the jobsite, a
  field check of the project is recommended to
  ensure that prior construction is suitable to
  accept the precast units
• This check should include location, line and
  grade of bearing surfaces, notches, blockouts,
  anchor bolts, cast-in hardware, and dimensional
  deviations
• Site conditions such as access ramps, overhead
  electrical lines, truck access, etc., should also
  be checked

117
Surveying and Layout

• Any discrepancies between actual conditions and
  those shown on drawings should be addressed
  before erection is started
• Surveys should be required before, during and
  after erection
• Before, so that the starting point is clearly
  established and any potential difficulties with
  the support structure are determined early.
• During, to maintain alignment.
• After, to ensure that the products have been
  erected within tolerances.

118
Loads on Structure

• The publication Design Loads on Structures During
  Construction (SEI/ASCE 37-02) provides minimum
  design loads, including wind, earthquake and
  construction loads and load combinations for
  partially completed structures and structures
  used during construction
• In addition to working stress or strength design
  using loads from the above publication, the
  designer must consider the effect of temporary
  loading on stability and bracing design

119
Temporary Loading Examples

• Columns with eccentric loads from other framing
  members produce sidesway which means the columns
  lean out of plumb
• A similar condition can exist whencladding
  panels are erected on oneside of a multistory
  structure

120
Temporary Loading Examples

• Unbalanced loads due to partially complete
  erection may result in beam rotation
• The erection drawings should address these
  Conditions

121
Temporary Loading Examples

• Some solutions are
• Install wood wedges between flange of tee and top
  of beam
• Use connection to columns that prevent rotation
• Erect tees on both sides of beam
• Prop tees to level below

122
Temporary Loading Examples

• Rotations and deflections of framing members may
  be caused by cladding panels. This may result in
  alignment problems and require connections that
  allow for alignment adjustment after all panels
  are erected

123
Temporary Loading Examples

• If construction equipment such as concrete
  buggies, man-lifts, etc., are to be used,
  information such as wheel loads and spacing
  should be conveyed to the designer of the precast
  members and the designer of the erection bracing

124
Factors of Safety

• Suggested safety factors are shown

Bracing inserts cast into precast members 3
Reusable hardware 5
Lifting inserts 4
125
Bracing Equipment and Materials

• For most one-story and two-story high components
  that require bracing, steel pipe braces similar
  to those shown are used

126
Bracing Equipment and Materials

• Proper anchoring of the braces to the precast
  members and deadmen must be considered
• When the pipe braces are in tension, there may be
  significant shear and tension loads applied to
  the deadmen
• Properly designed deadmen are a requirement for
  safe bracing
• Cable guys with turnbuckles are normally used for
  taller structures

127
Bracing Equipment and Materials

• Since wire rope used in cable guys can resist
  only tension, they are usually used in
  combination with other cable guys in an opposite
  direction
• Compression struts, which may be the precast
  concrete components, are needed to complete truss
  action of the bracing system
• A number of wire rope types are available
• Note that capacity of these systems is often
  governed by the turnbuckle capacity

128
General Considerations

• Careful planning of the erection sequence is
  important
• This plan is usually developed by a coordinated
  effort involving the general contractor, precast
  erector, precaster production and shipping
  departments and a structural engineer
• A properly planned erection sequence can reduce
  bracing requirements
• For example, with wall panel systems a corner can
  first be erected so that immediate stability can
  be achieved

129
General Considerations

• Similar considerations for shear wall structures
  can also reduce bracing requirements
• All parties should be made aware of the necessity
  of closely following erection with the welded
  diaphragm connections
• This includes the diaphragm to shear wall
  connections

130
General Considerations

• In order for precast erection to flow smoothly
• The site access and preparation must be ready
• The to-be-erected products must be ready
• Precast shipping must be planned
• The erection equipment must be ready
• Bracing equipment and deadmen must be ready

131
Questions?